Subject: Number Fifty-One in the Series--North American P-51 Mustang (1 of 10)

From: [email-masked]
Date: 8 Feb 93 17:38:18 GMT

>From [email-masked]

The P-51 Mustang was perhaps the most famous fighter of World War II, 
and, many would say, the best all-round piston-engined fighter 
produced by any of the combatants during that conflict.  Total 
production of all Mustangs amounted to 15,575 in the USA and 100 in 
Australia, ranking only behind the P-47 Thunderbolt in being the 
fighter manufactured in greatest numbers for the USAAF.  Mustangs 
accounted for 4950 of the 10,720 air combat victories claimed by the 
USAAF in Europe, and 4131 of the 8160 ground strafing claims made in 
the same theatre, accounting for 48.9 percent of total losses 
inflicted on the enemy.  They shot down more than 230 V-1 "buzz 
bombs", and they even managed to score some kills against Luftwaffe 
jet fighters.  

In 1934, James H. "Dutch" Kindelberger became president of North 
American Aviation, Inc.  Not only was Kindelberger an excellent 
businessman, he was also a capable aeronautical engineer.  As early as 
1938, Kindelberger had made numerous trips to Europe seeking orders 
for his company, and he had the opportunity to see up close some of 
the airplanes that would be in combat in the war that almost everyone 
believed would shortly be coming.  After hostilities broke out, 
Kindelberger eagerly sought out combat reports from both sides and 
developed some ideas of his own.  Although Kindelberger had no 
experience with fighters, he collaborated with his friend and 
colleague J. Leland Atwood to formulate an outline for a fighter 
project.  A project team was formed at North American, made up of such 
people as Raymond H. Rice, Edgar Schmued, Larry Waite and E. H.  
Horkey.  A sort of urban legend has grown up about Edgar Schmued, 
which claims that he had once worked for Willy Messerschmitt and that 
the Mustang was heavily influenced by the Bf 109.  

In April of 1940, Kindelberger was summoned by the British Air 
Purchasing Commision and asked to manufacture the Curtiss Hawk 87 
(P-40D) under license for the RAF.  Kindelberger countered that NAA 
could do better than that airplane and that they could design a REAL 
fighter in the same time that it would take to put the P-40 into 
production.  The British commission felt that they could take 
Kindelberger at his word, and on April 10, 1940 they accepted his 
proposal on the condition that the first prototype be ready in 120 
days.  The design was assigned the company project name of Model 
NA-73.  

At that time, the USAAC reserved for itself the right to block any 
foreign aircraft sales that it regarded as not in the Army's interest, 
for whatever reason.  On May 4, 1940, the US Army reluctantly agreed 
not to block the British sale, but they added a condition.  Two 
examples of the initial lot for Britain were to be transferred to the 
USAAC for testing free of charge.  

The NA-73X prototype contract was signed on May 23, 1940.  The British 
insisted that a heavy eight-gun armament be fitted.  NAA had actually 
been quietly working on such a fighter project since the summer of 
1939, and by that date they had actually already completed much of the 
detail design.  On May 29, a provisional RAF procurement was issued 
for 320 aircraft, contingent on satisfactory testing of the prototype.  
NAA agreed to start deliveries in January 1941.  RAF serial numbers 
were to be AG345 through AG664, and the aircraft was given the name 
Mustang I in RAF service.  

Another urban legend surrounding the Mustang is that it owed a great 
deal to the Curtiss P-40, and, in fact, stole numerous design features 
from that fighter.  Although NAA did pay $56,000 for technical 
aerodynamic data on the Curtiss XP-46, the NA-73X owed virtually 
nothing to any previous design and certainly did not owe anything to 
the Curtiss P-40.  

The NA-73 featured an all-metal stressed-ski structure, with the wing 
having a sheet-web main spar and an almost equally strong rear spar to 
carry the ailerons and the flaps.  Special attention was paid to 
features which would make the aircraft simple and inexpensive to 
manufacture.  The two wing spars had to be far enough apart to 
accommodate the length of a 0.50-in machine gun, with only the barrel 
protruding ahead of the main spar.  Most previous NAA aircraft had 
left and right wings bolted to a horizontal center section, but the 
Mustang had the wings meeting on the centerline, with dihedral 
emanating from that line.  

A special NACA laminar flow wing profile was adopted for the Mustang.  
This was an aerofoil which had a thickness that kept on increasing far 
beyond the usual location, i.e., to 50 percent chord rather than the 
usual 20 percent.  These profiles had little camber, the undersurface 
being almost a mirror image of the upper.  This wing was much more 
"slippery" than the old profiles, and provided lesser aerodynamic drag 
at high speeds than did more conventional aerofoils.  However, it also 
had less lift at low speeds, so the NA-73X had to have large and 
powerful flaps to keep landing speeds from being impractically high.  

