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Jun 30, 2011, 12:57 PM
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Dickeroo's Avatar

Would a 2-D computer have been able to predict these results?


Mike...

You've really illustrated something that probably won't show up with just computer data. Maybe I'm wrong, but seeing how things function in the real world is often different from how they perform under controlled conditions.
You've done some terrific work here.


Dick
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Jun 30, 2011, 03:52 PM
OpenTX University Staff
maguro's Avatar
Thread OP
Springer, to be of value the tip plates need to extend further above and below the wing and go beyond the leading and trailing edges. Here is a shot of the KF Test plane. The tip plates are made of 1/64" ply (because I had it on hand). The thinner the plate the better as far as drag is concerned.

Roger
Jul 01, 2011, 11:44 PM
Boffin
rpage53's Avatar
Quote:
Originally Posted by maguro View Post
Springer, to be of value the tip plates need to extend further above and below the wing and go beyond the leading and trailing edges.
To be of value, tip plates have to be very carefully experimented with because in virtually all cases, they just add drag. However, they may be useful to tame a nasty stall but are a detriment in all other flight profiles.

Hoerner tips (again when done properly) can reduce the stall speed with a minimal drag penalty.

The winglets that are increasingly popular on commercial jets are to increase lift during cruise without increasing wingspan in very crowded airports. If you don't have a wingspan limit, just increase the the wing and reduce the aspect ratio.

The winglets that Burt Rutan has popularized are also vertical stabilizers and in a flying wing design they may be necessary. But most of these additions to a wing are design compromises to correct other deficiencies.

Not that that is a bad thing, getting any craft to fly is a study in compromise. But there is no reason to design a model aircraft with tip plates.

Rick.
Jul 02, 2011, 02:34 AM
Tarot 550/600 & OMPHobby UK
Smoggie's Avatar
Rick,

Hoarner tips are primarily intended to reduce drag, not reduce stall speed. They work by forcing the tip vortex outward increasing effective aspect ratio and reducing induced drag.. or that's the theory.

Winglets work differently but their purpose is still drag reduction, not increasing lift. In level cruise flight any planes lift has to be equal to it's weight so the only way you could increase lift and maintain level flight is if weight was also increased.
Winglets work by reducing overall induced drag, they do this in a very clever way. The winglet interacts with the swirling tip vortex in a similar way to a sail boat tacking into wind, this creates a forward thrust just like the thrust that drives the sailboat into wind.

From NASA:
Quote:
Winglets, which are airfoils operating just like a sailboat tacking upwind, produce a forward thrust inside the circulation field of the vortices and reduce their strength.
But overall we agree, for most if not all model airplane applications wing tip 'add-ons' have an overall neutral or negative impact due to the weight and form drag they add.

Steve
Last edited by Smoggie; Jul 02, 2011 at 02:43 AM.
Jul 02, 2011, 09:15 AM
OpenTX University Staff
maguro's Avatar
Thread OP
I've built KFM models with and without tip plates. I always use very thin material in order to keep the drag to a minimum. I've never noticed any appreciable drag increase with tip plates, but high alpha handling is noticeably improved. Of course, I guess I can try doing tests with and without tip plates just to make make everyone happy.

Steve, you know, you would be an excellent candidate to do some of this testing. Want to volunteer?

Roger
Jul 02, 2011, 09:29 AM
Registered User
Quote:
Originally Posted by maguro View Post
.... tip plates. I always use very thin material in order to keep the drag to a minimum. I've never noticed any appreciable drag increase with tip plates, but high alpha handling is noticeably improved. ....
I've heard that much of the drag arises from the 90deg intersections between the tip plate and wing. The curved transitions from the wing to the winglets help reduce the amount of added drag.
Jul 02, 2011, 09:34 AM
treefinder
springer's Avatar
As I mentioned earlier, I've only done one tip plate wing, on 42" BB. And it's a great flyer, but I can confirm a noticeable drag from the OSG flights with the tips on one side only. I had to correct for straight flight. Obvious, but comforting to have personal real world validation.

Oh yeah, the OSW uses tips for yaw stability, so guess i've done two.
Jul 02, 2011, 09:40 AM
treefinder
springer's Avatar
Yea, Steve, you need to close the books, shelve the balsa and tissue for a bit, and whip out some foam test planes.

On the other hand it's an astute man that can see a possible addictive behavior and resist!
Jul 02, 2011, 10:35 AM
just Some Useless Geek
I'm not addicted! I'm not! I'M NOT!!

I can quit any time I want. I just don't want to, that's all.
Jul 02, 2011, 11:41 AM
fix-it-up chappie
tolladay's Avatar
Hello. My name is Eric, and I am a foamaholic.

And to continue the very bad humor; is it still a FK wing if it has 12 steps?
Jul 02, 2011, 11:50 AM
just Some Useless Geek
[Group] Hi, Eric.

[Eric] It's been six minutes since my last foamy flight.

[Group] Hey, man. One day at a time, y'know?
Jul 02, 2011, 12:33 PM
Tarot 550/600 & OMPHobby UK
Smoggie's Avatar
Roger,

I didn't consider the possible benefits to handling especially during high alpa.. I'll take your word for it that there is an advantage in those circumstances.. In fact to back that up i note that some of the latest 3D models use huge tip plates, which according to reports help prevent wing rock in harrier manoeuvres, amongst other 3D benefits.

Lately I'm doing too much flying to build anything...

Steve
Jul 02, 2011, 12:42 PM
Tarot 550/600 & OMPHobby UK
Smoggie's Avatar
Here's an article a friend of mine wrote a while back on the subject of wing tip designs.. It's written from the perspective of freeflight duration modelling but the principals involved are the same.
Jul 03, 2011, 10:55 AM
In Rc for a LONG TIME FFAA#1
laserman's Avatar
Quote:
Originally Posted by A Useless Geek View Post
I'm not addicted! I'm not! I'M NOT!!

I can quit any time I want. I just don't want to, that's all.

useless you should join us in the F.F.A.A thread where all of us foam addicts can help each other heheh

laserman F.F.A.A #1
Jul 08, 2011, 01:29 PM
Registered User
Quote:
Originally Posted by maguro View Post
I've built KFM models with and without tip plates. I always use very thin material in order to keep the drag to a minimum. I've never noticed any appreciable drag increase with tip plates, but high alpha handling is noticeably improved. Of course, I guess I can try doing tests with and without tip plates just to make make everyone happy.

Steve, you know, you would be an excellent candidate to do some of this testing. Want to volunteer?

Roger
Thickness of tip plate is almost immaterial, it's the surface area which creates drag, and the possible turbulence caused at the junction of plate and wing ; surfaces which meet at near to 90 degrees are great drag inducers, hence the root fairings between wing and fuselage on most low wing aircraft.


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