- EAA Ch 1

Communiqué
Issue # 3 Volume # 1
Low aspect ratio aircraft Part 1
Education Feb. 28, 2006
Photo from PS Magazine Dave Lauridsen
Barnaby Wainfan’s full-size Facetmobile sits in pieces behind him.
This radio-controlled version of the 2 seat Facetmobile, the FMX-5,
sustains him while he slowly rebuilds the crashed prototype.
DG2’s third speaker was Barnaby Wainfan.
I hope Mr. Wainfan’s spirit and structure was
captured in this following write up. He captivated
us with his humor, opinions, theories, ideas and
reflections of general aviations future. His vision
for general aviation covers the spectrum of cost,
performance, utility and a remarkable stealth
fighter looking aircraft.
Some say that in theory, there is no difference
between theory and practice. But, in practice
there is usually a difference. That’s where
Barnaby Wainfan merges his talents to
understand and practice these differences.
Mr. Wainfan has fully participated in his theories.
He built and flew an aircraft based on his theories
and visions. Placing him in the special category
of individuals many of us would like to be,
dreamer, designer and builder. He speaks from
personal accomplishment and knowledge. This
makes a very significant statement about Mr.
Wainfan’s opinions and assessments about low
aspect ratio aircraft and how they fly.
Mr. Wainfan did not just bring an aircraft design
but insight towards a look ahead of current
practices and technology, towards what might be.
Looking directly at what it will take to make
general aviation profitable and successful to a
larger group of individuals. Will his vision be
successful? Maybe not immediately, but general
aviation needs free thinking visionaries like our
early aviation pioneers. With out individual
inspiration trying to move aviation forward,
greater effectiveness will not happen. Many past
ideas which where long shots in many
individuals’ minds helped move aviation quickly
to the forefront of technology.
Wainfan’s
Facetmobile
is
a
total
package
idea
encompassing cost, technology, and general
aviations possible future growth for individual
sport pilots.
Most individuals find it impossible using their own
money to buy a new aircraft within their desired
specifications. Contrary to what aviation
magazines frivolously (or thoughtlessly) call
affordable, most people will not or can not afford
to pay more for a plane than they have or will pay
for their house. Are you not frequently
dumbfounded by how surprised aviation
magazines are by the declining General Aviation
sales?
In 1978, piston aircraft manufacturers in the
United States had a record year, with shipments
of 14,398 airplanes. It had been the best year for
general aviation in the history of the business,
and few had anticipated the dramatic downturn in
the light aircraft industry during the 1980s.
General aviation industry suddenly experienced a
free-fall drop in sales. By 1986, Cessna stopped
making single-engine personal-owner planes
altogether, and Piper filed for Chapter 11
bankruptcy. By 1990, the industry only shipped
608 airplanes and it appeared that the general
aviation industry would disappear from the
domestic scene. There are lots of reasons and
many theories about what has happened to
cause this.
1
The reason is very obvious to Mr. Wainfan.
Keep the price at the level of a luxury car while
having acceptable performance and you can
sustain a GA production line. With that comes
used aircraft that drift down to others who can not
afford (or unwilling to pay) the new price. He
made a valid point with historical data. Showing
that once an aircraft gets priced over a mid luxury
car, sales fall and at 1.5 times that price the
market collapses for that new aircraft.
Buying any aircraft brings a cost verses
performance dilemma. The aircraft that most
people can afford will not meet their performance
desires. A lot of performance requirements are
more wishes then requirements.
Wainfan’s
solution, make the aircraft fit a mission profile
with acceptable performance for sport aviation
and you might have an acceptable design. Look
to what has sold in the past in suitable numbers
for ideas of what will work. As Barnaby Wainfan
stated “Nobody builds a lot of a bad aircraft”
He also sited easy handling and pilot protection
as a high design consideration. You got to build
a safe aircraft for the 50 hours a year flyer.
Because, killing pilots is bad for business. Make
it pleasant to fly and when the pilot does
something dumb, you want it to take care of the
pilot. “The aircraft has got to save the pilot,
cause the pilot can not save the aircraft”. You
want an aircraft that will not stall or spin with a
“SPLAT FACTOR” that hits the ground flat and
slow. Low aspect ratio aircraft are good at this
with the safety of no spin and stall when
designed correctly.
His Facetmoble fits these
qualities.
bouncing past ahead of him. Mr. Wainfan then
concluded, “Any time parts of the aircraft leave
formation things are not what they should be”.
Mr. Wainfan’s aircraft was equipped with a BRS
parachute system. He did not need to use it
during the power failure but was prepared to. He
spoke very highly of the system and its designer
and knew personnel of two incidences in which it
had saved lives. The system is not a totally
foolproof as history has shown, no system can
be.
Which allowed Barnaby to produce
Wainfan’s Law “For every foolproof method
(system) that exists; there exists an equal and
opposite fool”.
Nothing revolutionary has driven the cost of small
General Aviation aircraft to a reasonable level, or
performance up to exceptional levels. Composite
where thought as a way to bring cost down. This
did not really work because of labor cost and not
seeing that each ply was counted as a part when
assembling. Legacy aircraft where designed
when labor was cheap and material was
expensive. Labor can account for 25% of the
cost just to drive rivets in some aircraft. NASA is
even studying the 1940’s SeaBee to find how it
was built to reduce cost. (See Write Up)
Cost of production comes at you from many
areas, parts, tooling, complexity, labor, etc. You
might have to look at a revolutionary design to
bring cost down. Mr. Wainfan did just that. He
built something radical with the help of friends
and family. This was possible because he had to
answer to only himself and his wife and not
bunch of other people. As a foreign visitor who
saw his FacetMobile told him “In America
anything is possible”.
This is where Barnaby Wainfan juggling act with
the many aspect of FacetMobile concepts and
Low Aspect Ratio (LAR) design comes together
as a revolutionary but viable design. Using flat
panels in a Facet type design allows the use of
manufactured panels. The flat panels are not as
efficient as smooth contours on an aircraft. It is
only costing you about 5% more in parasite drag.
But, you do not have to build a mold which you
could use as a swimming pool.
Barnaby Wainfan’s FacetMobile which made the cover of
Sport Aviation magazine. Look at how much room he has in
the cockpit; can he even touch the sides?
Once again personnel experience from
propulsion failure on take off at Blythe airport has
proven his theories. He turned back to the airport
knowing his aircraft would maintain control as he
landed at 30 knots. He made a skillful landing
which would have most likely caused no damage,
except, for hitting the airport fence. He knew
there was a problem when he saw his wheel
These panels can be cut with a CAD / CAM
automated machines, thus reducing labor cost,
lower parts counts, tooling and complexity
problems are mostly eliminated.
With the
premade flat panels you can purchase job shop
NC machine time with your tooling on a thumb
drive. Basically you can have the panels cut by
any qualified job shop. You do not have to buy
any expensive machines, only time on expensive
machinery. They are then designed to be self
jigging with concepts and fasteners technology
from space craft design. Accord to Barnaby’s
wife you have the IKEA aircraft. Barnaby is
working with Cerritos College and building a full
outer panel which will go thru load testing to
verify these concepts.
2
Low aspect ratio designs seem to have the same
reputation for efficiency towards induced drag as
the California Department of Motor Vehicle has
with motorists. A High Aspect Ratio aircraft like a
sailplane has the opposite reputation. Those
long slim wings holler high aspect ratio and
efficiency. For sailplanes L / D is the all out top
issue, designed for total performance. They do
their job of staying aloft very well on low amount
of energy. But, sometimes you need a glider with
LAR to get the job done, like Space Ship One.
What this means is you design for a mission,
exactly what Barnaby Wainfan has done with the
Facetmobile.
If you compare the overall package of a LAR
aircraft to conventional design you will see an
advantage. Induced drag is about more then
aspect ratio. It is about wetted area, aspect ratio,
and span loading. You must also look at parasite
drag which is affected by skin friction. There
might be more skin area in a low aspect design,
but the drag is off set by other avenues. For one
you have long cords on your airfoil, long chords
equate into high Reynolds numbers (RE). The
FacetMobile has an airfoil chord of about 14 feet
which gives it a RE of about 14,000,000. This
lowers your skin friction (Cf) down about 20%.
Intersection drag is usually lower with a LAR
because the wings, body, flight controls blend
together with less intersections.
When you
combine all this together, you have an aircraft
which can compete with a conventional design.
With LAR you get a light structure. The
FacetMobile’s weight was 370 pounds with a
useful load of 300 pounds. Light structure
reduces induced drag. Fuselage and wings
become a total package giving a BIG cabin. By
blending the body, wings and control surface you
reduce parasite intersectional drag. The
FacetMobile had a very tolerant weight and
balance and C.G. travel. The 14.5 foot chord
allows 15 inches of C.G. travel. Compared with a
Cessna 150 which has 3 inches of travel. You
also get a safe and well handling aircraft. In
extreme emergency, pull the power, pull the stick,
keep your heading, and your sink rate becomes
about 1000 feet per minute in the FacetMobile.
This is servable in most terrain for an emergency
landing.
the design of future Personal Air Vehicles. The
study examines building a low aspect ratio
airplane. This report NASA LARC NAG-1-03054
is worth reading. It is very well written and
presented. It explains Wainfan’s concepts very
well. I might make it an attachment to this
newsletter. If not you can find it at this internet
location.
http://members.aol.com/slicklynne/pavreport.pdf
There is hope that he will get a contract to fund
phase two of this study. I can not see a better
use of NASA funds then this. This concept could
revitalize sales and general aviation. Good for
sales, technology and American manufacturing.
Barnaby Wainfan’s Facet concept could do for
aviation what ATV and Jet Ski have done for off
road and water sports. Also, I would like to see it
take to the air
Q/A with Barnaby WainFan
Q: By moving the stabilizers inboard do you lose
efficiency?
A: Yes, a small amount, but by adding few more
feet of wing span it works out the same. It is also
cheaper to build with them inboard.
Q: Did you play with cant angle on the wing tips?
A: No, but on the FMX-5 the lower part was
moved for dihedral effect.
Q: How do you get in it?
Barnaby Wainfan’s Facetmobile concept aircraft
has safety, reliability and comfort, utility and
reasonable speed. Not forgotten is cost effective
construction. The aircraft should cost about half
of today’s present two place aircraft. In the sweet
spot; luxury car area of $50,000 to $60,000 while
looking radical and different at the same time. By
combining all these attributes he makes it a
meaningful and reasonable proposition for
aviations future.
A: This is a problem. In the FacetMobile you get
in through the bottom floor between the seats
and rudder pedals. The door opens up and you
go through the bottom. Future design might call
for a plug door with retract steps. Doors on the
bottom are great for working on the panel and
other areas as you stand on the ground.
In 2003, in partnership with the California Space
Grant Foundation, Barnaby Wainfan won a NASA
contract to study the application of Facetmobile
low aspect ratio airplane concepts. This was to
A: Similar to conventional aircraft. As you drop
the Aspect Ratio down the slope of the lift curve
gets lower. This means change of lift coefficient
per angle of attack gets lower. So a given gust
Q: How is it in gust and turbulence?
3
changes the lift coefficient less. Even though you
have more area it comes out about the same.
During turbulence there is a weather vaning
effect. The effect on the two place with a wing
load of 5 pounds per square foot wing load it will
act like a Cessna 150.
Q: How about cross wind landings?
A: You have to work at it, but it has a lot of rudder
power. It does want to point into the wind. The
Facetmobile has landed in 12 knot crosswind
with not much problem. You do not get the
rolling effect as in a long wing conventional
design. The landing gear is set for a negative lift
with the nose wheel down. Slip it in, fly the gear
down to the runway and use lots of rudder and
brakes.
Q: Stall effects?
A: Similar to a canard aircraft limiting effect.
Q: How high off the ground are you when getting
in and out?
A: High enough to be awkward, low enough to be
awkward. You lift yourself in. Next generation
might be taller and have boarding step/ladder or
go over the top. Entry and exits is a problem but
the issue has been dealt with on the Dyke Delta.
Q: How big is the propeller and is there a gear
reduction?
A: 62” 2 blade I designed built by Sensenich on
a Rotax Box. There was also a 60” 2 blade.
Q: Do you have plans for a Radio Control model
aircraft?
