P-51 Mustang

1. To report results of high speed and climb performance tests conducted at the manufacturer's factory on the P-51B-1-NA airplane, AAF No. 43-12093.

1. Airplane was tested at a take-off gross weight of 8430 pounds, and was equipped as a standard production fighter with four .50 caliber guns with the gun openings taped but shell ejection chutes open, three antenna wires and a short radio mast aft of the cockpit. Finish was filled and sanded and was supposed to be the standard production finish. Airplane equipped with the Packpard Merlin V-1650-3 engine with 11.5 inch and 10.1 inch diameter blowers, and with a four-bladed Hamilton Standard propeller, blade design No. V-6487A-24.

      Power data obtained from Packard power curve P-18, No. 5 dated Nov. 21, 1942 for the V-1650-3 engine with 11.5 inch and 10.1 inch blowers.

2. High speeds obtained with the oil cooler flap and coolant flap set for automatic opertation since there were no provisions on this airplane for selective operation and no time was available for a test installation of a selective control.

3. Climb Data, 3,000 R.P.M., Oil and Coolant flaps Wide Open.

1. To report time to climb as calculated from data given in Memorandum Report, Serial No. FS-M-19-1587-A.

1. Time to Climb; 3,000 r.p.m., oil and coolant flaps wide open.

The P-51B is a single engine, low wing, long range fighter. Its long range makes it ideal for escort purposes, and its performance as a fighter aircraft is better or at least equal to that of any enemy fighter that might be encountered. The rate of climb is good and the high speed in level flight is exceptionally good at all altitudes, from sea level to 40,000 feet.

The airplane is very maneuverable with good controllability at indicated speeds to 400 MPH. The stability about all axes is good and the rate of roll is excellent, however, the radius of turn is fairly large for a fighter. The cockpit layout is excellent, but visibility is poor on the ground and only fair in level flight.

High speed and climb performances have been completed on this airplane at a take-off weight of 9205 lbs. This loading corresponds to the average P-51B combat weight with full oil, 180 gallons of fuel and specified armament and ammunition.

The principal results are as follows:

For more of this report see HERE

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North American Aviation, Inc.
Inglewood, California
25-April-44
Preliminary Results of Performance Tests on
a P-51B Airplane with 44-1 Fuel
P-51B-5-NA, V-1650-7 Engine

Rates of climb at critial altitudes

Blower Setting	M.A.P.	Altitude	Climb ft/min.
Low	61"	9000	3830  -  3950
Low	67"	6500	4300  -  4370
Low	75"	3500	4650  -  4670
High	61"	22000	3030  -  3060
High	67"	19000	3440  -  3480
High	75"	17800	3650  -  3680 (Flight 32)
		16000	3740  -  3790 (Flight 33)
Climb data corrected to normal gross weight of 8,460 lbs.

Maximum speed at critical altitudes

Blower Setting	M.A.P.	Altitude	TAS corrected to standard conditions
Low	61"	15200	(418)
Low	67"	12100	(420)
Low	75"	7800	419  -  423
High	61"	26600	(436)
High	67"	24200	(441)
High	75"	21200	445
Values in parenthesis estimated from previous tests.

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Army Air Forces Material Command
Wright Field, Dayton, Ohio
15 May 1944
P-51B-15-NA 43-24777
(Packard Merlin V-1650-7)
Performance Tests on P-38J, P-47D and P-51B Airplanes
Tested with 44-1 Fuel. (GRADE 104/150)

1. Flight tests were started on P-38J, P-47D, and P-51B airplanes at Wright Field on approximately 20 March 1944 in order to measure the performance and note any effect on flight characteristics when flown with 44-1 fuel. Tests on the P-51B have been completed but tests on the P-38J and P-47D have not been completed to date.

2. All tests were flown with the airplanes loaded to their maximum combat gross weight. The P-38J airplane tested was P-38J-15, AAF No. 43-28392, equipped with Allison V-1710-89 and 91 engines with Curtiss electric three blade propellers. Gross weight at take-off was 17,360 lbs. with the c.g. at 26.72%. The P-47D tested was AAF No. 42-26167 and was equipped with Pratt & Whitney R-2800-63 engine and an A-23 turbo regulator. Gross weight at take-off was 13,320 lbs. with the c.g. at 29.5%, gear up.
The P-51B tested was the P-51B-15, AAF No. 43-24777 and was equipped with a Packard V-1650-7 engine with a 11 ft. 2 in., four blade constant speed propeller. Gross weight at take-off was approximately 9680 lbs. The weight included 265 gal. of fuel, full oil, and no ammunition (85 gal. in auxiliary tank instead of ballast for ammunition).

3. There was no noticeable change in handling characteristics of any of the airplanes tested when operating at the higher powers which were obtainable with the 44-1 fuel. Only a slight increase in vibration was noted at the higher powers. On one long range test made with the P-51B, there was no apparent trouble due to the 44-1 fuel.

4. All performance data obtained on the P-51B is included in the attached curves. It will be noted that all tests were run with the wing racks installed. Speeds would be approximately 12 mph faster with the wing racks removed as shown by the dash line curve on the Speed vs Altitude Curve. Approximately 16 MPH increases in speed below critical altitude and approximately 600 ft. per minute increase in rate of climb below critical altitude was obtained by using the 75” Hg. Manifold pressure allowed by 44-1 fuel. No tests were made on this airplane with standard fuel.

