Spitfire Combat Radius (range) evolution, limitations?

Shortround6 said:

Something to remember about the photo recon aircraft.

They weren't supposed to dogfight/ do hi G maneuvers.

Which means they could operate at higher gross weights and also operate at Center of gravity locations that might be dangerous for a plane trying to pull 5-6 gees.

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The fuel is burnt off, P51's didn't dogfight with full rear tanks or drop tanks and it had dangerous handling at take off, I find the mentality on here interesting, lets find every reason to not make it work instead of ways it can.

Shortround6 said:

You can have Boulton Paul build Spitfires instead of Defiants but until you sort the engine and propeller situation (summer of 1940?) you aren't going to get a very good even mid range Spitfire.

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Earlier than that, the first Hurricanes received VP props in February 1939 and de Hav was fitting VP props to spits before 1940, the C/S prop came along for Spits in Spring/Summer 1940. But let's not forget that VP/C/S props were already fitted to other RAF types at the time, which makes the decision to keep lumps of wood aboard fighter aircraft that could have benefitted with them better than any other type a strange one.

With our retrospectoscope we could state that BP built Spits had de Havilland props as fitted to Defiants, as standard, as the Daffy never had a wooden lump up front.

Fabric winged Hurris did perform poorly and definitely couldn't reach 300 mph in squadron service in 1938, despite what was advertised, but the benefit of the design was that the all-metal wing could be retrofitted as it was just the outboard wing panels that were fabric covered, the centre-sections were all metal, so the outer wings could be exchanged. Production of the all-metal outer wings standardised in 1939. The primary difference being the arrangement in gun bay access. We also know that the VP and C/S prop mods didn't take much time at all to implement, the Rotol C/S prop mod could be fitted to a fighter within the space of an hour or so, taking into account engine runs and paperwork etc...

PAT303 said:

The fuel is burnt off, P51's didn't dogfight with full rear tanks or drop tanks and it had dangerous handling at take off, I find the mentality on here interesting, lets find every reason to not make it work instead of ways it can.

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What I find interesting is idea that because something was doable in 1942 then they should have been doing it in 1939 or 1940.

It is not just the power to get the loaded plane off the runway. Although that applies in 1939-40
It is the power needed to get the loaded plane to perform at different altitudes. Like above FTH.
A lot of planes did pretty good down low, some didn't do so well at altitude. The P-40 being a prime example. And yet it's engine was only about 2000ft lower in FTH to a Merlin III.
The difference was it was trying to carry about 1 ton on the same engine power as a MK I Spitfire.

We also never seem to specify what "long range" means except that the long range Spitfire should have a radius of 75-100 miles more than a standard Spitfire ??
That seems to depend on the year it is being suggested. And/or drop tanks.

Of course objections are countered by the excuse of the long range Spitfire will burn off any extra weight and be in perfect fighting weight (over England weight)at whatever distance the Germans decide to engage.

A early Spitfire will burn around 120-150 gallons an hour for a single stage engine in combat. The MK Vs will burn 150 gallons an hour (at 16lbs boost) or 37 gallons for 15 minutes in combat.
so lets call it 30 gallons after any external tank is dropped. It is going to take around 30 gallons to get back across the channel (assuming a 100 mile crossing and giving you abut 30 minutes to find the airfield after you find land.
So on a regular Spitfire you have about 25 gallons to get back from wherever you engaged in combat over Belgium or France and get back to the coast where you can slow down.
With a 30 gallon tank in the rear of the fuselage that does extend things quite a bit but it depends on speed. If you are running at 2650rpm and 6lbs of boost you are using 70 gallons an hour. Granted you are flying at 331mph at 10,000ft.
Now can you drop down to 225mph or so just as soon as you are over water or will you wait a few minutes?
Of course the winds will automatically stop blowing for the Spitfire pilot.
And of course the Spitfire will have undiminished climb in combat because somehow it burned off the extra fuel load of the extra 30 gallon tank before it went into combat but it back (????) for the fight home.

