Flying With Realism - 2004/04

Flying
Realism
by Ralph Grose
With
THE ABILITY TO fly a model airplane in a smooth, precise,
scalelike manner without erratic motion is a skill for which many of
us strive. However, airplanes have a few inherent characteristics that
tend to inhibit smooth, exact control. If the pilot is aware of this and
understands how to compensate, he or she can do a more realistic
job of flying the aircraft.
The normal level turn will be more realistic if the pilot can
smoothly roll the airplane to the bank angle, hold the angle constant
throughout the turn with no climbing, diving, skidding, or slipping,
and then smoothly roll back to straight and level flight.
A skidding turn is a situation where the turn rate is too fast for
the angle of bank. The airplane will skid to the outside of the turn,
similar to the way a racecar would skid while turning too fast on a
moderately banked track.
A slipping turn is a case where the turn rate is too slow for the
angle of bank. The airplane will slip sideways toward the inside of
the turn; it may or may not lose altitude in the process.
You can recognize a slipping turn when you view it from the
ground; the wing on the outside of the turn (the high wing) will hang
back, and the airplane’s nose will be pointed slightly above the
horizon.
The three primary flight controls are elevator, ailerons, and rudder.
Their controls are as follows.
• The elevator is used to pitch the airplane about its lateral axis.
• The ailerons are used to roll the airplane about its longitudinal
axis.
• The rudder is used to yaw the airplane about its normal axis.
The three axes intersect at the airplane’s center of gravity.
The control functions overlap. As the pilot uses the ailerons
while entering a turn, one aileron moves down and the other aileron
moves up. This produces a differential in lift between the right wing
and the left wing, which causes the airplane to roll to the banked
attitude.
The aileron that moves down causes the drag in that wing to
increase. The aileron that moves up may reduce drag in that wing
for a small movement of the control and then increase the drag for a
larger movement.
In any case, there will be a differential in drag between the right
wing and the left wing, which will cause the airplane to yaw in a
direction opposite to the roll. This is called “adverse yaw” because
when the pilot uses the ailerons, as a rule he or she does not want
the airplane to yaw in the opposite direction.
While rolling to a banked attitude at the beginning of a turn,
adverse yaw will prevent the airplane from turning as fast as it
normally would for a given angle of bank. This causes it to start a
slipping turn.
The method to correct for adverse yaw is to use the rudder in the
same direction with the ailerons—right rudder control with right
aileron control. The rudder will cause a yawing moment in the
direction of the turn that balances the adverse yaw moment.
It takes practice to coordinate the two controls. Too much rudder
control will cause the airplane to skid and not enough will allow it
Drawings courtesy the author
April 2004 79
80 MODEL AVIATION
to slip. The general rule is to use enough
aileron control to make the airplane roll as
fast as you want it to and use just enough
rudder control to prevent it from slipping.
Many Radio Control (RC) pilots use the
ailerons alone to roll into or out of a turn.
This works reasonably well when making a
turn in a fast airplane that has a relatively
short wingspan, such as an aerobatic type or
a military fighter. There the slipping turn is
barely noticeable, especially if it is a steeply
banked turn.
However, it is still present to some
extent. If you look closely at the start of the
turning maneuver (while rolling in), you can
see that the outside (high) wing is hanging
back and the nose of the airplane is pointed
slightly above the horizon.
While entering a turn in a slow airplane
that has a long wingspan, the slipping turn is
obvious. If the model also has excessive
dihedral, the pilot may have difficulty
getting the airplane to start a turn at all
unless he or she uses the rudder along with
the ailerons.
While flying straight and level in a
straight climb or a straight glide, the total lift
in an airplane’s wing is essentially equal to
the airplane’s weight. The amount of lift in a
given wing is determined by a combination
of forward airspeed and angle of attack.
The angle of attack is the pitch angle
between the wing and the direction of flight.
While climbing or gliding, the airspeed is
typically slower than while flying level; thus
the angle of attack must be greater to
provide the same amount of lift.
