Escort Fighter Performance Comparison

[FLYBOYJ]

If you make up a Spitfire VIII using the various maximum size fuel tanks ever fitted to Merlin Spitfires with the external and/or rear fuselage tanks able to refill the main tanks after take off, the theoretical combat radius comes to around 500 miles, cruising all the way at maximum weak-mixture power setting of 320 mph at 20,000 feet using 66 gallons per hour, corresponding with an engine setting of 2,400 rpm, +4 lbs boost. Which translates to much but not all of Germany when based in England, taking direct courses. The requirements for combat, reserves and the need to burn off some of the rear fuselage fuel before combat means the external fuel limit is about 90 gallons.

Is this indicated in any performance chart?

 

[Shortround6]

theoretical combat radius comes to around 500 miles, cruising all the way at maximum weak-mixture power setting of 320 mph at 20,000 feet using 66 gallons per hour,

The requirements for combat, reserves and the need to burn off some of the rear fuselage fuel before combat means the external fuel limit is about 90 gallons.

It doesn't matter what the external fuel was, It the British wanted they could have come up with a 120 IMP gal drop tank.

What mattered was the roughly 54 Imp gal for the combat allowance and the 10-15 gal reserve for finding your own (or any) airfield after crossing the coast. Also the wind was usually coming from the west.
Your operational radius was the distance you could fly at the desired exit speed/s after combat and before having to hunt for a friendly airfield.

Again provisional numbers for the P-51B are 315mph at 20,000ft using 36imp gals GPH clean and 329mph at 20,000ft using 51 GPH with the pair of 75 US gallon drop tanks.

I am sure the Spit would show a difference with and without the drop tanks. A newer manual could very well show a difference in the P-51 numbers.

It is going to take 25-30 gallons just to warm up - takeoff - climb to 25,000ft (doesn't include form up on the charts but lets assume it does) so that takes care off most of the burn off of the rear tanks to get close to combat capacity. Warm up/take off is done on the main tank/s but any fuel over flow in cruise is routed back to the main tank/s so they are full or near fuel after a couple of hours.

 

[33k in the air]

That chart s wrong on so many levels. The Combat Radius for the P-47C without belly tank was 125+ mi CR. The Combat Radius of the P-47C/D with 75 gal c/l tank was 230mi (Aug 1943),with 2x150gal pylon tanks was 425mi circa March/April 1944. These values for 25K cruise zone altitude.

That chart appears to be based on the charts published in the document Eighth Air Force Tactical Development August 1942–May 1945 (Chart A and B, p.97 of document, p.119 of PDF). Below is what is shown on Chart A for the P-47:

May 1943 = 175 miles
June 1943 = 230 miles
July 1943 = 340 miles (1 x 75-gallon drop tank)
Aug. 1943 = 375 miles (1 x 108-gallon drop tank) (+33 gallons, +35 miles compared to 1 x 75-gallon)
Feb. 1944 = 425 miles (1 x 150-gallon drop tank) (+42 gallons, +50 miles compared to 1 x 108-gallon)
Feb. 1944 = 475 miles (2 x 108-gallon drop tanks) (+66 gallons, +50 miles compared to 1 x 150-gallon)

The increases are roughly one mile per additional gallon carried when drop tanks are used.

The accompanying text which describes the figures shown on the chart, however, says the 475-mile range was achieved with 2 x 150-gallon tanks. I think that text is a typo, as only an additional 50 miles is gained despite carrying an additional 150 gallons, which is out of place with the gains made from the prior drop tanks.

 

[Mike Williams]

When the Ministry of Aircraft Production began reporting external fuel tank production in December 1943 Spitfire 90 gallon tanks were being made at about 500 per month.