Level speed performance

	With Wing Racks		Without Wing Racks
	67" Hg., 3000 RPM	75" Hg., 3000 RPM	75" Hg., 3000 RPM
Max. speed at Sea Level	364 mph	380 mph	388 mph
Max. speed in MS gear	408 mph at 10400 ft.	411 mph at 7400 ft.	422 mph at 7400 ft.
Max. speed in FS gear	426 mph at 23900 ft.	431 mph at 20600 ft.	444 mph at 20600 ft.

Rate of Climb
With Wing Racks, 9,680 Lbs

	67" Hg., 3000 RPM	75" Hg., 3000 RPM
Max. speed in MS gear	3,920 ft/min at 5,600 ft.	4,380 ft/min at 2,300 ft.
Max. speed in FS gear	3,170 ft/min at 19,200 ft.	3,700 ft/min at 15,700 ft.

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Wright Field, Dayton, Ohio
20 May 1944
Flight Tests on the North American
P-51B-15 Airplane, AAF No. 43-24777
Using 44-1 Fuel Summary

The P-51B-15 airplane, AAF No. 43-24777 is a low wing fighter equipped with a Packard V-1650-7 engine. Equipped with an additional fuselage tank and wing racks to which may be attached fuel tanks the airplane has long range for a fighter.

The airplane is very maneuverable with excellent controllability at all speeds up to slightly over 400 MPH indicated, the highest speeds attained in level flight. Stability is good about all axes, and recovery from stalls is normal. The airplane has a fairly short radius of turn and an excellent rate of roll. Visability is poor in taxing and only fair in level flight. The cockpit layout in general is good.

All tests were made at a gross weight at takeoff of 9335 lbs. which included full oil and 265 gallon of fuel. Level flight and climb performance were completed with wing racks. In addition level flight speeds were obtained at the critical heights without wing racks.

In level flight the high blower critical altitude for 75 in. Hg. manifold pressure and 3000 RPM was 20,800 ft. At this altitude the airplane attained a maximum true speed of 444.0 MPH at 75 in. HG. manifold pressure without wing racks, a high speed of 431 MPH at 75 in. Hg. manifold pressure with wing racks, and a high speed of 417 MPH at 67 in. Hg. manifold pressure with wing racks. At 24,000 ft., high blower critical altitude for 67 In. Hg. manifold pressure and 3000 RPM, a maximum true speed of 426 MPH was attained.

In climb the low blower critical altitude for 75 in. HG. manifold presure and 3000 RPM was 2,200 ft. At this altitude the airplane attained a maximum rate of climb of 4380 ft/min. at 75 in. Hg. manifold pressure and 3,820 ft/min. at 67 in. Hg. manifold pressure. The service ceiling of the airplane was 40,500 ft. and the absolute ceiling was 41,200 ft.

High speed in level flight at 3000 RPM, mixture auto rich, and oil and coolant shutters in automatic.

		Present War Emer. Power			Proposed War Emer. Power
Altitude Ft.	Blower	Man. Press.	Std. BHP	True Speed	Man. Press.	Std. BHP	True Speed
0	Low	67.0	1580	361.5	75.0	1788	376.5
4000	Low	67.0	1622	380.0	75.0	1830	376.5
*7400	Low	67.0	1660	395.5	75.0	1868	395.5
**10300	Low	67.0	1695	409.0
17000	Low	52.8	1350	398.0
24000	Low	39.8	1037	385.0
18000	High	67.0	1390	408.0	75.0	1577	423.0
*20800	High	67.0	1390	417.0	75.0	1572	431.0
**24000	High	67.0	1390	426.0
28000	High	57.3	1200	419.0
32000	High	48.4	1038	410.0
28000	High	36.4	822	390.0

For more of this report see HERE P-51B High Speed Performance
Engineering Division's charting of
North Amerian Flight Test Data

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Army Air Forces Proving Ground Command
Eglin Field, Florida
7 July 1944
P-51B-15
43-24755, 43-24757, 43-24775
(Packard Merlin V-1650-7)
Service Test of Nominal 104/150 Grade Fuel Summary

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.

P-51-B-15 Airplane.

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Flight Test Engineering Branch
Wright Field, Dayton, Ohio
15 June 1945
Flight Tests on the North American
P-51D Airplane, AAF No. 44-15342

Summary

Fuel consumption and speed data listed in the flight operation instruction chart have been spot checked by duplicating in the test program some of the power settings shown in the T. O. By comparing the results obtained with the T. O. figures, a quick estimate of the validity of the T. O. may be made.

