1192

Item 1192

DESIGN: Dragonfly ~ Rotor - Hub - Droop & Rise Stop

Reason For:

There is a high likelihood that at very low RRPM, before the centrifugal force becomes significant, that the blades can droop or sail up in a gust. In the rear quadrants if the lower blade was to rise while the upper one was drooping the blades might close and cross the wrong way. A hub spring may help.

Outside Helicopters

Flettner FL-282:

Centrifugally operated droop stops are installed on the blades which allow them to he revved up at a coning angle of plus 1 deg. and still allow the blades to flap down angle of minus 5 deg. in flight. The stop is a cam, which is moved by a hinged weight, which flies out due to centrifugal force. At 110-120 rpm (approximately 65% of cruse rpm) the cam moves and allows the blade to fall to an angle of minus 5 deg. To set the stop for a coning angle of plus 1 deg. the blade must he raised by hand until a spring moves the cam into proper position, or this will he automatically accomplished if the collective pitch is at a large enough setting as the rotor slows down.

Potential Solution:

This idea is no good since having the rods rigid enough to withstand compresion will eliminate thre ability to flex under flapping and lead/lag. See idea 2.

Construct the two tie-bar assemblies so that they are capable of handle some compression. Place an open circle in the intersection point of the three rods. There is a 'pin' located in the center of the mast, just below or above the open circles in the tie-bar assemblies. This pin can be moved vertically by the pilot or by the reading of RRPM. The pin is rigid in the horizontal plane. when the pin is inserted into the hols in the two tie-bar assemblies, all three blades become unable to flap or lead/lag.

By providing droop-stops on all three blades non of the blades can 'sail' up because the droop stops on the other two blades are holding it down via the tie bars. The combined angle between the two blades is only 9.5º therefor the droop stop must allow for only 1 or 2 degrees of negative flap. Is this acceptable?

In addition, a hub spring may help.

Drawing:
later

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Last Revised: July 4, 2003