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The Spitfire Site

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Author Topic: Bubble Top  (Read 2292 times)
JamesF
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« on: May 01, 2011, 01:59:47 PM »

Anyone have any info on the bubble top canopy development?  I've heard the bubble top canopy came out in 1942 already, and despite test pilots reporting vastly improved visability, it onle came on line as such in I think 1944?  Apparently the low back of the fuselage could effect lateral stability (was less stable), but it sure looks pretty, although not "traditional"?  Perhaps the need to change production lines and drawings was going to cause too much trouble?  In Malasia, Ginger Lacey refused to fly a bubble top, saying that "it wasn't a Spitfire"!
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Edgar Brooks
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« Reply #1 on: May 01, 2011, 11:20:33 PM »

1942 is a bit early, according to my information; a rear view fuselage, for the VIII, was discussed, in the Local Technical Committee, 26-1-43, and JF299 was modified, with trials undertaken at Boscombe Down from 16-9-43. Further discussions took place in the L.T.C. 11-1-44, this time including the IX & XIV; at that time it looks as though the VIII was dropped from the equation (maybe not needed in the Med?)
 Finding out what, and why, things happened, isn't easy, but, so far, I've found that a decision was taken, to fit fuselage tanks behind the pilot, in all IXs & XVIs, in late 1944, but this was immediately challenged, due to the degredation of performance, at height, which was going to be vital, if, as expected, jets were going to be encountered at around 30,000'.
 It appears (no proof yet) that it was decided to keep the mods to low-level Marks (which included the R.V. XVI & IX,) and this delayed things even more, since the tanks meant that the wings had to be converted to "E" configuration, since the compressed-air bottles were displaced, and had to go into compartments formerly occupied by 2 .303". The other two compartments were "highjacked" by an extra pair of oxygen bottles, needed for the longer flights.
 The IID gyro gunsight was now available, but the "black boxes" had to be fitted before the tanks (another delay,) and the extra weight also meant that the aircraft had to have metal elevators. It's possible (again, no proof) that the XVIs had the altered u/c tracking, so needing more wing mods, and definitely needed stronger (4-spoke) wheels to cope with the under-wing bombs (more mods needed for the fittings.)
All of this meant that the R.V. airframes weren't cleared for service until January (at the earliest) 1945.
Edgar
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JamesF
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« Reply #2 on: May 02, 2011, 01:15:51 PM »

Thanks Edgar, that is very interesting.  Never coupled it to the XVI wing and rear fuel tank story.  I had heard another significant problem with the rear fuselage tanks was it put the aircraft on the rear Cof G limits, for example the P51 Mustang (dare I mention that name on this hallowed site!!??), pilot notes contain some dire warnings about pulling out of dives with a full rear tank, in that an uncommanded nose up pitch could result, leading to airframe overstress.  I think the Spitfire had the same problem?  You have answered some questions about the South African Air Force Museum Spitfire in that it was apparently a quite rare MkIX, but looked like a MkXVI to the casual observer being a bubble top/clip wing aircraft.  However it had a Merlin engine, no rear fuel tank and had the Oxygen and compressed air bottles in the standard place.  However the wing had the main wheel geometry change bulge and was an "e" wing, with the Hipano and a .5 Browning.  Incidently, the cannon and .5 were installed in the gun bays when the aircraft was re-built, and that was also to keep the empty weight C of G in a normal position from the datum.
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Edgar Brooks
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« Reply #3 on: May 02, 2011, 04:57:25 PM »

Other threads, on other sites, are jumping on the "low-back" bandwagon, due to the Tamiya kit of the XVI, so I've been going through some of my researches. The first "proper" low-back XVI didn't go for testing until March, 1945, which is a pretty good indication why so few saw action, I reckon. In 1942 the C-in-C Fighter Command wanted the .5" + 20mm armament, but the Air Ministry said that, from behind, it had no advantage over the .303", and they preferred the weight of shot from 4 x .303", in a deflection shot, (i.e. missing the armour) since it was more likely to disable the pilot, also given the relatively poor aim of the average pilot. When the gyro gunsight became available, opinions changed, almost overnight, since it increased a pilot's accuracy beyond measure. To fit the G.G.S. into the XVI had to be done before the tanks, though, because of the necessary extra boxes and wiring.
Edgar
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