Peter Stickney wrote:

I'm back, but an ahem, "flying visit" Trade Show season for us is
coming up, and I've just shaken off a 48 hour attack of the 24 Hour
Ebola...

In article ,
Guy Alcala writes:
The Revolution Will Not Be Televised wrote:

snip

I've managed to latch onto a few Spitfire Pilot's Notes.
Specifically, the Mk V/Seafire II/III, the Mk XII, the Mk XIV, and the
Seafire Fr. 46. (No Mk IX yet, dangit!) I'll gove more exact quotes
tomorrow, but I'll sum up a bit here, as appropriate.

snip Spit XIV tank sequence comments

Two at a time, not in squadron/wing formations, and not having to take off in IFR
conditions and climb above clouds on instruments. It was recommended to send them
to Malta singly, but Park preferred two so that if one had problems, the other
would have some idea where the a/c went down, so they might have some chance of
rescuing the pilot.

Oddly enough, the Spit V notes has an appendix to th handling
instruction for the 29 gallon fuselage tank/170 gallon super drop tank
combination. A few salient points: The aircraft is restricted to
straight and level flight until the drop tank and the rear fuselage
tank are empty. There are a lot of warning about how setting the fuel
cocks wrong will case teh system to siphon fuel overboard. The
sequence of use was to take off on the main tanks, switch to the
drop tank and run it dry (indicated by the engine cutting out - the
Spitfure Fuel gages must have been designed by the same bloke who did
the MG oil gage. Lucas, I think his name was.) The the rear tank is
emptied, (Same fuel gage), then the mains. The drop tank may be
jettisoned at any time, as long as you're straight and level, empty,
full, or in between. Nothing but straght and level until the rear
fuselage tank empties.

So - while it appears that the 29 gallon tank wa only intended to be
used with the 170 gallon tank for the Malta reinforcements, there's
really no reason why it might not have been considered, with the
proviso that you couldn't fly a real formation, or engage in combat
until it was empty, or that it couldn't be used with one of the
smaller "combat" tanks. Note though, that the 90 imp. gallon tank is
also restricted to straight and level flight.

That's a bit more flexible than I thought it would be.

I don't understand your conclusion. The pilot's notes essentially say it can't be used
for combat, which is exactly the _inflexibility_ I've been talking about. Did I get lost
somewhere? BTW, that fuel usage sequence sounds like a pure ferry setup for max. range,
unless the fuel feeds are vastly different between the Mk. V and later a/c. You'd want
to empty the drop first and retain the internal fuel, so that you could drop the external
tank for minimum drag if the winds were worse than predicted. Otherwise, for handling
purposes you'd want to empty the aft tank first, as with the Spit XIV notes.

snip much Gavin/Guy back and forth

On that basis, the use of the 29 gallon rear fuselage tank can't be
ruled out on the basis that the RAF preferred not to use it. If we
left it to RAF institutional preference alone there wouldn't have been
any rear fuselage tanks at all, but then nor would there have been PR
Spitfires to start with.

I think the Mk. IX could probably have gotten away with a 29 gallon tank or
something in that range, even with the original tail. I have serious doubts that
the Mk. V could have. Tuttle's comments imply negative longitudinal stability with
ANY fuel in the tank, and that means it is of no help to us for increasing fighter
combat radius. We could put the same fuel in a larger drop tank (at somewhat
higher drag, to be sure), say 120 gallons; the handling will be better than with
the rear tank, and it's a much simpler solution.

See above. I was rather surprised myself. The 90 gallon tank is
pretty much out as anything but a ferry tank,

I'm not sure what you mean by this. It seems to have been carried for combat missions
fairly routinely by Spits VIII/IX/XVI (indeed, the handling trials of the Spit XIV say
the a/c has no range without one, although that a/c admittedly has a more forward Cg than
the Merlin Spits), and while you certainly wouldn't want to get in combat with the thing
attached, it doesn't seem to have made the a/c longitudinally unstable by itself
(neutral, maybe), when full. It was certainly less Cg shift than carrying 66 or 75
gallons aft of the pilot's armor plate.


but an intermediate
choice of a 50 or 60 gallon tank would provide the same fuel capacity
over the 30 gallon combat tank as the aft fuselage tank would, without
much in the way of bad effects. (Didn't the Hurricane use a 50 gallon
teardrop or torpedo shaped tank? It might even be less draggy than
the 30 gallon blister.

Guy