High speed and climb performance have been obtained on this airplane at a take-off gross weight of 9760 pounds. Performance was obtained up to an altitude of 35,000 feet in increments of 5000 feet in a clean configuration. The clean configuration included one external bomb rack on each wing. Additional configurations were flown at 5000 and 15,000 feet including two 110 gallon tanks, two 500 pound bombs, and two 250 pound bombs. The principal results are as follows:

	1.	Maximum speed at critical altitudes
		High Blower
		War Emergency power (3000 RPM and 67") 26000'	442 MPH
		Military power (3000 RPM and 61") 28000'	439 MPH
		Normal Rated power (2700 RPM and 46") 29400'	420 MPH
		Low Blower
		War Emergency power (3000 RPM and 67") 10000'	417 MPH
		Military power (3000 RPM and 61") 13200'	413 MPH
		Normal Rated power (2700 RPM and 46") 16200'	387 MPH
	2.	Maximum speed at sea level
		War Emergency power (3000 RPM and 67")	375 MPH
		Military power (3000 RPM and 61")	364 MPH
		Normal Rated power (2700 RPM and 46")	323 MPH
	3.	Rate of climb at critical altitude.
		War Emergency power (3000 RPM and 67") high blower (19,000')	3200 ft/min.
		War Emergency power (3000 RPM and 67") low blower (4,800')	3600 ft/min.
	4.	Time to climb to service ceiling
		war emergency power 3000 RPM and 67") (41600')	28 minutes.

2-110 Gal. Tanks	2-500 Lb. Bombs	2-250 Lb. Bombs
5000 ft. 45	36	25
25000 ft. 47	33	23

For more of this report see HERE

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North American Aviation, Inc.
Inglewood, California
Report No. NA-46-130
2-6-46
Performance Calculations for Model P-51D Airplane
(N.A.A. Model No. NA-122)

Summary

	Maximum Speed – War Emergency Power        (3000 RPM. – 67" Hg. M.P.)
	At Sea Level	368 MPH
	At Low Blower A.C.A.*	414 MPH/11,300 ft.
	At High Blower A.C.A.*	440 MPH/24,500 ft.
	Maximum Rate of Climb – War Emergency Power        (3000 RPM – 67" Hg. M.P.)
	At Sea Level	3410 ft./min.
	At Low Blower A.C.A.*	3510 ft./min./7500 ft.
	At High Blower A.C.A.*	2680 ft./min./21,200 ft.
	Time to Climb to 20,000 ft. at War Emergency Power	6.4 min.

P-51D Calculated Altitude Performance

For more of this report see HERE

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North American Aviation, Inc.
Inglewood, California
Report No. NA-8284-A
11-1-45
Performance Calculations for P-51H Airplane
(N.A.A. Model No. NA-126)

Summary

	Maximum Speed – Combat Rating        (3000 R.P.M. – 90” Hg. M.P. – W.I.)
	In High Blower at A.C.A.*	471 m.p.h./22,700 ft.
	In Low Blower at A.C.A.*	449 m.p.h./9000 ft.
	In Low Blower at Sea Level	413 m.p.h.
	Maximum Rate of Climb – Combat Rating        (3000 R.P.M. – 90” Hg. M.P. – W.I.)
	In Low Blower at Sea Level	5120 ft./min.
	In Low Blower at A.C.A.*	5210 ft./min/4600 ft.
	In High Blower at A.C.A.*	3970 ft./min/18,300 ft.
	Time to Climb to 20,000 ft.
	with Combat Power (90”) Hg. M.P.	4.58 min.

P-51H Altitude Performance Brake Horsepower vs Altitude

For more of this report see HERE Also see:

P-51H Altitude Performance Brake Horsepower vs Altitude V-1650-9

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Flight Test Engineering Branch
Wright Field, Dayton, Ohio
1 May 1945
Flight Tests on the North American
P-51H Airplane, AAF No. 44-64161 Summary

A. Maximum speed at critical altitudes

High blower	(67.0" and 3000 RPM) 30750'	450.0 MPH
	(61.0" and 3000 RPM) 32550'	444.5 MPH
Low blower	(67.0" and 3000 RPM) 16400'	435.0 MPH
	(61.0" and 3000 RPM) 19300'	432.5 MPH

B. Maximum speed at sea level

	(67.0” and 3000 RPM)	358.0 MPH
	(61.0” and 3000 RPM)	351.0 MPH

C. Rate of Climb

1.     Sea Level
(67.0” and 3000 RPM)	3200 ft/min.
(61.0” and 3000 RPM)	2875 ft/min.
2.    Low blower critical altitudes
(67.0” and 3000 RPM)	3395 ft/min.
(61.0” and 3000 RPM)	3080 ft/min.
3.    High blower critical altitudes
(67.0” and 3000 RPM)	2640 ft/min.
(61.0” and 3000 RPM)	2360 ft/min.
4.    Time to climb to service ceiling
(67.0” and 3000 RPM)	23.7 min.
(61.0” and 3000 RPM)	24.6 min.

Speed Vs. Altitude Climb Data

For more of this report see HERE

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Flight Test Division
Wright Field, Dayton, Ohio
14 October 1946
Flight Test of the P-51H Airplane, AAF No. 44-64182 Summary

All tests at the fighter configuration (bomb and rocket racks only) were flown at a take-off weight of 9544 lbs.

Data at war emergency rating with water injection at 3000 rpm.

Altitude Ft.	True Air Speed MPH	MP "Hg.	Blower	Throttle Setting
S.L.	401	90	Low	Part
*6800	431	90	Low	W. O.
**13400	423	90	High	Part
***21200	451	90	High	W. O.
25000	448	78	High	W. O.
*Low Blower Critical Altitude for 90" Hg., MP
**Altitude for Blower Shift.
***High Blower Critical Altitude for 90" Hg., MP.

