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Bubble Canopies


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#1 Lightning

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Posted 22 November 2004 - 11:30 PM

Hi All,

Some of the best WWII fighters were switched to the bubble canopy during the course of their development. At first glance, this seems like a definite improvement with no drawbacks. But was it?

The obvious advantage was pilot visibility. Was the price paid all that worth it? You be the judge.

First of all, directional stability suffered because of the decrease in profile area due to the cut-down fusilage. This was particularly apparent in the P-51 and P-47. The Mustang had a tendency to "fishtail". The Thunderbolt actually became dangerous when the rudder was overused trying to correct for the loss of directional control. Dorsal fins were added to both aircraft as a fix, but
it is doubtful whether this completely cured the problem.

Then there is the decrease in top speed. A loss of three to five mph was imposed by the use of the bubble canopy.

Part of the advantage in increased visibility was offset by the view aft being obstructed by the armor plate directly behind the seat. in some cases, it was quite wide.The narrowness of some bubbles actually prevented the pilot from being able to turn his head adequately because his oxygen mask bumped up against it. He therefore couldn't see properly to the rear regardless of the presence of the armor plate.

Another serious problem, especially in hot climates, was the buildup of heat due to the "greenhouse effect". This was a real problem on long-range missions that could last over 10 hours!

Problems with the optics of the curved "glass" were also encountered. Distorions and reflections (espcially of the lighted instuments at night) were very annoying, to say the least.

There were also incidents where a jettisoned bubble canopy would release sooner from one rail than from the other causing it to flip off to the side rather than straight back and up. At least one pilot was seriously injured when he was struck on the side of the head before he even got out of the plane.

It was noticed by naval pilots that bubble canopies had a tendency to be pushed closed by aerodynamic forces. Since canopies are left open during carrier takeoffs and landings (to allow the pilot to escape should the plane go into rhe sea) this was undesirable.

The bubble canopy became the canopy of choice as aircraft development progressed. Later planes were designed from the beginning to have them, so the problems associated with them were anticipated and eliminated in advance. But for the WWII planes that received the bubble as an "after-market" add on, there was a price to pay. Was it always worth it?

Regards,
Lightning







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#2 PMN1

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Posted 23 November 2004 - 01:45 AM

quote:Originally posted by Lightning

It was noticed by naval pilots that bubble canopies had a tendency to be pushed closed by aerodynamic forces. Since canopies are left open during carrier takeoffs and landings (to allow the pilot to escape should the plane go into rhe sea) this was undesirable.




Did that have anything to do with the Hellcat and Corsair never getting a bubble canopy. The Bearcat did but was that because any opponents of bubble canopies were 'outvoted'?

#3 GregP

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Posted 23 November 2004 - 08:43 AM

The Corsair DID get a bubble canopy ... along with the mighty R-4360 and a great, big 4-bladed prop, but it was LATE in the wart and only a handful were made ... maybe 12, I think.

The Hellcat was not so modified since it would have interrupted production of a proven airframe that already had the best kill ratio in history.

Yes, the bubble canopy was worth it, and no .... no modern fighter pilot would want to fly in a fighter jet without a bubble canopy. The effect from loss of side area were compensated for by the fin additions, and the subsequent aircraft were very good, indeed.

#4 tenmmike

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Posted 23 November 2004 - 11:31 AM

directional stabilaty was corrected by adding approx 3sq ft to the vertical tail fin and a small dorsal fillet was added in june 44 to the p-51D-10NA and later models(some d-5 and earlier models with field mod kits) however the problem was again encountered with the expierimental p-51G with 5 bladed rotal wooden props but were very fast..similer (fillet was also(field) added to the p-47 to later "D"(standard on D-25) mods and kept geting larger through each mod till the "N" had a fairly large fillet)note this was in pieces taken from "MUSTANG DESIGNER the story of edgar schmued and the p-51" and my observations of p-47 photos and writings in AMERICAS HUNDRED THOUSAND"

#5 tenmmike

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Posted 23 November 2004 - 11:42 AM

quote:Originally posted by GregP

The Corsair DID get a bubble canopy ... along with the mighty R-4360 and a great, big 4-bladed prop, but it was LATE in the wart and only a handful were made ... maybe 12, I think.

