#1 Jet of World War II

Let's just say my reply has been delayed, but here goes.


The Revolution Will Not Be Televised wrote:

On Sat, 09 Aug 2003 18:50:48 GMT, Guy Alcala
wrote:

snip

[rear fuselage tanks in Spit Vcs]

I think you may be underestimating the difficulty re the Mk V. Quill, in His
"Spitfi A Test Pilot's Story," devotes an entire chapter to "Longitudinal
Stability and Increased Range."

Yes, but a close reading of that source and others leads me to the
conclusions which follow.

Ah, now we can compare close readings and interpretations of same. Onward.

He describes the weight additions and Cg
problems that led to the installation of bobweights on the Mk. Vs, as well as the
first fitting of a 75 gallon tank to a Mk. IX (ML 186), which he flew from
Salisbury Plain to the Moray Firth and back at low altitude and economical cruise
-- this a/c had a bob-weight in the elevator system plus an enlarged horn
balance. Quill writes that "the aeroplane was unstable to start with but as soon
as I had used up the rear fuselage fuel the handling was back to normal . . ."

Precisely the same condition as experienced with the rear fuselage
tank in the P-51B. I'll admit upfront that the CoG issues with the
Spit Vc/IX airframe were more serious, but this was not a binary
issue: it came down to what level of initial instability with a full
rear tank the institution concerned was prepared to tolerate.

I suggest, on the balance of evidence I've seen (which I admit is not
comprehensive), the RAF were far more sensitive to this than the USAAF
was. A case in point is the rear fusleage tank in the P-51B/Mustang
III. The instability caused by a full 85-gallon rear fuselage tank
was no different between Mustangs in RAF colours and those in USAAF
colours, the critical difference was the institutional appreciation
involved, which saw the RAF delete it entirely while the USAAF adopted
it happily. I suggest that the USAAF approach to rear-fuselage tanks
was materially different, and a similar need for long-range escorts
for a daylight strategic bombing strategy on the part of the RAF would
have entailed a similar approach as the USAAF adopted: i.e. the
instability would have been accepted in order to achieve the desired
operational aim.

Perhaps so, but again we're talking about the Spit, not the Mustang, and the former,
as you agree, had more problems with this.

I won't go into the institutional differences in detail here, but the
whole counter-factual only works if we adopt a USAAF-like commitment
to daylight strategic bombing. Absent that commitment, with all that
it entailed in terms of forcing long-range escort capacity regardless
of the difficulties (such as CoG issues with increased internal
tankage), and there wouldn't be any RAF daylight bombing effort to
start with. Without one, the other does not follow, but if we're
positing the first, we need to accept that this would modifiy
historical RAF fighter procurement and equipment beyond the historical
norm. In short, attitudes to things like the acceptable level of
temporary instability in a Spitfire with full rear-fuselage tanks
would have to change.

We agree on all the above, but I posit that the commitment would result in a shift to
Mk. VIIIs (or Mk. IXs with similar tankage), accepting the likely temporary decrease
in production.

While he and Joe Smith felt that some longitudinal instability at the start of
the flight was acceptable (as with the Mustang), the margins seem to have been
much smaller in the case of the Spit. The Mustang's stability was judged
acceptable once the rear tank was down to somewhere between 25 and 50% (opinions
differ),

Much like the behaviour of the actual Mk IX/XVIs with rear-fuselage
tanks in 1945.

True, but those Mk.IX/XVIs also had extra fuel in the regular fuselage tanks (ca.
94-96 gallons, depending on the source) forward of the datum. And correct me if I'm
wrong, but ISTR that only those a/c with cut-down rear fuselages got the aft tanks;
the aft fuselage of those a/c should have been lighter. Add in that the regular Mk.
IX was carrying around fixed ballast in the tail, and had CGs in the 4-5.0" aft of
datum range, when the Mk. Vs were in the 8-9" range. See

http://www.fourthfightergroup.com/eagles/ab197.html

as well as various Mk.V data from the same source:

http://www.fourthfightergroup.com/eagles/spittest.html

and if you want to extend the escort range it's the amount of fuel you
can carry internally to fight and return on that determines escort radius, no
matter how much fuel you hang externally to boost endurance.

Agreed. This is why the rear-fuselage tankage issue is critical to
this speculation.