Climb data for war emergency power rating (3000 rpm with water injection).

Alitude Ft.	True Air Speed	Rate of Climb Min.	Time of Climb Min.	MP "Hg.	Blower	Throttle Setting
S.L.	175	4680	.0	90	Low	Part
2200	181	4680	0.5	90	Low	W. O.
9600	202	3660	2.2	90	High	Part
16000	224	3680	4.0	90	High	W. O.
30000	283	1720	9.4	53.5	High	W. O.

Level Flight Data, Speed vs Altitude Rate of Climb Data

For more of this report see HERE Also see:

P-51H Speed Clean P-51H Speed with Racks P-51H Climb

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Rolls-Royce, Ltd
Hucknall
8 April 1943
Improved Performance Low Altitude Figher Aircraft.
'Mustang' AL.963 with Merlin 65 (Special).

General Conclusion:-

Preliminary flight performance data obtained on a Merlin 65 engine re-rated to +23 lb. boost prior to tests on R.M. 14 S.M. engine.

This engine was fitted with an S.U. injection pump to give the increased fuel flow requirments necessitated by the higher boost.

(1) Level speeds. An increase of 17 M.P.H. is obtained from G.L. up to 7,000 ft. and from 15,000 ft. to 19,000 ft.

(2) Climb. Rate of climb improved by 900 ft/min. from G.L. up to 4,000 ft. and 960 ft/min. from 13,000 ft. up to 15,000 ft.

Mustang AL 963 Climb and Level Speed Performance

For more of this report see HERE

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Aeroplane and Armament Experimental Establishment
Boscombe Down
31 May 1944
Mustang III FX.858
(Merlin 100)
Brief performance trials and position error measurement SUMMARY

Brief performance trials at combat rating have been completed on this aircraft at a take-off weight of 9260 lb. The principal results at 3000 rpm, +25 lb/sq.in. boost are as follow :-

Maximum rate of climb in MS gear4500 ft/min. at 1600 ft.  
Maximum rate of climb in FS gear4000 ft/min. at 13000 ft.
Service ceiling (100 ft/min)                   39800 ft.
Absolute ceiling                   40700 ft.
Maximum speed in MS gear419 mph at 5200 ft.
Maximum speed in MS gear455 mph at 17800 ft.

The estimated increase in rate of climb below full throttle height due to the use of +25 lb/sq.in. instead of +18 lb/sq.in. boost is about 850 to 900 ft/min., whilst the corresponding increase in all-out level flight is about 26 mph true speed.

For more of this report see HERE

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Aeroplane and Armament Experimental Establishment
Boscombe Down
25 June 1944
Mustang III FX.953
(Packard Merlin V.1650-3)
Position error, climb and level speed performance trials

Summary

Position error and performance trials have been completed on this aircraft at a take-off weight of 9200 lb. without external bombs or fuel fitted.

The principal results are as follows :-

1.   Climb

(a)	Normal rating  (2700 rpm., 46 in. manifold pressure)
	Max. rate of climb in MS gear	=  2060 ft/min at 16700 ft.
	Max. rate of climb in FS gear	=  1555 ft/min at 30200 ft.
	Service ceiling	=  40700 ft.
	Absolute ceiling	=  41300 ft.
(b)	Combat rating  (3000 rpm., 67 in. manifold pressure)
	Max. rate of climb in MS gear	=  3610 ft/min at 10600 ft.
	Max. rate of climb in FS gear	=  2690 ft/min at 23400 ft.
	Service ceiling	=  42800 ft.
	Absolute ceiling	=  43600 ft.

2.   Level speed

(a)	Max. cruising  (2700 rpm., 46 in. Hg. manifold pressure)
	Max. speed in MS gear	=  406 mph at 20600 ft.
	Max speed in FS gear	=  438 mph at 33000 ft. (approximately)
(b)	All out level  (3000 rpm., 67 in. Hg. manifold pressure)
	Max. speed in MS gear	=  424 mph at 15500 ft.
	Max. speed in FS gear	=  450 mph at 28000 ft.

For more of this report see HERE

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Aeroplane and Armament Experimental Establishment
Boscombe Down
16 December 1944
Mustang IV T.K.589
(Packard Merlin V.1650-7)
Position error of static vent and
brief level speed trials

Conclusions.

The maximum true airpseed of this aircraft, using 3,000 RPM in M.S. gear was 396 mph at 10,300 feet, with +18 lb/sq.in. boost, and 398 at 4,300 ft. with +25 lb/sq.in. boost.

Use of +25 lb/sq.in. instead of +18 lb/sq.in. boost increased the True Air Speed below full throttle height 25 mph.

TABLE I
Level speed performance M.S. gear,  3,000 R.P.M.  Radiator flap adjusted to give 8 1/2" gap
Corrected to 9,000 lb.

