The Great P-47 Range Debate on you tube now.

[ThomasP]

Hey Squish,

I found the specs on the 150 USgal fibre drop tank for the P-39 & P-40 (you are correct, it was made by Ohio Rubber). Unfortunately it was not pressurized, so I suspect using it on the P-47 would have involved the same problems at higher altitudes as with the 200 USgal ferry tank. I have to wonder how much it was used as I have never seen a photo of this tank on any aircraft.

 

[ColFord]

and a picture of (possibly) the only surviving 'Brisbane' tank known as of today

In varying conditions, with and without the braces, configured to fit the early Republic skid plate and the later USAAF standard lugs, certainly three still in existence down under. maybe four.

 

[Geoffrey Sinclair]

P-47 time line.

XP-47, XP-47A, XP-47B contract 17 Jan 1940 (Also Curtiss XP-46, XP-46A, 5 days later Lockheed XP-49)
P-47B/C contract 13 Sep 1940 for 773 aircraft from Farmingdale, also 54 P-43.

XP-47B first flight 6 March 1941
P-47D contract 14 Oct 1941 for 850 aircraft from Farmingdale

First production P-47B in December 1941
P-47D contract 31 Jan 1942 for 1,050 aircraft from Evansville
P-47G contract 31 Jan 1942 for 354 aircraft from Curtiss

Next 5 production P-47B in March 1942, then from May 1942

Switch from P-47B to C production September 1942, Curtiss first P-47G
Evansville P-47D production start October 1942.
Farmingdale passed 100 acceptances for the month in November 1942, then 200 in May 1943, reached 300 in July.

Farmingdale switch from P-47C to D production February 1943.

Republic Farmingdale (RE) built in order P-47B, P-47C, D-1, D-2, D-5, D-6, D-10, D-15, D-16, D-20, D-21, D-22, D-25, D-27, D-28, D-30
Republic Evansville (RA) built in order P-47D, D-2, D-3, D-4, D-11, D-16, D-15, D-20, D-21, D-23, D-26, D-28, D-30, D-40
P-47C with provision for Republic proprietary 200 gallon belly tank from September 1942.
P-47D-6-RE with standard belly tank shackles produced from mid July 1943
P-47D-4-RA with standard belly tank shackles produced from mid August 1943

Total of 602 P-47C and 849 P-47D from Farmingdale plus 414 P-47D from Evansville, total 1,865 with Republic fittings, once the decision was taken to switch to USAAF standard fittings no need for more Republic tanks. If there was a second Republic design in March 1943 for a 200 gallon tank meant for more than ferrying it was overtaken by events.

220 of the 602 P-47C were exported to Britain November 1942 to February 1943.

Evansville passed 100 acceptances for the month in September 1943.

3 P-47D delivered for USSR in September 1943, first foreign deliveries, 2 more for Britain in November.

On 17 October 1943 the 7 operational P-47 Groups with the 8th Air Force reported strength as 76 P-47C, 12 P-47C-2, 16 P-47C-5, 307 P-47D, 12 P-47D-1, 32 P-47D-2, 61 P-47D-5, 16 P-47D-6 and 1 P-47D-10

P-47D-15-RE with wing pylons produced from late October 1943
P-47D-16-RA (Or D-15) with wing pylons produced from end November 1943
P-47D-25-RE with increased internal fuel produced from March 1944
P-47D-26-RA with increased internal fuel produced from late April 1944

There do not seem to be any surviving Republic documents giving their views on events.

The USAAF was essentially a late 1943 to early 1944 air force, that is arrival of modern types in numbers, the result of when mobilisation started, training time, the laws of mass production and the distance to the front line.

To restate my opinion, the P-47 was meant as the next generation main USAAF single engine single seat fighter, it meant 3 production lines, not the 1 of the other fighter types, it meant a lot of pressure to deliver numbers quickly given the performance of the P-39 and P-40. The memos about P-47 being available in England in numbers in 1942 "Bolero" show some of the pressure. Republic would have thought it had done well, 305 gallons internal gave a range comparable to the twin engine P-38 and better than the P-39 and P-40, getting 200 gallons of fuel under the fuselage was also an achievement.

Lockheed built around 100 P-38 a month in 1942 and around 150 a month for the first 6 months of 1943, plus had others built as F-4 and F-5, it meant the USAAF struggled to keep at strength the 3 P-38 groups in the Mediterranean plus effectively various squadrons fighting the Japanese. In 1943 the 5th Air Force was essentially told no P-38 you have to take the P-47 if you want something more than the P-40.

After the unit moves to the 12th Air Force the 8th Air Force was down to 1 Spitfire group for its 6 heavy bomber groups. As of mid April 1943 it was 3 P-47 to 6 heavy bomber. It took until mid August for another P-47 group to go operational by which stage there were 3 medium and 16 B-17 heavy bomber groups as the B-24 were on detached service. Mid October 7 P-47 to 20 heavy bomber plus 4 medium.

Wherever the 8th Air Force went in 1943 it was not going to have a lot of fighters unless within Spitfire range.

