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Feb 27, 2018, 11:17 AM
flyin' fool
goldguy's Avatar
I do know that those triangular slots are used on pusher flying wing to cut down on the noise.
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Feb 27, 2018, 12:00 PM
Build, crash...repeat
AleRRon's Avatar
During my Google searching, I found that there are a number of fixed wing devices to combat tip stall. The vertical wing fins on the 3D foamie Yak along the chord keep airflow from progressing sideways towards the tips which would make the tips stall and ailerons ineffective. The real MIG 17F has these because the problem is worse in a swept wing plane. See pic. The dogtooth extension on the leading edge also generates vortex flow that keeps airflow from spilling sideways too; same effect as wing fences.
Feb 27, 2018, 12:04 PM
Build, crash...repeat
AleRRon's Avatar
Goldguy, you mentioned " adding a triangle of balsa or foam to the LE at the tips that's about 25% of the half span works as well. " Can you show me what that looks like? I can't picture it. thanks!
Feb 27, 2018, 02:24 PM
Build straight - Fly twisty
Whiskers's Avatar
Quote:
Originally Posted by AleRRon
Goldguy, you mentioned " adding a triangle of balsa or foam to the LE at the tips that's about 25% of the half span works as well. " Can you show me what that looks like? I can't picture it. thanks!
Look at the picture that is in his post.
Feb 27, 2018, 02:56 PM
An itch?. Scratch build.
eflightray's Avatar
Another 'trick' to reduce the chance of a tip stall on full size aircraft is a 'stall strip', a triangular section on the leading edge nearer the root.

In a sense it causes the inner section of the wing to stall before the tip is affected.

Here's a better (actual), explanation ---

How Do Stall Strips Work?

But it still all comes back to the basic, don't get your model in a potential stall situation.

Ray.
Feb 27, 2018, 04:14 PM
Build straight - Fly twisty
Whiskers's Avatar
Quote:
Originally Posted by eflightray
<snip> ... don't get your model in a potential stall situation.

Ray.
... unless (say) you wish to enter a true spin or snap roll or stall turn or 3 point landing or...
Feb 27, 2018, 06:55 PM
Build, crash...repeat
AleRRon's Avatar
I did look at the Yak that goldguy posted but I don't think the triangles one can add at the tips mentioned are on that Yak. Or I could be daft. Sounded like an alternative to washout. Goldguy am I missing it or do u have a pic of that?
Feb 27, 2018, 07:22 PM
flyin' fool
goldguy's Avatar
OK, here's my story of a quick fix for the tip stall..................

Way back in the beginning of time, or about 1976, I went to a fun fly in Sayer, Pennylvania, a very long drive from my digs, with an untested 23 sized Mini Master with a ST46 up front and entered it in a 'run what ya' brung' pylon race. It was it's maiden. At the first pylon I ended up on the ground in a flash, no harm done except to my pride.

A FB with much more experience took it up for me to see what the problem was, as I insured him it wasn't me. It went totally out control at every yaw input. He landed it, found a pieces of square balsa, sliced it in half and glued it on the LE as shown with 5 min. Hobby Poxy.

Some to the things mentioned here are probably totally foreign to you, but trust me, it really happened and is a true story.

Anyways .................. bidda bing, budda boom ............... FIXED!
Last edited by goldguy; Feb 27, 2018 at 07:29 PM.
Feb 27, 2018, 07:32 PM
flyin' fool
goldguy's Avatar
Thing is, the wing was covered with a painted iron on fabric and no matter how I tried, I couldn't add washout. It lasted for exactly 350 documented flight like that.
Feb 27, 2018, 08:51 PM
Build, crash...repeat
AleRRon's Avatar
Cool story and valuable lesson! Sounds and looks like "leading edge extension" cuff like in diagram below.
https://en.m.wikipedia.org/wiki/File..._annotated.svg
Feb 27, 2018, 09:02 PM
Registered User
radfordc's Avatar
Quote:
Originally Posted by goldguy
Also, if you can't twist washout into the wing, adding a triangle of balsa or foam to the LE at the tips that's about 25% of the half span works as well.
You're talking about a "stall strip". You generally put them near the root of the wing....not the tip.

