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Old Oct 13, 2003, 10:39 AM
Registered User
Burlington VT
Joined Aug 2003
379 Posts
ideas for a good airfoil for 24" Pitts?

Previously posted under Modeling Science, but there isn't much traffic over there- I was hoping you-all could help me out

I've been looking for an airfoil for my latest project, but I'm new to aerodynamic design and I'm not too confident in my airfoil selecting skills yet. Based on other 3D ships I've seen, I'm expecting a high percent thickness symmetrical airfoil with very little camber, but I don't know the names of any to compare in Profili.


I'm looking for a symmetrical airfoil with a good speed range for my 24" Pitts. The plane is based on Chris3d's micropitts plans scaled up 2.1X. The first rev. I made had the stock undercambered wings and flew great. It was a bit slow, and was nearly impossible to fly inverted though. My first attempt at a symmetrical airfoil didn't seem to produce much lift and was nearly an ounce heavier than the stock set. Not a particularly exciting combination even with LiPos. For Rev.2 I'm working with thinner foam and that should allow me to make a symmetrical wing without too much additional weight. Wings are removable as well, so I may end up trying different airfoils.

Here are the specs I can think of:

24" span for both wings with rounded tips
4 3/8" chord
approx. 200 sq. in. but it's a bipe, so effectively smaller
target AUW 9-11 Oz
2S1P Kokam 1200 LiPos
Four channel control T/A/E/R

I've stuffed a MiniAC 1215/20 in a GWS gear box for Rev.2
which is supposed to produce about 13Oz with a 9/7 prop at a 4.33/1 gearing. Previously (Rev.1) I was using a GWS300C with an A (3.67/1) gearbox with an 8/6 prop. I've bought a few pinions and spurs to mess around with the gear ratio too. I'm aiming for max thrust with an 8/6 or a 9/7 without overdriving the lipos. Bigger props will be tough to land with.

Information on other aerobatic planes and their airfoils would also be appreciated. The next project on deck is a 30" Sukhoi

If anyone has any ideas I'd appreciate the help.
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Old Oct 13, 2003, 02:24 PM
It's a Great Day to Fly
LenBFP's Avatar
Melbourne Beach, Florida
Joined Jan 2002
3,863 Posts
Here is a link to a couple of wings that were nicely aerobatic. The plans for the small one is on the same page near the bottom. It would probably work for your Pitts. It is symmetrical and flew real nice with a M100 motor. The big one was a blast with a SP300 geared. With a brushless like a Razor - whooho!

http://www.rcgroups.com/forums/showt...threadid=35077

Len
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Old Oct 14, 2003, 01:59 PM
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Burlington VT
Joined Aug 2003
379 Posts
Thanks for the link, I'll give that a try. I plan on making a few sets of wings one I get the motor gear ratio and prop figured out. Another airfoil I found in Profili is the "S8035 for RC aerobatic 14% thick" That one looks promising. Runners up are (all names from profili):

cap 21
ULTIMATE /JCE
12% Joukowski

semi-symetrical--
MH 42 (looks fun, but I think my reynolds numbers are too low)
CLARK Y (useful for a control pehaps)
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Old Oct 14, 2003, 02:11 PM
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Doug Cronkhite's Avatar
San Diego
Joined Feb 2002
1,614 Posts
If you want a full symmetrical section, just use a NACA 0010 or 0012. You'll be fine.
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Old Oct 14, 2003, 02:28 PM
Registered User
Burlington VT
Joined Aug 2003
379 Posts
I found some threads on the RCUniverse forum recommending the following:

S8035
RAF 30
NACA 00XX

There are close enough to each other that they'll be indistinguishable using my building technique. The only major difference that I can reproduce properly is the % chord of the max thickness. I can do this by moving the spar fore or aft. This affects the stall speed and ability to snap roll. Farther aft and it'll stall/snap easier.

Also a 12% root and 15% thick tip was recommended for sport planes, but my Pitts wing is constant chord, so I don't think that'll look right-

I'll play around with one of these to see if I can sort out the proper thickness and % chord in Profili for my application. Motocalc predicts a max speed of about 35 mph and a stall speed of ~15 mph, but I'm not sure how much of this is based upon the airfoil estimate MotoCalc uses.
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Old Oct 17, 2003, 01:13 PM
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St. Louis, MO
Joined Jan 2003
355 Posts
I couldn't tell you what type of airfoil to use, but I built the Herr Free flight 24" Pitts and she flew very well with the standard airfoil. I used a gws350 and made her full house.

There are several threads about my build of this plane. I sure do miss her...

Will
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Old Oct 17, 2003, 02:05 PM
Registered User
Burlington VT
Joined Aug 2003
379 Posts
I went with an S8035 14 percent thick with a 4 3/8" chord, 24" span. I have the wings painted, taped, folded up and glued.

I cut out outline patterns based on Chris3D's plans. The patterns are for top and bottom surfaces, joined at the LE. It's pretty easy really, just glue in a spar at the max thickness, I used a piece of foam with Carbon sheet laminated to the front edge. Cut yourself a rib pattern out of plywood, cut a buncha ribs from foam, hack out the section where the spar goes, and glue the LE half in front of the spar and TE half in back of the spar. Roll the pattern until the surfaces follow the ribs and glue them down. Start from the LE and glue down towards the TE. Then glue the tips together and tape to hold while they dry.

Now I have to shape and install the ailerons, add the torque rods (tubes are glued in) and connecting rods between top and bottom ailerons. Then mount it to the fuse. Should be done in another week, unfortunately I won't get the chance to work on it this weekend tho.

I'll post pictures of the finished plane. Looks like AUW will be about 11 Oz. Power to weight will be just shy of 1 to 1 according to MotoCalc with a 10x8 prop (which barely fits, three point takeoffs are a must). MotoCalc predicts a 3S1P 1200 pack will give near 2 to 1 performance! 3S looks like the way to go with brushless....
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