The result was a decision to bomb targets more according to their importance, with doctrine being once strength had been built up, 300 bombers a raid, the lack of defence in depth would keep bomber losses to acceptable levels. The 300 number did not change despite the growth in defences nor the trends in losses. Given the small number of raids on Germany through mid 1943 it was always possible to give a reason for heavy losses on a given raid along with a remedy. Looking at Mighty Eighth War Diary the heavy bombers and fighters largely went their own ways until mid 1943, often more protection to the mediums than heavies.

Roger Freeman tracks 8th Air Force external fuel tanks as follows, plenty of 75/84 P-39 and 150/165 P-38 tanks arriving in 1942, P-47 ferry tanks arrived in early 1943, they were quickly ruled inadequate. Local design for steel 100 gallon tank ran into a lack of steel. Result was switch to 108 gallon paper tank originally for Hurricanes, approved on 7 July 1943. Rigging 75 gallon tanks to use Republic fittings was done. In September the steel and paper tanks began arriving in numbers, with a 4 inch clearance some airfields were ruled too rough to allow the tanks. The flat 150 gallon belly tank was approved in mid August but took until March 1944 to arrive, the US design began arriving in February 1944. When the wing racks appeared the usual load was a 108 gallon on each, using the 150 gallon caused problems. AFHRA Reel A2069 Page 1551 to 1554 dated 4 October 1943 calculations state with 305 gallons internal the P-47D could use a maximum of 235 gallons external for range, combat radius 450 miles.

The USAAF asked Britain to supply drop tanks from at least early 1943 but did not place large orders until June and final design approval was in early October, by 1943 the British economy was fully stretched, little capacity for rapid changes or rush orders. With a world wide shipping shortage the last thing the allies needed was to ship large numbers of empty containers from the US to Europe, ideally they could come as parts to be assembled in Britain or be made locally.

When General Eaker wrote to Air Vice Marshall Freeman about drop tanks Eaker estimated fighters could have saved about two thirds the losses on the 10 October 1943 Munster raid, yet even if all the P-47 airborne that day were escorting the bombers the Luftwaffe was flying over twice as many fighter sorties as the USAAF did and concentrating on one of the two bomber formations, the USAAF fighters present would be outnumbered around 4 to 1.

According to Freeman some 108 gallon paper tanks were sent to the US in 1943 and the subsequent report said unsuitable for operations.

In December 1943, Ministry of Aircraft Production. External fuel tank production for P-47. No figures available before December.
5,943 x 90 Imperial/108 US Gallon, Paper composition
3,095 X 90 Imperial/108 US Gallon, Metal composition
First production of 150 US Gallon Metal composition tanks in February 1944.

For the P-47 to take full advantage of the 305 gallons internal fuel required wing racks. To get the P-47 close to the sorts of targets the 8th Air Force went after in Germany in 1943 required the redesign that gave it 370 gallons of internal fuel.

Given warm up and take off to safety height is on internal tanks the external tanks need to be able replenish the internal ones in flight or deductions need to be made from the internal fuel available after the external tanks are empty. Decide on the way out whether the fighters are at bomber speed, more range, less chance of stopping the interceptors, more chance of being the target, or at fast cruise, covering about 5 miles for every 4 the bombers move.

Start with 305 gallons
89 gallons Fuel Consumed for 5 minutes War Emergency Power & 15 minutes Military Power.
36 gallons for 30 minutes reserves at 50% power
180 gallons maximum left to come home on.
Now decide how high and how fast the return is, lower and slower more range, more chance of being intercepted on the way back, or whether the fighters try to stay with the bombers during the return. As a result plenty of ideas about combat radius.

AN 01-65BC-1A Pilot's Flight Operating Instructions for Army Models P-47D -25, -26, -27, -28, -30, and -35 Airplanes dated 25 Jan. 1945
America's Hundred Thousand Francis Dean
P-51B Mustang — North American Bastard Stepchild that Saved the Eighth Air Force James William "Bill" Marshall and Lowell F. Ford
Plate from a historical document entitled Extension of Combat Radius
Eighth Air Force Tactical Development — August 1942–May 1945
Tactics and Techniques Developed by the United States Tactical Air Commands in the ETO.

P-47 Combat range miles versus amount of internal and external fuel, gallons.
Source: HunThou, Internal 305, External 0, Combat Radius 125
Source: P-51B, Internal 305, External 0, Combat Radius 125
Source: ExtCmbRad, Internal 305, External 0, Combat Radius 150
Source: 8thTAC, Internal 305, External 0, Combat Radius 175, Note: 10,000 ft, May 43
Source: P-51B, Internal 305, External 75, Combat Radius 230
Source: ExtCmbRad, Internal 305, External 75, Combat Radius 250
Source: 8thTAC, Internal 305, External 75, Combat Radius 340, Note: 10,000 ft
Source: P-51B, Internal 305, External 108, Combat Radius 275
Source: ExtCmbRad, Internal 305, External 108, Combat Radius 300
Source: 8thTAC, Internal 305, External 108, Combat Radius 375, Note: 10,000 ft
Source: P-51B, Internal 305, External 150, Combat Radius 375
Source: 8thTAC, Internal 305, External 150, Combat Radius 425, Note: 10,000 ft
Source: 8thTAC, Internal 305, External 216, Combat Radius 475, Note: 10,000 ft 2x108
Source: HunThou, Internal 305, External 300, Combat Radius 425, Note: 2x150
Source: P-51B, Internal 305, External 300, Combat Radius 425, Note: 2x150
Source: ExtCmbRad, Internal 305, External 300, Combat Radius 500, Note: 2x150

ExtCmbRad, conditions
Escort fighter accompanying B-17 at 185 mph IAS
Full power (max continuous) climbing to 25,000 feet
Cruise at 210 mph IAS, 300 mph TAS
Tanks dropped when empty or at radius
15 minutes combat at military power
5 minutes combat at war emergency power
Return to base at required cruising speed accompanying bombers
30 minutes fuel reserve

What is really needed are the 8th Air Force planning documents through 1944 as experience built up and they were able to refine tactics and fuel loads for a given distance to target. Something coming in the new book I believe.

