When NAA began producing the NA-73 for Britain, according to a stipulation made in the sales contract, the fourth and tenth production airframes were to be handed over to the Army Air Corps, to be evaluated as part of the Army's fighter program.
An Authority for Purchase document (number 164265) was issued on July 24th, 1940 and called for the delivery of the two aircraft with the AAC designation of XP-51.
On September 20th of that same year, the Assistant Secretary of War approved the official contract. Both airframes were expected for delivery in February and March of 1941.
However, the start of production of the NA-73 was pushed back because of the crash of the NA-73X prototype and because NAA had to wait longer to receive the first Allison engines. To compensate for this, NAA decided to take the fourth and tenth aircraft in the assembly line and already install the Army engines, for delivery to Wright Field.
In December of 1940, the British let NAA know that they chose the name "Mustang" for their new fighter.
In March of 1941, some five months after NA-73 made its first flight, the Air Corps sent over Capt. Morris J. Lee out of California to test fly it. Lee made a report of his findings on March 22nd, 1941, but it was not what NAA hoped for.
His report was very brief and almost to the point of being insulting:
Shortly after Capt. Lee's downgrading report, the Air Corps was reformed as the Army Air Forces.
During World War I, early aviation became and increasingly important part of warfare. As a result, a division of the United States Army was created, the United States Army Air Service. On July 2nd, 1926, it changed to the United States Army Air Corps, which became the aerial warfare service component.
In 1940, the expected activation of Army General Headquarters prompted Army Chief of Staff George C. Marshall to request a reorganization study from Chief of the Air Corps Maj. Gen. Henry Harley "Hap" Arnold, resulting in a proposal for creation of an air staff on October 5th, 1940. Its goal was the unification of the air arm under one commander, and equality with the ground and supply forces.
Arnold's proposal was immediately opposed by the General Staff in all respects, rehashing its traditional doctrinal argument that, in the event of war, the Air Corps would have no mission independent of support of the ground forces. Marshall implemented a compromise that the Air Corps found entirely inadequate, naming Arnold as acting "Deputy Chief of Staff for Air" but rejecting all organizational points of his proposal. GHQ Air Force instead was assigned to the control of Army General Headquarters, although the latter was a training and not an operational component, upon activation in November 1940.
A division of the GHQ Air Force into four geographical air defense districts on October 19th, 1940, was concurrent with the creation of air forces to defend Hawaii and the Panama Canal. The air districts were converted in March 1941 into numbered air forces with a subordinate organization of 54 groups.
In the spring of 1941, the combat successes of the British Royal Air Force and the German Luftwaffe under centralized control made clear that the fragmenting of authority in the American air arm had resulted in a dangerous lack of clear channels of command. After a joint U.S.-British strategic planning agreement (ABC-1) rebuffed the long-held argument that the Air Corps had no wartime mission except support of ground forces, the War Department revised Army Regulation 95-5 on June 20th in an attempt to end the divisions without legislative intervention by Congress.
In creating the Army Air Forces with the Air Corps and the Air Force Combat Command (a redesignation of General Headquarters Air Force) as its major components, the War Department also authorized an Air Staff to manage planning and execution of expansion of the air arm and named Arnold as Chief of the Army Air Forces. It did not, however, end the dual chain of command difficulties, as air units of Air Force Combat Command still reported to Army GHQ as well as Headquarters AAF. Two further attempts by Arnold to implement his reorganization were again rejected by the WDGS in October and November.
Arnold made a decision to postpone any attempts to exploit the opportunity to push for an independent Air Force as he thought that it would "be a serious mistake to change the existing setup" in the midst of the crucial expansion effort.
By November, however, the division of authority within the Army as a whole caused by the activation of Army GHQ prompted Marshall to assert that he had "the poorest command post in the Army." Defense commands, particularly those affecting air defense, had in Marshall's words showed a "disturbing failure to follow through on orders."
Confronted with Marshall's dissatisfaction with Army GHQ, the General Staff reversed its opposition. Marshall appointed an Air Corps officer, Brig. Gen. Joseph T. McNarney, to chair a "War Department Reorganization Committee" within the War Plans Division, using Arnold's plan as a blueprint.