Not for combat radius/return, unless you can use rear fuselage tankage for that;
otherwise you're just extending the endurance and ferry range. The Mustang could only
retain a fraction (ca. 25-50%) of that rear tank fuel to use for combat without being
dangerously unstable, with the contemporary Spit possibly (probably?) being unable to
retain any of it; at best, it could retain the same fraction as the Mustang. The
Mustang with rear tank didn't have 269 U.S. gallons to fight and return on; it had
somewhere between 205 and 227, depending on what fraction of the aft tank capacity
allowed acceptable combat handling.

To be an acceptable long-range escort, the Spit still needed the extra forward
fuselage fuel of the later Mk. IXs and the Mk. VIIIs, plus the leading edge tanks of
the latter. The Mk. VIII carried 124 Imperial gallons internally (149 U.S), ALL of
which was usable in combat, plus whatever extra fuel usable in combat (if any) a rear
tank provided.


They key difference between the Mustang and the Spitfire here, I
suggest, is institutional, and not just a matter of engineering. The
two Mk IXs with internal capacity enlarged by Wright Field at the same
time (July 1944) are a similar example: the RAF turned them down,
while the USAAF were clearly prepared to tolerate engineering
trade-offs (such as changes to the wing structure) that the RAF
wasn't. I suggest this gives us an indication of the approach
differential involved on an institutional basis which transcends the
engineering problems.

In the case of the Spit wing it seems to have been a strength issue, at least
according to Quill

I fully accept that the Spit had less CoG margins to play with, but I
still believe the required engineering solutions were at hand. On a
chronological basis, the bob-weight issue first came into focus when
Tony Bartley returned to operations with 65 Squadron after a spell
working under Quill as a test pilot at Supermarine, in February 1942
(as mentioned in the memoirs of Quill, Bartley and the other flight
commander in 65 Sqn at the time, Geoff Wellum).

The bob weights were an immediate answer to the failure of squadrons
to properly maintain the equipped CoG of their aircraft. I suggest
that a greater institutional emphasis on maintaining correct CoG
weighting would have had an impact on this. More relevantly,
solutions to this issue which gave a much greater margin of CoG
movement were at hand, as Quill states in the same chapter, with the
trial and testing of an improved Westland elevator (October 1942) and
an increased elevator horn balance (tested early 1943). In addition,
long-range reinforcement flights from Gibraltar to Malta in October
1942 actually involved the use of a 29-gallon rear fuselage tank in
addition to the 170 gallon drop tank used in the Vcs involved. So I
suggest basic experience of rear-fuselage tankage, and measures to
combat the worst CoG issues resulting were at hand in plenty of time
to have an impact on the postulated fitting of rear-fuselage tanks in
the summer of 1943.

The difference being that the flights to Gibraltar were ferry flights, and no
formation maneuvering or combat flying with the aft tanks full was required. The
Mustangs didn't do so either, except by mistake; SOP on long missions was to take off
on the left wing tank (it had the fuel return line, so some fuel needed to be drained
from it or it would dump overboard), then switch to the aft tank once sufficient
height was reached, burn that down to an acceptable level for combat handling, then
switch to the drops and empty them before going back to the rear tank, and only then
to the main tanks.


Talking about the development of the Mk. XIV into the Mk. XVIII, Quill writes
that "the basic stability margins of this aircraft, with its more forward center
of gravity due to its heavier engine, and with the latest standard of modified
elevator and the larger vertical tail surfaces, were thought likely to be
adequate to enable the aircraft to be cleared for long-range escort duties
accepting some instability in the early stages. However, we had more difficulty
than we anticipated in reaching an acceptable standard of handling with the rear
tank in use and the war was over before it was possible to clear the aircraft
with the rear tank in full operation."

In the end, even the RAF cleared the rear-fuselage tanks for
production usage in 1945, and they were happy enough to fit half of
the tankage in the FR XIV and the full thing in the XVIII.

Again, both a/c with cut-down rear fuselages. Getting to our respective readings and
conclusions on Quill, I note that he says in the case of the Mk. 21 that he disagreed
with A&AEE on whether the Mk. 21's handling was acceptable at a certain point, and
that he felt that such handling deficiencies could be accepted to get an a/c with
superior performance into the field (he's also man enough to admit that he may have
been overconfident by this point that average squadron pilots wouldn't have had
serious difficulties, based on his own skills). Now, it may just be a question of him
not thinking to mention it, or the way he worded it, but he maentions no such
disagreement between himself and A&AEE regarding the handling of the rear fuselage
tank-equipped a/c; he just says that the handling wasn't acceptable for a long time,
and required a lot of development.

