|During 1942 and 1943 the British were testing aviation fuels that allowed for higher engine powers in their fighter aircraft than was possible using the standard 100/130 grade aviation fuel then in use.
Testing of a Spitfire IX by Rolls Royce, Hucknall in October 1943 determined:
The same aircraft was tested by the Aircraft and Armament Experimental Establishment (A.& A.E.E.), Boscombe Down in November 1943, the conclusion being:
The USAAF and Rolls Royce discussed the probable performance gains to be anticipated in the P-51B with improved fuel (160 grade) during a conference at Rolls Royce, Derby on October 23, 1943. These discussions took place six weeks before the P-51B first went operational. It was noted "that a maximum speed of about 450 MPH is predicted at 21,000 feet - optimum high critical altitude for use against the present FW-190 fighters. 3
Testing continued, with an Air Ministry Memorandum on Introduction into Service Use of 150 Grade Aviation Fuel of 25 January, 1944 summing up the position with respect to performance, production and requirements. The Memorandum concluded in part:
USAAF Materiel Command held a "Conference on National Advisory Committee for Aeronautics Test Program to Investigate 150 Grade Fuels" on 27-28, January 1944. It was concluded that "The program outlined should permit conclusive data to be obtained and should indicate the relative advantages of the various high octane fuel components for the preparation of satisfactory rich and lean rating fuels. It should also indicate the military value of these fuels for long range patrol or bombardment operation". It was recommended that "the program outlined should be carried out as expeditiously as is possible".
Using the fuel for Operation Overlord, the invasion of France, was being actively considered at the highest levels as of February 1944. General Dwight D. Eisenhower, commanding SHAEF, wrote to Army Chief of Staff General George C. Marshall and General Henry H. Arnold, head of the Air Force on 11 February, 1944 of the importance of using 150 fuel to the "fullest possible extent". 5 On 13 February, 1944 General Arnold replied that Xylidine, a necessary component for 150 grade fuel production, was being drummed for shipment and that information available to him "indicates satisfactory operation of Merlin and possibly R-2800 engines on this fuel". 6 On 21 February 1944 the Engineering Division of the US Army Air Force Materiel Command was instructed to initiate a test program on 104/150 Grade Fuel. 7
|As of 16 March 1944 "Accumulation of engine test data subsequent to the 4th of March 1944, has resulted in the clearing of the following engines at the specified power ratings in accordance with the requirements of 7-1/2 hour W.E.R. run:"
Flight Tests at Wright Field beginning 20 March 1944 found:
A Materiel Command Memorandum dated 13 May 1944 on "Preliminary Flight Tests of Fighter Aircraft Using PPF 441 Fuel at Increased War Emergency Rating" concluded:
Based on these preliminary flight tests, it is established that satisfactory operation is experienced on the P-47D airplane at 65" hg. M.A.P., on the P-51B airplane at 75" hg. M.A.P., and on the P-38J airplane at 70" hg. M.A.P. except in the case of the P-47D airplane in extended climbs with water injection. 14
Another Materiel Command Memorandum Report on “Use of PPF 44-1 Fuel in Fighter Aircraft”, dated 13 May 1944, summarized the advantages and disadvantages of using PPF 44-1 fuel in fighter aircraft based on tests conducted to date:
"Flight Tests of the North American P-51B-15 Airplane, AAF No. 43-2477 Using 44-1 Fuel" as reported by the Flight Test Engineering Branch dated 20 May 1944 states:
"Flight Tests on the P-38J Airplane, AAF No. 43-28392 Using 44-1 Fuel" as reported by the Flight Test Engineering Branch dated 5 July 1944 states:
"Flight Tests on the P-47D Airplane, AAF No. 42-26167 Using 44-1 Fuel" as reported by the Flight Test Engineering Branch dated 15 July 1944 states:
An Army Air Force Proving Ground Command Report “Service test of Nominal 100/150 Grade Fuel” dated 7 July 1944 determined the effect of nominal 104/150 grade fuel on the performance and maintenance of P-51B, P-47D, and P-38J airplanes.
a. In view of the inconclusive nature of test results, it is not possible to make any definite decision concerning the operational use of nominal grade 104/150 fuel and the attending higher emergency power ratings.
