Canopy Design

FLYBOYJ · May 4, 2008

Trebor said:
the hell kinda plane is THAT? I've never seen anything like that.

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drgondog · May 4, 2008

buzzard said:
A fair number of jet fighters were designed without bubble-type canopies. The F4D Skyray, F-8, F-5, F-102, F-106, Tu-128, MiG-23, MiG-25, Mirage III, Draken and Viggen come to mind. Some of these were designed as pure intercepters, but the F-8 certainly wasn't...

No, the F-8 was the last of the Gunfighters for 15 years, was the Fleet Air Superiority beast and probably did not have the bubble canopy because of the variable incidence wing behind the canopy - it and the other birds were designed before advanced computational models and computers made sophisticated designs cheaper to model and faster - to explore better canopy designs, for example.

Aircraft designers know that performance numbers impress the people who ultimately pay for the planes (politicians) more than less quantifiable qualities such as a pilot's ability to maintain situational awareness. And as Flyboy J mentions, trendy theories and doctrine also play a big role in the design of combat aircraft. Who needs to see what's behind you if automated BVR missile engagements are the way of the future?

Airframe designers, until you get to the Kelly Johnson level are obsessed with Performance and weight. Politicians are impressed by where the airframe is being built.

Politicians have had more than one single digit salute waved in their direction. The Navy, particularly with the F-111 and the VFAX (USN F-16) that politicians Mandated, unsuccessfully.. Evidently the Euro Fighter, F-22, F35 ignored the wisdom of 'who needs to see what's behind you".

Pre-WWII air doctrine was dominated by the bomber prophets, and WWI type dogfighting was largely seen as passe. With fighter designers concentrating on sheer performance, (with bomber interception as the primary role) they regarded streamlining as more important than rearward vision. Until the dogfights began...

This is certainly true for the USAAF bomber mafia - proponents of 'unescorted strategic daylight bombing'

The slight protection offered by the fuselage behind the pilot may have been of some use when rifle-calibre armament was the norm, but against .50 cal and cannon fire, most pilots would probably prefer to see the enemy coming, rather than be announced by shells rattling thru the 'razorback'. The Malcom hood is no substitute for a true bubble canopy. Even the post-war Spits had them. And since even fighters spend most of their time at cruise speed, being able to see a 'slower' enemy diving in on your six is worth a few MPH.

It is unlikely that current doctrines to provide bubble canopies to sub Mach 3 fighters is stimulated by concerns even for speed 'loss'. The high speed canopy configs have a lot more to do with best shock wave characteristics and stagnation heat dissapation (SR-71 comes to mind along with X-15).

At the end of the day, it seems like Lednicer's potential flow models show results that are counter intuitive - namely that drag is reduced with the bubble canopy of the 51D from the 51B, that flow reattached nicely with the Spit Malcolm Hood versus the 51B Birdcage canopy despite a less effective windshield angle.

The 51D was slower and climbed slower than the 51B because of the extra 10% Gross Weight as the critical factor (in my opinion), despite having better flow results with bubble canopy...the 51H had 300 more Hp than the P-51B and at max High Blower w/water injection and was 40+ mph faster (factory tests) at 100 pounds more weight (empty)..

without water injection the 51H 1650-9 was same performance as the 51B 1650-3 and still faster than the P-51B - implying that with same weight, and same general Hp that the 51H was slightly cleaner than the 51B.

BTW - I am still looking for the NAA original flight tests in 1945 which had a full set of tests with and w/o water injection - so this is a 'no proof' statement

I've always wondered how many '109 pilots died because of that crappy canopy. If they could make something like the Me 262, you'd think that, at the very least, the Galland hood could have been introduced by '42.

