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Old Oct 10, 2012, 09:53 PM
B for Bruce
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The 'Wack, BC, Canada
Joined Oct 2002
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I dunno.... it's looking a little more like Jurassic than swallow like to me. Especially if you go for translucent covering....

Seriously it looks fantastic. Should be highly interesting to see it flying.
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Old Oct 11, 2012, 09:18 AM
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Knoll53's Avatar
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So no comments on the pointy wing tips ???

That's GOT to create some problems. I can build them easy enough, but what happens to the spin behavior (for starters)? Currently thinking of a 10% thick SD8020 for the tips. Root will probably be a 12% thick PW51.

Kent
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Old Oct 11, 2012, 10:38 AM
I don't like your altitude
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Quote:
Originally Posted by Knoll53 View Post
So no comments on the pointy wing tips ???

That's GOT to create some problems. I can build them easy enough, but what happens to the spin behavior (for starters)? Currently thinking of a 10% thick SD8020 for the tips. Root will probably be a 12% thick PW51.

Kent
I'm quite sure you could build the tips as drawn,but they have got to be a"delicate"area.How about rounding the tip off at the 3rd rib in?Shouldn't detract too much from the overall appearance.
Speaking of appearance I thought swallows had a forked tail
Stuart
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Old Oct 11, 2012, 11:17 AM
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Switzerland, ZH, Wald
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Hi gentlemen,

With my experience, the tips will create problems! May be I am wrong, but i had massive problems with the little wing below.
But any way, the shape is very nice!!! I like it.

Gerd
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Old Oct 11, 2012, 11:56 AM
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Hi gentlemen,

With my experience, the tips will create problems!
Thanks Gerd. I thought as much.

I trust that you are not just referring to reduced roll rate. The pointy tips must have contributed to a more sinister problem, such as tip stalls. With your red bird, (beautiful model BTW) did you come up with any theories on how to solve this problem, while keeping the pointy tips?

I can tell you that my current approach is to use a thinner symmetrical airfoil at the tip and a little wash out.

Stuart: They won't be delicate if I build them with CF tow spar caps, solid balsa and a fiberglass skin. This design is all about the pointy tips. Think Samurai sword meets Pterodactyl meets Swallow.

Kent
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Old Oct 11, 2012, 01:02 PM
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Kent, UK
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any merit in this approach? ie extending the control surface to encompass the tip
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Old Oct 11, 2012, 01:24 PM
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Miniphase: I know that you are all over this elevon shape, so I'm just catching up with the theory. I have to admit, it just lookS right.

As an aileron, it would provide better roll rate and probably more drag at the tip, which would promote proverse yaw. All good for turns. As an elevator it would provide extra drag, which would be unattractive. Not the end of the world.

The inner flaps could be the dedicated elevator and the outer control surface could be a dedicated aileron. Is that the thinking???

Certainly would be a challenge to build. Even if the control surface was solid balsa and fiberglassed, the hinges would have to be very very strong. No off-the-shelf hinge (that I know of) would survive a cartwheel landing....which I'm sure to do sooner or later.

Currently I'm thinking that this will be primarily a thermal ship for Big Sur, which has turbulent air when the wind comes up. So moderate roll response is needed, but it's not a slope ship with maximum roll rate.

Sketch is original concept.

Kent
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Old Oct 11, 2012, 01:37 PM
I don't like your altitude
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Purely from a theory point of view,what effect would drag rudders have?Say from the 2nd rib to the 5th
Stuart
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Old Oct 11, 2012, 01:45 PM
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Drag rudders, when used individually, will promote proverse yaw, which can be needed in flying wings. I would think that the big vertical fin would provide adequate yaw stability. Turns can be accomplished with aileron and up elevator.

Kent
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Old Oct 11, 2012, 02:33 PM
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Kent, I was thinking more about the tiny, tiny tip chord and remember some of the smaller Horten models in the 90s has this kind of 'extended' control surface which moved the whole tip...can't quite recall the benefits but it seemed appropriate. We need a good dose of theory from Norm instead of my half assed assumptions!
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Old Oct 12, 2012, 07:47 AM
Herk
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Virginia USA
Joined Jun 2007
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Quote:
Originally Posted by miniphase View Post
Kent, I was thinking more about the tiny, tiny tip chord and remember some of the smaller Horten models in the 90s has this kind of 'extended' control surface which moved the whole tip...can't quite recall the benefits but it seemed appropriate. We need a good dose of theory from Norm instead of my half assed assumptions!
I agree. That part of the aileron will contribute a lot of drag when it's deflected. If there is washout it will help to reduced adverse yaw (I think). I'm pretty much convinced that factor is the secret to the very nice performance of flashted's version of a Paoli wing.

http://www.rcgroups.com/forums/showt...1564706&page=9

Video here: https://vimeo.com/user2017315/videos/page:2/sort:date
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Old Oct 12, 2012, 09:51 AM
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Hi Herk,

If the issue is adverse yaw, I would think that no special effort is required. This wing is a highly stylized version of a plank with a fin, which typically have no problem with adverse yaw.

