Tapered Rotors-An experiment

[theschultz]

Nice job. Keep up the good work. Nice little red machine in the background! I am slightly jealous, and more motivated! Where are you incidentally?

 

[Vance]

Thinking that a more effcient rotor spins slower to get the same lift is a common misconception based on thinking of the gyro as a shaft powered system. It is powered by the blades. You want as much available aerodynamic energy as possible to go into spinning the blades. For example, cleaning the blades is reported to give an increase in rrpm.

Hello Al,

I am laboring under the apparent common misconception that for a heavy machine like mine, 1350 two up with full fuel, with an 8.5 inch chord 30 foot rotor that my rotor is turning too fast for best efficiency,335 rotor rpm with a tip speed of 532 feet per second. I felt that increasing the solidity ratio would slow the rotor down and it would work better.

It sounds to me that Jon has increased the solidity and is getting less rpm as a result.

My common misconception conclusion would be that less rpm might be better.

I would like to better understand the best way to think about a rotor slow down.

I know they are testing on a much lighter gyroplane.

I find Jon’s experiments exciting never the less.

Thank you, Vance

 

[C. Beaty]

There are several ways of slowing a rotor, Vance.

Let it get splattered with bug guts and it slows down and becomes less efficient. That’s the kind of slowdown Al was talking about.

Increase the chord; it slows down and becomes more efficient, up to a point.

The ideal tip speed for gyros in our speed range is about 400 fps.

Tip speed is ~ 66 x square root of blade loading.

With a tip speed of 532 fps, your blade loading is ~ 65 lb/ft². Much too high if you don’t need to go faster than 100 mph.

 

[Al_Hammer]

Yes, Vance, I was referring to dirty blades vs clean, or efficient airfoil vs less efficient, such as what might happen if you squished an airfoil and inadvertently changed its L/D in the process.
There are other ways of slowing a blade, as Chuck just pointed out.

Jon said that the tapered blades have the same area, so I'm not sure what the new solidity ratio is, or if its substantially different. That could make a difference in rrpm and I frankly forgot to consider that before posting, so my apologies.

 

[Vance]

Thank you Al and Chuck, I was concerned that I had once again formed inappropriate fantasies.

The self adjusting part of the rotor magic still astounds me.

I have been told that shake is what makes people stay away from rotor diameters over 32 feet and chords over 8.5 inches. An auto in a Robinson 44 or a Bell 206 is a very smooth experience and both of them exceed those self imposed limitations so as is often the case, I am confused.

This apparent dichotomy brings me to the question; could tapered blades be another way to get more rotor solidity without as much shake?

Thank you, Vance

 

[Master Roda]

Thank you Mr. B.

Looks like I have my work "cut out" for me

 

[Al_Hammer]

Vance, the R44 has hydraulic controls and it is said to eliminate stick shake. So, not a fair comparison. The one time I took the controls of a 44, it was not boosted and the stick was very heavy.

 

[Vance]

I didn’t mean to make a comparison Al.

My observation is that Bell and Robinson found ways to overcome the shake, both cabin and stick. I understand they did it by applying several different schemes. Perhaps tapered blades are another way to increase the solidity without exacerbating the shake.

I have performed an autorotation to the ground in a Robinson 44 with the hydraulic boost off and although the stick was heavy and required a lot of movement before anything happened there was very little stick shake.

Thank you, Vance

 

[brett s]

Seems like the same sort of system a Bell 47 or Hiller 12 uses (mast suspended on rubber mounts) shouldn't be that hard to do in a heavy gyro.

 

[Vance]

I agree Brett.

I feel that some care would need to be taken to address the dissonance between the aircraft and the rotor in the control system.

I feel that Jon’s experiments are very interesting.

When I have done experiments with concepts I have found it is very easy to get focused on a desired result and overlook a potential benefit.

Thank you, Vance

 

[C. Beaty]

There is no magic bullet, Vance, and a shot in the dark seldom finds its mark.

Of course Bell and others can find solutions to the problem of high reciprocating masses by use of limber rotor pylons and tuned vibration absorbers. But it’s difficult, systematic work by people that aren’t merely tossing chicken bones up in the air to see how they land.

 

[Master Roda]

I agree Brett.

I feel that some care would need to be taken to address the dissonance between the aircraft and the rotor in the control system.

I feel that Jon’s experiments are very interesting.

When I have done experiments with concepts I have found it is very easy to get focused on a desired result and overlook a potential benefit.

Thank you, Vance

I agree with you on that point. I don't wan't to lose sight of the overall performance. Our standard airfoil has the best characteristics for our flight regime.

So far it still stands, the tapered blade doesn't shake as much in hard banks. Less rate of descent, lower rpm, same climb, glide ratio seems close so that will require actually measuring on the ground with stakes and what-not.

I'll be battling with chord thickness in the mean-time.

 

[Master Roda]

Seems like the same sort of system a Bell 47 or Hiller 12 uses (mast suspended on rubber mounts) shouldn't be that hard to do in a heavy gyro.

Our mast IS suspended in rubber mounts. Works very well. That coupled with our dampened hub-bar makes one very smooth machine.

 

[GyroRon]

Jon, Hi... I am Ron, GyroRon. I test things. I post results of what I test. I would be glad to test a set of your tapered blades, just send me a set and I will post what I find. Can even bring them to Mentone in August and demo them in person. My machine currently has 27 foot Dragon Wings. Thanks Ron

 

[Master Roda]

Thank you for the offer Ron, but were going to finish up testing this set before I move onto larger sets. You see, this is a set of 8x25's (actually 8.5"/7"x25') I'm testing. If you have a machine that could fly these blades, I would be willing to sell you a set at regular pricing after we finish testing. I think that's fair, don't you?

 

[automan1223]

Slide rule rule ?

Slide rule rule ?

I was just talking about this in another thread. Get out your slide rule and pocket protector and you have all your answers until you go and do something really innovative and then you need a better formula to match what you are flying in the "real world".

Great to see the progress. I knew they were better, Even Jim would not over estimate something by 2-300 fpm on a whim.

They must be a better blade. !

Great work !!! :whoo:


QUOTE=Master Roda;299002]How is this for variations:

Tapered:
20 MPH, 4500 Engine RPM, 900 FPM max
Standard:
20 MPH, 4500 Engine RPM, 1100 FPM max

Of course, as I said, this is preliminary data.....means nothing really....right?[/QUOTE]

 

[down under]

The one very interesting thing that has come up in the testing is that airfoil shape is only a small part in the design of a blade.
On these tapered blades the airfoil has been squashed in cord width at tip with no loss of performance, plus gains have been made in some areas.

 

[RotoPlane]

Yep….makes me wonder how much more effective these tapered blades would be if they also had a scaled airfoil thickness taper…..and for a more linear span lift, larger span taper angles (~.5"/foot)…..

I think Jon will do what it takes…..within fabrication reason.

 

[Master Roda]

There must be something in the water here lately because I've just found a way to taper my thickness without spending a crapload of money. Jim is keeping me from releasing my build data of course as it is proprietary. Sorry about that.

Thank you guys for following me on this thread. I really need the positive encouragement. It's hard to slip this in between regular work.

I want very badly to contribute my talents to the gyro community. This is only one step in that direction.

 

[scott heger]

Jon, keep up the good work, keep thinking outside the box. I appreciate you new efforts. If you build them, I will fly them. You guys are great.

Scott Heger, Laguna Niguel,Ca N86SH SportCopter Vortex#054, tenth year in flight.