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

fannum said:

I'd suggest that a lot of the reason for a turtleback was tradition

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Depends where you're looking. Not a lot of traditional headrests in these images:











In fact, the Gloster Gladiator was the only RAF interwar fighter that had a raised rear fuselage. Even then, it was more of an addition ontop of the Gauntlet-style fuselage to align with the cockpit canopy, rather than being a fully integrated part of the fuselage structure.

PlasticHero said:

Look at the tail of the Texan, it looks pretty thin and with a "sorta" bubble canopy, the theory of lack of directional stability on the Mustang does seem less likely to me. I agree with drgondog

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There is no doubt about the lack of directional stability of the early P-51's as the addition of the dorsal fin was to address just this problem.

And it looks cool.

er . . . coolER.

PlasticHero said:

This is a question that I have been curious about for years. The open cockpit planes had no structure behind the pilot so why did designers build closed cockpits with a high back? I'm going to put up 5 fighters that we all know and see how their designs differ with the year of first flight.
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Of all of these, only the Zero had good visibility and as the designs were modified over the years, bubble canopies were added to the Allied planes. I think the Germans didn't have time or resources to develop a low back. Even without the ability to produce the large one piece canopies, the Allies could have gone with the greenhouse design that the Japanese used. I'm sure the pilots would have always preferred to have better visibility, but there must have been some other reason the designers put a higher priority on. The only things I can think of is aerodynamic considerations to get a little more speed or possibly ease of production and lower cost. Anyone with other ideas or information? Thanks for your consideration.

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PlasticHero said:

This is a question that I have been curious about for years. The open cockpit planes had no structure behind the pilot so why did designers build closed cockpits with a high back? I'm going to put up 5 fighters that we all know and see how their designs differ with the year of first flight.
View attachment 729002
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View attachment 729005
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Of all of these, only the Zero had good visibility and as the designs were modified over the years, bubble canopies were added to the Allied planes. I think the Germans didn't have time or resources to develop a low back. Even without the ability to produce the large one piece canopies, the Allies could have gone with the greenhouse design that the Japanese used. I'm sure the pilots would have always preferred to have better visibility, but there must have been some other reason the designers put a higher priority on. The only things I can think of is aerodynamic considerations to get a little more speed or possibly ease of production and lower cost. Anyone with other ideas or information? Thanks for your consideration.

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No offense, but the Mustang shown above would've been built in either late 1942 or in 1943 ... it's a P-51B Merlin Mustang, and was built as late as mid-1943.

The only "Mustang family" aircraft (it wasn't even NAMED anything) in 1940 was the NA-73x more-or-less "Mustang Prototype."

PlasticHero said:

This is a question that I have been curious about for years. The open cockpit planes had no structure behind the pilot so why did designers build closed cockpits with a high back? I'm going to put up 5 fighters that we all know and see how their designs differ with the year of first flight.
View attachment 729002
View attachment 729004
View attachment 729005
View attachment 729006
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Of all of these, only the Zero had good visibility and as the designs were modified over the years, bubble canopies were added to the Allied planes. I think the Germans didn't have time or resources to develop a low back. Even without the ability to produce the large one piece canopies, the Allies could have gone with the greenhouse design that the Japanese used. I'm sure the pilots would have always preferred to have better visibility, but there must have been some other reason the designers put a higher priority on. The only things I can think of is aerodynamic considerations to get a little more speed or possibly ease of produThisction and lower cost. Anyone with other ideas or information? Thanks for your consideration.

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This is my second attempt to reply ... probably my fault. I wanted to comment that the Mustang shown for 1940, wasn't built until 1943 ... it's a P-51B. Sure, it has a "closed cockpit with a high back" - similar to that of the original NA-73X "pre-prototype" of the Mustang Family. I've attached a line drawing of the NA-73X below.

Cheers.

I acknowledge that I didn't spend the time to get the first model of each type. I know that this crowd would know what the early Mustangs, and the others were like. I found this...

This says "to be installed on P-51B, P-51C, and P-51D. If it was supposed to be because of the reduction of area on the B, why does it need to be installed on it? Is it only an improvement to the rudder itself? Other makes that got bubble canopies didn't need an increase in the rudder area. If anyone here is a patron of https://www.youtube.com/@GregsAirplanesandAutomobiles , I would love to ask him if he knows.