If you only use a 30 gallon internal tank and no drop tank you aren't going to fly much further than using a 30 gallon drop tank. Don't think A Spitfire with a 30 or 34 gallon drop tank qualifies as a long range fighter.

P-51 had several advantages over the Spitfire for this type of work, One of which was that they decided to run the planes heavier than "normal". The P-51 was rated at 8 Gs at 8000lbs gross weight and they ran them much heavier even without the rear tank. However if you stick about 500lbs of fuel in a 9600lb airplane things don't change as much as they do if your try to stick 500lbs of fuel in a 7500lb airplane. Of course that is putting the 500lbs of fuel in a plane with a Merlin 60 series engine.
You have room to put 500lbs inside a Spitfire V but now you have an under 7000lb plane you are putting it into. You have to be a little more careful where things go and what happens to the performance.
Oh yeah, I keep forgetting, all the extra weight will disappear when the long range Spitfire actually has to fight.
If you are planning on sticking the fuel tanks in the back of the fuselage from the factory of the Spits you can beef up whatever you need to to.

PAT303 said:

Spitfires were used for the first and last leg out and back in daylight raids but only to about 150 miles which really was pointless, at the same time the P47 was limited to about 350 miles before turning back, the Spit ''if'' fitted with aux/drop tanks that were approved for service it could have gone out to 450-500 miles depending on circumstances, my argument is the Spit could have done more if they simply filled them with more fuel but they weren't, the P47 started escorting with ferry tanks, that's how desperate the USAF were for escort fighters.

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Initial P-47C/D Combat Radius in May 1943 through June 1943 was 125mi +. 350mi CR wasn't attained until Jan 1944.

PAT303 said:

I'm not arguing with you, the fact is they did it, it's that simple. Once the 60 series Merlin arrived the Spit had the engine power to get more fuel off the ground that was it and every other single engined fighters biggest problem pre 1942.

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Not so. The issue wasn't horsepower but a combination of a.) insufficient internal fuel and b.) external wing racks plus plumbing.

PAT303 said:

The fuel is burnt off, P51's didn't dogfight with full rear tanks or drop tanks and it had dangerous handling at take off, I find the mentality on here interesting, lets find every reason to not make it work instead of ways it can.

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I find your mentality interesting, too. The Spitfire was one of the greatest fighters ever produced. Why are you so hot to change it? It performed it's job exceedingly well in most cases, and a couple of late models got more fuel, as you suggest. The earlier ones DID NOT and were still used to great effect and as they were designed to be used.

Your attempt to make everyone realize that it COULD have been a long range fighter is a "What If," and what ifs have no correct answers because real events trump any "might have been" with what actually happened. There is absolutely nothing wrong with your "What If," but it will forever remain a "What If," and will never get realized. Since YOU know what you want from the modified Spitfire, then yes, it could have been done, very likely as you want it to have been done.

But, in real life, it wasn't until the PR Mk. IX and the PR Mk. XIX ... and their fuel additions weren't an exact match for what you suggest, but they did have additional fuel for some long-range reconnaissance. They weren't front-line fighters due to the extra fuel and reduced armament package and, as a result, lower load factors when fully-fueled, too. That was not what a front-line air-superiority fighter needed to be competitive, but yes, they COULD have been made into all long-range PR aircraft. They just weren't and very certainly didn't need to be. They were pretty darned good as they were actually built, and other aircraft fulfilled the long-range missions. It makes no sense to modify Spitfires into long-range airplanes and then have already-long-range Mustangs / Thunderbolts / Lightnings fly the missions the modified Spitfires would otherwise have flown ... all it does is cost money and reduce readiness.

But, hey, sure they COULD have done it. It's just that nobody who mattered at the time pushed for it as a course of action.

To further expand on this.