That's interesting and has got me curious now as to when the 90 gallon tanks started to be used on Spitfires operationally. I have a few docs on hand and will dig around for others:

http://www.wwiiaircraftperformance.org/111-kennedy-10sept43.jpg

 

[drgondog]

That chart appears to be based on the charts published in the document Eighth Air Force Tactical Development August 1942–May 1945 (Chart A and B, p.97 of document, p.119 of PDF). Below is what is shown on Chart A for the P-47:

May 1943 = 175 miles
June 1943 = 230 miles
July 1943 = 340 miles (1 x 75-gallon drop tank)
Aug. 1943 = 375 miles (1 x 108-gallon drop tank) (+33 gallons, +35 miles compared to 1 x 75-gallon)
Feb. 1944 = 425 miles (1 x 150-gallon drop tank) (+42 gallons, +50 miles compared to 1 x 108-gallon)
Feb. 1944 = 475 miles (2 x 108-gallon drop tanks) (+66 gallons, +50 miles compared to 1 x 150-gallon)

The increases are roughly one mile per additional gallon carried when drop tanks are used.

The accompanying text which describes the figures shown on the chart, however, says the 475-mile range was achieved with 2 x 150-gallon tanks. I think that text is a typo, as only an additional 50 miles is gained despite carrying an additional 150 gallons, which is out of place with the gains made from the prior drop tanks.

Dean Published the AAF Combat Radius Tables for several of the conditions above. Reference pp 599-600.Also note the differences between 10K and 25K altiude with 10K cruise achieving a delta of ~+25-50mi for in-line. His source for the 'practical' Combat radius was developed by USAAF at Wright Field 1943-1945.

From a practical standpoint there also was a difference between Wright Field/contractor collaboration Range tables, the Operating Manual Tables and Operations in ETO. Notably the 108gal single went into Operations in September but no VIII FC P-47 penetrations as far as Bremen occurred until November 13, 1943. Strikes Occurred, but without fighter escort at the target. The escorted strike on Bremen , with the 4th penetrating deepest, launching from forward base Shipdam near coast, Direct air miles in 325mi range.

Despite having 108 gal external, the escort was not going past Quackenbruck, Lingen and Munster in October, so AFAIK Bremen Target Escort (optimal as little essing performed) first occurred on November 13th, 1943. The 55th FG (P-38s) got several that day and the 355th performing Withdrawal support at Bremen got several VCs just west of Bremen as B-17s were returning home. The 355th staged at Bungay for the mission, well forward of Steeple Morden, about 325 mi to Bremen w/108 gal tank. .The Only Group level missions in excess of Bremen was when they were able to mount 2x150 'flat tanks' to cross over 400 mi CR in April/May 1944.

To the table/data above the first 108 gal belly tank missions were flown in late September, 1943. To the table above the value '475' for 2x108 tanks in Feb 1944, only a very few P-47C/D had been depot modified with interanal plumbing and racks by February, The -15/-16s were arriving but not operational in squadron levels until late March.

Here is the bottom line between the various and contradictory CR charts. A.) none match up to he Wright Field published charts that Dean drew from, b.) no fighter missions actual combat radius in context of extremes for losses and victory credits in air combat are closely aligned wth the combat radius values specified Eighth Air Force Tactical Development August 1942–May 1945 (Chart A and B, p.97 of document, p.119 of PDF). The contradiction doesn't make 'them' wrong but does raise into question the practical standard for operations planning using various sources.

For my book (deathless prose to be sure) I based much of my range tables on Dean and performed my own Breguet calcs using published fuel consumption rates published in various flight tests and bench tests. There were Contradictions requiring judicious application of silver dollar to resolve. The tie breaker wa always, 'so how far did they plan to go, with reserve for weather/winds and combat and loiter time on return'.

On March 29 the 56th penetrated as far as Dummer Lake in the 390 mi range from Boxted w 1x150s and as far as Stuttgart with 2x150s n late April. (420mi) on a Sweep with no escort duties. Until the P-47s got their 65 gal increase internally they were limited to a Brunswick/Stuttgart radius of operations.

 

[33k in the air]

Dean Published the AAF Combat Radius Tables for several of the conditions above. Reference pp 599-600.Also note the differences between 10K and 25K altiude with 10K cruise achieving a delta of ~+25-50mi for in-line. His source for the 'practical' Combat radius was developed by USAAF at Wright Field 1943-1945.

