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North American P-51 Mustang (Part 3)
By Joe Baugher
On April 30, 1942, Ronald W. Harker, a test pilot for the British Rolls-Royce engine manufacturer, took a brief hop in a RAF Mustang at the airbase at Duxford. Like lots of other pilots, he was highly impressed with the Mustang. It was 30 mph faster than the Spitfire VB at similar power settings and had nearly twice the range. Upon landing, he is reported to have said that the airplane would be a natural for the new Merlin 60 series of engines that Rolls Royce was just beginning to produce.
Rolls Royce management immediately jumped into action. They requested that three Mustangs be loaned to them so that they could fit them with Merlins. Rolls Royce studied various Merlins, including the single-stage Mk XX and the two-stage Mk 61. The two-stage Merlin was the better choice because of its far superior high-altitude performance. The Merlin Mk 61 engine crankshaft was geared to two supercharger blowers stacked in series. Because of the rapid compression of air, the temperature of the air after it passed through both stages of the supercharger increased by 200 centigrade degrees. In order to lower this temperature and thus increase the mass flow of the air entering the engine, an intercooler was added, requiring an extra radiator. After much thought, it was decided to mount the extra radiator under the nose, in the same duct as the ram inlet for the updraft carburetor.
This conversion was authorized on August 12, 1942. Four Mustang Is were allocated to the program (AM208, AL975, AM203, and AL963). They were assigned the designation Mustang X. The first Mustang X took to the air on October 12, 1942. No two of these Mustang Xs were exactly alike, but they all featured small chin-type radiators underneath the engine and four-bladed propellers to absorb the extra power. These Mustang Xs were to be kept busy throughout the rest of the war, testing various later marks of the Merlin engine.
One of the more bizarre proposals considered by Rolls-Royce was the possible installation of a 2400 hp Rolls-Royce Griffon 63 engine mounted amidships in a Mustang airframe a la P-39 Airacobra, driving a contrarotating propeller via an extension shaft. The cockpit was to be moved forward to a position well ahead of the wing. It was anticipated that this modification would make it possible to achieve speeds as high as 500 mph. A mockup of this configuration was carefully prepared, but the concept was abandoned before work could proceed any farther.
Meanwhile, in May of 1942, Rolls-Royce had informed Major Thomas Hitchcock, US military attache in London, that they planned to convert Mustang airframes to the Merlin engine. It just so happened that Major Hitchcock had been thinking of just this idea himself. He passed the word along to Wright Field and to North American Aviation. At this time, negotiations were taking place with the Packard Motor Car Company of Detroit for license manufacture in the United States of the new Merlin engine with the two-stage supercharger. On July 25, 1942, North American was authorized to convert two Mustangs to Merlin 65 engines imported from England. These aircraft were considered sufficiently different from the existing Mustang that they were given a new designation--XP-78.
NAA selected two P-51s from the batch of Mustang IAs that had been repossessed from the RAF by the USAAF. Their serial numbers were 41-37350 and 41-37421. NAA gave the project the company designation NA-101. The designation of these two aircraft was changed to XP-51B while the work was progressing. Although the early work by Rolls-Royce in conversion of Mustangs to the Merlin engine provided valuable insight to North American engineers, the British engine manufacturer did not directly participate any further in the project.
The North American engineers moved the carburetor air intake from above to below the nose in order to accommodate the Merlin's updraft induction system. The intercooler radiator was added to the radiator group already located inside the scoop underneath the rear fuselage, and the ventral radiator group was made noticeably deeper than before and had a sharp-angled inlet standing more than two inches away from the underside of the fuselage. The matrix and door arrangement of the ventral radiator system were modified. Instead of the oil cooler being situated in the center of a circular coolant radiator, it was relocated to the front of the duct and provided with its own ventral exit door. Further downstream, in a greatly enlarged duct, was the huge rectangular coolant matrix, with a much bigger exit door at the rear.
The airframes were strengthened in order to make full use of the increased power available. New ailerons were fitted and the underwing racks were increased in capacity to take two 1000-lb bombs or their equivalent weight in drop tanks. A new four-bladed Hamilton Standard hydromatic paddle-bladed propeller was fitted. Provisions for fuselage- mounted guns were totally eliminated, plans being made for four 0.50-in machine guns mounted exclusively in the wings.
The first XP-51B was flown by Bob Chilton on November 30, 1942. It was initially flown without armament. The performance improvement was nothing short of astounding. The XP-51B achieved a level speed of 441 mph at 29,800 feet, over 100 mph faster than the Allison-engined P-51 at that altitude. At all heights, the rate of climb was approximately doubled.
