Twin-Engine Propeller-Driven Aircraft Configurations

Gateway News
American Institute of Aeronautics and Astronautics, St. Louis Section
http://www.me.wustl.edu/ME/orgs/aiaastl/
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NOVEMBER 2001
Twin-Engine Propeller-Driven Aircraft Configurations
by John Leonard
C
ausal observation of twin engine propeller
aircraft reveals that most configurations consist
of a forward wing with nacelle-mounted engines on
each side and a single tail empennage. However,
about a third of the aircraft are of various engine and
airframe arrangements. The purpose of this article is
to review the alternative ways in which a twinengine propeller-driven aircraft can be put together
(excluding bi-planes and helicopters.) Interestingly,
25 different configurations were identified in this
study, and illustrated in Figure 1. Aircraft are
arranged in nine categories, as much as possible,
with similar configuration traits. Each configuration
category is identified with a sample aircraft. A few
aircraft do not fit perfectly a single category and thus
span multiple categories. Additional configurations
have been proposed, but all of the ones shown here
were actually built and flown. Baseline twin engine
configurations have been around for years; however,
the design alternatives provide the most interest.
Several of the alternate configurations are morphological extensions of the baseline. Lengthening
the nacelles and shortening the baseline central fuselage results in a twin boom configuration. Carry
this further with elimination of the center fuselage
and a twin fuselage configuration emerges.
Developers have moved engines closer together
resulting in a reduced spacing configuration. The
final movement of the engines to the centerline produces the centerline thrust configurations as a limiting condition. Moving the engines (or at least the
propellers) outward results in the wing tip configura-
tions. The engines can be turned around resulting in
a conventional pushers configuration. And sometimes the engines are located roughly where they are
on the baseline, but attached to the fuselage or wing
by pylons. Aerodynamic advantages can be obtained
by switching the wing and tail, resulting in a canard
configuration. Flying wing configurations, on the
other hand, dispense with the tail (and sometimes
most of the fuselage) all together. Sketches that are
straddling the regional dividing lines in Figure 1
incorporate the features of both groups.
Of the 25 configurations identified, the question
arises as to how popular is a particular configuration? A review of 292 aircraft: British, Canadian,
French, German, international, Israeli, Italian,
Japanese, Russian, and US origin provides the breakdown shown in Figure 2. This list is arranged in the
order of decreasing popularity. For each of the identified aircraft, a sample aircraft name is given along
with the configuration type. For example, the
Lockheed P-38 is a twin boom arrangement with
tractor propellers. (It shares these configuration
traits with the Fairchild C-82, C-119, XC-120, IAI
Aravia, and others).
Figure 2 also shows that the baseline configuration accounts for about 66 percent of all configurations, while the P-38 type is second with about 6 percent. The other 23 configurations make up the
remaining 28 percent. Another interest note, of the
25 configurations, 13 did not have a production
representative.
Figure 1. Twin-Engine Propeller Driven Aircraft Configuration
the two engines cancels each other out. Drag was
also reduced in these configurations by eliminating
some of the interference drag between the nacelles
and wing. Getting the engine off of the wing naturally results in a cleaner, more efficient wing. This
inspired the Macchi M.C.72, Douglas XB-42, and
Dornier Do-335 (all centerline thrust engine arrangements) to be fast propeller driven aircraft. An aft
pusher engine also tends to reduce the fuselage base
drag by pulling the air around the fuselage. The
Cessna Skymaster is reported to be faster with the
front engine out than with the rear engine out.
What advantages can be attributed to the alternative twin engine configurations? Speed is certainly
an advantage for the majority. The twin boom P-38
was much faster than contemporary WW II twin
engine fighters. A twin fuselage configuration, as on
the P-82, increased speed, payload, and range over
its single engine predecessor. These benefits were
due in part to reduced frontal area, drag, and more
powerful engines. The centerline thrust arrangements deals with a serious twin engine aircraft problems; engine out controllability. With both engines
thrusting on the aircraft centerline, an engine failure
does not produce a yaw moment, plus the torque of
2
purpose baseline configuration
is a compromise that satisfies
most user requirements.
Twin engine propeller configurations were of more interest
before the days of jet propulsion. However, turboprop aircraft continue to be designed
and produced for private and
commercial use. In fact, Sukhoi
is presently building a new turboprop light transport (the S-80)
of twin boom configuration.
