Working on an airfoil, what do you think?

[Chuppster]

I'm working on an airfoil for an aerobatic airplane. It's symmetrical, with a 170mm chord and an 840mm span. I plan to use a "C" spar, and peel the paper off the inner leading edge to have a formed LE. Ideally I want good low/mid speed performance. Does this profile look reasonable?

 

[FastCrash45]

It looks like a good, aerobatic wing. I only know the basics of the theory so i couldnt explain it.

 

[Grifflyer]

Looks good, you might want to increase your leading edge radius for aerobatics close to stall speeds. A sharp (small radius) leading edge typically has a shallow stall angle. That means it will stall sooner than a blunt (large radius) leading edge.

 

[Chuppster]

Looks good, you might want to increase your leading edge radius for aerobatics close to stall speeds. A sharp (small radius) leading edge typically has a shallow stall angle. That means it will stall sooner than a blunt (large radius) leading edge.

With this being a fold-over wing, can this be accomplished by doing a single bevel over a double bevel? Or do I need to increase the wing thickness?

 

[Grifflyer]

No need to increase the wing thickness, were trying to make the leading edge a bit more blunt, so you could still do a double bevel but cut it at 20-30 degrees instead of 45.

 

[Chuppster]

No need to increase the wing thickness, were trying to make the leading edge a bit more blunt, so you could still do a double bevel but cut it at 20-30 degrees instead of 45.

Alright, I'll give it a shot. Thanks! One thing I didn't mention, I plan to bevel the TE on the bottom to clean it up a bit.

 

[Grifflyer]

Nice, I beveled the TE on the P-39 I had at FF and I found it helped to add a paper foldover to clean it up a bit more.

 

[Hai-Lee]

What internal support structure are you going to be using to support and stabilize the profile during the build and when in flight?

Hav fun!

 

[Chuppster]

What internal support structure are you going to be using to support and stabilize the profile during the build and when in flight?

Hav fun!

I was planning on using a "box" spar, kind of like the FT Edge. I may use a thin piece of foam on one side to serve as a "stop" so that building the wing symmetrical would be easier.

 

[TEAJR66]

Looks great. You can make that leading edge more blunt by not cutting a bevel. Just open the score cut with the back of a skewer, and reinforce the leading edge with a piece of tape before you fold over.

 

[Merv]

Your airfoil will be great. I agree with @Grifflyer & @TEAJR66, a blunter, more rounded leading edge will work better, less pitch sensitive. Ed has a nice rounded LE on the Armin wing.

I have struggled to get a symmetrical wing. If I install the spar before I fold the wing, they never come out symmetrical. For me the secrete is to fold the wing, glue the TE, and then insert the spar. You will need to spread the top and bottom a bit to get the spar in.

 

[TEAJR66]

You can double bevel the leading edge and make each break section flat. Like the FT 3D. I have a couple designs with flat panel, symmetrical wings. They fly just fine. But if rounded is your goal, less score cutting and folding, with more bending and molding.

 

[hotwax]

Hallo Chuppster,

i tried a profile of similar thickness and chord on my FB Joke and was not happy about the result. It was very draggy. Center of lift was very far forward. At these low Reynolds numbers 15 % thickness seems to be too much.

I suggest thinning your profile down to 20 mm to reduce drag. A more pointed nose gives better stall at a low wing loading.

Just try