Escort Spifire (1 Viewer)

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They miss two important factors.
1. The fighters, at least in areas where enemy fighters are likely to be encountered, need to cruise much faster than 220mph and more likely than not, faster than 260mph.
P-51s routinely cruised at a bit over 300mph.
It could take a Spitfire V (with under 85 gallons of fuel on board) over two minutes to accelerate from 200-220mph to full speed (350-360mph?) by which time the attackers are long gone.
Granted the MK IX had more power but adding 300-400lbs of tanks and fuel is NOT going to help acceleration.
2. Take-off and initial climb out was done on internal fuel as was combat (mostly) so radius is governed by internal fuel remaining over Germany (target) after 15 minutes combat. Spitfires were figured to have around a 24 Imp gallon "fuel allowance" which covered take-off and about a 20minute reserve to find their own (or any) airfield upon return. At about 18lbs boost a two stage Merlin was using about 3 IMP gallons a minute so 5 minutes is 18 imp and figure between 2 and 2.5 IMP gallons a minute for military power so 12 gallons for 10 minutes ? (Americans figured 5 minutes WER and 15 minutes at either military or max continuous).
So it is whatever internal tankage they can scheme minus about 54 gallons for the trip back. MK XIII with larger lower tank, wing leading edge and 35 gallons in rear fuselage has 157 IMP gallon without drop tanks or around 100-105 IMP gallons for trip back after dropping tanks and fighting for 15 minutes.
Not dividing total fuel in half. Exiting German airspace and crossing France/Low Countries at 220mph is asking to get bounced by a plane/s doing well over 300mph.

MK Vs were recommended to fly at 300mph at 20,000ft using 2400rpm and +1 1/2 lbs and using 46imp gallons an hour or 2200rpm/1 3/4 lbs for 263mph. I doubt the MK IX is going to be very different.
Every minute at combat settings is 3-4 minutes even at medium cruise speeds.
 
There is also the fact that the P-39 and P-40 were very useful in other theaters. Replacing them to try and turn a short range interceptor into a long range escort isn't likely to shorten the war overall.
 
I enjoyed the read, and I can understand the points the author was trying to make. But without a significant redesign to reduce drag the Spitfire was not going to come up to snuff as a long range escort fighter. But I think it is important to restate the obvious. The Spitfire excelled at what it was designed to do, a short range interceptor. If Submarine wanted to I am sure they could have designed an excellent long range escort fighter but that is not what they were tasked with. To me that is always the flaw with what if comparisons and extrapolations. The British were very specific in their design requirements and the Spitfire was a stupendous example of it's type. But to make it into something it was not intended to be is simply wishful thinking. And not very clear thinking. Heck you could add 4 more engines and a bunch of machine guns and canons to a PBY but that would not make it a successful escort fighter.

The design modifications necessary to turn the Spitfire into a successful long range escort fighter would inherently make it an altogether different aircraft in my humble opinion.
 
There is a manual for the MK IX, XI and XIV here.

Spitfire IX, XI XVI.pdf

It is post war so perhaps they weren't taking quite the risks there were during the war but:

Under managing the fuel system with rear tanks fitted, it says to start, warm up, and take-off on the main tanks. Once reaching 2,000ft switch to rear fuselage tanks until they are down to 30 gallons, then switch to the drop tank. A lot like the Mustang.

Under take-off: with rear tanks full the aircraft pitches upon becoming airborne and it is recommended that the undercarriage not be retracted, nor the sliding hood closed, until a height of at least 100ft has been reached.

Under general flying. Stability.
with rear tanks full there is a very marked reduction in longitudinal stability, the aircraft tightens in turns at all altitudes and in this condition is restricted to straight flying and only gentile maneuvers; accurate trimming is not possible and instrument flying should be avoided when ever possible.
When a 90 gal drop is carried in addition to full fuel in the rear tanks the aircraft becomes extremely difficult and tiring to fly and this condition restricted to only straight flying and only gentile maneuvers at low altitudes.

There are further comments on the planes with "rear view" fuselages.