Based on the recommendations of McNarney's committee, Roosevelt issued Executive Order 9082, which changed Arnold's title to Commanding General, Army Air Forces effective 9 March 1942, making him co-equal with the commanding generals of the other components of the Army of the United States.
On that date, War Department Circular 59 formalized the changes, abolishing Army GHQ and organizing the Army into three autonomous components: the Army Air Forces, the Army Ground Forces, and the Services of Supply, each with a commanding general reporting to the Chief of Staff.
It was the most radical reorganization of the aviation branch in its history, developing a structure that both unified command of all air elements and gave it total autonomy and equality with the ground forces.
The British originally requested four 20mm cannons as their armament of choice for the Mustang. Due to a shortage in Hispano 20mm cannons, NAA chose not to opt for the cannons when developing the NA-73.
In February of 1941, the British Purchasing Committee asked NAA to reconsider the 20mm cannon armament. NAA decided to look into the incorporation of the cannons in their design and opened up a new charge number, NA-91.
At that time, British funds for purchasing US war material were running short. The United States was still neutral at that time, however President Roosevelt acknowledged the importance of its British and other foreign allies. In mid december of 1940, he introduced a new policy initiative whereby the United States would lend, rather than sell, military supplies to any nation deemed "vital to the defense of the United States" for use in the fight against Germany. Payment for the supplies would be deferred, and could come in any form Roosevelt deemed satisfactory.
Secretary of War Henry L. Stimson told the Senate Foreign Relations Committee: "We are buying...not lending. We are buying our own security while we prepare. By our delay during the past six years, while Germany was preparing, we find ourselves unprepared and unarmed, facing a thoroughly prepared and armed potential enemy.”
In March of 1941, Congress passed the Lend-Lease Act (subtitled “An Act to Promote the Defense of the United States”) and Roosevelt signed it into law.
Under this policy, the United States was able to supply military aid to its foreign allies during World War II while still remaining officially neutral in the conflict. Most importantly, passage of the Lend-Lease Act enabled a struggling Great Britain to continue fighting against Germany virtually on its own until the United States entered World War II late in 1941.
To handle any foreign orders, an office at Wright Field known as Defense Aid was created. The office was opened in May and was superseded by the Office of Lend-Lease in Washington, DC, in October of that year. Defense Aid "procured, stored, issued, and transported supplies and equipment for beneficiary foreign governments ”.
As stated in the article on NA-73X, the contract NAA closed with the British contained a clause to deliver the fourth and tenth production Mustang to the USAAC for testing and evaluation purposes.
NAA Construction number 73-3101 was the fourth NA-73 production Mustang (often incorrectly cited in various books, articles and website as AG348, which is not the case, AG348 was production number 73-3102).
However, since the commitment to provide the Army Air Corps with an example was now two months behind schedule, an Allison engine belonging to the Air Corps had been rushed to the plant and installed on airframe 73-3101 so it could be rushed out in advance of the rest.
Because of that, 73-3101 became the second NA-73 to fly when Bob Chilton made the first test on May 20th, a power calibration and aileron trial flight.
As an official Air Corps type, the plane bore the designation XP-51 and was given US serial number 41-038. Some of the parts were still handmade, not yet standard production pieces, and even some AT-6 components were still used.
The first XP-51, 41-038
Chilton flew 21 more tests in the XP-51 from May 24th to July 2nd.
With credit available on the Lend-Lease basis the British intensified their buying programme, but before any aircraft could be leased a US military agency had to order. As such, those aircraft were seemingly built for the USAAF and given appropriate designations and serial numbers.
NAA received a Department of the Army contract (DA-140) on June 30th, 1941 on behalf of the BPC for 150 cannon armed Mustangs under its NA-91 programme. The order were built under the Defense Aid Contract DA-AC-140 and were named P-51-NAs (derived from the XP-51 designation). The USAAC considered calling their new asset “Apache”, but since the British name Mustang was already commonly used, the name “Apache” would be dropped in favor of “Mustang” in the first months of 1942.
The British accepted their first Mustang Mk. I example, given British serial number AG346, in August, at NAA.
