1181

Item 1181

DESIGN: Dragonfly ~ Rotor - Hub - Layout

Overview:

Faster response to cyclic inputs, because of offset hinges.

Less vibration, because the blades' centers are close to the rotor's virtual center, similar to teetering hinge.

The stagger between the two rotorhubs and/or the angle between the two masts angle can be smaller then that of a conventional intermeshing configuration.

There should not be any Ground Resonance, because the blades are inter restrained in-plane.

Mockup Pictures:


Bottom view ~ Showing flight control mechanism	Bottom view ~ With pair of tie-bar assemblies added

Drawing: 3 blades

Modifications Required:

To lower elevation when grip is flapped up, so that there is clearance for the blades of the other rotor to pass over the top. This is particularly critical in roll when one rotors grip is at the extreme up flap and the blade passing over is at the extreme down flap.

Remove the top portion of the grip, increase the strength of the lower portion and have a pin, with a large shallow crown (carriage bolt), connect the two.
Lower the outer side of the lead/lag bushing. This should not be a problem, because it is the inner side that is taking the centrifugal load.

Lower the top of the lead-lag bearing and housings, so that there is more clearance for the other rotor's blade to pass over the top. The yoke appears to be the critical clearance point. Increase the diameter of this bearing to offset the loss of surface area.

A hinge spring, plus stronger blades and hub will reduce the amount of required flapping angle somewhat. This is moving in the direction of an ARR.

Incorporation of delta-3:

Forget about delta-3, by flap hinge geometry. It looks like the delta-4 component (lead/lag) is 45º out of phase with the cyclical Coriolis.

Going with delta-3 by twisted spline geometry

Notes:

Universal Joint in Control Linkage:

See; DESIGN: Dragonfly ~ Control - Flight - Torque Tube & Joint - Layout

Hinge Location:

The axes of the pitch and lead/lag hinges intersect. The flapping hinge is directly above the previous two hinges, by approximately 1", therefore its axis intersects the lead/lag axis.

Arm Length:

The offset is 13.5". They are quite long so that there is good clearance between the blade root and the other rotor's hub. These rotors are intended to work with a 22º angle and 24" stagger.

Phase Lag:

The large flapping hinge offset will result in a significantly reduced phase lag. Will there be a conflict between high controllability vs. high stability? Ref. DESIGN: Dragonfly ~ Control - Flight - Assembly - Phase Lag

Flap:

A flap of 10º will result in a vertical change of the universal joint of 0.063". The torque tube is about 12" long therefor the angular chang at the pitchboss is 0.03º and this is insignificant.

Lead/Lag:

The undersling will significantly reduce the primary cause of lead/lag. See; DESIGN: Dragonfly ~ Rotor - Disk - Lead-Lag

Lubrication of Yoke's Bearings and Bushings:

There must be a means of retaining the oil (or grease) at the inner end of the yoke. Consider a rubber boot which can move with the rotation and axial motion of the torque tube.

Potential Problems:

Drag from poor aerodynamics. Can be faired somewhat and the forward velocity is not intended to be fast.

High weight ~ Could the hub frame be eventually made from composite and honeycomb.

Will the lead-lag action want to change the relative lengths of the two lead-lag 3-bar tie-bars. Will elongation of glass thread handle this change? It looks like 5º of lead on one blade will result in a tie-bar change in length of 0.0027". This should be insignificant since 5º is much more than lead/lag will be, the bars will be preloaded and E-glass will stretch. What is the termal coefficient of expansion of E-glass and the aluminum thread. Perhaps eventually the carbon thread and the composite hub will both be carbon and have identical rates of expansion.

The overall weight must be reduced. Elastomeric pitch bearings will help.

Related Web Pages at this Site:

OTHER: Flight Dynamics - Rotor Hub - Offset Teetering Hinge Concept

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Initially displayed: March 30, 2003~ Last Revised: October 9, 2004

The above utility invention is openly and publicly disclosed on the Internet to negate an entity from patenting it, to the exclusion of all others whom may wish to use it. ~ Reference patent law 35 U.S.C. 102 A person shall be entitled to a patent unless - (a) the invention was known ... by others in this country, ..., before the invention thereof by the applicant for patent.