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Old Mar 25, 2010, 07:56 AM
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airfoils in full size aircraft are optimized for radically different Reynolds numbers. The airfoils won't work the same when we scale them down and change the Reynolds numbers.
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Old Mar 25, 2010, 09:03 AM
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I don't really remember my fluid dynamics classes but from what little I do recall, you can scale down the air foil, airframe etc, but you can't scale down the properties of the fluid. The only way to properly do this is to make substitutes that scale down the relationships between the surfaces and the fluid. So in this case, Dag has used a different air foil that allows him to scale down the relationship since air is air is air.

Hope that makes some sense. I really wasn't very good in fluid dynamics.
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Old Mar 25, 2010, 09:17 AM
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Recorded an old movie a couple of nights ago. Jet Pilot with John Wayne. There was about 5 minutes of a B-36 in flight. It did not have jet engines. Most of the aircraft in the movie were F-86's

Mike
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Old Mar 25, 2010, 09:40 AM
Put a bigger motor on it!
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Costa Mesa, CA
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Originally Posted by dag214 View Post
With the size wing I have I figured I only needed 2 degrees of up wing incidence so at cruise I am just a bit nose high as the full-scale 36 was in cruise.

Thanks, Dag
Do you have washout in the wing?
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Old Mar 25, 2010, 09:40 AM
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Kinda reminds me of a certain Devo video........

Whip it good, Dag!
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Old Mar 25, 2010, 02:51 PM
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Speaking of fluid dynamics and building theories, there is a very interesting article about Howard Hughe's flying boat and the wingspar construction, in the latest edition of
Vintage Aircraft Magazine published by the Vintage Aircraft Association of the EAA.
Not available at magazine stands, to VAA members only.
His long time engineering associate felt that Hughes may have decided not to fly it again because the wingspar may have been underdesigned and a strong wind gust in flight, he felt it might have failed.
A most interesting story and theory
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Old Mar 25, 2010, 03:00 PM
I fly, therefore, I crash!!!
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Joined Jan 2008
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Originally Posted by ErcoupeEd View Post
Speaking of fluid dynamics and building theories, there is a very interesting article about Howard Hughe's flying boat and the wingspar construction, in the latest edition of
Vintage Aircraft Magazine published by the Vintage Aircraft Association of the EAA.
Not available at magazine stands, to VAA members only.
His long time engineering associate felt that Hughes may have decided not to fly it again because the wingspar may have been underdesigned and a strong wind gust in flight, he felt it might have failed.
A most interesting story and theory
It certainly is....however....he flew it once... that was all it needed, and history was made...

SteveT
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Old Mar 25, 2010, 07:05 PM
It only takes one good idea
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Originally Posted by gtfreeflyer View Post
Do you have washout in the wing?
Yes,
1.5 degrees.

One thing I hate about logging on while I am traveling is no pics to up-load. I think these threads are useless with out pics. I see all the time threads started with no pics, and goes for weeks with no pics, drives me nuts.

And boy do I hate traffic getting out of Laguardia .

Thanks, Dag
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Old Mar 25, 2010, 07:13 PM
It only takes one good idea
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One other thing about airfoil design, think of it like this. Most airliners have a really funky airfoil that looks almost like a inverted modified Clark-Y, the reason is the best cruise performance for a specific altitude range, and the only way to get that airfoil to slow down enough to land is a complex flap, slat, spoiler, LE device system. Now on RC most of use can't design all that in just for getting slow, and most of use are not flying at 30k feet where the air is thinner. So we modify our RC aircraft airfoils to work for the performance range we want. If I built a 100% scale XB-70 wing, or a F-104 wing, I would have a VERY hot flying plane, but I cheat in a NACA airfoil that has a thicker wing, with less pointy lead edge, and now I have a RC plane that would be more forgiving, and still look close to scale if done right.

Thanks, Dag
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Old Mar 25, 2010, 07:53 PM
I fly, therefore, I crash!!!
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Originally Posted by dag214 View Post
One other thing about airfoil design, think of it like this. Most airliners have a really funky airfoil that looks almost like a inverted modified Clark-Y, the reason is the best cruise performance for a specific altitude range, and the only way to get that airfoil to slow down enough to land is a complex flap, slat, spoiler, LE device system. Now on RC most of use can't design all that in just for getting slow, and most of use are not flying at 30k feet where the air is thinner. So we modify our RC aircraft airfoils to work for the performance range we want. If I built a 100% scale XB-70 wing, or a F-104 wing, I would have a VERY hot flying plane, but I cheat in a NACA airfoil that has a thicker wing, with less pointy lead edge, and now I have a RC plane that would be more forgiving, and still look close to scale if done right.

Thanks, Dag
Hi Dag...

Didn't the F-104 have an almost completely flat airfoil?? Seems I remember reading that. If I remember correctly the interior of the wing was a machined solid piece, with a thin skin over it....and an extremely sharp leading edge..
I know the wing was so thin that they had to use multiple hydraulic cylinders on the control surfaces, as the wing was too thin to put "normal" ones in it.

SteveT
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Old Mar 25, 2010, 08:00 PM
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Originally Posted by Draknkep View Post
Hi Dag...

Didn't the F-104 have an almost completely flat airfoil?? Seems I remember reading that. If I remember correctly the interior of the wing was a machined solid piece, with a thin skin over it....and an extremely sharp leading edge..
I know the wing was so thin that they had to use multiple hydraulic cylinders on the control surfaces, as the wing was too thin to put "normal" ones in it.

SteveT
I'm no expert but in this cutaway diagram the wing does not look solid (though it's not very hollow):



- Birger
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Old Mar 25, 2010, 08:03 PM
It only takes one good idea
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Fishers, Indiana
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Quote:
Originally Posted by Draknkep View Post
Hi Dag...

Didn't the F-104 have an almost completely flat airfoil?? Seems I remember reading that. If I remember correctly the interior of the wing was a machined solid piece, with a thin skin over it....and an extremely sharp leading edge..
I know the wing was so thin that they had to use multiple hydraulic cylinders on the control surfaces, as the wing was too thin to put "normal" ones in it.

SteveT
Kelly Johnson designed it with a Bioconvex 3.36%

Attched is a cutaway of the wing.

Thanks, Dag
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Old Mar 25, 2010, 08:28 PM
Sideslip!
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West Chester, OH
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my arm has more wing area than that thing. How does it fly?
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Old Mar 25, 2010, 09:04 PM
War Eagle!
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United States, AL, Huntsville
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fast?
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Old Mar 25, 2010, 10:26 PM
I fly, therefore, I crash!!!
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San Jose, CA
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Hi Guys...

I meant to say that it was machined out of a solid piece, but from the drawings, it doesn't look that way.

SteveT
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