A: There is an accurate 3 view on the web site:
http://members.aol.com/slicklynne/facet.htm
The Model Builder magazine has a peanut Scale
from a friend of mine. There is an unauthorized
electric model. I got a call asking where do I put
the C.G. trying to help a fellow modeler I gave
him the information. Then I was told that they
where going into kit production. He did not even
give me a kit. So the easy way to build a model is
to buy one from the rat bast$%^& who ripped me
off.
If you like to see the aircraft it is located in the
EAA Chapter 96 hanger. Mr. Wainfan stated he
is usually (but not always) in the hanger on
Sundays working on restoration from 10:30 to
3:30. Come on out, see the aircraft.
The following article was appropriated from
EAA Chapter 96, January 2005, Volume 1
Peninsula Flyer Newsletter
Q: How did you determine location of the C.G.?
A: Combination of analysis and flying radio
control models. Classical delta wing math works
just fine. Did a lot of conformation flying with
models aircraft and moveable ballast to find the
ugly areas. We where also able to get wind
tunnel data before we flew the FacetMobile.
Q: What are those ugly things you found when
you started to moving the ballast back and forth
on the model?
A: The classic things you get with C.G. to far
back it gets touchy in pitch. As the C.G. moves
forward you run out of elevator power. But the
design proved very C.G. tolerant.
Q: Was the airfoil shape based on anything or
pure experimental?
A: No, not pure experimental. A whole lot of
ideas came from American Aircraft Modeler,
model aircraft called THE THING built by a man
named (Bill Potter ?). This model was flat top and
one day I flipped it over and it flew just fine. By
building models looking at lifting body literature
and British deltas. A lot of work was done to
arrive at the shape. Many models died for the
glory of science.
Barnaby Wainfan
The Man, The Myth, The Legend
Excerpts from the Internet and
publication: - Mike Hoedel
Popular Science
Great engineers can intuit how a design will
come together, but their intuition is guided by a
'gut-level' understanding of how the laws of
physics work. And then those engineers will go
back and do the calculations to verify that their
intuition was right. If the numbers don't work, then
they start over again and solve the problems that
were bedeviling their design. But no matter how
much intuition they bring to the process, their
final answer must be one that does not violate
the laws of physics. And this brings us to
Barnaby Wainfan. Simply put he is one of the
brightest engineers I have ever met. And he
understands - and can explain - the dynamic
relationship between creativity and engineering
better than just about anyone I know. Barnaby is
the lead aerodynamicist at a major aerospace
company. He designs and builds his own
airplanes. He consults with various companies on
aerodynamics. He has even appeared on an
episode of Junkyard Wars where he led a team
of people in the construction of a glider in just 10
hours.
4
Barnaby is not just a brilliant engineer; he is also
a talented songwriter. Working with his friend
Steve Desmond - Barnaby did the words, Steve
the music and performance - they have put out a
CD of their songs that captures a bit a Barnaby's
outlook on the world.
Barnaby Wainfan has seen the future of general
aviation, and it looks like a stealth fighter. His
design for an inexpensive home-built two-seat
general aviation airplane, the Facetmobile, is a
delta shaped blended-wing aircraft composed
entirely of sharply angled flat planes— just like
the Lockheed-Martin F-117, which was unveiled
to the public six months after Wainfan began
building his design. That’s a coincidence, says
Wainfan, an aerodynamicist at Northrop
Grumman. The F-117 is built with flat facets to
reduce its radar signature; the Facetmobile, to
cut costs. The parts are flat so that a home
builder could make them on a table. “Airplanes
are too expensive,” Wainfan says. “A new
airplane should cost the same as a car, not a
house. People tend to think about performance,
performance, performance— higher, faster,
farther. For me, it’s about simpler, safer, less
expensive, more fun. The Facetmobile is for
people who fly because it’s good for their soul.”
says the penalty in drag is minor— and worth it,
given the ease of construction. Wainfan, 49, a
small, intense man with an unruly mop of gray
hair and a bushy goatee, first flew the
Facetmobile in 1993. That year, he flew it from
his home airport in Chino, California, to Oshkosh,
Wisconsin, and back, a distance of about 2,350
miles. The following year he was taking off from
Blythe, California, when the engine quit at 500
feet. Wainfan walked away from the crash
unscathed, but the plane was a wreck.
Forecast: Calm - Today the Facetmobile, or what
remains of it, resides under a dusty black tarp in
the EAA Chapter 96 hangar in Compton,
California. After it gets new landing gear and a
new covering of fabric, it will be ready to fly
again— if Wainfan ever gets around to it. “I’m
trying to support a family of five with a job in the
aerospace industry,” he says. “There are
compromises you have to make. Like John
Lennon said, ‘Life is what happens while you’re
busy making other plans.’” No one doubts that
the Facetmobile can fly, or that it could be built
inexpensively. “It’s a safe, viable concept,” says
Jack Cox of Sportsman Pilot magazine. The real
question is whether Wainfan will ever find the
time or money necessary to turn it into a viable
business proposition. “If you have the resources
to help,” his Web site appeals, “please contact
us.”
Wainfan’s primary influence was the Dyke Delta,
a homebuilt delta-wing aircraft that was
introduced in 1962.
For more information, visit
Barnaby’s website at:
www.members.aol.com/wainfan/
NASA LARC NAG-1-03054 NASA PAV
Wainfan’s primary influence was the Dyke Delta,
a homebuilt delta-wing aircraft that was
introduced in 1962. Futuristic-looking for its day,
with a vertical tail but no horizontal stabilizer, the
Delta could cruise at 170 mph and climb at 2,000
feet a minute. Wainfan’s Facetmobile achieved
110 mph with just a 46hp engine; a larger version
with a bigger engine could easily match the
Delta’s performance. The airplane’s flat-panel
construction makes for rougher aerodynamics
than the Delta’s (or those of virtually any other
airplane out there, for that matter), but Wainfan
(Personal Air Vehicle) Project Study
http://members.aol.com/slicklynne/pavreport.pdf
Radio Program with Barnaby Wainfan interview
http://www.hour25online.com/Hour25_Previous_
Shows_2002-07.html#barnaby-wainfan_2002-0730
5
demonstrator made by conventional aviation
construction methods. First flight was made on
30 November 1944.
However, Republic Aviation's president Alfred
Marchev realized that if Republic was going to
win the expected post WW2 personal airplane
market boom, they had to make something
different at a price affordable for the masses.
Marchev ordered a complete redesign of the
Seabee to reduce the cost dramatically. The
seemingly impossible goals Marchev set for his
engineers were: a four seat amphibian aircraft at
a sales price of $3500 - the conventional
prototype would have an estimated sales price of
$13000! The engineers took the challenge.
Several changes were made; the tapered
cantilever wings were replaced by constant chord
strut braced wings, the partly buried retractable
wheels of the RC-1 were replaced by wheel
Design study of crashworthy general aviation aircraft via Karl Bergey.
This is from the late 70’s or early 80,s
Republic Seabee Dissected for
NASA!
Study the past to learn the future
Barnaby Wainfan mentioned this in his
speech so I looked it up.
A few years ago NASA, together with some major
universities and commercial enterprises started a
project
called
SATS
Small
Aircraft
Transportation System. The purpose of the
project is to develop technologies to make
personal aircraft affordable. In 2004 Munro &
Associates, an engineering and manufacturing
consultant company based in Troy, MI,
purchased Seabee s/n 1054 for the purpose of
studying the design and manufacturing methods
used on the Seabee. The Seabee was delivered
by truck to M&A on 15 March 2004 and soon
work was started to dissect the Seabee for a
detail benchmark study of the Seabee design.
As a part of the SATS project, M&A made a Lean
Design study of the Seabee for NASA.
retracted in the free air. Numbers of parts were
reduced substantially by introducing deep die
press forming methods from the automotive
industry, and wherever possible automotive parts
and components were used in favor of overpriced
aviation industry parts. In order to reduce the
costs of the engine installed, Republic even
acquired the engine manufacturer. Republic also
negotiated large quantity rebates from the
vendors. Unfortunately, several factors made big
problem for the Seabee production and sales.
When the Republic Seabee amphibian was put
into production in 1946, this was the result of a
design and development process never seen
before in the aviation history. For the first time an
aircraft manufacturer seriously looked to the
automobile industry to take advantage of
automotive design and manufacturing methods
for reducing production time and costs. The first
Seabee prototype, the RC-1 Thunderbolt
Amphibian
NX41816,
was
a
concept
6
Important manufacturing tools such as sheet
metal presses got delayed from the tool
subcontractors, material and labor costs
increased forcing Republic to increase sales
price twice in less than a year. Production
deliveries got delayed and production rates were
never even close to the original goal of making
400 Seabees per month - 5.000 in one year. In
June 1947 Republic was forced to stop
production when sales failed, after only one and
a half year and 1060 built. On 2 October 1947
Republic announced that the Board had made
the final decision to terminate the Seabee project
in favor of military aircraft such as the new F-84
Thunderjet fighter jet.
Then - more than a half a century later - NASA
starts looking into the future of personal aircraft
transportation. It is realized that in the future it
might be necessary to transfer more of the
personal transportation from the roads to the air,
to avoid further congestions.
Select technologies can be common between
automobiles and general aviation aircraft.
The innovations and technologies being
developed by MISATS are aimed at small aircraft
private and business commercial smaller airports
around the country.
MISATS is the only SATS program working to
improve the viability of the general aviation
business model through aircraft design,
manufacturing, training and infrastructure.
Ultimately, MISATS plans are launching a
compelling three year air vehicle design and
fabrication program. The goal is to build a flying
demonstrator that with the transition into a
business venture that can provide these vehicles
to the nation
MISATS – The Michigan Small Aircraft
Transportation
System
is
a
non-profit,
government-industry-university
consortium
formed to transfer select commercial and
automotive technologies to general aviation
applications.
Once
developed,
these
technologies will be integrated into the SATS
national research program.
Innovations
developed by MISATS will be eligible for
commercialization by private companies with
competitive business models. These companies
will then be positioned for leadership in a
revitalized and a commercially viable general
aviation industry.
MISATS is a contributor to the long-term NASA
SATS vision of a National personal air
transportation system that is safer and more
efficient than the current commercial air travel
system. SATS is a long range national vision with
objective spanning out 25 years. The NASA goal
is to reduce inter-city travel times by half in 10
years and by two-thirds in 25 years.
NASA's
strategy
for
general
aviation
revitalizations of aviation industry is challenging.
The plans calls for the delivery of up to 20000
aircraft in 20 years, with some very demanding
parameters. Aircraft price and cost of operation
must be slashed dramatically, but improve
performance and safety and vastly simplifying
their operation.
Munro & Associates started MISATS with the
NASA approved goal to demonstrate that
automotive style systems integration, Six Sigma
quality, Lean Design and lean manufacturing can
radically reduce aircraft complexity, while
revolutionizing safety, efficiency and affordability.
MISATS operates under the long term objectives
that; aircraft can be designed and manufactured
at unit cost comparable to automobiles.
AIRFOIL SELECTION
ISBN 9-9921-4657-5
Airfoil selection is an outstanding new book by
airfoil expert Barnaby Wainfan which will aid the
reader in understanding and choosing airfoils for
light aircraft. This book is a collection of a series
of articles originally published in Kitplanes
magazine and reprinted in book form with the
cooperation of Kitplanes editor, Dave Martin. All
articles by Barnaby Wainfan. 57 pages, illustrated
Future Thought
We would like to hear from anyone who has an
idea for a future presentation:
Example would be a PLANS DAY:
Some of use would bring in plans which we have
studied. Then we could explain or just let others
view and look at them.
There is always
something to be learned when you see what
other designers have done to solve a problem or
design idea.
7
Or a Build and Break it project:
Something small a wood rib, small spar, etc.
Design it as a group, determine what it will hold
and break it to find out if we were right.
Bring your idea for a design day:
Even if it is only on a napkin, a few words would
always be welcomes about you idea.
Please bring any ideas, every idea is welcomed
or send it and it can be published in the
newsletter.
FlaBob High
John spoke about Wathan Aviation High
School at the meeting. If you know of anyone
who might be interested in going to this High
School please contact them. There is a flyer
with phone numbers and details attached to this
newsletter. Print it and pass it around.
There were some outstanding displaces on
aviation related subject in the hanger. The
students did a great job detail specific aviation
subject matters. I enjoyed looking them over. I
wish I had brought a camera so there would have
been pictures for the newsletter. Next Time.
