GrantR
Senior Member
- Joined
- Jul 16, 2007
- Messages
- 1,329
- Location
- Plains, GA
- Aircraft
- Kolb MarkIII and a "Jake" Gyroplane
- Total Flight Time
- About 85 fixed wing 3 gyro
I hope the following makes sense and is correct. This is the way I see how CLT is important and how some people may misinterpret its important in gyroplane design and how some may falsely think a HTL machine is stable due so some of the flying characteristic it may have.
When a Gyroplane is in normal steady flight the rotor is loaded and it is holding up its own weight and the weight of the airframe. The weigh of the rotor however is separate for the weight of the airframe. The weight of the airframe hangs below the rotor by the control hinge bolts therefore the airframe is like a pendulum or a swing hanging from a limb unless the pilot has a death grip on the stick and has it locked in place.
So with that being said, any additional thrust added from the engine in this steady state of flight would cause the airframe to swing forward regardless of the engine thrust line since the airframe is rotating around the pivot point in the control block. This would appear to be stable since this is a nose up tendency with power increase and a nose down with power reduction.
This can be though of like a pusher vs tractor airplane. Pushers have the thrust about the lifting force which causes a nose down pitch with power increase and tractors have the thrust line below the lifting force which causes a nose up pitch with thrust increase.
Of course a gyroplane will never have the engine thrust above the rotor so no downward pitching in stable flight.
Since the rotor supports its own weight when it is producing lift the rotor weight is not relevant and neither is the vertical cg during steady flight.
Now all this changes when the rotor loses lift and gets unloaded. If the gyroplane experiences 0 or negative lift the rotor quits pulling on the airframe at the pivot point(no lift no pull) so the engine thrust is not acting around this pivot anymore. The vertical cg of the airframe changes or moves up the airframe as the weight of the rotor is added since it is not being supported by lift. In this state the gyroplane airframe and rotor become one as they are essentially floating along. Now this is the critical point where CLT is important. If the thrust line is high, engine is producing a lot of thrust and there is little to no rotor lift the gyroplane will rotate around its vertical cg and bunt over.
When a Gyroplane is in normal steady flight the rotor is loaded and it is holding up its own weight and the weight of the airframe. The weigh of the rotor however is separate for the weight of the airframe. The weight of the airframe hangs below the rotor by the control hinge bolts therefore the airframe is like a pendulum or a swing hanging from a limb unless the pilot has a death grip on the stick and has it locked in place.
So with that being said, any additional thrust added from the engine in this steady state of flight would cause the airframe to swing forward regardless of the engine thrust line since the airframe is rotating around the pivot point in the control block. This would appear to be stable since this is a nose up tendency with power increase and a nose down with power reduction.
This can be though of like a pusher vs tractor airplane. Pushers have the thrust about the lifting force which causes a nose down pitch with power increase and tractors have the thrust line below the lifting force which causes a nose up pitch with thrust increase.
Of course a gyroplane will never have the engine thrust above the rotor so no downward pitching in stable flight.
Since the rotor supports its own weight when it is producing lift the rotor weight is not relevant and neither is the vertical cg during steady flight.
Now all this changes when the rotor loses lift and gets unloaded. If the gyroplane experiences 0 or negative lift the rotor quits pulling on the airframe at the pivot point(no lift no pull) so the engine thrust is not acting around this pivot anymore. The vertical cg of the airframe changes or moves up the airframe as the weight of the rotor is added since it is not being supported by lift. In this state the gyroplane airframe and rotor become one as they are essentially floating along. Now this is the critical point where CLT is important. If the thrust line is high, engine is producing a lot of thrust and there is little to no rotor lift the gyroplane will rotate around its vertical cg and bunt over.
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