Probably the relative same number as the P-40, P-47D Razorback, P-51B, Hurricane, etc. I also suspect (can't prove) that there was little difference in total flat plate drag between the Birdcage, Malcolm Hood and Bubble at least not enough to slow it down more than external fuel or cannon pod mounts.

kool kitty89 · May 4, 2008

I meant that the turtleback/razorback configurations of the high performance jets would imply that it was advantageous from a drag stand point, otherwise it would make no sense not to use a bubble canopy.

I never disagreed with the visability advantage the bubble canopy gave.

I also agree that the razorback itsself would add next to no protection, but armor (particularly head armor) can be added more effectively w/out trying to maintain rear view. But in some cases (like the many models of the P-39) head armor was omitted to allow the rear view, this would leave the pilot vulnerable though.
Another option was to fit a slab of bulet proof glass behind the pilot which would give both advantages. (this was done on many Soviet P-39's, as head armor allowed almot no rear visibility for that a/c, some Bf 109's wih Galland hood used that too iirc)

There are compromise canopy designs as well, other than the Malcolm hood (which really isn't better than a clearview un-bulged canopy hood). Replacing some of the rear fusalage decking with plexiglass can be almost as effective as a bubble canopy. The P-36 is the first major example I can think of, with scallopped rear fusalage sides, same as used on the P-40. The P-40N utilized a frameless hood and plexiglass decking extending to the top of the fuselage.
The Finnish Myrsky used a similar design, as did the Galland hood (albeit less extreme). As did the spitfire, and (barely) the Hellcat.

drgondog · May 4, 2008

renrich said:
If you will notice, almost all post WW2 US fighters have bubble canopies whereas most Soviet fighters (after Mig 15,17) had a kind of razorback type design. There must be some drag factor working there. From my tiny experience flying an L39, one is strapped in so tight you can't turn around and look behind very far anyway. I have a friend who was an IP in Huns at the Fighter Weapons School(2000 hours in Huns) whom I asked about that. He said it was difficult to see much of the rear 180 degrees and he knew one hot pilot who in ACM disconnected most of his harness so he could utilise the bubble canopy.

Rich - the design factors driving a canopy design include shock wave characteristics for supersonic flight, temperature and visibility. The 50's and 60's (through 68 timeframe) designers weren't much concerned with visibility because 'gunfighting was dead' and the 102/106 and 105 were designed with entirely different missions than air to air against fighters.

I must confess that I would not be loosening up 'much' particularly in an F100's relatively small cockpit vs say compared to an A-10 or F-105 or and F-15but I'm sure he knows what he is talking about.. just enough to enable a slightly greater swivel but not enough slack to whack your head against the canopy in an 8g turn?

drgondog · May 4, 2008

kool kitty89 said:
I meant that the turtleback/razorback configurations of the high performance jets would imply that it was advantageous from a drag stand point, otherwise it would make no sense not to use a bubble canopy.

More likely for the M 2.5 and above performers heat was a bigger factor.

I never disagreed with the visability advantage the bubble canopy gave.

I also agree that the razorback itsself would add next to no protection, but armor (particularly head armor) can be added more effectively w/out trying to maintain rear view. But in some cases (like the many models of the P-39) head armor was omitted to allow the rear view, this would leave the pilot vulnerable though.
Another option was to fit a slab of bulet proof glass behind the pilot which would give both advantages. (this was done on many Soviet P-39's, as head armor allowed almot no rear visibility for that a/c, some Bf 109's wih Galland hood used that too iirc)

Moot point in one sense. US armor plating was maybe able to stop 7.92 rifle bullet as most were 1/4 to 3/8" steel.

There are compromise canopy designs as well, other than the Malcolm hood (which really isn't better than a clearview un-bulged canopy hood). Replacing some of the rear fusalage decking with plexiglass can be almost as effective as a bubble canopy. The P-36 is the first major example I can think of, with scallopped rear fusalage sides, same as used on the P-40. The P-40N utilized a frameless hood and plexiglass decking extending to the top of the fuselage.
The Finnish Myrsky used a similar design, as did the Galland hood (albeit less extreme).

