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Old 01-03-2009, 10:10 PM
Join Date: Oct 2004
Location: Arroyo Grande, CA
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Default RE: Sterling Spitfire

I now have in my possession what I think of as the "big three" Sterling kits. Breitling P-51, Harris Spitfire, and Hester P-63. The P-51 isn't mine yet. A friend has offered it to me at a very reasonable price with the provision that it has to be my next project. Not sure I want to commit to that.

But comparing the three kits is interesting. First the quality. Both the P-51 and the P-63 have quite good balsa. They're not as light as a really premium kit, but both are plenty acceptable. The Spitfire, as I've mentioned before, is a disaster in wood selection. I'm not sure, but it looks like the P-51 and P-63 are early 1960's production and the Spitfire may be early 1970's.

The wing airfoils look almost the same on all three planes. The thickness percentages vary slightly, but they all look generally like NACA 24xx series, which were very much in vogue at the time on such planes as the Astro Hog and Taurus. Wing and tail incidences vary wildly. Here are the measurements that I got off the plans:

P-51 Wing +1° Stab +4.2° Engine 0°

Spitfire Wing +3.4° Stab +1.3° Engine 0°

P-63 Wing +2.2° Stab +4.5° Engine 0°

To an aero engineer, this is like looking at a mystery novel. Why so different on each plane? I didn't check the fuselage sides to confirm that the wood matches the plans, but assuming the plans are correct then some construction mods are probably in order. The zero lift angle of the NACA 2415 is -2°, so we would like the stab to about 1° positive relative to wing chord line. Here is what I'd suggest:

P-51: Reduce stab incidence from +4.2 to more like +2°

Spitfire: Reduce wing incidence to about + 0.5, or maybe a combination of wing at +2° and stab at +3°

P-63 This one is just about right. Maybe reduce stab to +3.5° But if you're using a fairly heavy modern engine, +4.5 will probably work out.