Spitfire Combat Radius (range) evolution, limitations?

[drgondog]

When did the US decide that bombers needed escorting at all times? Initial British reservations about the B-17 were dismissed because there werent enough of them for mutual defence. It became increasingly obvious to some, not all, that even the heavy defence of the B-17 was not sufficient, so when was the decision made by the USA and why would the British develop the Spitfire as an escort before that date. They had a long range fighter that they ordered in 1940 called a "Mustang". It is a rhetorical question because I have a book on the development of the P-51B.

The Blitz Week followed by Scheinfurt-Regensburg two weeks later made it crystal clear that LW would inflict politically unsustainable losses. After Eaker and Asst Scy War Lovett appealed to Arnold, all summer planned P-38H and J deployments were re-directed to ETO, and all P-51B deployments were directed to ETO.

The AAC/AAF did not 'order' Mustangs until A-36 ordered in April 1942. In the next several months, the XP-78 (XP-51B) was approved, the NA-99 (P-51A with contract conversion to NA-104 P-51B-5), the P-51B-1 and C-1 were ordered. The priority for combat tanks were placed in even higher priority but MC was very delinquent in delivering until summer 1943.

 

[drgondog]

So, basically, it depends on the specific escort role?

Fighters in close escort will have their range extended when fighters in earlier stages of the relay have theirs extended, while fighters performing sweeps ahead of the bomber formation will gain little, or no, benefit?

If I understand your question, yes - it depends. If the target radius was within Combat Radius of the P-47D then the planners hd far more flexibility (Very Rare after March 1944 until Transportation Plan of May 1944 when many more tactical range rail and infrastructure and airfield targets were selected.

P-51 and P-38 combat radius were maximized when RV was relatively near the assigned targets - cruise in a straight line at 300mph TAS at 25K w/75gal combat tanks - 270mph TAS with 110gal combat tanks. Sweep efficiency even better as there was no need to Ess over bombers while keeping fuel efficiency and tactical speed in the optimal performance envelope.

The key technical improvements were 85gal fuse tank (P-51B Dec 1943), 55gal Leading Edge tanks (P-38J Dec 1943) and 65gal extension to main fuse tank (P-51D-25 June 1944).

The key attributes of P-51B/C and P-38J were the increase to internal fuel (47% P-51B), (36% P-37J), and finally 21% P-47D.

 

[Zipper730]

Just as an item of confusion: Wasn't a Spitfire Mk.IX a modified Mk.V revised to standards similar to the Mk.VII/VIII?

 

[GregP]

Correct, the Spitfire IX was basically a Spitfire V with a 2-stage Merlin (60-series) instead of a single-stage engine (XX or 40-series). Other changes were relatively minor and sometime included a larger fin and rudder ... sometime not. Like most other aircraft that got a power increase, they didn't add the extra tail volume at first, but did later. In the P-51D and P-47D, they added a dorsal fin. In the Spitfire, they made the fin and rudder taller.

Early Spitfire IX drawing:

It was converted from a MK. V airframe.

Later Spitfire IX:

Note the extra fin and rudder height, almost always needed when power was added. They ALSO added a 4-bladed prop to they IX instead of a 3-bladed unit on the Mk.V, so they added area forward of the CL that would require more tail authority.

The Mk. XVI had the same airplane and tail with a cut-down read fuselage and a bubble canopy. Spitfire XVI:

You might find this interesting:

 

[wuzak]

The Mk. XVI had the same airplane and tail with a cut-down read fuselage and a bubble canopy. Spitfire XVI:

The Mk XVI was the Mk IX with a Packard engine, the Merlin 266.

No all Mk XVIs had the cut down fuselage/bubble canopy. And we can see that the Spitfire XIV was built in both standard canopy and bubble canopy versions without change of designation.

Correct, the Spitfire IX was basically a Spitfire V with a 2-stage Merlin (60-series) instead of a single-stage engine (XX or 40-series). Other changes were relatively minor and sometime included a larger fin and rudder ... sometime not. Like most other aircraft that got a power increase, they didn't add the extra tail volume at first, but did later. In the P-51D and P-47D, they added a dorsal fin. In the Spitfire, they made the fin and rudder taller.

The Mk V had 40-series engines in production. No production V had a XX-series engine.

Remembering, also, that the Mk V was a Mk I/II fitted with the Merlin 45. That was chosen because it would bolt in as nearly a direct swap, whereas the Merlin XX would have required fuselage changes.

