UniCopter ~ Trim, Stability & Control - Control

Overview:

The rigid connection of rotor to fuselage may make the helicopter's control sensitivity very (too?) responsive. If the pitch control, roll control or yaw control is not effective enough at high forward speed, an elevator, rudder or opposed elevators could be added to the tail. This might be particularly relevant to pitch, which might suffer from over sensitivity in hover and insufficient control at fast forward speeds.

See also: UniCopter ~ Control - Flight

For general information, see:- OTHER: Dynamics - Control

Control Analysis:

Control Inputs:

The Absolutely Rigid Rotors (ARR) may result in the requirement for large stick forces. See the frictional force required on; DESIGN: UniCopter ~ Rotor - Hub - Bearings - Pitch - Roller & Ball

The free stream velocity is probably going to be used to adjust opposed lateral cyclic and/or ABC

Control Sensitivity:

On the UniCopter, this sensitivity will be offset (to some as of yet uncalculated amount) by the rotational inertial of the two counterrotating ARRs that will dampen the pitch or roll motions.

Control Moment:

Tip-path-plane tilt, in the Unicopter, will attempt to produce a moment about the rotor hub(s) directly.

Cyclic Stick and Change of Attitude:

The rotor disk does not flapback.

Pitch Change & Autorotation:

The lateral torque from the rotors (outside of disk advancing) will be attempting to pitch the nose down while under power. If the rotor torque is reduced or the engine quits in flight, the nose will rise because of the loss of torque. At hover, the pitching moment caused by this torque is;

Torque (approximate) at rotors: Q [ft-lb] = 5252 * HP / RPM = 5252 * 60 / 480 = 656 ft-lb

Angle of masts from vertical = 9º

Torque in X-Z plane = 656 * sine(9º) = 656 * 0.156 = 102 ft-lb

This nose out moment at the onset of autorotation MAY be advantageous.

Notes re Rotor Torque and Pitching Momentum:

The gyroscopic effect of the two rotors might help resist the upward pitch upon the loss or reduction of engine power; and this may be good, or may be bad, or may be irrelevant.

Working Papers:

 DESIGN: B323 MAKE:

Items:

DESIGN:

 Name Item UniCopter ~ Trim, Stability & Control - Control - Equations 1088 UniCopter ~ Trim, Stability & Control - Control - Rotor Coordinate Conversion 0919 Ref: DESIGN: UniCopter ~ Rotor - Disk - Location of Center of Thrust 0908

Same Page ~ Different Craft: ~ SynchroLite ~ Dragonfly ~ AeroVantage

Last Revised: December 4, 2008