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Airfoil recco...

Old 08-02-2008, 04:58 PM
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CoosBayLumber
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Default Airfoil recco...

I found a common airfoil, the N.A.C.A. 0419 which fits most of the lines to an airfoil I am trying to replicate.



But...


It is ok only over a portion of the lines I need.

What I really need is a reccomendation as to something a bit "pointier" over the first 20% there of. Thinner top and bottom equally, to get a bit more speed, but still remain very aerobatic.




Wm.
Old 08-02-2008, 06:27 PM
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Tall Paul
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Default RE: Airfoil recco...

At model Reynolds Numbers, all that really matters is a smooth curve.
Fat for aerobatics, skinny for speed.
Use what you know has worked.
Old 08-03-2008, 05:04 PM
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Default RE: Airfoil recco...

Wait a minute...... 0419?

The "0" is the amount of camber and the "4" is the location x10 where that camber peaks and the "19" is the thickness. So you've got a 0% camber at 40% and it's 19% thick? The first "0" cancels out any need for the second number so you've really got yourself a NACA 0019.

I'm guessing that this is a typo then?
Old 08-03-2008, 06:38 PM
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Default RE: Airfoil recco...

Nope.

According to Compufoil that is what fits the majority of the lines of the foil.


Wm.
Old 08-04-2008, 03:00 AM
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Default RE: Airfoil recco...

Did it alter the shape if you change the input to a 0019? If not then Compufoil is whacky on this issue. Your 0419 really is the same as a 0019.

I just did a "0419" with my Profili and it came out just as I suspected. It's a totally symetrical 0019 shape.
Old 08-04-2008, 07:26 PM
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Default RE: Airfoil recco...

When I insert your numbers to my version of Compufoil or Anderson. I get a terribly bulged nose instead. When using my number. the Max goes more to the rear.

I don't know their methods fo calcing it, but do get a disturbance at the lower nose area.


Wm.
Old 08-05-2008, 09:55 PM
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Default RE: Airfoil recco...

I hate to say it William but your programs are not operating according to Hoyle.

The first zero nuetralizes any meaning from the 4. It has to since the camber amount is zero and it doesn't make any difference where a zero camber appears. Perhaps there's a default non zero value in the program that isn't recognizing the contradiction in the parameters? <shrugs>

Anyhow be it a 0019 or a 0419 this is what it should look like. How does this mesh with what you're seeing from Compufoil?
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Old 08-05-2008, 10:07 PM
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Default RE: Airfoil recco...

Tried it this afternoon again. Still comes up in that the Max. thickness is substantially more forward then what you have shown. Comes in at about the 10 to 20 percent area when I use the 0019. Comes in as you have shown when a 0419 is called up.

Wm.
Old 08-06-2008, 06:40 AM
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da Rock
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Default RE: Airfoil recco...

If you look at the coordinates of the 4-digit NACA airfoils, you'll see that the "00zz" ones have their max thickness at 30% chord.

It appears that when they wanted the max thickness of their 4-digit symmetrical profiles to be other than .3C, they named the "4-digit" something like 0012-B or 0012-64.

I'd suggest that the software that, "Comes in at about the 10 to 20 percent area when I use the 0019." isn't working by the old NACA conventions even for the plainer 4-digit ones. My vote is that software isn't to be trusted to recreate by NACA's 4-digit conventions, and especially when the naming isn't logical by NACA's conventions.

If that software had been attempting to draw a true NACA 0019, the max would have been at 30%. I would guess that software assumes some value for the LE radius and then attempts to smoothly draw a profile that has it's max thickness at 0%. And the smoothing logic ultimately decides where the max thickness results. Whereas, when it's working the "0419", the software has no trouble smoothing from the LE radius back to a 19% thickness at 40%.

The software really doesn't sound like it's working 4-digit NACA profile conventions at all.
Old 08-06-2008, 08:24 AM
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Default RE: Airfoil recco...

Rock......

One thing that has annoyed me for an awful long time is that the bottom half of certain airfoils in Compufoil tend to be about 1/2% longer than the upper half. Sometimes even up by the nose there are a few Zig-zags indicated.

I mentioned this to Eric at C.F. and mainly his responce was that it did not do it there, so did not exist, so don't mention it ever again.

Now finding other things not calculating exactly.

Wm.

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