While the airplane is in a banked
attitude, the lift has a horizontal
component that causes the model to turn
(fly in a circle). Since, while turning, the
wing must continue to provide lift to
support the weight of the airplane and
additional lift to make it fly in the circle,
the total lift must be greater than it was for
straight flight; otherwise, the airplane will
pitch down and begin to lose altitude.
Assuming that no power has been
added to increase airspeed, increasing the
angle of attack must create the additional
lift. To prevent loss of altitude while
turning, the pilot must use elevator control
to pitch the airplane to an increased angle
of attack and consequently increase the
total lift of the wing.
The rule is to use just enough upelevator
control in proportion to the angle
of bank to keep the nose pointed directly at
the horizon all through the turning
maneuver. While rolling into the turn, the
angle of bank gets steeper and the upelevator
control must be increased as
needed. As you roll the airplane back to
straight and level flight, you must
gradually release the elevator control or
else the airplane will begin to climb.
While the airplane is turning, the wing
on the outside of the turn is moving in a
larger circle than the wing on the inside of
the turn. Since each wing will get all the
way around its circle in the same length of
time, the outer wing is traveling at a faster
airspeed and therefore is producing
slightly more lift and drag than the inner
wing.
The unequal lift of the right wing
versus the left wing will cause a weak
rolling moment in the direction of the
turn. This will slowly increase the angle
of bank beyond that which the pilot
intended; this is called the “overbanking
tendency.”
The unequal drag will cause a yawing
moment opposite the direction of the turn
that will prevent the airplane from turning
as fast as it normally would for the
steeper bank angle. Hence the
overbanking tendency also causes a
slipping turn (same as the effect of
adverse yaw). The overbanking tendency
is more prevalent while making a shallow
turn in a slow airplane that has a long
wingspan.
What is the solution? After rolling into
the turn, neutralize the ailerons and the
rudder, continue to hold up-elevator to
prevent a diving turn, and then hold a
small amount of aileron control opposite
the direction that you are turning.
This is a case in which you do not use
rudder along with the ailerons. The
opposite aileron control used by itself will
cause a rolling moment that will balance
the rolling moment caused by the unequal
lift (which is caused by the unequal
speed). The adverse yaw moment that you
get when using the ailerons will balance
out the unequal drag (which is caused by
April 2004 81
the unequal speed). Continue to hold the
opposite aileron until you are ready to roll
out of the turn.
The preceding descriptions of adverse
yaw, overbanking tendency, and additional
lift needed while making a turn may seem
confusing. However, although it does take
practice to properly coordinate the
controls, the procedure for making a level
turn is simple. To make a level turn to the
left:
1) Use left aileron and left rudder
together until the desired bank angle is
reached; simultaneously use enough upelevator
to keep the nose of the airplane
pointed at the horizon.
2) Neutralize the aileron and rudder.
3) While turning, continue to hold the
up-elevator and hold just enough right
aileron to prevent the airplane from
overbanking.
4) Roll out of the turn using right
aileron and right rudder; simultaneously
relax the up-elevator.
Dihedral is a feature that provides stability
about the airplane’s longitudinal axis. The
wings form a slight V angle as viewed
from behind. Dihedral is effective only
when the airplane is skidding or slipping.
If momentary turbulence causes the
airplane to roll to a banked attitude, since it
is not turning at that time it will begin to
slip forward and sideways toward the
lower wing. The dihedral angle has the
effect of increasing the angle of attack on
the lower wing and decreasing it on the
higher wing. This causes a differential in
lift between the wings. As a result, the
airplane will tend to roll back to the level
attitude.
Aircraft designers seem to like large
dihedral angles. This does make the
airplane more stable. Some pilots—myself
included—prefer an airplane that does not
have so much dihedral; excessive dihedral
exaggerates our errors whenever we fail to
coordinate the controls perfectly.