Height  ft.	T.A.S.  m.p.h.	A.S.I.  m.p.h	P.E.C.	C.E.C.	Boost  lb/sq.in.
0	379	374	+5.25	-.25	+25.0
2,000	388	372	+5.25	-1	+25.0
*4,300	398	370	+5.25	-2	+25.0
6,000	398	362	+5	-2.75	+23.0
8,000	398	351	+5	-3.25	+20.6
10,000	397	340	+4.75	-3.75	+18.3
12,000	395	329	+4.75	-4.25	+15.9
0	354	349	+5	0	+18.0
2,000	362	347	+5	-.75	"
4,000	370	345	+4.75	-1.5	"
6,000	379	344	+4.75	-2.25	"
8,000	387	342	+4.75	-3	"
*10,300	396	338	+4.75	-3.75	"
* Full throttle heights

For more of this report see HERE

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Mustang IV TK.589, Boscombe Down, July 1944

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V-1650-7 Engine Performance Data (Static)
R.D.E.1.(a) 1/9/44

Combat Conditions
3000 r.p.m. + 25 lbs/sq.in. B.H.P. at S.L. = 1940
Max. power in "M.S." gear = 1940 B.H.P. at S.L.
Max. power in "F.S."  gear = 1810 B.H.P. at 12,000 ft.
Supercharger change height = 5,000 ft.
3000 r.p.m. at 67" Hg. boost pressure. B.H.P. at S.L. = 1630
Max. power in "M.S." gear = 1,700 B.H.P. at 5,750 ft.
Max. power in "F.S."  gear = 1,555 B.H.P. at 17,750 ft.
Supercharger change height = 10,500 ft.
3000 r.p.m. + 61" Hg. boost pressure. B.H.P. at S.L. = 1490
Max. power in "M.S." gear = 1580 B.H.P. at 8,500 ft.
Max. power in "F.S."  gear = 1400 B.H.P. at 21,000 ft.
Supercharger change height = 13,400 ft.

Climb and cruise
2,700 r.p.m. + 46" Hg. boost pressure. B.H.P. at S.L. = 1050
Max. power in "M.S." gear = 1150 B.H.P. at 11,250 ft.
Max. power in "F.S."  gear = 1080 B.H.P. at 22,000 ft.
Supercharger change height = 14,250 ft.

Weak mixture cruise
2,400 r.p.m. + 36" Hg. boost pressure. B.H.P. at S.L. = 730
Max. power in "M.S." gear = 820 B.H.P. at 13,000 ft.
Max. power in "F.S."  gear = 755 B.H.P. at 22,500 ft.
Supercharger change height = 16,250 ft.

V-1650-7 Engine Performance Data

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The Merlin engined P-51 went operational 1 December 1943 with the 354th Fighter Group based in Boxted UK. By D-Day, seven 8th Air Force Groups would join them as well as seven RAF Squadrons. In the MTO, the 31st and 52nd Fighter Groups exchanged their Spitfires for Mustangs in spring 1944. The P-51B that equipped these units was delivered with the Packard Merlin V-1650-3 until April 1944, when replacement aircraft began to be delivered with the V-1650-7 engine featuring maximum power peaking at lower altitudes. The P-51 operated on 100/130 grade fuel with War Emergency Power limited to 67" up to June 1944.

On 29 March 1944 the Commanding General, Army Air Forces authorized the procurement of the necessary parts to modify all P-38, P-47 and P-51 airplanes in the United Kingdom for the use of Grade 150 fuel, subject to the relevant engines being cleared to use the fuel. ^{1 2}   During March & April 1944 flight tests were conducted at Wright Field on the P-51B-15 airplane, AAF No. 43-24777, using 44-1 fuel, at the request of the Power Plant Laboratory, Engineering Division. ³   These tests were made to determine the performance of the airplane at the higher powers allowable with 44-1 fuel as compared with the performance at powers allowable for standard aviation fuel. Parallel tests were conducted by Proving Ground Command at Eglin Field, Florida on P-51B airplanes, AAF Nos. 43-24755, 43-24757, and 43-24775. The Power Plant Laboratory concluded in a 19 April 1944 memorandum report that the "Packard built Rolls-Royce V-1650-7 engine will satisfactorily comply with a 75 In. Hg manifold pressure war emergency rating with Grade 44-1 fuel". ⁴   As a result of the engine clearance and airplane trials the P-51-B airplane was cleared for operation at 75" Hg by late April. ⁵   The modifications required to the P-51 to use the 150 grade fuel were: modify manifold pressure regulator, modify supercharger volute drain valve, install new type induction center manifold extension gland seals, use of Lodge RS5/5 or KLG RC5/3 spark plugs, installation of bulged exhaust stacks, and reset supercharger aneroid switch. ⁶   By June 1944, final release on Project P.P.F. had been made approving 75" manifold pressure for the P-51 (both the 1650-3 and 1650-7 engines), as well as increased powers for the P-38 and P-47. ⁷

Deliveries of Grade 100/150 aviation fuel to Eighth Air Force fighter airfields commenced in June 1944. ^{8 9 10}  This coincidentally occured about the same time as the introduction of the P-51D into service.   Even though the USAAF had cleared the P-51 for 75" Hg., the Eighth Air Force chose 72" Hg as the P-51's War Emergency Rating. ^{11 12}   Apparently there is more to the story, however, as Encounter Reports demonstrate that 75" Hg was used operationally. ^{13 14}

By January 1945, fourteen of the Eighth Air Force's fifteen Fighter Groups were operating Mustangs, the sole holdout being the 56th FG in P-47's. Maintenance difficulties with spark plug fouling led to the decision to convert all fighter groups to 100/150 grade fuel reformulated with increased levels of ethylene dibromide (1.5T). Deliveries of PEP, as the new 100/150 blend was called, began to be issued to all fighter groups in February 1945. The use of PEP, however, cooroded the valve seats of the V-1650 at an unacceptable level. Consequently, the standard 100/150 (1T) grade fuel was reverted to by the end of March 1945. ^{15 16}   The Eighth Air Force also had hoped to supply the 352nd and 361st Fighter Groups based on the continent with 100/150 grade fuel. This was deemed impractical from a logistical viewpoint, although admittedly such difficulties did not prevent the RAF's 2nd TAF from being supplied with 100/150 grade fuel. ¹⁷

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.

