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Item 1256

DESIGN: UniCopter ~ Pusher Prop - Configuration - Propeller - Single

For UniCopter with one propeller.

[Alternate A], the original layout, had the propeller on an extension of the engine's crankshaft.

[Alternate B] has the engine higher than the Propeller. See below for more information. Forget.

Use with Variable Speed Rotor, Propeller is aligned with engine's crankshaft.

General Information:

Diameter: 60". If the blades are given a 3º pre-cone then the diameter of the propeller could be approximately 4" greater.

Number of blades: 4

Lycoming 0-320 Rated RPM: 2700 Now considering O-360

Lycoming 0-320 Operational RPM: 2400

Lycoming 0-320 Static RPM: 2300

Reduction - Engine to Prop: 1:1 ?

Features:

Large chord and high thrust on outer portion of blades.
Small chord and low thrust on inner portion of blade.
Alternatively - if always rotating: ~ If propeller is to provide air flow for cooling then the inner portion will have a small chord but greater pitch than the outer portion of the blade. This will provide engine cooling when the blades are feathered during hover. This inner portion will have very high pitch during fast forward flight but because the scoops are driving air into the engine compartment, the angle of attack should not be excessive. It should be noted that the greatest demand on the engine is during fast forward flight.
Alternative - if only rotating during cruise: ~ If sheaves are used then locate short shrouded blades on the driven sheave, inside the engine compartment. This fan turns when the rotor turns. At cruise the scoops will provide additional airflow and may also offload the fan.

Thoughts:

If the rotors can have a reduced stagger or less drag then perhaps there should be a single tail boom. This means that the propeller hub must rotate about the boom.

Yaw Control: Rotor created yaw control could be augmented by lateral cyclic control of the propeller. The propeller may already require pitch control (collective control). This lateral cyclic control would only be required when the craft is in hover or slow speed flight and at this time it's collective is not being used. During cruise the rudder will provide all yaw control.

Reference:

DESIGN: UniCopter ~ Fuselage - Tail - Twin Boom

Potential Problems:

Cross-coupling. A quick advancement of the cyclic stick may impart a roll, plus a weaker yaw to the craft. This is because the advanced cyclic has increased the pitch of the propeller blades and this has increased their induced drag. The increased drag will 'rob' some of the power that is going to the rotors and the additional torque from the propeller will cause the cross-couplings. Not if all or most of the PRPM speed control comes from the airspeed of the craft.

As the craft's forward velocity increases, the induced drag will decrease.

Counter-rotating propellers on a common axis or separate axii will overcome the cross coupling; but this is getting to be one hell of a lot of blade. Maybe not if the diameters must be kept small.

Alternate B ~ No

Drawing:

Notes:

Torque to the prop can be removed when the craft is on the ground and when it is hovering. This will provided greater safety on the ground and consume less power when hovering. This means that both the rotor and the propeller can independently disengaged from the engine.

The prop can be stopped with the blade tip at a position that gives the greatest ground clearance.

The thrust angle of the propeller does not have to be parallel to that of the crankshaft.

The clutch may be a tension sheave on the T2 side of the V-belt.

The sub-frame that supports the rotor sheave and the propeller sheave might be bolted to the engine. Note that the tension from the two V-belt sets pull in opposite directions.

Not direct coupling the propeller to the engine's crankshaft allows for the rpm of the, small than standard, propeller to be increased

Last Revised: July 12, 2008