Wing fences. - RC Groups
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Oct 13, 2017, 02:21 PM
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Discussion

Wing fences.


Have any of you guys experimented with wing fences at model scales?

I have a wing that has a tendency to tip-stall. It's tapered, with a swept-forward TE.

At the moment, I'm controlling that with a combination of inboard flaps, and reflexed ailerons. But, I'm looking for a better solution, because the reflexing means an increase in flying speed. OK, it's only a bit, but if it can be avoided ...

Just wondering whether I can expect worthwhile improvement to the handling, by the fitment of fences.
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Oct 13, 2017, 02:54 PM
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richard hanson's Avatar
Need more info
Size n weight and aspect ratio
Do they work
Absolutely
We use em on tiny 100 sq inch or less acrobats such as yak n extra weighing 2 ounces
Locating full chord upper surface plates at mid panel, they definitely reduce wobble in very high alpha flying
Maybe not the info you needed
Oct 13, 2017, 03:18 PM
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Span is 78".
Root chord is 16 inches. Tip chord is 11"
No sweepback.
Constant section, no camber, no washout.
12% thickness, as I recall.

Aspect ratio is 5.8 approx.

Not sure of the a/c weight ... somewhere around 10 or 11lbs, I think. I can go measure it, if it's really important.
Oct 13, 2017, 03:21 PM
B for Bruce
BMatthews's Avatar
I've read of a few cases where turned down Hoerner style tips were reported to help with tip stalling. Also the same from folks that swore that larger airfoil shaped end plates helped in much the same way. Pictures seemed to show the end plates being roughly 8 to 10% of the wing chord in extension beyond the airfoil line. So a 10" wing chord would seem to call for tip plates that are roughly 3/4 to 1" larger all around than the wing section.

On the other hand I can't recall ever reading where such end plates caused a problem or hurt the slow speed end of things.

Tape on some stiff cardboard plates and try it?

This is all just spewing back what I've read over the years. I've never flown a model with such plates. I've built and flown a couple of models with the Hoerner style tips many years ago. But I never tried taking them off to see what, if any, difference they made.
Oct 13, 2017, 04:26 PM
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richard hanson's Avatar
Quote:
Originally Posted by bogbeagle
Span is 78".
Root chord is 16 inches. Tip chord is 11"
No sweepback.
Constant section, no camber, no washout.
12% thickness, as I recall.

Aspect ratio is 5.8 approx.

Not sure of the a/c weight ... somewhere around 10 or 11lbs, I think. I can go measure it, if it's really important.
Your model is about the same. In size n weight as any pattern model
Not a floater but still very manageable wing loading
The addition of mid panel plates about 2” high may steady things at absolute min speeds
Don,t bet on it
Same on tip plates
But, simply slashing tips at 45 degrees can steady things a bit
We tried this on Dalotels and they reliably fell out on landings ,very straight ahead
It adds a slight dihedral effect
Oct 13, 2017, 08:49 PM
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Quote:
Originally Posted by bogbeagle
I have a wing that has a tendency to tip-stall. It's tapered, with a swept-forward TE.
At the moment, I'm controlling that with a combination of inboard flaps, and reflexed ailerons. But, I'm looking for a better solution, because the reflexing means an increase in flying speed. OK, it's only a bit, but if it can be avoided ...
As I'm sure you're aware, the name of the game is to get the stall to progress from root to tip, rather than the other way around.

One way of doing this is wing twist, which of course is no help if the wing is already built. You're essentially doing that with deflected surfaces.

Have you tried increasing the inboard flap deflection, and eliminating the aileron reflex?

Fences might work. Another idea might be slats on the aileron portion of the wing, or some kind of turbulators (vortex generators).
Oct 14, 2017, 04:49 AM
Registered User
Here's the flaps on the wing in question. As best I can estimate, full extension gives about 25 degrees... which is quite effective, in terms of drag and lift.

I know that I can get quite a bit more movement. That's worth a go. This wing has been on a couple of models, prior to this one ... and I DID use more flap extension.

This is a good example of a wing that is 're- purposed' and is now being asked to give a little bit more than was originally intended. It was originally on a plane of lighter weight, operating off a more generous runway.

I'd avoid slats, because I want to retain the aerobatic potential as much as is possible.

It's not awful, it's just that when you try to squeeze that last little bit out of it, there's some 'wing drop' or oscillation ... if it's flown without the reflex. This happens right at the end of the hold-off, in the last half-second before the wheels touch, and the stick is well back... and the model will drop onto one wheel.


I just weighed it ... 11lb 7 oz. 8servos, flaps, two batteries, OS 1.20, sprung nosegear ... it piles up. That's a very reasonable 25oz wing loading.

.
Last edited by bogbeagle; Oct 14, 2017 at 06:00 AM.
Oct 14, 2017, 11:55 AM
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richard hanson's Avatar
Sounds pretty normal to me
Oct 14, 2017, 02:09 PM
An itch?. Scratch build.
eflightray's Avatar
It just needs an extra lever ---



Oct 26, 2017, 08:42 AM
Registered User
OK.

I squeezed an extra 10 degrees of flap extension out of the system ... so, now I have about 35 degrees.

I got the chance to fly the model, this morning, in somewhat unpleasant conditions ... and I can report a definite improvement in low-speed manners. So, good call, there.

The flaps, being somewhat Fowler-ish, are very powerful, which is why I initially elected to use only a moderate extension.

Anyway, I can fly the hold-off until the whole wing quits flying. This happens quite abruptly, with good control right up to that point. Normal landings are very controllable, though a good deal of power is required to control the approach.

I still have several degrees of aileron reflex dialled-in; this only comes into play with the last few degrees of flap travel.

Had lots of fun shooting approaches, this morning. Especially the Khe Sanh sort ... get close and high, power to idle, full flap and dive to whatever you think is the flap-limiting speed. Don't mess-up the round-out! A short float generally then terminates in a gentle touch-down.


I would still like to experiment with vortilons, fences or droops. But, it's a built-up wing and I'm reluctant to start cutting into it. A foam wing would make a better candidate.
Oct 27, 2017, 10:28 AM
An itch?. Scratch build.
eflightray's Avatar
I very rarely have a plane stall, ...... but then it might be because I don't tape pieces of wool to the wings


Ray.


Airflow during a stall. (2 min 29 sec)
Oct 27, 2017, 11:33 AM
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richard hanson's Avatar
Golly that was so realistic!
I have never seen a wing that looked like that
my planes all have fairly flat surfaces and no squiggles on hem
Must not be airfoils huh?
Oct 30, 2017, 06:15 AM
Registered User
These days you could use a tiny camera and threads to do the same thing on a big model like this.

bogbeagle:
To do a Khe Sanh approach correctly, don't you need someone downwind of the runway with a gun?


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