2.   a.   This fuel was first service tested by Technical Operations Section, this headquarters, in October 1943, said service test lasting through until March 1944, at which time it was recommended that if extra performance from P-38, P-47 and P-51 aircraft was desired it could be secured by the use of this fuel. It was pointed out at that time that the only apparent deleterious effect of this fuel on any one of the three types was the extra lead fouling of spark plugs.

       b.   A decision was made in May 1944 to have all fighter units supplied with this fuel no later than 1 June. As of that date operations with this fuel continued until approximately 1 February 1945 when all fighter units switched to “Pep” (100/150 plus 1.5 T’s ethylene dibromide). As of 1 April 1945 all units switched back to 100/150 fuel containing 1.0 T ethylene dibromide.

3.   At the time the 150 grade fuel was first used all three fighter types listed above were in operational use by this Air Force. Shortly after June 1 P-38 units were re-equipped with P-51 type aircraft so that experience with 150 grade fuel in P-38 aircraft is limited. Gradually, conversion of P-47 outfits to P-51’s took place during the Summer and Fall of 1944, and as of approximately 1 November only one P-47 group remained in this Air Force.

4.   Maintenance difficulties can be summarized as follows:

a.   P-38 (V-1710 Engine).

Spark plug leading was increased. The extent of this leading was such that plug change was required after approximately 15 hours flying. This conditions was aggravated considerably by low cruising powers used to and from target areas, while trying to get the maximum range possible. It was found, however, that regular periods of high power running for a minute of two in most cases smoothed out any rough running engines unless the cause was other than leading.

b.    P-47 (R-2800 Engine).

Spark plug fouling was the only maintenance difficulty encountered during the period in which 150 grade fuel was used. Spark plug life was reduced by about 50%, the same low power cruising as described above being the principle cause for the extra fouling. No deleterious effects on diaphragms, fuel hose or any other rubber of synthetic rubber materials were noted.

c.    P-51 (V-1650 Engines).

The same type of lead fouling as described in a and b above happened in the case of the P-51 except that is was probably more serious than in either of the other two types. Using 130 grade fuel with 4½ cc. of lead, the average operational P-51 could last 5 missions (roughly 25 hours) before the fouling required plug change. With 150 grade fuel containing 6 cc. of lead, 10 to 12 hours, or normally 2 missions, was the average length of time between spark plug changes or cleaning. At various times in the six months of operation of P-51 aircraft on 150 grade fuel many other maintenance difficulties were attributed to the fuel, but final analysis proved that the only real effect of the fuel was the lead fouling. Some units maintained that they had some deteriorations of seals, but this was not borne our throughout the command, nor was there any concrete evidence that it existed in the units.

The excessive fouling of spark plugs usually exhibited itself in roughing up of engines after a couple of hours of low power cruising. Periodic bursts of high power in most cases smoothed the engine out. However, if the engine was allowed to go too long a period without being cleaned out, the accumulation of lead bromide globules successfully withstood any attempts to blow them out. In some instances, long periods of idling while waiting for take-off and a failure to use high power on take off resulted in loss of power during take-off run and in some cases caused complete cutting out with subsequent belly landing. The cases of cutting-out on take-off definitely attributed to excessive fouling were comparatively few, although numerous enough to list it as an effect of the extra lead.

As a result of several months operational use with the fuel, an SOP – designed to reduce power failures on take-off, leading troubles in flight, and other things which were causing early returns and abortive aircraft – was published. This is inclosure no. 1. Almost immediately after this section published this SOP practically all of the troubles then existing ceased, although it was necessary to change plugs after each two missions or thereabouts.<:p>

In an effort to reduce the lead fouling, tests were conducted by this section with 150 grade fuel containing 1.5 T’s of ethylene dibromide. A total of about 120 hours was run by this section and the three squadrons given the “Pep” fuel for accelerated service tests. The results of these service tests showed a considerable reduction in lead fouling with no apparent effects otherwise. As a results, all fighter units of the Air Force were put on Pep fuel late in January 1945. About thirty days thereafter a sharp increase in valve trouble was experienced with the V-1650 engine. Inspection of engines at overhaul revealed that the hydrobromic acid was eroding the silchrome valve seat inserts to such an extent that after approximately 100 hours of operation all the valve clearance was gone. This 100-hours is the minimum life some engines going 170 to 180 hours before this condition prevailed. There are no other deleterious effects of this fuel noted. As of 1 April 1945 fighter units of the Air Force returned to the use of 100/150 grade fuel containing 1.0 T of ethylene dibromide. ¹⁸

