RotoPlane
Gold Supporter
Chuck, to move forward I need some clarification on your below statements (in bold text).
The first quote seems to say to me that an articulated two-bladed rotor with a hinge on either side of the center of rotation would not vibrate intolerably with a spring restraint, where a flexing fiberglass non-hinged rotor would…..yet the second quote tells me both would vibrate intolerably.
It seems to me that both of these rotorheads could be subjected to a spring restraint either by the bending of glass or by the weight of a tilted airframe and vibrate due to the "T-bar" effect. I really hope I'm wrong and the articulated hinged head would work just fine with two blades.
When you said "hinged", were you referring to a head hinged on the center of rotation, like a teetering head?
Ed, with a Hiller servo rotor, you can slow response enough that the counterweight can catch up with the main rotor blade in small models.
Also, no one really cares how much a model vibrates so long as the radio doesn’t shake apart.
Teetering is commonly locked out in RC models to permit inverted flight. Vibration would be intolerable in a full size machine with a hingeless 2-blade rotor.
If you’re going to dispense with flap hinges in a full size machine, you’d better have at least 3 blades.
Ed, with a 2-blade rotor, any flapwise stiffness results in vibration.
Look at all the reports of shake from just sticky teeter bearings. Those were mainly tilt head machines where the pilots muscles supplied the spring restraint against flapping when the teeter bearings stick.
In one instance a number of years ago before universal internet, a Mini-500 helicopter owner in South Africa contacted me about lateral 2/rev shake he was experiencing and it was sticky teeter bearings.
With 3 or more blades, spring restraint against flapping becomes a steady force. You can sorta view it as single-phase vs.3-phase power. With 3-phase power, you can generate a rotating magnetic field and motors don’t need starting capacitors; with single-phase power, the magnetic field just pulsates and you need something to provide a phase shift for starting. But single-phase motors always buzz and vibrate more than 3-phase motors.
The first quote seems to say to me that an articulated two-bladed rotor with a hinge on either side of the center of rotation would not vibrate intolerably with a spring restraint, where a flexing fiberglass non-hinged rotor would…..yet the second quote tells me both would vibrate intolerably.
It seems to me that both of these rotorheads could be subjected to a spring restraint either by the bending of glass or by the weight of a tilted airframe and vibrate due to the "T-bar" effect. I really hope I'm wrong and the articulated hinged head would work just fine with two blades.
When you said "hinged", were you referring to a head hinged on the center of rotation, like a teetering head?