Suppose I am flying a full-scale
Aeronca Champion. (It has excessive
dihedral and exhibits significant adverse
yaw.) Failing to use enough rudder control
along with the ailerons, I have rolled into a
turn and then neutralized the ailerons and
rudder in the usual way. The adverse yaw
prevents the airplane from turning as fast
as it normally would for the angle of bank I
have. This causes the airplane to slip
toward the low wing, and the excessive
dihedral provides a strong rolling moment
that tends to make the wings roll back to
the level attitude.
If I try again, still failing to use enough
rudder control, the excess dihedral makes
the wings roll back to level again. Unless I
begin to use enough rudder control, I will
eventually learn that I must continuously
hold aileron control in the direction of the
turn to maintain a constant bank angle, and
I end up with a slipping turn throughout
the maneuver.
Had I properly coordinated the controls
as previously described, the adverse yaw or
the overbanking tendency could not have
caused the airplane to slip, the excess
dihedral would not have been in effect, and
the Champion would have performed a
smooth turning maneuver as well as any
other airplane.
Although some of us do not appreciate
excessive dihedral, it turns out that it is the
feature that makes the Aeronca Champion
an excellent primary trainer. The
Champion encourages—in fact, insists—
that the new student use the rudder along
with the ailerons to roll into or out of a
turn. Otherwise, a sloppy maneuver will be
the result.
Unlike with a model airplane, where
you can only see a poorly executed turn if
you look for it, the pilot of a full-scale
airplane can feel a poorly executed turn—
and it feels bad. Therefore, a pilot who
received primary training in the Champion
will probably have learned good
coordination of the controls and will
display it throughout the remainder of his
or her flying career.
Torque Effect: The propeller turns
clockwise as seen from behind. The air, in
holding it from spinning still faster, exerts
a counterclockwise moment that causes the
airplane to roll to the left. In addition, the
air pushed aft by the propeller tends to
spiral about the fuselage, striking the
vertical tail surface on the left side. This
causes the airplane to yaw left.
The torque effect is partly a rolling
tendency but mostly a yawing tendency. It
is more noticeable when using full power
combined with slow speed, such as just
after takeoff or while making a steep
climb.
Some airplanes have the vertical fin
offset, which causes a yawing moment to
the right to balance the torque effect at the
airplane’s cruising speed. The rudder trim
control on our RC models’ transmitters
may be used for the same purpose.
An airplane can be trimmed to fly
straight and level at only one airspeed at a
time; it will be out of trim at any other
airspeed. Assuming that the model has
been trimmed to fly at the airspeed you
intend to fly it, the normal way to correct
for torque is as follows. When you enter a
climb or when you are using additional
power above cruising, use right rudder
control to balance the left yaw moment.
When the engine is throttled down to
idle, the torque effect is almost
nonexistent. However, the trim settings
that correct for torque while flying straight
and level are still in effect. So while
attempting to glide straight ahead, the pilot
may need to hold a small amount of left
rudder; otherwise, the airplane will slowly
turn to the right. MA
Ralph Grose
10071 Fox St.
Riverside CA 92503
[email protected]
Our Full-Size
Plans List
has hundreds
of models
to choose from.
See page 207
for details.