I'm certainly not going to claim, based on such flimsy evidence, that this is
definitive proof that the a/c couldn't have been flown in operations with an aft tank
with accceptable handling much earlier given sufficient motivation, especially given
your comments re the prevailing attitude of the A&AEE. But I do think it at least
suggests that the Cg problems were real and agreed to be so by both the A&AEE _and_
Quill. And that's as far as I'm prepared to gaze into my crystal ball. Your reading
may well be different.


I suggest
with the equivalent of Eaker, Spaatz and Arnold lighting fires under
people's arses to increase range in 1943, this would have happened
earlier.

Not Eaker or Spaatz; it was Arnold through Giles. From "To Command the Sky":

"Under the pressure of events in Europe, in June 1943 Arnold gave Barney Giles [DCAS]
6 months 'to get a fighter that can protect our bombers. Whether you use an existing
type or have to start from scratch is your problem. Get to work on this right now
because by January '44, I want fighter escort for all our bombers from U.K. into
Germany.'"

As to someone lighting fires for the R.A.F., that was what Pete and I were
postulating, only for the Spit IX/VIII, with the highest priority to getting increased
range British fighters in the U.K. soonest, with all other Spit improvements pushed
back. Grabbing available Mk. VIIIs first (the MTO and CBI/PTO will just have to suck
it up for a while), at the cost of MK.XII/XIV production, then either expanding Mk.
VIII production at the cost of the Mk. IX or (if possible) transitioning to Mk. IXs
with the extra leading edge tanks of the VIII, with aft fuselage tanks and whatever
airframe mods required to pack usable _combat_ fuel in.


I'm happy to accept that the Vc would have had proportionately more

CoG problems than the Mustang, but the overall problem seems
identical. Allowing for some flexibility in terms of the final
compromise (maybe a tank size between the 29-gallon ferry tank of 1942
and the 75-gallon rear tank of 1945) would seem reasonable, but
dismissing the option altogether goes too far, I think. Operational
neccessity was a powerful advocate. Absent the need to escort their
own bombers in long-range daylight raids, the RAF had no need to
pursue the issue with the same vigour and tolerance for compromises
that the USAAF had, so I don't think we can take their historical
behaviour absent this need in the first place as the ultimate
determinant factor when we speculate on their behaviour in a scenario
where this factor exists.

I agree, but see my comments re the difference between ferry fuel and combat fuel.

[Spiteful tail]

I suggested the larger Mk VIII tail for similar reasons, given that it
actually was produced in a relevant timescale. Increasing the tail
area was a significant issue, and there were moves afoot to do so in
production long before the Spiteful tail. Again, not an optimal
solution, but an improvement that works towards operational utility in
the timescale involved without major production issues coming into
play.

Sure, and that with an aft tank was next on the agenda after boosting production of
the standard Mk. VIII/leading-edge tank Mk. IX. Either of the latter should have given
us an escort radius of 250-300 miles.


The two-stage Merlin was shorter and lighter than the Griffon, but was still
about 6" longer (second stage supercharger case) and 200 lb. heavier than the
single stage Merlins, and the Mk. Vs had already been suffering from overstess
breakups due to too far aft Cg prior to the fitting of bobweights. I don't think
Mk. Vs would have worked.

Well, I appreciate your point, but I have to disagree. Remedial
measures were in hand - Quill attributes the bob-weights and horn
balance eliminated the overstressing issue, and these were in play
before the time-scale in question in the summer of 1943.

The Mk V would clearly not be optimal as a long-range escort on
performance grounds, but then neither was any wartime mark of Spitfire
on other grounds. The key issue for the adoption of the Mk V is
availability, and again, as I suggest, this would be played out at an
institutional level. We have to arrive at some manner of execution
which addresses known historical factors which work against this
speculation and the biggest of these, beyond the engineering problems
involved, was the doctrinal reluctance of RAF high command to tolerate
range increases rightly or wrongly perceived as coming at the expense
of combat performance. Without eliminating or at least addressing
that intangible, the whole scenario is a non-starter.

It's interesting to see in the Mk. IX weight and loading chart I referenced above that
the a/c (AB 197) weight includes "Ballast consisting of 5 x 17.5 lb. standard weights
is permanently fitted on a bar situated in the fuselage adjacent to the tail wheel."

