Re: Calling Guy Alcala: The Return of the Spitfire Mk VIII LR escort from Beyond the Grave
- From: Admiral Sir Francis Haddock <Gavin.Bailey@xxxxxxxxxxxxxxxxxxxxxxxxxxx>
- Date: Sun, 20 Nov 2005 10:14:31 +0000
On Sun, 20 Nov 2005 18:32:14 +1100, "Geoffrey Sinclair"
<gsinclairnb@xxxxxxxxxxxxx> wrote:
>What about fuel reserves?
No planned, literally. I think the margin for reserves, such as it
is, comes out of the 15 minute combat rating and the assumption that
the cruise consumption all the way out and all the way back could be
reduced for a reduction in TAS.
>The 23 gallons allocated to climb, assuming 1.1 gallons per minute,
>yes I know this is wrong, would leave the Spitfire around 20 to 30
>miles from the airfield it took off from.
30 miles, I estimate, but this might be consumed by high-level
assembly and meeting the bombers.
>In effect a 25 gallon reserve would deduct some 140 or so miles
>from the range and 70 miles from the radius.
Sure but in a world where some of the Spit IX's escorting the first
Schweinfurt raid ran themselves out of fuel over the channel and
glided back to the English coast, I think the lack of reserve is not
ahistorical. It seems to have been left to individual pilots and
their formation leaders to monitor their fuel consumption and act
accordingly, allowing more aggressive leaders to risk running out of
fuel entirely (e.g. the loss of 133 squadron over Britanny).
>Hang on,
Looks like my sums were at fault here. I shall chastise my pet
mathmetician.
>The original design has 63 gallons or 304 miles for cruise, the
>extra 75 gallons internal fuel adds 362 miles,
125 minutes total cruise endurance on internal fuel (minus climb and
combat allocations, no reserve), giving a still air range of 666
miles.
>an extra 90 gallons
>external fuel adds 434 miles less the effects of drag on the tank,
>all up 1,100 miles or 550 miles radius.
My guess was an extra 81 minutes endurance at 300 mph for the same
fuel consumption, giving 405 miles range.
This gives a total estimated range of 1,071 miles, for a radius of 535
miles.
>All of the above ignoring the inevitable loss of range thanks to the
>weight of fuel and especially the drag of the external tanks(s).
The weight isn't going to make a substantive difference as I see it,
except to initial rate of climb. I've factored in the assumed drag
for the tank-carrying stage, which can only be on the outbound leg.
>Put it another way, for the Spitfire 23 gallons for take off and climb,
>36 gallons for combat, 25 gallons for a reserve, 4.8 miles per gallon
>at 320 mph at 20,000 feet. Maximum internal fuel 199 gallons
To quibble, I prefer 197 (probably down to the precise capacity of the
two wing leading-edge tanks).
[Official range figures]
>Yet the figures above give the mark VIII a maximum radius of 150
>miles at 20,000 feet or less than 25% of the official range.
Yes, I've posted on this issue before, the RAF were just as
conservative with the Mustang III range.
>Mind you given the weight of fuel involved there would have to
>be some airframe strengthening, since 310 British gallons of
>100 octane fuel weighs 1 long ton. The extra 75 gallons internal
>fuel alone comes to 541 pounds, the external 90 gallons another
>650 pounds. Then add the weight of the tanks. The maximum
>permissible weight for a wartime Spitfire VIII was 8,000 pounds,
>with normal loaded weight around 7,800 pounds. Also we have
>definition problems, the mark XIV figures are take off 8,475 pounds,
>maximum permissible 8,500, then10,280 pounds maximum overload.
>Carrying a 90 gallon tank meant the mark XIV weighed in at 9,278
>pounds for example. So a Spitfire VIII should have a maximum
>overload weight of over 9,000 pounds.
The issue here can be resolved by operational necessity - after all,
the weight of the fuel was a reducing problem as it was burned off.
[Mustang range]
>Vickers apparently had a proposal for 197 gallons of internal fuel
>something like 47 + 49 in the front fuselage 2 x 18 (1 in each wing)
>and 66 gallons in the rear fuselage, which I know totals 198 gallons.
>Then add external tanks. Even with this arrangement the Mustang
>has more internal fuel.
Sure, but the idea was not to out-Mustang the Mustang, simply to
optimise a long-range escort Spitfire within a credible historical
context. The rear fuselage tankage was tried and introduced by 1945,
and the internal and overload tankage is historical and even
contemporary with a last-quarter of 1943 initiative.
>All up I suspect giving the Spitfire a 400 mile combat radius over
>Europe was quite possible, 500 miles would be the absolute limit
>and require significant work given the stability problems reported
>with the rear tank,
I think issues like the elevator horn balance enlargement and change
of elevator as reported by Quill were all possible to assist. This
leaves the Mk VIII (LR) unpleasantly longitudinally unstable on
take-off and until about 30 gallons of fuel in the rear fuselage tank
have been burned off.
>After all the gallons being mentioned should this be the time to point
>out a US mile is about 0.0002% longer than a British one?
I think as sub-contractors to the MAP we can safely ignore margins of
such magnitude, as the MAP certainly will.
[Historical detail on US penetrations and escort ranges]
Thanks. This ties in with my idea of having the Spitfires working
within (and slightly extending) the P-47 escort range, both as
additional escorts to the 8th AF and escorting strikes on German air
fields likely to be used to intercept them.
>Note there was a major shortage of drop tanks in 1943, given the
>time taken to agree they were needed and agree on the specifications
>for the tanks.
Aha. this was certainly the case for the 8th AF, but Fighter Command
and Mediterranean Air Command were happily using 30, 45 and 90-gallon
drop tanks and had been since 1942.
>>Can I now re-equip 2 Group with Stirlings to be escorted by them?
>
>Last quarter of 1943?
Yup.
>Admittedly the peak Stirling bomber production
>was in May (81), June (82) and August (82) 1943 but the decline in
>bomber versions set in quite rapidly in 1944 even as the total number
>of Stirlings built remained roughly constant, in January 1944 around half
>the Stirlings delivered were transports and the percentage increased
>roughly mid year as production was cut back.
Yes, but this is a factor of their historical removal from bombing
operations. This time out, I can dispute reduction and elimination of
production with Harris, although this might cost him some Lancasters
in late '44 or '45 as a consequence.
I'm trying to get 2 Group into action with bombers that operate
roughly at the same heights as their Bostons and Mitchells did, but
carry more than twice the bombload and have a longer range.
>Admittedly if you can show the use of such escorted missions then
>the line was still going at near maximum capacity to June 1944, then
>deliveries dropped. So 834 bomber versions delivered in 1943 out
>of 836 Stirlings built. In 1944 it was 298 bombers out of 675 Stirlings
>delivered. The first half of 1944 saw the delivery of 234 bombers
>out of 441 Stirlings produced. There was 1 bomber and 202 transport
>versions delivered in the first 9 months of 1945.
This is plenty to re-equip the six to eight two-flight squadrons
involved in 2 Group, and can see me hitting German fighter airfields
with about 250,000 lbs of HE bombs in one 18-aircraft attack instead
of about 72,000 lbs using the medium bombers.
All I need now are some .5in MG's to replace their .303's, and I've
got a viable force for daylight ops in support of the 8th AF.
Air Marshall Gavin Bailey
--
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- From: Geoffrey Sinclair
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