For what it's worth, Eighth Air Force Tactical Development August 1942–May 1945 was prepared by the Eighth Air Force and the Army Air Forces Evaluation Board (European Theater of Operations) and published in July 1945.

So it seems there are different sets of figures from what would seem to be official sources.

 

[drgondog]

Yes - and to be clear all the Wright Field and Contractor Range Tables were established in clear weather in many cases close to STP in controlled conditions and many authors did Not understand even the fundamentals of publishing the boundary conditions to proclaim what a Combat Radius actually was.

It was - and is - a planning document for a pilot or operations officer to understand an ideal flight plan to go from A to B - then draw conclusions for the group CO/Squadron CO to evaluate adverse winds aloft encountered contrary to briefed weather, loiter for early R/V, seein a bomber force in trouble past the 'point of no return' based on the 20 minute combat burn.

AFAIK, there was no single document in which the 'Bible' was collectively agreed until 1945. Additionally the individul Pilot Operating Manual Tables exhibited straight line travel for the selected assumptions. including fuel burn rate vaues baked for each MP/RPM recommendation, internal/external tanks and altitudes based on their own flight tests. That said, Materiel Command was in the approval cycle.

I also recall that in our earlier discussion n this subject months ago, one of the 8th AF radius charts WAS accompanied by some boundary conditions very much like the AAFMC 1945 chart values (in some cases) but not referencing MC or Contractor charts.

I will state unequivocally that the optimistic CRs were composed by Brequet equations which are reasonably sohisticated and far easier with computers to integrate each leg with sfc values for propsed RPM/Boost per leg (withut having to worry about wingman jockying throttle trying to stay on element leader's wing who in turn is trying to stay with the boss). Actual ETO/Combat variables took a chunk out of each segment thus calculated.

 

[Glider]

The following couple of pages may be of interest as the describe the use of 90 gallon tanks as a routine operation from around December 1943. The problem being the shortage of the tanks.

 

[Geoffrey Sinclair]

Is this indicated in any performance chart?

Yes if you are referring to the fuel consumption. Cruise 320 mph TAS at 20,000 ft, corresponds with an engine setting of 2,400 rpm, +4 lbs boost, consumption 66 gallons per hour. In the following I will add 20 gallons for a reserve, which would be around 30 minutes at 170 mph IAS. And ignore the obvious consumption penalties for carrying external loads, hauling a heavier load to altitude, penalties for formation flying, variations between individual aircraft and pilots when it came to fuel consumption, or an allowance for faulty navigation. Or the gains from using economic cruise for part of the outbound and return

It doesn't matter what the external fuel was, ... It the British wanted they could have come up with a 120 IMP gal drop tank.What mattered was the roughly 54 Imp gal for the combat allowance and the 10-15 gal reserve for finding your own (or any) airfield after crossing the coast. Also the wind was usually coming from the west. ... It is going to take 25-30 gallons just to warm up - takeoff - climb to 25,000ft

The RAF allocation was 23 gallons for take-off and climb to 20,000 ft and 36 gallons for 15 minutes of combat, where do the figures quoted above come from?

Your operational radius was the distance you could fly at the desired exit speed/s after combat and before having to hunt for a friendly airfield.

As I have been using. Spitfire VIII 124 gallons internal.

Spitfire VIII in 1945 with 75 gallon rear fuselage tank, 40 gallons need to be used before it is considered safe to enter combat leaving 35, giving 124+35 = 161 -36 -20 = 105 for return, 40 internal + 90 external -23 = 107 gallons outbound.

The early 1943 Spifire VIII 124-36-20 = 68 gallons for return, 90 external -23 = 67 gallons outbound. That gives a nominal combat radius of around 300 miles.

Therefore the comment about an external fuel limit of around 90 gallons.

The what if later 1943 Spifire VIII equipped and able to enter combat with a full 33 gallon rear fuselage tank, that adds 80 miles to the nominal combat radius.