The British also specified that a liquid-cooled inline engine be used, 
and the Allison V-1710 twelve-cylinder Vee was the only American-built 
engine which fit the bill.  The Allison V-1710 was a little bigger 
than the Merlin, slightly lighter, and similar in power at low 
altitudes.  However, at higher altitudes the Allison suffered from a 
rapid drop in power in comparison to the Merlin.  NAA briefly 
considered using a supercharger to improve high-altitude performance, 
but ruled against it on the grounds of a tight schedule.  

The Allison engine had a downdraft carburetor, so the ram inlet of the 
NA-73X was located above the cowling.  Radiators for cooling the 
ethlyene glycol and lubricating oil were located in a single 
heat-exchanger installed underneath the rear fuselage in a streamlined 
duct.  The drawback of such an arrangement was the extra weight and 
combat vulnerability of the long pipes that led to and from the 
engine.  Military innovations such as self-sealing fuel tanks, cockpit 
armor, and a bulletproof windshield were to be provided from the 
start.  

In a contract approved on September 20, 1940, it was agreed that the 
fourth and tenth production NA-73s would be the planes diverted to the 
Army.  The designation XP-51 was to be assigned to these two planes.  

On September 24, 1940, the RAF increased their Mustang I order to 620 
planes.  

The NA-73X prototype emerged from Inglewood plant in only 102 days, 
thus meeting the 120-day deadline with time to spare, although the 
airplane rolled out of the factory without an engine, which had been 
delayed at the Allison factory.  The engine that was eventually 
installed was an unsupercharged Allison V-1710-F3R liquid-cooled Vee, 
rated at 1100 hp.  The NA-73X bore the civil registration NX19998.  
Veteran test pilot Vance Breese flew it for the first time on October 
26, 1940.  Weights were 6278 lbs empty, 7965 lbs normal loaded.  It 
was a clear 25 mph faster than the P-40, even in spite of being 
powered by the same engine.  

Following tests, there were several changes in the geometry of the 
ventral ducting and the controllable flaps.  By the time that the 
NA-73 had been cleared for production, the duct had had its inlet 
moved downward so that its upper lip was lower than the underside of 
the wing, thus avoiding the ingestion of a turbulent boundary layer.  

On November 30, 1940, while on the third test flight of the NA-73X, 
another test pilot forgot to change fuel tanks, ran out of gas, and 
suffered a forced landing in a farmer's field.  This mishap put the 
prototype out of action for several months.  However, since this 
accident was not the fault of the aircraft itself, this did not unduly 
delay the program.  

Since the NA-73X had encountered very few problems during tests, 
production for the RAF began almost immediately.  The first production 
Mustang I for the RAF (AG345) flew for the first time on April 23, 
1941, well behind the original schedule.  It was retained by NAA as a 
development machine, and was used in an extensive series of tests to 
iron out bugs and eliminate problems.  Perhaps the most noticeable 
change was the extension of the carburetor inlet right up to the nose 
in order to give good ram recovery at extended angles of attack.  This 
machine was initially unpainted, but it later got an RAF paint job 
with camouflage, but it remained at Inglewood and did not ever get any 
guns.  

Armament was fitted to the second aircraft off the production line 
(AG346).  It was equipped with four 0.50-in machine guns and four 
0.30-inch guns.  Two of the 0.50-in guns were mounted in the lower 
fuselage and were synchronized to fire through the propeller arc.  The 
rest of the guns were mounted in the wings and fired clear of the 
propeller arc.  This aircraft was accepted by the RAF in September and 
started a long journey to Britain, finally arriving in Liverpool on 
October 24, 1941.  It lacked a radio, a gunsight, and certain other 
equipment which was by contract to be supplied by British 
manufacturers.  Once the British equipment was installed, the complete 
aircraft was evaluated at the Aeroplane & Armament Experimental 
Establishment at Boscome Down and by the Air Fighting Development Unit 
at RAF Duxford.  

The newly-arrived Mustang was quickly recognized as being the best 
fighter aircraft yet to be delivered from the USA.  It was found to be 
superior to the Kittyhawk, Airacobra and Spitfire in both speed and 
maneuverability at low altitudes.  Maximum speed was 382 mph at 13,000 
feet.  The armament of four 0.50-inch and four 0.30-inch machine guns 
was heavy and effective.  Handling was excellent.  The range was 
nearly double that of any RAF single-engined fighter.  It was 25 to 45 
mph faster than the Spitfire V at altitudes up to 15,000 feet.  The 
problem was the rapid fall-off in performance at altitudes above 
15,000 feet, caused by its low-altitude Allison engine.  This was more 
than just a minor deficiency, since most aerial combat over Europe at 
that time was taking place at medium to high altitudes.  Consequently, 
it was decided that the Mustang I could be best used for low-level 
tactical reconnaissance and ground attack, where full advantage could 
be taken of its exceptional low-altitude performance.  

