A033

DESIGN: SynchroLite ~ Control - Flight

Control Moment:

Using the SynchroLite for comparative purposes, but with the following adjustments;

Twist is set to 0º

Alpha @ zero lift is set to 0º

For 500-lb lift at hover; the collective pitch is 5.7º

For 1,000-lb lift at hover; the collective pitch is 8.3º

Therefore, the addition in collective pitch to double the lift is 2.6º

This might mean that a collective of 0º and a cyclic of 2 * 2.6º = 5.2º will provide 500-lb of thrust; with all this lift on one side of the disk.

Assuming that the mean lift is at 75% of rotor radius 75% of the rotor radius is 8.667 ft * 0.75 = 6.5 ft. = 78"

On SynchroLite I the vertical distance between the rotorhub and the center of gravity is 60' - 16.72' = 43.28"

For a teetering rotor:

Sin(A) = a/c

The sin of 5.2º is 0.0906

c = 43.28"

Therefore the length of the moment arm is 0.0906 * 43.28" = 3.92" = 0.327'.

For an absolutely rigid rotor;

a/b = 43.28"/78" = 0.555 = inverse Tan(29)

Moment force; Cos(A) = b/c therefore b = cos(A) * c = cos(29) * 500 = 0.874 * 500 = 437#

Moment arm: Cos(A) = b/c therefore c = b / cos(A) = 78" / cos(29) = 78" / 0.874 = 89" = 7.4'

Moments:

With a teetering rotor and a cyclic of 5.2º the moment about the rotorhub will be 500# * 0.327' = 163 lb-ft.

With an absolute rigid rotors the moment about the rotorhub will be 437# * 7.4' = 3250 lb-ft. Which is the same as 500# * 6.5' = 3,250 lb-ft

Vibration Isolation:

If isolation mounts are used to connect the power train to the fuselage then the mixer box and the base of the collective lever must be rigidly braced to the power train. This is necessary because the differential movement between the mixer box and the swashplates will effect the blade pitches.

This bracing might consist of only two composite tubes, one going from the mixer box to each side of the power train. This will tie the mixer box to the power train vertically and laterally but will still allow there to be independent longitudinal motion. The collective lever, for the same reasons, must be rigidly connected to the mixer box.

This will add 1-2 lbs to the weight of the craft. Dare the power train be hard mounted to the fuselage; and pad the seat?

_____________________________

To minimize the remaining vibration, and the forces returning from the rotor, to the collective lever a low ratio worm gear could be used. The larg motion of the collective lever may mak this quite attractive; if it is needed. [Source ~ MDD p.98-101]

Same Page ~ Different Craft: ~ UniCopter ~ Dragonfly

Last Revised: May 13, 2008