The USAAF now finally had an aircraft which could compete on equal terms with the Fw 190 and the later models of the Bf 109. The USAAF was finally fully sold on the Mustang, and a letter contract for 2200 P-51Bs was issued. The engine was to be the Packard V-1650-3, based on the Merlin 68. All airframes were to be manufactured by North American at their factory in Inglewood, California and at a completely new plant built in great haste at Dallas, Texas. Inglewood-built Mustangs were designated P-51B, Dallas-built Mustangs were designated P-51C. These aircraft were almost identical, and can generally be distinguished only by serial number.
The first P-51B flew on May 5, 1943, and the first P-51C flew on August 5 of that year. Inglewood built 1988 P-51Bs and Dallas built 1750 P-51Cs. The P-51Cs on the 1942 and 1943 budgets were given the company designation NA-103. 1350 NA-103s were built. Texas-built aircraft in the 1944 budget were designated NA-111.
Initially, the P-51B and C had the Packard V-1560-3 engine rated at 1400 hp for takeoff and 1450 hp at 19,800 feet and carried four 0.50-inch machine guns with a total of 1260 rounds. There were four hundred P-51B-1-NAs and 250 P-51C-1-NTs built.
800 P-51B-5-NAs were built, all of them powered by the V-1650-3. In the pursuit of still more range, a P-51B was experimentally fitted with an extra 85 US gallon self-sealing fuel tank behind the pilot's seat, bringing the total fuel to 419 US gallons (including 2 drop tanks). This extra fuel made the directional stability of the Mustang quite poor, so that the pilot would have to spend the first hour or so concentrating on keeping his airplane pointed in the right direction until this new tank was finally empty.
The last 550 P-51B-5-NAs were fitted with this extra tank, becoming P-51B-7-NAs. Some earlier P-51Bs and Cs were modified in the field to accommodate this tank. In service, however, the directional instability caused by the presence of a full fuel tank behind the pilot's seat was a hazard for new or inexperienced pilots, and the tank was usually restricted to 65 US gallons. This extra tank, nevertheless, still made a crucial difference in combat radius, and it was standard equipment in all future production versions.
With the introduction of the P-51C-5-NT onto the Dallas production line, the Packard V-1560-7 engine was adopted as standard. It offered 1450 hp for take off and a war emergency rating of 1695 hp at 10,300 feet. Maximum speed at 20,000 feet was reduced from 440 to 435 mph, but increased from 430 to 439 mph at 25,000 feet. 398 P-51B-10-NAs, 390 P-51B-15-NAs, and 1350 P-51C-10-NTs were built, all powered by the V-1650-7 engine.
A total of 91 aircraft from the Block-10 production lot (71 P-51B-10-NAs and 20 P-51C-10-NTs) were fitted with two oblique K24 cameras, or a K17 and a K22, to become F-6C photo aircraft. Most of these aircraft retained their guns.
The first combat unit equipped with Merlin-powered Mustangs was the 354th Fighter Group, which reached England in October of 1943. The 354th flew their first cross-Channel sweep mission on December 1, 1943, and scored their first victory on a mission to Bremen on December 16. However, inexperienced pilots and ground crews and numerous technical problems limited operations with the P-51B/C until about eight weeks into 1944. From the early spring of 1944, the Merlin-powered Mustang became an important fighter in the ETO.
In March of 1944, Merlin-powered Mustangs accompanied B-17 Fortress and B-24 Liberator bombers all the way on a 1100-mile round trip to Berlin. The ability of escort fighters to accompany bomber formations all the way to their targets and still effectively counter intercepting Luftwaffe fighters after jettisoning their nearly empty drop tanks caused the German defenses no end of problems, and added considerable impetus to the American daylight bombing offensive.
Most of the P-51B/Cs were assigned to the 8th and 9th Air Forces in England, with a lesser number with the 12th and 15th USAAF in Italy. The P-51B/C remained the prime Mustang variant in service from December 1943 until March of 1944, when the bubble-topped P-51D began to arrive. However, P-51B/C fighters remained predominant until the middle of 1944, and remained in combat until the end of the war in Europe even after the arrival of large numbers of P-51Ds. Even as late as the last month of the war, 1000 out of the 2500 Mustangs serving in the ETO were of the P-51B/C variety.