Now add 65 gallons of extra internal fuel and you have over a third more fuel to come home on.
Source: HunThou, Internal 370, External 0, Combat Radius 225
Source: T&T, Internal 370, External 0, Combat Radius 230, Note: 2x1000lb bomb
Source: ExtCmbRad, Internal 370, External 0, Combat Radius 250
Source: T&T, Internal 370, External 0, Combat Radius 260, Note: 2x500lb bomb
Source: T&T, Internal 370, External 0, Combat Radius 280
Source: T&T, Internal 370, External 108, Combat Radius 360, Note: 2x500lb bomb
Source: T&T, Internal 370, External 108, Combat Radius 400
Source: T&T, Internal 370, External 300, Combat Radius 575, Note: 2x150
Source: HunThou, Internal 370, External 300, Combat Radius 600, Note: 2x150
Source: ExtCmbRad, Internal 370, External 300, Combat Radius 700, Note: 2x150

General Eaker asked Arnold for Mustangs and Lightnings in June 1943 and received the 20th and 55th FG along with P-51.

AIR 19/524 RAF Thunderbolt imports mark I = P-47D-15 to D-23, mark II = P-47D-25 and later blocks. First mark I in January 1944, next in April, final in August. First mark II in May 1944, final in September 1945. Distribution India 215 I and 534 II, Middle East 22 I and 48 II, UK 2 I and 4 II.

 

[Squish]

When you look at the 1943 P-47 Operating Instructions, the cruise data only shows 12,000 feet altitude in the tables. Hough and AAF found that with the 200gal tank that a.) cruise speed should not exceed 200mph IAS, and b.) that the tank would not draw fuel above 22,000 feet.

It was never designed as a 'combat tank' for several reasons. First, it was extremely draggy and dangerous to jettison in flight. Second, the original four point design created difficulties to correctly mount and secure with the four point mount scheme. Last but not least it was not designed to be pressurized internally to enable forced pressure from the engine vacuum system. The G9 and K-1 submersible pumps enabled higher altitudes but equally cumbersome to install in the tank.

The flying qualities above 200 mph degraded quickly making the P-47 increasingly unstable and difficult to fly in formation. Note again that 200mph IAS is the upper limit cruise speed at 32" MP.

My point of contention isn't that the Republic/ORC 200 Gallon was a bad design but rather that it being a bad design doesn't preclude it's dual use as a combat tank. Basically we are in agreement that the tank is a piece of crap.


My hypothesis is basically the following;

The Mar.27 memo established desire to use some form of 200 gallon tank for combat range extension.

Republic designed the 200 gallon tank in response to the de-facto RFP for a 200 gallon combat extension tank and then send the blue prints to their list of subcontractors. Without the blueprints it would be impossible to tell if there would be any external differences in the metal or paper tank. There however was only one set of drawings for the 200 gallon tank so it leads me to believe that a metal one would be identical.

The only tank that was procured for the P-47 in 1942 with the old centerline system was the ORC tank. This is in spite of Bolero having a requirement for combat tanks. Why didn't anyone design a novel combat tank for the P-47 if the 200 gallon one was only for ferrying?

The answer is that Republic, the AAC, or some combination of both thought this tank was combat capable. It isn't until the tank gets to Europe and they attempt to actually use it that 8th AF discovers that the tank is a complete lemon. This prompts Bradshaw to ask once again to adapt the plane to Lockheed wing tanks.

Not only does it prompt Bradshaw to request the plane be adapted to wing tanks but it also prompts AAC to amend T.I 1016 to specify that drop tanks cannot adversely alter the flight characteristics of the aircraft. This is I want to say the July or August revision; it is the same revision that also causes the AAC to specify that drop tanks need to be able to draw fuel to the critical altitude of the aircraft, and what prompts fitting of K-1 pump to Republic ORC tank in testing.

Basically I think my opinion is that the tank and the situation around it is probably even worse than you think. I think Republic did a half assed job on it and then claimed it filled the requirements. And the AAC took Republics word for it in 1943 in order to expedite delivery of planes.

 

[Squish]

There are several errors in the above charts. They were later corrected when FAREP (April 45) presented tables for all conditions of fuel and gross weight by model. There is also

The P-51B yardstick range was 975 mi with 180-gal internal fuel only. GW =9237. Escort range 175mi.
P-51B Internal fuel 269 gal range, GW = 9830. Yarstick Range 1,350. Escort range 375mi
P-47D yardstick range was 835mi with 305-gal internal fuel. GW=13, 580mi. Escort range=125mi.
P-47D yardstick range (D-25) was 1020 mi, GW=14,400. Escort Range=275mi.

