Tuesday, May 25, 2010

Analysis of the Belite airfoil

Hi everyone,

A Belite follower (Theodore Fails) wanted to analyze our airfoil, so I sent him a CAD drawing of a rib cross section. Ted did a very able job of tracking down the likely origin of our airfoil. It's fascinating stuff. I thought of summarizing it, but Ted's letter to me is well written and is a good aeronautical detective story. With Ted's permission, here is his analysis. Enjoy!!

-- James Wiebe


Here is progress report on analysis of the Belite airfoil:

1) It is clearly a Riblett airfoil, but it is outside of the matrix of airfoils covered in the book "GA Airfoils." From personal discussion and correspondence with Mr. Riblett, I was able to extrapolate from his data and closely duplicate the Belite airfoil. (Mr. Riblett, at age 80 was delightfully cogent on the subject, though he could not recall if he had in fact designed an airfoil for Kitfox. He did have some suggestions for Ultralight wings which I will cover below.)

2) The Belite airfoil has a built in 2.37 degree angle of incidence, giving some nominal lift at zero angle of attack.

3) The actual designation of the foil, using Riblett's method of nomenclature is GA30-8M12. "GA" means it is a Riblett foil using his method of direct addition of form ordinates to camber ordinates. "30" means that maximum foil thickness occurs at 30% of chord. "-8M" means that the camber is a slight modification from Riblett's camber level -8. Perhaps "-8.16" would be a better description, since the Belite foil is about 16% more cambered than Riblett's -8 camber. "12" means that the maximum foil thickness is 12% of chord. Maybe GA30-(8.16)12, whatever.

4) In my talks and correspondence with Mr. Riblett he suggested that for Ultralight foils, that a good choice would be a GA25-815 foil. It would be thicker overall and thicker at the leading edge, allowing a larger spar. Whether it would be worth the cost of the change or not is an open question, or even if it would improve performance at all.

5) See attached jpeg showing the Belite foil overlaid on the GA30-812 foil. The GA30-812 is closest foil that falls within the span of Riblett's data. As per 3) above, the Belite foil is more cambered than any of Riblett's standard foils. (His book covers four camber levels, -2, -3, -4, and -6. He sent me some unpublished data adding camber level -8.)

6) The small amount of washout in the Belite wing is also in accordance with Riblett design parameters. This allows a lower stall with good control and pays a lower price in drag a cruise speeds. Good stuff.

Sorry it took so long, but after I got a copy of the Riblett book and your foil did not match any of his, I naturally assumed it was something entirely different, so off I went on a wild goose chase. After learning a LOT about a LOT of other foils, I decided to just give Harry a call. The Belite just Looked like a Riblett foil.

The next step for me is to do some computational fluids testing of some foils that I am interested in. I like your airfoil ... very much. I will include it in my test matrix, and let you know the results if you have any interest.

Lastly, I am curious about the bracket drawings that you sent. Being a manufacturing engineer in my day job, I wonder how you actually make these things. Hog-out? Weldment? Sheet metal fabrication? What sort of quantities do you buy in? FYI, I have a Haas VF-3 and I know how to use it! If I get a moment I may examine these items for structural optimization, you may be able to save some mass or cost or both.

Anyway, sorry for the delay, and again, let me tell you how much I admire what you are doing in the Ultralight market. Keep up the great work.


1 comment:

xaminmo said...

Kitfox used the same airfoil at root and tip.

For the Skystar Kitfox I, II and III = Avid Airfoil
Skystar Kitfox Lite & Speedster = Riblett GA30U-612

Ref: David Lednicer
Analytical Methods, Inc.
2133 152nd Ave NE
Redmond, WA 98052

The Avid [Flyer] Airfoil was custom designed by Dean Wilson:
The STOL section is a custom 13% thickness airfoil designed originally as a high lift section by Dean Wilson to fit around the 2.5” spar diameter particularly at the leading edge.
The Speedwing section is based on the STOL having more or less similar pressure gradient and mean line but the camber is reduced by approximately 30%.
Both airfoils are therefore specific to the Avid aircraft.
The closest match to the Speedwing section is a NACA 2212 though there are differences.
NACA 44xx series would provide too much pitching moment for the airframe's length and its limited tail volume and should be avoided.
Ref: Graham Laucht