P-51Bs and Cs were assigned to the following fighter groups in the European Theatre:
4th Fighter Group, 8th Air Force
20th Fighter Group, 8th Air Force
335th Fighter Group, 8th Air Force
339th Fighter Group, 8th Air Force
352nd Fighter Group, 8th Air Force
357th Fighter Group, 8th Air Force
359th Fighter Group, 8th Air Force
361st Fighter Group, 8th Air Force
479th Fighter Group, 8th Air Force
354th Fighter Group, 9th Air Force
363rd Fighter Group, 9th Air Force
52nd Fighter Group, 12th Air Force
325th Fighter Group, 15th Air Force
31st Fighter Group, 15th Air Force
332nd Fighter Group, 15th Air Force
Perhaps the best known P-51B aircraft is "Shangri La", a P-51B-5-NA (Ser No 44-6913) flown by the Fourth Fighter Group ace Don Gentile.
The Merlin-powered Mustang entered service in the China-Burma-India (CBI) theatre in September 1943. These aircraft were assigned to the 23rd and 51st Fighter Groups of the 5th Air Force. Early in 1944, the 311th Fighter Group of the 10th Air Force saw action in Burma with its Mustangs, flying in support of airborne troops attacking Japanese lines of communication. The top Mustang ace of the CBI theatre was Major John C. "Pappy" Herbst, with 18 kills.
In late 1942, a deal was worked out between Britain and the USA in which Spitfire VBs would be transferred to the 8th Air Force in England, mainly for use as fighter-trainers. This cleared the way for Lend-Lease supplies to continue of the new Mustang model to the RAF. The RAF equivalent to the USAAF P-51B/C was the Mustang III. The RAF ultimately received 274 P-51Bs and 626 P-51Cs. RAF serials were FB100/FB124, FB135/FB399, FR411, FX848/FX999, FZ100/FZ197, HB821/HB962, HK944/HK947, HK955, HK956, KH421/KH640, SR406/SR438, and SR440. Serial numbers FX848, 849, 907, 909, 910, 911, 913, 914, 915, 916, 918, 927, 928, 932, 948 were handed back to the USAAF upon arrival in Britain. HK944/947, 955, 956 were ex-Twelfth USAAF aircraft.
KH490 crashed in the USA before delivery. Serial numbers SR406/438 and SR440 were a mixed bag of P-51Bs and Cs delivered to the RAF from the USAAF--US serial numbers were respectively 43-12162, 43-12407, 43-12412, 43-12473, 43-12484, 43-12427, 43-70114(?), 43-12189, 43-12177, 43-7039, 43-6831, 43-12155, 43-12188, 43-12456, 43-12480, 43-12399, 42-10663(?), 42-106683, 42-106630, 42-106687, 43-7071, 43-7144, 43-5595, 43-7171, 43-6829, 43-12420, 43-7152, 43-7135, 42-103209, 42-106478, 42-106431, 43-7007, 43-12420, 43-7159. (Question marks denote serial numbers which are probably erroneous).
A total of 59 Mustang IIIs were diverted to the Royal Australian Air Force and to other Allied air arms.
After these Mustang III aircraft had been delivered to England, the RAF decided that the hinged cockpit canopy offered too poor a view for European operations. A fairly major modification was made in which the original framed hinged hood was replaced by a bulged Perspex frameless canopy that slid to the rear on rails. This canopy gave the pilot much more room and the huge goldfish bowl afforded a good view almost straight down or directly to the rear. This hood was manufactured and fitted by the British corporation R. Malcolm & Co., and came to be known as the "Malcolm Hood". This hood was fitted to most RAF Mustang IIIs, and many USAAF P-51 received this modification as well.
The first RAF base to receive Mustang IIIs was at Gravesend in Kent. The Mustang III initially equipped No. 65 Squadron in late December of 1943, followed by No. 19 Squadron in March of 1944. Later the Mk. III also equipped Nos 64, 65, 66, 93, 94, 112, 118, 122, 126, 129, 165, 234, 237, 241 249, 250, 260, 268, 306, 309, 315, 316, 345, 430, 441, 442, and 516 Squadrons and No. 541 Squadron of RAF Coastal Command. These units included four Polish squadrons (306, 309, 315, 316), three RCAF, and one Free French.
The new RAF Mustang IIIs began operations late in February 1944, escorting US heavy bombers as well as both US and RAF medium bombers.
Numerous RAF Mustang IIIs were diverted to the interception of V-1 "buzz-bombs". Some of them were "souped up" by using a special high-octane fuel and internal engine adjustments in order to increase the intake manifold pressure and made it possible to achieve a speed of 420 mph at 2000 feet. Since the typical V-1 flew at 370 mph, this made the "souped-up" Mustang very useful against these weapons.
About 100 P-51Bs and Cs were supplied to the Chinese Air Force in 1943-44.
During late 1944, French units acquired some F-6Cs and began to operate them over Germany in January of 1945 on photo-mapping missions.