Shortround6 said:

So which Spitfire, the
MK I
MK II
MK V
Or the MK IX (or MI VIII)

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Spitfire I 1938, wooden prop and 1030hp at around 18,000ft using RAM but Performance is severely restricting at other altitudes. S
Spitfire I 1939. two pitch prop, performance is somewhat better ?(at least take-off is) , At some point in 1938-39 you know that 100 octane is coming but you don't know when and you don't know what increase in performance it will allow.
Now there are a few things that a really limiting the Spitfires performance here in the first year or so of production.
One is that you can't actually use the the performance of the Merlin engine with either propeller unless you are near the 16,250ft FTL. The props (both of them) require the engine to be throttled down to around 2400rpm or less at low altitude instead of the 880hp at 3000rpm that the engine was capable of making with 87 octane fuel. Spitfire with wooden prop can't use 2400rpm until 3,000ft is reached in level flight. 100 octane fuel with be of absolutely no help because the engine can already turn the prop too fast and cause a loss of thrust.
This is the British self inflicted wound. They have the fasted fighter in the world if everything was running right but low altitude speed and climb are both crippled by the crappy propellers.
The Spitfire and Hurricane should not be trying to lift anymore fuel because their climb rate is so poor due to the need to run the engines so far below full throttle.
In late 39 three things start to happen. 1. the constant speed prop finally breeches the British costal defenses and they see that a change in climb rate to 20,000ft easily 20% or more is well within reach. 2. tests with 100 octane fuel show that even more performance in emergency situations is possible. countered a bit by 3. Increased protection and/equipment cuts into the new performance capabilities. At least you can climb the planes using 2600rpm and 6lbs of boost or will be able to so soon.
Now in Nov 1939 the Merlin is allowed to use 12lbs of boost but without a CS prop this is not going to help a whole lot.
Using 12lbs of boost increases fuel consumption by about 40% over using 6lbs.
By the BoB all operational squadrons have got CS props of some sort and the old climb limit of 2600rpm and 6.14lbs has been changed to 2850rpm-3000rpm further improving climb.
How soon anybody knew this in order to take advantage of it (like order a long range Spitfire version) is certainly subject to question.

The Merlin had the highest FTH/critical altitude of any engine in 1938/39. This also means that on 87 octane fuel it had to be throttled down more than most of it's contemporaries which hurt take-off and low altitude climb, even when CS props showed up.

August 1940 also sees the first Spitfire II's show up. The Merlin XII gets a bit higher FTH with a slightly higher supercharger gear ratio. However with some stronger components and with 100 octane fuel the Take-off rating gets a major boost and the climb rate also gets boosted. Engine is still rated at 12lbs boost though. The British do try to hang a fixed tank under the wing.
The Spitfire V shows up with the Merin 45 and while the Hooker supercharger increases the FTH by several thousand feet ( and increases the ceiling and climb rates at higher altitudes) it does nothing for the take off rating (about 10HP) and doesn't increase the "normal" climb by much. It takes a while for boost pressures over 12lbs to show up and you don't use the higher boost pressures for take-off or climb. It does provide for better combat ability with a heavier weight for the 5-15 minutes you are using "combat power".
16lbs of boost used up fuel at about 70% higher than 6lbs of boost though. MK V also (mostly) got the 20mm guns and sucked up a few hundred pounds of weight that way rather than carry more fuel.

Please note that the BF 109F1/2 was about 350lbs lighter than a Spit V depending on guns and the F4 was going into production in the summer of 1941 with a more powerful engine than the F1/2. Adding several hundred pounds to the Spitfire V with the existing engines and having them fight over eastern Belgium or the Dutch-German border may not have worked out well for the British.

The British 100 octane fuel of 1940 was not quite the same as the 100 octane fuel of 1942. I don't know when it changed but tests of BoB fuel came up as 100/115 to 100/120
I would also note that it took a very long time for the Merlin to be OK'ed for climbing at more than 2850rpm and 9lbs of boost (a 30 minute rating) so there is no help for better climb there.

Shortround6 said:

are we going to to turn into the early long range escort? Or several versions with increasing ranges?

