3-Bladed Rotor

[Kugel]

For a fixed gross takeoff weight, will there be a difference in rotor disk diameter (blade length) for 3-bladed rotor versus a 2-bladed rotor?

[Kugel]

Can a safe, effective, 3-bladed rotor be made with only flapping hinges?

I have an idea (probably not new) for a 3-bladed rotor head with under-slung flapping hinges. However, I read in another post that a 3-bladed system would also require drag hinges. The flapping hinges I understand; the drag hinges, I don't understand.

This head would be fixed in pitch, but still move in roll.

Thanks in advance for any input!

[JPHarrison]

A Cierva C.30 was tested with a single hinge on each of its three blades, the hinge inclined in both flapping and flapping axes to couple the two motions. Hinge dampers were not required with a certain coupling arrangement. More details are available in the following reference, specifically that discussing ground resonance:

Rotary Wing Aircraft: A series of articles, Aircraft Engineering [1/1940-8/1940]; James A.J. Bennett

[Kugel]

Originally Posted by JPHarrison

...... the hinge inclined in both flapping and flapping axes to couple the two motions..........

Is this what you meant to say? I am sorry, but I do not understand that statement. Can you please clarify?

Thanks for the input.

[JPHarrison]

A hinge may be oriented to provide blade motion about any combination of the flapping, drag, and feather axes.

For example, delta-three hinge is inclined to couple blade flapping and feather motion and is an extremely common feature on rotor systems.

The Fairey Gyrodyne rotor blades were attached to the hub with hinges that coupled flapping/feathering, and drag/feathering.

More details available in the following references:

The Era of the Autogiro, James A.J. Bennett, Journal of the Royal Aeronautical Society Vol. 65 (October 1961), pp.649-60

Principles of Helicopter Engineering, Shapiro J., Temple Press Ltd, London, 1955

[Kugel]

Thank you Mr. Harrison for the replies and references.

Sorry that I did not respond to you, sooner.

[Fl90]

Kugel, the disk loading will not change if you add a blade and keep the diameter the same. The blade loading will change if you add a blade of equal chord. Lower blade loading will allow lower tip speed. There are a bunch of variables and purposes that would dictate the use of one over the other.

Phil.