A V with Merlin XX would have been more competitive with the Fw 190A and Bf 109F-4 than the actual Mk V was.

 

[tomo pauk]

A V with Merlin XX would have been more competitive with the Fw 190A and Bf 109F-4 than the actual Mk V was.

Would you please elaborate on this?

 

[wuzak]

Would you please elaborate on this?

The second gear would have allowed much better performance at lower altitudes, with similar, or better, performance at higher altitude.

The 45 had the same supercharger as the XX. The XX's high gear was slightly higher than the 45's only gear, which meant a slightly higher FTH than the 45.

The V/45 would have had a small advantage at and just before FTH, and, perhaps, at the gear change point of the XX. Basically the V/XX would have been superior, except for a small altitude band.

 

[tomo pauk]

The second gear would have allowed much better performance at lower altitudes, with similar, or better, performance at higher altitude.

The 45 had the same supercharger as the XX. The XX's high gear was slightly higher than the 45's only gear, which meant a slightly higher FTH than the 45.

In theory - yes, the Mk.XX should've provided better high-alt performance, but in reality both were giving about the same power when operating in the FS gear (obviously the only S/C gear available for the Mk.45). Reason probably being that S/C of the Mk.XX was using up more HP there, due to the higher gearing (9.45:1 vs. 9.09:1)?
Yes, the presence of the MS gear on the Mk.XX would've added some performance at very low altitudes.

The V/45 would have had a small advantage at and just before FTH, and, perhaps, at the gear change point of the XX. Basically the V/XX would have been superior, except for a small altitude band.

Mk. XX was also slightly heavier, 1450 lbs vs. 1385.
I reckon that Mk.V/XX would've been superior at really low altitudes, comparable vs. historical Mk.V at medium altitudes, and climbing a tad worse at higher altitudes, with about same speed.
Best thing with Mk.V/XX is that it would've been available already in 1940 - basically a 'MK.III minus'?

 

[33k in the air]

The Blitz Week followed by Scheinfurt-Regensburg two weeks later made it crystal clear that LW would inflict politically unsustainable losses.

Not just politically, but operationally. Even a 5% loss rate is substantial if sustained over a period of time: a starting force of 100 bombers, suffering a constant 5% loss rate per mission, would be down to 63 aircraft after just 9 missions.

 

[Zipper730]

Okay, it seems the issues that have been covered so far are...

Variants & Fuel Loads
With the Spitfire IX/XVI being modified Mk.Vs, why did they become more popular than the Mk.VII and Mk.VIII's? Also, why would the IX have features (i.e. reprofiled elevators) the VII & VIII didn't (unless I'm wrong)?

Regarding internal fuel-loads, I have the following for the Spitfire variants

Mk. I thru II
Upper:......./..48
Lower:......./..37
Total:............85

Early PR Variants
Forward:......85
..Upper:.......48
..Lower:.......37
Underseat:.-80
..Under:.......30
..Aft:.........../50
Wing:...........Unknown
Total:...........165 Minimum

Mk. V
Forward:.........85
..Upper:........./48
..Lower:........./37
Aft:................-29 (w/ 170 gal slipper tank)
Total:....../...../114

Mk. IX
.......................(Mod 1335)....(Mod 1377)....(Mod 1414)
Forward:...........85....................96...............-96
..Upper:............48...................-48..............-.48
..Lower:............37...................-48................48
Aft:................../74.................../74.................66
..Upper:............41.................../41...............-33
..Lower:............33....................33.................33
Total:..............159............../--170............._162

While I think this was covered, but with rear-tankage being used on the Spitfire IX/XVI only with orders from the Squadron commander on the razorback models, and under no circumstance on the cut-back models: This was post-war, correct?

As for what drop tanks were available and when, I'm not sure what was available at what time, though I have a feeling the 170 gallon slipper was available when the 29 gallon tank was available on the Mk.V since the 29 gallon tank couldn't be used without the 170 gallon slipper. It seems that by 1942, the 90 gallon slipper was available as the FAA was using it. I'm not sure when the 89 gallon tank used on the P-40 first became available for use (was this 89 US or Imperial?).

There were also torpedo-tanks, which were just regular drop-tanks most ordinary aircraft used, I'm not sure what was available when, as well.

Procedures & Tactics
I remember reconnaissance variants of the P-38 used a ferry-climb power-setting, which apparently gave superior range over combat climb (I'd have figured it'd work the other way, but almost all my knowledge on aircraft is based on jets). If this is correct, could that have been used on Spitfires for escort to increase range?