Build your own FACETMOBILE
Card Modeling or Paper Modeling is the art of
creating scale models with paper. Models are
built up from appropriately colored, cut, and
folded pieces of paper, usually a stiff cardstock.
Many models are available as kits, with preprinted pieces to be cut out and assembled by
the modeler. It's also possible to build entirely
from scratch. Paper models can be surprisingly
sturdy, and can stand up to handling well. They
derive their strength from their structure; even
seemingly flimsy paper can be strong when it's
shaped properly.
This model builds into a 1:48 scale replica of the
Facetmobile, and may be built as a static display
model or (without propeller and landing gear) as
a glider. You will need a printer capable of
handling card or cover stock to print the parts
sheets. I built this paper model and it does fly. I
transferred ownership and further test flying to
Robert Jordan, have him fly it for you.
What this is and what it is not!
It is important to remember that this newsletter is
merely a conduit for information passed among
members sharing their experiences. Its
established
purpose
is
fellowship
and
encouragement. It is NOT the intent to give
authoritative advice on aircraft construction
or design. The Editor and the contributing
writers disclaim any liability for accuracy or
suitability of information that is shared. You can
assume that all or some of the information in
each issue is not correct for aircraft design.
This is simply a collection of notes which where
taken at the Design Group meeting and placed
with other items into a newsletter format. Lots of
items will come from the meeting as best as one
can interpret what is stated. Many items will
come from other sources such as books and
internet files (Grabbing from any source to make
it useful and a lot will come from the internet to
expand what was talked about at the meeting,
like the V-173 and Aspect Ratio material in this
issue. (I will take it where I can get it).
Speak out if you were wrongly quoted or
something misinterpreted, no harm was implied,
only lack of knowledge in understanding and
interpreting what was said. This will only be sent
by email to anyone whom would like to receive it.
If others would like to contribute articles, stories
and materials in the future feel free. The
newsletter should provide a way for us to
communicate with each other. It is a place for
those of us who want to network, connect and
share information to do so. Anyone can write
anything to whomever about any aircraft or
aviation design ideas. With any luck we will learn
something from everyone and hopefully someone
can learn one thing from us.
This newsletter is also located at this Web Site
for download or viewing. This Web Site is
hosted by EAA Chapter One and I would like to
thank them for this services.
http://www.eaach1.org/design.html
I have included this model with the newsletter,
build it its fun. Also go to this site, there are
many types of these paper aircraft being offered.
http://www.currell.net/models/mod_free.htm
Next Issue Part 2 Low Aspect
Ratio Paraplane and Ed Marquart
8
ASPECT RATIO
In aerodynamics, the aspect ratio is an airplane's
wing's span divided by its standard mean chord
(SMC). It can be calculated more easily, however
as span squared divided by wing area:
they must be as efficient as possible in every
respect in order to stay aloft.
To better understand low aspect ratio you need
the theory about the Cl / Cd curve and its
meaning, the relation between glide ratio and the
needed power to keep flying. Also; Reynolds
numbers and surely about induced drag.
Why don't all aircraft have high aspect-ratio
wings? There are several reasons:
Aspect ratio or
(or AR in many other books)
can be defined also as:
= b2 / S
= S / k2main
= b / kmain
With:
= aspect ratio
S = wing area
b = span
kmain = main chord
Informally, a "high" aspect ratio indicates long,
narrow wings, whereas a "low" aspect ratio
indicates short, stubby wings. So, low aspect
ratio's are airplane with a small span in relation to
their wing area.
Aspect ratio is a powerful indicator of the general
performance of a wing. Wingtip vortices greatly
deteriorate the performance of a wing, and by
reducing the amount of wing tip area, making it
skinny or pointed for instance, you reduce the
amount of energy lost to this process, induced
Structural: the deflection along a high aspectratio wing tends to be much higher than for one
of low aspect ratio, thus the stresses and
consequent risk of fatigue failures are higher particularly with swept-wing designs.
Maneuverability: a high aspect-ratio wing will
have a lower roll rate than one of low aspect
ratio, due to higher drag and greater moment of
inertia, thus rendering them unsuitable for fighter
aircraft.
Stability - low aspect ratio wings tend to be more
naturally stable than high-aspect ratios. This
confers handling advantages, especially at slow
speeds.
Practicality - low aspect ratios have a greater
useful internal volume, which can be used to
house the fuel tanks, retractable landing gear and
other systems.
Looking at a low aspect ratio will help you
believing that it is less trouble to fit the cockpit,
engines, fuel and cargo into the wing. The result
is a clean wing without humps or any extra
external volumes as fuselages, engine pods and
stuff. A clean wing leads to less overall parasite
drag. This could lead to a better glide ratio if
there wasn't something as induced drag. But
there is. Just look at the size of the wingtips. Can
you imagine the air leak over this wingtip? I bet
you can. So, to get a Cl / Cd curve of the total
airplane you don't need to add the drag of things
like fuselage, engine pods or so, but you sure
need to add the induced drag. And it is not small !
The L/D ratio is very important. Not only does it
determine the glide performance of the aircraft,
but as we will soon see, it determines range,
endurance and climb performance as well. It
therefore behooves us to consider what factors
determine the value of the L/D ratio.
Since the L/D ratio is simply lift divided by drag
we will start by doing the algebra:
L = CL x S x ½rV2
D = CD x S x ½rV2
Notice that S, r and V cancel out. These
elements affect both Lift and Drag equally and
therefore cancel out in the ratio.
drag. This is why high performance gliders have
very long, skinny wings; with no engine power,
Thus, the L/D ratio is simply equal to:
L = CL
D CD
You can see that the higher aspect ratio aircraft
clearly has a much higher L/D max. Therefore,
the high aspect ratio aircraft will glide much
further.
CL changes only with angle of attack. But what
about CD?
You can also see that the optimum CL is much
lower for the low aspect ratio aircraft.
CD is the sum of Cdi and CDP. We also learned
that Cdi changes with angle of attack. But, CDp
changes only when the shape of the aircraft
changes (for example when gear or flaps are
extended.)
This means that aircraft with short wings must fly
at a small angle of attack in order to be efficient.
Conversely, an aircraft with longer wings will be
more efficient at a somewhat higher angle of
attack. The higher the aspect ratio the greater the
angle of attack the aircraft must fly at in order to
be efficient.
Mathematically we can express L/D as follows:
L = CL =
CL
D CD (CDp+ CL 2 / peAR )
From the above we can see that L/D changes
with angle of attack (i.e. CL) changes in
configuration (i.e. CDp) and changes in design
(i.e. AR. and e.)
If you have a calculator capable of plotting an x-y
coordinate graph program the L/D equation
above
into
your
calculator.
Choose
representative values for e and CDp:
e.g. e =.8 CDP = 0.025
It is important to remember that small angles of
attack correspond to high indicated airspeeds
(relatively speaking) Large angles of attack
correspond to relatively slower speeds.
Thus, we can summarize by predicting that a
glider, with its long wingspan will have a high L/D
max, and as such will be able to glide a long way.
However, it will inherently need to fly at a large
angle of attack and therefore, be quite slow.
A low aspect ratio jet fighter will not be able to
glide very far. However, it will be at its most
efficient when skimming through the air at a
relative low angle of attack and high speed.
Most birds have wings with a high aspect ratio,
and with tapered or elliptical tips. This is
particularly noticeable on soaring birds such as
the albatross and eagle. Doves and woodpeckers
have a low aspect ratio. To get away from
predators quickly these birds make sharp turns.
The shape of their wings allows them to do so.
On the other hand, falcons and frigate birds have
high aspect ratios, giving them the ability to
sustain high-speed flight for long periods.
However, these birds do not have wings that can
be flapped as rapidly as their woodpecker
cousins who have better maneuverability.
Then choose a value for AR. If you choose a low
value for AR (e.g. 3 or 4) you will get a graph
similar to the one shown to the above.
If you choose a higher value for AR (e.g. 9 or 10)
you will get a graph similar to the second one
above.
In addition, the V-formation (echelon) often seen
in flights of geese, ducks and other migratory
birds can be considered to act as a single swept
wing with a very high aspect ratio - the vortices
shed by the lead bird are smoothly transferred to
the next and so on. This confers a huge
efficiency advantage to the flight as a whole perhaps as much as a 100% improvement
compared to a single bird in flight. Note that the
usual common explanation of the V-formation that following birds are "shielded" from air
resistance by the bird in front - may be
misleading. While birds do "take turns" at being
the lead bird, it is probably to give those at the
tips a rest - they are the ones that will experience
the most drag when the vortices are finally shed.
However, the full explanation of this behaviour is
still the subject of research and debate; scientists
still do not claim to have fully understood the
phenomenon.
The wetted aspect ratio
The wetted aspect ratio is a good indication of
the aerodynamic efficiency of an aircraft. It is a
better measure than the aspect ratio. It is defined
as:
where Sw is the wetted surface of the whole
aircraft in contrast to the wing area used for the
definition of the aspect ratio.
A good example of this is the Boeing B-47 and
Avro Vulcan. Both aircraft have very similar
performance although they are radically different.
The B-47 has a high aspect ratio wing, while the
section (the critical section) reaches its 2-D
maximum Cl.
When the sweep is very large, or aspect ratio
low, this approach does not work. Separation
tends to occur near the leading edge of the wing,
but unlike in the low sweep situation, the
separated region is not large and does not
reduce the lift. Instead, the flow rolls up into a
vortex that lies just above the wing surface.
Rather than reducing the lift of the wing, the
leading edge vortices, increase the wing lift in a
nonlinear manner. The vortex can be viewed as
reducing the upper surface pressures by inducing
higher velocities on the upper surface.
The net result can be large as seen on the plot
here.
Avro Vulcan is a low aspect ratio blended wing
body. They have, however, a very similar wetted
aspect ratio. The Vulcan is a Thick Delta which
has a L/D of 17 about the same as the B47 but a
aspect ratio of 3.
Low Aspect Ratio Wings at
High Angles of Attack
At high angles of attack, several phenomena
usually distinct from the cruise flow appear.
Usually part of the wing begins to stall
(separation occurs and the lift over that section is
reduced). An approximate way to predict when
this will occur on well-designed high aspect ratio
wings is to look at the Cl distribution over the
wing and determine the wing CL at which some
The effect can be predicted quantitatively by
computing the motion of the separated vortices
using a nonlinear panel code or an Euler or
Navier-Stokes solver.
This figure shows computations from an
unsteady non-linear panel method. Wakes are
shed from leading and trailing edges and allowed
to roll-up with the local flow field. Results are
quite good for thin wings until the vortices
become unstable and "burst" - a phenomenon
that is not well predicted by these methods. Even
these simple methods are computation-intensive.
where Λ is the leading edge sweep angle. If this
acts as an additional normal force then:
Cn' = Cn + (Cn sin α - CL2/π AR) / cos Λ
and in attached flow:
CL = CLa sin α with Cn = CL cos α
Thus, Cn' = CL cos α + (CL cos α sin α - CL2/π AR) / cos Λ
= CLa sin α cos α + (CLa sin α cos α sin α - (CLa sin α)2/π AR) / cos Λ
= CLa sin α cos α + CLa/ cos Λ sin2 α cos α - CLa2/(π AR cos Λ) sin2 α
CL' = CLa [sin α cos2 α + sin2 α cos2 α /cos Λ - CLa/(π AR cos Λ) cos α sin2 α]
= CLa sin α cos α (cos α + sin α cos α/ cos Λ - CLa sin α /(π AR cos Λ))
If we take the low aspect ratio result:
CLa = π AR/2, then:
Polhamus Suction Analogy
A simple method of estimating the so-called
"vortex lift" was given by Polhamus in 1971. The
Polhamus suction analogy states that the extra
normal force that is produced by a highly swept
wing at high angles of attack is equal to the loss
of leading edge suction associated with the
separated flow. The figure below shows how,
according to this idea, the leading edge suction
force present in attached flow (upper figure) is
transformed to a lifting force when the flow
separates and forms a leading edge vortex (lower
figure).
CL '= π AR/2 sin α cos α (cos α + sin α cos α/ cos Λ - sin α /(2 cos Λ) )
Cross-Flow Drag Analogy
An even simpler method of computing the
nonlinear lift is to use the cross-flow drag
analogy. The idea is to add the drag force that
would be associated with the normal component
of the freestream velocity and resolve it in the lift
direction. The increment in lift is then simply:
Δ CL = CDx sin2α cosα.
