# Drag reduction of a gyrocopter rotor

The taper and washout maybe gets you 1.5% overall in the aircraft. Barely noticeable. Easier and better to make the rotor 6” longer and get noticeable performance difference.
This method is so inexpensive that we can hope that manufacturers are already pushing it to its limit (i.e. to the maximum root stress at rest).
If they wish to further increase the diameter for noticeable improve performance, this can only be achieved by judicious selection of the blades taper.

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I calculated the difference in drag between a conventional two-seater rotor (28 ft x 8.5 in) with a lift of 990 lbs, and an enlarged rotor (36 ft) thanks to tapered blades whose taper and chord were chosen to preserve the same coning, undersling and rest stress in the roots.
This results in a reduction in drag wich increase the rate of climb of 140 ft/mn at 40 mph.

Of course, the advantage of a large diameter is particularly apparent at low flight speeds, when induced power is predominant.

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Jean Claude's calculations are comprehensive and accurate for rotor blade performance and design.

The other point of the “physical equation” is that a larger diameter rotor on a gyroplane creates a lower disk load.

Using the gyroplane weight of 990 lb (449.1 kg) example. The disk load of a 28 ft (8.5 m) diameter rotor is 1.61 lb sq ft (7.86 kg sm). The disk load for a 36 ft (10.8 m) diameter rotor is 0.97 lb sq ft (4.74 kg sm). A lower disk load means less drag. Less drag with the same horsepower means greater performance.

Be careful though, a lower disk load also creates a slower turning rotor (lower RPM), thus reducing the Vne of the gyroplane.

Wayne

Be careful though, a lower disk load also creates a slower turning rotor (lower RPM), thus reducing the Vne of the gyroplane.
Are you thinking of Vne limited by retreating blade stall?
Lower rpm and greater span (rotor diameter) can yield the same tip speed.

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Be careful though, a lower disk load also creates a slower turning rotor (lower RPM), thus reducing the Vne of the gyroplane.
The lower tip chord of the tapered blades limits the rpm drop of large rotors . This results is a lower Mu ratio and higher Vne.

Are you thinking of Vne limited by retreating blade stall?
Lower rpm and greater span (rotor diameter) can yield the same tip speed.
JIm,

Yes, lower Vne in relation to reteating blade stall.

The lower tip chord of the tapered blades limits the rpm drop of large rotors . This results is a lower Mu ratio and higher Vne.
Jean Claude,

You are absolutely correct, because the tapered rotor blade (less surface area) creates less induced drag when compared to a constant cord rotor blade of the same diameter

I failed to qualify my statement in relation to a longer constant cord rotor blade that would be less costly to manufacture.

Wayne

I failed to qualify my statement in relation to a longer constant cord rotor blade that would be less costly to manufacture.
Yes Wayne,
Here you can see my comparisons for an enlarged 36 ft rotor with rectangular blades.
As you pointed out, the latter would have a very slow rpm and the Vne would therefore be reduced.
But above all, the blades would have to be weighted to maintain the coning, and root stress at rest would become unbearable, except with the use of very expensive unobtainium.

Jean Claude,

That is an excellent comparison. Quite a measurable difference.

Thank you,

Wayne