On August 24th, 1941, the first XP-51, 41-038, was flown to Wright Field for conducting official performance tests. When it arrived on scene, a safety inspection was made, balance checks were made and the aircraft was weighed. The aircraft was entrusted to a junior officer, 2nd Lt. Winthrop Towner, who did little flying with the NAA prototype. Material Command was already bogged down in testing other aircraft such as the P-39, P-38, P-47 and various other experimental planes, which were given a greater urgency with other developments. Moreover, the XP-51 was considered "a foreigner", because it was designed by a German and built by request of the British.
Furthermore, the person in charge at Material Command, General Oliver Echols, had personal issues against NAA and its Mustang project... but more on that a bit later on...
NAA engineers came over to install several "upgrades" to the airframe before any official testing could be done: backfire screens were installed, as well as new ailerons and flap bracket bolts.
Between October 8th and December 22nd, the XP-51 underwent some performance tests at Wright Field. Still carrying the short carburator scoop, and with a full load of ammuniation and 170 gallons of fuel (total weight 7,934lb), the Mustang was clocked at 382mph at 13,000ft.
NAA had guaranteed 375 mph, which was slightly exceeded in a flight of around 750 miles at a cruise speed of 325mph.
On October 21st, test pilot Bob Chilton arrived at Wright Field to evaluate a Spitfire Mark V and Hurricane Mark II.
Whilst walking the flightline, Chilton was suprised to see the XP-51 tied down to the ramp. Upon checking the aircraft's log, he was puzzled to see that it only had about one hour of flight time since its arrival on August 24th. Chilton adressed 2nd Lt. Towner, about this. Towner simply stated: "It’s a low priority program and we’re not done testing it."
The XP-51 was flown one more time the following day and subsequently readied for a ferry flight to Langley, Virginia, to be evaluated by NACA, after being fitted with an experimental gun charger.
Meawhile, on October 24th, the first Mustang I, AG346, was shipped to Britain.
December 7th, 1941, changed everything. Japan had bombed the US naval base at Pearl Harbor, Hawaii, and thus dragged the US into the war it had tried to avoid up till now.
The USAAF in Hawaii at that time consisted of the 18th Bombardment Wing at Hickam Field, the 14th Pursuit Wing at Wheeler Field, and a small gunnery training detachment at Bellows Field. Although newer and more aircraft were requested, at that stage of the war there were only 12 B-17D Flying Fortresses, 33 B-18 Bolo, about 12 A-20 Havoc bombers, 39 P-36A fighters, and 87 P-40B and 12 P-40C Tomahawk fighters. On the morning of December 7th, most of these aircraft were unfueled, unarmed and parked closely together on the ramp.
Following the devastating attack, the USAAF realized it still had no world-class fighters to take into combat. The P-39 and P-40 were all that was to be available even until the end of 1942, a full year later.
What was Material Command doing and why were the Mustangs not tested more rapidly?
Let's take a closer look at Materiel Command and the "Oliver P. Echols - NAA" fued...
Materiel Command
Air Force Materiel Command traces its heritage to 1917 at McCook Field, a World War I-era, experimental engineering facility in Dayton, Ohio. With the creation of the U.S. Air Service in 1918, the organization became known as the Engineering Division and was expanded to include responsibility for the Air Corps' logistics system. It was redesignated the Air Corps Materiel Division in 1926. As the largest branch of the Air Corps, the Materiel Division was responsible for all aircraft and equipment research, development, procurement, maintenance, supply and flight tests.
Major General Oliver P. Echols was the Air Force's chief materiel officer throughout World War II. More than any other man under the commanding general of the Army Air Force, General Echols was responsible for the development, procurement and supply of aircraft and aeronautical equipment for the Air Force.
On March 15th, 1941, the Air Corps established a provisional Maintenance Command at Patterson Field, in Dayton, Ohio, to operate under the Chief of the Materiel Division. This command was originally set up as a provisional unit because the War Department was hesitant to approve the change. This put all the aircraft maintenance and supply activities, from those at the large US depots to those at forward deployed outposts, under the new command, and put Echols in charge of establishing this new command.
In June of that year, the new command moved from Patterson Field to Wright Field co-locating it with the Materiel Division. In addition to the sheer growth in scope and responsibility of the Materiel Command, the other main reason for this new command was the likelihood, at the time, that the government was going to take all procurement from the Armed Forces and give it to a civilian agency. Given this probability, Air Corps officials wanted to separate the maintenance, storage, and supply functions that the services would retain. At the time, Brig. Gen. Echols gave “convincing arguments against making the separation” to General Brett who was the acting Chief of the Air Corps.
