A067

DESIGN: UniCopter ~ Control - Flight

Outside Helicopters

Sikorsky XH-59A with Advancing Blade Concept:

Control System:		Range - deg.			Travel - in.
		Original:	Modified:	Modified:
		xxxxxxxxxxxxx	Helicopterxxxx Mode:	Auxiliaryxxxxxxx Propulsion Mode:	xxxxxxxxxxxx
Collective		5 to 23	2 to 20	2 to 20	10
Differential Collective, Pedals		3 to -6.1	4.2 to -7.2	4.2 to -7.2	+/- 3
Longitudinal Cyclic		3 to -6.1	6 to -12	6 to -12	13
Lateral Cyclic		+-2.2	+-6.25	+-6.25	9
Differential Long. Cyclic		+-1	+-1	+-1
Differential Lat. Cyclic		+-2	+-2	0 to 4.5
Differential Coll. Trim		+-1	+-1	+-1
Elevator		Locked at 7.6	Locked at 0	Locked at 0
		+-25 available	+-25 available	+-25 available
Rudder		+-30	+-30	+-30
Elevator Trim Tab		+-10	+-10	+-10
Rudder Trim Tab		+-15	+-15	+-15
Swashplate Phase Angle		40	0 to 70 Flight Adjustable	20 to 50 Flight Adjustable
				40 normal setting
Pitch SAS Authority +-10%		None	+-1.8	+-1.8
Roll SAS Authority +-10%		None	+-1.2	+-1.2
	Helicopter	+10	+10	-5
	Aux. Propulsion	0	0	0

Pitch Angle Considerations:

"It is also observed that a flap frequency above 1/rev significantly reduces the tilt required for a given center-of-gravity offset and hence reduces the cyclic control travel." ~ [Source ~ HT p.248]
Explanation of above Change

Comment by DBJ:

The ABC blades are rigidly affixed to the hub but they have flex. The vertical flex (flapping) is probably the reason for having an active variable swashplate phase angle.

The loads on the pitch rods are fairly light. This is said to be because of the rigidity of the blades. The UniCopter's blades are to have greater rigidity and this should make the loads proportionately even lighter.

Patents:

US 4,008,979 ~ CONTROL FOR HELICOPTER HAVING DUAL RIGID ROTORS ~ Feb/1977 ~ United Technologies

Canadian 1053211 ~ CONTROL FOR HELICOPTER HAVING DUAL RIGID ROTORS ~ United Technologies Have hard copy.

Boeing VTOL UAV Dragonfly:

Hans G. mention that he read in an article that there are problems due to excessively high control loads. They are changing the material in the control linkages from aluminum to steel. ~ September 29, 2002

The first prototype crashed while in helicopter mode on March 23 in Yuma, Ariz., and will be used to supply spare parts for the second prototype. ~ September 11, 2004

Additional information about the Dragonfly

UniCopter

Notes:

The following has not yet been upgraded to take the addition of a Pusher Propeller and Reverse Velocity Utilization.

Swashplate Phase Angle: Unlike the conventional helicopter with its 90 degree (or less) phase lag, the UniCopter is 0 degrees. I.e. no phase lag. The Sikorsky ABC had a flight adjustable swashplate phase angle with a range of 0 to 70 degrees.

Yaw control See: DESIGN: UniCopter ~ Rotor - Disk - Yaw - Similar to Side-by-side DESIGN: UniCopter ~ Rotor - Disk - Yaw - Similar to Co-axial

Control stick dampening may be required. The hydraulic system may provide dampening.

Torque ~ Pitch Cross-coupling: A change of torque in the intermeshing configuration causes a change in pitch. See: OTHER: Flight Dynamics - General - Cross-Coupling

Duplicity of Hydraulic Controls: There exists the possibility of locating a second set of hydraulic controls offset at 60 degrees to the primary set.

See also: UniCopter ~ Stability

Governor: The rigid rotor gives the pilot responsive control over the cyclic moments. It therefor would seem that the pilot should have direct control over the vertical force as well, at least in hover and at slow speed. This means that the pilot should control the collective lever and the governor should control the engine. In other words, do not use the rotor governor in this situation. Perhaps a combined rotor & engine governor should be employed.

Free Air Velocity Indicator: It might be used for both mechanical rotor pitch adjustment and for the air speed indicator gage in the panel. Consider locating it at the top of the vertical stabilizer. Here it is located in relatively clean air. It might also incorporate a direction indicator.

Range: On a conventional helicopter the total of collective and cyclic should be 35º plus. With the rigid rotors, this can probably be less.

Linear Actuator and Ball Screw: If the flight-control system is to be electrical (i.e sidearm controller and electrical mixerbox) then the pitch link might be replaced by a ball screw, with the same axis as the pitch bearings. It would be moved by a linear actuator. Triple redundancy?

A Reality Check

Although the design changes gave the Cheyenne [Lockheed AH-56A] a very stable and vibration free ride the design was too complex and it contained a large number of failure points that were catastrophic in nature. ~ From LZ on PPRuNe:

Alternative:

All Electric Flight Control:

High torque, small rotational angle, electric motors/actuators at the root of the blades. One for root controle and the other for tip control Independent Root & Tip blades.

Same Page ~ Different Craft: ~ SynchroLite ~ Dragonfly

Last Revised: June 3, 2006