https://en.wikipedia.org/wiki/Stall_strips
"Stall strips typically consist of a small piece of material, usually aluminium, triangular in cross section and often 6-12 inches (15–30 cm) in length. It is riveted or bonded on the point of the wing’s leading edge, usually at the wing root.
Latest blog entry: Assembling a Spandau kit.
Feb 27, 2018, 11:21 PM
flyin' fool
goldguy's Avatar
Not really, it's more about the shape of the leading edge . As in ............ it would be the same as if you sanded the LE with a greater radius near the root and lesser at the tip. One is blunt and one sharp, one stalls before the other.
Mar 02, 2018, 09:38 PM
Registered User
portablevcb's Avatar
Most planes can be made to tip stall, some easier than others. As you have seen, too much elevator throw at speed can induce it with most airplanes. Sometimes it is 'fun' to exploit it, ie, a snap roll.

To 'combat' issues with tip stall try flying more maneuvers where you stall the plane on purpose. Start 'three mistakes high' so you have room to recover and go at it.

Start with a straight ahead slow speed stall. Just fly level and slowly reduce speed keeping the plane flying level by increasing elevator. Then fly level at low speed and yank the elevator with a very high control throw.

Then increase the speed a bit and do the same thing. Then go into a climb under power and keep increasing the climb angle until it stalls.

Then do the same maneuvers but in a steady turn.

While doing all this pay attention to how your plane responds to the controls as you get near the stall.

Once you know how the plane responds then adjust the control throws to limit the issue. I make sure that when on low rates I will not get a high speed stall (full speed, full elevator results in climb, not a stall). Then go on to snap rolls and intentional spins.

charlie

PS be aware of spin recovery before you start, 1. controls neutral, 2. cut power, 3. full rudder in opposite direction of spin (no aileron), 4. when spin stops slowly add power and elevator to recover from the dive. Yes, that's why you need to be three mistakes high. It can take a while to recover from a well developed spin.
Last edited by portablevcb; Mar 02, 2018 at 09:46 PM.
Mar 02, 2018, 10:32 PM
Build straight - Fly twisty
Whiskers's Avatar
I like down elevator to unstall a plane and stop a spin.
My right thumb does it instantly without being told.
It works very fast, and I've saved FPV planes that have dropped into a spin on final.
For that you have to be quick or it's all over.
Mar 12, 2018, 10:21 PM
Build, crash...repeat
AleRRon's Avatar
I’m still a lousy pilot so I really want to build planes that are resistant. I recently came across a couple of good methods.

One is the Flitetest airfoil wing. It uses a foam spar and a rather angular airfoil using two creases. The upper airfoil foam sheet extends from the wing root to the tip, but the bottom flat sheet does not go all the way to the tips. This leaves the tips as a simple undercamber wing. This has more lift than the actual cambered airfoil and therefore stalls less easily and at slower speeds than the rest of the wing. Wallah, the wing tips stall later than the wing root, and tip stalling is avoided and the plane doesn’t crash at slow speeds such as when trying to land. Brilliant I think! Very easy to build and it works. I have a few planes with this design and they can just glide with the motor cut, to land very nicely.

There is also an interesting way to build washout in a foam wing by making the top sheet a little longer so as to twist the wingtip leading edge downwards. Hard to describe but I think this Flitetest article does a good job, https://www.flitetest.com/articles/m...etrical-w-ings

Two other methods:
Make the wingtip with a thicker airfoil than the root. A higher camber (thicker) airfoil generates more lift and stalls at slower speeds than a thinner one. This can be done in a straight wing shape by making a spar at the tips taller than at the root, or in a tapered wing, keep the spar height constant resulting in a proportionally thicker airfoil at the tips.

Make the wingtip leading edge rounder (larger radius) than the root LE. This also delays stalling.
Anyone want to test some of these?


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