PlasticHero said:

I acknowledge that I didn't spend the time to get the first model of each type. I know that this crowd would know what the early Mustangs, and the others were like. I found this...
View attachment 737835
This says "to be installed on P-51B, P-51C, and P-51D. If it was supposed to be because of the reduction of area on the B, why does it need to be installed on it? Is it only an improvement to the rudder itself? Other makes that got bubble canopies didn't need an increase in the rudder area. If anyone here is a patron of https://www.youtube.com/@GregsAirplanesandAutomobiles , I would love to ask him if he knows.

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According to a short memoir written by a NACA engineer, the dorsal fin was to keep the horizontal stabilizer attached to the plane during high-speed rolls.; Of course, I cannot re-find the document, so ill post what Wikipedia has to say: "Despite these modifications, the P-51Bs and P-51Cs, and the newer P-51Ds and P-51Ks, experienced low-speed handling problems that could result in an involuntary "snap-roll" under certain conditions of air speed, angle of attack, gross weight, and center of gravity. Several crash reports tell of P-51Bs and P-51Cs crashing because horizontal stabilizers were torn off during maneuvering. As a result of these problems, a modification kit consisting of a dorsal fin was manufactured. One report stated: "Unless a dorsal fin is installed on the P-51B, P-51C and P-51D airplanes, a snap roll may result when attempting a slow roll. The horizontal stabilizer will not withstand the effects of a snap roll. To prevent recurrence, the stabilizer should be reinforced in accordance with T.O. 01-60J-18 dated 8 April 1944 and a dorsal fin should be installed." The engineer also said it was not a 100% fix.

This is the stab mod but I do not appear to have the dorsal fin mod.

I think the AirCorps Library website has the T.O. for the dorsal fin mod.

Technical Order No. 01-60J-6B dated 27 January 1944

"Due to recent horizontal stabilizer failures which are believed to have resulted from slow rolls, all P-51B and P-51C airplanes will not perform slow rolls pending completion of present investigation and necessary corrective action"

and (as per MiTasol's post above)

Technical Order No. 01-60J-18 dated 8 April 1944

"To reduce the possibility of empennage failure the horizontal stabilizer and fin of affected P-51 series airplanes will be reworked in accordance with the applicable sections of the instructions contained in paragraph 2. as follows: . . ."

and

Technical Order No. 01-60J-6C dated 6 June 1944

"Due to horizontal stabilizer failures which are believed to have resulted from slow rolls all P-51B, P-51C, and P-51D airplanes will not perform slow rolls pending the installation of dorsal fin and rudder reverse trim tab, and compliance with T.O. No. 01-60J-18."

The first issue with Merlin Mustang exhibiting yaw (and yaw damping) issues - actually due the instability caused by throttle advance/reduction. The effects of the increased vortex strength of the combined four blade prop and new Merlin were suspected - and the first dorsal fin was applied to AL 963 at R-R.

The second problem to be solved after investigations of failed fin/rudder and elevator and entire empennage - Most but not all believed to be roll issue ia asymmetric loading (side on fin, up/down on elevator due to combined rudder and roll). If you visualize a hard rudder input, roll manuever initiated
you can visualize a side load on the fin/rudder plus a differential up/down load on the elevator due to both the prop vortex and the rolling manuever.

The Dorsal Fin assisted in streamlining the flow impinging on the elevator.

The three solution approaches were a.) design and install dorsal fin in favor of increased fin/rudder area of added 'fin cap' - for both P-51B/C AND P-51D; b.) Beef up the H.Stab via doubler plate to reduce stress from torsional loads applied to empennage, and: 3.) design a rudder boost tab actuated by rudder in yaw and turn, but which added to rudder force input from pilot. By all acounts the rudder boost tab reduced roll manueverability as function of added rudder input force on rudder pedal.

The original release of the DF and RBT were announced in the April 1944 NAA Service News release as kits. If you examine T.O. 01 -60J-18 above, both the DF and RBT mods were ordered for all P-51B/C/D (save P-51D & D-1 42-106539/540) in the field, or as may arrive later.

The Production insert was P-51D-5-NA 44-13903 and P-51C-10-NT ( D-5-NT and K-1-NT both hadthis from the beginning).

I have talked to many pilots with experience in both Allison and Merlin powered Mustangs, and with/without B/C/D. The stories (i.e John Muszala II at Pacific Fighters and my father) are similar. In order of manueverability (P-51A, P-51H, P-51B/C without DF/Rudder boost, P-51D without DF/Rudder Boost, P-51D with DF/Rudder boost and change of elevator incidence). Allegedly (hearsay to me) those that flew the Xp-51 and also succeeding Mustangs say that it - other than roll advantage of P-51B/D/H - was the 'sweetest'.

