DESIGN: AeroVantage - Transition Mechanism - Proposed Methods - Upper and Lower Arms

• It would be nice if the rear PropRotor was at higher elevation. One reason being a ground clearance during hover. The vertical center to center distance between the fore and aft proprotors is currently 18.3". Arranging the two proprotors at the same elevation in cruise will reduce the 18.3" difference by 4.6".
• Halfway throughout the transition the wrist mechanism will have to switch something so that the Y-axis rotation of the motor does not reverse direction.
• It is not, currently, aerodynamically very clean.
• How to have the frame strong enough to resist bending. The weight can be kept low by the use of composite construction.
• See concern on [Shoulder], below, re Double Enveloping Worm Gearing

• This mechanism has better stagger and gap. See the information below in 'General Notes'.
• This mechanism might be simpler.
• This mechanism may be more effective.

• Linkage: 6 bar, 1 degree of freedom (rotation). Reference; Watt-1, Linkage.
• The longitudinal PropRotor gap ratio between hovering and cruise is; Hover gap = 79.6 + 107.4 = 187". Cruise gap = 79". Change = 108". This is considerably greater than the values for 1642, which are Hover gap = 152". Cruise gap = 85". Change = 67".
• This increased gap during hover should allow for larger diameter rotors and lower disk loading, if desired. It should also give greater controllability in hover.
• The reduced coaxial cruise gap is also an advantage.
• The shoulder rotation is 180º.
• The elbow rotation is 180º.
• The wrist rotations are 90º.
• Consider making the mechanism in full-size or 1/8th scale.
• This information will probably change when fore-aft balance is worked out.

• General:
• The final unit in the power train is a worm that drives a pair of wormgears. See [Shoulder] below.
• Alternative A:
• A single drive motor is located in the fuselage. It drives a cross-shaft out to the transition mechanisms in each wing. At the mechanisms is a crown and pinion gear set that reduces the rpm and drives a common shaft to the front and the rear worm gear boxes. The worm drives will have a common high ratio of approximately 70:1
• Alternative B:
• There is a separate motor in the port and in the starboard transition mechanism. The motor drives a common shaft to the front and the rear worm gear boxes. The worm drives will have a common high ratio of approximately 70:1, therefore a spur gear reduction, or a pair of planetary gear reducers will be required between the motor and the worm gear box. Perhaps the simplest might be a combined motor with planetary drive through a miter or spur gears to the worm gear boxes.
• 

• Rotation:
• The inner arms rotate 180º between cruise and hover. The upper arm and the lower arm rotate about their respective shoulders in opposite directions,
• Option A/ ~ by Worm & Wormgear:
• A wormgear is located at each of the four 'shoulders' Four per craft or four per side to be decided later. They have lateral axes.
• A worm is located between each pair of upper and lower shoulder wormgears. The worms have longitudinal axes and each forward worm is coaxial and connected to an aft worm.
• This results in all the 'inner arms' rotating at the same rate.
• The normal maximum ratio is approximatly 70:1 but larger ratios can be purchased.
• Note: Double Enveloping Worm Gearing has 2 to 4 time the strength of Single Enveloping Worm Gearing. However, if it is to be used, and it should, then the line between the centers of the upper and lower wheels must be normal to the axis of the worm.
• Option B/ ~ by Spur Gears and X-shaft:
• A spur gear is located at each of the four 'shoulders' Four per craft or four per side to be decided later. They have lateral axes. The upper shoulder gear engages with the lower shoulder gear.
• A lateral X-shaft, which has a small spur gear at each end, connects the forward upper shoulder gears. Rotating this X-shaft extends and retracts the mechanism. The aft mechanism has a similar arrangement.

• Elbow:
• This is a simple hinge that rotates 180º about a lateral axis.
• The angle of the elbow is based on the action at the shoulder (worm gearbox) and at the wrist (stops and cams).

• Wrist:

• Description of Rotation (from cruise to hover):
• In the above sketch the box represents the motor. The left-hand sketch [0] shows the cruise position with the crossed lies on the outside left of the motor representing the center of the PropRotor.
• The lower arm [blue] and its attached cam do not rotate in respect to the motor during the first 45º of the motor's rotation. They are held in position by a fixed stop on one side. On the other side the other rotor's came is holding them.
• At 45º both arms are against their fixed stops and the cams are not stoping rotation of either arm. This position has to be thought through. A device might have to be added to assure that the correct action takes place.
• Now the upper arm [red] and its attached cam do not rotate in respect to the motor during the second 45º of the motor's rotation. They are held in position by a fixed stop on one side and on the other side the other rotor's came is holding them.
• Sketch is of the forward PropRotor and it's arms only. The rear PropRotor utilizes same metrology.

• The fixed stop in the wrist limit the maximum angle between the upper and lower outer arms to 98.6º. The outer arms only have this angle between them when the inner arms have rotated 90º of their total 180º rotation (I.e. midway).
• The minimum angle between the upper and lower arms is 9.3º, and is when the inner arms are at each end of their rotations.
• Wrist Rotation Lock:
• Done by cams that hold one arm in its extreme position while the other rotates.
• A pin or some mechanism may be required to assists (or assure) that the switch over of the rotational motion takes place properly.

• Based upon Leishman:
• Leishman says, "... the wake of the upper rotor contracts quickly (within 0.25R below the rotor) so it can be considered fully contracted by the time it is ingested by the lower rotor. The ideal wake contraction is 0.707 but in practice it is found closer to 0.8." [radius, not area]
• Since the forward disk has an area of 55 ft² and a [50" radius], it means that the rear disk must have a radius of 40" radius and an area of 35 ft².
• Total weight of craft = 1325 lb.
• Total disk area = (55 ft² + 35 ft²) * 2 = 180 ft²
• The ratio of the fore and aft disk areas is 1.62:1.
• Disk Loading = 1325 / 180 = 7.36 lb/ ft²
• The forward arm distance from the center of the hovering motor to 25% of wing's chord; for large disk = 77" = 6.42 ft.
• The rear arm distance from the center of the hovering motor to 25% of wing's chord; for small disk = 101" = 8.42 ft.
• Forward moment = 55 ft² * 2 * 7.36 lb/ ft² * 6.42 ft = 5,198 ft-lb.
• Rear moment = 35 ft² * 2 * 7.36 lb/ ft² * 8.42 ft = 4,338 ft-lb.
• To longitudinally balance the thrust on the blades quarter-chord means that there must be a rearward shifting of the transition mechanism by 7" However the wormwheel will interfere with the wing's spar.
• 1/ Perhaps the inboard portion of the spar could be aft of 25% of chord and returned to 25% outboard of the transition mechanism.
• 2/ Better yet, the rear motor is driving a smaller rotor, therefore load it up more. Theoretically, the fore and aft motors could be equal distance from the 25% of chord except that the higher pitch of the rear rotor might be close to stall, or a higher rpm will not be optimal and the greater disk loading will demand more power. Perhaps move the rotors aft slightly, just not the full 7"
• Also it will be advantageous to reduce the disk loading (larger diameter rotors -re. Inefficient electric power); as long as the ground clearance on the front PropRotor in cruse configuration is great enough.

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