A138

DESIGN: Electrotor-Simplex ~ Rotor

Optional Arraignments Under Consideration for Electrotor-Simplex Rotor-Hub and Flight-Control:

See 1475.html

Notes:

Downward Teetering over Pilot:

There is no reason for the blades to teeter down at 90º ψ over the pilot since roll consists of tipping one rotor disk outward while leaving the other one horizontal. To stop perturbations from teetering the blade excessively downward at this azimuth consider incorporating both of the following.

Locate a static hub spring at approximately 45º ψ to force the root of the blade upward.
Locate a bar(s) behind the pilot's head that slopes upward. This bar would have a Teflon upper surface. Reinforce the leading edge of the blade where it could make contact with this bar. This bar would physically slide the blade over the head of the pilot.

Concern:

Gimbaled Rotors and Gyroscopic Precession:

The motor on the gimbaled rotor moves with the tip path plane. Will motor on the gimbal configurations result in gyroscopic precession; and is this good or bad.

The use of the motor's gyroscopic precession on the Electrotor-Plus cycles at the rate of the rotor's rotational speed. I.e. it cycles with the teetering. The motor's gyroscopic precession on the gimbaled Electrotor-Simplex only comes in to effect when the cyclic stick is moved and therefor it is not an advantage.

. During a longitudinal change (craft pitch change) the GP of the two rotors should self cancel each other in the interconnecting control linkage. During a lateral roll one rotor will not tilt, however the GP in the downward heading rotor (left rotor on roll to the left) will want to pitch up at the front. I think that this pitch up may transfer through the control linkage and attempt to pitch both rotors up at the front. This maybe OK during forward flight since the stick should be pulled back slight during any roll to maintain elevation. During hover it make want to back the craft up.

Having said all of the above, if the GP of the Predator motor was a serious amount would it's cross-coupling not detrimentally affect the model airplane during aerobatic flight.

From Rick

The airplane is travelling approx. 150mph or more in a straight line. It has a mass exceeding the motor. There is effect on the airplane from torque and gyroscopic precession that the pilot has to overcome with his controls, if you ask any pilot -- both in model and full size aircraft. In fact aerobatic pilots make use of this force feedback to make unusual maneuvers. They also offset the engine mounts in all aircraft to help compensate so precession acts at an angle to rotational axis. I still think it's a problem because without modeling the situation you really don't know what will happen - that's what bothers me - the unknown! I don't believe it's a situation where this pitch up may transfer loads to the control system - it will transfer --- the question is how much? and when?

Vibration - Rotor Induced:

The operation depends on varying the collective pitch by varying the rotor RPM. This varying rpm will very likely result in sympathetic (self-exciting) vibrations in the frame and long spars at specific RRPMs.

In addition, the changing difference in the rpm of the two rotors will probably add to this problem. Can encoders and a controller be used to keep the rpm of both rotors the same?

Perturbations:

See the concerns on the linked page; OTHER: Miscellaneous - Thoughtless Ideas - Auto-Collective Rotor Hub

Friction:

Will the friction in the slim large diameter ball bearing be excessively high?

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Last Revised: November 23, 2007