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Mar 12, 2018, 10:56 PM
flyin' fool
goldguy's Avatar
The KF airfoil is stall proof.
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Mar 13, 2018, 11:06 AM
Build, crash...repeat
AleRRon's Avatar
Maybe, but I am exploring various ways of designing airfoil wings that combat tip stalling. Sometimes a Kf wing is fine and sometimes you want a more scale looking wing. All depends on what the aim is. But itís a good point, probably a stress free way to build a wing you donít have to worry about and gets you out flying more and designing less.
Mar 13, 2018, 04:28 PM
Build straight - Fly twisty
Whiskers's Avatar
The KF airfoil is stall proof only in the minds of those in the KFm Unconditional Love And Worship thread.
In the real world, they stall. This can be seen on many, many videos posted here. I'ts funny how this fiction persists.
Mar 13, 2018, 05:37 PM
Warbirds Lover
Dreamcatcher's Avatar
Hi,
I suffered a tip stall on my semi scale mini Pitts s2 some days ago...
At the second (and last) flight of the day, i was testing some "somenzini like" spin / negative high G arrial tricks. At the moment i started to pull gently on the elevator stick while i was increading the RPM to recover the plane of her dive, I totally and instantly lost the control of the plane that entered a very fast half roll and crashed.
I will post the video soon.
May be somebody will be able to give me an explanation of the behavior of my (Rip) mini Pitts s2...
At my eyes i would say that she suffeted a dynamic stall / wing tip stall.

Stay tuned..
Mar 13, 2018, 05:54 PM
Build straight - Fly twisty
Whiskers's Avatar
Probably what used to be called a high speed stall, now called an accelerated stall.
Been there, done that. Makes life interesting.
Mar 13, 2018, 06:12 PM
Jack
jackerbes's Avatar
Quote:
Originally Posted by goldguy
The KF airfoil is stall proof.
I had a feeling that someone would rebut your statement, and I have to agree with the argument that they will stall.

But if there is a wing that has a more gentle stall and a quicker recovery from it I don't know what it would be. KFm wing stalls at low speeds and with neutral or fairly neutral controls are characterized by a slight rising at the nose, than a slight nose drop, a bob back up, and and quick recovery. They never drop a wing and turn into a disastrous tip stall.

If you put a KFm wing into the wind and just let it run out of speed, it will continue the stall and recover process until it runs out of altitude. And the "landing" won't be too back if you're over deep grass or cushioning weeds.

You can see a couple of typical stalls, this on the Big Blu 96" KFm9 glider, at 1:44 and 2:00 in this video.

Big Blu 96 - 96" KFm9 Winged Glider Maiden Flight (5 min 18 sec)


Jack
Mar 13, 2018, 06:14 PM
Jack
jackerbes's Avatar
Quote:
Originally Posted by Whiskers
The KF airfoil is stall proof only in the minds of those in the KFm Unconditional Love And Worship thread.
In the real world, they stall. This can be seen on many, many videos posted here. I'ts funny how this fiction persists.
"..minds of those in the KFm Unconditional Love And Worship thread..."

That is an uncalled for insult. It is OK to like something. Even to like it a lot!

Jack
Mar 13, 2018, 06:21 PM
Build straight - Fly twisty
Whiskers's Avatar
And it's OK to have Unconditional Love And Worship if you like something a lot.
No argument from me...
Mar 13, 2018, 06:51 PM
Jack
jackerbes's Avatar
I must be thin skinned, I read you comment now and it seems mild with no insult intended. Please take mine the same way...

Have you ever built and stalled anything KFm? You might enjoy it and see what makes us think that way.

Jack
Mar 13, 2018, 07:19 PM
treefinder
springer's Avatar
just sittin' back and watchin' the show!
Mar 14, 2018, 01:18 AM
Build straight - Fly twisty
Whiskers's Avatar
Quote:
Originally Posted by jackerbes
<snip> Have you ever built and stalled anything KFm? You might enjoy it and see what makes us think that way.

Jack
I have a couple of planes with KFm wings. One of them, a profile aerobatic thing, is my go-to plane if I need to fly in rough conditions. It flies really well but it stalls the same as my other planes that have conventional wings. This particular plane had an earlier version with a flat plate wing. It also flew well, but the KFm4 winged version glides much better.
I once had a KFm2 winged powered glider that also flew well but had a vicious tip stall if it was mishandled.
My attitude is that I much prefer the look of the non stepped wing and I'm very happy to make the extra minimal effort to make it.
My aim is always to make a plane that flies really well. It's why I don't do scale.
If I thought a KFm wing would give me a better plane I'd use it. My experience so far has not taken me along that path.
Mar 16, 2018, 04:36 PM
Build, crash...repeat
AleRRon's Avatar
I dunno guys, we may be talking about two different stalls. Every plane and wing will stall at a certain speed and angle of attack. I'm only talking about tip stalling. If I understand it correctly that's when at certain conditions of airspeed and angle of attack, the wingtips lose lift and stall before the wing root. This results in the wingtip dropping. This causes the plane to rotate very quickly- worse than just a roll and generally out of control. Usually during slow speeds such as landing and/ slow speed turning. Usually close to the ground and resulting in a crash.
Last edited by AleRRon; Mar 16, 2018 at 04:38 PM. Reason: Spelling
Mar 16, 2018, 07:00 PM
Warbirds Lover
Dreamcatcher's Avatar
This is what i think was a tip stall :
tip stall (1 min 29 sec)


:-(
Mar 16, 2018, 07:03 PM
Build straight - Fly twisty
Whiskers's Avatar
Given that the thread is titles "Tip stall" I think we understand that.
You are right when you note that tip stalling occurs, "Usually during slow speeds such as landing and/ slow speed turning."
All aircraft, full size and model, have a finite flight envelope. Venture outside the envelope and bad stuff will happen.
So right there you have a way to beat tip stalling. Fly competently.
A thing that traps a lot of RC pilots is the folly of throttling down when flying down-wind.
The plane looks to them to be going OK, but in fact it is teetering on the brink of a stall. And that is what it does immediately a turn is initiated. The 'inside' wingtip has the lowest airspeed and that is where the stall first occurs.
Also, people get too hung up on trying to land at a ridiculously low airspeed. They come waffling in on the edge of a stall and then add a little bit of up elevator to slow the plane just a bit more. Or the breeze drops 1 knot.
Either way the plane is likely to drop a wing and auger in.
Having said that, it's true that various devices can be employed to delay stalling at the wing-tips. Several have been mentioned above. They all work to varying degrees, but in many ways the best thing to do is to keep the plane above its critical airspeed.
Mar 16, 2018, 07:09 PM
Build straight - Fly twisty
Whiskers's Avatar
Quote:
Originally Posted by Dreamcatcher
This is what i think was a tip stall : :-(
That looks more like a mechanical failure or an attack of Dumb Thumb.


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