Why were most early WW2 fighters designed with limited rear visibility?

[Shortround6]

Great photos, the P-51 brought all the latest technology together to make the Cadillac of the Sky.

I am not so sure I want a 1941 Cadillac of the sky.

 

[buffnut453]

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.

Thing was:

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.

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.

 

[SaparotRob]

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.

I think these might be the first pictures I've ever seen of a razor back with the tail fillet.

 

[PStickney]

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.

 

[buffnut453]

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.

Thanks for those additional details. That's about what I expected. That said, I still think the driving factor was the desire to reduce drag, particularly given the available power of inline engines in 1935-1937. As engine power increased thru 1943, it offered opportunities for different canopy approaches which, fortuitously, coincided with the evolution of technology to manufacture large blown canopies.

 

[BarnOwlLover]

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.

 

[buffnut453]

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.

Yes, but the Miles M.20 dates from 1940 which is 4-6 years after the Me109, Spitfire, and Hurricane were all first designed. That's a long time given the pace of technological and aircraft development that was happening during the period.

 

[pbehn]

Making blown or bubble canopies optically perfect was a big problem, this is why there is a clear panel in the side.

 

[pbehn]

BiffF15 I presume things have improved in the modern age, the distortion in that Spitfire canopy is visible, it looks like a Salvador Dali painting when you look through it.

 

[drgondog]

NAA first used 'draped' method for the teardrop canopies, and the P-51D &D-1 canopy process was different from the P-51B-1-NA modified in te same hanger. The blown version produced at Dallas was the final version, giving better vision down and to the rear.

The curved windscreen of the NA73X was replaced by flat panel for the same reason (distortion of view to 11 and 1 O'clock).

The three piece scheme a la A6M was the original concept to replace the Mustang P-51B birdcage - with cut down after deck - but the draped process improved to the point of being considered suitable for production in spring 1943.

 

[Shortround6]

Making blown or bubble canopies optically perfect was a big problem, this is why there is a clear panel in the side. View attachment 733904

Picky, picky, picky...
You want rearward vision AND you want to see clearly

 

[MIflyer]

That said, I still think the driving factor was the desire to reduce drag,

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.

The US went nuts with babble canopies right after WWII, with the XB-42, B-47, XB-52, and XC-74 all getting bubbles. (Bubble canopies on a cargo plane??? Yes!) This fascination did not last long. The XB-42 crew was highly irritated by having to look through two panes of glass a few feet from each other and talk on the intercom to discuss things; when discussions were required .the pilot and copilot ducked down and talked face to face.

The realities of air combat in Vietnam led to the F-14 and F-15, which finally had big beautiful bubble canopies again. Then Stealth came along and kicked that can into the gutter. You don't have to worry about looking behind you if they don't even know you are there.

 

[MikeMeech]

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.

Hi
The M20 canopy was not one piece it was two piece, see drawing from 'Miles Aircraft - The Wartime Years':

Mike

 

[MikeMeech]

Making blown or bubble canopies optically perfect was a big problem, this is why there is a clear panel in the side. View attachment 733904

Hi
The "Clear Panel" is usually called the 'Push-out Panel', so one assumes that it was to be ejected. It is sometimes said that it was used so a hand could be put out to clear the windscreen of oil etc. however, the pilot could just open the canopy for that purpose. There was one problem early on in that in a dive over 300 mph it was found very difficult to eject the canopy to bail out so it is more likely that this push-out panel allowed pressure to equalise. The panel starts to disappear from Spitfires during Mk. V production probably due to improved canopy ejection release. The canopy would not have lasted in service if you could not see through it.
Also the British introduced the fighter canopy with a smaller teardrop perspex blister on each side from the PR Type D early on in the war for better visibility so presumably the canopy could be seen through quite well.

Mike

 

[BiffF15]

BiffF15 I presume things have improved in the modern age, the distortion in that Spitfire canopy is visible, it looks like a Salvador Dali painting when you look through it.

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.

In the Eagle we would get minor distortions and or scuffs that could be buffed out. They also treated the front / windscreen with a Rain X type water repellent coating. Also if you see that the front windscreen appears slightly darker tint than the back portion you are looking at the increased strength version first introduced on the E model. Increased bird strike resistant.

 

[Airframes]

The Spitfire canopy "push out" panel was purely for equalising pressure in the case of an emergency (i.e., a bail out).
Early Mk1 and MkII Spitfires did not have the later Martin (Baker) wire canopy ejection system, therefore the canopy had to be slid back in order to bail out. At high speed, or in certain "G" conditions, the outside air pressure prevented the canopy from opening, but by knocking out the panel, the pressure was reduced, allowing the canopy to be slid back, in most cases.
The later system provided a rubber ball grip on top of the front frame of the canopy. If this was pulled, it released Bowden cables from the studs on the canopy runners, allowing the canopy to be blown off by the slipstream.
However, after some failures of the canopy to clear the airframe, again due to air pressure or aircraft attitude, the familiar crow bar was added to the cockpit door, to assist in prising off the canopy, and also for use if the entrance hatch jammed, mainly after a belly landing.

 

[Jabberwocky]

Making blown or bubble canopies optically perfect was a big problem, this is why there is a clear panel in the side.

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.

 

[Airframes]

See post 56 above,
The panel in the early Spitfire canopy had nothing to do with clear vision.

 

[GreenKnight121]

I think these might be the first pictures I've ever seen of a razor back with the tail fillet.

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.

Drgondog has provided original documentation showing that the instability had a different cause than the canopy change, so I am now better informed!

 

[GreenKnight121]

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.

See post #53 above... the Miles M20 main canopy was made in two halves (left & right) that were bolted together at the top.