Additionally the tables you retrieved were incorrect in the following:
P-51B with only 180 (184) gallons internal fuel had GW=9237 (not 9,050) pounds, never carried 108 0r 150-gal drop tanks. Only when all P-51Bs were upgraded to 269-gal internal fuel (kit and factory by Feb 1944) were 108-gal tanks added to inventory for Mustangs in May 1944. Heretofore all 108-gal drop tanks went to P-47 missions.

The label 'Two 150-gal tanks' for the gross weight addition of ~2,100 pounds over the GW of P-51B w/o 85-gal fuse tank would have been correct ONLY for the addition of 2x108-gal drop tanks plus the 85-gal fuse tank. In any case the yardstick range for P-51B with only 180 gal Internal fuel plus 2x75-gal wing tanks was 1575mi.
The Yardstick range of the P-51B with 269gal (265 in chart and table) plus 2x75-Gal was 1850.

Additionally incorrect in the above table for the P-47D with 305 gal internal and 2x150-gal externals. The GW is correct (15,600) but the yardstick range was 1,525mi, much more than 1,045mi shown (but still 300mi shorter than P-51B with 180-gal internal plus 2x75-gal externals.

The P-38H/J/K on internal fuel of 300-gal was also severely understated. All at 17,000 to 17,600 pound GW had yardstick ranges near 900 mi, which increased to 1,175mi when the 2x55-gal LE tanks were added.

Suggest you find AAF Tactical Planning - Characteristics and Planning Chart, AAF Materiel Command, Technical Division. It is a monthly release of performance, range and weight tables for all AAF aircraft (incl. XP-51F and XP-72). These reports are the source data for FAREP, although FAREP made multiple mistakes in the transformation of the data. Also The Characteristics and Performance Charts from same sources are what you see in the contractor Pilot Operating Manual


In turn, the sources for the AAFTP and CPC chart data were the actual contractor Performance Analysis Reports for each model.


The AAFTP data is what I founded all my FAREP tables presented in my new book.
First

Here is something I found interesting in FAREP. At some point I will vacuum up all of the range estimates and try to itemize how they were made and how one is conflated with the other etc since they do seem to be all over the place. I think it would be possible to build the process in Excel and then be able to get a decent approximation of how winds aloft etc would impact range on any given day.

I am including a bad-cropping of the FAREP reference chart. Yes I know that you have said that it is wrong. We are not going to worry about that because it is the chart that Greg referenced in his video and it is what I have quickly on-hand to make back-of-napkin style calculations. The version of this chart that Greg referenced in his first video is also uncorrected and shows P-47D-Late with 700 miles of range instead of 625 miles.

The values in the FAREP chart show a range of 350 miles for the P-38J + Twin 150's without the extra internal fuel of later models. It shows 650 miles for P-38J + Twin 150's with the extra internal fuel. Our other chart shows 200-300 miles for early P-38J + Twin 150s and it shows 375-475 miles for the late P-38J + Twin 150s.

The difference between the two charts are as follows;
Early P-38J = 50 - 150 miles less than FAREP chart. (14% - 42% Reduction)
Late P-38J = 175 - 275 miles less than FAREP chart. (27% - 42% Reduction)

This comparison is probably a bit skewed; it is late at night for me but I don't think we need to take the FAREP numbers and cut them all by 42%. Maybe a more logically consistent way of looking at this is referencing the differences between the offensive fighter mission profile and escort mission profile noted in our 2nd image.

If we compare the sets of high estimates for both we still see about a 30% reduction in range from flying escort mission profile with "S"-ing with the bombers vs the pure fighter mission.

For the sake of argument, what happens when we take the range estimates for the P-47 and 2x150s and multiply by 0.7? We get a new range of 437 miles for a P-47 w/ twin tanks + 370 gallons internal. It would also give us a range of 350 miles for P-47 w/ twin tanks + 300 gallons internal fuel.

How would these findings line up with 8th AF kill claims in Europe and specifically when performing the escort mission and not a fighter sweep?

 

[drgondog]

Here is something I found interesting in FAREP. At some point I will vacuum up all of the range estimates and try to itemize how they were made and how one is conflated with the other etc since they do seem to be all over the place. I think it would be possible to build the process in Excel and then be able to get a decent approximation of how winds aloft etc would impact range on any given day.
View attachment 885770
View attachment 885771

View attachment 885772

I am including a bad-cropping of the FAREP reference chart. Yes I know that you have said that it is wrong. We are not going to worry about that because it is the chart that Greg referenced in his video and it is what I have quickly on-hand to make back-of-napkin style calculations. The version of this chart that Greg referenced in his first video is also uncorrected and shows P-47D-Late with 700 miles of range instead of 625 miles.

The values in the FAREP chart show a range of 350 miles for the P-38J + Twin 150's without the extra internal fuel of later models. It shows 650 miles for P-38J + Twin 150's with the extra internal fuel. Our other chart shows 200-300 miles for early P-38J + Twin 150s and it shows 375-475 miles for the late P-38J + Twin 150s.

The difference between the two charts are as follows;
Early P-38J = 50 - 150 miles less than FAREP chart. (14% - 42% Reduction)
Late P-38J = 175 - 275 miles less than FAREP chart. (27% - 42% Reduction)

This comparison is probably a bit skewed; it is late at night for me but I don't think we need to take the FAREP numbers and cut them all by 42%. Maybe a more logically consistent way of looking at this is referencing the differences between the offensive fighter mission profile and escort mission profile noted in our 2nd image.