Roger Freeman combat radius, 8th Air Force,
P-47 280 miles 84 gallon external tank, August 1943
P-47 325 miles 108 gallon external tank, September 1943
P-47 375 miles 165 gallon external tank, February 1944

Keeping the Spitfire able to reach about as far as the P-47 as the aim, given how much combat the P-47 saw in the time period.

 

[PAT303]

Keeping the Spitfire able to reach about as far as the P-47 as the aim, given how much combat the P-47 saw in the time period.

Exactly, we don't need to fly to Berlin or do anything fancy, just get the Spit into Germany late '42 onwards, P47's saw continuous air combat with the limited range they had, the Spit could have joined them.

 

[drgondog]

For what it's worth, Eighth Air Force Tactical Development August 1942–May 1945 was prepared by the Eighth Air Force and the Army Air Forces Evaluation Board (European Theater of Operations) and published in July 1945.

So it seems there are different sets of figures from what would seem to be official sources.

As long as the subject has been beaten to death, the primary issue is that the Combat Radius as defined, is a straight line optimal climb from take off to cruise, cruise, fight and return.

ETO added much longer engine start and taxi for 48+ airplanes, staged take off usually in pairs, forming up fights, squadrons into group before climb, fly essentialy straight line to coast, branch to R/V - with weather always a wild card.

The P-47 ops were even more complicated because much of its history in ETO was close escort, requiring 'essing' for at least one squadron from R/V to R/V,then return. With the long range role, both the Mustang and P-38 flew many missions picking p the baton from the jug groups much farther away from base before any 'essing' required - usually much closer to target.

Another consideration for you in your own analysis - is to look at the encounter reports and note that almost zero P-47 Victory credits and MACRS were beyond the target for their escorted bombers. These docs paint a clearer picture of the radius of action to return to base on remaining internal fuel after a fight. Those reports are a clearer Practical marker for the mission planning application of 'real Combat Radius' vs 8th AF or MC publications.

Only when the P-47D-25 with 370gal internal were the 'extended CR' feasible.

The longet mission I found in 1944 for P-47D-25+ (with 370 gal + 2x150s) was July 7, 1944 when the 78th swept to Leipzig and Dec 4 when 56th swept to W/Brandenburg.

 

[GregP]

It doesn't matter what the external fuel was, It the British wanted they could have come up with a 120 IMP gal drop tank.

What mattered was the roughly 54 Imp gal for the combat allowance and the 10-15 gal reserve for finding your own (or any) airfield after crossing the coast. Also the wind was usually coming from the west.
Your operational radius was the distance you could fly at the desired exit speed/s after combat and before having to hunt for a friendly airfield.

Again provisional numbers for the P-51B are 315mph at 20,000ft using 36imp gals GPH clean and 329mph at 20,000ft using 51 GPH with the pair of 75 US gallon drop tanks.

I am sure the Spit would show a difference with and without the drop tanks. A newer manual could very well show a difference in the P-51 numbers.

It is going to take 25-30 gallons just to warm up - takeoff - climb to 25,000ft (doesn't include form up on the charts but lets assume it does) so that takes care off most of the burn off of the rear tanks to get close to combat capacity. Warm up/take off is done on the main tank/s but any fuel over flow in cruise is routed back to the main tank/s so they are full or near fuel after a couple of hours.

I don't think you will see 315 mph @ 36 gph @ 20,000 feet. Maybe 56 gph, but not 36 gph unless you are at sea level, 1600 rpm, and 220 mph.

 

[33k in the air]

As long as the subject has been beaten to death . . .

Perhaps so, but I still find the discussion useful precisely because the sources differ on the figures, and only by discussing it can such differences be sorted out and the truth, however imperfectly, approached.

Another consideration for you in your own analysis - is to look at the encounter reports and note that almost zero P-47 Victory credits and MACRS were beyond the target for their escorted bombers. These docs paint a clearer picture of the radius of action to return to base on remaining internal fuel after a fight. Those reports are a clearer Practical marker for the mission planning application of 'real Combat Radius' vs 8th AF or MC publications.