The Hellcat was not so modified since it would have interrupted production of a proven airframe that already had the best kill ratio in history.

Yes, the bubble canopy was worth it, and no .... no modern fighter pilot would want to fly in a fighter jet without a bubble canopy. The effect from loss of side area were compensated for by the fin additions, and the subsequent aircraft were very good, indeed.

the contracts for the F2G-series were terminated and only ten (five F2G-1s and five F2G-2s) were completed Posted Image

#6 robert

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Posted 23 November 2004 - 02:29 PM

Interestingly enough, the first bubble canopy fitted to a P-47 was taken straight from a Hawker Typhoon. P-47D-5-RE airframe (serial number 42-8702) was converted and tested in July 1943.

#7 Ricky

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Posted 23 November 2004 - 06:15 PM

Didn't bubble canopies also cause more drag than canopies like the Hellcats that were faired into the fuselage?
It would be interesting to see if there was any difference in performance between (for example) a 'Razorback' P-47 and the modified P-47 with bubble canopy (assuming all that has changed is the rear fuselage, canopy, and ventral fins).
I would assume that the extra drag would be cancelled by the lost weight from the ccut-down rear fuselage, but am prepared to admit that I know very little of what I am talking about here.:)

#8 Lightning

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Posted 23 November 2004 - 10:46 PM

Hi GregP, tenmike, Ricky,

The F2G was called the "Super Corsair". It was specifically designed to combat the "Devine Wind" (I never could spell "Kamakaze") attacks late in the war. It was a fast, low-altitude variant. The F2G was a standout air racer in the hands of pilot Cook Cleland in the Thompson Trophy race at Cleveland, Ohio in the late 1940s. That very same airframe has been rescued from the scrap heap and has been beautifully restored in its original race color scheme (Race 57, if I remember correctly).

It's not a slam-dunk that all later pilots and designers favored the bubble canopy. Quite a few later first-line fighters/fighterbombers did not use it: The F4D; A4D; F8U; A7; F-84 Thunderjet/Thunderstreak series; F-102; F-104; F-106; and F-111 are some examples. In addition, if you'll look closely of some of the other post-war fighters, you'll see some bubbles that are not true bubbles at all-- Some were just clear enclosures having dividing frames and blocked-out portions to the rear.

The present day crop of fighters (F-14; F-15; F-16; F/A-18; F-22; F-35; etc.) have gone back to the bubble, but that does not, in any way, guarantee that all future designs will follow suit.

The bubble canopy did decrease performance in some WWII fighters. The P-51D was three to five mph slower than the P-51B/C. It also suffered from deminished directional stability over the earlier models. Quite a few Mustang pilots stated their preference for the "B/C" models over the "D" version. Their were additions to weight in the "D", but the bubble was definitely aerodynamically inferior to the original "flush" canopy with its attendant built-up rear fusilage.

It is interesting to note that the XP-47J that Republic used to squeeze every last mph out of, had a conventional framed canopy. That didn't stop it from attaining almost 500 mph in level flight! I believe this was in 1943, so I can't state for certain that a bubble canopy was available at the time, but I believe it was. These tests led to the definitive P-47M/N models late in the war, and they did have bubble canapies. That was the trend at the time. Sometimes trends are right; sometimes they are wrong.

What's my personal oppinion? I can truthfully say that I don't know. There is one advantage that the bubble has that I can't dispute: It looks a heck of a lot better!