The plot below shows each of these
computations compared with experiment for a
80° delta wing (AR = 0.705). In these calculations
a cross-flow drag coefficient of 2.0 was used.
The suction force includes a component of force
in the drag direction.
This component is the difference between the nosuction drag:
CDi = Cn sin α, and the full-suction drag: CL2 / π AR
where a is the angle of attack.
The total suction force coefficient, Cs, is then:
Cs = (Cn sin α - CL2/π AR) / cos Λ
Another case with much higher aspect ratio is
shown below. Note that the very simple model
seems to do nearly as well as the more involved
suction analogy.
Flaps are often not used on SST designs due to
difficulties with longitudinal trim. Designs with tail
surfaces or canards can employ some flaps,
increasing the effective alpha limit by 2-3
degrees. Clearly, conventional slats do not help
these designs as they produce little change in CL
at a given angle of attack. However, studies have
shown that some types of leading edge vortex
flaps, intended to strengthen the leading edge
vortices can be used to further increase the
maximum usable CL.
Span Loading
Low aspect ratio seems to go against the
principle of using a high aspect ratio design to
keeping induced drag down. Not really, when
you look at the numbers;
CDi = CL2 / πAR
The maximum lift of a low aspect ratio wing is
significantly increased by the presence of these
vortices and is limited either by vortex bursting or
by allowable angle of attack. Vortex bursting is a
phenomenon in which the structured character of
the vortex is destroyed resulting in a loss of most
of the vortex lift. It occurs due to adverse
pressure gradients acting on the vortex. When
the vortex burst occurs on the wing (as opposed
to downstream of the wing) the lift drops
substantially. Although there are some empirical
methods for predicting vortex burst, the
phenomenon is quite complex and difficult to
predict accurately. For many SST designs,
however, the maximum CL may be predicted by
assuming that the vortex does not burst at the
maximum permissible angle of attack. Because
of the length of the fuselage, this angle may be
restricted to a value of 10-13 degrees. Using this
value in the above expression for CL leads to a
reasonable estimate for maximum lift on such
designs.
A flow pattern, similar to that of the highly swept
delta wing, is found at the tips of low aspect ratio
wings and over fuselages. The vortex formation
significantly increases the lift in these cases as
well. Especially in the case of fuselage vortices,
the airplane stability is affected. Interaction with
downstream surfaces is often important, but hard
to predict. Computations of lift at a specified
angle using the cross-flow drag analogy can
easily include the component associated with
fuselage lift as well.
If we do a little substituting with CL and AR we
get;
L2 / q2S2
S / π b2
Multiply the coefficient by qS , so you get actual
drag you have;
Di = ( L / b ) 2 . ( 1 / π q )
Look at this part it is squared, this has a lot of
effect on your design. Anytime something is
squared it can help you or cause you major
concerns. When a number is squared growth
climbs fast. Lift is needed to over come weight
and weight has a terrible effect on induced drag.
Induced drag rises with weight and it also goes
down with weight reduction. (This kind of works
like that great tasting chicken at the EAA Chapter
1 provides at their meetings. A few grams of
chicken in our airframe become pounds of
payload on our bodies.) LAR aircraft have the
ability to make light structures keeping this
formula in check. What this is telling us is that
SPAN LOADING HAS A MAJOR EFFECT ON
INDUCED DRAG!
Arup S-4 (foreground) demonstrates the practicality of a low aspect ratio
wing. Both Arup S-2 (background) and the S-4 were frequently used as
flying billboards during their accident-free careers.
Snyder's first aircraft was known as the Dirigiplane,
Monowing, and finally Arup S-1, at various stages of its
development. Rudders are at the after edges of-the vertical
stabilizers; elevator extends across the wing trailing edge;
ailerons are at the top of the vertical stabilizer, forward.
A
podiatrist from South Bend, Indiana, was responsible
for one of the more distinctive and successful tailless
designs of the Depression. Dr. C.L. Snyder, intrigued with
the flying qualities of a felt heel lift that he had idly tossed
through the air one day in 1926, pursued his idea from the
primitive model stage to unpowered and powered gliders,
and finally to several highly successful disc-type aircraft.
Like Junkers, Soldenhoff, and Rumpler, Snyder's goal was
to develop of the flying wing for air transport purposes. He
envisioned an aircraft with a wing 15 feet thick with a 100foot span and a 100-foot chord. The passengers were to
be seated in the wing with a clear view forward through
the plastic leading edge of the wing. Snyder's early glider
experiments led to the formation of the Arup
Manufacturing Corporation in 1932 to refine his initial
experimental configuration to a practical aircraft. Aided by
the engineering skills of Raoul Hoffman and with Glenn
Doolittle (racing pilot Jimmie Doolittle's cousin) acting as
test pilot, Dr. Snyder produced three more variations of the
basic disc-shaped Arup S-1 powered glider. Of the three,
Arup S-2 and S-4 proved to be more durable and practical,
making hundreds of flights during the mid-1930s, including
impressive demonstration flights for the NACA, CAA, and
the Army.
The Arup experienced an accident-free service life. Some
of its pronounced advantages over more conventional
aircraft were greater lift and safety, increased cruising
range, lower takeoff and landing speeds, and stall-proof
flight characteristics. Dr. Snyder's Arups were not
commercial successes, however. He had inadequate
working capital, inexperienced management, and an
aircraft that just did not "look right."
Raoul Hoffman, Dr. C.L. Snyder's engineer at Arup, left
that company in 1933 and moved to Florida where he
designed an Arup-type aircraft for a Chicago industrialist.
The Hoffman flying wing, like the Arups, had performance
figures that were guaranteed to appeal to those citizens
who wanted to replace the family automobile with an "air
flivver." Unfortunately, Hoffman's aircraft caught fire in
flight from a broken fuel line and crashed, killing the pilot.
The airfoil was stated to be a Munk-designed, reflexed
NACA M-6 of about 12% thickness.
Built in St. Petersburg, Florida, this unusual tailless aircraft resembled the
Arup disc designs. A 1934 design by former Arup engineer Raoul
Hoffman, the wing was a semicircle to which floating tip controllers were
added to serve as ailerons. Elevators were located in the wing's trailing
edge.
S-2 aka Snyder A-2 1933 = 1pC flying wing; 36hp Continental A-40; span:
19'0" length: 17'2" v: 97/x/23; ff: 5/28/33 (p: Glenn Doolittle). Raoul
Hoffman, C L Snyder. Developed from Snyder's flying-wing glider, Arup 1
Dirigiplane, which was ultimately fitted with a Heath-Henderson motor.
Wing-tip "ear" ailerons, STOL flight characteristics. POP: 1 [X/R12894].
S-3 1934 = 2pC flying wing; 70hp LeBlond 5DE; span:
22'0" length: 17'6" load: 490 v: 97/90/20; ff: 7/15/34.
Larger version of S-2 with ailerons moved flush with the
wing-tips, tricycle gear. POP: 1 [14147], destroyed by an
unsolved arson fire after its test flight.
S-4 1935 = Remake of S-3, with 70hp LeBlond; span:
22'0" length: 18'6" load (included two parachutes, just in
case): 550 v: 110/x/28 ceiling: 9,000'; aspect ratio 1:1.78;
ff: 3/19/35. Small elevators added atop fin. Some reports
tell of a return to conventional gear, but photos in Aug
1935 Popular Aviation show a nose gear. POP: 1 [14529].
Disposition unknown. US patent #2,062,148 assigned to
Cloyd Snyder in 1937 for a variable wingform aircraft. A
smaller 1p replica was built and flown c.1985 in Bristol IN.
SNYDER, C.L. (later w/HOFFMAN, R.): U.S. Pat. No.
1,855,695: “Aircraft”, 4/26/32 (filed 9/8/30; a controllable
“compartment” lifting body with straight l.e. joined to
curved t.e., and length approximately equal to span; pref.
embodiment describes pilots, passengers, engines, etc.
inside airfoiled, possibly buoyant body):
The Arup S-1 was nicknamed "The Dirigiplane"
as it was designed to hold buoyant gas. It did use
a classic Clark-Y airfoil. Another nickname was
"Monowing".
The Arup S-2 did fly in 1933. It had an enclosed
cockpit, a engine in front and a single vertical tail.
There are two pictures of the Arup S-2 and both
show a different placement of the ailerons. The
first picture (seen on nurflugel-website) shows
ailerons added to the wingtips as extra surface in
the shape of a half moon. The ailerons were fully
rotating, which means that this extra surface did
completely turn around a axis and was not made
in two separate parts (one fixed, the other
rotating). The other picture shows ailerons placed
next to the elevator at the rear of the airplane.
The picture of the Arup S-4 on the Nurflugel-site
shows the Arup S-2 in the background with the
last mentioned ailerons.
Clearly it was planned for mass production. But it
was a bad economical time, the "Great
Depression", and no buyers were found. Pity...
because it flew well. The S-2 flew hundreds of
hours and Dr. Snyder took his young son and
daughter with him on several trips. That is
something you don't do if you are not sure about
safe flying.
The Arup S-3 and S-4 did probably have the
same airfoil as the S-2. They were further
refinements of the S-2. Both did have a classic
tail. The S-4 had ailerons placed in the trailing
edge of the wingtips.
South Bend Regional to
unveil historic display
05/15/2003
Dr. Snyder’s low-A/R “Dirigiplane” glider flew and was then
motorized in 1932 as the S-1. Highly successful powered
versions, like the 1933 ARUP S-2 (above), grew
protruding fuselages with airfoil contours to the extent
thought necessary on such a small plane.
While the aircraft and proposals appearing below featured
patented ideas that could serve as bases for all-wing or
BWB aircraft, the following aircraft incorporate pertinent
features which appear not to have received patent
recognition. Related patents are mentioned. These all
reflect a shared adventurous spirit among a variety of
Burnelli’s contemporaries working independently, but
embody relevant ideas appearing before and up to the
filing or publication dates of Burnelli’s tailless aircraft
patent.
A full-size replica of a "flying wing" aircraft
designed in the 1930s by a South Bend podiatrist
turned aeronautical engineer goes on display
Friday at the South Bend Regional_Airport.
The two-seat replica of Cloyd Snyder's "Arup
Flying Wing" was assembled by retired engineer
Bernard
Rice.
Snyder dreamed up his revolutionary aircraft
design in the spring of 1926 after he threw a felt
boot heel across a room and noticed that it flew
quite well.
Four versions of the plane were developed during
the 1930s, but the Great Depression forced
Snyder to abandon plans for a commercial 100passenger
model.
All four Arup models were eventually destroyed
by vandals. Rice reconstructed his model from
photographs. It's 19 feet long with a 22-foot
wingspan.
Vought-Sikorsky V-173
"Flying Pancake"
Type:
experimental prototype
(Fighter)
Crew:
1, Pilot
Armament:
none
Specifications:
Length:
26' 8"
Height:
12' 11"
Width:
23' 4"
Gross Weight: 2,258 lbs
Propulsion:
No. of Engines: 2
Powerplant: Continental A-80
Horsepower
80 hp each
Prop diameter:
16' 6"
Performance:
Range:
limited (20 gal. of fuel)
Max Speed:
138 mph sea level
Climb:
to 5000 ft in 7 min
Ten years after the first Arups appeared in the
1930s, another disc-shaped oddity could be seen
flying around the Connecticut countryside. The
Vought V-173 "Flying Pancake" was the
brainchild of Charles H. Zimmerman, who built
his flying wing while employed as an engineer
with the National Advisory Committee for
Aeronautics
(NACA).
NACA's
light-plane
research study of 1933, which provided the
incentive for other tailless designs in the 1930s,
also inspired Zimmerman to design a passengercarrying aircraft that would land and take off like
a helicopter and once airborne, convert to
conventional flight. Perhaps influenced by the
Arup design, Zimmerman built test models that
received NACA endorsement.
Few aircraft flown during World War Two can
surpass the Vought V-173's startling frisbee-like
appearance or its remarkable capabilities. The
unprecedented speed range of this low-aspect
wing type of aircraft potentially ranged from under
48 kph (30 mph) to more than 805 kph (500
mph). The experimental V-173 performed well
enough during testing to warrant the
development of a full-scale military version.
