B291

DESIGN: UniCopter ~ Control - Flight - Directional

Outside Helicopter

Kaman Huskie:

Huskie - Yaw It that the Huskie uses both differential collective and opposed longitudinal cyclic to yaw.

Sikorsky ABC:

At low speeds, yaw control is provided by differential collective pitch between the rotors. At 60-80 knots, the differential is phased out using "q" sensing to transfer to conventional rudder surfaces.

UniCopter

Notes:

Re Precone/Decone and anhedral rotors.

Note that as the obliquity reduces toward zero, so does the effectiveness of opposed longitudinal cyclic reduce toward zero.

If the obliquity can be down around 3º and the stagger be reduced then yaw by differential collective (like coaxial), with a little lateral cyclic might be ideal. The remaining problem will be the crossed pedals during low torque or low collective as during autorotation.

The vertical stabilizer will have a surface area of approximately three sq-ft. The moment arm from the center of the rotors to the center of the vertical stabilizer will be approximately eight feet. A side wind of X mph will exert a moment of X lb. about the center of the rotors. What is the maximum amount of side wind can the yaw control offset?

See DESIGN: Dimension & Area - Axis - Y (lateral) for area and moment about the rotors.

The vertical stabilizer should probably have a rudder. The actuation of this rudder will reduce the surface area during yaw, and could deflect the efflux.

For Additional Yaw Control Consider:

Pusher Propeller(s):

If a single prop then consider a simple 'swashplate' (I.e. Horizontal cyclic control ~ in addition to blade adjustable pitch control (collective)) to vary the thrust on each side. This could also vary the engine cooling by varying the thrust at the top. Can this even be done?

If twin props at the sides are used then give each the ability to have independent reverse thrust.

Have the exhaust and cooling gases exit at the end of the boom. Locate a rotateable thrust vector device here that normally directs the exhaust downward Or it may be better to just extend the rudder down into the flow (as mentioned above). This will results in; 1/ counteracting the nose up pitching force that is caused by the X-Z plane component of the rotors torque, so that should the engine quit then the downward pitch of the nose will not be as great. 2/ the longer exhaust may reduce the sound level of the exhaust. The pedals will cause it to roll right or left, to assist with yaw. See: DESIGN: UniCopter ~ Trim, Stability & Control - Control # Pitch Change & Autorotation. The rotatable device could be replaced by an extension to the rudder. The forward thrust would assistt with forward flight but be slightly detrimental upon power loss - but the angle is smaller than the Kaman. Should the device that drives the fan be located up stream or down stream from the overrunning clutch? Downstream will provide additional yaw during autorotation but will result in a faster descent rate.

Consider the use of a bellmouth as an alternative to extending the rudder down ward into the flow. Consider giving the fan (fenestron) variable pitch so that the power consumption is related to the amount of yaw desired. ~ from Peter R-B

Later combine the above with the other related notes, [B291 & UniCopter_Cooling] and just reference it from here. It relates to Engine - Cooling, Yaw and Stability re: reduced negative pitch during forward flight

Could a 2" high flat bar be located along the top of the boom. It would pivot along its bottom edge (X-axis). The pivoting would be controlled by the pedals and it would direct the downwash from the rotors to the left of the right. This is nowhere near as good as 1. It should be only be located under the outer 1/3 or 1/4 of the rotor disk so that it is always in the downwash, (even during autorotation?) Perhaps the efflux could be used in conjunction with the rotors' downwash to create a Coanda effect, left or right.

Consider using a turbine. Amongst other things it may provide better efflux for; yaw, forward thrust and change in pitching moment upon loss of engine.

For UAV UniCopter:

If the worm and wormgear is to be used then the slow-speed rotors will probably have a precone of 5º. This should allow opposed longitudinal cyclic to provide some yawing moment.
In addition, differential thrust will provide yaw. Example; The advancing blade is outboard. If the port rotor has it's thrust increased, it will probably want to roll the craft to starboard and side-shift the craft to port. The very small stagger should sause the effects to be minimal and controllable; paticularly if used in conjunction with the opposed longitudinal cyclic and the special vertical stabilizer(s) below.

Potential Means of Improving Yaw Control:

OTHER: Flight Dynamis - Variable Vertical Fin Concept (VVF)

OTHER: Flight Dynamics - Control - Twin Vertical Stabilizers

The vertical stabilizer is not in the downwash from the rotor in forward flight and climb. It therefor appears that a ruder on the back of the vertical stabilizer having a vertical hinge will provide directional control in forward flight, be it powered or autorotation

Last Revised: July 13, 2008