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I don't doubt that you could cram another 20-30 gallons into a Spitfire with not a big reduction in performance. The question is does that really do anything?
Or do you need another 20-30 gallon inside and 45-90 gallons outside in order to reach the targets you are interested in?

It is about 260 miles or more depending on airfeilds to fly directly from Ipswich to Cologne. Granted Wellingtons and the like aren't going to fly as high or as fast as the B-17s but it that isn't going to work then you might as well forget the whole idea.

Shortround6 said:

Please note that the BF 109F1/2 was about 350lbs lighter than a Spit V depending on guns and the F4 was going into production in the summer of 1941 with a more powerful engine than the F1/2. Adding several hundred pounds to the Spitfire V with the existing engines and having them fight over eastern Belgium or the Dutch-German border may not have worked out well for the British.

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actually delivery of F-4 started in May

Shortround6 said:

This is the British self inflicted wound. They have the fasted fighter in the world if everything was running right but low altitude speed and climb are both crippled by the crappy propellers.

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Per Spitfire: the History, Spitfire with

So, the "performance" numbers say there isn't much to choose between a wooden 2 blade fixed pitch and metal 3 blade CS propeller. If DH and Rotol can only make a limited number of CS propellers, they are better served to be manufacturing them for Battles, Blenheim, etc as the bombers have a critical need for them in takeoff performance.

Now, add 100 octane fuel into the Merlin and suddenly you need to re-equip all your fighters with coarser propellers to take advantage of the power increase. If you are re-propping and your propeller manufacturers now have capacity to deliver the CS unit, it saves you having to re prop again when next power increase comes along. It also improves take off distance, etc.

Similarly, early fighters would have benefit from Merlin X with more power to propeller in MS for take off, then shifting to FS at altitude, but again Halifax, Wellington & Whitley needed it more, just to get off the ground.

Zipper730 said:

I was curious about two matters

1. There was a mention on of an early PR variant that possessed a 20 imperial gallon tank underneath the pilot's seat: I can't seem to find anything specific on this one. I can find mention of a 29 gallon tank that was located behind the pilot (this was also fitted to the Spitfire Mk.V for ferrying), as well as one variant that had a 30 gallon tank in a blister under one wing (it counterbalanced the weight of a cam in the other wing). I'm curious if it existed at all, or was mixed-up with these developments (This keeps getting lost in the discussion, and honestly, it's like trying to nail jello to a wall).

2. I remember that, when the early Spitfire Mk.I's were switched from a fixed propeller, to a twin-pitch propeller, to a constant-speed propeller, that there was ballast added in the aft fuselage to balance this out. In the Mk.VII/VIII/IX and beyond, was this ever removed in non PR variants? I remember this was done on the P-51B/C's that were fitted with the 85 US gallon tank since it would have put the plane out of the C/G limits, and when the fuel was lowered to either 55-60 gallons, you'd end up with the C/G in roughly the same position you'd be in if the ballast was retained.

3. When did the Seafire's adopt the 89 US gallon P-40 tank? I know it was definitely in place by 1945 (and that might very well be the year it was adapted to the aircraft, for all I know).


While I thought the lines making the Mk.VII & VIII were converted to the Mk.XIV/XVIII, what happened to the lines that produced the Mk.VII?


The XV's flight manual indicates 9-3/4 imperial gallons per wing not 19.5 per wing.


Which variant are we talking about? As for the wing-capacity, do you mean 25 imperial gallons in the wing-root, or 50 gallons in each wing? I remember hearing that it was possible to put room for 53 imperial gallons of fuel in the wing-leading edge inboard of and outboard of the 20mm cannon, though I'm not sure the RAF would have accepted such a configuration even if it was possible to work a fuel line around the back side of the Hispano cannon.