The fued between Echols and NAA started back in 1940 when Echols was angered by NAA's agreement to design a fighter rather than build P-40s for the British. Materiel Command in 1940 had lost control of NAA and Echols neither forgot nor forgave that. When the Mustangs first arrived at Wright Field, Echols used Lee's report to indicate its disinterest in a fighter having modest armament and low-altitude capability. The Air Corps wanted the P-40F.
When the Mustang became the subject of a possible buy for the Air Corps in 1942, Echols tried to stop NAA’s production of fighters for the US.
On February 25th, 1942, the Army promoted Echols to Major General. On March 9th, 1942, a presidentially approved reorganization of the War Department changed the Materiel Division to the Materiel Command. The change established the Headquarters of the Materiel Command in Washington, DC, and on verbal orders of the Commanding General of the Army Air Forces the Materiel Division at Wright Field became the Materiel Center.
It was at this time that General Frank B. Wolfe became the dominant personality in the operation of the Materiel Center, at Wright Field.
Just as Echols had predicted, in 1943, the Army and the Air Corps went through a significant reorganization. This reorganization appointed Echols the Assistant Chief of Air Staff for Materiel Maintenance and Distribution, and subsequently ended his time in direct command of the activities at Wright Field, though he would remain intimately involved and very influential in the continued activities of Materiel Command. On April 6th, 1943, the Materiel Center at Wright Field was re-designated the Materiel Command. Its functions remained the same, but this put General Echols in a position of less direct authority... paving the way for the Mustang to make its entry...
Following the 1935 USAAC design competition for a new fighter, the Seversky P-35 came out as winner and was ordered into production. Following the 1935 competition, the Army began setting up various other circular proposals in order to find better fighters and bombers. The following two proposals were:
Specification X-608 led to the first flight of the Lockheed XP-38 on January 17th, 1939, while X-609 saw the Bell XP-39 fly on June 23rd ,1939.
As the war escalated in Europe, many aircraft manufacturers came up with prototypes and designs to be tested and evaluated. Many of them passed through to Wright Field.
Some Army Air Corps/Army Air Forces fighters that first flew during that period but did not pass prototype or limited production stages before December 1941, such as the Curtiss P-37, XP-42 and P-46, the Seversky XP-41, the Republic P-43, P-44 and XP-47, the Bell P-45 and the Douglas P-48.
The XP-39 made its maiden flight on April 6th , 1938 and was being produced at this time. The RAF had initially ordered 386 P-39Ds, which would later be extended to 675. However, after the first Airacobras (as the P-39 was named by the British) arrived at No. 601 Squadron in September of 1941, they were promptly found to have an inadequate rate of climb and performance at altitude for Western European conditions. In the end, only 80 were adopted, all of them with No. 601 Squadron.
About 200 P-39s were transferred to the Soviet Union by the British.
Following the attack on Pearl Harbor, another 200 examples intended for the RAF were taken up by the USAAF as the P-400, and were sent to the Fifth Air Force in Australia, for service in the South West Pacific Theatre. By that time, nearly 600 P-39s had been built. Largest operator of the P-39 was the Soviet Army through the Lend-Lease program.
Within the USAAF, the P-400 was deployed mainly to training units, although some saw combat in the Southwest Pacific including with the Cactus Air Force in the Battle of Guadalcanal. Although they were often outclassed by Japanese fighter aircraft, it performed well in strafing and bombing runs, often proving deadly in ground attacks on Japanese forces.
The most prominent fighter within USAAF at that time was the P-40, which was mass produced and operated by many foreign air arms as well. P-40Bs were the first USAAC fighters to be drawn into combat in WW2 during the attack on Pearl Harbor, on December 7th. Although being caught by suprise and suffering many losses on the ground, a couple of P-40Bs managed to scramble in the air and attack and destroy Japanese aircraft.
At dawn on December 7th, 1941, 2nd Lt. George Welch (left) and 2nd Lt. Kenneth M. Taylor (right), were coming back from a Christmas dinner and dance party at a rooftop hotel in Waikiki, that ended in an all-night poker game.