KK - the Malcolm Hood was also 'bulged' on the sides and really did offer better visibility to 730 on either side and better visibility over the trailing edge of the wing - not to mention no stiffeners or other distractions that a P-51B or 109G had...

kool kitty89 · May 4, 2008

I also agree that adied pylons or gun pods will have a greater (and more predictable) effect on drag than changes in canopy design.

But then there's cases like with the P-80 where the Lockheed tip-tanks actually reduce drag and increase wing efficiency and roll rate. (acting as primative winglets, resulting in a reduction of vortex at the wingtips)

But that's kind of counterintuitive, like the case with the P-51's canopy.

drgondog · May 4, 2008

kool kitty89 said:
I also agree that adied pylons or gun pods will have a greater (and more predictable) effect on drag than changes in canopy design.

But then there's cases like with the P-80 where the Lockheed tip-tanks actually reduce drag and increase wing efficiency and roll rate. (acting as primative winglets, resulting in a reduction of vortex at the wingtips)

But that's kind of counterintuitive, like the case with the P-51's canopy.

KK - in a sense yes. In the early days of wind tunnels and airfoil theory, the wing extended to each side of the wind tunnel and drag figures were lower than in real life.. why? The 2-D effect permitted no induced drag at the tip.

The P-80 wing tank assisted the 2-D Flat Plate effect and reduced induced drag. Winglet on modern aircraft combine that effect with also reducing the concentrated tip vortex - also reducing drag.

As to assisting roll rate for the P-80 I really have no opinion... that IS counter intuitive because a wing tank would INCREASE rolling moment of Inertia which would tend to slow rate of roll.

kool kitty89 · May 4, 2008

On the Malcolm hood, I was comparing an unbulged framless canopy, not the "birdcage type" but I do agree that the bulge does help a little.

And another thing to note with the P-40N is that the frameless hood has the larger bordering frame at it's base, which blocks some of the view that the older framed one didn't.

And as to the armor plate, the thin walled 20mm HE mine rounds also had very poor penetration (as did the HE 13 mm rounds) causing mostly surface damage to the aluminum structure, so the armor plate (or thick armor glass slab) should usually be able to block that as well.

kool kitty89 · May 4, 2008

For roll the P-47N had added outer wing tanks in the longer wings, but the clipped tips gave it roll better than the normal wing.

On the P-80 the better roll may be with empty tanks, I read the same for the F9F's perminant tip tanks.

And is the 2-D effect the same as the "endplate effect."

claidemore · May 5, 2008

buzzard said:
I've always wondered how many '109 pilots died because of that crappy canopy. If they could make something like the Me 262, you'd think that, at the very least, the Galland hood could have been introduced by '42.

Back in 1938? they tied a couple 109 airframes to a radial engine for testing. Those two 'radial 109s' did have a bubble canopy, much like the one used an the FW190.

Yet they did not introduce the bubble canopy into production 109s. I asked Soren why, he said it was because they caused more drag. Not sure if thats true, or if they didn't want to go to the trouble of retooling production (odd since the Soviets did it for Yaks and La5s), or if it was a stability issue. (109 has a fairly small vertical stabilizer.)

kool kitty89 · May 5, 2008

Also the Galland hood offers pretty good visibility with that narrow fuselage, and it was a fairly simple conversion from the older canopy design. And due to the small fuselage there isn't much space to cut away decking for a bubble canopy, meaning that the added view wouldn't be much better than with the Galland hood. A sliding canopy has other advantages over the hinged on though.

Plus the pilots field of vision is also limited by how far he can turn and look over his shoulder anyway, without a mirror. (usually limited to something like 280-300 degrees) Granted another advantage of the bubble canopy would be the internal mounted mirror. (otherwise necessitating an external mirror which added drag)

Plus buzzard's original comment was on the delay in implementing the Galland hood, the "crappy canopy" being the older one.

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