Under acrobatics.
Acrobatics are not permitted when carrying any external stores (except the 30-gallon "blister" drop tank) nor when the rear fuselage tanks contain more than 30 gallons of fuel, and are not recommended when the rear fuselage tanks contain any fuel.

Italics are in the manual.

Under stalling it is recommended to increase the landing speed by 10-15mph if the rear tanks are full.

Under flying limitations.
The MK IX and XIV are rated for a take-off weight of 8700lbs but only from a smooth hard runway, the max landing weight is (except in emergency) 7450lbs.

rear tanks are only to be used by special authority and never on planes with "rear view" fuselages.

There are several comments that suggest that flying or landing when overloaded was not good.

Now some of these problems may have been somewhat remedied by the fitting of larger tail surfaces. Some of the weight problems might have been solved by beefing up the the structure. But converting standard MK IX or MK XIVs doesn't look like a good idea.
 
But without a significant redesign to reduce drag the Spitfire was not going to come up to snuff as a long range escort fighter. But I think it is important to restate the obvious. .

A complete re design to reduce various forms of drag and increase internal fuel would result in something that was rolling out of two factories in the USA called the P 51 Mustang. No doubt the range of the Spitfire could have been improved but what would the RAF escort with it? Long range daylight bombing was a US doctrine. Also the Spitfire should have been retired long before it did, the Tornado/Typhoon and other 2000BHP fighters should have taken over.
 
The design modifications necessary to turn the Spitfire into a successful long range escort fighter would inherently make it an altogether different aircraft in my humble opinion.

I think you've hit the nail on the head. Converting something designed for one role into something capable of carrying out another usually involves compromise, often making the result less capable in either role.

The American's made a bit of a dog's dinner of increasing the range of their own fighters, and they had a far more pressing need for such aircraft in 1943 than the RAF did. I don't think the drop tank fiasco needs another airing here.

The P-51 was an absolutely exceptional aircraft, it is easy to argue that it was the best all round single engine fighter of the war, and the USAAF was fortunate to have it for its escort role.

Put it this way, if I've got to fly to Berlin and fight by day, I'll take a P-51. By night I'll be happy in a Mosquito ;)

Cheers

Steve
 
They miss two important factors.
1. The fighters, at least in areas where enemy fighters are likely to be encountered, need to cruise much faster than 220mph and more likely than not, faster than 260mph.
P-51s routinely cruised at a bit over 300mph.
It could take a Spitfire V (with under 85 gallons of fuel on board) over two minutes to accelerate from 200-220mph to full speed (350-360mph?) by which time the attackers are long gone.
Granted the MK IX had more power but adding 300-400lbs of tanks and fuel is NOT going to help acceleration.
2. Take-off and initial climb out was done on internal fuel as was combat (mostly) so radius is governed by internal fuel remaining over Germany (target) after 15 minutes combat. Spitfires were figured to have around a 24 Imp gallon "fuel allowance" which covered take-off and about a 20minute reserve to find their own (or any) airfield upon return. At about 18lbs boost a two stage Merlin was using about 3 IMP gallons a minute so 5 minutes is 18 imp and figure between 2 and 2.5 IMP gallons a minute for military power so 12 gallons for 10 minutes ? (Americans figured 5 minutes WER and 15 minutes at either military or max continuous).
So it is whatever internal tankage they can scheme minus about 54 gallons for the trip back. MK XIII with larger lower tank, wing leading edge and 35 gallons in rear fuselage has 157 IMP gallon without drop tanks or around 100-105 IMP gallons for trip back after dropping tanks and fighting for 15 minutes.
Not dividing total fuel in half. Exiting German airspace and crossing France/Low Countries at 220mph is asking to get bounced by a plane/s doing well over 300mph.

MK Vs were recommended to fly at 300mph at 20,000ft using 2400rpm and +1 1/2 lbs and using 46imp gallons an hour or 2200rpm/1 3/4 lbs for 263mph. I doubt the MK IX is going to be very different.
Every minute at combat settings is 3-4 minutes even at medium cruise speeds.
I think you are overstating the long range cruise speed of the Mustang.

