1188

Item 1188

DESIGN: Dragonfly ~ Rotor - Hub - Bearings - Lead/Lag

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; 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.

Loads on Bearing:

The Radial Load on the Leading Bearing: [F_r]:

3,577 lbf * (d / (u + d)) = 3,577 * ((1.58 / (1 + 1.58)) = 2190 lbf = 9,741 N
Ultimate load:

2,190 lbs * 4 [LLF] * 1.5 [SF] = 13,143 = 58,462 N

Note: this value is probably too high. See 'States' below

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.

Considerations:

The flapping hinge removes any vertical loads, therefore the only load that that this bearing is subjected to is a radial one caused by the centrifugal force of the blade.

The direction and types of loads is determined from DESIGN: Dragonfly - Rotor - Load Distribution

There will be a slight vertical moment on this bearing due to the undersling.

A light thrust washer should be located on both ends of this bearing, for containment only.

Low frictional characteristics are not vital in the drag pivot, since in conventional rotors a damping device must be added to control the motion of the blade about the drag pivot. ~ [Source ~ MDD p.22]

Use a bushing? What type of material? See Rexnord Tuflite composite bearings with unique journal bearing bores on; OTHER: Mechanical - Bearing ~ Teetering Bearing

Bearing Selection:

A: Probably do not use a bearing

Consider Four-point Contact Bearing SKF QJ 205. page 324

ID = 25 mm.

OD = 52 mm.

Width = 15 mm.

Mass = 0.16 K

Basic Load Ratings

Dynamic = 25.100 N, = 5,643 lb-force

Static = 20,000 N, = 4,496 lb-force

The newer idea is to use 2 (Item 0593)bearings

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

Additional Information:

OTHER: Mechanical - Bearings

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Last Revised: November 5, 2004