If we compare the sets of high estimates for both we still see about a 30% reduction in range from flying escort mission profile with "S"-ing with the bombers vs the pure fighter mission.

For the sake of argument, what happens when we take the range estimates for the P-47 and 2x150s and multiply by 0.7? We get a new range of 437 miles for a P-47 w/ twin tanks + 370 gallons internal. It would also give us a range of 350 miles for P-47 w/ twin tanks + 300 gallons internal fuel.

How would these findings line up with 8th AF kill claims in Europe and specifically when performing the escort mission and not a fighter sweep?

I think my comments were about the data tables which were early derivations. The Chart above is correct in my estimation.

As to 'actual' for escort I have compiled tables for my new book - comparing FAREP, 8th AF Tactical, versus 'Actual', then developed another Map to compare against the FAREP escort map. The latter is the same as from my P-51B Mustang: Bastard stepchild book - but radius struck from 56th FG at Halesworth on the East Anglia coast.

I researched all 56th FG Victory credits from May 1943 through May 1944. The reason is that the 56th was 50 miles CLOSER to German targets and I wished to give the P-47 range the best possible values in the comparisons. The other P-47 fighter groups were based farther inland at Debden, Duxford, Steeple Morded and their victory credits as a function of different external drop tank configurations were closer to their home bases than the 56th FG VC's. Source Eight AF Victory Credits Board, 1945.

In comparison to the above charts for escort with combat, the 56th's farthest victory credit was 309mi with 108-gal drop tank in Nov 1943. Withe 2x150-gal the 56th farthest victory credit was 420mi in May 1944.

The chart above has 300mi for 108, and 500mi for 2x150.

My analysis is not set in stone because a.) there is no ability to track actual airmiles of an escort mission along a zig zag inbound bomber course. It has no ability to calculate the actual fuel used in the combat and certainly no accounting for WEP, if used in any of the encounters.

From personal anecdotes I am not aware of any usage above military power as it isn't mentioned in encounter reports.

Conclusions? Actual combat radius experienced with combat was less than FAREP tables and charts for any version of P-47D (or M), about right for P-38J and P-51B with extra internal fuel.

Factors? FAREP is a straight line, single fighter, simple performance calculation with no consideration for Group level operations which include lengthy taxi/idle time during squadron assembly to the active runway, take off in pairs, formation assembly while orbiting, flight operations in which a wingman will always use more fuel than leader trying to maintain formation, weather/wind conditions, etc.

The beneficial factors which improved range from FAREP were improved cruise MP and RPM settings developed over time, favoring reduced fuel consumption below the FAREP 60% power assumption.

 

[Squish]

Not only does it prompt Bradshaw to request the plane be adapted to wing tanks but it also prompts AAC to amend T.I 1016 to specify that drop tanks cannot adversely alter the flight characteristics of the aircraft. This is I want to say the July or August revision; it is the same revision that also causes the AAC to specify that drop tanks need to be able to draw fuel to the critical altitude of the aircraft, and what prompts fitting of K-1 pump to Republic ORC tank in testing.

Small correction on this point. It is not T.I 1016 that is amended. It is Military Requirement Policy 8 that is revised.

From this in March 1943.

To this in August of 1943.

 

[drgondog]

Small correction on this point. It is not T.I 1016 that is amended. It is Military Requirement Policy 8 that is revised.

From this in March 1943.
View attachment 885906

To this in August of 1943.
View attachment 885907You weren't wrong. TO 1016 was the Order, what followed by Operational Requirements was the Policy. Note 'e.' that the tanks should be 95% consumable to the critical altitude at military power. That simply impossible for the Republic 205-gal tank for any model P-47.

Gen Muir Fairchild was Chief OC&R, Plans Division, vice to Barney Giles. He was the Pentagon based visionary that steam rolled Echols for the A-36, then P-51A and all the priorities 'from on high' to expedite assets for the XP-51B. Fairchild was the CUSTOMER, a fact that Echols didn't particularly respect during the A-36 vs XA-32war, then the P-51A continuation when Mat.Cmd wanted to shut down Mustang production in favor of increased B-25s at Ingelwood.

What this memo proves (among many) is that the senior AAF HQ officers were thinking about droppable tanks for escort 17 months before Schweinfurt-Regensburg mission.

It is also important that neither the P-38J, nor P-47C/D, nor P-51B originally delivered the ability to draw 95% fuel from droppable tank to critical altitude for each engine type. They all used internal pumps to draw fuel, added submersible pumps in Main (P-38 and P-51) to improve altitude capability - but only when Cass Hough developed the slave exhaust pressure to force fuel out of the drop tanks did each fighter achieve critical altitude with drop tanks. P-47C (field mod) was first in August 43, P-51B in October 43, and P-38J in Feb 1944 (Field mod).

 

[ggiumarra]

I am at Kew. Wasn't looking for anything regarding this issue, but stumbled onto a couple of docs that might be interesting for some here - I haven't had time to read any of the more recent posts so I'm not sure how these fit in, but hopefully they will be helpful to the discussion in some way. The context of these files is RAF drop tank production for their own fighters from mid 1943, but I was surprised to see P-47 drop tank production receive a lot of attention in the docs (this is just a sample, but a representative one I think).

