Re: Mustang & Spitfire

On Jan 8, 11:50 pm, p-stick...@xxxxxxxxxxx wrote:
On Jan 8, 6:31 am, Eunometic <eunome...@xxxxxxxxxxxx> wrote:



On Jan 7, 6:19 am, "Jim Hawkins" <jimhawk...@xxxxxxxx> wrote:

I've always been intrigued by the performance differences between these two
warbirds. Same engine, more or less the same size. I know that the
1941-designed Mustang had the benefits of a few years intensive aerofoil
development which the 1935-designed Spitfire didn't, but is that the only
factor ?

The NAA/NACA 45/100 laminar flow airfoils had two main advantages:
1 They were so thick that the Mustang could carry as much fuel in one
wing as the earlier spitfires could in their entire fuselage. The
earlier Spitfires carried all fuel between the engine and pilot right
where the centre of lift of the wing was. Early P-51's carried all
their fuel in the wings. This location is extremely important as it
meant there wouldn't be any trim changes as fuel was used up and also
so that the stability of the aircraft wasn't effected. An aircrafts
wing is placed so that when flying it is nose heavy and wants to pitch
down, the tail plane is given a negative incidence to counter balances
this. This is where stability comes from. The Spitfire had less room
in its wings so it carried its fuel in a tank between pilot and engine
right over the wing,

That's pretty much true, but there's another factor as well - Take a
good look at an Inboard Profile (Side view cutaway) of a Spit and a
Mustang. On the Spit, the cockpit is well aft, meaning that any
attempt to use the fuselage volume aft of the cockpit will result in
moving the CG way too far aft, (Not to mention having less volume in
general - a Spit is substantially smaller). Even the drop tank
mountings on the centerline on a Spit had an adverse effect on the CG.
This is borne out in the notations in the Pilot's Operating Handbooks
for both aircraft,
The Mustang is restricted from severe maneuvers with the Aft Fuselage
tank full,
The Spits with rear fuselage tanks are restricted from anything but
straight and level flight,



2 The airfoils didn't suffer as much from compressibility so could be
much thicker and drag didn't increase as rapidly as speed increased.
In fact they were so good they were used as the basis of all
supersonic post war airfoils.

The airfoil on the P-51 didn't have substantially better drag
characteristics - but this wasn't particularly relevant at the speeds
that propeller driven fighters could achieve.
Where the P-51's airfoil _did_ pay off was that there was less of a
shift in the Center of Moment. This meant that it was less
susceptible to nose tuck when it did start going transonic. It's
worth noting that Dive Recovery Flaps were evaluated on the Mustang,
and were determined to be unnecessary.



The laminar flow aspects didn't count for that much:-painted metal
skins simply aren't smooth enough.

Just so,



The P-51 also has a superior recovery of waste engine heat through its
radiator design. Overall the P-51 could carry more fuel plus it was
more aerodynamic.

The question is could British industry have come up with a long range
solution as good as the Mustang in an appropriate amount of time.
Maybe.

I doubt it. It's not that the Brits were poor designers, but the
record shows that
they never got the knack of large lightweight structures.
Compare, for example, the Short C Class flying boats to the Martin
130s and
Boeing 314s, or the Hastings to a DC-4.

As far as I can see the only good engine, suitable for high altitude
work, in Britain till 1943 was the Merlin. The Sabre was unreliable,
the Griffon didn't have a two stage supercharger yet and in any case
there were no more than 1000 Mk.XIV Spits built with at most 300 in
service by late 1944. The Vulture could have been a good engine but
was abandoned. Centaurus was also not available.

The Griffon. relatively speaking, was a Fuel Hog, Consider, if you
will, the
range numbers for a Spit XIV vs. a Spit 9.
The Vulture might have been fixed - if somebody had discovered
Frictionless
Paint and could dope out its cooling problems, (That _was_ sacrasm,
btw)



The Merlin had to be used, other wise Britain could use a oversized
aircraft, powered by a Sabre, with wet wings like the P-47N which was
far better in range and performance than the P-51D.

Well, not _far_ better, and performance in service didn't exceed the
P-51D,
let alone touch that of teh P-51H. It's worth noting that the last
P-47s in USAF
service were Ds.



I know that the Spitfire was designed and used primarily as a home defence
fighter, while the Americans primarily needed long-range escort fighters.
But suppose the WW2 roles had been reversed, with America taking on the
night bombing whilst Britain did the daylight stuff. Would Britain have
been able to develop a Spitfire version into the highly succssful long-range
escort that the P51-D became ? If not, why not ?

Probably not, though maybe.

Spitfires latter had tanks added to the rear fueselage. 37.5, 44
gallon but more usually 66 gallon (tear drop canopy versions) 75
gallon (conventional canopy versions) tanks added well behind the
pilot but so did the Mustang as standard from the P-51D onwards.

So both the Spitfire and Mustang were upgraded with a rear tank.

Thus Mustang still has a fuel advantage over the Spitfire though as a
percentage the gap had reduced since the Mustang also had a tank of
the same size added to the rear fuselage as well.. Later a pair of
12.5 gallon tanks and then even a 6.25 gallon pair of tanks could be
added to the wing leading edges of the Mustang but even this didn't
close the gap out.

In both cases of Spitfire and P-51D handling was terrible till only
the final 25 gallons of the tail tank fuel remained. This meant
using up fuel in the tail tank first, which meant that the drop tanks
could still be full when contact with the enemy was made when they
would need to be ditched. It was impracticable.

The Spit was far more affected by the aft fuel tanks. They were much
further
aft of the CG, and the drop tanks also moved the CG aft. Pilots who
have
flown P-51s with the aft tanks were comewhat cautious with the tanks
full,
but not overly concerned. It was less stable, to be sure, but was
statically stable,
The Spit was seriously unstable,

IIRC, Jeffrey Quill's "Spitfire: A Test Pilot's Story" discussed
lateral stability in depth as well as well as a brief mention of
range. I believe he said something to the effect that Supermarine/
Vickers didn't have the design resources to solve the stability/range
issues until near the end of Spitfire development. Did the last Marks
have significantly better range? Given greater engineering resources
could they have produced a Spitfire in '43 or '44 with a rear fuselage
fuel tank and sufficient stability?

Jim



Could the British then radically re-engineer an aircraft, like the
Spitfire, to get P-38 and P-51D like range?

Perhaps a radical wet wing, with a completely new structure, similar
to the way that Republic engineered the P-47N could be made.
Production of normal spitfires could not be interrupted so these wings
would need to be built in a seperate factory. I would use a P-51
style retraction mechanism and compromise on armament a little to
carry more fuel in the wings.

So where do you put the guns and ammunition? You've just filled the
wing
up with spars, wheels, and fuel, and coolant,



A streamlined slipper tank was designed for the Spitfire, the idea
being that it wouldn't effect performance much.

Less Interference Drag, more profile drag, and a seriously adverse
effect on
the CG, It didn't have much benefit at cruise EAS (Equivalent Air
Speed)



I would say that the NACA would definetly have shared the secrets of
the supercritical wing with British aerodynamic experts.

When they got round to developing it, 30 years later,
Unless you're conflating Laminar Flow with Supercritical.

--
Pete Stickney

.

Relevant Pages

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  • Re: Mustang & Spitfire
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