Unfortunately, enthusiasm for new turbojet
powered aircraft reduced interest in slower-speed
tactical aircraft such as the XF5U, the V-173's
successor and the type became an aeronautical
dead-end.
Scientific experimentation with low-aspect ratio
flying wings (short wingspan and long chord)
began in the late 1920s, under the guidance of
Dr. Cloyd Snyder, an Indiana podiatrist with a
fascination for aviation. He became intrigued
when he tossed a felt heel inset and discovered
that it glided remarkably well. Conventional
wisdom, up to that time, dictated that an airplane
wing was most efficient if the ratio of the
wingspan to its chord was 6:1. Nonetheless, in
the early 1930s, Snyder enthusiastically devoted
his savings and time to experiments that
demonstrated the practicality of low-aspect ratio
wings, especially in low-speed flight. Snyder's
greatest contribution over earlier tests of lowaspect ratio wings was the substantial rounding
out of the normally square trailing-edge corners
of the wings, which significantly improved the liftto-drag ratio of the airfoil. His first effort was a
horseshoe-shaped glider, later converted to a
powered model. Three other Snyder Arup models
verified the benefits of the low-aspect ratio
design, which held the promise of takeoffs and
landings at speeds under 48 kph (30 mph) and
cruise speeds of more than 209 mph (130 mph).
Before his company went out of business, Snyder
inspired several other pioneers. One of these,
Charles Zimmerman, an engineer for the National
Advisory Committee for Aeronautics (NACA forerunner of NASA), became intrigued with the
short-takeoff and landing potential of the
horseshoe-shaped wing after witnessing a 1933
ARUP demonstration in Washington. He quickly
set about conducting his own experiments.
Zimmerman's access to NACA wind tunnels
allowed him to explore the most efficient
variations of Snyder's wing designs.
By 1935, Zimmerman
had settled on an
improved
twin-engine
version of the Snyder
wing and completed a
single-person prototype
powered by two 25horsepower motors. The
model
never
flew
because
of
engine
difficulties, but a number
of large rubber bandpowered
models
arrangement was awkward and uncomfortable.
Vought
engineers
then
constructed
a
conventional cockpit with the pilot in a seated
position, although the lowered instrument panel
and leading edge windscreen remained in place
(though this proved to have little value). To allow
sufficient ground clearance for the enormous
three-bladed propellers, the fuselage inclined
upwards at a twenty-two degree angle when
sitting on its fixed landing gear. The pilot entered
the cockpit through a trapdoor in the floor, which
he reached by ladder.
Zimmerman intended the V-173 to "hang on its
props" by hovering in
a vertical attitude.
This, combined with
the requirement of the
low-aspect ratio wing
for a large induced
airflow, necessitated
enormous (16 ft 6 in)
diameter
propeller
blades. However, he
was never able to
convince Vought to
expend
sufficient
convinced
his
funds to develop an
The all-movable, or "flying" tail of the V-173
superiors to allow him
adequate
control
"Zimmer-Skimmer" is quite evident in this view of
to approach aircraft
system for hovering or
the disc shaped aircraft. During its successful
manufacturers
to
ultra low-speed flight,
flight test program, the "Flying Pancake"
construct a full-size
and the aircraft never
experienced several crashes, but sustained little
low-aspect
flew in this flight
damage because of its very low landing peed. Test
demonstrator.
With
regime.
On
one
pilots Were unable to spin the aircraft and were
NACA’s concurrence,
occasion, Zimmerman
amazed at its rapid deceleration as it was pulled
in 1937, Zimmerman
bypassed
Vought
into a tight turn.
approached
United
entirely and submitted
Aircraft and Vought
this proposal directly
made a proposal to the US Navy on August 15,
to the Bureau of Aeronautics, who rejected it
1939 for a full scale prototype. On May 4, 1940, a
specifically because he had bypassed Vought.
contract was in hand.
Zimmerman was very personally involved with
the project and plant personnel took to calling the
unusual aircraft the "Zimmer Skimmer."
Zimmerman found success with the Vought
The V-173 made its first flight on November 23,
Division of United Aircraft, which was on the
1942, with Guyton at the controls. Heavy control
lookout for innovative approaches to fighter
forces almost led to a forced landing during the
aircraft design. By 1938, Zimmerman, now
otherwise successful test, but the addition of
working full-time for Vought, had constructed the
large trim tabs between the rudders, referred to
V-162, an electrically powered remote control
as stabilizing flaps, helped to alleviate the
model with a 0.91-meter (3-foot) wingspan that
problem on subsequent flights. Other problems
flew well enough to earn Navy research funds.
included poor visibility over the large wing and
By March 7, 1939, Vought had completed
resonance vibrations from the large propellers
designs for a full-size wood and fabric prototype,
operating at high angles of attack, which
the V-173, and submitted them to the Navy. On
necessitated the addition of dampers. As the
May 4, 1940, the Navy issued Vought a
induced airflow of the propwash generated much
construction contract for the aircraft. The twinof the lift on the low aspect ratio wing, an engine
engine design relied on a 7.01-meter (23-foot)
failure could result in an immediate loss of
diameter horseshoe shaped wing, equipped with
control, which added to the stress of flight-testing.
twin vertical stabilizers. On the V-162, the entire
Additionally, power-off gliding characteristics
rear section of the fuselage hinged like an
were substantially different without the induced
elevator, but on the V-173, two small "ailevators"
airflow of the propellers.
(aileron/stabilator) extended outward from curved
One problem inherent in low-aspect ratio wings
tail of the horseshoe wing. Twin vertical
was a significant amount of induced drag.
stabilizers and rudders stood up from the wing,
However, Zimmerman came up with a novel
aft and inboard of the stabilators. Zimmerman
solution. The V-173's large propellers counterimbedded the cockpit in the leading edge of the
rotated away from the fuselage so that the airflow
wing with the intention that the pilot would fly the
from the prop wash would help to mitigate the
aircraft while lying prone to reduce drag and
large wing-tip vortices produced by the lowmaximize the effect of the induced airflow from
aspect ratio wing. The landing flare also proved
the propeller thrust. However, the program test
pilot, Boone Guyton, quickly found that the
problematic as the large ground effect "cushion"
of the wing prevented the tail from quickly settling
to the ground upon landing, thus greatly
extending the landing roll. Heavy braking was not
an option because it could cause the top-heavy
aircraft to nose-over. The solution was the
addition of a spoiler on the aft edge of the low
aspect ratio wing, which the pilot could deploy
after touchdown to bring the tail-wheel rapidly
into contact with the runway.
In spite of teething troubles with the innovative
aircraft, Guyton and other pilots found the V-173
to be a remarkable aircraft. In addition to its
short-field capabilities, the broad speed
eed range of
the aircraft proved to be an important asset in
emergencies. One example occurred on June 3,
1943 when pilot Richard Burrough's experienced
an engine failure and made a forced landing on a
beach that resulted in the aircraft flipping over.
However, the V-173 touched down at a mere 24
kph (15 mph) and did not suffer significant
damage. Burroughs was uninjured.
Charles Lindbergh developed a keen interest in
Zimmerman's project, which he observed during
his visits to the Vought-Sikorsky plant while he
served as a consultant. However, he initially
declined Zimmerman's invitations to fly the
aircraft. Lindbergh correctly ascertained that if the
tall, slender landing gear encountered soft
ground, the aircraft would flip over onto its back
with nothing but the fragile canopy to keep the V173's weight off the upended pilot. When he
witnessed Richard Burrough's crash on the
beach, which proved the canopy would safely
protect the pilot, Lindbergh decided that he would
take the airplane for three uneventful trial flights
on November 15, 1943. Subsequently, the V-173
suffered through two other crashes, though
neither was severe. On May 26, 1945, Burroughs
made a forced landing on a golf course. In 1947,
Boone Guyton crashed into high-tension wires on
takeoff, though both he and the aircraft survived
relatively intact considering the nature of the
accident.
While the unusual shape of the aircraft attracted
considerable attention in the local community, the
innovative nature of the technology kept it out of
the media, and security was heavy around the
aircraft. Germany also conducted its own lowaspect ratio research during the war, including
the development of the Sack AS 6 (the "flying
beer tray"), similar to the earlier Snyder designs.
The V-173 proved to be under-powered, yet its
low aspect ratio wing allowed it to take-off at a
mere 46 kph (29 mph). In calm winds, this
required a take-off run of only 61 meters (200 ft).
Landings were possible in considerably less
distance. It could successfully maintain controlled
flight at a 45 degree angle-of-attack - three times
that of aircraft with conventional wings. The
aircraft bled speed rapidly when entering a tight
turn - a characteristic that could prove highly
advantageous in a dogfight.
The V-173's unique flight characteristics
substantiated Navy interest in a full-size fighter or
attack aircraft as the wind-speed generated by an
aircraft carrier or other naval vessel steaming into
a breeze would allow for vertical takeoffs and
landings. This increased the amount of deck
space for other aircraft or allowed for the
construction of smaller ships. In September 1941,
even before the first flight of the V-173, the Navy
was so intrigued in the concept that it contracted
with Vought-Sikorsky to build two VS-315s, which
were larger fighter versions of the V-173. Funding
problems and technical difficulties delayed
completion of the aircraft, designated the XF5U,
until 1947, by which time the Navy had become
more interested in high-speed jets than a
propeller-driven fighter with short take-off and
landing capability. The Navy had the XF5U
scrapped before it could make its first official
flight, though it had reached completion and had
begun taxi tests. Guyton flew it briefly in ground
effect so that he could say it had flown.
The XF5U was a remarkable aircraft in concept,
though its construction posed serious technical
challenges. The large Pratt & Whitney R-2000-7
engines could not drive the propellers directly
because of the curve of the wing that arced
towards the rear of the aircraft. This necessitated
an extended transmission system with a gearbox
that turned ninety-degrees as well as ninetydegree drive shaft coupling in the engine, which
together greatly increased the complexity of the
aircraft. The likelihood of gearbox failure in the
system was high and would have immediately
caused the aircraft to go out of control. The large,
four bladed propellers incorporated a novel
flapping hinge system to allow them to cope with
the asymmetric loading conditions at high-angles
of attack. This system, although innovative,
would have taken considerable time to perfect.
Vought rolled out the V-173 during public
displays for several years after it had finished its
132 flight hours of testing on March 31, 1947 - its
190th flight. In 1949, the company officially
transferred the V-173 to the Smithsonian
Institution. The internal structure of the aircraft
rendered it unsuitable for disassembly and the
aircraft had to travel by barge from Connecticut to
Virginia.
Overview
The basic wing area (427 sq ft.) and planform
(less ailevators and propeller nacelles) of the V173 and XF5U-1 were identical. The airfoil was
the NACA 0015 section on the V-173 and the
NACA 0018 section on the XF5U-1. Two
Continental A-80 engines, rated at 80horsepower each, turned two 16.5-foot threebladed propellers on the V-173. The aircraft had
long fixed main landing gear and a 22-degree
nose-high static ground angle. Wheel fairings
were added after the first flight. The pilot cockpit
enclosure had a windowed leading edge ahead
of the pilot for down vision, and four segmented
leading edge inlets (left and right) for engine air.
For light weight, the airframe structure was made
of wood with fabric covering. With a wing loading
of only 5 lbs/sq ft, the V-173 could lift off in 200
feet in a calm, and with a zero run against a 25knot headwind. However, with a power loading
of 14-lbs/hp maximum, level flight speed was
only 138 mph.
The pilot could enter or egress from the cockpit
through a hatch in the cockpit floor or through a
sliding canopy.
The first flight was of only 13 minutes duration
because of very heavy longitudinal stick forces,
and having only 20 gallons of fuel aboard. The
stick forces were subsequently lightened by
adding the trailing-edge stability flaps and
ailevator trim tabs. The airplane accumulated 131
hours in several hundred flights, many of which
were flown to exhibit the outstanding STOL
characteristics.
Vought’s Chief experimental
pilot, Boone T. Guyton, made 54 flights.
Guyton summed up his observations as:
I was able to apply full power, raise the nose as
high as it could be held, and have control about
all three axes without stalling. The aircraft could
not be completely stalled or even approach a
spin condition. A notable characteristic was high
deceleration in a tight turn due to the aspect ratio
(drag due to lift), and low power loading. Engineand propeller- related vibration showed the need
for articulated (i.e., flapping) propellers. Today,
with its vertical tails and ailevators removed, the
V-173 is in storage at the Smithsonian
Institution’s Air Museum warehouse in Silver Hill,
Maryland.
