Item 1036

DESIGN: UniCopter ~ Rotor - Blade - General - Taper

Sikorsky ABC:

Sikorsky would have increased the taper ratio from 2:1 to 3.6:1 if they were to produce a second version. This might help the UniCopter as well but the close proximity of the large chord roots may cause excessive aerodynamic interaction.

 Advantages:

Taper will shorten the thrusts moment arm, from the center of thrust to the hub..

Taper will increase the x-sectional area of the blade near the root and lessen it nearer the tip. This will result in the x-sectional areas at each blade element being closer to the required structural strength at the respective elements, and this is essential for an Absolutely Rigid Rotor.

Relationship in Respect to Twist:

Both taper and twist improve the rotor's figure-of-merit during hover, but if both are incorporated in the blades then the total improvement is somewhat less then the sum of the two individual improvements. Taper offers the above two advantages whereas twist is detrimental in fast forward flight (and in autorotation), therefor it appear that a small amount of twist will be advantageous, but it should be secondary to taper. See NACA Technical Note No. 1542, p. 9

Re; Active Blade Twist:

The greater the taper the greater the advantage of ABT w/ Reverse Velocity Utilization will be during fast forward flight. This is because the blade roots will be able to contribute to lift instead of detracting from it.

Inverse Taper:

" (Some preliminary studies indicate that perhaps inverse taper holds some promise in this regard.)" ~ by Prouty [RWP1 p.649] and Graviman (Mart)

By self; A superficial evaluation appears to show that utilizing inverse taper blades on an ABC rotor would reduce or possibly eliminate the requirement for a low RRPM in cruise and a high RRPM in hover. The rotor's strength and weight may be heavier, but the reduction in the transmission weight by the elimination the variable speed or two-speed requirement may not offset this weight increase. The reduction in transmission complexity may be an advantage. Where should I put the below rough calculations?

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Last Revised: December 29, 2007