Note that 90 imperial gallons =108 US gallons and I believe a lot of these actually ended up being used by P-51Bs but hopefully someone here would know about that more definitively.

 

[Squish]

I am at Kew. Wasn't looking for anything regarding this issue, but stumbled onto a couple of docs that might be interesting for some here - I haven't had time to read any of the more recent posts so I'm not sure how these fit in, but hopefully they will be helpful to the discussion in some way. The context of these files is RAF drop tank production for their own fighters from mid 1943, but I was surprised to see P-47 drop tank production receive a lot of attention in the docs (this is just a sample, but a representative one I think).

Note that 90 imperial gallons =108 US gallons and I believe a lot of these actually ended up being used by P-51Bs but hopefully someone here would know about that more definitively.


View attachment 886029

View attachment 886030

This is actually a really good find!

 

[ThomasP]

Thanks, ggiumarra

This answers a couple of questions I had re the Bowater tanks.

 

[ggiumarra]

Thanks, ggiumarra

This answers a couple of questions I had re the Bowater tanks.

Ok, I did notice that name (Bowater) in the docs - my method is to take pics like mad during the limited time I'm at an archive and then take the time to fully analyze them later, so I'm not sure what that name refers to other than maybe it was a manufacturer that made drop tanks - so what are the questions you got answered? If it's just relates to earlier discussion, maybe you can link to that.

 

[ggiumarra]

Here is a question I have been wondering about that relates to this topic. If it has been addressed already - in this thread or elsewhere - maybe someone could direct me where.

I do believe that one of the arguments against using Thunderbolts as long-range bomber escorts earlier is that the 200 gal. drop tanks they were using did not feed fuel at high altitude. But in a bomber escort relay system the escorts that will be protecting the bombers at the greatest distance don't need to accompany the bombers the entire way, and, as I understand it, normally did not (one reason being, I believe, that they could thus minimize fuel wasting weaving on much of the outbound journey). I also understand that AAF fighters that comprised the final relay were rarely engaged by GAF fighters when they flew independent of bombers. So why couldn't P-47s that constituted the final relay just make the trip to their rendezvous point at whatever altitude made the most sense tactically up to the height limit of their drop tanks' fuel feed and then just climb up to the bombers' altitude (or above as the case may be) when closer to the bombers they were going to protect thereby enabling them to use up more of the fuel in their drop tanks and thus extend their effective radius? Presumably the bombers could have been escorted up to that point by other P-47s that did not carry drop tanks that would turn back when relieved by the next relay.

 

[Greg Boeser]

It's all a matter of timing. In early 1943, there were only 3 USAAF fighter groups in England. Close escort or sweeps were the two main mission types. The Luftwaffe tended to ignore sweeps, since they did not pose a threat. By fall it was up to eight. You need adequate numbers before you can implement a relay system.

 

[drgondog]

Here is a question I have been wondering about that relates to this topic. If it has been addressed already - in this thread or elsewhere - maybe someone could direct me where.

I do believe that one of the arguments against using Thunderbolts as long-range bomber escorts earlier is that the 200 gal. drop tanks they were using did not feed fuel at high altitude. But in a bomber escort relay system the escorts that will be protecting the bombers at the greatest distance don't need to accompany the bombers the entire way, and, as I understand it, normally did not (one reason being, I believe, that they could thus minimize fuel wasting weaving on much of the outbound journey).

One of the issues encountered with the Republic tank was repeated failures to jettison the tank. A second issue is that the P-47 became increasingly difficult to fly at TAS above 200mph. This was 'marginal' airspeed in hostile skies.

These two factors led to a conclusion that standard operating procedure was to climb to 18-20,000 feet with the tanks but jettison before crossing the Axis held coast, which further led to only filling the tank to 100-gal (US)..

There were two 'standard' escort types. "penetration' involved cruising in straight line to R/V then 'weave' at high cruise above a bomber box traveling at 150mph TAS at 25,000 feet. At combat or limit of endurance, break escort and cruise back in a straight line. 'Withdrawal' was cruise outbound in straight line to R/V with returning bombers and repeat the same process as above.

Neither of those two were availed by a semi-full, non-pressurized tank at 25 to 30,000 feet with remaining fuel that could not be used at those altitudes

I also understand that AAF fighters that comprised the final relay were rarely engaged by GAF fighters when they flew independent of bombers. So why couldn't P-47s that constituted the final relay just make the trip to their rendezvous point at whatever altitude made the most sense tactically up to the height limit of their drop tanks' fuel feed and then just climb up to the bombers' altitude (or above as the case may be) when closer to the bombers they were going to protect thereby enabling them to use up more of the fuel in their drop tanks and thus extend their effective radius? Presumably the bombers could have been escorted up to that point by other P-47s that did not carry drop tanks that would turn back when relieved by the next relay.

On the first Schweinfurt mission August 17th, the 56th FG did precisely that for the Withdrawal escort. He led the mission inbound at 18,000 feet until all of the 200 gallons loaded for that mission and dropped the empty tanks over Belgium, then climbed to 28,000 feet on internal fuel, met harassing GAF fighters near Aachen for a successful interception at the R/V point.

