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Old Jul 20, 2009, 04:02 PM
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Effect of durface roughness on CG position and stall

I discovered, the hard way, that for good low speed handling and performance a rough finish is better than a smooth, glossy one!
I had been flying a wing that was basically an Electro Bee wing, with a different engine mout and a slightly "drooped" LE extension on the tip section, for a couple of years. <<<<<the surface finish was quite rough, apart from a couple of crossed tapes for structural reasons it was just EPP with paint sprayed on it. As the low speed and srtall characteristics were excellent, I could fly this in quite a restricted area. Also, I could fly it with a CG way behind that quoted by the manufacturer, which improved the climb performance considerably.
Having decided that it looked rather tatty, 3 weeks ago I decided to give it a face-lift with a layer of Oracover. The result was a disaster, the good low-speed handling and stability was gone, the CG had to be advanced ti prevent a tendency to spin-in on the approach, and the climb rate became marginal!
So rather eluctantly, I ripped off the nice glossy cover, and lo-and -behold, I had my old wing again!
Searching literature on wind tunnel tests at low Re Numbers, I discovered that this was in fact a well established fact for some airfoils tested with different surface roughnesses.
But CG-calculator is a good starting point anyway.
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Old Jul 21, 2009, 08:51 AM
internet gadfly
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Colorado
Joined Aug 2006
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Yep, it's common knowledge that boundary layer trips can change the lift and drag but it's not so well known that tripping the BL can also make the pitching moment more linear. One piece of thick tape on the lower surface about 10% in front of the elevons can really make a difference on a smooth wing
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Old Jul 29, 2009, 11:58 AM
Someone is going to get wet...
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The Mitt
Joined Oct 2007
984 Posts
CG calc....

Thanks for this very helpful calculator, looks like it might work. The wing is balancing at about where I had guessed it might. This at least gets me into the ballpark and to have a better chance of surviving its maiden flight.

Mudman1959 Wings Up... Wheels Down...
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Old Jul 29, 2009, 06:20 PM
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USA, NC, Hendersonville
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I asked the other day if anyone knew the cg for the 25" demon (ck) and never got an answer ..........

thanks for your hard work. Now I know
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Old Aug 02, 2009, 10:02 AM
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mexico city, mexico
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But then seems that the c.g. location is calculated the same way for stab airplanes.

Then if I want to test a flying wing making a small scale depron wing, it would give
the same result for both configurations flying wing or stab airplane
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Old Sep 11, 2009, 05:53 AM
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anyone; what angle diference between the root airfoil and tip airfoil have you found to work ? an old book by frank zaic recomends 6 degrees this doesn,t seem like enough the book was published in 1944 so things have probably changed.

regards clark
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Old Oct 01, 2009, 03:57 PM
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hey guys i have a question about cg location . i built a wing that has a center section more like a delta with outer wing panels swept back and tapered . i guess you would call a blended wing. what i did was find the cg of the center section and then the outer wing panels and put the cg between the two cg locations.does that sound logical or am missing something?
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Old Oct 02, 2009, 02:40 AM
Per Ardua Ad Astra
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Australia, VIC, Rosebud
Joined Feb 2007
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Quote:
Originally Posted by z80
I wrote a little CG calculator for flying wings. If you have a HTML 5 browser supporting the canvas object you will get a little image of the wing too.

http://fwcg.3dzone.dk

Bug reports and suggestions are very welcome.
Great calculator mate!

Made the job really easy.

The maker of the Windrider Ebe Beevolution said to balance it just 14" out from the nose on the leading edge, but no way would it balance from there.

I didn't know what to do. Glad I found your post - brilliant!

Hope your winter is not too cold. We are enjoying a nice (but windy) Spring down here.

Kev
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Old Oct 23, 2009, 03:52 AM
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Wonderful! Helped me out so much, thanks alot.
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Old Nov 16, 2009, 02:43 PM
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Thanks z80!

bought the 2 foam wing halves for an assassin wing from a friend. no instructions, no anything else ... so i'm starting the build yesterday and am thinking, how the devil am i going to find the cg? decided to join rc groups today to see if i could find the answer and here it is. fantastic. your cg calculator is going to really come in handy. thanks so much for your contribution !
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Old Jan 01, 2010, 04:35 PM
24 yrs. of Aircraft flying
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United States, GA, Rockmart
Joined Oct 2004
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I never even paid attention to this thread, Thanks for your work I just love this prog I use it allot latley. I had asked how to find the wing area of a plane and someone gave me the link. thanks
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Old Jan 01, 2010, 10:13 PM
Per Ardua Ad Astra
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Australia, VIC, Rosebud
Joined Feb 2007
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Quote:
Originally Posted by windmill200 View Post
bought the 2 foam wing halves for an assassin wing from a friend. no instructions, no anything else ... so i'm starting the build yesterday and am thinking, how the devil am i going to find the cg? decided to join rc groups today to see if i could find the answer and here it is. fantastic. your cg calculator is going to really come in handy. thanks so much for your contribution !
Welcome to RC Groups!
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Old Jan 05, 2010, 06:21 PM
bill bailey
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I am a Queanslander now living in Marybourough
Joined Aug 2007
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Lifting Body Aircraft

Hi Guise

I have just finished drawing a set of plans for the " FACET " but I have no clue
as to the correct C/G position .

This is a lifting body aircraft - or is it just a flying wing by another name ?

Either way if you could give me some suggestions I would be most grateful .
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Old Jan 06, 2010, 11:33 AM
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cg

Thanks for the info ,now I thick I can confidently build my own foamies aicraft
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Old Feb 03, 2010, 07:27 AM
Aka: Tom Jenkins
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Palm Beach County, Fl.
Joined Aug 2008
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Quote:
Bug reports and suggestions are very welcome
Something happened to the image the calculator creates, either my java or something went out or the page is goofed. please advise
Also how would you calculate and incorporate a cranked leading edge on a delta cg?
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