1187

Item 1187

DESIGN: Dragonfly ~ Rotor - Hub - Bearings - Flap

Forces:

The following forces are;

From one blade.
Located in the yoke, at the intersection of the feathering axis of the blade and the vertical axis of the drag and flapping hinges.
At 100% RRPM (no overspeed).
From GW at hover.

The values below all originate at; A087.html - Initial DESIGN: Dragonfly ~ Rotor - Hub - Blade Forces - Preliminary

Centrifugal:

The centrifugal force is 3,577 lbs [15.911 N].

Moment from Thrust:

The thrust is GW / 6 blades = (550 / 6) = 92 lbf

The center of thrust is at 75% of disk radius = 0.75 * 96" = 72"

The distance from the yoke to the center of thrust is 72' - 13.5' = 58.5"

The moment is therefore 92 * 58.5 = 5,382 lbf-in = 608 N-m.

Moment from Engine Torque:

The maximum torque from the engine, per blade is 63 lbf-ft = 756 lbs-in = 85 N-m.

The center of drag is at 75% of disk radius = 0.75 * 96" = 72"

Therefore the drag is 756 lbs-in / 72" = 10.5 lbf

The distance from the yoke to the center of drag is 72' - 13.5' = 58.5"

The moment is therefore 10.5 * 58.5 = 614 lbf-in = 69 N-m.

The Combined Moment from Thrust and Engine Torque:
√((608)² + (69)² ) = 612 N-m

Loads on Bearing:
Load will probably be slighty greater than one half of Lead/Lag load.

States:

High Thrust:

Radial force inward toward the mast, since the thrust component exceeds the centrifugal component. ⁽¹⁾

Hover:

No load since the thrust offsets the centrifugal force.

No Thrust:

Radial force outward away from the mast, since there is only a centrifugal force. ⁽²⁾

Parked:

Small radial force outward cause by the moment of the weight of the blade.

Negative Thrust:

Radial force outward away from the mast, since there is only a centrifugal force.⁽³⁾

Notes:

At high thrust the blade's CG will be above the teetering hinge, therefore the centrifugal force will have a downward component and will want to reduce the tension on the tie-bar.

At no thrust the blade's CG will be below the teetering hinge, therefore the centrifugal force will have an upward component and will want to reduce the compression on the tie-bar.

At negative thrust the blade's CG will be below the teetering hinge, therefore the centrifugal force will have an upward component and will want to reduce the compression on the tie-bar.

Factors:

Limit load factor for above rotor thrust loads and centrifugal loads = 4

Safety factor for above rotor thrust loads and centrifugal loads = 1.5

Greatest load are; 2,746 lbs. * 4 * 1.5 = 16,476 lbs. Compression and 2,133 lbs. * 4 * 1.5 = 12,798 lbs. Tension.

Bearing Selection:

A: Consider Control Bearing, Single row ball bearing, Torrington AW8AK page 10, Item 0196

ID = 0.5"

OD = 1.125"

Radial limit load rating = 2,250 lbs. each. Two required.

B: Consider bushings

Better yet seriously consider Rexnord Tuflite composite bearings with unique journal bearing bores on; OTHER: Mechanical - Bearing ~ Teetering Bearing

C: Consider full compliment needle bearings.

Additional Information:

See the hard-copy of the Robinson R-22 rotor; Illustrated Parts Catalog - Section 6 and Maintenance Manual - Section 9 for design etc. of this flapping hinge.

Flettner FL-282:

The vertical and horizontal hinges as well as the pitch axis have needle bearings. The thrust bearing for the pitch change axis is also a needle bearing. The loading on the bearings of the vertical and horizontal hinges is of the order of magnitude of 5000 psi based on the nominal projected area of the bearing. No trouble has been experienced with these bearings under this loading.

OTHER: Mechanical - Bearings

Thought:

The use of fairly stiff elastomeric bearings for the flap hinges will result in them acting similar to hinge springs. This might require slightly stronger in-plane blades but might also eliminate the need for droop stops and give better control.

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Last Revised: October 19, 2004