T
RAINING
M
ANUAL
–
L
ANCAIR
IV/IVP
AERODYNAMICS AND PERFORMANCE
FACTORS
Thin air at high altitudes has a significant impact on an airplane’s flying
characteristics because surface control effects, lift, drag, and horsepower are all
functions of air density. Pilots who operate aircraft at high speed and high
altitudes are concerned with the forces affecting aircraft performance caused by
the interaction of air on the aircraft. With an understanding of these forces, the
pilot will have a sound basis for predicting how the aircraft will respond to control
inputs.
A.
Reduced weight of air
The reduced weight of air moving over control surfaces at high altitudes
decreases their effectiveness. As the airplane approaches it absolute altitude,
the controls become sluggish, attitude is difficult to maintain making altitude and
heading difficult to maintain. For this reason, most Lancairs are equipped with an
autopilot. Winglets increase wing area, however aileron area has stayed the
same, requiring more control force input.
B.
Determined weight of air
The internal combustion engine requires a given weight of air to produce a
specified horsepower. For a given decrease of air density, horsepower
decreases at a higher rate, which is approximately 1.3 times that of the
corresponding decrease in air density.
C.
Maintaining level flight
For an airplane to maintain level flight, drag and thrust must be equal. Because
density is always greatest at sea level, the velocity at altitude given the same
angle of attack will be greater than at sea level, although the indicated air speed
(IAS) will not change. Therefore, an airplane’s TAS increases with altitude while
its IAS remains constant. In addition, an airplane’s rate of climb will decrease
with altitude.
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2007
LOBO
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