Merlin Mustang cowlings (B/D, lightweights, H and F-82)

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Staff Sergeant
Nov 3, 2022
Mansfield, Ohio, USA
I've been looking at photos of various Merlin Mustangs, and on a lot of them (especially the P-51H and the Merlin F-82s) there seems to be a kind of sharp "bump" behind the spinner over where it would seem that the valve covers would be (in that area). I know that on the B/D types that there's a cowling bracket there (though this seems to make the bulge less pronounced). And while it's seemingly more pronounced from some angles on the H and the XP-82/P-82B, the XP-51F/G doesn't seem to really have such bulges or angling on their cowlings in that area. Of course, I should point out that I don't have as many detailed photos of the lightweight Mustangs as I do the other variants.

But and I just seeing things or is there something to this? It also seems that the H/F-82 cowlings at the front of the aircraft may seem to be more "tightly wrapped" around the front of the engine (mostly near the reduction gear) than on the B/D or the F/G.
I don't see any bumps.

I DO see an exhaust manifold cover streamlining the exhaust manifold pipes, but the cowling doesn't look as if it has bumps like a Griffon Spitfire has for the Griffon valve cover clearance.
I've also wondered if the B/D, F/G and the P/F-82 had different spinner sizes? This is probably hard to judge without tech drawings because each design iteration differed from each other.
I think the F-82 had a bigger spinner. The actual shape of the fuselage is NOT identical to a P-51 of any sort.

Unfortunately, I have not seen the only F-82 operating these days up close and personal, but the spinner LOOKS bigger. It may be bigger, or it may be the same size and the different fuselage lines are fooling us. It is basically a P-51H fuselage with a 67-inch fuselage plug aft of the cockpit area. So, it is likely to be the same spinner and prop, logically. Looks different because the fuselage looks different.
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The other thing is that in side profile, the H and the F-82s have the "angled up" engine cowling. Where the upper surface coming up from shortly behind the spinner at an angle instead of a flattening curve as on the other Merlin Mustangs and the lightweights. Of course, without technical drawings we can't draw conclusions, as even though there's a few P-51Hs still around and 3 Merlin powered F-82s (one airworthy, the other two in the USAF Museum), there's no complete XP-51F or G models. Only so far the fuselage and some other part of a XP-51G that's supposedly part of a long term restoration.

I do have some illustrations that seem to suggest that the B/D spinner was slightly longer than the F/G spinner, but I'm sure how accurate they are (though dimensions are given on them), but don't give spinner diameter, either.
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I do guess after watching a video and seeing a few more photos is that the bump I see (B/D type P-51s have them, too, as do the Allison Mustangs) is where around where the front of the valve covers are mounted isn't so much for clearance, but an "illusion" caused by the cowling transitioning from being round behind the spinner to being more oval shaped from around the engine and conforming to the rest of the fuselage.

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