The Vought V-173 "solution" to wing-tip turbulance

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rtfm

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Hi,
I was watching a History Channel documentary on early aircraft, and heard about Charles Zimmerman's Vought V-173 (and successors). All wings suffer from wing tip vorices and the drag associated with this, but low aspect ratio wings suffer to a relatively greater degree.

According to the documentary, however, Zimmerman overcame this drag:
His solution to the problem (of wing tip vortices) was breathtakingly simple <snip snip> he decided to move the engines to the wing tips so that the propellers pushed the air back under the wing"
I found this fascinating.

The question immediately occured to me - how much propeller slipstream effect would be required to offset the wing tip vortices? And this was followed immediately by another... Depending on how much slipstream would be required, might it not be possible to mount small (electric?) props on the wingtips of an "ordinary" plane to counteract the vortices? Some extra thrust, possibly reduced wing tip drag, and possibly with minimal weight penalty.

Of course, it all depends on how effective this prop slipstream effect would be, and whether the benefits would outweigh the cost/effort/complexity involved.

Worth a few thought-experiments? Anyone keen to put on the white lab coat and indulge in some mental scenarios?

Duncan

A table-napkin example...
Wing-tip electric motors.jpg
 
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rtfm

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Hi8,
Poking around on the web, I came across this...
Wing tip turbines.jpg

Interesting... But what is the magnitude of the problem which trying to be solved? Is it worth the effort?

Duncan
 

Jay Kempf

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Hi,
I was watching a History Channel documentary on early aircraft, and heard about Charles Zimmerman's Vought V-173 (and successors). All wings suffer from wing tip vorices and the drag associated with this, but low aspect ratio wings suffer to a relatively greater degree.

According to the documentary, however, Zimmerman overcame this drag:


I found this fascinating.

The question immediately occured to me - how much propeller slipstream effect would be required to offset the wing tip vortices? And this was followed immediately by another... Depending on how much slipstream would be required, might it not be possible to mount small (electric?) props on the wingtips of an "ordinary" plane to counteract the vortices? Some extra thrust, possibly reduced wing tip drag, and possibly with minimal weight penalty.

Of course, it all depends on how effective this prop slipstream effect would be, and whether the benefits would outweigh the cost/effort/complexity involved.

Worth a few thought-experiments? Anyone keen to put on the white lab coat and indulge in some mental scenarios?

Duncan

A table-napkin example...
View attachment 23509
Seems plausible. You aren't using much alternator capacity when you are cruising. Not sure how you would estimate the HP required to create the vortex and so how much it would take to neutralize it. Seems you would get some effective span out of such an effort if you could optimize it which would reduce drag. A way to visualize it is a fixed rotor vane in a turbine. Those fixed blades are turned the opposite way that the driving compressor vanes are which is supposed to encourage the flow to be axial instead of swirling through the housing. What you are talking about doing is the free stream version. A non-driven propeller would just create too much drag but a driven one might work. Interesting thought. Probably some NACA study out there on it. Seems to obvious not to have been done before.
 

rtfm

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Hi,
Thought I was playing in the sandpit all on my own - thanks Jay.

I also came across this...
ancien_minix_aero.jpgin-side-left-view-with-minix-2_10779617.jpg
And this later version of the device...
nouveau_minix_aero.jpg

The Minix wing tip can be retrofitted to any aircraft wing. Its cylindrical shape prevents the airstream from trying to 'curl' around the edge of the wing, which is how the wing-tip vortex is created. The simulation diagrams below show how much smoother the airflow comes off the wingtip with a Minix cylinder fitted - and the developer claims that prototype testing has shown a 6% gain in drag efficiency at Mach 0.8 - the typical speed of an airliner.


Above: regular wing tip showing turbulent vortex


Above: Minix wing tip showing smooth airflow with no vortex
On top of the reduced vortex effect and overall aerodynamic drag, the Minix system produces increased lift at the wing tip, which is especially useful during landing. And Hugues claims it should also be cheaper to produce than a traditional winglet.
The Minix system can also be fitted to wind turbine blades for a similar gain in performance as wing-tip drag is eliminated. Hugues claims an extraordinary 14% greater annual electrical output from a minix-fitted turbine.

Mmmm I wonder... I plan to have removable wing tips so that I can try out a few of these ideas, and see for myself if any of them actually work.

Food for thought...

Duncan
 
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rtfm

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Me again,
After some digging, I found the inventor's web site, and read that he had actually undertaken wind tunnel tests using his device. Here is the text from his site (Minix - an aeronautic decisive result)
After to have tested 22 différent devices in several wind tunnel campaigns, the last one was the better. A new numerical simulation test of the flows around of a plane wing with or without Minix device confirmed these tests that have been doing at the same flow conditions of a real flight (airspeed 100 m/s, Reynolds 7.5 10+6, AOA 4°). Trapézoïdal wing light aircraft "EUROPA", average chord 1164 mm, Aspect ratio 8 (AR), wing taper 0.78, Dykins profile 12%.
A confidential report of 25 pages give following results:
- An induce drag decrease of 8%,
- A lift increase of 5,5%
- An increase on the L/D of 2,4%
- An increase 9% of wing aspect ratio
- A centring of the vortex on the Minix,
- Fluidity of the vortex go out of the Minix.
- These résults could be optimized by a more detailed study (modification of all the leading edges and helicoid slot of the surface of Minix in order to reduce the parasite drag and the shape drag.
These are some pretty impressive numbers for what looks like a very simple device. Fascinating...

