Item 0897

DESIGN: UniCopter ~ Rotor - Disk - Yaw - Method Similar to Side by Side

Overview:

Re Precone/Decone and anhedral rotors. Note that as the obliquity gets small, the ability to used opposed longitudinal cyclic diminishes to no ability.

Yaw control at the rotor disks is by opposed longitudinal cyclic.

Yaw control is similar to that used on side by side helicopters.

To yaw the nose to the left the pilot will apply left pedal.

Drawing:

 

Description of Operation:

See DESIGN: UniCopter ~ Rotor - Disk - Location of Center of Thrust

Assumption: When in hover with full opposing longitudinal cyclic, the center of thrust will be located at r = 20% R and the azimuths will be ψ = 180º for the port rotor and 0º for the starboard rotor. This 20% may be high considering that collective is being applied also. Check it on the above web page. The good news is that ABC will move the center of lift closer to the longitudinal centerline of the craft and this will increase the 55º angle somewhat.

Referring to the above drawing;

The gross weight is 700 pounds, therefor the lift per rotor is z = 350 pounds.

At an angle of 9º the thrust is T = 354 pounds, per rotor and the horizontal force is y = 56 pounds.

Since R = 96", then r = 19.2".

The yaw momentum is therefor 56# * 19.2" * 2 rotors = 2,150 in-lb = 179 ft-lb.

Sine of 55º = 0.82

179 ft-lb. * 0.82 = 147 ft-lb.

The efflux will add to this; during normal conditions but not in autorotation.

The rudder will help with yaw if the craft has forward velocity

For comparison with the SynchroLite see: MAKE: Control - Flight - Directional

Improvement:

The 3º pre-cone should improve the yawing force of the opposed longitudinal cyclic method. This is because the thrust from the forward portion of one disk will be directed back by 3º as well as outward by the 9º due to the mast angle. The thrust from the rear portion of the other disk will be directed forward by 3º as well as outward by the 9º due to the mast angle.

Means of Enhancing the Yaw Control:

Consider having the parasitic drag in balance at all azimuths, then add Variable Vertical Fin Concept (VVF)

Autorotation:

If differential collective is not used then I don't think that the pedal inputs will have to be reversed. It will be like the side-by side. This has to be looked into and thought through,

Back to top | SynchroLite Home Page | UniCopter Home Page | Nemesis Home Page

Last Revised: February 24, 2005