A070

DESIGN: UniCopter ~ Vibration ( & Noise?)

Vibration re: Rotor:

On the Good Side:

The rotor induced vibration in the Unicopter should be less that that which was experienced in the Flettner and Sikorsky ABC because:
    1. The inertia of the rigid rotor and drive-train assembly, which consists of six blades, two hubs and two secondary transmissions should help dampen the vibrations, before they pass through the vibration mounts to the fuselage.
    2. The pilot is located very close to the craft's center of mass and therefor the moment arms will be quite short.
    3. The relatively fast RRPM will result in frequencies that are not so discomforting to the pilot. The Unicopter will be (700/60)*3 = 35 Hz. in roll and 70 Hz. in heave. (600/60)*3 = 30 Hz. in roll and 60 Hz. in heave.

For Additional Information see:

OTHER: Aerodynamics - Vibration - Rotor Induced

SynchroLite ~ Special Tool - Flight Data Acquisition

SEMI-ACTIVE CONTROL OF HELICOPTER VIBRATION USING CONTROLLABLE STIFFNESS AND DAMPING DEVICES

http://etda.libraries.psu.edu/theses/approved/WorldWideFiles/ETD-194/Final_draft.pdf

Vibration re: Engine:

Without looking, I think that the Rotax 912 engine has only one power stroke per crankshaft revolution. There must be a torsional shock absorption device between the engine and the rotors or propeller.

A Lycoming engine will be turning at approximately 2400 rpm ( 40 Hz). This will affect pilot and craft more than the faster Rotax. It should also be noted that the preferred anti-vibration mount is the Dynafocal, but on helicopter installations the conical mount is used. This is because the relative motion between the engine and the drive train must be limited. Perhaps the mount between the drive frame and the fuselage can be the Dynafocal.

Noise re: Rotor:

Excerpt from http://www.enae.umd.edu/AGRC/Aero/merits.html

Rotor noise has its origin from the rotor blades (so-called thickness noise) and from the blade tip vortices. While the vortices themselves generate little noise, large amounts of noise are produced when the blades interact with these vortices - so-called blade vortex interaction or BVI noise. On single rotor helicopters, this mainly occurs under conditions of descending and maneuvering flight. However, for coaxials and tandems this condition is more prevalent under all flight conditions as the wake system from one rotor is ingested into the other. Thickness noise is related to the volume of air displaced by the rotating blades, which can in turn be related to rotor solidity. For the same gross weight, single and twin-rotor systems tend to have similar overall thickness noise, but may have significantly different noise directivities. Both coaxial and tandem rotor machines produce strong BVI noise, which tends to dominate the noise signature of the machine in the frequency region that is sensitive to the human ear, and so makes them subjectively 'noisy.'

Bryan D. Edwards and Charles Cox, Revolutionary Concepts for Helicopter Noise Reduction---S.I.L.E.N.T. Program , NASA/CR-2002-211650, May 2002, pp. 86, (3.3MB PS, 817KB PDF).

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Last Revised: December 24, 2003