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Old Aug 08, 2011, 02:41 AM
Grumpy old git.. Who me?
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Originally Posted by springer View Post
I suppose one could attribute that to different style wing/planes, but it is pretty consistent across all the planes I've done as KFM's.
That's one point that occurs to me also... If all the planes a modeller builds are lightweight foamy models then it's not surprising they mainly fly in a similar way to each other. Stall behavior could be as much due to other similarities between the models as to the fact they all have KF airfoils?

Just a thought......

Steve
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Old Aug 08, 2011, 03:49 AM
internet gadfly
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Originally Posted by Dickeroo View Post
Dr. Nicholaides was kind enough to give me a copy of a book called See The Wind Blow by F.N.M. Brown who had done extensive work on all different types of objects in a smoke tunnel that he had designed.
I had to look up "See The Wind Blow" by F.N.M. Brown to see if it's available. Not surprisingly Amazon was the first link on the google results page but when I went there all it said was that "See The Wind Blow" is out of print but you can get this other book for $309.95 That's $1.13 per page! Ridiculous! I got the hardcover edition of "Album of Fluid Motion" by Milton Van Dyke for $0.29 per page. Of course these days there are several free flow visualization galleries on the internet such as eFluids.com. And of course you can watch everything from 1940s NACA wind tunnel tests the guys doing tuft tests on their model airplanes.

--Norm, who still prefers books but loves the interweb
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Old Aug 08, 2011, 10:24 AM
In the 20' glider range
anti-gravity's Avatar
Boise, Idaho
Joined Jul 2009
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Quote:
Originally Posted by JetPlaneFlyer View Post
PS.. why not include 3d planes in the discussion? The Ultimate AMR and Yak 54 3D models I'm currently flying are just normal RC model airplanes that are perhaps a bit lighter and a bit more powerful than 'average' sport models. If i reduce the control throws to low rates they fly just like a good sport model. Even on low throws and not using 3D power to hover, flown just like a conventional sport model, these model stall in a quite gentle way.. probably as gentle as any KF airfoil plane (especially the Ultimate).

Steve
The reason I say I would not include 3d airplanes is this.

Most 3d airplanes have 1:2 or more (or less) power ratio. With that kind of power you are flying the plane by the prop. Not the wing. (in a high alpha situation) In the case of a glider you are flying it by the wing, all the time.
So when you say you are putting your 3d plane into a high alpha maneuver and it wont stall, that is because it is flying like a kite. Strictly from the AOA and the power pulling it forward.

I certainly believe that 3d models can use an airfoil to there advantage, heck, I own one that does. But when the ability to pull have unlimited vertical, the airfoil makes no significant difference.
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Old Aug 08, 2011, 11:10 AM
In the 20' glider range
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Boise, Idaho
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Originally Posted by JetPlaneFlyer View Post
Dick,

The 20' KF sailplane video posted earlier in this thread is a case in point where a KF wing plane stalls and looses considerable height.. The ground stopped it losing more but even if it had been two or three times higher I don't think it would have recovered: http://www.rcgroups.com/forums/showp...&postcount=378

It looks to me that too far back CG was the main problem with that glider, compounded by being a bit underpowered... but it does show that not all KF planes stall the same way, and neither do conventional airfoiled planes.
Putting aside the other comments in this post, it would have recovered.

I am flying a plane 5 times the size, and 7.5 times the weight (assuming the average kf foamie is roughly 48 in. WS and around 2 lbs)

Yes it is going to take more time than the average kf foamie, because it is a lot bigger. A lot heavier. An so on.

Listen, I have never taken classes on this. So I don't know the math and the facts about airfoils. I know a lot, but not as much as I could.
But, even if you know what is going to happen on paper, it doesn't mean that is going to happen in real life.
Right now you are sitting behind your computer making assumptions. Yes, I believe that you have the knowledge. Then tell me you have never used in in real life, and it makes it useless.

But what do I know, I am just a kid. A kid who doesn't know the facts, but has done it all in real life. The real life, where mother nature states all rules.
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Old Aug 08, 2011, 11:21 AM
Grumpy old git.. Who me?
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Cole,

That's true but with my 3d models i can also do a stunt called a 'escalator' which involves cutting the power completely, pulling in up elevator until the model stalls, then descending at high alpha with power off. The model remains controllable throughout and can be flown out of the stall simply by releasing the elevator. If you have a 3D model then you have probably tried this one yourself?

So even without using thrust, the stall on these models is very gentle, controllable and recoverable. The trick with these models is i think more to do with having low wing loading than anything else.

Steve
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Old Aug 08, 2011, 11:27 AM
Grumpy old git.. Who me?
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Originally Posted by anti-gravity View Post
Then tell me you have never used in in real life, and it makes it useless.
Cole,

Sorry but i must correct you on this.. I've been designing, building and flying models for over 40 years. I've had a number of plans and kits manufactured and my designs have even won a contest or two.. I say this not to brag but to correct the point you try to make about me sitting behind a desk and spouting theory without putting it into practice.