Ayres is building the
Loadmaster, for FedEx, which is
a side-by-side coupled tractor
configuration. The Bell/Boeing
team is just starting production
of the V-22 with wingtip mounted engines and propellers. Adams Aircraft is starting certification on
their M-309 centerline thrust general aviation twin.
The Rutan Defiant canard tractor/pusher and the
Embraer/FMA CBA-123 fuselage pylon mounted
pusher are recent designs. In the future twin engine
propeller configurations will continue to be developed along with the more common baseline configuration. However, special missions may require innovative solutions.
Figure 2.
Twin engine flying wings have two benefits
inherent to their configuration. First, structural
weight is less because the weight and lift are spread
across the span so that the local lift supports the local
weight (engines, fuel, payload.) Second, without a
fuselage or empennage, drag and weight of these
items are eliminated. Wing tip propeller configurations allow large propeller diameters for V/STOL aircraft, and large amounts of lift from the available
power. In these configurations, propellers or engines
are usually shafted together to prevent a catastrophic
yaw moment in the event of an engine failure.
Canard configurations typically have reduced drag
because both wing and tail produce lift. Classical
wing and tail configurations have a down load on the
tail that must be compensated with additional lift of
the wing. Each of these alternate configurations has
a particular mission advantage; however, the general
ADAM M-309
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Liberty Bell 7 at the Science Center
by Karen Copper
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Saturday, 21 July 2001 marked the 40th anniversary of Gus Grissom’s infamous suborbital flight
and the accidental sinking of the Liberty Bell 7 spacecraft. The St. Louis Section of AIAA along
with the Boeing St. Louis Leadership Association and INCOSE co-sponsored a commemorative event.
The recovered and restored Liberty Bell 7 spacecraft was on display for the summer at the St. Louis
Science Center during its’ national tour.
The spacecraft was actually “home” for the anniversary! The Mercury
space capsule was designed and manufactured in St. Louis at McDonnell
Aircraft Company. Many of the folks who had worked on the project
attended the event. In addition to the touring display, Boeing’s Historian,
Larry Merritt provided many photographs and memorabilia items from his
personal collection and the McDonnell archives. It was a truly unique and
special display for those involved in aerospace in St. Louis.
One hundred-thirteen folks came out to view the display. George
Baldwin, a retired McDonnell pad foreman at Cape Canaveral brought his
collection of Mercury and Gemini memorabilia to share. Some grandchildren attended and learned not only about the early days of space exploration but also of their grandparent’s part in history. It was
a wonderful night to reminisce
and reacquaint with our own
history.
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Second Family Fun Day Paper Airplane Contest
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The second Family Fun Day Paper Airplane Contest was held on Saturday, 5 May at the Ladue
Middle School. Fifty-seven people attended and their enthusiastic feedback indicated a desire for
this to be an annual event! Participation was as follows:
Age Category
2-4
5-7
8 - 11
12 - 15
Adults
Participants
8
3
13
6
13
Time Aloft Winner
Zachary Zuckerman
Alexander David
Daniel Nixon
Tom Kovacs
Gene David
2.6 sec
5.4 sec
5 sec
6.7 sec
9.9 sec
Distance Winner
Peter Jone
Sam Zuckerman
Mitchell Kramer
Christopher Peters
Mark Bierenbaum
27.6 ft
63.3 ft
57.2 ft
76.5 ft
83+ ft
A huge “Thank You” goes to:
Ken Blackburn for speaking, providing design guidance, demonstrating and judging the events. Ken
donated copies of his latest paper airplane publications as attendance prizes.
Martin Long for arranging our use of the Ladue Middle School’s gym and cafeteria.
Andrew and Zachary Cary for helping to enter the contest results and prepare lunch.
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2001 – 2002 St. Louis Section
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NOVEMBER 2001
Chairperson
Peggy Holly
Vice Chairperson
Andy Hesketh
Secretary
Bob Dowgwillo
Treasurer
Karen Copper
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Dianne Chong
John L. Mohr
Rudy Yurkovich
Monday, 7 January 2002,
5pm - 7pm, in Boeing Building
100, Conference Room 2A
(behind the main auditorium)
General
Aviation
Safety
Seminar
Saturday, 19 January 2002, 0730 to 1400
January Dinner Meeting
“Strategic Thinking with Scenarios” Parks College of Aviation,
presented by Solutia Inc.
Tuesday, 15 January 2002
Boeing Bldg 100 Prologue Room
Advanced Reservations Required of
non-Boeing Employees.
St. Louis University
Anheuser Busch Auditorium,
John Cook Hall