1352

Item 1352

DESIGN: UniCopter ~ Rotor - Blade - NACA 00xx - Elastomeric Active Twist Brg.

Overview:

The torque tube is firmly affixed to the blade's spar and skin from approximately r = 105" (r/R = 0.92) outward to the tip. Objectively (hopefully), a change of pitch at the root of the torque tube will result in exactly the same change of pitch at the tip end of the blade.

The ID of the Spar and the OD of the Torque Tube are equal at approximately r = 74" inward toward the root. There is an increasing gap between the torque tube OD and the opening for the Torque Tube in the Spar. This gap, or at least the tip end of it, is filled with an elastomeric bearing. The bearing is intended to assist in transmitting twist from the torque tube to the spar. In addition, the wall of the elastomer is thicker at its root end and this means that it will transmit more torque at its tip end then at its root end. This change in thickness is proportional to the amount of twist along the span of the blade.

The elastomeric is responsible for transmitting a lot of the torque from the torque tube to the spar and skin.

Axial X-section through the Elastomer:
There appears to be no reason for the shims. ~ May 26, 2005

There is the ability to locate cylindrical shims (as shown above), with different diameters and lengths, inside the elastomer. This is standard for a conventional radial elastomeric bearing but I don't believe that it will be necessary.

Consider:

Consider having an extension on the elastomeric where the core's edges are. This will eliminate the feather thin edge and may be better in transferring the torque from the elastomeric to the core.

Note:

The following notes discuss the use of shims. They are left in the text to help explain the function of the elastomeric.

The greatest number of elastomer layers is at the root end since this is the end where the greatest difference between tip and root pitch (torque tube) will exist. The maximum twist between the root and the tip will be from + 12º to -12º approximately.
The removal of layers when progressing toward the tip allows the torque tube to transmit a portion of its rotation to the spar. This means that the small diameter and weaker tip end of the torque tube does not have to transmit as mush rotation to the blade.
Because of the length and potential weight of the bearing, the elasticity should be very week and the thickness of elastomers and shims be very thin.
The elastomer will stop two or three inches from the tip end so that the end of the tube can be bonded directly to the spar, along with the 'paddle'.
For the sake of weight reduction, it might be advantageous to divide the long elastomeric bearings up into shorter lengths.
The tubular shims may not serve any purpose. A better arrangement may be simply to have the wall thickness of the elastomer (rubber) increase, just as the OD and ID of the torque tube does, from tip to root.

See MAKE Rotor - Blade - NACA 00xx - Elastomeric Active Twist Bearing 1343, particularly the section 'Manufacturing'.

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Initially displayed on or before September 19, 2004: Last Revised: September 3, 2005

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