352nd FG Mustang being fueled with 150 Octane Gasoline

Those RAF Mustang units tasked with defending against the V-1 were modified to operated at +25 lbs./sq.in. - the equivalent of 80" Hg. ^{21 22}   On 24 August 1944, by which time the V-1 threat had subsided, the Ministry of Aircraft Production directed Rolls Royce: "all Packard Merlin V.1650-7 engines to be modified to operate at 25 lbs. boost". ²³   Raising the WER rating from 67" Hg to 80" Hg increased Sea Level speed by 30 mph. ²⁴   On 18 September 1944 ADGB noted, that with respect to the Mustang III/Packard Merlin 1650-7, "A total of over 7,000 hours have been flown at a maximum boost pressure of + 25 lbs./sq. in.". ²⁵   The RAF's Mustang Pilot's Notes gives the Combat Engine Limitation as "81 ins. boost for 5 minutes when using 150 grade fuel". ²⁶   Combat Reports and Squadron Operations Record Books show 150 Grade fuel and +25 lbs boost was used operationally over the continent by UK based Mustangs of ADGB. ^{27  28}

Encounter Reports noting high boost obtained with 150 grade fuel

1st Lt. Raymond R. Flowers, 1 November 1944, 20th FG“I closed steadily pulling over 70 inches.”

1st Lt. James F. Hinchey, 14 November 1944, 353rd FG“For fifteen minutes at 74” hg and indicating 600 mph…”

2nd Lt. Thomas R. Drybrough, 27 November 1944, 353rd FG"I had been pulling over 70" H.G. and was indicating about 425 MPH at approximately 14,000 feet."

1st Lt. Charles E. Yeager, 13 September 1944, 357th FG“I rolled over and was pulling around 70”Hg.”

Capt. Charles E. Yeager, 6 November 1944, 357th FG“I got behind him and was pulling 75” Hg.”

Lt. Col. Roy A. Webb, 25 June 1944, 361st FG“I closed very slowly and pulled as much as 70 inches of mercury.”

1st Lt. Thomas H. Hall, 15 August 1944, 364th FG“I put on 70 inches and gradually pulled up on them.”

Lt. Col. Kyle L. Riddle, 24 December 1944, 479th FG"I pulled about 70" to 75" mercury..."

F/Lt Pearson, 5 April 45, 65 Squadron"Opening up to 70 inches I overtook him..."

F/Lt. G. M. Davis, 23 March 1945, 129 Squadron"Opened up to +25 lbs of boost 3,000 revs and dived down to engage."

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Notes

1.  CTI-1659: Modification of Fighter Aircraft for use of Grade 150 Fuel Material Command, Technical Instructions, 29 March 1944.

2.  Project P.P.F. 4 April 1944

3.  Flight Tests on the North American P-51B-15 Airplane, AAF No. 43-24777 Using 44-1 Fuel

4.  75" Hg. clearance for V-1650-7 Material Command, Engineering Division, 19 April 1944.

5.  Project PPF: P-51B airplanes are cleared for operation at 75", 29 April 1944

6.  Instructions for Modification of P-51 Airplanes for Project PPF

7.  Project P.P.F. - Installation and Operating Instructions, 20 June 1944

8.  Grade 150 Aviation Fuel Chief, Petroleum Section, 13 June 1943.

9.  361st FG - 150 Octane Fuel delivered week ending 18 June 1944.

10.  359th FG - Engineering Report for June 1944 noting "change to one hundred fifty octane gasoline".

11.  Grade 150 Aviation Fuel Supply Division, 11 July 1944.

12.  78th FG Engineering Report for December 1944 noting "boosts set to draw 72 inches" when Group converted to P-51s.

13.  Capt. Charles E. Yeager, Encounter Report 6 November 1944, 357th FG

14.  Lt. Col. Kyle L. Riddle, Encounter Report 24 December 1944, 479th FG

15.  339th FG Aviation Fuel Report for February 1945

16.  Grade 100/150 (1 ½ T) Fuel Headquarters Air Technical Service Command in Europe, 28 March 1945.

17.  Request for Grade 100/150 1.5 T Aviation Fuel for Eighth Air Force Units on the Continent J.H Houghton, Dir. of Supply, 5 February 1945.

18.  Use of 100/150 Grade Fuel by Eighth Air Force Headquarters Eighth Air Force, Technical Operations, 4 April 1945.

19.  TI-2010, Addendum 1: Power Plant Fuel (PPF) 100/150 Grade Fuel Air Technical Service Command, Tech. Instr., 13 December 1944.

20.  78th FG Supply Report for December 1944 noting "During the latter part of December they were shipped 820 barrels of 150 octane by rail".

21.  No. 316 Polish Squadron Operations Record Book, 1 July 1944

22.  Technical Note No.Aero.1501(Flight) Improvement of Performance of Fighter Aircraft Operating Against the German Flying Bomb

23.  Requisition MER/388/43

24.  Crossbow fighters, low level speed table

25.  Summary of Use of 150 Grade Fuel

26.  Mustang Pilot's Notes, Engine Data

27.  Combat Report: F/Lt. G. M. Davis, 23 March 1945, 129 Squadron "opened up to +25 lbs of boost"
     Combat Report: F/Lt Pearson, 5 April 45, 65 Squadron

28.  118 Squadron Operations Record Book, 8 March 1945 "Aircraft being modified to take 25 lbs boost and 150 octane."

