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PPO Power Push Over. A forward flip supported by a high prop thrustline (HTL) in a gyroplane configuration that is pitch unstable. PPO can and is often induced by PIO or severe downdraft. In normal flight when the gyroplane rotors are properly loaded a PPO will not happen. If a gyroplane's rotors becomes unloaded (large reduction in rotor angle of attack) the engine pushes the nose of the gyroplane over ( in a leverage-type action ) and is unrecoverable. Although not the only cause, the typical cause of PPO is PIO.

PIO Pilot Induced Oscillation. Pitch oscillations in which pilot reaction time equals or exceeds machine reaction time, which makes the oscillations worse. Typically, only gyroplanes that are not well-damped in pitch are susceptible to PIO. PIO can be reduced, ot eliminated, by having a pitch-stable gyroplane and/or a well trained pilot. The term PIO is a bit of a misnomer, since the oscillations might be induced by upsets outside of the pilot control, such as a wind guts or a power surge.

Pitch Stable Gyroplane. A gyroplane that quickly returns from an upset to trim airspeed and rotor AOA, without pilot intervention. Stable gyroplanes are less susceptible to PIO/PPO.

Statically Pitch-Stable Gyroplane A statically stable gyro tends to maintain its airspeed and rotor AOA when disturbed (say, by a throttle change or turbulence).

Dynamically Pitch-Stable Gyroplane A Dynamically stable gyro is a statically stable gyro that has enough damping so that any oscillations caused by its stable reactions die off quickly.

Pitch UnStable Gyroplane A gyroplane that does not return to trim airspeed and rotor AOA when disturbed. Grossly pitch unstable gyroplanes require constant pilot input in order to stay right side up. These gyroplanes are highly susceptible to PIO and PPO.

HTL High Thrust Line. The propeller thrust line passes well above the gyroplane center of gravity (CG) (typically 2" or more).

CLT. Center Line Thrust. The propeller thrust line passes through the gyroplane center of gravity (CG). Rarely gyroplanes are exactly CLT.

NCLT. Near Center Line Thrust. The propeller thrust line passes close to the gyroplane center of gravity (CG), typically within 2 ".

LTL. Low Thrust Line. The propeller thrust line passes well below the gyroplane center of gravity (CG) (typically 2" or more).

HTL Gyroplane. A gyroplane design that has a High Thrust Line. These gyroplanes may be pitch unstable and may be susceptible to PIO/PPO if not properly stabilized. A popular way to stabilize HTL gyroplanes is by adding a well-designed Horizontal Stabilizer.

CLT Gyroplane. A gyroplane design that has Center Line Thrust. These gyroplanes can not PPO. These gyroplanes can be unstable or stable. The horizontal stabilizer is making the CLT gyroplane more pitch stable.

LTL Gyroplane. A gyroplane design that has a Low Thrust Line. These gyroplanes can not PPO. These gyroplanes are inherently stable as long as the engine is producing thrust. The horizontal stabilizer makes the LTL gyroplane more pitch stable.

Blade Unloading (Rotor Thrust is Reduced). A dangerous condition in which the rotorblade's Angle of Attack (AOA) drops below the angle required for normal flight. This can be caused by a number of factors such as pilot stick input, PIO, downdraft and other zero-G manouvers.

Low G or Zero G event (same as blade unloading) The initial instant of a low G event happens, not because RRPM has dropped (it hasn't had time to do that, yet) but because rotor angle of attack has been reduced. If the low AOA keeps up for more than a second or two, RRPM starts to drop and can get to a point of no return. BUT (a huge but), if the gyro normally relies on the rotor thrust to stay upright, (such as in a HTL gyroplane without an effective Horizontal Stablizer) the gyro is apt to PPO/torqueover/dragover long before a serious loss of RRPM has had time to occur.

Bunt Bunt is often meant as a slang word for PPO but other things can be a 'bunt' then a PPO. The term "Bunt" can be confusing and a more exact term should be used in technical discussions.


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Terms to Avoid in Discussions:

Bunt Bunt is often ment as a slang word for PPO but other things can be a 'bunt' then a PPO. Bunt can be confusing and a more exact term should be used in technical discussions.

HCLT or LCLT Mis-used Acronyms. "High Center Line Thrust" this is like saying Skinny Perfect Weight Person, "Low Center Line Thrust" is like saying "Fat Perfect Weight Person". These terms should not be used as they are oxymoronic. Either your thrust is passing through the center of gravity or it is not.

Pilot Push Over A dangerous manouver likely to be fatal. The problem with is term is that it can be confused with PPO-POWER Push Over. If someone has another term for this please advise. If not please be sure to make clear you are not talking about a PPO.
 

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