Other
GregP pilots had v-n diagrams back in WWII times. I remember looking at a number of pilots handbooks on avialogs (F4U and A-26) and they had the v-n diagram within them. I don't know if the RAF had the same stuff in their documentation, but it stands to reason that they probably would.

 

[wuzak]

I don't recall the elevators being reprofiles specifically for the IX, or any late model Spitfires.

There were changes to them, but I thought that was relatively early in production. Maybe even Mk II.

 

[PAT303]

but it still wasn't enough to make the Spitfire a long-range airplane.

So a Spit with a 96G main, 75G rear aux, twin 13G leading edge and a 90G drop tank is not a long range fighter?.

 

[PAT303]

Added how much fuel when ?

Once the 60 series Merlins came into production, from the MkVIII-IX.

 

[PAT303]

The Mk XVI was the Mk IX with a Packard engine, the Merlin 266.

And from what I have read all of them had 33+33G rear aux tanks from the factory

 

[PAT303]

Best thing with Mk.V/XX is that it would've been available already in 1940 - basically a 'MK.III minus'?

The MkIII was an improved aircraft in every way over the MkV, it just did everything better.

 

[drgondog]

So a Spit with a 96G main, 75G rear aux, twin 13G leading edge and a 90G drop tank is not a long range fighter?.

Fuel capacity is not the only issue, but clearly without the 90gal drop tank it has more internal fuel than P-51B without 85 gal fuselage tank. The combat radius of Spit powered by 1650-3 or -7 equivalent, and using same set of assumptions AAF set for CR, it should be able to go ~ 300 miles and fight for 20 minutes. Better than P-47 with 108gal combat tank.

The 90 gal external tank was a ferry tank IIRC and would not be permitted in AAF for combat ops. The two week desperation trial of the 205gal ferry tank was limited (high drag, unpressurized).

Was the 90gal tank pressurized?

 

[PAT303]

Maybe even Mk II.

That's correct, reprofiling them totally transformed the handling above 350mph as per Winkle Browns writing.

 

[GregP]

I don't recall the elevators being reprofiles specifically for the IX, or any late model Spitfires.

There were changes to them, but I thought that was relatively early in production. Maybe even Mk II.

Check this out, Wayne:

Note the difference between the early, rounded fin and rudder (mostly converted Mk.V airframes with a 2-stage Merlin (61 or 66) and the Late Mk VII / IX fin and rudder. Center bottom is the stab and elevator change for late Mk. IX. The counterbalance area had been increased to make the pitch forces a bit lighter.

And a Merlin 266 is just a Merlin 66 made by Packard. It fits in the same engine mounts and sheet metal as a Roll-Royce Merlin 66. But, I'm sure you knew that.

 

[GregP]

So a Spit with a 96G main, 75G rear aux, twin 13G leading edge and a 90G drop tank is not a long range fighter?.

No.

It's a photographic airplane and had best not get tangled up with ANY fighter with that much fuel as it would be meat on the table. But, it could go fast and take pictures quite well, which is what it did in real life. With the drop tanks gone, unless approved by the commander, you will be missing the 75-gal rear aux volume and you are down to 122 gallons, which is enough for cruising for maybe 2 hours give or take a bit depending on cruise speed, with a bit of reserve. That is not long-range in anybody's book, likely even yours if you think about 8-hours missions a P-51 flew routinely.

 

[wuzak]

Note the difference between the early, rounded fin and rudder (mostly converted Mk.V airframes with a 2-stage Merlin (61 or 66) and the Late Mk VII / IX fin and rudder. Center bottom is the stab and elevator change for late Mk. IX. The counterbalance area had been increased to make the pitch forces a bit lighter.

I did not know that the elevator was upgraded that late.

But it was not actually a required modification to make the IX, as had been claimed. It was more of a general improvement.

The fin is the same in the I, II, V, IX, VIII and XIV. It was the rudder that was changed. Obviously for directional stability.

Late model Spitfires (20-series) got the fin and rudder from the Spiteful, which was larger and had a different shape.

And a Merlin 266 is just a Merlin 66 made by Packard. It fits in the same engine mounts and sheet metal as a Roll-Royce Merlin 66. But, I'm sure you knew that.

Of this I was aware.

Was pointing out that the difference between the IX and the XVI was that the former had a Rolls-Royce engine and the latter had a Packard engine. Some XVIs had the cut down rear fuselage, just as some XIVs had the cut down rear fuselage.

Here is a XVI without the bubble canopy

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