They were still wearing mess dress uniforms when the Japanese attacked Pearl Harbor. Welch telephoned the auxiliary Haleiwa Fighter Strip on Oahu's North Shore to have two Curtiss P-40B Tomahawk fighters prepared for takeoff.
Taylor immediately drove his Buick at high speed to Haleiwa to join the air battle.
Taking off with only .30-cal ammunition in the wing guns, Welch claimed two kills of Aichi D3A Val dive bombers over Ewa Mooring Mast Field.
The first Japanese aircraft was only damaged and made it back to its carrier, while the second was finished off by Ken Taylor, shortly before he landed at Wheeler Field to get .50-cal ammo for his two cowl guns.
On his second sortie, Welch shot down a Val (which was behind Ken Taylor, and crashed in the community of Wahiawa) then one Mitsubishi Zero fighter.
Both men were awarded the Distinguished Service Cross for their actions that day.
The P-40 went on to serve with many fighter groups in the Pacific, CBI and MTO theater.
As far as to other experimentais were concerned: those that were finally built and flown all turned out to be stunning failures in concept and/or performance, with the exception of the Lockheed XP-38 and the Republic XP-47B.
The XP-38 first flew on January 27th, 1939 and was sent to Wright Field the following month for testing purposes. After the inital compressibility issues were overcome, it was finally put into production. The first unit to receive P-38s was the 1st Fighter Group. First blood by a P-38 was drawn on August 9th, 1942, when 2 P-38Es of the 343rd Fighter Group, 11th Air Force, at the end of a 1,000 miles (1,600 km) long-range patrol, stumbled upon a pair of Japanese Kawanishi H6K "Mavis" flying boats and destroyed them.
The P-38 went on to be one of the most success long range escort fighters in the Pacific Theater of Operations and the China-Burma-India Theater of Operations and produced some of America's top aces, such as Richard Bong (40 victories), Thomas McGuire (38 victories) and Charles H. MacDonald (27 victories).
After initial testing, Republic and the USAAC concluded that the XP-47 was inferior to German fighters. Subsequently, Republic went to work on a new design. The wing surface area was enlarged, and self-sealing fuel tanks and armoring were added. With the introduction of Pratt & Whitney’s R-2800 Double Wasp engine, the original XP-47 design was abandoned, and a bold, new design emerged. This new design was designated XP-47B, while the XP-47 and XP-47A programs were dropped. The USAAC ordered a prototype of the XP-47B in June of 1940.
The Republic P-47B Thunderbolt would see entry into service with the 56th Fighter Group at Bendix Field, New Jersey, in June of 1942.
Seeking what many publicists now called “game-changing” fighters, the War Department ordered prototypes of three novel designs from Vultee, Curtiss, and Northrop. Although its calculated top speed was a remarkable 510 mph, the XP-54 twin-boom prototype never flew faster than 403mph.
Demonstrated top speeds for the other two were 390mph for the XP-55 and 465mph for the XP-56. Disappointing and tricky to fly, none were ordered into production.
Thus AAF hopes for the future rested more and more on the rather virtually unnoticed North American Aviation prototypes.
As mentioned earlier, Material Command's indifference to the XP-51 was made clear in a document titled "Future Development of Pursuit Aircraft" , created by the Pursuit Board during meetings held between October 11th and October 30th, 1941. Within the document, a statement was made to “Make a thorough study of our current program for pursuit aircraft.”
As a response to that document, about 18 experimental and 8 production aircraft were listed. Again, NAA's fighter was not one of those. With all of those advanced experimental types under consideration, the USAAF still felt there was no need for the XP-51.
Below is a promotional video of the operations at Wright Field during WWII. The Mustang is show at about 0:12:25, but obviously nothing is spoken about the difficulties the Mustang faced gaining acceptance at Materiel Command.
Unwanted project
While all this was going on, Kindelberger was giving his all in pressing government officials to advance the P-51 program. Lickily, NAA already had several British orders on the table, which would secure production of the fighter for NAA into September of 1942,
However, Dutch knew that direct USAAF orders were needed to guarantee further production of NAA's new fighter.
On December 16th, 1941, NAA delivered the second XP-51, which received serial number 41-039, to Wright Field.
