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Old Apr 26, 2012, 12:22 AM
deltas are cool
AIR SALLY's Avatar
Tehachapi ,CA.
Joined Apr 2006
21,280 Posts
we used french curves to draw them ,it is a semi symetrical foil and fairly thin for the size of wing .....thick enough to get the gear in . have been drawing our own foils for years ...so far we have'nt missed yet ,C/N has done 2 other F-5's so he know about what is needed .....but we might not be able to tell you why we did it that way ...neither of us have a eng. degree....thats why we just work on full scale planes...but i did sleep in my own bed last night if anything it looks like a eppler foil.....guessing some where between 7%-9% thickness.@ 3 degrees of washout .
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Old Apr 26, 2012, 05:40 AM
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Dionysus's Avatar
McQueeney TX
Joined Oct 2005
581 Posts
OK, I noticed some secrecy here, I couldn't get Nut to cut me a set or share the templates so I could build a plane with this wing. That's cool, it's probably not that critical, like you say, just enough to get the gear in. I don't think you could "miss" with a jet, I bet this thing would fly with a flap piece of foam.
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Old Apr 26, 2012, 09:28 AM
Retired and Lovin' it!
United States, KY, Sturgis
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Dionysus, I can't speak for CN or Air Sally here but I have been doing my own airfoils for years using the same methods that AS just described. I draw a straight line to the length of the chord, then draw another straight line vertical at about 30% of the chord line. The length of the vertical line is determined by the percentage of thickness of the wing, i.e., if the chord is 12 inches, with 10% thickness, then the vertical line is 1.2 inches in length. If the foil is symmetrical, then .6 above the chord line and .6 below. If semi-symmetrical, then you choose what looks about right for you. I set the leading edge radius with a TLAR calibrated eyeball keeping in mind that a sharper leading edge will tend have a sharper stall break. Then connect all points with French curves and straight edges. You'ld be amazed how well this works. No secrets!

Tony
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Old Apr 26, 2012, 09:46 AM
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Dionysus's Avatar
McQueeney TX
Joined Oct 2005
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Thanks Tony.

I'm going to use Profili 2, it makes it easy. I'm going to use the NACA 64-008A.

Just for reference the T-38, F-20 and F-5 use the root = NACA 65A004.8 and tip = NACA 65A004.8

Found some stuff in my T-38 searches.
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Old Apr 26, 2012, 12:11 PM
Retired and Lovin' it!
United States, KY, Sturgis
Joined Jul 2007
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Profili works great too. I am not proficient in CAD so I hand draw my plans. Its more of a pain to copy and print Profile outlines and then transfer to my hand drawn plans.

Tony
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Old Apr 26, 2012, 01:38 PM
deltas are cool
AIR SALLY's Avatar
Tehachapi ,CA.
Joined Apr 2006
21,280 Posts
what?! C/N wont give you a wing template ???? he must have lost it ,there was nothing secret about it i bet he'd make a set of cores for a F-86 cockpit personally i think we should make a semi kit for this plane
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Old Apr 26, 2012, 03:09 PM
DELTAS RULE
corsair nut's Avatar
tehachapi, CA
Joined Jan 2006
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i never said i wouldnt give him the airfoils, not sure where he got that. i sent him a pm.
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Old Apr 26, 2012, 07:28 PM
EDF Jet Jam 2015 , May 28-31
Kevin Cox's Avatar
St. Louis Intl, Missouri, United States
Joined Jan 1997
6,905 Posts
I'm sure that CN is among many others that just manipulate existing airfoils to serve their needs. I am guilty of this myself...when someone ask, it is a modified Clark Y.
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Old Apr 27, 2012, 05:26 AM
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Eddie P's Avatar
United States, NV, Reno
Joined Mar 2000
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The flat plate guys have shown a lot of good use with just... flat plates as wings! I think however once the wing begins to earn it's keep, aka the wing loading going up and or G loading increases, and or speed is reduced to 20 percent above stall speed and lower, etc... a real airfoil begins to show it's advantages. Subtle changes can make a difference but how much and how can you tell when flying from a remote position with a model? And what is a "real airfoil"? That's debatable for sure!

Some anecdotal tales of small airfoil changes making big differences are like with the Grumman AA-1 Yankee; they changed the leading edge radius just a little to tame the stall from early models and lost about 10 knots in cruse speed. The DC-8 initially had a different leading edge and to make promised fuel burn and cruise numbers the leading edge was reduced in radius a little and then modified on older birds and brought forward into new models as standard. For models, in an old thread I recall where a guy made a B-58 in 2002 he initially just made a flat bottom wing and he noted the model was "a dog". He then modified the wing to include the scale-like conical leading edge droop and was delighted to see cruise speed increase and partial throttle performance improve noticeably. Yeah, so I guess I fall in the "airfoil geek" camp where I believe some differences can be expected from notable changes in an airfoil, the larger/heavier the model the more notable. But for sure I think a french curve and a "that looks about right" (TLAR) method will be far and away "good enough" for decent performance in a model airplane with a moderate wing loading.
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Old Apr 27, 2012, 10:31 AM
Faith in Lift.
Pilatuspc12's Avatar
United States, CO, Hotchkiss
Joined Oct 2006
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Eddie, with these relatively large jet models, wouldn't reynolds numbers come into play? Thanks,
Randy
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Old Apr 27, 2012, 10:52 AM
Build'em and Crash'em
Ken Lapointe's Avatar
Narragansett, RI
Joined Oct 2000
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Understand of course that the airfoil you started with on the template may not be the airfoil you end up with after glassing, sanding and painting
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Old Apr 27, 2012, 11:48 AM
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Eddie P's Avatar
United States, NV, Reno
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Quote:
Originally Posted by Pilatuspc12 View Post
Eddie, with these relatively large jet models, wouldn't reynolds numbers come into play? Thanks,
Randy
Yes but I also included an example of an RC airplane to balance it out It's still fluid dynamics even at the low RN of model airplanes. Not as critical but still the physics apply IMHO enough that guys like CN are not wasting their time when they try to add a natural flowing shape to the wing with a french curve even on their own designs. When I was going to college we had a subsonic wind tunnel and a supersonic wind tunnel. We were using model airplane size sections and they certainly made a difference in the wind tunnel among different sections, and that was the point of the whole testing apparatus, to test different airfoils. The small sizes were still bound to natural laws. Anyhow, I do concede that at our lighter wing loadings we can certainly get away with a lot but if someone were to say airfoils don't make a difference in models I'd say they were painting with a pretty broad, generalized and messy brush IMHO.
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Old Apr 27, 2012, 10:02 PM
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bd5wingnut's Avatar
Austin, Texas
Joined Dec 2005
254 Posts
I agree with Eddie P.

For the most part... When you are talking about powered models in the lower Reynolds numbers range. If you mount a telemetry device and flew untold hours, allowing for all the atmospheric variables, you would see a difference. But when using the calibrated eyeball ground observation method...

Go to the "serious sailplane forums", not the clueless foamy crowd, and read the discussions on airfoil selection. There is a huge difference when you do not have a fan pushing you around.

Peace, Wolf
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Old Apr 30, 2012, 12:58 PM
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New Bern, North Carolina, United States
Joined Oct 2004
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I just want to thank Falcon 5 for taking care of my F9 at SEFF. He flew the crap out of her and made her look good.
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Old Apr 30, 2012, 01:01 PM
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Austin, Texas
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Quote:
Originally Posted by ATIS View Post
I just want to thank Falcon 5 for taking care of my F9 at SEFF. He flew the crap out of her and made her look good.
Videos or didn't happen... LOL

Wolf
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