Worthy of our interest....
Ralph Taggart`s article, posted in the May 2000 issue of "KitPlanes" magazine,
"Let's tackle the Gyroplane Horizontal Stab controversy", is brought to our attentiion by GyroNut Jack Ronda. While written in regard to the full sized aircraft, it applies considerably to our smaller R/C model versions....
French GyroNut Jo Jo Chaulet, and our own Rick Anderson both noted this to be true while recently developing the small (non-heli mechanically controlled) pure autogyro versions of the full sized aircraft....
The following are extracted highlights from Ralph's comments that are of value and interest to us...
"The C.G. [center of gravity] of a gyro-plane is the point in space where the aircraft is balanced, with respect to mass, in all three axes. The most significant parameter for positive pitch stability appears to be the relationship of the vertical c.g. to the engine's thrustline."
"PIO recognition and recovery is simple,
but if recovery is not initiated by the third or fourth cycle, the rotor typically strikes the tail or the prop or both."
"While there never was any doubt that most gyros could fly wilthout a stab, the issue essentially was whether they would be safer and easier to if an effective horizontal stab were present."
"If the engine thrustline is aligned with the vertical c.g., no pitching moment is generated, no matter what the magnitude of the engine thrust vector"
Case 1. Point C. on Figure 1. If the engine thrustline is aligned with the vertical c.g., no pitching moment is generated......... in effect, engine thrust will not rotate the nose.
Case 2. Point B. If the thrustline is below the c.g., the airframe pitches up with applied thrust --- with the magnitude of the pitching moment increasing with the larger values for offset and / or thrust. This positive pitching moment tends to be stablizing because it acts to load the rotor system.
Case 3. Point H. If the engine thrustline is above the vertical c.g., the result is a negative pitching moment that --- lacking any counteracting aerodynamic force --- will pitch the nose down. If the offset is significant and the engine is producing a lotof thrust, the accelerating rotation can exceed the rate at which the rotor can keep up, resulting in a rotor strike on the prop and / or tail. While unloading a gyro rotor is never a good idea, there are no immediate consequences if the engine thrustline is on or below the vertical c.g. However, if the thrustline is above the c.g., even a transient loss of loading could have catastrophic consequences. This tuck and strike sequence is the common element in both PIO and bunt-over accidents. and it now seems that the relative position of the engine thrustline and vertical c.g. plays a significant role.
Finally the Stabilizer issue....
"We've come a long way from since the early years of the "great stab debate" where one instructor derisively referred to putting on the "training wheels"
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rev...9-00... jb