In article ,
(The Revolution Will Not Be Televised) writes:
On Wed, 17 Sep 2003 01:38:38 -0400, (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...

The excuses an engineer will come up with in order to lock himself
into a darkened room with his slide rule....

Well, we all have our faults.

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.

Peter, I've scanned the whole Mk IX Pilot's Notes for you and Guy, but
my last attempt to send you extracts bounced due to lack of space on
your mail account. I can't put them up on a website at the moment, so
I can only email them. Contact me at -



if you have another account I could send the scans to you at.

I do, and I shall.


[rear tank in Mk XIV]

So, it was there, and it was a somewhat useful amount of fuel, but it
really wasn't considered a good thing.

The FR XIV was the only XIV to get rear tanks, the fighter version
with rear tanks mutated into the Mk XVIII when it started to be
produced on the XIV production lines in the summer of 1945.

There's no doubt that that this represents further evidence of
institutional RAF intolerance to longitudinal instability caused by
rear fuselage tanks to my mind, and it reflects the post-war position
as indicated by Pilot's Notes instructions for other versions of Spit
with the rear tanks.

I can certainly accept that this institutional intolerance existed, as
I have been asserting that from the start of my contributions to this
thread, but as I've said to ACdre Alcala, that intolerance needs to be
balanced against operational need: the the case of the Spit IX/XVI
and Mustang IV, the RAF accepted rear fuselage tankage at the price of
instability for pressing operational reasons. As soon as the war ends
and those operational reasons no longer apply, the institutional norm
will obviously reassert itself. Where I think we should be careful is
using post-war, peacetime evidence of this dynamic and reading it back
into operational service requirements where evidence exists that the
RAF was prepared to compromise their attitude.

I'd love to see the Pilot's Notes for the Mustang IV, as I suspect
they will have some interesting comments on handling and use of the
rear-fuselage tank.

Would you settle for the RAF Mustang III Pilot's Notes? I managed to
land a copy of those, as well. WRT the fuselage tank, the procedures
and warnings are teh same as those for the USAAF: Burn teh fuselage
tanks down below 40 gallons before switching to the drops, and avoid
fighter-type maneuvers befire then. It's interesting to note the
difference in the wording, between the two aircraft. The Spit is
definitely in the "Don't do anything!" category, and the Mustang is in
the "We really don't recommend this, but..." form. No admittedly, the
Mustang's fuel tank position is much better, in terms of its effect on
stability, and the Mustang was a bit more stable than the Spit to
begin with. I wonder how much of this is the manufacturer's bias
leaking through.


[snip Spit V with 170 gal overload tank and 29 gal rear fuselage tank]

Nothing but straght and level until the rear
fuselage tank empties.

Yes, but this is for an aircraft in ferry trim, and I don't think any
larger conclusions can be safely drawn when it's CoG standard was so
different from ordinary aircraft (no cannon, radios repositioned, etc)

True, but ferry trim in thas case includes the 1225#
Mondo-Pregnant-Guppy ferry tank, which had its own bad effects.
Adding the Hispano guns actually moves teh CG forward - those long
barrels & springs & things add weight forward, so that will make
things better. The Browning Guns have most of their weight in the
breech, and move teh CG aft. So, A Spit Vc with 2 Hispanos could
still work.

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.

My thinking was for an extra 29 gallons for early formation flight on
the climb for maybe 20 minutes, with any remainder contributing to the
flight reserve fuel load. As Guy has pointed out, rear fuselage
tankage capacity which comes at the expense of stability cannot be
considered optimal or even tolerable for combat conditions. In
response my contention is that the requirement is for endurance
coverage of long oversea flights out over the North Sea to potential
combat areas over Holland and Germany in the summer of 1943, and the
29 gallon tank in addition to the 90 gallon drop tank would increase
the operational radius in this respect, even if the combat endurance
when the aircraft got there was minimal.

Actuall, the 29 gallons would basically get you through your 20
minutes form-up and climb. Merlins tend to be a bit thirsty at that
point, burning something on the order of 80-100 Imp. Gal/Hr.

The 90 gallon tank is pretty much useless as a combat tank. Again, no
maneuvering flight allowed, and teh tank's to be punched off
immediately when emptied. Not much use if you're in Bad Guy Country.

A 29 gallon fuselage tank, combined with a less-disruptive and more
tactically useful 50 or 60 gallon tank will give about the same amount
of fuel as the 90 gallon tank, without (after the fuselage tank's been
used) the combat restrictions, and the extra drag of teh 90 gallon
tank.

