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Old Mar 30, 2011, 09:57 AM
Designer
Joined Mar 2011
8 Posts
Question
Best aerofoil for 48" acrobat plane

Hello to everyone

I'm building a model of Extra 300 which has wingspan 121 cm (48").
However, it's stopped me at the wing. In fact I have a dilemma which profile should I use on this plane. As far as I was reading the forums I am inclined to use NACA 0012 but I'm not sure. I'm building a similar plane as EF Extra 300 48" with changes. but I would like that the aerofoil would have similar characteristic like EF Extra.I would ask for your suggestions because I don't know any more who to ask.

For rudder and elevator the aerofoil which I have chosen is NACA 0009. (if isn't good please tell me which is better)

I apologize for grammatical mistakes because I did't use English for 4 years.

Thank you very much,
GS

P.S. If anyone wonder, why I am not buying a model. I build because it is a challenge. And meanwhile the building I pick up a lot of knowledge. Buying the model is the Easiest thing.
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Old Mar 30, 2011, 03:55 PM
B for Bruce
BMatthews's Avatar
The 'Wack, BC, Canada
Joined Oct 2002
11,350 Posts
Another good option would be the Eppler 474. The Eppler being more stall resistant than the NACA0012. Or an inbetween solution that is slightly more stall resistant than the 0012 but not as good as the 474 would be the NACA0015.

Which you want to use will depend on how light you can build the model and how careful you are to avoid tip stalls when you don't want them. If you know you can build the model to a light weight then go with the 0012 as it will be easier to force a good snap roll on command and with any care at all you can avoid tip stalls when flying slow. If you know you're a heavy builder then go with the 474 and the stall resistance to make the model safer to fly.

If you're a REALLY light builder you may find that you need to modify the 0012 by slighty sharpening the leading edge later on to aid in producing a nice sharp stall. Or you may want to look at going from the 0012 at the wing root to the NACA0010 at the tip to again produce a wing that stalls sharply and snaps well on command while still flying reasonably gently the rest of the time.

From this description you may have guessed that all else being equal that a thinner version of the basic NACA symetrical 00xx series stalls easier than the thicker ones. And that is correct. And all else being equal a smaller radius leading edge tends to stall sooner and more deeply than a more rounded one.

Best of luck with the build and flights.
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Old Mar 31, 2011, 01:42 AM
Designer
Joined Mar 2011
8 Posts
Thanks for quick reply.

This was a great help.

I have one aerofoil but i don't know which is it. This aerofoil is from another plane of mine which I bought in shop. Can you tell me if it's good?


Thank you
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Old Mar 31, 2011, 02:28 PM
B for Bruce
BMatthews's Avatar
The 'Wack, BC, Canada
Joined Oct 2002
11,350 Posts
Well, the leading edge radius is a bit sharp so it would tend to stall a bit earlier and more abruptly than a NACA airfoil of the same thickness.

It may be that I didn't stress the importance of picking the airfoil to achieve the stall charactaristics you want. On aerobatic models you often want to force a stall in order to perform a lot of the maneuvers. Snap rolls is the obvious one and a lot of the 3D stuff folks like now is another. The Lomcevak (sp?) also comes to mind. But on the other hand you don't want the model to stall so easily that it becomes a danger to itself during normal flying. How the model stalls is related to the wing loading. That's why I rambled on about this airfoil and that airfoil and the weight of the model you are hoping to build. It's all a matter of getting the airfoil to work well with the model's final flying weight and wing loading.

If you flew the model with that last airfoil and found that it flew well and in a manner you want for the new one then using that airfoil again and building your new model to match the wing loading will produce similar aerobatic performance as the ARF kit that the airfoil comes from.
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Old Apr 10, 2011, 06:59 AM
Designer
Joined Mar 2011
8 Posts
Thanks. That was great help. I think That I will choose NACA0012 aerofoil for start and after first flight i will see if it's good or there are needed some changes.

Thanks again for all help. But if I need anything I'll ask.


that it's extra which I build
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Old Apr 13, 2011, 09:52 AM
Designer
Joined Mar 2011
8 Posts
I started to draw. Before me is a lot of work but it is the beginning. If anyone is interested I can keep posting but if not I'll show you when the plane is complete.

LP, Gs Aviator
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Last edited by GS_Aviator; Jul 14, 2013 at 12:04 PM.
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