Here's the tactical planning chart for the Mustang:

http://www.wwiiaircraftperformance.org/mustang/p-51-tactical-chart.jpg

LR cruise was typically lower than what you indicate and for maximum endurance speeds were in the region of ~220-250 mph.
 
The US combat radius of action charts (not the one above) were based on.
A. Warm up and take-off equivalent to 5 minutes at normal rated power (max continuous)
B. Climb to 25,000ft at normal rated power (distance covered in climb not included in radius)
C. Cruise out at 25,000ft and 210 mph AIS. This is equivalent to 315 mph true.
D. Drop external tanks and/or bombs before entering combat.
E. Combat 5 minutes as War Emergency Power and 15 minutes at military power.
F. Cruise back at 25,000ft and 210mph AIS
G. No account is taken of decreased fuel consumption during decent.
H. Allowance is made for 30 minutes reserve at minimum cruise power
I. No allowance is made for formation flight or evasive action other than the 20 minutes combat.

combat radius of all P-51s with 184 US gallons (no rear tank, no drop tanks) is given as 150 miles.
combat radius of all P-51s with 269 US gallons (full rear tank, no drop tanks) is given as 375 miles.
combat radius of all P-51s with 334 US gallons (no rear tank, 75 gallon drop tanks) is given as 460 miles.
combat radius of all P-51s with 419 US gallons (full rear tank, 75 gallon drop tanks) is given as 700 miles.

P-51s used the rear tank until about 35 US gallons left before switching to drop tanks.

Fight chart for P-51D no load.
P-51FOIC.gif


Please note right hand column, at 25,000ft the plane is burning 59 US gallons per hour to fly 335mph. Engine is turning 1850 rpm in high supercharger.
Another chart in the manual shows 60 gal per hour at 25,000ft giving 305mph true using 2100rpm.

Also please note that a Spitfire IX was good for somewhere around 408-417mph (?) at 25,000ft using 3000rpm and 18lbs boost (66inches?) this depended on exact model of engine. The Melrin 66 being on the low side for speed and altitude and the Merlln 70 being on the high side of speed and altitude.
Mustang without tanks at 25,000 could Cruise at 413mph true using 98 US gallons (81.6 IMP) using 2700rpm and 46in (8lbs ?) boost.
They didn't (at least not often) but that is an example of the drag difference.

Spitfire is going to have to come close the requirements/conditions a through I above in order to judge ability to escort. Not cruise at a speeds and altitudes that were proved near suicidal in 1941 during the lean forward into France campaign.

Please note that it takes a Mustang with 75 gallon drop tanks and running 2700rpm 52 US gallons to reach 25,000ft (includes 15 gallons for warm up take-off) it takes 24 minutes and can cover 91 miles but the first planes up have to wait for the last plane or the formation is strung out for miles.
 
A good read, interesting "what if", I think a better "what if" would be the USAAF recognizing the Mustangs potential in 1941 and have an operational Packard/Merlin version operational six to ten months earlier than historical. I'm not sure the real life timeline would allow that but on the face of it, it seems as plausible as a long range Spitfire.
 
I would also take issue with this.

"The greatest need (and opportunity) for a long-range escort Spitfire was between August 1942, when the Eighth Air Force began its daylight campaign over Europe, and early 1944 when the Merlin Mustang appeared in strength."

There may well have been an opportunity for a long range Spitfire, we could have flogged it to the Americans for a start, but from a solely British perspective, what was the need?
The RAF didn't need a long range escort fighter, the USAAF did. This was essentially an American problem, not a British one. The British had long since adopted a night bombing campaign, for which a long range, single engine, escort fighter was not required. .
The two nations may have been closely allied against Germany, but the realities of such an alliance are not always quite those of the 'Why We Fight' type of propaganda.

