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Old Oct 06, 2011, 01:48 PM
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I brought the test plane home in a bag today. I was flying inverted and close to the ground, turned sharply, then pulled when I shoulda pushed. It was all over in a second.

The good news is that it is repairable (hey it's foam), and it should be back in the air again soon. This time with some improvements in the fuselage design.

Roger
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Old Oct 06, 2011, 04:18 PM
Build straight - Fly twisty
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The more I think about testing wings the more I become convinced a wind tunnel is the way to go.
The more I think about wind tunnels, the more problems I foresee.
However, comparing the lift and drag and stalling characteristics of various wing sections should be doable, and the tuft thing would be easy.
Springer, you are well placed to be the Wind Tunnel Guy. An engineer with wood-working skills, with a barn... the list goes on.
Time to 'go with the (air) flow!'
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Old Oct 06, 2011, 06:35 PM
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A wind tunnel is exactly what we need. I've asked before. So far, no one with a wind tunnel has offered to help.

Universities don't seem to be interested in an airfoil that would only be of use to R/C modellers. Even Dr. Mark Drella, who developed airfoils for R/C sailplanes, shows nothing but disdain for KF airfoils. It's very hard to get past this prejudice.

If you know of a wind tunnel in Australia that might offer to help, please send them to us.

Roger
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Old Oct 06, 2011, 07:10 PM
treefinder
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You guys! always tempting us off topic!

on topic: I think a wind tunnel would be a super winter project, and I probably have all the materials (including 1/6, 1/4, 1/3hp motors), However the other list (the honeydo list also goes on, so I'll have to see how to fit it in. ('course I'm retired, so I just sit around and do nothing all day anyway.....)

Off topic: "Universities don't seem to be interested in an airfoil that would only be of use to R/C modellers. Even Dr. Mark Drella, who developed airfoils for R/C sailplanes, shows nothing but disdain for KF airfoils. It's very hard to get past this prejudice." I guess I don't care much for "this prejudice" one way or the other. I'm perfectly happy for Dr. Drela to spend his days developing more hard to make airfoils to wring the next 1% or less improvement out of already hard to make efficient airfoils. I'll just keep tinkering with my easy to make airfoil in my scratch designed and built foamies and have just as much fun! And every once in a while i'll build a conventional wing just to remind myself of why I like KFM's. PV2 gets a conventional companion to her KFM2 wing when I get serious with the wbpu and filters.
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Old Oct 06, 2011, 10:35 PM
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Springer one thing to take into account with the w.t. Is flow straightening the easy way if if you can get straws that are in boxes is to cut them in half and voila instant straightener for the air flow

jim
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Old Oct 07, 2011, 06:52 AM
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Quote:
Originally Posted by maguro View Post
I brought the test plane home in a bag today. I was flying inverted and close to the ground, turned sharply, then pulled when I shoulda pushed. It was all over in a second.
Sorry to hear that, it's all too easy to do

Steve
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Old Oct 07, 2011, 07:36 AM
Jack
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Quote:
Originally Posted by springer View Post
Ha! I get my own perverse kick out of finding out who will actually dig down and find the actual web page! Should have known it wouldl be you, Jack!
Grrr! I hate it when people use me!

I think it is an issue with the HTML programming or programmers. When you click a link and it takes you to a page but does not give you the new URL in the location window. So then if you bookmark it you have to find and go through all the same links every time to get to where you thought the bookmark would take you.

I did some HTML programming once and finally figured out that you can get the whole URL it from the link that takes you there if you right click on the link and choose "Copy link location...".

All that is more than many people want to know but, surely, you wouldn't want to deprive an anal retentive old machinist from the joys of being pervasive, would you?

Jack
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Old Oct 07, 2011, 03:23 PM
treefinder
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Perverse pleasure, muhaha! I actually was just too lazy to go down to the actual page (s) that had the plans and copy the url. But it all worked out well: I got someone to dig down & you got to explain!
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Old Oct 07, 2011, 10:13 PM
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Well, shoot, here I was all getting primed to start on the winter wind tunnel project, and I stumbled across this post (#285 by John McGinnis) http://www.oshkosh365.org/ok365_Disc...d=3339&page=15 that I found a link to in the "constructive biplane interference" thread in Modeling science forum. Maybe we don't need them anyway? or maybe I'm just getting lazy, or maybe I just want to cut more foam! It was an interesting and surprising commentary, tho...
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Old Oct 07, 2011, 11:56 PM
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Interesting reading.
Let's not be put off by it however. We are not 'doing' wing-tips with all the problems that would entail. We are looking at comparing wing sections, and we can use wing-cords similar in size to our final wing. No messing with scale factors for us.
McGinnis mentions micro turbulence. This would be a nightmare if maximizing laminar flow was the aim, but of little concern in strictly comparative testing.
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Old Oct 08, 2011, 07:01 AM
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Yeah, i'm sure you're right, i'll try to stay on track. But it was an interesting read if a bit jargon filled.
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Old Oct 08, 2011, 01:53 PM
just Some Useless Geek
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Yes, yes, we need more undetectable sarcasm in a medium in which we can't see each others' expressions. [ahem]

Wind tunnels don't seem to be helping us out here a whole lot. The efforts of those who have conducted real world experiments under fairly well controlled conditions has led to a pretty good grasp of what's happening, though.

You know, if some folks want to construct wind tunnels of sufficient proportions and of sufficient airspeed that they can test actual size models in them then I'd guess we can get some good science. Otherwise we are always going to be suffering the insecurity of scale, are we not?
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Old Oct 08, 2011, 05:46 PM
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No so Mr Geek.
Comparative testing of model wing sections should be quite doable.
Scale effects are not a factor, because the test sections will be close in size to real world foamy model practice.
The units of measurement will not need to be accurate in absolute terms, just repeatable. If it can be demonstrated that *this* section makes more lift with less drag than *that* section... then good science will have been done.
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Old Oct 10, 2011, 10:57 AM
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Okay, I'll buy that in the short term. Since we are concerned about the effects of scale, though, I'd want any science "proven" in a wind tunnel to be applied to actual flying models in an A-B comparison the way Bruce does it. (The template for science research in this arena, by the way.) It is far too easy to point to data accumulated in a sterile laboratory environment and say that it is definitive when it may, in fact, not include some factors that are uncontrolled in the Real World.

Flying is the true test. Although I appreciate all the efforts of those who spend a lot of time, effort, materials, and money to gather such data, I remain skeptical that the purity of the science applies to the kind of stuff we're doing down at the 200 gram AUW foamy level. Unless and until we can definitively correlate wind tunnel test data with actual flight results we're gonna hafta do all of our testing twice.

What a pain. Such is R/C.
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Old Oct 10, 2011, 12:25 PM
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Quote:
Originally Posted by A Useless Geek View Post
Okay, I'll buy that in the short term. Since we are concerned about the effects of scale, though, I'd want any science "proven" in a wind tunnel to be applied to actual flying models in an A-B comparison the way Bruce does it. (The template for science research in this arena, by the way.)
As Feynman would say, the easiest person to fool is yourself.

Without on-board instrumentation, very little data can be gathered from an RC model. Correlating wind tunnel to real-world will be a bit of a challenge, I think.
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