Most of the first 20 RAF Mustang Is were retained for special 
measurements and trial installations.  Mustangs delivered under the 
original contract were similar to the original model but had an F-24 
camera mounted in an installation immediately behind the pilot's head 
armor, looking obliquely out to the left and to the rear.  A single 
gun camera was added near the left wing tip. 

It was initially feared that the Mustang I might be mistaken for a Bf 
109 during the stress of combat, and most of the Mustang Is in 
front-line RAF service had bright yellow bands painted across their 
wings.  

The first RAF unit to receive the Mustang was No 26 Squadron at 
Gatwick which began to operate the fighter in February 1942.  In 
April, two more squadrons received Mustangs, and eight more in June.  
Most of the aircraft went to Army Cooperation Command, usually 
replacing Curtiss Tomahawks or Westland Lysanders.  The first Mustang 
combat mission was undertaken by Flying Officer G. N. Dawson of No.  
26 Squadron on May 10, 1942, strafing hangars in France and shooting 
up a train.  

The first Mustang I operational sortie was on July 27, 1942.  Mustang 
Is participated in the disastrous Dieppe landings by British commandos 
on August 19, 1942, where it saw the first air-to-air action.  During 
this operation, pilots of No 414 Squadron of the RCAF were attacked by 
Fw 190s.  An American RCAF volunteer, F/O H. H. Hills, shot down one 
of the enemy, which was first blood for the Mustang.  

In October of 1942, On a mission to the Dortmund-Elms Canal and other 
objectives in Holland, the Mustang I became the first single- engined 
fighter based in the UK to penetrate the German border.  By this time, 
the Mustang I equipped Nos 2, 4, 16, 26, 63, 169,239, 241, 268, and 
613 Squadrons of the RAF, plus Nos 400, 414 and 430 Squadrons of the 
RCAF, and No 309 (Polish) Squadron of the RAF.  

In December 1940, the RAF ordered 300 more of the Mustang Is which 
embodied only minor modifications.  These were designated NA-83 by the 
factory.  RAF serials were AL958/AL999, AM100/AM257, and AP164/AP263.  

Mustang I AM106 was experimentally fitted successively with eight 
rocket projectiles on zero-length launches, special long-range fuel 
tanks, and eventually with two 40-mm Vickers cannon in underwing 
mountings.  

With the passage of Lend-Lease, 150 more Mustangs were ordered by the 
US Army, all of which were intended for delivery to Britain.  These 
were designated Mustang Mark IA by the RAF and NA-91 by the factory.  
The Mustang IA differed from earlier versions in having the machine 
guns replaced by four 20-mm wing-mounted Hispano cannon, with most of 
the long barrels protruding well ahead of the wing.  For contractual 
purposes, these aircraft were given the US designation of P-51 and 
assigned the USAAF serials 41-37320/37469.  The RAF serial numbers 
assigned to this lot were FD418/FD567.  The Allison V-1710-F3R engine 
was given the US Army designation V-1710-39.  Throughout 1941, the 
Army referred to these aircraft under the name *Apache*, but this was 
changed to *Mustang* at about the time the deliveries began in mid- 
1942.  

The British did not get all of these NA-91s.  Since the RAF deliveries 
took place after Pearl Harbor, many were repossessed by the Army 
before they reached England.  These included RAF Mustang IA serials 
FD418/FD437, FD450/FD464, FD466/FD469, and FD510/FD527.  The Army 
planes were armed with four 0.50-inch machine guns rather than the 
20-mm cannon and were fitted with two K-24 cameras in the fuselage.  
Most retained their RAF camouflage and serial numbers, although some 
were indeed painted with their equivalent USAAF serials.  These were 
designated as tactical reconnaissance aircraft and were designated 
F-6A, but this designation was soon changed to P-51.  

Tactical reports from RAF army cooperation units were laudatory.  The 
Mustang I and IAs were able to take an incredible amount of battle 
damage.  The long range of the Mustang made it an excellent tactical 
reconnaissance aircraft and its heavy armament made it effective 
against most ground targets.  In 18 months of operation 200 
locomotives and 200 barges were destroyed or severely damaged, and an 
undetermined number of enemy aircraft were destroyed on the ground.  
This was accomplished at the expense of only one Mustang being shot 
down by enemy fighters, five lost to flak, and two vanishing with no 
record of their fate.  At low altitudes, the Mustang was faster than 
either the Bf 109 or the Fw 190.  At sea level, the Mustang could run 
away from any enemy aircraft.  The flaps were very useful in combat to 
reduce the turning radius.  

Mustang Is and IAs served with the RAF up until 1944.  It knew few 
equals in the role of low-altitude interdiction and reconnaissance.  

In March of 1943, a batch of 35 P-51/F-6As were assigned to the 154th 
Observation Squadron at Oujda in French Morocco.  This was the first 
US Mustang unit.  Its first mission was a photographic coverage of 
Kairouan airfield, Tunisia on April 10, 1943.  

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.  

  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.   (708) 713-4548