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Split tip rotors
Now there is something different..
https://www.flightglobal.com/helicop...138504.article https://cimg4.ibsrv.net/gimg/pprune....6d8a9ad8c8.jpg Meanwhile, Bell also appears to be seeking to bring to rotorcraft the performance gains fixed-wing aircraft have obtained from the use of split-tip winglets, such as those produced by Aviation Partners for the Boeing 737NG. The patent application for the split-tip rotor blade notes that in wind-tunnel testing of the design, lift rose by about 13.5% and drag reduced by about 17%. “Accordingly the lift/drag ratio was increased by about 36.91%”. This, Bell says, “can result in fuel savings of about 15-17%”. Bell was granted a US patent for the design on 21 April. Although the airframer gives no detail of specific applications for the split-tip rotors, a drawing within the patent documents shows an aircraft bearing a strong similarlity to its 505 light-single. |
Those things will have to put up with a huge amount of stress.
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The primary claims of the patent are really stating the use of split winglets in general. Dihedral as shown on a helicopter rotor blade does not really make much sense at all, but since all the aerodynamic modeling described in the patent was for improved L/D with dihedral fixed wing applications, I guess thats the way they tried to made the extra claim 11 for a helicopter application.
Accordingly, it can be advantageously utilized with fixed wing aircraft, helicopters, propeller blades, fans, wind power turbine blades, cooling fan blades, aerodynamic spoilers, and other devices utilizing airfoils. In reality, this is sort of taking the BERP concept to the extreme, where it used a well-integrated notch shape to create a smaller vortex that interfaced with the main one, this concept achieves a similar effect with 2 discrete tips. |
It's remarkable....
“Accordingly the lift/drag ratio was increased by about 36.91%” ... including the resolution of their wind tunnel tests! |
In the hover, I can see it would have an advantage. Be interesting to see how it is in forward flight, with the blades passing the fore/aft position.
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As Ray Prouty was keen to stress - what you gain in the hover, you lose in forward flight and vice versa where helicopter design changes are concerned.
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Having once, rather unscientifically, split a set of Wessex blade tip-caps on a tree which snuck in too close towards us while we were dropping troops on a hillside in NI, I can vouch for the fact that they don't always result in an improvement in performance.
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Would be interesting to see the track and balance procedures on those type of blades. Hopefully we wouldn't have to go back to Zeiss each blade or start using BBs to product balance again.
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Would be fun using the flags on a pole and trying to hit the top blade...
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Save fuel in flight........use more getting the RTB sorted though. Cool concept i always understood the anhedral was the way forward with the paddle tip to elongate the chord. Either way its going to interesting to hear the noise they make.
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Originally Posted by Thud_and_Blunder
(Post 10795646)
Having once, rather unscientifically, split a set of Wessex blade tip-caps on a tree which snuck in too close towards us while we were dropping troops on a hillside in NI, I can vouch for the fact that they don't always result in an improvement in performance.
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Originally Posted by NutLoose
(Post 10794777)
Now there is something different..
https://www.flightglobal.com/helicop...138504.article https://cimg4.ibsrv.net/gimg/pprune....6d8a9ad8c8.jpg All the most recent wingtip modifications on civil jets extend both above as well as below, so I'd have thought that helicopter blades would be similarly fitted. |
Originally Posted by etudiant
(Post 10802507)
Is there a reason for not having the split tips go up and down respectively?
All the most recent wingtip modifications on civil jets extend both above as well as below, so I'd have thought that helicopter blades would be similarly fitted. |
Originally Posted by Bell_ringer
(Post 10802597)
may have something to do with the desire to keep the tailboom in one piece.
Suggests though that the idea of an electrically powered tail rotor would fit with this split rotor blade idea. It obviates the need for a TR drive shaft, so the geometry can be a lot more flexible, |
Originally Posted by Bell_ringer
(Post 10802597)
may have something to do with the desire to keep the tailboom in one piece.
Noise wise, my first guess is that it would be quieter and at a higher frequency. A large amount of helicopter noise is from the blade hitting the vortex from preceding rotor - less then intensity of that vortex and you should reduce the noise. But there will be more (smaller) vorticies so the frequency would increase. |
Originally Posted by Robbo Jock
(Post 10794902)
Those things will have to put up with a huge amount of stress.
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I don't know why I keep thinking of this, but wouldn't the split tip begin whistling under certain conditions.
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wouldn't the split tip begin whistling under certain conditions |
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