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The Mk21 had the tank under the seats, enclosed is the drawing from the original pilots notes

Vincenzo said:

actually delivery of F-4 started in May

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thank you.

don4331 said:

Per Spitfire: the History, Spitfire with

2 blade wooden propeller - 9.4 minutes from S.L to 20k'; 363 mph @ 12.5k', 31.9k' ceiling​

3 blade metal,2 pitch propeller - 11.4 minutes from S.L to 20k'; 367 mph @ 12.5k', 34.4k' ceiling​

3 blade metal, CS propeller - 10.7 minutes from S.L to 20k'; 364 mph @ 12.5k', 34.5k' ceiling​

So, the "performance" numbers say there isn't much to choose between a wooden 2 blade fixed pitch and metal 3 blade CS propeller. If DH and Rotol can only make a limited number of CS propellers, they are better served to be manufacturing them for Battles, Blenheim, etc as the bombers have a critical need for them in takeoff performance.

Now, add 100 octane fuel into the Merlin and suddenly you need to re-equip all your fighters with coarser propellers to take advantage of the power increase. If you are re-propping and your propeller manufacturers now have capacity to deliver the CS unit, it saves you having to re prop again when next power increase comes along. It also improves take off distance, etc.

Similarly, early fighters would have benefit from Merlin X with more power to propeller in MS for take off, then shifting to FS at altitude, but again Halifax, Wellington & Whitley needed it more, just to get off the ground.

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That is not what the the results say. While the 2 blade wood and the 2 pitch metal agree with your numbers the 3 blade Rotol propeller has 7.7min to 20,000ft, 354mph at 18,900ft and a service ceiling 34,700ft. What is a bit puzzling is why the plane with the 2 blade wooden propeller has a max speed of 363mph at 12,500ft. There should have been few, if any, Spitfires using wooden props when 100 octane fuel was approved and allowed the 12lbs of boost at that altitude.
There was a test of a plane that armed with two 20mm and four .303 guns that has the same climb to 20,000ft and the same ceiling that you post but it was using a 2 pitch prop and not a CS prop. It speed of 364mph was done at 18,600ft instead of 12,500ft.


Some (or at least one) of the early tests seem to have propellers that were not set up for optimum engine performance.

Unfortunately the Blenheim's were saddled with two pitch propellers until the MK V model.

I believe you are wrong about the need to re-pitch propellers with the use of 100 octane fuel. The speed of the aircraft didn't change much, or at least the top speed.
So the same pitch propeller should have given you the same speed at the same propeller rpm at the same altitude.
The problem with the fixed pitch and the 2 speed props was that they could NOT open the throttle in parts of the flight envelope without over speeding the prop for the air they were going through, like a boat cavitating it's propeller at slow speed.
A CS prop would keep the angle of the prop at a good angle for the speed of the airplane and increase the angle of attack of the blades as the speed increased until the max speed of the airplane was reached. It would allow for much improved acceleration to reach the top speed.
Few of the early Spitfires were faster at low level even with 12lbs of boost than they were at 18-19,000ft using 6lbs of boost so the need to re-pitch the props should have been minimal. The test of the cannon armed Spit with the two speed prop shows the ASI of the plane only changed from 289.5mph at 13,000ft to 285mph at 18,600ft while the true airspeed changed from 339mph to 364mph. Engine rpm on the fixed pitch prop went from 2860rpm to 3045rpm with the boost staying at 6.3lbs the whole or for each test.

Hey Don4331,

I think Spitfire: The History has the numbers you posted mixed up, or misrepresented (accidentally).

Do the ROCs the Spitfire book mention include the weights of the aircraft during the tests?

According to the actual results of testing done by A&AEE at Boscombe Down:

Rotol CS____ 6050 lbs_____+6.4 lb or FT______7.7 min to 20,000 ft
DH 2P______ 5930 lbs_____+6.4 lb or FT_____11.4 min to 20,000 ft
Wood FP____5820 lbs_____+6.4 lb or FT _____ 9.4 min to 20,000 ft

Whoops! I see Shortround6 beat me to it.