Alas, I don't have access to archives I can visit in person, so I'm limited to what has been digitized and posted online. This is both great and frustrating. It's great in that I can view information I'd probably never be able to see otherwise, but it's frustrating because there is still so much material that has yet to be digitized. That said, I'm thankful for everything that has been digitized and made more readily accessible.

Only when the P-47D-25 with 370gal internal were the 'extended CR' feasible.

The longet mission I found in 1944 for P-47D-25+ (with 370 gal + 2x150s) was Oct 7, 1944 when the 78th swept to Leipzig and Dec 4 when 56th swept to W/Brandenburg.

Were these the 'flat' 150-gallon tanks or the P-38's teardrop-shaped tanks? The 150/165-gallon P-38 tanks were definitely used in the Pacific by P-47s, based on photos of wartime P-47 units in the PTO.

 

[drgondog]

Perhaps so, but I still find the discussion useful precisely because the sources differ on the figures, and only by discussing it can such differences be sorted out and the truth, however imperfectly, approached.



Alas, I don't have access to archives I can visit in person, so I'm limited to what has been digitized and posted online. This is both great and frustrating. It's great in that I can view information I'd probably never be able to see otherwise, but it's frustrating because there is still so much material that has yet to be digitized. That said, I'm thankful for everything that has been digitized and made more readily accessible.



Were these the 'flat' 150-gallon tanks or the P-38's teardrop-shaped tanks? The 150/165-gallon P-38 tanks were definitely used in the Pacific by P-47s, based on photos of wartime P-47 units in the PTO.

Both but mostly 'flat' because it could be attached to C/L ack, whereas the round crosssection 150 was a potential hazard. Kenney was 'different' from Eaker/Doolittle in command style,

 

[drgondog]

I don't think you will see 315 mph @ 36 gph @ 20,000 feet. Maybe 56 gph, but not 36 gph unless you are at sea level, 1600 rpm, and 220 mph.

I think this is best chart. Racks only Cruise - 2050RPM 29" 52gph 303mph for 25K http://www.wwiiaircraftperformance.org/mustang/P-51D_15342_AppendixB.pdf

May 1945 Flight tests for range in P-51D-15

 

[PAT303]

Despite having 108 gal external, the escort was not going past Quackenbruck, Lingen and Munster in October, so AFAIK Bremen Target Escort (optimal as little essing performed

He's another idea, lets forget the escorting in 1942-43, just send Spit V's and P47's out as far as they can go, say 200 miles and let MkIX's go as far as they can go which will be over 400 miles, instead of escorting per say lets make them fighter sweeps so they can fly at their best altitude an speed, the Luftwaffe are going to engage if there is a bomber mission going on so the fighters can engage independently of they are doing.

 

[33k in the air]

He's another idea, lets forget the escorting in 1942-43, just send Spit V's and P47's out as far as they can go, say 200 miles and let MkIX's go as far as they can go which will be over 400 miles, instead of escorting per say lets make them fighter sweeps so they can fly at their best altitude an speed, the Luftwaffe are going to engage if there is a bomber mission going on so the fighters can engage independently of they are doing.

Here's a better idea: put a Merlin into a P-51 airframe in early 1941 instead of late 1942.

 

[Shortround6]

Here's a better idea: put a Merlin into a P-51 airframe in early 1941 instead of late 1942.

About the 42nd time somebody has suggested this

 

[Shortround6]

just send Spit V's and P47's out as far as they can go, say 200 miles and let MkIX's go as far as they can go which will be over 400 miles, instead of escorting per say lets make them fighter sweeps so they can fly at their best altitude an speed,

And this would work so much better than the whole "lean to France" thing why?

The Germans had had almost 2 years of experience in avoiding fighter sweeps and trying to bounce small pockets of bombers (used as bait) and small pockets of fighters (disconnected from the main groups).

A fighter sweep that is even 10 minutes off in timing is going to be 50 miles from the bombers. (assuming the fighters are doing 300mph).
The Germans had radar, they had the ability to plot tracks. Maybe not as well as the British but this was 1942-43 and not 1940.

 

[33k in the air]

About the 42nd time somebody has suggested this

Great minds think alike (and with the benefit of hindsight)!