barit1,
I find it most interesting that the NACA research on early laminar-flow airfoils found its first implementation in an aircraft designed for the export market.
Yeah, it is unusual. Regardless, the P-51 ended up one as the USAAF's best fighters. Fast, nimble, and possessed sufficient range to escort strategic bombers to and from their targets.
The British were visiting US manufacturers, and as the story goes, they asked NAA to become a second source for the Curtiss Kittyhawk. NAA countered with their own design, the NA-73, incorporating US taxpayer-funded research, and won the British contract.
They did if I recall, buy the plans for the Curtiss P-40 though. I don't know if any of the P-51 was derived from the P-40, though I suppose there are some superficial resemblances.
bearfoil,
Interesting point. The P-51 was initially supplied to the British as the APACHE, with an Allison engine.
Yeah, the V-1710
Carbureted and non turbo, it was a failure.
Why was the USAAC/USAAF so averse at first to using turbochargers? They work better than superchargers, and the technology existed since at least 1918.
Brian Abraham,
The cusp on an aerofoil (not all have them) refers to an aerofoil where the trailing edge is reflexed down forming a concave profile on the lower surface at the trailing edge. Typical of super critical aerofoils as here.
Yeah, the instant I saw the cross section I noticed the parallels. A supercritical foil is flatter on the top, a little blunter in the front, with the trailing edge drooped, and the cusp on the bottom side.
I assume with the shape of the foil being what it was, they weren't just trying to produce laminar flow over the wing, but to also weaken shockwave formation at high speeds (That or they just got lucky with the latter...)
PBL,
Thanks for saying what "crest" means. I'd not heard that term before.
I actually thought that was a common aerospace engineering term.
It wasn't so obvious to me what it meant, because I could think of two plausible meanings. One was point of maximum thickness; the other was point of maximum upwards deviation from chord. You will appreciate the two are not necessarily the same, in particular for convex-concave airfoils, although I guess they mostly are for biconvex airfoils - and of course for symmetrical ones!
I suppose when I said it I was thinking of the point of maximum upwards deviation from chord as well as the thickest point on the wing. I didn't actually give it as much thought (the fact that the two are not necessarily the same) as I probably should have.