With the swept back and washed out tip panels, there should be some added yaw stability and proverse yaw similar to the same effect that Horten style ships use.

I'm not sure what nice performance you are thinking of with flashted's video. Turn response? Sink rate? The video I saw was in slope lift. Even my draggy Komet looks good in slope lift. May be flashted's wing performs great. I just wouldn't know it by the video. Am I missing something?

Kent
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Old Oct 12, 2012, 07:00 PM
Herk
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Virginia USA
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Kent - you are right - sloping is flying, but with area, control and balance almost anything will fly on the slope.

What I was referring to when I mentioned Ted's plane is it's handling, stability, balanced turns and smooth turn reversals. I have not determined yet exactly where his CG was during that video, but the general info from him makes me think it's well behind what would be normal for a Horten type design.

However what I said was not an advertisement for his model. I knew beforehand that wide ailerons that go all the way to the tip, create extra drag when they are deflected. When you combine that concept with twist - you are moving in the direction of creating proverse yaw. The Paoli has a cambered airfoil all the way to the elevon area - then a lot of up elevon deflection when it's in trim. That makes a case for proverse yaw when the aileron function is used. And yes proverse yaw is even helpful when there is a fin installed - especially if there is no coupled rudder function.

Blah blah blah Yak Yak Yak ---- anyway that's what I was thinking.
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Old Oct 12, 2012, 09:49 PM
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nmasters's Avatar
Colorado
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Quote:
Originally Posted by miniphase View Post
Kent, I was thinking more about the tiny, tiny tip chord and remember some of the smaller Horten models in the 90s has this kind of 'extended' control surface which moved the whole tip...can't quite recall the benefits but it seemed appropriate. We need a good dose of theory from Norm instead of my half assed assumptions!
I haven't gotten my certificate of upgrade from half ass either, Paul, but I'll share what little I know about tiny tips

I suppose that making a large portion of the tip a horn-balance might reduce the drag of a pointy tip by keeping it at a low AoA relative to the fixed part.

There are two problems with high taper ratio that I can think of right now:

First is simply that, If you try to force it to carry an elliptical lift distribution, the tip will always be stalled. This is simply because if the taper ratio is less than 0.35 the tip just doesn't have enough surface area to carry its share of the load. Going with a bell shaped lift distribution would solve this problem: at least for low AoA.

The second problem is that low Reynolds numbers also mean low CLmax so regardless of what your basic lift distribution looks like the tip just isn't going to be able generate much force. This is probably what the big horn balance you remember is about. Normally a horn balance is providing an aerodynamic balance and a place to put a mass balance. The horn balance is a symmetrical section that goes to a lower AoA when the elevon is deflected up. So when the inboard section has a camber change the very tip just has an AoA change.

BTW The part of a bird's wing that corresponds to your thumb probably plays a roll in high AoA by generating a leading edge vortex. A part that can float open like a Handley-Page slat would be interesting but certain fixed features will do the job just fine. Vortilons are common on full sized swept wings. A dogtooth is a common feature on some older fighters:
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Old Oct 13, 2012, 11:02 AM
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Good discussion. I probably don't say it enough, but all comments are welcomed and appreciated. You can bet that pointy wing tips are all new to me. One thing is clear. The red elevon would produce lots of drag when deflected and as much proverse yaw as needed.

In the sketch the red elevon could be thought of as 2 separate flying surfaces.

The inboard portion is a conventional control surface that modifies the air flow for the main wing which is in front of it. Changing it's camber and AoA.

The outer portion is it's own little ting wing. It's not unusual for elevons to deflect 15 to 20 degrees which would certainly stall this little wing. So in this case, the big outer portion of the red elevon it is acting primarily as drag device. This stalled little wing would transition into the inboard convention elevon portion. Could this stalled little wing promote a tip stall over a larger portion of the wing tip? Just a thought.

I would think that proverse yaw could be "dialed-in" to a standard plank with the us of aileron differential. This could produce a coordinated turn possibly without a fin at all. Leaving the fin's primary purpose that of yaw stability. Seems workable to me, but again maybe I'm missing something.

In order to make the wing tip stall resistant, currently I'm thinking of using a SD8020 airfoil at the tip and maybe 4 degrees of total wing twist starting at the inside edge of the elevon. Then if the elevon can be designed such that it does not induce a stall, then all should be workable. In order to do that, the elevon is limited to 20% to 25% of the wing chord.

I may be under estimating the proverse yaw provided by aileron differential. If so, a rudder could fill in the gap.

Kent
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