Unfortunately, a similar chart for a Mk. V doesn't seem to be available on the site,
but I have my doubts that the Mk. V was carrying around any such ballast in 1943, or
if it did, so far aft. Of course, AB197 was a very early Spit IX (the report date
seems to be June 10th, 1942), so that ballast was probably reduced as more operational
equipment was added, but it at least suggests (combined with the Mk. V's further aft
Cg vs.the Mk. IX as reported in various tests on the site) that the Mk. V was pretty
much at the limit, while the Mk. IX had considerably more Cg range available.


If Mk. VIII airframes were available we would have taken them as is, and asked
for more. Even the unmodified Mk. VIII would get us to the Ruhr at least,
probably a bit further.

This would have impacted on IX production, specifically at Castle
Bromwich, which hadn't fully gone over to the IX until October 1943.
I fully appreciate the operational benefit of the VIII vs IX in this
situation, but I fear you underestimate the pressures for maximal
production which argue against converting all IX production to VIII
airframe standard. There were major political ramifications to
cutting back IX availability while there was a world-wide need for
them, including lend-lease supply to the USA and Soviets, and even
more the internal RAF requirements for offsetting wastage and
re-equipping units in combat over the Channel and in the MTO.

I don't underestimate the pressures, I just think (as you mentioned a few paragraphs
above) that if the decision had been made to go over to daylight, fighter range
extension would have increased in priority and changes would have to have been
accepted, whatever the disruption elsewhere. Because otherwise, it wasn't going to
work.

No need to - the supply of two-stage Griffons was the main bottleneck
for Mk XIV production, and there would still be unmodified Mk VIII
airframes available by the end of 1943 for conversion to Mk XIVs as
the Griffons came along.

Lots of Mk.VIIIs were what we needed, not the Mk. XIV, so we would have grabbed
those airframes.

The Mk XIV was settled long before production started in October 1943,
the number of airframe's you'd be losing in that year (six for
development work most of which didn't need massive work for Mk XIV
testing and ended up testing contra-props instead, maybe 20 for
delivery to operational squadrons) is trivial. Simply cutting out the
Mk VIII airframe allocation to the Mk XII production might free twice
as many as that.

And we'll be happy to take them, and we'll just have to accept the occasional FW-190
Jabo getting through. But we'll also take the airframes that became 610 Squadron's
Mk. XIVs in January 1944.

If we're talking about an operational need in the summer of 1943,

No, the postulated date of the decision (to go over to days) was sometime in the fall
of '43, although the exact date was a bit unclear. It seemed to be in the
September/October timeframe, but we were unable to get ACM Kramer to be more precise.

as I
am, then Mk XIV production isn't a bottleneck in terms of Mk VIII
supply until early 1944, by which time minor contractors (e.g.
Westland) could have been added to the Mk VIII production line even if
it wasn't possible to have Castle Bromwich churning them out full-time
in the short term to the exclusion of all else.

If you're positing a earlier beginning to this, e.g. at the end of
1942, then the industrial variables change, but so do the political
ones. Frankly, I can't see the RAF even attempting anything like a
significant daylight strategic campaign until the USAAF showed the way
in the spring and summer of 1943.

Agreed.

The delay in the Mk. XIV would have been a question of
development manpower available. They were still working out the bugs on the Mk.
XIV at the time, and we would have told them to put that on the back burner and
get tanks into the leading edges of Mk. IXs, convert over to Mk. VIII production,
and/or devote much more effort to qualifying a rear fuselage tank.

I don't think the Mk XIV is as big an issue as you feel it is in terms
of design load, nor the rear-fuselage tankage.

Lacking better data, we'll have to disagree on this point.


What really counted
would have been converting all IX production to VIII-standard, and for
that you'd need Castle Bromwich to join Eastleigh in producing Mk
VIIIs at a time when I just can't see the whole of Spitfire supply,
world-wide, being permitted to be disrupted to facilitate one
campaign. If you have CBAF converting to Mk VIII production from July
or August 1943, you'll have no shortage of airframes for the Mk XIV
and Mk VIII production in 1944. There was a further institutional
concern with maintaining the competitiveness of the Spitfire after the
experience of the Mk V at the MAP in 1942, and this would beed to be
addressed with the Mk XIV (and this would have been useful in 1944
anyway).

