From Foal to Thoroughbred

North American's P-51 Mustang

by Jeff Ethell

Copyright © 1993 by the Confederate Air Force and Jeff Ethell. All rights reserved.

"Sired by the English out of an American mother," said Assistant U.S. Air Attache in London, Maj. Thomas Hitchcock, in 1942. The North American P-51 Mustang, against steep odds emerged at the end of World War II as the finest all-around piston-engine fighter in the service.

During the first months of the war, the British and French renewed their efforts to purchase U.S.-built aircraft, settling on the P-40. Lt. Benjamin S. Kelsey, head of the Army Air Corps Pursuit Projects Office at Wright Field, and his boss, Col. Oliver P. Echols regretted this since it would push a new Curtiss fighter, the XP-46, off the assembly lines. Air Corps commander Gen. H.H. "Hap" Arnold decided he could not spare the four month lag in production to change from the P-40 to the P-46 — if America were drawn into the war, quantity would be drastically needed.

In January 1940, recalled Kelsey, "Echols made a suggestion to the Anglo-French Purchasing Commission to find a manufacturer who wasn't already bogged down in high-priority stuff. Curtiss-Wright and the Air Corps would make available all the data we had on the XP-46 to help them build a new fighter. This was our secret talk in the halls to get P-46s in place of the P-40, to find some way of getting around the problem."

Scouting for other companies to build the P-40, Commission was drawn to North American Aviation (NAA) which had done a sterling job in providing Harvard trainers. The company made it clear they had no desire to build another firm's fighter…they wanted to design one themselves. Commission member Sir Henry Self approached NAA president James H. "Dutch" Kindelberger about designing such a fighter. By April 1940 NAA Vice President J. Leland Atwood had negotiated an agreement. Donovan R. Berlin, designer of the P-40 had spent the better of the past two years developing the XP-46. With his go-ahead, Atwood bought the data along with results of how the aborted belly radiator scoop worked on the original XP-40, for $56,000. On May 4, North American signed a Foreign Release Agreement with the Air Corps permitting the sale of the Model NA-73 overseas providing two examples were supplied to the Army. Kelsey and Echols had maneuvered hard to get their new fighter built at a time when the Air Corps had no procurement money.

North American's Chief Engineer Raymond Rice and his team, under Chief Designer Edgar Schmued, began a seven-day work week to produce the fighter. Wing design under Larry Waite incorporated, at the insistence of Edward Horkey, the NACA laminar flow wing section which was not in the original concept. Kelsey had pushed behind the scenes with NACA's Eastman Jacobs to get the wing into the project and soon Jacobs was with the NAA team on the West Coast. "All this happened," recalled Kelsey, "without anybody at Wright Field having the foggiest notion of what was going on. We had to stay out of it because it was a British procurement." The North America team's genius resulted in the best design possible around the radical NACA laminar flow wing section. Though the Curtiss data was shipped by crate to California, Atwood later said not much of it was used in the final design. Others inside the industry, particularly Don Berlin and others at Curtiss, said otherwise from the time the Mustang became famous.

There was no 120-day requirement for completion of the prototype, as has often been asserted. The only completion date noted in the contract was initial delivery by January 1941 and all 400 aircraft delivered by Sept. 30,1941. Using internal systems from the Harvard such as hydraulics, wheels, brakes and electrics, the men at North America pushed the NA-73X out of the shop in a remarkable 102 days minus engine, which arrived 20 days later. It was not until Oct. 26, 1940 that Vance Breese took the prototype into the air from Mines Field, California for the first time.

The ventral radiator scoop for oil and glycol cooling needed aerodynamic refinement. The problems it caused weren't solved until the scoop was redesigned and lowered away from the boundary layer disturbances on the underside of the fuselage. The initial Mustangs, as a result, did not fully realize the benefit of the "Meredith effect" that created thrust with the exit air, offsetting the drag caused by the scoop.

The first Mustang I, British production number AG354, was first flown on April 23,1941. The Air Corps was to have received their first example, designated XP-51, in February 1941 and the other in March, but the first airframe didn't arrive at Wright Field until August 24, the second came in December. Contrary to the long-standing story of official neglect delaying acceptance of the fighter by the newly redesignated Army Air Forces, there were numerous additional problems, not the least of which was chaos resulting from the bombing of Pearl Harbor eight days before the second XP-51 was delivered. According to a 1942 P-51 acceptance report, production delays, bad weather, gun charging system problems, needed refinements to the Allison engines and the higher priorities given to other aircraft already being evaluated hampered the process.

On July 7,1941, over a month before the first XP-51 arrived at Wright test, the AAF placed an order for 150 P-51s to be furnished to the RAF. Only 93 ended up with the British. Fifty-five were kept by the RAF, two being set aside for the XP-78 project (later XP-51B) to fit a Packard-built Rolls-Royce Merlin engine to the airframe. This promising start was slowed by lack of funds since no more money was available in that year's budget for fighter aircraft. Between Echols, Kelsey and Kindelberget enough money was found in the attack portion of the AAF budget. The solution was, according to Kelsey, finding the next number allocated for an aircraft, which happened to be A-36. Adding bomb racks and dive brakes to the airframe, and calling it an attack bomber instead of a fighter, kept the production line open. This risky move by a few maneuvering Army officers showed anything but neglect.

Before the first P-51 flew, an order was placed for 500 A-36 aircraft on April 16, 1942. By March 1943, when the first AAF Mustangs were ordered into combat in North Africa, the RAF's Army Co-Operation Command had been flying the fighter in combat for 10 months. Though British and American pilots found the Mustangs to be faster than anything around at low level, it suffered greatly from lack of high altitude performance. Waiting in the wings was a wizard for the Yank. Just as Merlin was able to transform a young boy into King Arthur, so could the Rolls-Royce wizard of the same name transform a spirited American pony into a firey thoroughbred.

After flying a Mustang I in April 1942, Rolls test pilot Ronald W. Harker went back to his company and asked if a Merlin 61 engine could be fitted to the excellent low drag Mustang airframe. Harker believed that the combination could result in the best fighter of the war, in spite of the British Air Ministry asking, "Why waste time on an untried, American-built aeroplane?" In spite of much opposition, five aircraft were set aside for modification.

Rolls let North American know what they were up to so NAA set aside two P-51 airframes to receive the American-built Packard Merlin. A friendly competition developed to see who would be the first to fly a Merlin Mustang. The British only just beat the Americans — Rolls flew their first conversion on Oct. 14, 1942 while NAA had the XP-51B (originally designated the XP-78) up on Nov. 30.

The results were stunning and almost exactly one year later the P-51B entered combat over Europe. In spite of serious teething problems brought on by rushed development, the Merlin Mustang could fly farther into enemy territory than any other fighter on the same amount of fuel, thus saving the AAF's strategic bombing campaign from annihilation at the hands of the Luftwaffe. By the end of World War II the P-51 reigned supreme on all fronts, its pilots having claimed more than 5,000 enemy aircraft destroyed, more than either the P-38 or the P-47.

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