0860

Item 0860

DESIGN: UniCopter ~ Rotor - Disk - Yaw - Method Similar to Co-axial

Overview:

This yaw control is similar to that used on coaxial helicopters.

This method does not require that the rotors have Independent Root & Tip Control.

Drawing:

Description of Operation:

The rotors turn outside forward.

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

Referring to the above drawing; The collective for the port rotor will be increased so as to give 100 lbs more thrust and also additional rotational drag. The collective on the starboard rotor will be decreased so as to give 100 lbs less thrust and also reduced rotational drag. At the same time, the starboard rotor will be given a small amount of left lateral cyclic. This will result in a decrease of 58 lbs of lift on the left-hand side and a decrease of 42 lbs of thrust on the right-hand side of the starboard rotor.

Results:

The increased drag from the CW rotating port rotor and the reduced drag from the CCW rotating starboard rotor will cause the craft to yaw in a CCW direction.
The craft will;

Sideslip to port; because;
The total vertical rotor thrust has not changed and the CW and CCW rotational forces about the for-aft (X) axis are balanced but.
The lateral components of the force vectors are not balanced.

The above has been partially incorporated into the hydraulic control system drawing 0857.

Downward pitch at the nose; because;

The craft will be rotating about the oblique port rotor.

A solution should be to slightly increase the cyclic thrust at 180º azimuth on one or both rotors.

A compromise will be to allow the craft a slight lateral 'list' to starboard of 2º to 5º, by letting the thrust of the port rotor be slightly greater than that of the starboard rotor. This should eliminate the sideslip and the nose down pitching. Not that the greater the rate of yaw, the greater the want to list.

Notes:

The less the obliquity and the less the stagger, the less the sideslip (from lateral tilt) and the less the pitching down of the nose (from the yawing).

Related Material:

OTHER: Flight Dynamics - Control - Twin Vertical Stabilizers

OTHER: Aerodynamics - Variable Vertical Fin.

Autorotation:

The pedal inputs will have to be reversed, just like on coaxial helicopters. This pedal reversal will be in conflict with DESIGN: UniCopter ~ Rotor - Disk - Yaw - Method Similar to Side by Side , if both methods are used.

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Last Revised: October 24, 2005