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The pilot should turn on the master switch during the walk-around pre-flight inspection to insure that the
rotating beacon and strobe lights (If present) are functioning. If all or part of the flight is to occur at
night, the navigation lights, instrument panel lights, taxi and landing lights should also be checked for
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proper operation.
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Electrical System
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Propulsion System
Propulsion System
The propeller is a rotating airfoil. It is subject to drag, stalls and other aerodynamic factors that apply to
any airfoil. The propeller provides the thrust to pull the aircraft through the air. As seen at right, the cross
section near the hub of the propeller is thick, and has a fairly large angle of attack. The angle of attack
and the thickness decreases toward the tip of the blade. Since the linear speed at the tip is much faster
than at the hub the change in angle of attack provides uniform thrust along the surface of the blade.
The propeller is normally connected directly to the engine crankshaft. Some aircraft , however, employ
gear arrangements between the engine and the propeller.
Propellers fall into two main categories.
· Fixed Pitch
· Controllable pitch
Controllable pitch propellers allow the pilot to set the pitch of the blades, either directly or via a
governor, to the best angle for the flight condition and performance desired. Usually for takeoff, a fairly
“flat” angle of attack and high engine RPN is used to produce maximum horsepower and thrust. As
altitude is gained the pilot can reduce RPM and increase pitch for a cruise climb condition. Once cruise
altitude is reached the throttle, mixture and propeller pitch can be adjusted for the desired cruise
performance.
The pilot has only one method of controlling thrust on fixed pitch propellers; that being adjusting engine
RPM. With controllable pitch propellers, the pilot can adjust two controls; these being RPM (throttle)
and Manifold Pressure (propeller pitch control). The Tachometer indicates RPM and the Manifold
Pressure Gauge indicates the manifold pressure.
On constant speed propellers, a governor automatically adjusts the pitch of the propeller blade whenever
the engine throttle setting is changed. Low RPM and High Manifold pressure should be avoided, as this
places undue stress on engine components, and can lead to eventual engine failure.
For any given blade angle, the propeller has an ideal geometric pitch. It is designed to travel a certain
distance in one revolution. However, due to slippage, the ideal geometric pitch is never attained.
Therefore the effective pitch is always less than the geometric pitch. The propeller is never 100%
efficient.
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http://www.uncletom2000.com/gs/propul.htm [1/23/2003 11:18:55 AM]
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Stall Warning System
Most aircraft are equipped with a Stall Warning system of some type. On some older aircraft, a small
moveable flap located on the leading edge of the wing engages an electrical switch in the cabin, which
activates a stall warning buzzer or horn. On some later aircraft, the system is pneumatic, with a small slot
in the leading edge of the wing. Both types sense approach to stall, and sounds a device in the cabin,
warning of impending stall.
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Weight and Balance
WEIGHT AND BALANCE
Overview
Weight affects the flight performance of an aircraft in many respects. An airplane which is overloaded
will be deficient in performance because:
Higher takeoff speed is required.
Longer take-off run.
Reduced rate of climb performance
Shorter range of flight
Reduced cruise speed
Reduced maneuverability
Higher stall speed
Higher landing speed
Longer landing roll
Balance Principles
As shown in the figure below, the aircraft is somewhat like a childs "teeter-totter" with respect to
longitudinal balance. For the plank to be in balance, The sum of the moment s on each side of the pivot
point (fulcrum) must be equal. A MOMENT is simply the weight multiplied by a moment arm
(distance) from some reference point. In this example, the moments are measured from the center
fulcrum point.
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As seen, the plank is in balance because the sum of the moments on each side equals 5000 pound inches.
　
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