All I can add is that there used to be a report (I think on the "WWII Aircraft Performance" website but I am not seeing it now) that gave the Spitfire Mk I ROC with different props and the different weights in a single table in the report. It seems to have disappeared.

In relation to the introduction of 100 octane fuel you might be interested in this.

TonyT said:

The Mk21 had the tank under the seats, enclosed is the drawing from the original pilots notes

View attachment 666065

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That is Spiteful. Note the wing shape and layout, as well as undecarriage.

Does anyone have the dates when the various Spitfire drop tanks entered service?

I believe the 30 & 45 gallon slipper tanks were on the Mk.V in 1941 (but when?) and the 90 gallon slipper tank by the time the first aircraft were being delivered to Malta in Feb 1942. The 170 gallon ferry tank was first used in Oct 1942. And there was a 50 gallon "torpedo" tank from shortly before D-Day.

This whole discussion about turning the Spitfire into an escort fighter kind of reminds me of the tourist asking the Irishman for directions and the reply "Well sir, if I were you, I wouldn't start from here".

EwenS said:

In relation to the introduction of 100 octane fuel you might be interested in this.

100-Octane

soc.history.war.world-war-ii.narkive.com

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That thread has a bit of good info and some rather dubious info.

"What the high octane did do for the engine was allow the Rolls Royce
engineers to introduce a more efficient supercharger for the Merlin
that forced more air and fuel into the intake manifold than the
version used in the Mk1's."

RR (see Hooker) did develop a more efficient supercharger but it was in addition to the high "octane" fuel.
Using 87 octane fuel the Merlin was limited to about 6-6.5lbs of boost in a Merlin III using the supercharger gears the Merlin III used. A few other early Merlins used a different boost limit depending on the supercharger gear ratios involved.
Using 100 octane fuel the Merlin III could handle 12lbs of boost from the start and could handle 16lbs of boost if they didn't really care about engine life.
However the "old" supercharger would only give 16lbs of boost at 5500ft and would only supply 6 1/4lbs at 16,250ft.
The "new" supercharger would supply 16lbs of boost at 11-12,000ft which shows some of the efficiency. This supercharger was used on the Merlin 45 and it's decedents and was also used on the Merlin XX and it's decedents.

Edit,' Hooker was working on the "new" supercharger (actual just a modified cover and inlet for the existing supercharger, same impeller, same volute, same rear case and same exit to manifold) in 1939, it just took a while to finalize things and assign production priorities.'

"But this did not necessarily give it a higher ceiling than the Bf109,
nor did it give it a better performance at extremely high altitude."

Actually the Merlin III did have better perform in the Spitfire than to 109E had, at least most of the 109s in the BoB.
It may not have been a lot but it was there.
However the same engine in the Hurricane did NOT have superior performance. The larger Hurricane used up more of it's power in drag and had less for climb.
The slower Hurricane also had a bit less RAM in the intake duct which also hurt the altitude performance. When a Spitfire I was operating at around 28,000ft it was no "boost" to the engine. This is not correct, it was providing no "boost" on the gauge which was refenced to sea level. If the gauge was reading -0.5lbs it shows the supercharger was compressing the air to almost 3 times what the air entering the intake was.
109 was about 300-400lbs lighter than a Spitfire I so it had about a 5% advantage in power to weight if the engines in both planes were making the same power.
There are often a lot of things affecting performance. We have to be sure we are weighing in all the factors we can.
109s in the BoB were getting a small sprinkling of the DB610N engine.

EwenS said:

This whole discussion about turning the Spitfire into an escort fighter kind of reminds me of the tourist asking the Irishman for directions and the reply "Well sir, if I were you, I wouldn't start from here".

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We aren't turning the Spit into an escort fighter, we are just giving it longer legs, it's biggest Achilles heal.

drgondog said:

Initial P-47C/D Combat Radius in May 1943 through June 1943 was 125mi +. 350mi CR wasn't attained until Jan 1944.

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There we go, all the more reason to add fuel to the Spit wouldn't you say?.