From August 22-27 VIII FC installed the new Republic Keel kit for P-47C-2 through P-47D-4 in theatre and began using the US steel 75-gal tanks left behind when P-39s and P-39s departed for Torch. These had to be modified for the pressurization line from the vacuum pump exhaust forced into the thank. Both lines were located aft of the bomb rack.

The first Bowater-Lloyd tanks had 2-band/lug plate attach scheme for Republic's 28" OC skid plate mounts, but the subsequent 108-gal tanks delivered beginning late September conformed to B-7 rack standard 14" OC lugs and had the second line for pressurization.

And yes, beginning in May 1944 P-51B/C were using Bowater tanks. Each mount on a P-51 required routing the fuel and pressure lines from the leading edge to the Bowater pipes aft of the bomb rack attach point to adopt to P-47 scheme

 

[ThomasP]

Another factor was where you might run into the enemy. IIUC at the time the P-47s were using the 200 USgal ferry tanks for combat missions the Luftwaffe were beginning to harass the bomber formations more or less as soon as the bombers crossed the English Channel. This means the P-47s had to be at escort altitude about the same time. The Spitfires could only escort to about 125 miles, so the next leg escorts had to be in position before then.

For mission planning in late-1943 P-47C at 15,000 lbs TOGW (with full ammo and a full 200 USgal ferry tank) takes about 110 USgal to climb from SL to 25,000 ft using Normal power and covers about 50 air miles distance during the climb. The P-47C used up about 30 USgal during WUTTO (Warm Up-Taxi-Take Off), so about the time they crossed the shores of France or Belgium they had already used up a minimum of 140 USgal. Since the 200 USgal ferry tank could not be used reliably above 18,000-20,000 ft they had to switch back to internal fuel and use up ~20 USgal climbing from 20,000 to their escort altitude of 25,000 ft. So a minimum of 50 USgal was used from internal tankage, which left the escorting P-47s with a maximum of about 255 USgal internal fuel for the rest of the mission.

Carrying the 200 USgal ferry tank into defended territory meant that you could not reliably predict what range you could accomplish with it, since you might have to drop the tank at any point during your travels into occupied territory. You might be jumped as soon as you crossed the French coast, or not until your maximum ROA. Planning for the use of the 200 USgal ferry tank past the coast during a bomber escort mission is a no go.

Combat fuel usage at 20 minutes of Military power or 15 minutes at Mil and 5 min at WEP (I am not sure if the R-2800-31 had a WEP rating at this time) used another 90-100 USgal, leaving only about 155-165 USgal for the rest of the mission.

Any fuel reserve/allowance for safety would cut into this even more. I think the normal amount was about 30 minutes at best cruise for range, so that would be another 16 USgal not available for range.

This leaves the maximum fuel available for range at about 139-149 USgal. The most economical settings for the R-2800-21 powered P-47C/D used 32 USgal/hr at 10,000 ft. Most economical fuel consumption for range at 25,000 ft was about 100 USgal/hr. Since you will take the same amount of time traveling to and from the target as the bombers you are escorting, regardless of what your TAS is, and since the average distance from the bomber & fighter bases in England to Berlin was about 550 miles, a P-47 escort fighter would have to have a minimum still air flight time of about 7 hrs in order to be able to escort the bombers all the way out and back. That is a theoretical minimum time. In real life the bombers took around 9 hrs(?) on average when bombing Berlin.

Unfortunately, the P-47C using the 200 USgal ferry tank under the necessary mission parameters at the time only had enough internal fuel left for a maximum theoretical range of about 4 hr 20 min. Any increase of fuel usage due to the mission profile - ie use of higher speeds than ideal, any head winds encountered, any doglegs in the mission course, any increase in fuel consumption due to formation flying, etc - significantly reduces the practical maximum range.

The above is why, in late-1943, the P-47C with 305 USgal internal plus the 200 USgal ferry tank only had a practical escort radius of about 340 miles, and only when operating from the closest airfields in SE England. They could not quite reach Bremen.

Bleh!

 

[ThomasP]

Hey ggiumarra,

re

. . . so what are the questions you got answered?

I have been trying to find out when the Bowater metal & paper 45 & 90 Impgal tanks first went into production, and when they first entered service. A fair amount of the time in the various books written about the WWII aircraft and operations they will mention the tanks, and sometime include pictures of the tanks being carried on various aircraft, but as often as not they do not identify the type (ie metal or paper) and/or get the type wrong.

I learned a while ago that the British painted the metal tanks light grey, and the paper tanks silver, so in some pictures I can make out what type of tank it is. I have found mention of the use of the 45 Impgal metal drop tanks (as opposed to the earlier fixed combatable tanks) by the Hurricane in late-1941, but do not know for sure if this is accurate.

I am hoping someone finds original source documents on when the different Bowater tanks were first issued and used operationally by various aircraft types, but so far I have not run across this info.

 

[drgondog]

Unfortunately, the P-47C using the 200 USgal ferry tank under the necessary mission parameters at the time only had enough internal fuel left for a maximum theoretical range of about 4 hr 20 min. Any increase of fuel usage due to the mission profile - ie use of higher speeds than ideal, any head winds encountered, any doglegs in the mission course, any increase in fuel consumption due to formation flying, etc - significantly reduces the practical maximum range.

