0088

Item 0088

DESIGN: SynchroLite ~ Rotor - Hub - 2-blade Teetering - Layout

May be changed to control system geometry because of combined Hooke and Delta3 oscillation. October 19, 2001~Where did this come from?

See Revision Required at bottom of page.

Drawing:

Undersling: See [Rotor - Disk - Undersling] 0734

The pre-coning angle of the hub is 1.8706 degrees. See [Rotor - Disk - Coning Angle] 0735

The center of gravity is at 37.812" radius. See [Rotor - Disk- Centers of Forces] 0729

The undersling is sin(1.8706 degrees) * 37.812 = 1.2343".

Reduce slightly for percussion (i.e. off-centered hub) and make 1.2343" - 1/16" = 1.1718"

Pitch Horn & Drag Brace:

The intent is to locate the pitch horns on the trailing edge side of the blades. This is to maximize the vertical clearance between the rotor hub components and the blades on the other rotor. The pitch horn and drag brace are to be a common unit, which clamps to the outside of the blade grip. The drag brace, which attaches to the trailing edge of the blade, must be removable so that the blades can swing back for transportation.

October 14, 2001 ~ D.K. has suggested that the drag brace be replaced by a Bell 206 style of latch, so that the blades are easly removable for a more compact form of transportation.

Teetering (Flapping) Hinge and need for Lead-Lag:

It is extremely probable that there is lead-lag between the 2 pair of rotors in forward flight. The teetering of the blades and the Coriolis effect will cause it. This problem may put excessive loading on the shafts, gears and bearings of the power train. It may also oscillate at 2-P which in turn will compound the problem. This lead-lag must be taken care of and it should also probably be dampened.

The individual blade will not require lead-lag but the complete rotor (hub & 2 blades) will. Theoretically it can be located at any location between one hub and the other.

Can rotor hub have limited rotational freedom and a type of brake disk, where adjustable pressure is used?Consider Type L jaw coupling. Morse has 3 insert materials, Buna-N, Urethane and Hytrel (page D11). The metal hub would serve as a template for machining the aluminum rotor hub. An oversize insert will, obviously, be selected. This coupling might also serve for alignment for transportation.

Teetering Hinge Idea:

(1-Dec-98) Can the axle of teetering have its angle, in plan view (azimuth), advanced by up to 5-10 degrees? This might cause both the blades to move forward (accelerate) and change the pitch in both so as to counter the desire to flap.

Rick says that K-Max teetering hinge is approximately 20 degrees CW from standard.

Material:

Consider titanium from Tubesales (UK) Limited.

Undersling (Teetering Height):

See: DESIGN: [Rotor - Disk - Undersling] 0734

Teetering Angle:

The V angle is 25 degrees.

Therefore half the above is 12.5 degrees.

The coning angle is 1.6911 degrees.

Therefore the neutral angle from horizontal is 14.2 degrees.

If the teetering (in the lateral direction or all directions??) is limited to 8 degrees then the minimum angle above the horizontal is 6.25 degree. This is a vertical height of 3.16" above the other rotor hub. Required vertical movement of pitch rod at 4.5" off centerline of mast (as per Indian) and giving 40 degrees of pitch change is 3.15". This will not work. See drawing 0409.

Teetering Stops:

Dick DeGraw mentioned something about giving resistance to extreme teetering.

DESIGN: SynchroLite - Rotor - Hub - Teetering Bearing w/ Hub Spring may take care of this concern.

Flapping Static Stop:

A fixed position stop will be required on both sides of both hubs so that a blade will not teeter down into a blade or the hub of the other rotor, during flight.

Flapping Restrainer:

Idea (1):

A removable flapping restrainer will probably be required to stop the lower blade going fully up to the static stop and the upper blade going fully down to the static stop during low rotor RPM. This device will probable engage and disengage by centrifugal force on weighted and spring loaded moment arms.

Hiller FH-1100 has centrifugal droop stop. See service manual, figure 51-101-1

Idea (2):

Use an elastomeric that resists teetering. The rate of resistance must be exponential to the degree of teetering. This is probably not a good idea since it might present too much resistance in the required range and not enough at the extreme ranges to prevent blade clash. 0799.html DESIGN: SynchroLite - Rotor - Hub - Teetering Bearing w/ Hub Spring may take care of this concern.

If this device is attached to the mast and not the hub then its weight will have no adverse effect on the moments of the rotor disk. It might also be a good idea to have its default position in the non-restraining position; so that it could never inadvertently lock the teetering action.

To be thought through and all recalculated:

The top of the pitch link to the swashplate must be centered on the teetering hinge because delta-3 by flap hinge geometry is being used. This puts the top of the pitch link at 75⁰ to the feathering axis. The pitch link will be vertical and the bottom will have the required phase angle of 75⁰.

If coning hinges are to be used, to try and minimize vertical vibration, then see [0813].

The Rotor - Hub clearance shows clearances with the pitch horn located at the rear of the blades. The current Control - Flight is designed for a pitch horn at the front of the blades.

Revision Required:

The bearing package must accept an inward axial load

Back to top | SynchroLite Home Page

Last Revised: November 17, 2004