But was it? After all, with no armament, the Cg moved forward. No radio (mounted
aft of where the cameras would be) moves it forward again. And quite early, they
got external fuel, in 30 gal. blister tanks under the wings.

Not only that, but a PR Spit wasn't expected to be maneuvering - It's
job was to be as high as possiblem where nobody had any maneuver
margin. They'd get to height as soon as possible after tankeoff, and
stay there.

On the other hand they were required to evade contact with
manoevreability when required. PR pilots were always expected to drop
external tanks on contact.

Yabbut, evading contact with maneuverability in this context consists
of seeing the Me (Fw's aren't going to get that high) coming up, and
making a course correction such that the interceptor has to make a
major change to cut you off. The changing again. Where there wasn't
much of a speed advantage, they can't get up to height in time to
catch you, amd, with an Me 109, you can very well run him out of gas.
If ye does goet up high, dogfighting isn't the high-G high-powered
affair that it is in the thicker air below 20,000'. Instantaneous G isn't
very high - on the order of 1.5-2 G, at best, and speed bleedoff is
pretty high. It's more of an Elephant Ballet than cut-and-thrust
fencing.


A good chunk of the aft fuel would get burned off in the
climb. It's also worth noting that the PR Spits had no disposable
load other than fuel. On the fighter Spits, the ammunition was aft of
the CG, (but not too much) and contributed to any stability problems.

There's also the issue of aft ballast, which varied greatly over the
life of the Spitfire, and over the lifespan of individual marks. The
V is a case in point, and where the equipment loading becomes
bewildering.

Yep. The thing with teh ballast, though, is that since its fixed, its
effects are predictable. It's teh shifting of weight around that's
the problem.

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

Ah, but it was actually used by Spitfires and Seafires (with even
worse CoG issues than the Spit V) in combat operations. Examples
include Salerno and Normandy. There was a slipper-tank version and a
later torpedo-tank version. I suspect they would have been used
despite the tank shortcomings: the stability problems would lessen as
the fuel was consumed, and the 8th AF fighters demonstrated that
unpressurised, unreliable paper-mache tanks still could give a useful
benefit to escort radius.

Still a big drag hit, though.

the USAAF 108 gallon tanks weren't, strictly speaking, paper-mache,
they were "fiber impregnated with resin", or, in more modern terms,
epoxy over a cardboard form.

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.

They actually used a 45 gallon slipper tank as well as the 30 and 90
gallon versions. The 44 gallon Hurricane tank was an unpressurised,
unjettisonable ferry tank, with one carried beneath each wing to give
88 gallons ferry capacity. I have actually seen a photo of a Spitfire
on Malta with an improvised 2 x 44 gallon fuselage tank, although I
suspect this was a local modification made possible due to the
presence of old Hurricane ferry tanks from ferry flights from
Cyrenaica and the lack of the newer slipper tanks until later in 1942.

Whatever happened, the tanks were going to be jettisoned before
initiating combat, so I don't think the 90 gallon tanks - which should
be substantially emptied and consequently lighter before the aircraft
got to the prospective combat area anyway - would in those
circumstances impose as much of a performance restriction as we might
suppose.

True - I was thinking in terms of a way to add 90 gallons to a Mk V's
fuel capacity (Which would be about 50% of total fuel anyway) withoug
the stability and drag penalties that the 90 gallon tanks imposed.
(It's not much good being an escort fighter if you cruise slower than
the bombers that you're escorting.) To my ming, 29-30 gallons
internal, with another 60 or so external would about do it, especially
if the 60 gallon tank has no restrictions.


Remember, I'm not asserting that any of this was an optimal solution
for long-range escorting, or could have competed with aircraft that
were better suited to expanding their internal fuel capacity. I'm
trying to work along the lines that would be dictated by operational
neccessity and addressed with existing equipment and experience in
certain circumstances.

Well, in htat case, gin up a 60 gallon tank, and add teh 2 13-gallon
leadig edge tanks. The 80 gallon tank would give you about 40% of teh
total fuel, allowing it to be empty before the target area is reached,
and the 13 gallon tanks can be swapped in as a Deport-level job. They
fit in the leading edge outboard of the 20mm gun bays. but inboard of
the .303s, and slotted in between a pair of ribs. That sort of
sheet-metal work would be well within what they could do withoug a
need fr a factory-level rebuild.

--
Pete Stickney
A strong conviction that something must be done is the parent of many
bad measures. -- Daniel Webster