The above is why, in late-1943, the P-47C with 305 USgal internal plus the 200 USgal ferry tank only had a practical escort radius of about 340 miles, and only when operating from the closest airfields in SE England. They could not quite reach Bremen.

Max Combat engagement/combat radius for P-47 in 1943 was to Bremen with the 108-gal Bowater tank November 1943 309 miles from Halesworth for 56th FG. The combat radius (actual) did not improve until the flat 150-gal tank was used during Big Week - achieving a combat radius (with fight) to Hannover (347mi) from Halesworth. For most other P-47 equipped FG (i.e. 355th, 4th, 78th) the bases were 40mi father away than Halesworth.

The longest escort/combat engagement with the 205-gal tank was July 28, 1943 when the 4th FG engaged at Emmerich, GY inbound to R/V with returning bomber force. There was no essing - just immediate combat. It was a Withdrawal Escort but It was more like a Fighter Mission. The range from Debden was 269 mi. The 75-gal tank achieved an Escort mission combat radius of 260mi.

The last mission with 205-gal Ferry tank was in August - circa the 26th. It was used less than 30 days before 8th switched to 75-gal steel tanks.

Bleh!

 

[Squish]

Hey Squish,

I found the specs on the 150 USgal fibre drop tank for the P-39 & P-40 (you are correct, it was made by Ohio Rubber). Unfortunately it was not pressurized, so I suspect using it on the P-47 would have involved the same problems at higher altitudes as with the 200 USgal ferry tank. I have to wonder how much it was used as I have never seen a photo of this tank on any aircraft.

I think I remember glancing somewhere in the case history that the AAC did attempt to pressurize this tank and it wasn't satisfactory. I want to say there was also the same tank contracted by McKenzie Muffler that probably could have been pressurized.

But don't take that as gospel truth. I've poured over the case history a lot last week and I might be hallucinating/remembering wrong detail.

The USAAF was essentially a late 1943 to early 1944 air force, that is arrival of modern types in numbers, the result of when mobilisation started, training time, the laws of mass production and the distance to the front line.

I am currently working on something of an alternative history scenario that is basically amounts to "What sequence of events would have to happen for P-47 to be able to escort to Schweinfurt in 1943.?"

1. The largest obstacle is the lack of wing tanks and the decision to go with centerline tank in 1942.

2. The next hang up is the pressurization of tanks. Gregs 200 gallon metal tank probably would have existed if McKenzie Muffler was selected as the sub contractor instead of Ohio Rubber Company The tank would then at least be able to be pressurized in August 1943 but doesn't solve the "everything else" wrong with the tank.

3. Presumably if the wing tank solution is available in early 1943 then triple-relay system could be implemented with combination of triple 75 gallon tanks that were on hand and the 150 gallon Lockheed tanks leftover from P-38.

4. This is assuming that the vacuum slaving system is ready to go by then and I believe that it was or could be.

Even with those 4 assumptions we run into a bunch of other problems. Of which are the following.

1. Can the 2x150 gallon tank P-47 actually provide target escort to Schweinfurt? It can make it if they don't have to S-weave with the bombers but might be just short if it does not.

2. If it cannot make it to Schweinfurt then does the roughly 1/3rd of the fighter strength at the time make a material difference if forced to perform a fighter sweep? Or does Luftwaffe GCI just route their fighter formations around the escorts? This was something they could do in 1944 and 45 but that system is probably less efficient in 1945? What do the numbers look like in August?

Gregs hypothetical 200 gallon tank doesn't make it if you apply 70% correction factor to his estimate which was the cited discrepancy in one of our previous documents. It reduces his estimated range to around 300 miles. This also assumes that 70% correction factor in FAREP is accurate.

3. How many missions in 1943 did the 8th Airforce take that would have required the 2x150 tanks. They only had around 800 on hand so that is optimistically only 400 sorties.

 

[ThomasP]

re

I think I remember glancing somewhere in the case history that the AAC did attempt to pressurize this tank and it wasn't satisfactory. I want to say there was also the same tank contracted by McKenzie Muffler that probably could have been pressurized.

The 150 USgal made by McKenzie Muffler was the 150 USgal Lockheed design of drop tank made out of steel. It gets a bit confusing because the 165 USgal DT was referred to as a 150 USgal DT as often as not in various USAAF publications, including many of the P-38 manuals. Some of the Material Command & and other organizations memos do so as well. Some of the part number listings referred to the 165 USgal DT as 150 USgal all the way through the war. Examples are the P-38 illustrated Parts Catalog dated Aug'45 and the P-51B/C/D/K PFOI manual from 1944.

I ran across a document a number of years ago that said the original USAAF specification that applied to the early-war to mid-war DTs required them to have a completely filled capacity of 110% of the designated volume. Hence the 150 gallon actually could hold 165 gallons, the 75 gallon could hold 82.5 gallons, the 100 gallon could hold 110 gallons, etc. There was another part of the specification explaining that this was to ensure that the designated tank size (eg 150 gallos) could be filled to this amount while mounted on an aircraft at any expected angle encountered in the field, as well as providing expansion space. Mission planning officers and ground crews were expected to know what-was-what as far as as not over-filling the tanks.

This designation system changed at some point, but I have never run across a document saying when or why.