P-51B High Speed Performance

P-51B High Speed Performance

Mustang III V-1650-3 Aircraft Data Sheet

Mustang III V-1650-7 Aircraft Data Sheet

Mustang IV V-1650-7 Aircraft Data Sheet

Performance Data on Fighter Aircraft (climb, dive, turn and roll)

V-1650-3 & 7 Power Curve

V-1650-7 Low Blower Power Curve

V-1650-7 High Blower Power Curve

Merlin 61 and 65 Engine Chart

V-1650-3 Engine Chart, 5-15-43

Power Required and Power Available for the P-51A, P-51B and P-47B Airplanes.

Test to Determine the Effect of an Additional 85 Gallons of Internal Fuel on Performance and Handling of the P-51B Airplane

Stability on P-51B Airplane, AAF No. 43-12095

Estimated P-51B Mustange Performance with Improved Fuel (160 Grade)

P-51D and P-51K Flight Operation Instruction Chart

P-51D Roll

Pilot's Flight Operating Instructions, P-51-D-5 (April 5, 1944)

P-51 Tactical Planning Characteristics & Performance Chart

XP-51F Performance Curves

P-51F Airplane, Performance with War Emergency Power

XP-51G Performance Curves

XP-51G Estimated Performance

P-51H (NA-117) Airplane Performance

P-51H Altitude Performance (90" Hg M.P. & H20 Injection - 3000 R.P.M.)

Comparative Fighter Performance (P-47D, P-51H, XP-80A)

P-51H Engine Powers

P-51H Speed Clean

P-51H Speed with Racks

P-51H Climb

P-51H Standard Aircraft Characteristics, 22 March 1949

P-51H Characteristics Summary, 22 March 1949

P-51H Characteristics Summary, 19 May 1950

Pilot's Flight Operating Instructions for P-51H-1, -5, 10 Airplanes

Use of AN-F-33, Grade 115/145 Fuel

Note on Dive Tests on ‘Mustang IV’

Compressibility Dive Tests Part I on North American P-51D Airplane (Mustang IV), AAF No. 44-14134

P-51D AAF No. 44-141134 - Mach 0.85 dive

Spin tests P-51B Airplane, AAF No. 42-12136

Packard V-1650 Engine Performance Data, 1 September 1944

Packard/Merlin V.1650-7 - Mustang III +25 lbs. sq./in. Boost Operation Using 150 Grade Fuel, 4th September, 1944

Re-rating of Engines from 18lbs to 25lbs. Boost Pressure, 6th September, 1944

Mustang III Pilot's Notes, Engine data

Captain L. Carson of the 357th wrote of a 25 July 1944 combat:   "I was at house top level, flat out at 72 inces of HG and 3,000 rpm."
      Carson, Leonard K. Pursue & Destroy, (Sentry Books Inc., Granada Hills, California, 1978), p. 66.

Captain L. Carson of the 357th wrote of a 30 March 1945 combat:   "I had the throttle through the gate at 72 inches of mercury and 3000 rpm."
      Carson, Leonard K. Pursue & Destroy, (Sentry Books Inc., Granada Hills, California, 1978), p. 121.

Upon converting to P-51s, the 78th Fighter Group undertook the following:   "A few of the tasks were installing wing tank pressurization kits; G-suit hookups; guns sighted in; invasions strips removed; engine boost set to draw seventy two inches; landing gear switches modified; compass swung; blower switches installed; K-14 gunsights mounted; making fifty pairs of P-51 wing covers; fourty-one seat covers; repacking 155 dingies; 112 type S-1 and 170 type B-8 backstyle parachutes; and sewing up 98 silk pilot scarves."
      Fry, Garry L., Eagles of Duxford, The 78th Fighter Group in World War II., (Phalanx Publishing Company Ltd. St. Paul, MN, 1991.) p. 89.

James Tuder, crew chief with the 78th Fighter Group recalled:   "My pilot aborted a mission one day while we were using 150 octane fuel in the Mustangs. It was colored purple with dye to expose fuel leaks, not green like the 100/130 octane gas.
      Fry, Garry L., Eagles of Duxford, The 78th Fighter Group in World War II., (Phalanx Publishing Company Ltd. St. Paul, MN, 1991.) pp. 106-107.

7th Fighter Command based on Iwo Jima:   "In no wind conditions it was sometimes necessary to use 80 inches of manifold pressure from the Merlin engines at 2,800 to 3,000 rpm. It was virtually the only condition in which P-51 pilots went to 3,000 rpm (except for war emergency power) and none of them liked to do so."
      Barrett Tillman, Mustangs of Iwo Jima (Flight Journal, Ridgefield CT, Summer 2002) p. 27.

Major James B. Tapp of the 78th FS, 15th Group wrote:   "The Command had begun using the 115/145 Octane leaded gasoline."
      Major James B. Tapp, 7th Fighter Command History (External Link Open in new tab).

78th Fighter Group P-51 marked to be serviced with 100/150 Grade fuel

353rd Fighter Group P-51 marked to be serviced with 100/150 Grade fuel

357th Fighter Group P-51 marked to be serviced with 100/150 Grade fuel

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By Brent Erickson, Neil Stirling, and Mike Williams
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