Cheers

Steve
 
Technically a long range (or longer range) Spitfire could have been built. However it wouldn't quite be the quick and easy "conversion" some people are hoping for or putting forward.
There were only 4 squadrons of MK IX Spitfires operational at the time of Dieppe , Aug 19th 1942 so the idea of hundreds of special MK IXs being available only few months later seems a bit optimistic. Please note that in Aug 1942 work was being done on both sides of the Atlantic at putting Melrins in Mustangs.
I don't know what the airfield situation was in 1942, early 1943 but over loaded MK IXs were only supposed to operated from smooth, hard surfaces. Adding 300-500lbs of internal fuel and a 90Imp gallon (648lbs of fuel+tank) pushes the Spitfire into the overloaded catagory no matter how you arrange the tanks.
Some of the flight problems could have been solved (metal elevators, larger tail fin, etc) but that requires at least some change in manufacture and flight testing.
Even with the drop tank gone a MK IX would be operating in a slightly overloaded condition, that means a slightly lower "G" limit unless certain parts are beefed up, Later Spitfires did get beefed up structure so it was possible, but again we don't know what the engineering load (drawing office) was or what any changes to manufacture would be.
The MKVIII is a better starting point (was beefed up) but the first production MK VIII wasn't delivered until Nov 1942. First operational squadron was No 145 in June of 1943 at Malta.
 
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A couple of points. The P-51B/D cruise settings for optimal miles/gallon at 25,000 feet with 110 gallon external tanks was close to 260mph +/- TAS, with 75 gallon tanks between 285mph+/- and 295mph+/-TAS at 25,000 feet depending on Gross weight. For normal (max) load out at Take Off was ~11,200 and at that weight it would be closer to 285 mph at 25,000 feet then get progressively better as fuel was consumed. When tanks were dropped, the cruise would be 295-300mph TAS at 25,000 feet.

What might get lost in this discussion is that a Spit IX with a 1650-3 or -7 and 200 total US gallons internal fuel would have about the same or better range as the P-47D with 305 gallons at 25,000 feet. The cruise speed would be lower than a P-51B/C because the Parasite Drag was about 25% higher - at the same 'best gallons/mile' settings, so the comparable range would be less than a P-51B/D with no 85 gallon fuselage tank. The Combat Radius of all three, with only internal fuel as stated above, would be somewhere around 200 miles.

A 200 mile combat radius for a Spit IX would have dramatically increased its tactical footprint over France, Belgium and Holland, further increasing pressure on JG 2 and 26.
 
I re-read this article, and I don't see where he gives any thought to how this escort Spitfire is to become operational in early 1943, other than rather offhanded comments about Bell and Curtiss stopping P-39 & P40 production. I'm not a production expert but I don't think you can just show up at a factory with plans in hand and start cranking out airplanes the next day.

In fact as I read this, testing and evaluation seems glossed over, or airily dismissed, and getting them operational doesn't seem to be addressed. So I'm not seeing this plane reach ETO based squadrons much before the P-51B/C did historically, or am I missing something?
 

Of course in theory the available Merlins could be bolted onto P-51 airframes rather than Spits. This would probably be best for the overall outcome. But both because the P-51 potential was late recognized and real world considerations, it's a nonstarter.
 
Which Merlins and which P-51 airframes?
The Merlins that went into the MK IX Spits were in England. The air frames were in Los Angles California.
P-51B airframes had a 7in splice put into the airframe to help accommodate the larger radiator/intercooler among other changes so you can't just take standard Allison Powered Mustang Is and yank the engines and drop in 2 stage Merlins.

Rolls Royce Mustang conversion
0Mk%201%20conversion%20works%20carried%20out%20by%20Rolls-Royce%20Flight%20Test%20Establishment..jpg


under the "hood"
P-51BC_02.jpg


engine test bed aircraft, not operational fighters.
First flight Oct 13 1942 Work had started back in July of 1942. Please note first flight is 5 days after North American gets a contract to build 1350 P-51Cs (with Merlins) at it's Dallas Plant.

It took a number of test flights and changes to get cooling problems worked out and reduce drag. Initial testing of the RR conversion showed a top speed of 422mph.
 
To have an operational daylight single engine escort in 1943 you have to convince those with the "bomber will get through" doctrine that they are wrong. Historically they were needed at the beginning of 1943 but also historically no one believed they were needed or that it could be done.
 

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