The last P-51B passed out of service in 1949, having been re-designated F-51B in 1948.
Specs of P-51B-1-NA:
One 1620 hp Packard Merlin V-1650-3 twelve cylinder Vee liquid-cooled engine. Maximum speed was 388 mph at 5000 feet, 406 mph at 10,000 feet, 427 mph at 20,000 feet, 430 mph at 25,000 feet, 440 mph at 30,000 feet. Range on internal fuel was 550 miles at 343 mph at 25,000 feet, 810 miles at 253 mph at 10,000 feet. With maximum external fuel, maximum range was 2200 miles at 244 mph. An altitude of 5000 feet could be attained in 1.8 minutes, 10,000 feet in 3.6 minutes, 20,000 feet in 7 minutes. Service ceiling was 42,000 feet. Weights were 6840 lbs empty, 9200 lbs normal loaded, 11,200 lbs maximum loaded. Wingspan was 37 feet 0 1/4 inches, length was 32 feet 3 inches, height 8 feet 8 inches, and wing area was 233 square feet.
Specs of P-51C-10-NT:
One 1695 hp Packard Merlin V-1650-7 twelve cylinder Vee liquid-cooled engine. Maximum speed was 395 mph at 5000 feet, 417 mph at 10,000 feet, 426 mph at 20,000 feet, 439 mph at 25,000 feet, 435 mph at 30,000 feet. Range on internal fuel was 955 miles at 397 mph at 25,000 feet, 1300 miles at 260 mph at 10,000 feet. With maximum external fuel, maximum range was 2440 miles at 249 mph. An altitude of 5000 feet could be attained in 1.6 minutes, 10,000 feet in 3.1 minutes, 20,000 feet in 6.9 minutes. Service ceiling was 41,900 feet. Weights were 6985 lbs empty, 9800 lbs normal loaded, 11,800 lbs maximum loaded. Wingspan was 37 feet 0 1/4 inches, length was 32 feet 3 inches, height 8 feet 8 inches, and wing area was 233 square feet.
Serial numbers of P-51Bs:
43-12093/12492 North American P-51B-1-NA Mustang
43-6313/7112 North American P-51B-5-NA Mustang
43-7113/7202 North American P-51B-10-NA Mustang
42-106429/106540 North American P-51B-10-NA Mustang
42-106541/106738 North American P-51B-10-NA Mustang
42-106739/106978 North American P-51B-15-NA Mustang
43-24752/24901 North American P-51B-15-NA Mustang
Serial numbers of P-51Cs:
42-102979/103328 North American P-51C-1-NT Mustang
42-102979/103328 North American P-51C-1-NT Mustang
42-103329/103778 North American P-51C-5-NT Mustang
42-103779/103978 North American P-51C-5-NT Mustang
44-10753/10782 North American P-51C-10-NT Mustang
44-10783/10817 North American P-51C-11-NT Mustang
44-10818/10852 North American P-51C-10-NT Mustang
44-10853/10858 North American P-51C-11-NT Mustang
44-10859/11036 North American P-51C-10-NT Mustang
44-11037/11122 North American P-51C-11-NT Mustang
44-11123/11152 North American P-51C-10-NT Mustang
43-24902/25251 North American P-51C-10-NT Mustang
Although literally hundreds of P-51Ds are still in existence today (many of them still flying), very few P-51B/C fighters have survived to the present, even in museums. Ed Maloney's Air Museum in Ontario, California, the National Air Museum, and the Movieland Museum of the Air are reported to have P-51B/C aircraft on display. No others are known to exist. Anyone have further details?
Sources:
American Combat Planes, Ray Wagner, Third Enlarged Edition, Doubleday, 1982.
The American Fighter, Enzo Angelucci and Peter Bowers, Orion Books, 1987.
War Planes of the Second World War, Fighters, Volume Four, William Green, Doubleday 1964.
United States Military Aircraft since 1909, Gordon Swanborough and Peter M. Bowers, Smithsonian, 1989.
Fighting Mustang: The Chronicle of the P-51, William N. Hess, Doubleday, 1970.
Classic Warplanes: North American P-51 Mustang, Bill Gunston, Gallery Books, 1990.
Famous Fighters of the Second World War, Volume I, William Green, 1967.
The North American P-51B and C Mustang, Richard Atkins, Aircraft in Profile, Doubleday, 1969.
British Military Aircraft Serials, 1912-1969, Bruce Robertson, Ian Allen, 1969.
Joe Baugher
AT&T Bell Laboratories
2000 North Naperville Road
Naperville, Illinois 60566-7033
