Improving the main rotors performance

[royden]

Hi everyone.
If I wanted to improve the performance of the main rotor, would it be better to widen the chord of the rotorblades or to increase the length of the rotorblades ?

 

[Chaingang]

Hi everyone.
If I wanted to improve the performance of the main rotor, would it be better to widen the chord of the rotorblades or to increase the length of the rotorblades ?

I have the exact same question. I wonder if the width actually helps after you go past the density ratio, at that point it seems like only length would help. also was wondering how much the inner 1/3 offers in lift because I see sone bars that come to the 1/3 length of the blade and it seems that much loss, even thoght offers little lift, cound be significant. Also, if you added the seconf set of teeters like one model did for a breif time, was that any good after you go past the density ratio.

 

[MikeBoyette]

My old man experimented with doing exactly this. He discovered that the inner third of the blade virtually does nothing. By widening the cord the entire length of the blade you increase disk solidity which does help with over all ability to lift more weight for same disk size but not as much as increasing the length of the disk. He even tried a criss cross four bladed system with some success. This allowed him to reduce the disk size from 27 feet down to 24 feet on the same machine. The problem was the scissors affect. Dad put a device that allowed some in plane compliance to reduce this affect. The machine flew it on was a very light 618 two place and it worked very well. He actually flew a fella that was almost 400 lbs in the back seat with plenty of power left over. The two bladed system he could only put someone about 340 in the back seat and was full power to fly them. The one issue we found was the left to right speed of the controls was almost twice as fast without affecting the fore and aft. He was happy with the system until we put it on a larger heavier machine. We put it in a rotary powered machine that was quite heavy and after about three flights all four blades suffered from the trailing edge of the blades ripping. It was determined that the amount of in plain compliance needed to increase with the amount of weight of the machine. It was abandoned. I wrote an article about it in the Rotorcraft magazine in I think 1996-1997? It was quite an interesting experiment.

 

[Jean Claude]

Theoretically, if we assume that the total weight of the gyroplane is constant, increasing the chord, without changing the diameter or pitch setting, improves the efficiency of the rotor. This is due to the fact that the friction losses of the blades on the air decrease with the cube of the Rrpm.
However, the blade mass will also need to be increased if the same coning, thus low vibration at 2/rev is to be maintained.
So, in my opinion, assuming constant payload and coning, increasing the chord is detrimental to performance because of the additional total weight required

 

[BEN S]

I cant speak to the math of it, but when I got my blades I spoke with Jim V about it. I was more interested in nimbleness in the air then say speed or weight concerns.
Imstead of the usual 8 inch chord blades on the Vortex we went with 7 inch like my old ones, but he used a custom hub bar to increase the disc diameter to account for the heavier upgrades.

 

[Jean Claude]

Nimbleness is a much more complex issue because it depends not only on the diameter, chord, and mass of the blades, but also on their torsional flexibility which delays the "cyclic pitch" imposed by the root far away to tip

 

[BEN S]

It worked. Rig is still fun.