I suspect F.21
development would have been held up at Supermarine, as the Mk VIII
airframe (which was the basis of the Mk XIV) was already in series
production. This just means the RAF don't get two squadrons worth of
F.21s in spring 1945, after interminable airframe development work
throughout most of 1944 delays them anyway. No great loss there,
methinks.

See comments above.

I think we disagree over what precisely Supermarine were working on at
the end of '43 and which would subsequently have been affected by the
LR development required.

Right.

Frankly, I don't think much development was
required to field a usable (albeit sub-optimal) LR Spitfire in 1943,
and the things which I believe would have been affected by any
prioritisation would have been the F.21 and the Seafire. It was all
just a question of priority.

No question about it.

See my comments on Spit V Cg problems above. In 1943, with lots of Mk. IXs not
able to do much, I think the effort needed to go there or into the Mk. VIII.

Ideally, yes. But I suggest we have to work closely within the
context of what was likely given the RAF's preconceptions and
requirements at the time. Frankly, I think no LR escort force was
going to impinge upon new production Mk IX supply until the concept
had been proven. Hence the movement of the existing Vc force in 12
Group (which did historical do USAAF daylight escorting) into an LR
mode.

RAF Spits had been escorting U.S. a/c from 1942, so IMO there was no question as to
operational utility, just a question of priority.


The
Spit V was just too inferior at B-17/24 heights, even assuming it could carry the
fuel (better than nothing, I grant you, but I expect fighter squadron morale
would have been the pits).

The key here is having the Vs unshackled from their range limitations.
They were not the best escorts, but they would have been the most
likely to be available. There's no question in my mind that VIIIs/IXs
or even P-47s would have been better. But a 1943 LR effort was not
going to suffer the same critical limitations the RAF and the Spitfire
V force endured over the Pas de Calais in 1941-42, in terms of
operational scope and endurance. Actually escorting a bomber force
the Germans were compelled to consider attacking would have been a
major advantage by itself. The tactical background was going to be
different, and more in their favour, than it was over the Channel on
short-range operations. As it was, in the summer of 1943 the V force
operating over Holland with Vs don't seem to have been demoralised. I
tend to be a little sceptical of Caldwellesque claims in this respect.

They were still in for a hard time, though, I agree. But as a
component part of a diffuse deep-penetration escort, they wouldn't be
carrying the burden alone. And most of all, the Luftwaffe wouldn't
have the freedom to avoid engagement en masse whenever they couldn't
get the tactical advantage, as they could with shorter-ranged Circus
operations.

Good points, and I don't disagree about the utility of the Mk. V as 'certainly better
than nothing,' and better to lose people one at a time rather 7 or 8 at a time Again,
my main concern with the V is whether they could in fact have been given the radius
(not range).

snip various areas of agreement

AOC 12 Group: "Clearly other commands want the LR Spitfire as well.
I suggest the VCAS recommends increased tankage production and the MAP
is instructed accordingly."

And that's what we planned to push for: Mk. VIIIs or Mk. IXs with VIII tanks,
plus whatever extra fuel Supermarine could make work until the Mustangs were
available in sufficient numbers. Ideally, we wanted the Mk. XVI a year earlier.

I don't think the early XVIs actually had the rear-fuselage tankage
when they first came off the production lines (September 1944),

Right, I should have said the rear fuselage tank (and I think they only came in with
the cut-down rear fuselage) about 16-18 months early, as i forget just when those
versions came out, but I think it was only in '45.

but I
think the main reason the tanks didn't appear earlier has far more to
do with institutional preconceptions than the real engineering
problems involved. When it comes to it, if we push the tankage issue
for Spits, there's no reason for them to delete the rear-fuselage
tanks in their Mustangs, either.

Well, if they didn't need them for their own purposes, why carry the weight around?

snip more agreement

Just my opinion, though.

Agrees with our reasoning exactly, with the reservations stated re the Mk. V.

Please desist from this moderate rationality or I will complain to
your ISP.

Did I mention that I have INCONTROVERTIBLE PROOF that the U.K. government has been
testing UFOs ( and dissecting ALIEN CORPSES) at their base at Machrihanish, cleverly
disguising test flights of same as those by Aurora and, in times past, SR-71s? Wait,
I hear the black helicopters coming to get me. I can feel the beams as they try to
alter my brain. Excuse me while I done my tinfoil hat.

Guy