Learn to Fly The Box Canyon Easy in, sometimes hard out..

The Box Canyon
Easy in, sometimes hard out..
Provided by
www.mountainflying.com
Conditioned
Response
Even the unconcerned aviator flitting
through the mountains at cruise power
and cruise airspeed must cultivate a
conditioned reflex to maintain a position
allowing a turn to lowering terrain and
guarding against flight beyond the pointof-no-return.
These axioms must be a conditioned
reflex rather than instinct, because
instinct may be wrong in an airplane.
BOX CANYON OPTIONS
Released from the confines of the
traffic pattern, you find yourself heading
for the mountains to swoop over ridges
By Sparky Imeson
and soar beside majestic peaks. Caught
up in the thrill, you lose track of your
position and suddenly find yourself in
ground
where
an
escape
turn
must
be
a box canyon requiring course reversal
BOX CANYON TURN
made. It will be approximately 500-feet maneuvering to escape what might
become a precarious position.
Mountain flying, like Mother Nature, if there is not sufficient room to turn AGL.
can be harsh and unforgiving for the around.
novice (and especially the complacent
experienced pilot) who fails to adhere
The second law requires the pilot to
to the two basic premises for mountain establish a turn-around point whenever
flying. It is really a simple matter to flirt flying upslope terrain. The point-of-noreturn
is
One small step can put you a mile above everyone.
defined as
a point on
the ground
of
rising
t e r r a i n
where the
terrain out
climbs the
aircraft.
Learn to Fly
with the mountains if you always remain
in a position to be able to turn toward
lowering terrain and then never fly
beyond the point of no return.
The first law, being able to turn away
from the terrain while having some extra
altitude to descend, encompasses the
idea that you never enter into a canyon
16
The turna r o u n d
point
is
determined
as
the
position
where,
if
the throttle
is reduced to idle, the aircraft could be
turned around during a glide without
impacting the terrain. Obviously, if you
exercise this option, the power is not
reduced to idle. This is merely a gauge
to judge and establish the point over the
January 2011 • www.fly-low.com
Photos furnished by www.
mountainflying.com
Contact your local FBO
or flight school and ask
for a trial flight. You’ll
be hooked and your life
will never by the same.
The hammerhead turn or wing over may
appear to be viable options to extricate
yourself from the predicament. Pilots
have, in all seriousness, asked my advice
about performing a hammerhead turn as
an emergency procedure for getting out
of a tight spot. The hammerhead turn is
an aerobatic maneuver. Definitely it is
best to avoid this maneuver in a “tight.”
fast in this case), it still takes twice the without your airplane’s wings, do steep turns left and right.
amount of time to complete the turn not exceed the limit load factor. For
around (four times further traveled).
certification the airplane must be able to Next the instructor demonstrates a
withstand the ultimate load factor for a climb attitude at the best rate-of-climb
What about using flaps during this period of fewer than 2 seconds without airspeed. The student mimics this
steep turn? Use them as appropriate permanent deformation of the structure. attitude. The airplane can be returned
to the flight conditions. Flaps were Otherwise the airplane may experience to level flight and the airspeed indicator
can be covered and the student, by
invented to allow an airplane to increase structural failure.
learning the pitch attitude in relation to
its approach angle without an increase
the horizon is able to fly at the best ratein airspeed. They work because lift and
NATURAL HORIZON
of-climb airspeed within plus or minus
The wing over (another aerobatic drag are directly proportional. If the lift is
maneuver) is more often performed increased (by applying flaps to increase It is imperative that the pilot know his one knot.
while playing in the mountains
attitude in order to
This natural horizon is easy to use in the
rather than being used as an
safely perform flight
emergency escape maneuver.
flatlands
as a reference for basic attitude
in a canyon, more
flying.
In
the mountains the natural
especially the box
The hammerhead turn and
horizon
may
disappear. By visualizing a
canyon turn. Attitude
wing over requires the pilot
horizon,
basic
attitude flying can still be
is the relationship of
to preplan, allowing sufficient
maintained.
