thanks HiTech.
here's what i understand so far
Gyroscopic Action(precession) this effect is based on one of the properties that apply to any object rotating in space, even a rotating airplane propeller.
All practical applications of the gyroscope are based upon two fundamental properties of of gyroscopic action:
1. Rigidity in space
2. Precession (the one important to this discussion)
Precession is the resultant action or deflection or deflection of a spinning rotor when deflecting force is applied to its rim.
the rotating propeller of an airplane makes a very good gyroscope and thus has similar properties.
anytime a force is applied to deflect the prop out of its plane of rotation, the resulting force is 90 degrees ahead of and in the direction of application. this causes a pitching moment a yawing moment or a combination of the two depending on the point at wich the force was applied.
the magnitude of this moment depends on several variables. one is the amount of force applied. as a result of gyroscopic action any yawing around the vertical axis results in a pitching moment. Any pitching around the lateral axis results in a yawing moment. this effect has always been associated with tailwheel aircraft and most often occurs when the tail is being raised during takeoff roll causing a yawing moment to the left on clockwise rotating props.
conversely if an aircraft begins a climb from level flight the force applied to the spinning propeller will be at the bottom of the prop. then deflected 90 degrees clockwise resulting in a yawing moment to the right. the size of the moment would be dependent upon the force used to begin the climb. however once a stabilized climb is established and the force has ceased this effect is negated and the effects of p-factor wich cause a left yawing moment take hold. yet even the asymetrical prop loading can be categorized as a force acting on the right side of the propeller disturbing its plane of rotation. hence deflected 90 degrees clockwise produces a pitching moment. however the overall effects of P-factor are much more significant in terms of yaw due to unequal thrust.
Asymmetric Propeller Loading(P-factor) the effects of P-factor ussually occur when the airplane is flown at high angles of attack. ie. takeoff turns and climbs.
asymmetrical loading of the prop simply means that the load on the upward moving blade is different from the load on the downward moving propeller blade.
when an airplane is flying at a high angle of attack (ie: the propeller axis inclined upwards from the direction the aircraft is moving) the thrust generated by the downward moving blade is much larger than the thrust created by the upward moving blade.
this is due to the downward moving blade meeting the oncoming relative wind at a greater angle of attack and velocity than the upward moving blade.
since the propeller blade is an airfoil, increased angle of attack and velocity mean increased lift, or in the case of the propeller blade, more thrust.
thus the downward moving blade on the right side has more thrust than the upwards moving blade, causing the airplane to yaw to the left.
at low speeds and/or when the airplane is maneuvering and pulling High G loads the yawing tendancy is greater because the airplane is at a high angle of attack.
as the airspeed is increased and the aircraft is not pulling G's the airplanes angle of attack is reduced, the asymmetrical loading decreases and the yawing tendancy is decreased.
then there is the good old
Torque reactionthis effect is based on newtons third law of motion which states that for every action there is an equal and opposite reaction.
most airplane propellers rotate in a clockwise direction. this produces a force that tends to roll the airplane counterclockwise about its longitudinal axis.
this reaction can be understood by visualizing a rubber bad powered model airplane.
wind the rubber band up so that when released it will rotate the prop clockwise.
if the fuselage is released while the propeller is held, the fuselage will rotate in a counterclockwise direction.
This effect of torque reaction is the same in a real propeller drvien airplane, except that, instead of the propeller being held by hand, its rotation is resisted by air.
Torque reaction is stronger when power is significantly advanced while the airplane is flying at slow airspeed.additional effects are the spiralling slipstream wich causes a left yawing moment greatest at low speeds (clockwise prop) the slipstream from the prop spirals back around the fuselage and strikes the left side of the vertical stabilizer and rudder. at low speedsand high power the spiral is very compact and powerful. as speed increases the spiral elongates and the flow along the fuselage becomes more equal.
also for multiengine aircraft with wing mounted propeller driven engines there is the effects of the accelerated slipstream (also known as induced airflow). a substantial amount of lift is derived from the propellers spiraling slipstream as it passes across the area of the wing behind the propeller. the effect is not apparent on single engine airplanes with a centerline mounted engine.
in summary:
gyroscopic precession: potential for both yaw and pitching moment depending on where the force applied
yaw and/or pitchp-factor: asymetrical thrust causing a yawing moment when the axis of the propellers rotation is not parallel to the aircrafts direction of travel through the air. caused by high angles of attack.
yawtorque reaction:
roll spiraling slipstream:
yaw accelerated slipstream:
roll is induced if an engine is inoperative or power output is changed. lift is lost on one side while not on the other.
phew. that was a lot of writing
I believe p-factor is to weak.
also torque effect from changes in power at low speed is not powerful enough.
[This message has been edited by Citabria (edited 01-13-2001).]