Near the end of December, a report was issued which contained several constructive comments about the XP-51:
The latter was probably caused by a very bad landing by Capt. Lee on November 26th, which damaged the right main gear and destroyed the tailwheel and lower rudder surface (following the landing, the airframe was inspected by NAA and deemed safe to fly, with flight tests resuming November 30th).
Meanwhile, Chilton was displaying the XP-51 to almost any interested Army officer. Pilots from the nearby 79th Pursuit Squadron, 20th Pursuit Group, were allowed to fly the Mustang Is by NAA at Inglewood and they all liked new fighter.
Maj. Thayer S. Olds, 79th PS CO, reported on January 2nd, 1942 to the Commanding General of the IV Interceptor Command, that he and his pilots had nothing but praise for the Mustang. Interesting side note is that two 79th PS pilots would go on to be test pilots for NAA, namely Louis S. Wait and R.C. Chilton.
On January 1st, a request was made to Wright Field Experimental Engineering to estimate the possible improvements which might result from putting an Allison V-1710-61 in place of the -39. Multiple speed runs were made with taped gun ports and in a normal combat configuration. Results pointed to an improvement in critical altitude from 13,000ft to 16,300ft and a slight increase in top speed to 383mph.
Wherever the Mustang was flown and tested, nothing but praise was given to the airframe. Below is a report made up by leaders of the 4th Interceptor Command, who tested the Mustang alongside the P-40, P-38D and P-66. In contrast to Capt. Lee's report, they had nothing but praise for the Mustang.
The last paragraph stated: "In accelerating from wing-to-wing position with a P-40 flying at top speed the rate of seperation of the Mustang from the P-40 had to be seen to be believed."
The report was forwarded to Brig. Gen. William Ord Ryan, the Commanding General 4th Interceptor Command, who attached the report to a letter adressed to Gen. "Hap" Arnold.
Ryan’s letter to Arnold was sent approximately three weeks after Col. Ira Eaker flew the Mustang during a visit to NAA, on his way to HQ-AAF for his VIII Bomber Command assignment. He stated, “I thought that the Mustang was the best fighter that I had flown. It was somewhat underpowered, but I knew it was possible to correct that with bigger engines coming along.” He later mentioned his impression of the Mustang when he arrived at HQ-AAF to meet with Spaatz.
Approximately two weeks after receipt of this letter from Gen. Ryan, Arnold and Spaatz visited NAA in January 1941 and came away with the impression that “the Air Force should have P-51s.”
In January of 1942, Carl Andrew "Tooey" Spaatz was promoted to Major General and became commander of Air Force Combat Command. Despite praising the P-51, his statement was that escort fighters were not needed to win the war in Europe: “I do not believe escort fighters can be developed to accompany medium and heavy bombers over their tactical radius of operations which will be different in overall dimensions than the bombers they accompany. If better armament can be devised for escort fighters for this purpose, the same armament should be put on the bombers.”
For a long period to come, bomber crews were still being sent over Germany without escorts, with high command still believing in the self-defending bomber.
Not a single attempt proved successful until the very end of 1943. Hap Arnold stood very much alone in his drive for developing long range escort fighters and in searching for solutions to increase the range of single-engined fighters. Most planners came up with ideas for large, twin- (or more) engined escorts which could carry very heavy armament and several crewman to operate multiple guns. More armament and crew meant a heavier load, which resulted in even greater fuel capacity needs. Because no succesfull solution was thought of, fear grew that no escort fighters would ever come available.
To make matters worse for NAA, the Air Corps had assigned the Merlin 28 (Packard V-1650-1) to Curtiss for installation in their P-40F. Needles to say, this made the XP-51, powered with the non-supercharged V-1710 even more excess.
Meanwhile, Rolls-Royce and Packard had begun development on the two-stage Merlin 63 (Packard V-1650-3). Material Division had been made aware of the physical dimensions and weight of the proposed engine a year and a half before Packard sent the first one to NAA. While at Curtiss, Donovon Berlin (designer for Curtiss) wanted the V-1650-3 for his P-40.
In January of 1942, Echols wrote to Arnold that "... the P-40 series cannot feasibly accommodate the present Rolls-Royce Merlin 63 of the proposed stepped-up Allison engines withour major modification to the aircraft design."
