1708

Item 1708

OTHER: Miscellaneous - Thoughtless Ideas - Coaxial - Rigid-Teetering Rotors

Advantages of a larger rotors:

The required power will be less.
There may be a safe autorotation velocity, if auto collective torque-pitch is incorporated.

Disadvantages of a larger rotors:

The vibration frequency will be lower (more uncomfortable).
The force by the pilot will be greater.

Potential solutions to larger rotors.

Posted on Rotary Wing Forum:

Here is a brand new simple idea; ~ the product of a deranged mind.
The objective is to combine the advantages of the rigid rotor and the teetering rotor, to give better cyclic control.

Consider a pair of coaxial rotors that have teetering hinges, short spans, and rigid blades. In addition, the rotors have a fairly small vertical gap between them.

In this gap between the two rotors is a large swashplate type of device. It is extremely robust and it is spring-loaded in such a way that it wants to maintain its disk normal to the mast.

From each end of the upper rotor's hub-bar there is a push-pull rod that is connected to one of the rotating rings on the super swashplate. From each end of the lower rotor's hub-bar there is a push-pull rod that is connected to the other rotating ring on the super swashplate.

The object of this arraignment is to create a pair of rotors that act in a manner partway between that of a teetering rotor and that of a rigid rotor. Basically they will be rotors with hub springs, except that in this case the compression springs are pushing against the counter rotating rings on the super swashplate; not tabs on the mast. This will, hopefully, be a simplistic compromise between good controllability and minimal vibration.

This rotor is controlled by a compromise between weight-shifting and a gyrocopter pitch-change type of control.

The second reason for this arraignment is to assure that the closely spaced teetering rotor blades do not clash. When the blades start to approach each other, as they rotate around the mast, the upper and lower push-pull rods from the upper and the lower rotors will also be approaching each other. The passing of the push-rods will force the blades on both rotors to be parallel to each other at their point of crossing. In other words, the rotors are free to teeter, under hub spring restraint, however they are forced to be coplanar when the blades cross.

Now. Will it work?

This idea for Torque/Pitch Collective Rotor Hub might be added later to give the craft full flight control.

Dave

Vibration:

If the rotor diameters were increased to 5-ft radius then their rotational speed will be approximately 1050 rpm. With 2 blades the vibration will be 35 cycles / sec. From the graph on OTHER: Aerodynamics - Vibration - Rotor Induced - Overview it can be seen that a velocity of 1" per/sec should not represent any significant vibration.

Concerns:

There are 3 fixed locations on each hub-bar mechanisms; the teetering hinge bearing and two locations where the rods meet the swashplate expansion could put an excessive loading and therefore wear on any of a number of bearings.

There may be the need for some 'give' when the blades cross.

To rectify both concerns consider making the short connecting rods of a slightly elastic material or a very strong 'spring' loaded. or perhaps elastomeric rod ends;
http://www.enidine.com/pdffiles/Enidine%20By%20Design/CGRODBBI-Rod%20End.pdf

Last Revised: February 16, 2009