Charles H. Zimmerman promoted his “Flying
Pancake” design from 1933 to 1937 while
working for the National Advisory Committee for
Aeronautics (NACA) at Langley Field, Virginia.
He filed for a design patent on April 30, 1935 and
was granted patent #2,108,093 on February 14,
1938. With the concurrence of NACA,
Zimmerman
approached
United
Aircraft
Corporation with his novel design in 1937 and
joined United’s Chance Vought Aircraft Division
in that year as project engineer. By August 15,
1939, drafting, engineering design, and
aerodynamic studies were far enough along for
Vought to submit a proposal to the U.S. Navy for
a full-scale prototype of the V-173. The U.S.
Navy placed a contract for one V-173 on May 4,
1940. First flight of the airplane was on
November 23, 1942. Success!!
To best appreciate the very-advanced V-173
design concept, one must go back to 1930 when
Charles Zimmerman graduated from the
University of Kansas with a degree in electrical
engineering and an introductory course in
aerodynamics that helped him secure a job with
NACA. Initially, Zimmerman made a name for
himself by designing a free-spinning wind tunnel
and then a free-flight wind tunnel.
What made airplanes fly was the stuff that young
NACA engineers lived and breathed. This
fascination led Zimmerman to design the V-173
as a flying wing, to minimize wetted area and
parasite drag, and to put the propellers at the
wing tips, rotating so as to oppose induced drag.
It was known that a finite aspect ratio wing had a
bound lifting vortex along the quarter chord line
which, when viewed from the rear, rotates
clockwise at the port (left) wing tip, and
counterclockwise at the starboard (right) wing tip,
causing downwash aft and rotates the lift vector
back to cause induced drag such that:
CDi = CL2/pe Aspect Ratio
Where “e” is the airplane efficiency factor
determined by wind tunnel test.
Zimmerman knew that a right-hand propeller
generates a strong right rotational component to
the slipstream. Hence, a right-hand propeller on
the starboard wing tip and a left-hand propeller
on the port wing tip should reduce induced drag.
The theory of wing lift and induced drag, together
with experimental data available for propeller
slipstream rotation lead to:
CDi = CL2/pe (1-FOO) Aspect Ratio
That’s right, it was called “FOO Factor” or FQ ,
and had theoretical values from 0 to 1 or more,
depending on shaft horsepower. With power off,
FOO=0 and induced drag was proportional to lift
coefficient squared and inversely proportional to
wing aspect ratio. In a high-powered climb, FOO
could be greater than one and induced drag
became induced thrust. This was true not only
theoretically, but actually, as shown by powered
tests of a 1/3-scale V-173 model in the Langley
full-scale wind tunnel (December 1941).
Numerous
free-flight
(rubber-band
and
electricpowered) and captive wind tunnel tests
were conducted between 1933 and 1943. These
tests showed that:
Symmetrical trailing edge flaps provided
insufficient roll and pitch control. Therefore,
“ailevators” were added to the basic design.
(Ailevator was coined from aileron plus elevator
and the spelling was later changed to ailavator.)
Propeller cross-shafting was required for safety
of flight with one or both engines out.
Twin fins and rudders were always part of the
design for directional stability and control.
Vought VS-315 (XF5U-1)
Large diameter propellers at the wing tips,
rotating up inboard
Ailavator surfaces for roll and pitch control
The XF5U-1 was designed as a land-based or
carrier-based fighter to be used with or without a
catapult, with an arresting gear. The airplane
incorporated certain unusual design and
structural features.
The letter of intent for the Vought VS-315 (XF5U1) was issued September 17, 1942. The XF5U-1
was a twin-engine, single-seat, low aspect ratio
flying wing type of airplane, manufactured by the
Chance Vought Division, United Aircraft
Corporation, Stratford, Connecticut.
The first XF5U-1 airplane (Bureau Number
33958) was used for static tests; proof loads,
extended to ultimate, largely confirmed structural
design predictions. The second XF5U-1 airplane
(Bureau Number 33959) was used for
experimental flight test and concept validation. It
was never flown because many hours of engine
run-up showed excessive mechanical vibration
between the engine-propeller shafting, gear
boxes, and airframe structure. The airplane was
taxi tested on February 3, 1947 at Stratford,
Connecticut, but, again, vibration levels were
considered excessive. The airplane was being
readied for shipment by sea through the Panama
Canal to Edwards AFB, California, when the
contract was canceled (March 17, 1947) because
of still unsolved technical problems and the lack
of Navy R&D money.
The jet age had arrived, but V/STOL had not.
Basic characteristics were:
Flying wing, elliptical platform
The wing, the basic outline of which was defined
by two ellipses, so arranged that the major axis of
one coincided with the minor of the other,
comprised the main structure of the airplane, with
the exception of the pilot’s cockpit and the
horizontal and vertical tail surfaces. The greater
part of the wing surfaces and internal structure
was composed of Metalite, a “sandwich” material
providing a particularly strong and light type of
construction. The four-bladed counter-rotating
propellers were driven by cross-shafting and gear
boxes connected to both engines. If one engine
failed, it could be de-clutched from the system
and the airplane flown with the remaining engine
and both propellers operating.
Circular air
intakes in the wing leading edge provided
carburetor, engine and oil cooling air. Two
vertical tails with rudder and fins provided
directional control. Two Metalite ailavators, with
trim tabs across 70% of their trailing edge and
with balance weights on the tips, provided lateral
and longitudinal control. The pilot’s cockpit was a
complete monocoque shell with a formed
plexiglass canopy. The stick and rudder flight
controls were manual except for proportional
hydraulic boost to the ailavators.
Neither the first nor second airplane had
armament, although there were provisions for six
50-caliber machine guns and ammo boxes. Two
Pratt and Whitney R-2000-7 radial engines with
cooling fans and superchargers were mounted
upright in the wing.
The 16-foot diameter propellers were unique for
the time and bear some mention. Because of the
activity factor, twist and shape, the props were
manufactured by Chance Vought Aircraft of
Stratford, Connecticut. The two hydraulically
operated,
fast-acting,
electro-mechanically
governed propellers each had four Pregwood
blades and load-relieving hubs which differed
from the conventional four-way hub in that the
blades were free to “flap” in pairs about the shaft
axis. Low pitch stop was 15 degrees, high pitch
stop was 70 degrees. The propeller pitch control
set the left-hand propeller governor mechanism
which controlled the right-hand propeller
governor mechanism electronically and adjusted
the propeller blade angle. Movement of the pitch
control lever upward decreased pitch, and
downward increased the pitch. Full forward
position governed takeoff rpm (2,700): full aft
position gave approximately 1,300 rpm in take-off
slot and 800 rpm for flight. These were propeller
rpm’s. There was also the more conventional
throttle control which operated in three slots:
“WARM-UP”, “TAKE-OFF” and “FLIGHT”.
Rear View on 21 August 1947
with taped-on work areas and
engine panels removed. The
good size "stabilizing flaps "
can be seen between the two
vertical fins.
Another unique feature of the
XF5U-1 was the stability flap,
located symmetrically about
the centerline of the airplane at
the wing trailing edge. The 15
sq. ft. hinged surface required no pilot control but
automatically provided for change in airplane trim
with change in attitude. The air loads upon the
flap adjusted deflection against a spring loaded
strut. The stability flap was linked to the tail wheel
to insure locking in the up position when the tail
wheel was extended.
Mr. Matthews seems to be enamored of the
XF5U-1. Also that we had whole squadrons of
Go-229 (Horten) flying wings zooming over the
snowy slopes of Mt.Ranier-in'47.
Well, the Flapjacks were certainly cutting
edge,but wrong edge,Propellers even those
turned by gas turbines even the abilty to hover
was secondary to going fast and far.The steam
catapult, angled flight deck and far more relialble
pure jets (also the breaking of the sound barrier)
finished Propeller driven Naval Aircraft.Period ,no
more,with the A-1 skyraider and the F4U- drived
AU-2 soldiering on.
Mr.Barrett Tillman is an execllent aircraft
historian, his books on Naval Aviation are at the
top of the Historian's Craft.-With no mention of
any speculation of the XF5U-1 being other than a
one-off (actually there was a static test airframe)
prototype.
Another source "U.S.Naval Fighters 1922 to
1980,s" by Lloyd S. Jones (Aero Pub. 1977.) has
a very consistant, accurate,(and a great three view of the XF5U-1) account of the whole V173/XF5U-1 saga-including the Protoype's
Demise at Edwards in a very public death by
wreckingball,exactly 50 years ago to the day
March 17,1949.
Also contained in "Naval Fighters" is a history of
all the Protoypes of fighter aircraft used by the
US Navy.Insightful.Why fool around with nasty,
unreilable turboprops such as the Allison T-40
the only reasonably available big (ah ,notice I
didn't say reliable) Turboprop. by the time the
XF5U-1 was at Edwards, the N. American
F86/FJ-2 was already in production, along with
the Grumman F9F Panthers and of course that
particularly nasty surprise-the MiG-15 in Korea. It'
easy to see why the XF5U had no merit because
of the advances in Technology.
The XF5U discoidal aircraft was an invention of
Charles H. Zimmerman, who conceived the
design in the early 1930s. He won a 1933
National Advisory Committee for Aeronautics
(NACA) design competition with a disc-shaped
concept capable of flying at high speeds or
hovering;
NACA
rejected
further development because
they thought the design was
"too advanced".
Zimmerman
was
not
discouraged and in his spare
time built a number of test
models, including a rubberband powered flying version.
His original plan was an aircraft
which carried three crew, in a
prone position to allow maximum streamlining.
The idea was subject to a 1938 patent he filed.
Zimmerman joined Chance Vought Aircraft in
1937, and there was able to produce an electric
powered model of his design, designated V-162,
flown by remote control in test situations,
tethered in a hangar. The rear fuselage was
hinged to act as an elevator.
Zimmerman provided an original blueprint to the
US Navy (featuring no horizontal stabilisers) in
March 1939. A month later, the Navy asked
NACA (which later became NASA) to investigate
the proposal. In October 1939 manufacture by
Chance Vought of a small scale model for wind
tunnel testing was approved. The design was
referred to as V-173.
This revealed problems with the trailing edge
"ailevator" design, and horizontal "flying tail"
stabilisers were introduced. After full-scale wind
tunnel tests in September 1941 at Langley Field,
Va., the Navy asked Vought to build two military
versions of the aircraft, to be designated XF5U-1.
One would be for flight testing and the other for
static testing.
The first flight took place of a V-173 on 23rd
November, 1942. Soon after takeoff, Boone T.
Guyton, Vought's chief test pilot, found the
controls sluggish, and had to struggle to make a
wide turn back to base. Otherwise the design
was a promising one, and a wooden mock-up
XFU5-1 was completed the following June.
Flight tests progressed slowly but satisfactorily.
On July 15, 1944, a development contract
consolidated the V-173 and XF5U-1 programs.
By the end of the V-173 flight tests convinced
Boone Guyton and designer Zimmerman that the
design had potential. They had faced financial
and technical problems but had persisted. One
major problem was the propellers, initially the
same as those used on the F4U-4 Corsair. These
had to be replaced with flapping blades to avoid
vibration; a four-bladed design was finally
produced, each propeller having one pair of
blades staggered ahead of the other pair set at
right angles.
The twin 1,350 hp Pratt & Whitney engines gave
the XF5U-1 an excellent speed range of 40 mph
to 425 mph, much better than the usual 1 to 4
ratio of landing speed to top speed of other good
designs. Water injected engines gave a 20-460
mph range, and gas turbines allowed 0-550 mph.
The ship carried 261 gal. of internal fuel, and six
20 mm cannons, three stacked vertically in each
"wing root".
In June 1947, Boone T. Guyton flew the V-173 to
Floyd Bennett NAS for a Navy Day display. As he
neared the base, bathers on the Long Island
Sound beaches saw a silver and yellow disc
moving slowly overhead and rushed to report a
"flying saucer". Guyton participated in the display
then returned to the Vought factory at Stratford,
Conn. This was the final performance of the
Flying Flapjack.
