My aerodynamics kahunas say that prewar conventional wisdom held that a faired-in cockpit (think 109/Spit/P40) yielded reduced drag and hence more speed.
It probably was not enough to offset the tactical downside--reduced visibility especially in the important rear hemisphere.
I've noted elsewhere that a couple of aces said they preferred the B/C Mustang fitted with a Malcolm hood, which could be more bulged than the 360-degree canopy, to the extent that it was possible to look aft UNDER the horizontals.
We still live with the aerodynamic downside of 360-degree canopies because even with FIGHTERJETS (gaaak) it takes fuel to push that bubble thru the atmosphere.
I think these might be the first pictures I've ever seen of a razor back with the tail fillet.To add to earlier exchange -
The first DF installed by R-R on AL963 circa Dec 1942. Reported to NAA in Feb 1943.
NAA designed and tested both DF and Fin aps in mid 1943 on P-51B-1-NA 43-12095, then dispatched 43-12095 to NACA Langley
NAA installed DF on P-51D-5-NA 44-13255 #4 in March 1944.
March 1944 production drawings released
March 1944 the first production insertion for new DF Planned for mid Block P-51D-5-NA and entire last block (NA111) P-51C-10-NT
P51C-10-NT #1 44-10753 July 1944
P-51D-5-NA #651 44-13903 July 1944
T.O. issued April 1944 to install field kits on P-51B/C and P-51D April 1944
Kits delivered to BAD2 Warton for both airframe types n June 1944 and distributed to Service Groups June/July 1944 for local FG installation.
The design objective was aerodynamic 'smoothing' of prop votex on empennage to reduce up/downloads on Horiz.Stab and side loads on Fin/Rudder.
Empennage failure was linked to strong Yaw inputs and asymetric loads in sideslip/snap roll at high speed.
Reverse Rudder Boost tab was also included in the DF installation. The penalty was slightly lower Roll rate and increased force on rudder pedals at high speed.
The DF served zero structural pupose. It added nothing to 'bend' resistance of Fin/Rudder due to side loads.
The quick answer is that early 1940s plastics technology wasn't capable of producing a large blown shape. That technology was developed in the U.S. and Britain in, basically 1943,This is the only explanation that makes sense to me. With the exception of the Gladiator, pretty much all 1930s biplanes had fully open cockpits with no rollover structure. Thus the pilot had truly unrestricted vision to the extent that he could move his head. With the advent of the new monoplane fighters in the mid-30s, almost all of them have high-faired fuselages. Given that none of these early monoplane fighters (Me 109, Hurricane, Spitfire) were originally designed with armour protection for the pilot, it seems illogical to me that the higher fuselage line was deliberately implemented to allow fitment of armour plate.
The only other factor that might have been at play is the ability of nations to produce large, one-piece blown sliding canopies of the type fitted to the P-51D. The IJNAF got around the problem by designing a multi-pane canopy. Clearly, Spitfires were fitted with blown canopies even with the high-back fuselage. However, I don't know if the technology permitted the creation of much larger blown canopies. This may have been a secondary consideration, though. I still strongly suspect that aerodynamics/speed were the driving factors for the high-back fuselage in early monoplane fighters.
The quick answer is that early 1940s plastics technology wasn't capable of producing a large blown shape. That technology was developed in the U.S. and Britain in, basically 1943,
Note that the Germans, Japanese and Soviets never got them. It wasn't a trivial issue - Postwar, as pressurization was required, and jets came into the picture, blown plastic canopies were, quite literally, strained to the limit - hence the white fiberglass tape reinforcement "framing" on straight-wing F-84s, the B-45s, and the Navy's AJ Savages. The Soviets didn't have it - compare the Mig-15/17 canopy to the F-86 - smaller, and multi-piece with heavy framing.
Although coming late to the party here - Others have pointed out the teardrop framed canopies on the A6M and Ki-43 from Japan. We can't leave out the P-38 and P-39, which had framed teardrop canopies as well.
However, in 1940, the Miles M20 "emergency fighter" had a blown, one piece bubble canopy. Not sure how good it was, but it can be argued that it pointed in that direction. Same with the Fw-190's canopy and the multi-piece all around canopies on the La-5 and Yak-1b and later Soviet fighters.
Indeed, and look at the second and third generation of jet fighters. The F-80, F-86, early F-84, FD-1, and F9F had those beautiful blown canopies like the P-51, P-47, and F8F. But the F-100, F-102, F-104, F-105, F-106, F-111, and F4H were not similarly endowed. The F-103 and F-108 had no way to look back at all. Drag was all important, along with the strength needed to withstand supersonic speeds. And of course they started using the canopies for other things. ARN-6 antennas were mounted there in the F-86 and F-94 and in the F-86 and F-84 they clearly chose to locate the Cabin Outflow Valve in the back of the canopy. Of course the F-102, F-103, F-108, F-106, and F4H were designed as interceptors using missiles to intercept bombers, and the chance of dogfights was thought to be remote; the pilots would likely never see their target visually and looking out for someone in your Six was all but unthinkable. And by the way, we lost an F-102A in Vietnam due to a Mig attack.That said, I still think the driving factor was the desire to reduce drag,
HiHowever, in 1940, the Miles M20 "emergency fighter" had a blown, one piece bubble canopy. Not sure how good it was, but it can be argued that it pointed in that direction. Same with the Fw-190's canopy and the multi-piece all around canopies on the La-5 and Yak-1b and later Soviet fighters.
I think it might not be as distorted looking out as it appears to be looking in. I think the sun / light angle is being captured at its greatest in that shot.
Making blown or bubble canopies optically perfect was a big problem, this is why there is a clear panel in the side.
I had seen a couple before, but only a very small minority of the P-51B-C photos I've seen, and I have read the "directional stability loss with the loss of side area" explanation in several publications, so that was what I was going with.I think these might be the first pictures I've ever seen of a razor back with the tail fillet.
See post #53 above... the Miles M20 main canopy was made in two halves (left & right) that were bolted together at the top.Beat me to it.
There were issues making curved canopies which were optically flat (didn't distort the pilot's view) during the 1930s. And, the larger piece of canopy and more bulged it was, the more difficult it seems to have been.
I know that the RAF spent a lot of time trying to get it right, working with various manufacturers. They must have cracked the solution by the end of the 1930s though, because the Miles M.20 had a full bubble canopy by September 1940.