Well, yes, they are inlines in the aircraft world, but only because the other big engines were shaped like corncobs. They are V-12's, absolutely awesome engines as are the Griffen bomber engines. 30,000 feet was quite common with power to spare, so 40 was probably doable. OK, just looked it up. How does 41,900 feet sound for a service ceiling! They were compound supercharged, with one feeding into the other. I'll be crewing the #10 formula plane "El Bandito" in Reno late this summer. The owner/pilot flew P-51's and I'll be sure to ask more about them. Check this out
http://www.aviation-history.com/north-american/p51.html Armond