Performance gains. - Attempts were made throughout the test to determine the average gain in performance due to the increased power rating allowed by the special fuel. Speed runs and climbs were made by approximately twenty-five pilots of all grades of experience. Speed curves shown in Inclosure 3 are average curves drawn from all data obtained from all three airplanes of each type. Data are not reduced to standard conditions, but are plotted against pressure altitude from actual free air temperatures. All flights were made with full military load.
By 29 May 1944 the Test Program of Grade 100/150 Fuel carried out under the juristiction of the Materiel Command at Wright and Eglin Fields had been completed and the fuel released for service in the European Theater of Operations. 18 By 20 June 1944 "Final release on Project P.P.F. has been made approving 70" manifold pressure for the P-38, 65" manifold pressure (with and without water injection) for the P-47, and 75" manifold pressure for the P-51 (both the 1650-3 and 1650-7 engines)." 19 The P-47 was released for 70" Hg. MAP using Grade 100/150 fuel with water injection by 24 June 1944. 20
In late Winter of 1943-44 the Allied Expeditionary Air Force (A.E.A.F.) decided, pending further trials, not to employ 150 Grade Fuel for Overlord due to spark plug issues, however, it was intended that 150 Grade would be used when proved satisfactory. 21 Meanwhile, cross channel operations by two squadrons of P-47’s and one P-38 using 150 Grade fuel revealed an increase of speed and climb characteristics at the expense of spark plug difficulties. 22 The Production Division was directed on 28 March 1944, under the authority of the Commmanding General, Army Air Forces, to modify all P-38, P-47 and P-51 airplanes in the United Kingdom for the use of Grade 150 fuel, with the necessary modification kits to be shipped to the European Theater of Operations within 30 days. 23 It was decided that Grade 150 fuel was to be the only fuel available for AAF fighter airplanes in the United Kingdom. 24
Successful service tests led in May 1944 to the Eighth Air Force Fighter Command requesting that it "be supplied immediately with grade 150 aviation fuel for use in P-47, P-51 and P-38 planes". 25 Deliveries of Grade 100/150 aviation fuel to AAF Stations commenced within a week of the landings in France. 26 27 The change over to 150 grade fuel necessitated the resetting of all aneroid switches on the P-51s. 28
150 grade fuel continued to be used by 8th AF units through 1944. 31 The WER engine limitation for the P-51 continued to be 72" Hg. 32 Eighth Air Force Fighter Groups converted to a new blend of 150 grade fuel, with increased amounts of ethylene dibromide (1½ T) in early 1945. 33 P.E.P, as the new fuel was called, was tried in order to remedy lead fouling of spark plugs. While spark plug fouling was eliminated, PEP was found to have an undesirable effect on valve seats. As a result of excessive maintenance required on the V-1650 engines, General Doolittle of the Eighth Air Force decided in late March 1945 to revert to the normal 100/150 (1 T) grade fuel. 34
Technical Operations, Eighth Air Force issued a 4 April 1945 memorandum in which 100/150 grade fuel experience in the Eighth Air Force was summarized. It is reproduced in full below:
1. The following is a summary of 100/150 grade fuel experience in Eighth Air Force.
Following successful testing, the Spitfire IX's Merlin 66 was cleared in March 1944 to use +25 lbs, obtainable with 150 grade fuel. 36 In early May, No. 1 and No. 165 Squadrons comprising the Predannack Wing, were the first to convert their Spitfires to +25 lbs boost and employ 150 grade fuel on operations. 37 38 Air Defense Great Britain (A.D.G.B.) shared a report, dated 16th June 1944 with A.E.A.F. summarizing the RAF's experience with using 150 Grade Fuel in Merlin 66 engines. All pilots reported most favorably on the value of the high boost pressures obtainable with 150 Grade Fuel, however, Technical Staff felt that before the fuel was introduced on a large scale that the causes of backfires must be established and that at least 12 engines should complete 200 hours each. 39 By the end of July the backfires were overcome through fairly straightforward adjustments. 40 By 12 August 1944, 16 Squadrons in A.D.G.B. had been modified to to operate with 150 grade fuel. 41
The increased performance obtained with 150 Grade Fuel was put to good use by Mustangs, Tempests, Spitfires and Mosquitoes in intercepting V-1 Buzz Bombs launched against Britain beginning mid June. Performance increases at sea level were as follows: 42 43