Pluse some photos of the device being tested on an RV8 HERE
essai_rv8_09.jpg

Duncan
 

BBerson

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Low aspect ratio only suffers from excess induced drag at low speed. At low speed large vortex circulation exists.
This would require large props to extend about half the semi-span, I think. (Like V-173)

The V-173 might benefit (AR=1), but for normal aspect ratio I think the parasite drag of this scheme would negate any good.
Sailplanes have the best tip design.
Other tips (as shown) are pure bunk, in my opinion
 

autoreply

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Other tips (as shown) are pure bunk, in my opinion
And mine.

I've talked to those guys at Le Bourget (2005 I think). Impressive stories, but their (his) understanding of aerodynamics seemed limited and in a way it's a device with >100% claimed efficiency.
"Whirling", "circulating" etc are often words that are used, but are also an indicator of a limited understanding of aero. The air round the tip is a result from, not a cause for induced drag.


When you have an optimal wing shape (tapered), I don't think the props on the tip will improve much. Induced drag occurs due to displacing a limited amount of air with a finite speed. Displace more air slower=>less induced drag.

Unless your props displace a significant amount of air (see the Vought), you won't have much benefit I'd think.
 

Monty

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Induced drag is due to the creation of lift. It will be there as long as you are producing lift. Vorticity is constant, you can spread it out in a more diffuse way to limit viscous loss, but total vorticity will remain the same, no matter what sort of device or gimmick you put on the aircraft.

This problem then becomes an accounting exercise. My guess is even the V-173 suffered from poor accounting. To counter the vortex the engines must produce extra power. The actual "induced" drag is quite low relative to form and interference. Induced drag only matters because it is always there, so over time it adds up. In the case of the 173 you can think of the engines producing a tiny amount of vertical lift by counteracting the vortex. You have to burn fuel to do that. Fuel that isn't pushing the aircraft forward.

Same difference in the end, and I would hate to loose an engine on a twin with the engines on the tip of the wing.

As to the toilet paper tube on the end of the wing...IMO...bunk. Let's see it compared to a properly designed sheared tip. I would also like to see a proper wetted area drag study, once again, compared to something other than a truncated or rounded tip.

Accounting, all in apples please.
 

Jay Kempf

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Induced drag is due to the creation of lift. It will be there as long as you are producing lift. Vorticity is constant, you can spread it out in a more diffuse way to limit viscous loss, but total vorticity will remain the same, no matter what sort of device or gimmick you put on the aircraft.

This problem then becomes an accounting exercise. My guess is even the V-173 suffered from poor accounting. To counter the vortex the engines must produce extra power. The actual "induced" drag is quite low relative to form and interference. Induced drag only matters because it is always there, so over time it adds up. In the case of the 173 you can think of the engines producing a tiny amount of vertical lift by counteracting the vortex. You have to burn fuel to do that. Fuel that isn't pushing the aircraft forward.

Same difference in the end, and I would hate to loose an engine on a twin with the engines on the tip of the wing.

As to the toilet paper tube on the end of the wing...IMO...bunk. Let's see it compared to a properly designed sheared tip. I would also like to see a proper wetted area drag study, once again, compared to something other than a truncated or rounded tip.

Accounting, all in apples please.
Yup, but well managed details could make some benefit. I'll give you an analogy of someone I know that did a very unpopular thing in the air intake world in racing. He put a small electric fan on the inlet of his car. All laughed because of all the turbulator propellers for intake ducts that are sold supposedly increasing gas mileage. This was different. He tied it to the WOT switch on the Fuel injection. The fan made the airbox just barely positive pressure as opposed to a large negative. It only worked at WOT because if you don't have the throttle mashed you are mid throttle and you have the throttle valve partially closed so no real benefit. For him he knew that you always need to be at WOT in the right gear in every tricky part of the courses he drove to be competitive and that little fan gave him a measurable lap time advantage. That was a real detailed solution of using excess alternator capacity to solve a flow problem with a slight augmention.

Those round constricting duct tips are a huge drag source. CFD will be misleading on that sort of thing. Testing would have to be very finite and very well thought out to get inside instrument error. The slits are ejecting a curtain wall of air to make a virtual straightening vane. When you make air take a 90 degree turn you lose efficiency not gain it. But letting the large deflections build in the vortex makes huge drag too but only at higherish angles of attack. The only place a wing tip like that could make a benefit is by reducing fuel flow at cruise by reducing drag. At that point you might be able to clean up a blocky wing that doesn't have reduced tip cord and pressure balancing of the outboard stations ala Schumann. Almost no one in the homebuilding field has access to adequate resources to do an R&D program like that. The Rutan cartop method might work and some free CFD and a willing participant. But how much money do you have to spend to save a few bucks of fuel at cruise on a two seater rich person's toy?
 