F u l l - S i z e P l a n s
956 Grumman F-4F Wildcat ..........................................................................$11.25
Jim Ryan’s RC Electric fighter spans 30.6 inches
No. 904 Y2K Racer: Sport Electric FF by Charles Fries spans 18 inches A
No. 905 Buhl Sport Airsedan: RC Scale model by Phillip S. Kent spans 72 inches E
No. 906 Grumman Ag-Cat: Rubber powered FF FAC Giant Scale by Rees spans 36 inches C
No. 907 Bristol Brownie: RC Scale by Robelen for geared six-volt Speed 400 spans 44 inches C
No. 910 3Quarters: RC sport model by Randolph for Norvel .074 spans 45 inches B
No. 911 P-47: RC Scale Electric model by Ryan for Speed 400 spans 31 inches C
No. 912 Simple Simone: CL trainer by Netzeband for glow .15 engine spans 36 inches B
No. 916 Piper Malibu Mirage: Rubber-powered Giant Scale by Fineman spans 431/2 inches C
No. 917 Sir Lancelot: RC sport model by Henry for O.S. .61 spans 72 inches D
No. 918 Skyraider: CL 1/2A Profile by Sarpolus for Norvel BigMig .061 spans 29 inches B
No. 925 Bird-E-Dog: Ernie Heyworth and Ed Lokken’s RC Electric Sport Scale model C
No. 926 JoeCat: RC sport jet by Beshar for Toki .18 DF unit spans 37 inches C
No. 927 Kairos: CL Stunt model by Dixon for .46-.61 engine spans 58 inches C
No. 928 Beta Blue Chip Racer: Rubber-powered FF Scale model designed by Tom Derber B
No. 929 Dewoitine D.338: Multimotor RC Electric Scale by Mikulasko spans 781/2 inches E
No. 930 Westland Lysander: RC Scale model by Baker for .25 spans 56 inches E
No. 931 1959 Ares: Champion RC Aerobatics model by Werwage spans 501/2 inches C
No. 932 Wing400: RC Electric flying wing by Hanley for Speed 400 spans 36 inches B
No. 933 Kepler 450: CL speed-limit Combat model by Edwards for .21-.32 two-stroke A
Plan does not include full-size template shown on page 40 of the August 2002 issue.
No. 934 VariEze: FF Peanut Scale canard by Heckman spans 13 inches A
No. 935 Classic 320: 1/2A Classic Power design by Pailet for Cyclon .049 or equivalent B
No. 936 Prince: RC sport Pattern model by Robelen for O.S. .25 spans 51 inches C
No. 937 Clean Cut: RC sport aerobatic model by Sarpolus spans 90 inches E
No. 938 Diamond Gem: Compressed-air-powered FF sport model by Ken Johnson B
No. 939 Project Extra: RC Scale Aerobatics model by Mike Hurley spans 106 inches **$49.50
No. 940 Cessna No.1: RC Electric Sport Scale by Papic spans 321/2 inches B
No. 941 Mooney and Beechcraft Bonanza CL 1/2A profile sport models by Rick Sarpolus B
No. 942 Zenith CH 801: FF Rubber Scale model by Fineman spans 20 inches A
No. 943 Wildman 60: Old-Time Ignition CL Stunt model by Carter spans 59 1/2 inches C
No. 944 Shoestring: Semiscale RC sport Pattern design by de Bolt spans 60 inches D
No. 945 F-86 Sabre: Semiscale CL Stunt model by Hutchinson spans 56 inches E
No. 946 Electric Zephyr: Electric RC Pylon/sport model by Smith spans 40 inches B
No. 947 Chester Special: O.S. .40-powered CL Scale model by Beatty spans 43 inches **$27.00
No. 948 Moffett Reduxl: High-performance Rubber-powered FF design by Langenberg C
No. 949 Scratch-One: Electric RC sailplane/basic trainer by Aberle spans 45 inches B
No. 950 BareCat 650-C: CL sport Stunt model by Netzeband spans 54 1/4 inches E
No. 951 Douglas O-46A: RC Sport Scale model by Baker spans 54 inches E
No. 952 Lavochkin LaGG-3: Felton’s CL Sport Scale design made from cardboard E
No. 953 USA-1: Multiple-award-winning CL Stunt model by Werwage spans 61 1/2 inches C
No. 954 B-2 Spirit Stealth Bomber: Electric FF model by Ken Johnson spans 42 inches B
No. 955 Electric Flash: Electric-powered RC park flyer by Stewart spans 44 inches C
Full-size plan list available. A complete listing of all plans previously published in this
magazine through no. 952 may be obtained free of charge by writing (enclose 78¢
stamped, pre-addressed #10 business-size letter envelope) Model Aviation, 5161 E.
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