Winglets on Rotors

gyrodeputy

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A few years back winglets on rotors became popular on fixed wing. I am told this was to create more efficent airflow over the tip of the wing and not allow air to spill of the side.

So here is the question...has it ever been tried on a rotor?

Obviously not to the scale of the wing that I have the picture of, but both above and below the tip of a rotor.



Could it work?
Would it be more efficent?
Has it ever been tried?

Hoping Master Roda will weigh in here and give us some expert opinons.

Just pondering the concept.

Stay safe.
 

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Most fixed wing winglets give an effective increase in aspect ratio as if you had a longer span while leaving a manageable size to the aircraft, and they cut drag losses at the tip. The issues aren't quite the same for rotorcraft.

Nonetheless, there are several rotor designs with shaped tips. For example, check out the "BERP" tips (British Experimental Rotor Program) as used on the Westland Lynx:

http://www.cfd4aircraft.com/int_conf/IC1/papers/Brocklehurst.pdf
 
In my recent experimentation, the rotor blades that performed best were the ones with tips like on the Apache and BERPs. I think that it cleans up the wash over the tips to reduce drag. On large FW aircraft winglets can save as much as 10% on fuel useage by reducing drag.
 
Heath (utahgyrocop) I like your thinking because I used to ponder these things myself as well. Then every time I learned a bit more about rotors I realized there is so much more to consider in the quest for improvements. In a hover or at low speed a winglet may have the advantage of keeping the air in the best place possible but with forward speed the 3 inch vertical winglet looks like a very thick and draggy disc to the oncoming airflow and then disadvantages start to pop up.

At that point I realize my lack of knowledge and put my ideas to rest. Then a few years later BERP technology like Joe and WaspAir mentioned bring this whole subject back into the game. I grasp the idea but am not qualified to have meaningful input. I am just an observer.


BugDevHeli did something similar by extending the winglets into a ducted fenestrom type of affair with a few extra blades added. I reproduced a couple of his pictures below . That is about all I am qualified to do on this subject and it's not very much :)
 

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I thought winglets served to stop the differntial airpaths, top (outward) and bottom (inward), from coming together at the tips and created vortices which create enormous drag at the tips and can even cause high speed wings to lose effectiveness completely. I thought Lear had these problems extensively, and the earlier jets were actually unstable in some flight conditions and fell out of the sky.

The faster the wing goes, the more economical winglets become. A gyro wingtip is going well in excess of 300 mph, and that more than qualifies it as a suitable candidate for winglet rotors in my thinking. but, then, I don't understand these things very well. In my mind, winglets should be used on props too.

Take a close look at the prop tip grind on my gyro at Wrens. One of a kind. I like it. It may not actually DO anything, but I FEEL like it produces more push, and that's all that matters when I'm flyin.

I hope someone posts some photos or has a story about this being tried already.
 
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Greg,

Back thirty years ago Piper Aircraft came out with a version of the Navaho. It differed from the original by having "Q-tip" props and Fowler wing tips. The prop blades were bent over like it had made a gear up landing. If my memory serves me correctly, these mods were good for a few hundred pound additional gross weight and some twenty knots of speed. I don't know wether the cost or performance killed the project. More modern aircraft that I'm familiar with like the Canadair Challenger has winglet but they were more for fuel consumption than performance. The FAA limits you to .85 mach in flight so gas savings are important.

Helicopter on the other hand, you're seeing more and more blade tips. Just recently, I read about new rotor blades on the UH-60's that have leading edge mods to reduce noise. This was in addition to the swept blade tips already used. Just about all the new high performance helicopters have exotic blade tips! Even the Cartercopter has advanced tips. Tips also help with retreating blade stall...how I don't know but that's what I've read.

To answer your question about winglets. Yes, they would probably improve performance but how to do it is the question.:D
 
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My understanding is that winglets are important in high Cl conditions, that is at high angle of attack/high lift conditions, where the induced drag becomes prominent.
The rotor tip is mostly not in that regime.
Also, the induced drag is also a function of the wing stretch, which is high for a rotor, giving low induced drag.
Jet powered aircraft are at a high Cl when flying high because of the low density (albeit flying fast). The question is if the increased drag of the winglet on a rotor can be compensated by the other factors, such as noise abatement etc.
 
Walter,

My curiosity got the best of me and I did a web search on BERP 1-4 blade tips. I found it all very interesting. The latest BERP 4 is said to reduce vibration, increase cruising speed, increase payload, improve ceiling and hover performance. The author of the article described the tip as looking like a snow shovel attached to the blade.:lol:

I've built a Delta 3, 4 bladed rotor system with the same tip profile as the AH-64 Apache. It had a 45 degree sweep and it's cord was approx. double of the main blade. It was by far the best perfomer of all the models that I've built so far. If I had to quess why, it would be an increase of wing area in the driven portion of the blade and improved laminar air flow at the tips.:noidea:
 
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