On March 17, 1947 the Navy had cancelled the
XF5U-1 development, preferring to go with jet
aircraft. The static test aircraft had already been
demolished during laboratory tests, and the Navy
ordered destruction of the flying version. Its
engines, instruments and other salvageable
items were removed and the airframe placed
under the steel ball of a demolition crane. The
first few drops failed to dent the aircraft.
After careful measurements the ball was dropped
between the main beams and spars, and the
aircraft was eventually reduced to crumpled
wreckage. The V-173 was approved for display at
the Smithsonian.
Air Age Publishing Apr 2005
Before the V-173 was flight-tested, the full-size
aircraft was put through its paces in the Langley
Field wind tunnel. Vought's chief test pilot, Boone
Guyton, Richard Burroughs and several Navy
pilots flew it for a total of 131 hours. It also made
several forced landings because of mechanical
problems, but there was little damage because it
flew so slowly. Following numerous successful V173 test flights in 1943, the design work on the
XF5U-1 full-power Navy fighter was begun.
In planform, size and configuration, the XF5U-1
was identical to the V-173 prototype. The
differences between the two lay in engine power
and weight The V-173 weighed 2,250 pounds
and-had 160hp. The XF5U-1 weighed five times
as much and was powered by two Pratt &
Whitney R-2000-7 air-cooled radial engines, each
capable of 1,600hp. Propeller feathering could be
adjusted by the pilot, and the articulation selfadjusted through 20, 1-degree arc positions.
The XF5U-1 was designed to carry bombs or
belly tanks on pylons under its wing. Its
armament consisted of six, 20mm cannon, and
its top speed was calculated to be around
500mpb with a range of approximately 1,000
miles.
By March 1948, the work had been completed,
but when further test were canceled, the Navy
ordered Vought to destroy this remarkable
aircraft and all the drawings and photographs
pertaining to it! Fortunately, some photos and
drawings did survive. The official explanation of
the Navy's seemingly irrational decision to
destroy all traces of the XF5U-1 was that it could
now operate jet aircraft from its carriers. It
considered propeller-driven fighters to be
obsolete.
Although it can't be substantiated, a more logical
rationale for the destruction of the XF5U-1 might
be found by taking a closer look at the official
explanation. After the end of WW II but before the
conflict in Korea, Congress was understandably
reluctant to spend more money on the military.
The Navy was seeking appropriations for
additional carriers. If the honorable gentlemen on
the hill were to learn that the Navy had a highperformance fighter that could be flown off any
small vessel, why would any new aircraft carriers
be needed?
We can only empathize with Charles Zimmerman
and imagine what he must have felt as he
watched 15 years of pioneering work destroyed
by a wrecking crew's steel ball. The real loss,
however, is discovered in the realization that
more than half a century ago, we were offered a
new, potentially safer, form of flying.
After the "Skimmer" program was ended, Charles
Zimmerman returned to the Langley Research
Center in Virginia and was eventually appointed
director of aeronautics at NASA headquarters.
One of Zimmerman's most intriguing theories was
that of the vector flight principle. Canadian
engineer Lewis McCarty adopted it to design and
build one of the world"s simplest helicopters. With
the DeLackner Aircraft Co., he built and
successfully flew a number of very unusual
rotary-wing aircraft.
Luckily, the V 173 was spared the fate of the
XF5U-1 and is now in the possession of the
National Air Museum. Plans are in the works for a
group of Vought retirees in Dallas, Texas, to
restore this rare old bird.
Before he died in 1996, Charles Zimmerman's
lifetime achievements were recognized when he
was made a Fellow of the American Institute of
Aeronautics and Astronautics; he was also
awarded the Wright Bothers Medal.
-Frank Gudaitis
SACK AS-6
In June of 1939, the first National Contest of Aeromodels
with Combustion Engines took place at Leipzig-Mockau.
Arthur Sack, who dreamed of a circular-winged aircraft,
entered his AS-1 model, but unfortunately, it had to be
launched by hand and had poor flying characteristics.
Ernst Udet, who was at the time Germany's Air Minister,
encouraged Arthur Sack to go on with his research. Sack
built four additional models of increasing size, culminating
with his first manned aircraft, the Sack AS-6.
The AS-6 was constructed at the Mitteldeutsche
Motorwerke company, with the final assembly taking place
at the Flugplatz-Werkstatt workshops at the Brandis air
base in early 1944. The AS-6 was a strange
conglomeration from other planes, including the cockpit,
seat and landing gear from an old, wrecked Messerschmitt
Bf 109B and the Argus As 10C-3 240 horsepower engine
from a Messerschmitt Bf 108 liaison aircraft. The wing
assembly was new, with plywood forming both the ribs
and covering. Ground taxiing tests were performed in
February 1944, with the first test proving that the rudder
was not strong enough and some structural damage
ensuing. Five takeoff runs were made during the second
test on the 1200 meter (3940') Brandis landing strip.
During these tests, it was determined that the control
surfaces were in the vacuum area behind the circular
wing, and thus did not operate adequately. The right
landing gear leg was also broken during the final attempt
of the second test. It was thought that the problems arose
due to the low power output of the engine, but because of
a wartime shortage of more powerful engines, it was
decided to change the incidence angle by moving the
landing gear backwards by 20 cm (8"). Since the next
wingspar was located 40 cm (16") farther aft, it was
purposed to attach the landing gear here, but this
introduced the problem of having the landing gear too
far aft and thus the plane could tip forwards on takeoff,
destroying the propeller. To compensate for this, brakes
from a Ju 88 were installed, 70 kg (154 lbs) of ballast
was added just ahead of wingspar number 3 and the tail
control surfaces had 20 mm (3/4") of corrugated plate
added. The third test took place on April 16, 1944 on the
700 meter (2300') Brandis landing strip. The plane
traveled 500 meters (1640') without the tail lifting, although
a small, brief hop was achieved. On the fourth and final
test, the jump was longer, and the AS-6 became airborne,
but an immediate bank to the left due to the torque of the
engine became evident. The small span wings were too
short to compensate for the engine's torque. The pilot
recommended a more powerful engine and more wind
tunnel tests, and Arthur Sack went back to the drawing
board for the remainder of the war.
During the summer of 1944, JG 400, who flew the
rocket-powered Messerschmitt Me 163B "Komet", was
moved to Brandis. They found the AS-6 there and tried to
fly it, but the only attempt resulted in a collapsed landing
gear leg. The AS-6 was damaged in a strafing attack
during the winter of 1944-45, and was broken up to
salvage the wood. All that was left was the miscelleneous
metal parts, and these were thrown into the aircraft
salvage area. In all probability, this is why American troops
who entered the Brandis air base in April 1945 found no
traces of the Sack AS-6.
ZERO ASPECT RATIO ?
Zimmerman Flying Platform
"Whirligig"
Charles Zimmerman conducted some of the
more unusual vertical flight experiments of the
late 1940s and early 1950s with several flying
platforms controlled by the pilot's balance. These
unusual aircraft successfully vindicated his belief
in the feasibility of an extremely simple aircraft
that flyable by anyone that was capable of riding
a bicycle. Unfortunately, Zimmerman's prototype
flying platforms were not scaleable into larger
models suitable for production. However, several
of the engineering principles pioneered in
Zimmerman's projects have found new life in
other segments of aeronautical engineering. Most
notably, the ducted fan remains one of the most
efficient means of vertical lift. The roadblocks
encountered by Zimmerman and his successors
have not stopped a number of dreamers and
visionaries over fifty years later from attempting
to create their own "flying carpets" that are similar
to the ideas espoused by Zimmerman.
Charles Zimmerman worked at the Langley
Aeronautical Laboratory as an engineer for the
National Advisory Committee for Aeronautics
(NACA - forerunner of NASA) until 1938. He left
to work for Chance-Vought developing his ideas
for a Short Takeoff and Landing (STOL) aircraft,
that eventually took form as the V-173 "Flying
Flapjack" (see NASM collection). After the Navy
cancelled an improved version (XF5U-1)
Zimmerman struck out on his own to develop a
small, vertical takeoff aircraft that an average
person could easily fly. He hypothesized that if a
small horizontal platform, with a person balancing
on top, was lifted upward by thrust vectored
downwards, then the pilot's innate kinesthetic
responses would stabilize the platform and
provide for pitch and roll control. Although the
high center of gravity of such a configuration
would seem inherently unstable, Zimmerman
proved otherwise. Like riding a bicycle, if the
platform tilted in one direction, then the pilot
would naturally lean in the other direction to
remain upright. This natural balancing tendency
placed the center of gravity above the thrust axis,
creating an upward pitching moment that
counteracted the toppling action that resulted in
neutral stability. The pilot could then control the
aircraft by simply leaning in the desired direction
and the platform would tilt and gain momentum.
The gyroscopic action of the rotors further
increased stability, and helped to dampen abrupt
movements.
In 1947, Zimmerman completed a prototype
aircraft to validate his hypothesis. Known as the
"Flying Shoes," this tiny construction consisted of
a steel tube truss with two vertically-mounted 65
hp four-cylinder, two-stroke target drone motors
driving 76 cm (30 in) diameter rotors. The pilot
stood on top of the truss and relied on a vertically
mounted pole for balance. The "Flying Shoes"
flew no more than a foot off the ground while
tethered. Because two motors almost never
produced identical amounts of thrust, the platform
exhibited considerable instability and tilted into
the lower-powered engine, regardless of the
balancing action of the pilot. Zimmerman filed a
patent application for an improved model that
surrounded the rotors with an airfoil shaped ring.
This "ducted-fan" increased thrust by reducing
the induced drag of the propellers, and increasing
their efficiency, as well as creating a venturi
effect that increased the airflow through the rotor.
The net effect of the ducted fan was equivalent of
using propeller blades 40 percent longer, but
without the need for a bigger engine to drive
them.
In 1948, Stanley Hiller, president of Hiller
Helicopters, became aware of Zimmerman's
work, and seeing a future opportunity for his
company, purchased the rights to the "Flying
Shoes." Zimmerman was not interested in
forming a business to pursue the development of
his discovery and elected to return to Langley
Aeronautical
Laboratory
to
pursue
his
aeronautical research. Although, he made
considerable progress in the advancement of
hypersonic theory, he did not give up on his flying
platform research. After discussing his ideas for a
new platform with his superiors, they allowed him
time to pursue the development of small flying
platforms to support the growing interest in
alternative forms of vertical lift.
Determined to avoid the difficulties he
experienced with the "Flying Shoes," caused by
the differential thrust of its engines, Zimmerman
came up with a novel solution. His next flying
platform, known as the Jet Board, would not rely
on any engines at all. Instead, it used pressurized
air for thrust. The jet board deserves recognition
the one of the simplest manned vertical takeoff
aircraft in history. The 48 cm (19 in) x 74 cm (29
in) platform had foot straps for the pilot, a simple
steel-tube landing gear, and connections for the
two fire hoses that supplied the thrust from the
ground-mounted gas bottles. The pilot wore a
parachute harness attached by a static line to an
overhead cable to prevent injury in case the
operator lost control, though the platform itself
was not tethered. Zimmerman made the first
flight of his new platform on February 2, 1951.
The platform was so stable that he did not even
realize he had left the ground. Even in gusty
winds, the intuitive balance response of the pilot
was enough to keep the platform level.
Zimmerman also experimented with small gas
bottles mounted to the platform, which allowed it
to fly freely, but with a very limited endurance.
While the Jet Board underwent testing,
Zimmerman began work on a rotor-driven model.
This was necessary as the fire-hose/gas bottle
system was clearly not practical for free-flying
aircraft, and Zimmerman's funding originated
from a NACA program dedicated to the
construction of propeller-driven vertical flight
aircraft. The new design, nicknamed the
Whirligig, used a 2.13 m (7 ft) diameter twobladed rotor mounted on the underside of the
platform. As on the Jet Board, a fire hose/gas
bottle propulsion system powered the rotor with
high-pressure gas exhausted at the rear of the
rotor tips. However, the Whirligig's platform was
considerably larger and heavier to prevent the
pilot from inadvertently contacting the rotor.
Consequently, the pilot had to use larger
movements to make the weight-shift control more
effective. A handrail surrounded the pilot, which
allowed the pilot to make safe and smooth
adjustments. The Whirligig made its first flight on
October 21, 1953.