Monty

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Yup, but well managed details could make some benefit. I'll give you an analogy of someone I know that did a very unpopular thing in the air intake world in racing. He put a small electric fan on the inlet of his car. All laughed because of all the turbulator propellers for intake ducts that are sold supposedly increasing gas mileage. This was different. He tied it to the WOT switch on the Fuel injection. The fan made the airbox just barely positive pressure as opposed to a large negative. It only worked at WOT because if you don't have the throttle mashed you are mid throttle and you have the throttle valve partially closed so no real benefit. For him he knew that you always need to be at WOT in the right gear in every tricky part of the courses he drove to be competitive and that little fan gave him a measurable lap time advantage. That was a real detailed solution of using excess alternator capacity to solve a flow problem with a slight augmention.

Those round constricting duct tips are a huge drag source. CFD will be misleading on that sort of thing. Testing would have to be very finite and very well thought out to get inside instrument error. The slits are ejecting a curtain wall of air to make a virtual straightening vane. When you make air take a 90 degree turn you lose efficiency not gain it. But letting the large deflections build in the vortex makes huge drag too but only at higherish angles of attack. The only place a wing tip like that could make a benefit is by reducing fuel flow at cruise by reducing drag. At that point you might be able to clean up a blocky wing that doesn't have reduced tip cord and pressure balancing of the outboard stations ala Schumann. Almost no one in the homebuilding field has access to adequate resources to do an R&D program like that. The Rutan cartop method might work and some free CFD and a willing participant. But how much money do you have to spend to save a few bucks of fuel at cruise on a two seater rich person's toy?
Regarding the alternator, once again-accounting. In the end all energy must come from the fuel. The example of the race car is not the same as the aircraft. In the race-car case we are talking about a transient condition. You store some energy during braking in the battery, and then apply it to the intake during WOT. A round about way to employ regenerative braking.

Doesn't work that way in an aircraft because of steady state operation. Any energy the alternator supplies to the air via whatever means ultimately comes from the crankshaft, and the fuel burned to turn it.

The same thing is ultimately true for the car example, but there the figure of merit is lap times, and the fuel is already expended. In your example a little less heat is rejected to the environment through the brake rotors. This energy instead finds it's way to the battery and ultimately the fan in the intake.
 

Hot Wings

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Accounting, all in apples please.
And audited by the lift and drag sensors in a wind tunnel.

But I'm not so sure I'd be as quick as some of the others on this thread to dismiss the idea of the rolled wing tip as being totally without merit. Start with a winglet. There is strong evidence that they do work. Add a winglet to first and reduce the span of the first. Repeat. The result is a curled tip similar to that shown. Getting a winglet optimized is hard enough. Optimizing something like this!? I've got better things to do and will leave this task to others :lick:
 

bmcj

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I'm not sure if you can eliminate vorticity, but devices such as winglets give you a larger effective span which, in turn, gives you better span efficiency. It also by necessity adds bending moment at the root.
 

autoreply

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But I'm not so sure I'd be as quick as some of the others on this thread to dismiss the idea of the rolled wing tip as being totally without merit.
It might very well have merit. But no more (and probably less) than a nicely rounded tip. What the CFD shows is local disturbance, not induced drag.

The fundamental problem is that a small device can't affect a large volume of air, so it's fundamentally impossible to be of much use. A winglet that size would also have a maximum positive effects of fractions of a percent.
 

addicted2climbing

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I remember a while back that there was a wingtip design that was being tested that I think was called a "gate wingtip" and it looked like a set of vertical blinds on the wingtip. I am curious whatever happened to that design and if it ever worked.. Anyone know?

Marc
 

ultralajt

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The simpliest way from design and manufacturng point of view is just to add some more span at same area.
 

Dan Thomas

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The simpliest way from design and manufacturng point of view is just to add some more span at same area.
That's about what Steve Wittman did. He tried a winglet on his Tailwind, and didn't see much gain. Then he laid that winglet flat, extending the span a bit and giving the wing a small tip, and got a big gain.

Old, square tips:

Wittman-Tailwind-W8-a19045525.jpg



New, tapered tips:

p1845.jpg

The Hummel Bird made some gains with the same idea.

To me, the tip vortex will be small if the tip is small, and less energy will be lost to it. Isn't that why the Spitfire's elliptical wing worked well? And the deHavilland DH88 Comet?

3709873899_853ca2b597.jpg

Maybe I'm haywire, but I see this sort of fast bird, too. And what is his wingtip treatment?

fastest-bird-Spin-Tailed-Swift.jpg

The Spine-Tailed Swift, clocked at 106 MPH. Fastest bird in the world.

Dan
 

autoreply

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Winglets are always superior to an extension in span, the only exception being stealth aircraft. Lower bending moments for lower induced drag, more lift and less frontal drag in comparison to any other tip device or span extension.
Load_Lift.jpg
Masak Winglet Design Considerations

The only two drawbacks is that they're rather complicated to make and very complicated to design correct. Simply adding your own designed "winglet" is about as likely to be succesful as an airfoil drawn by a graphic artist. Elliptical wings are only ideal in misunderstood theory (applying 2D theory to a 3D problem)
 
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