The
base of the mountains,
the airplane to the
at
least
six
to
eight
miles away, will
airspeed to transition to
horizon. The natural
represent
the
natural
horizon. What
a climbing pitch attitude.
horizon is “hidden” in
When you find yourself in
if
the
airplane
is
closer
than
the six to
the mountains.
an emergency situation your
eight miles? Visualization is still used.
airspeed is likely to be close
The natural horizon Perhaps the mountains in the distance
to a stall. Neither option is
is used to teach are visible out the side window. Project
desirable or available.
flying
by
outside the same horizon visually to the front of
visual
reference. the airplane.
Until you have practiced
The
instructor
the box canyon turn and
demonstrates the nose
BOX CANYON TURN
understand the mechanics
position in relation to
of and the ramifications of an
the horizon for level
To explain the box canyon turn it is
unintentional stall close to the
flight, the wing position in relation to necessary to consider two scenarios. In
terrain, the safest and most commonly the camber of the wing), the drag is the horizon in level flight, and the nose
Cont’d on page 22
used method of course reversal for increased (and hence, no increase in position in relation to the horizon during
escaping the tight, that is, the rapidly airspeed during a steep approach).
rising terrain or the narrowing confines
of a canyon, is to make a steep turn at a
For most airplanes the addition of flaps,
slow speed, using flaps if prudent.
up to half the total available, provides
more lift benefits than drag because
The stall speed of an airplane increases the drag can be “subdued” with excess
as the square root of the wing load factor. power.
In a level, coordinated 60-degree bank, At a high-density altitude it may not
regardless of airspeed, the airplane be possible to use full flaps without
experiences a 2-g load factor. The square intentionally losing altitude to maintain
root of 2 is 1.41, so there is a 41 percent a safe airspeed. If a trade-off between
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increase in stall speed.
altitude and airspeed cannot be made
because of rapidly rising terrain, limit
Most pilots could care less about a the use of the flaps to the extent that the
formula for determining the radius of airplane will maintain a constant altitude
turn. Since this isn’t “Math 101,” we during the turn.
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aren’t concerned with computations,
only the fact that the radius of a turn
Remember too that flaps reduce the
is equal to the velocity in true airspeed structural strength of the airplane. The
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(knots) squared, then divided by a POH (pilots operating handbook) may
constant of 11.26 times the tangent of say the airplane is certified for 3.8 gs,
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us the radius of turn can be shortened percent reduction). Many of the normal
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by either reducing the true airspeed, category airplanes are stressed for 3.8
or by increasing the angle of bank. The gs (g = gravity units). This is the limitgreatest benefit is from a combination of load factor that should not be exceeded
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both slowing and banking.
during maneuvering flight. Okay, some
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The ratio of turn radius to an increase you know, that 50-percent safety factor
in airspeed at a constant bank varies required by regulation to be built into
as the square of the true airspeed. If the airplane? Shouldn’t the airplane be
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www.fly-low.com • January 2011
17
The Box
Canyon
Air Show Photos by Carl Wilcox
Check next month for more....
Easy in,
sometimes
hardCont’d
out..
from page 17
the first, the pilot is flying along at cruise
power setting and cruise airspeed. In the
second case, the pilot is flying at minimum
controllable airspeed. This minimum
controllable airspeed is probably not an
intentional flight condition.
Flying over water beyond the poweroff gliding distance from the shore,
sometimes causes the oil pressure gauge
to begin ticking. And it hasn’t done that
before. Next the engine may appear to
give a little shudder of roughness. This
might happen several times before
you again approach the safety of the
shoreline.
A similar phenomenon occurs when
flying upslope terrain in the mountains.
Your left arm becomes shorter. This is a
normal self-preservation aspect of flight.
You unconsciously pull away from the
rising terrain and often the deterioration
of airspeed goes unnoticed.
Disclaimer
For the pilot who does not violate the
basic premises, there would be no need
for this maneuver. For the pilot who does
violate the basic premises, it might be
best to consider making a steep turn at
the slowest speed consistent with safety.
So, rather than using the box canyon
turn to extricate yourself from situations
caused by bad judgment, consider the
box canyon turn a training maneuver
used to enhance your understanding of
flying and improve your flying skills.
The box canyon turn varies from the
steep turn in that it is either performed
from level flight at such a slow airspeed
that an unintentional stall is imminent, or
some excess airspeed at the beginning of
the maneuver allows the nose to be raised
above the horizon prior to initiating the
bank and the airspeed, during the turn,
will be too slow to sustain level flight.