It is highly lickely that the American Air Force would indeed have put the V-1650-3 in a P-40 if it had fit. At that time, the AAF still had no plans to order Mustangs for itself once production for the British would come to a halt. As it would turn out through the long summer of 1942, NAA would surely benefit of this setback for Curtiss...
In February of 1942, Kindelberger wrote to Gen. Arnold: "approximately 220 have been delivered and the production rate is now 78 per month. It is our duty to point out that the time has come, if not actually past, when continuity of production of this model can be maintained. If additional airplanes are ordered at once, the new features can be engineered and incorporated and comparatively little loss of production will result. If such an order is not forthcoming, arrangements will be made to dismantle and store the tools and the plant will be rearranged to produce only B-25 airplanes.”
Later that month, the Military Requirements Department of the Air War Plans Devision (AWPD - an American military organization established to make long-term plans for war), expressed the need for some sort of fast fighter/ground attack aircraft that was able to provide close air support and perform tactical reconnaissance duties. Major General Muir Stephen Fairchild, the Director of Military Requirements proposed the P-51 for this role to the USAAF.
Dutch Kindelberger would receive some support from Lt. Col. Benjamin Kelsey of Material Command. He pointed Dutch in a direction which might aid in keeping the Mustangs in production. As the USAAF was running out of funds for the development of fighter aircraft. The USAAF did have funds left for the development of a dive-bomber, and they were despirately looking for one. Tales of Germany's weapon of terror, the Junkers Ju-87 Stuka dive bomber reached top command in the US. Several dive bomber projects were under development at that time, but none of those put forward impressive performances.
Kelsey came up with an idea to get NAA involved in the design, which would lead to the development of the A-36 Mustang (NAA charge number NA-97).
In late February, early March, the head of the AWPD, Col. Howard Arnold Craig, required NAA to produce dive-bomber versions of the Mustang. Responding for Material Command was Lt. Col. Patrick Weston Timberlake, Echol's Assistant for Procurement Services, he sent a memo to Col. Craig on March 5th, 1942:
"1. As a result of investigation of the proposal to a board of officers in your office last week with the view of utilizing the P-51 as a dive bomber, the following is submitted.
2. It is the opinion of the Materiel Division that the production of the P-51 airplane at Inglewood should not be continued for the following reasons:
a. No engines are immediately available due to the planned increase of production of Bell P-39s to 600 per month.
b. A potential loss of two B-25s per day would result if the P-51 line is continued at Inglewood.
c. A development project is required to convert the P-51 airplane to a dive bomber, requiring special study of the dive brake design, bomb racks, and cannon installation.
3. The Materiel Division is making a study with the view of setting up the P-51 production line in Kansas City when engines and GFE are available."
It is obvious that Materiel Division once again fought against further development of the P-51, this time trying to stop its production altogether. Where the notion of further Mustang production causing the production of B-25s to diminish is unclear. When NAA was asked to produce P-40s under license, it was never stated that this would slow down B-25 production.
On March 1st, the first XP-51, 41-038, was sent to the Langley Field NACA facility where it was handed over for further flight test evaluations.
For some unknown reason, Lt. Col. Timberlake changed his mind about the dive bomber Mustang variant. On March 22nd, he stated that 500 Mustangs could be produced as A-36 dive bombers once the British contract ended later that year.
On April 16th, the contract was finalized and on April 19th, Maj. Gen. Muir Stephen Fairchild, Director of Military Requirements, sent out a formal request to Materiel Command for the 500 Mustangs. He expressed his desire to quickly convert the P-51-NA mustang as an interim dive bomber. That way, he would not have to wait for NAA to develop and test the necessary design changes to make it a dive bomber, and hoped to have some Mustangs produced as fighters, stating "those produced without dive brakes can be used as fighters, fighter-bombers, observation airplanes or in operational training units."
Since Echols was lower in the chain of command to Maj. Gen. Fairchild, this made 2 superior officers demanding the development of the A-36. He had no choice but to concede and approved the A-36.
He did however stick to Materiel Commands plans and order the specific development for the dive bomber variant, thus eliminating the chances of the Mustang being used as a fighter.
Not to be deterred, Kindelberger and his team were already working on the following evolution of the P-51, namely charge number NA-99, which was a pure machine gun armed fighter variant of the Mustang. In August of 1942, NAA proposed to change the 500 A-36A aircraft to the P-51 type.