Testing proceeded smoothly, first indoors, then
outside. However, Zimmerman noted that the
Whirligig was less stable than the Jet Board,
especially in windy conditions. This resulted from
the greater weight of the Whirligig, which made it
harder for the pilot to adjust the center-of-gravity
of the platform effectively. Additionally, the larger
surface area of the platform created turbulence in
forward flight, further reducing its stability,
compared to that of the smaller Jet Board.
The U.S. Army and Navy developed an interest in
flying platforms as personal air scooters for a
variety of military applications and subsequently
issued contracts to Hiller Helicopters and De
Lackner Helicopters for development of a
practical flying platform. However, the Hiller VZ-1
and the De Lackner HZ-1 possessed several
technical flaws that made them unsafe to fly
operationally. On both designs, the high loading
of the propeller blades prevented autorotation,
and production models would have required a
backup engine to prevent the fatal consequences
of an engine failure. Combined with the
substantial fuel load required for operational
missions, the weight of the platforms exceeded
the level at which weight shift alone could provide
effective control, which necessitated control
surfaces. This eliminated all of the advantages of
kinesthetic control. The idea reappeared during
the 1970s, in a project that relied on a reliable,
lightweight cruise missile motor for propulsion.
However, stability problems and noise issues
doomed the project. Hiller and several other
manufacturers experimented with the ducted fan
in an Army "flying jeep" contract, but the
performance levels of these machines fell below
that provided by conventional helicopters, and
budget priorities prevented further work. More
than four decades later, similar flying car
proposals occasionally resurface. Charles
Zimmerman's flying platforms did not ignite a
transportation revolution of the twentieth century,
but are undoubtedly one of the most innovative
approaches to vertical flight, and may yet have a
role to play in personal transport.
EXHIBITS
Flying Platform:
The Hiller Aviation Museum houses some of
the most unique flying machines imaginable. One
such craft, the Flying Platform, is the prototype
developed from National Advisory Committee for
Aeronautics (N.A.C.A.) engineer Charles H.
Zimmerman's concept known as the "Flying
Shoes". Charles Zimmerman, to the amusement
of his engineering peers, proved the theory that
rotors on the top (i.e. helicopters) are inherently
unstable. Zimmerman theorized a person's
natural balancing reflexes would suffice in
controlling a small flying machine. Charles coined
the term "kinesthetic control," similar to riding a
bicycle or balancing a surfboard.
Complementing
Zimmerman’s
"kinesthetic"
theories, the Hiller Advanced Research Division
(A.R.D.) incorporated a five foot fiberglass round
wing, (ducted fan) with twin counter rotating
coaxial propellers powered by two 44hp/4000
rpm, four cylinder opposed, two-cycle, Nelson H59 Engines. The Nelson engine was the first twocycle engine certified by the FAA for aircraft use.
Utilizing the Bernoulli principle, 40% of the
vehicle's lift was generated by air moving over
the ducted fan's leading edge. The remaining
60% of lift was generated by thrust from the
counter rotating propellers.
Hiller Helicopters, on 17 September 1953 signed
a contract with the Office of Naval Research's
Naval Sciences Division (ONR) to incorporate
Alexander Satin's ducted-fan research with
Charles Zimmerman's "kinesthetic" theories. The
classified project was turned over to the ARD at
Hiller Aircraft, and construction began in January
1954. Nine months later the ARD group, working
in complete secrecy, delivered the prototype
model 1031 Flying Platform. The first free flight of
the Flying Platform took place on 27 January
1955, and went in the record books as the first
time man had flown a ducted fan vertical take off
and landing (VTOL) aircraft. In April of 1955 the
veil of secrecy was lifted and all the world wanted
a vectored thrust vehicle for their own
NASA PIONEER DIES; HE
REVOLUTIONIZED AIRCRAFT, FLIGHT
TESTS
DATE: Wednesday, May 8, 1996
Charles H. Zimmerman, an aerospace research
pioneer at NASA's Langley Research Center,
died Sunday in Hampton. He was 88.
He joined the Langley Laboratory of the National
Advisory Committee for Aeronautics, forerunner
of the National Aeronautical and Space
Administration's Langley Research Center, in
1929.
He conducted studies on aircraft stability, tail
spinning and low-aspect-ratio airfoils. He wrote
several NACA reports on his airfoil concept.
``Charlie was a great inventor. Those airfoils
were like early unidentified flying objects,'' recalls
John Duberg, a fellow researcher who became
an associate director at the Langley center from
1975 through 1980.
Zimmerman invented the world's first free-flight
wind tunnel at the Langley center and was in
charge of the development and testing of the
original NACA free-spinning wind tunnel. He also
invented a V/Stol (vertical/short takeoff and
landing) flying wing aircraft in the 1930s.
In 1937, Zimmerman joined the Chance Vought
Division of United Aircraft Corp. to supervise
construction and flight testing of the V-173 Flying
Wing and construction of the XF5U-1 flying wing
fighter. In 1948, he returned to Langley to
supervise research on aircraft stability and to
lead research on advanced aircraft wings.
He was one of a three-man study group who
recommended in 1953 that the nation become
involved in research for space flight. He headed
the Space Task Force in NACA headquarters in
1958, then became chief of the engineering and
contract administration division for Project
Mercury, the nation's first manned space flights.
In 1962, Zimmerman was named director of
aeronautics
at
NASA
headquarters
in
Washington. A year later, he became chief
engineer and retired in that position at the U.S.
Army Materiel Command in 1967.
A memorial service will be held at 10 a.m.
Wednesday at St. John's Episcopal Church in
Hampton.
Assembly instructions for
the FMX-4 “Facetmobile”
About the Facetmobile
The FMX-4 Facetmobile is the creation of aviation engineer Barnaby Wainfan. It is a
homebuilt, one-person aircraft designed on the lifting body principle. Unlike a
conventional aircraft, where lift is created by wings, the entire body of the Facetmobile
generates lift. The FMX-4 has flown over 130 hours since 1993 and has apparently very
good flight characteristics. In 1995 the plane was damaged when an engine failure caused
a forced landing, but it is presently being repaired and will some day fly again. A larger
two-seat version is also planned. More information about the Facetmobile can be found
on the internet at http://users.aol.com/slicklynne/facet.htm
The Model
This model builds into a 1:48 scale replica FMX-4. It may be built as either a static display model or a glider. A word of caution: this model is
not suitable for assembly by very young children, due to the use of sharp tools and the complexity of some assembly steps. Previous experience
with card modeling would be helpful. If you have any comments or suggestions regarding this kit, I can be reached by e-mail at models@currell.net
Model parts are contained in the document fmx4_parts.pdf. Print out the parts document on 8.5"x11" or A4 size white paper card stock suitable
to your printer. 67 lb. cover stock (approx. 8.5 thousandths of an inch or 0,2 mm thick) is recommended.
Tools
Before beginning, you will need the following tools and materials:
a) a sharp knife for cutting
e) a scoring tool or blunt knife for creasing the fold lines
b) a flat cutting surface
f) a glue applicator such as wooden toothpicks or a small paintbrush
c) a ruler or straight edge
g) (for static display model only) a paper clip or similar stiff wire
d) white glue
h) (for static display model only) needle-nose pliers to bend wire to shape
Hints
a)
b)
c)
d)
e)
Select a well-lit, comfortable work area that will remain undisturbed when you are not there.
Keep your hands and tools clean when working, to avoid getting glue on visible parts of the model.
It’s easier to stay organized if you only cut out those parts you need for each step.
Make sure your knife is sharp. When cutting straight lines, use a straight-edge.
Study the diagrams carefully, and always test-fit the parts before applying glue
Assembly
In these instructions, the directional terms are given from the pilot’s point of view. “Port” and “starboard” refer to left and right sides respectively.
Scoring of parts is indicated by thin black lines outside the part’s outline, and by dashed or shaded lines on the part’s surface. Score parts before
cutting them out. In the diagrams, subassemblies are identified by a number within a circle (e.g.
), corresponding to the step in which it was
assembled.
(Step 1) fold and glue the internal formers to the non-printed side of base A5. Attach A15 first, aligning the bottom fold with the front fold line
of A5. Glue A8 to the base and to the shape printed on A15. Fold and glue the inside tail fins, and attach to the base (step 2).
Add nose weight to the base (step 3). If building a glider model, a weight of 2.5 grams (roughly the weight of a U.S. penny) is recommended. For
a static display model, use two pennies (5 g) or more. Attach connecting strips A4 to the non-printed side of top surface A1 (step 4).
Glue the upper body to the base (step 5). This is best done by gluing the rear control surfaces together first, followed by the middle glue tabs on
the upper body. Finally, attach the nose section of the upper body to the base, using the front tabs and the connecting strips as gluing surfaces.
Add the upper engine housing A9 using the locating slots (step 6). Fold and attach the outer fin surfaces A2 and A3.
If building the static model, cut and bend a paper clip or other stiff wire to the shapes shown on the parts sheet. Slide plate A11 over the nose
strut and glue to the model underside (step 7), ensuring the strut lines up with the printed locating guide. Attach the lower engine housing A14
using the locating slots (step 8), sliding over the nose strut if present. Glue the engine plate A12 to the front of engine housing.
The remaining steps are only applicable to the static display model. (Step 9) attach the main struts to the mounting plate A13, sandwiching each
strut between the side flaps of the mounting plate. Glue the plate to the model underside as indicated by the printed shape.
Glue the propeller halves together (step 10) and attach to the aircraft nose. Assemble the wheels and attach them to the wheel struts.
Flight (glider version)
First attempts at flight should be done in a grassy or carpeted area to avoid damage to the model. Bend the rear control surfaces up slightly and
throw the model forward. Try different rudder and aileron positions to see what works best.
fmx4_inst.pdf v1.0
August 2002
© Ralph Currell
www.currell.net
Page 1 of 2
1
A15
Internal structure
2
Attach this part first.
A8
3
Nose weight
Upper body connecting strips
Flying model:
use 2.5 grams (1 penny)
A10
A4
Static model:
use 5 grams (2 pennies)
or more
A1
A5
Open slots
(2 places)
(Inked side
facing down)
4
(Inked side
facing down)
5
Fins (inside surfaces)
Attach upper body to base
A7
Glue upper body
to base in three stages:
port top
A7
Open slots
(2 places)
First
Top view of finished assembly
Glue tabs together
as shown
port top
3
Second
Third
(also glue body surface
over connecting strips
added in step 3)
4
A6
(mirror image
of A7)
6
7
Fins and upper engine housing
A2
8
Nose wheel strut
(omit this step if building
flying model)
Lower engine housing
A14
A11
N11
Slide over strut,
if present
Slide over strut
7WD
Nose strut
A3
A2,A3 (mirror image)
A9
N11
Make from paper
clip using template
on parts sheet
7WD
A12
9
Main wheel strut
(omit this step if building flying model)
10
Wheels and propeller
(omit this step if building flying model)
A17
A16
Assemble as shown
A18
2 pieces
Main strut
A13
Make from paper
clip using template
on parts sheet
fmx4_inst.pdf v1.0
August 2002
© Ralph Currell
www.currell.net
Page 2 of 2
ins
A
Nose wheel
cm
Main gear
top view
front view
1
Open slots
in nose
(2 places)
W
D
side
view
11
7
2
N
3
N
D
W
11
7
4
5
Open slots
in nose
(2 places)
ar
bo
ar
d
to
p
6
po
r
tt
op
st
ins
Templates for landing gear struts
(paper clip or other stiff wire)
8
7
9
10
11
Open
hole
12
15
16
14
18
Open
hole
13
Open hole
(2 places)
17
Open hole
(2 places)
fmx4_parts.pdf v1.0 ©2002 by Ralph Currell
cm
A
Design Group 2
Meeting # 5
April 15, 2006
10:00 am
M
eeetting
ing S
chedule:
Me
Schedule:
2006 Meeting Schedule
10:00 am
FlaBob Airport
Chapter One Hanger
April
May
June
July
August
September
October
November
December
At FlaBob Airport
15
27
24
15
26
16
28
18
16
Check this site for any schedule updates and
changes.
In Chapter One Hanger
http://www.eaach1.org/calen.html
Check this site for newsletters
http://www.eaach1.org/design.html
John D. Lyon
Will present at the next meeting
Thoughts on a Project to Reproduce the
Lockheed Model 33 "Little Dipper