1089

Item 1089

OTHER: Aerodynamics - Vibration - Rotor Induced - Analysis of Twin Rotor Helicopters

Vibration encountered by a helicopter with two main rotors, which are in addition to those encountered by a craft with a single rotor, as noted in [1020.html].

ID 17/

Source - Rotor-to-Rotor Interaction (downwash & downdraft):

I think that: An Intermeshing helicopter, with minimal rotor rigidity (teetering head etc.), will experience the single rotor and fuselage vibration [1020], plus vibration from rotor-to-rotor interaction (downwash & downdraft). See Prewitt report. The fact that the the advancing blade and its tip are located above and inside the planform of the other rotor's disk my result in the the tip vortex striking the retreating blade on the other rotor. If this vortex is small the inertia and rigidity of the lower blade may dampen much of the vibration.

Number of Blades: Twin 3-blade rotors will have 9 crossings per rotor revolution. Twin 4-blade rotors will have 16 crossings per rotor revolution. This means that the 4-blade rotors will increase the frequency by 78%. In addition, this frequency might be higher if the 4-blade rotors have a saller diameter than the 3-blade rotors. This is in addition to ID 19 below.

See: OTHER: Aerodynamics - Vibration - Rotor Induced - Rotor-to-Rotor Interaction 1296

See: OTHER: Aerodynamics - Vibration - Rotor Induced - Analysis of Flettner FL-282 ~ Intermeshing 1086

ID ??

Source - Oscillation about the crafts Z-axis from H-force:

I think that this might be a source during forward flight.

The use of delta-3 on the Kaman plus its lead-lag friction device is another consideration with coned rotors.

ID 18/

Source - Rotor-to-Rotor Interaction (BVI):

I think that: Re UniCopter

	Intermeshing & RRR:	Hover:	Transition: μ ≈ 0.1?	High Speed
?/	At 90º azimuth, where the vortex will be the greatest it will strike the mid portion of the lower blade.	x	x	x
?/	At 180º azimuth,	x	x	x
?/	At 270º azimuth,	x	x	x
?/	At 0º azimuth,	x	x	x

The above should probably go into specific helicopter pages.

ID 19/

Source - Lateral Dissymmetry of Lift (and Drag?): (in UniCopter)

I think that: An intermeshing helicopter, with extremely rigid rotors, will experience the single rotor and fuselage vibration [1020], plus vibration from rotor-to-rotor interaction [above], plus a rotational vibration, caused by thrust, that is normal to the azimuth of the blade crossing. See Sikorsky reports.

See: OTHER: Aerodynamics - Vibration - Rotor Induced - Analysis of Coaxial 0893

For 3-blade rotors see; DESIGN: UniCopter ~ Rotor - Disk - Lateral Dissymmetry of Lift and Drag? - (3-blades)

For 4-blade rotors see; DESIGN: UniCopter ~ Rotor - Disk - Lateral Dissymmetry of Lift (Drag?) - 4-blade Rotors

Vibration Acceptability:

OTHER: Aerodynamics - Vibration - Rotor Induced - Overview