We have learned the airplane always
stalls at the same critical angle of attack.
22
January 2011 • www.fly-low.com
When banking the airplane, the stall
speed increases (remember, it increases
as the square of the wing load factor?).
Whenever the airplane is banked in
a coordinated turn, it is balancing
the centripetal force (horizontal lift
component that causes the turn) and
the centrifugal force (the force of the
turn). The turn takes place because
the centripetal force pulls the airplane
towards the inside of the turn.
Without a compensating increase in
the amount of total lift during a turn, the
airplane will lose altitude. The total lift
(lift) is divided between a vector force
that sustains the weight of the airplane
and its contents (weight). The portion of
lift that is directed sideward (centripetal
force) causes the turn. The centrifugal
force acts towards the outside of the
turn.
steep turns.
Procedure from
Cruise Flight
The box canyon turn could be described
as a combination of the steep turn and
wing over. The nose is raised above the
horizon, but nowhere near the 40-degree
attitude of the wing over. About five to 20
degrees is about right, depending on the
airspeed.
This does two things for you. First it
trades airspeed for altitude and second,
it slows the airspeed for a smaller radius
of turn.
rollout.
through about 45 degrees toward zero
degrees during the rollout.
Initiate the turn - the procedure
requires coordination to accomplish all
Initiate the turn - the procedure
items at the same time:
requires coordination to accomplish all
items at the same time:
•
Increase pitch attitude
•
Increase power
•
Maintain pitch attitude initially
•
Begin a bank
•
Increase power
•
Apply full flaps
•
Begin a bank
•
Apply full flaps
At approximately 45 degrees of bank
increasing toward 60-90 degrees:
At approximately 30 degrees of bank,
increasing toward 60-90 degrees:
•
Relax back pressure from the
control wheel
•
Relax back pressure from the
control wheel
Recovery - at approximately 45 degrees •
The pitch attitude will fall below
of bank, decreasing from 60-90 degrees: the horizon
At the same time, full power is added
and full flaps (providing the airspeed
•
Increase back pressure on
is within the flap operating range) are
the
control
wheel to arrest any loss of
applied while beginning the bank. The
altitude.
bank will be a minimum of 60 degrees
To maintain level flight while turning it and may approach 90 degrees.
•
When the airplane is in a position
is necessary to increase back pressure
that allows, reduce flaps to one half
(more lift equals an increase in angle of
To insure that the g-load factor is not
attack). This increases the load factor exceeded during the steep bank it is
Procedure from Climbing Flight
and stall speed.
When operating near cruise airspeed
necessary to relax the back pressure
the
box canyon turn was described as a
once the bank passes about 45 degrees.
Some pilots get into trouble with the The back pressure is not increased again combination of the steep turn and wing
box canyon turn without realizing it until the bank passes through about 45 over where the nose was raised above
because they have been “conditioned” degrees toward zero degrees during the the horizon.
to maintain level flight when performing
Hopefully, the airspeed is near the best
rate-of-climb speed or best angle-of-climb
speed. This is usually a critical situation
because the airspeed will probably be
slower than Vy or Vx due to the “short
arm” effect.
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While applying full power and full flaps,
a bank is established at a minimum of 60
degrees. Again the bank may approach
90 degrees.
Recovery - at approximately 30
degrees of bank, decreasing toward zero
degrees:
•
Increase back pressure on the
control wheel
•
Reduce flaps to one half
Summary
The box canyon turn is at best an
emergency procedure only to be used
when all else fails. It is necessary
and prudent to practice it with an
experienced instructor. Without practice
it is very easy to get into an accelerated
stall condition that will exacerbate the
original situation.
The best advice is to avoid situations
which might require a box canyon turn
course reversal. In more than 40 years
of flying in the mountains I have always
relied on and used the steep turn for
course reversal.
Previously we stated that the back
pressure was relaxed to insure that the gEditor’s Note: For the best mountain
load factor was not exceeded. This is not flying reading material or just plain good
as much of a problem at low speed, but it instruction on taildraggers or for a safe
still exists. The main reason for relaxing way to fly any plane go to:
the back pressure now is so the airplane
www.mountainflying.com.
does not stall. The back pressure is not
increased again until the bank passes
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23