Steve
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Old Aug 08, 2011, 11:47 AM
In the 20' glider range
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Boise, Idaho
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Quote:
Originally Posted by JetPlaneFlyer View Post
Cole,

That's true but with my 3d models i can also do a stunt called a 'escalator' which involves cutting the power completely, pulling in up elevator until the model stalls, then descending at high alpha with power off. The model remains controllable throughout and can be flown out of the stall simply by releasing the elevator. If you have a 3D model then you have probably tried this one yourself?

So even without using thrust, the stall on these models is very gentle, controllable and recoverable. The trick with these models is i think more to do with having low wing loading than anything else.

Steve
Share with me how the airfoil effects this stunt.



Quote:
Originally Posted by JetPlaneFlyer View Post
Cole,

Sorry but i must correct you on this.. I've been designing, building and flying models for over 40 years. I've had a number of plans and kits manufactured and my designs have even won a contest or two.. I say this not to brag but to correct the point you try to make about me sitting behind a desk and spouting theory without putting it into practice.

Steve
I am talking about a Kf plane. I completely believe you on the regular airfoil side of things. And about designing, building and flying models for over 40 years.
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Old Aug 08, 2011, 12:04 PM
Grumpy old git.. Who me?
JetPlaneFlyer's Avatar
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Originally Posted by anti-gravity View Post
Share with me how the airfoil effects this stunt.
I really don't think the airfoil has an awful lot to do with this, or at least it's contribution is secondary. The airfoil on my 3d planes is nothing 'special', it's a very conventional looking medium thickness symmetrical airfoil, possibly a NACA 0012 or something very similar. The entire point i was trying to make is that conventional airfoil can have very safe and gentle stall behavior if the overall plane is appropriately designed. Stall behavior is as much influenced by other factors (wing loading, wing planform shape, wing twist, CG location etc) as it is by the type of airfoil used.


Quote:
I am talking about a Kf plane. I completely believe you on the regular airfoil side of things. And about designing, building and flying models for over 40 years.
Just because I've never made a plane with a KF airfoil does not make the rest of my experience [Quote]"useless". KF planes follow the same basic physical laws as any other plane.
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Old Aug 08, 2011, 01:22 PM
treefinder
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Quote:
Originally Posted by JetPlaneFlyer View Post
That's one point that occurs to me also... If all the planes a modeller builds are lightweight foamy models then it's not surprising they mainly fly in a similar way to each other. Stall behavior could be as much due to other similarities between the models as to the fact they all have KF airfoils?

Just a thought......

Steve

After writing about the consistency, I thought myself about the fact that I tend to build for light wing loading (as do most foamy flyers) and that may be a significant aid to gentle stalls, but the differences still persist on planes that I've made with more than one wing. And I've made planes with squarish straight wings, rounded tips, tapers, etc and the KFm's still seem better behaved than others.
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Old Aug 08, 2011, 02:50 PM
Grumpy old git.. Who me?
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Another common factor among foamy models is that they are made out of foam

Yeah I know it's a statement of the obvious but untreated foam usually has a slightly rough surface finish which could (and in fact must) serve to turbulate the boundary layer so might very well delay stall at low Re numbers.

All sorts of factors could be playing their part...

Steve
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Old Sep 03, 2011, 11:08 AM
fix-it-up chappie
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I saw this photo and had to post it here. It looks like 2 or 3 KF steps on the bottom of this vulture wing, and one of the most unusual wingtip designs I have ever seen. I don't even know what you would call that. A fence? Fringe?

The photo makes me wish for an equally good shot of the upper surface to see how it is shaped.

I dare say, this is one of the most "competitive" gliders available. Mind you the prize is a bit different from what we're used to seeing at most competitions (can you imagine a first prize at the nats being a 3-day old carcass?), and the on-board real time computer flight system is a big leg up (especially since it can constantly reconfigure the airfoil shape), still I think this is the direction that competitive gliders will likely arrive at in the distant future.
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Old Sep 03, 2011, 03:03 PM
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Originally Posted by tolladay View Post
I saw this photo and had to post it here. It looks like 2 or 3 KF steps on the bottom of this vulture wing, and one of the most unusual wingtip designs I have ever seen. I don't even know what you would call that. A fence? Fringe? .

Eric...

Wouldn't you know that nature is always a couple of steps ahead of us?

Dick

Thanks for posting this terrific picture.
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Old Sep 03, 2011, 04:39 PM
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Now if we could get a nice video of the wing in flight with a few rows of yarn tufts...

Roger
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Old Sep 03, 2011, 05:57 PM
Build straight - Fly twisty
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Australia, QLD, Little Mountain
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But the vulture is not flying. It looks like it's standing still and flapping its wings.
Perhaps that's its 'low lift / zero thrust wing configuration.
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Old Sep 05, 2011, 10:15 PM
Build straight - Fly twisty
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Australia, QLD, Little Mountain
Joined Feb 2010
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Further to this I searched 'vulture in flight' in Google Images.
There is nothing there that looks to me like a stepped wing section.
But Dragonfly wings are another thing altogether:
http://jeb.biologists.org/content/203/20/3125.full.pdf
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