The Royal Aircraft Establishment (RAE) reported in Technical Note No.Aero.1501(Flight) that a Mustang III (Merlin V-1650-7), flying at +25 lb./sq.in. as received from Squadron, obtained 382 mph at sea level. 44 404 mph was obtained at sea level after "cleaning up" the aircraft by removing the bomb racks and aerial bracket, repainting the wing's leading edge and rubbing down the aircraft. 316 Squadron was one of the Mustang units to convert to 150 grade fuel, their Operations Record Book stating for 1.7.44 "18 A/C test after modification to +25 lbs boost". 45 610 Squadron uprated thier Spitfire XIVs on 14 July, the Operations Record Book stating "A technical party visited the unit to modify the aircraft to fly at 21 lbs boost on 150 octane petrol". 46 These squadrons did more that just chase "divers" as 315 Squadron demonstrated with their Mustangs when they shot down 6 Me 109's, 1 Me 110 and 1 Fw 190 while escorting Beaufighters to Norway on 30 July 1944. 47 85 and 157 Squadrons were two of the Mosquito units operating at +25 lbs boost with 150 grade fuel. 48 49 By mid August the V-1 diver threat was largly eliminated with the advance of the allied armies beyond the launching areas. The ADGB squadrons that had converted to 150 grade fuel now found more time to operate over the continent. The Spitfire IX Squadrons were permanently pulled off anti-diver duty on 10 August and went over completely to escort work, sweeps and armed recces. They paid their first visit to Germany on 27 August 1944. 50 51 316 Squadron flying their Mustangs downed 3 Me 109’s and a Fw 190 five miles N. of Chalom on 14 August. 52 315 Squadron met with remarkable success on 18 August, claiming 16 Fw 190’s shot down near Beauvais with their boosted Mustang III’s (II./JG 26 admitted to 8 killed and 2 wounded). 53 By this time Headquarters, Air Defense of Great Britain required all Packard Merlin V-1650-7 engines in the Mustangs to be modified to operate at 25 lbs. boost. 54 55 56 57 The Spitfire XIV squadrons quickly got into the swing of it with 350 Squadron scoring on 19 August by shooting down a Ju 88 on the outskirts of Brussels. 58 By early September the Spitfire XIV units were engaged in operations over Germany. 59 60 61 62 63
On 18 September 1944 A.D.G.B. very positively summarized the experience gained to date using 100/150 grade fuel. However, due primarily to logistical difficulties, such as the interchange of squadrons between A.D.G.B. and 2nd T.A.F., it was decided that UK based fighter squadrons should revert to the use of 130 grade fuel. 64 Its uncertain as to the degree to which this decision was carried out as of November 1944 Fighter Command was still using 2,000 tons of 150 grade fuel per month. 65 With the adoption of 150 grade fuel by the Second Tactical Air Force, any logistical difficulties to Air Defense of Great Britain (A.D.G.B.) use of 150 grade fuel were removed. By early 1945, United Kingdom based Mustangs of A.D.G.B. were operating at +25 lbs/sq.in/80" hg. with 150 grade fuel on operations over the continent and Germany. 66 67 68 69 Eventually all Rolls-Royce Merlin and Griffon engines were cleared to operate on 150 grade fuel, as well as Centaurus, Hercules, Sabre II and Pratt & Whitney Double Wasp engines. 70
J.H Houghton Colonel A.C. Director of Supply described the supply position as of 23 November 1944: 73
It was decided that the Second Tactical Air force would change over from 100/130 grade fuel to 100/150 grade fuel from the 15th December 1944. 74
No. 42 Maintenance Group:
The shipping of fuel from Antwerp started on 2 January, 1945: 75
100/150 grade fuel was introduced into Spitfires of 83 and 84 Groups during January 1945: 76
On the 5 February 1945, J.H Houghton Brigadier General, U.S.A. Director of Supply, reported that the R.A.F on the Continent were using 100/150 grade fuel: 77
Deliveries continued at an increasing rate: 78
Units modified their aircraft for increased power with the change over to 150 grade fuel. 79 80 81 82 83 84 85 86 87 88 89 90 10 92 In May 1945, just days before the ultimate defeat of the Nazis, one Canadian Wing of Spitfires reverted to 130 grade fuel just in time to perform "stylish" formation shows over vanquished Germany. 93
1. Spitfire J.L.165 with Merlin 66 at 25 Lbs. Boost Pressure, Dor/Chr/RLS.1/MNH. 8.10.43
100/150 Grade Fuel Specification
By Neil Stirling and Mike Williams, All Rights Reserved