Chilton stated that XP-51F was best of all.

In my opinion, the razorback style was a continuation of the bi-wing designs much like the Model T looked a lot like a horse drawn buggy. Also as a safety feature to protect the pilot in the early fighters in case they ended up upside down, which happened frequently.

Once you took the biplane's upper wing off the the pilots head was the "high point" of the airplane if the plane wound up upside down.
That "headrest" wasn't going to add any speed to the airplane due to streamlining.
The high backs looked cool though.

This quote is from the wiki page on the P-51 "Several crash reports tell of P-51Bs and P-51Cs crashing because horizontal stabilizers were torn off during maneuvering. As a result of these problems, a modification kit consisting of a dorsal fin was manufactured." Also "One of the few remaining complaints with the Merlin-powered aircraft was a poor rearward view." I will acknowledge that wiki is not a perfect information source. I feel "rather" confident that the dorsal fin question raised here is NOT to fix a reduction in side area but a fault in the rudder and tail. It seems that once the low back aircraft design was accepted, very few designed since then, had high backs. For example, Phantom, Mig-21, F-102, F-105, Lightning, Mirage do and if you think about what they were conceived for, it's bomber interceptor or tactical bomber. Their initial mission did not depend heavily on Mk1 eyeball and the gain in aerodynamic efficiency made up for lack of visibility.

Was rear or any other type of visibility ever mentioned in a specification?

PlasticHero said:

I acknowledge that I didn't spend the time to get the first model of each type. I know that this crowd would know what the early Mustangs, and the others were like. I found this...
View attachment 737835
This says "to be installed on P-51B, P-51C, and P-51D. If it was supposed to be because of the reduction of area on the B, why does it need to be installed on it? Is it only an improvement to the rudder itself? Other makes that got bubble canopies didn't need an increase in the rudder area. If anyone here is a patron of https://www.youtube.com/@GregsAirplanesandAutomobiles , I would love to ask him if he knows.

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In addition to what pothers have posted in reply to your post, here are earlier posts about the issue... wherein my incorrect understanding was corrected:
Why were most early WW2 fighters designed with limited rear visibility? & next post
Why were most early WW2 fighters designed with limited rear visibility? & next 2 posts


In post #38, drgondog posted both the page you did but also the page for the P-51D installation (albeit in a yellow page format).

yankeeclipper747 said:

In my opinion, the razorback style was a continuation of the bi-wing designs much like the Model T looked a lot like a horse drawn buggy. Also as a safety feature to protect the pilot in the early fighters in case they ended up upside down, which happened frequently.

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How exactly?

Again, I go back to the RAF which went from the Gauntlet:



To the Gladiator, which was not a "razorback" by any means:



To the Hurricane and Spitfire with "razorbacks."






Please explain how any "razorback" fuselage design was simply copied from the biplanes to the early RAF monoplane fighters?

Streamlining in an attempt to wrench every last knot of speed from the available propulsive power (which was still pretty limited in the late-1930s) makes a lot more sense, IMHO.

The streamlining idea also makes sense given the RAF's experience with the Schneider Trophy races. The Supermarine S6 fuselage looks a lot more like the Hurricane and Spitfire fuselage than the Gauntlet or Gladiator:

I was on Greg's Airplanes earlier today and he said that bubble-top P-47Ds were about 500 lbs heavier than the razorback Ds. Any truth to that?

Probably but that does not mean it was all in the structure for the canopy and the canopy itself. The rear fuselage may have been lighter but the canopy tracks and their support would have offset that to an extent.

The canopy would almost certainly be heavier but what other changes came in with the canopy?

Did the engine weight go up with the horsepower? Additional armour plate? Increased radio equipment? Local structural changes to carry the extra radios? etc etc

MiTasol said:

Probably but that does not mean it was all in the structure for the canopy and the canopy itself. The rear fuselage may have been lighter but the canopy tracks and their support would have offset that to an extent.

The canopy would almost certainly be heavier but what other changes came in with the canopy?

Did the engine weight go up with the horsepower? Additional armour plate? Increased radio equipment? Local structural changes to carry the extra radios? etc etc

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Yeah, the first thing I thought of is that the plexiglass has got to be heavier than aluminum. I figure rails and supports should be about the same, though.

The other, unrelated changes might well be the source, you're right.

I just don't trust his claims too much and thought I'd ask here.