Regards,
Lightning



#9 robert

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Posted 24 November 2004 - 12:45 AM

Originally posted by Lightning

Hi GregP, tenmike, Ricky,

It's not a slam-dunk that all later pilots and designers favored the bubble canopy. Quite a few later first-line fighters/fighterbombers did not use it: The F4D; A4D; F8U; A7; F-84 Thunderjet/Thunderstreak series; F-102; F-104; F-106; and F-111 are some examples. In addition, if you'll look closely of some of the other post-war fighters, you'll see some bubbles that are not true bubbles at all-- Some were just clear enclosures having dividing frames and blocked-out portions to the rear.

Absolutely true - many of the greatest jet fighters of the 1960s, including the English Electric Lightning, McDonnell-Douglas F-4 Phantom, MiG-21 (especially the later versions), SAAB J 35 Draken, and Dassault Mirage III did not have bubble canopies. All had canopies integrated into the spine.

The present day crop of fighters (F-14; F-15; F-16; F/A-18; F-22; F-35; etc.) have gone back to the bubble, but that does not, in any way, guarantee that all future designs will follow suit.

The Eurofighter Typhoon is interesting in that the single-seat version has a bubble, while the two-seater's canopy is faired into the spine.

What's my personal oppinion? I can truthfully say that I don't know. There is one advantage that the bubble has that I can't dispute: It looks a heck of a lot better!

Looks are a simply a matter of taste - there's no definitive right or wrong. But I have to strongly disagree with you on that - the faired canopy versions of the Spitfire, Thunderbolt, and Mustang are much more attractive to me than the bubble canopy versions. I will agree with the Yak.


#10 PMN1

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Posted 24 November 2004 - 01:44 AM

quote:Originally posted by GregP

The Corsair DID get a bubble canopy ... along with the mighty R-4360 and a great, big 4-bladed prop, but it was LATE in the wart and only a handful were made ... maybe 12, I think.


Ahh, I'd forgotten about the Goodyear!!

[:I]

What was the difference between the shore-based F2G-1's and shipboard F2G-2's?


#11 tenmmike

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Posted 24 November 2004 - 11:13 AM

quote:Originally posted by PMN1

quote:Originally posted by GregP

The Corsair DID get a bubble canopy ... along with the mighty R-4360 and a great, big 4-bladed prop, but it was LATE in the wart and only a handful were made ... maybe 12, I think.


Ahh, I'd forgotten about the Goodyear!!

[:I]

What was the difference between the shore-based F2G-1's and shipboard F2G-2's?

folding wings on the FG-2 as far as i know...............to the other posts regarding none bubble canopies at the time of the aircraft yall are listing most if not all of them were designed as intercepters (dog fighting not that important)as a primary mission as opposed to a air superiority aircraft of tha later type

#12 GregP

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Posted 24 November 2004 - 11:14 AM

The bubble canopy DOES decrease performance by a few percent, b ut it reaps benefits in visibility. It has the disadvantage of being "hot" in the sun, but sunscreen is easy to use.

The faired in canopies are alright for planes that are not intended to fight other planes, but not for a fighter, the 1950s notwithstanding. Back then, every designer was sure no one else could come up with a plane fast enough to sneak up on his new Mach 2 speedster. Now we know that is a load of malarkey.

Everyone in the major aircraft design business has a fast jet with good features, so there is no more excuse for a faired canopy unless there is a REALLY good RWAR.

#13 Lightning

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Posted 24 November 2004 - 11:46 PM

Hi robert and GregP,

You know, robert, you've made a good point regarding looks. When I think of the "Malcomb Hood" and the Spitfire-type "blown",canopies, I can't really disagree with you. (And maybe also regarding performance aspects vs the bubble.)

GregP: Sunscreen and sunglasses don't lower temperature, and the heat was far more of a problem than sunburn or glare.

Also, there were complaints by pilots that the bubbles were more susceptible to picking up oil film and dust during taxying. Why, I don't know, but do know that the complaints were made. This would, to some degree, offset some of the visibility advantage of the bubble.

A serious safety concern was the inadequate turn-over protection provided by the bubble. The armor plate behind the pilot was just not strong enough. The built-up rear structure of the earlier versions provided far better protection. This was especially important for tail-wheel types.

Regards,
Lightning







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