To further emphasize Materiel Command's indifference: the second XP-51, 41-039, which was delivered to Wright Field in December of 1941, remained untouched until April of 1942. It sat there while other pursuit models were continuously scheduled for flight testing first, primarily Echol's favorite, the XP-46.
The Mustang Mk. I was already being used operationally at this time by the RAF. They already came to appreciate the low level capabilities of the aircraft and praised its performance. The Luftwaffe already operated its latest fighter, the Focke-Wulf Fw 190, which was proved superior to the British Spitfire V. By the end of 1941, a Rolls-Royce Merlin 61 was mated to the Spitfire V. By mid-1942, the Merlin engined Spitfire IX retook the advantage.
When Rolls-Royce test pilot, Ronald Harker, was invited by the RAF to Duxford to fly a Mustang Mk. I (AG422) in April of 1942, he was immediately impressed by the aircraft's performance. Although the Mustang weighed more than the Spitfire, it used less power to fly faster. No one could explain why at the time, but the extreme low drag of the airframe amazed him. Harker too noticed a rapid drop in performance above 15,000ft.
After his test flight, Harker declared that the Mustang could perform much better if it was re-engined with "...a powerful and good engine like the Merlin 61. Its performance should be outstanding, as it is 35 mph faster than a Spitfire V at roughly the same power".
The following day, he sent a letter to Rolls-Royce and convinced Rolls-Royce Director Ernest Hives to try and re-engine the Mustang.
As was expected, the news was dismissed by Echols and Materiel Command.
When Brig. Gen. Fairchild told his equal, Brig. Gen. Grandison Gardner, Commanding General of the Air Proving Ground Command at Eglin, in April of 1942 to “...test the armament installations on all current production aircraft.”, Materiel Command sent over several aircraft to be tested... but not the P-51.
In the final weeks of May, the USAAF sped up its process to acquire Mustang IAs for both ground support and reconnaissance fighters. By May 20th, 57 NA-91s out of a total of 150 scheduled for delivery of Mustang IAs for the RAF, were kept aside and redesignated P-51-NA. These would become the first Mustangs operated by the USAAF in the war.
Material Command was still busy testing and examining various designs. Amongst the experimental designs that were being testedthe P-35 and P-36 were already becoming obsolete, as were the P-39, P-40 and P-43 at that stage of the war. Various other airplanes would never be produced, such as the XP-52, XP-54, XP-55, XP-56, XP-59, XP-62, XP-67 and XP-69.
This left the USAAF with both the P-38 and P-47 as their best fighters in 1943. As such, both were forced to be the escorts of choice. Production of the P-38 was slow. Additionaly, Army generals were trying to get the P-38 to about every theaters of operations (particularly those theaters where Army troops were present). This resulted in a shortage of P-38s to go around.
USAAF's top priority was to beat Germany and send in bombing raids continuously to destroy vital targets. The P-38 was available in 1942 and should have been used to attain that priority. The missed opportunity, for various reasons, to operate P-38s in the European Theater of Operations (ETO) through all of 1943 resulted in severe losses of bombers and their crews.
41-039 was assigned to NACA Langley Memorial Aeronautical Laboratory, Virginia, from March 9th, 1943 to January 15th, 1944. It's post-War fate is unclear, but it did not survive.
41-038 however still exists today and is on display at the EAA Foundation Museum at Oshkosh, Winsconsin. After the war it was stored at NASM until the EAA Foundation aquired it in 1975. It was reserialized as N51EA and became the subject of a restoration.
It even flew again from 1976 until 1982, when it was finally retired and put in the EAA museum, where it is still on display today!
Hives convened another conference with the Air Ministry for June 1942. Because the issue of re-engining brought forth increased communications between NAA and Rolls-Royce, one of the men required to be present was Maj. Thomas Hitchcock, Jr., America’s Assistant Military Attaché at the London Embassy.
Thomas Hitchcock Jr. came from that strata Americans once referred to as “high society” and was from a family which mixed socially with the Roosevelts. He was born in 1900 and by 1917 wanted to be a fighter pilot in the Great War. His father received help from former President Theodore Roosevelt and Tommy was able to join the famed Lafayette Escadrille, a unit of American combat pilots in French service. During one air battle Tommy was shot down and captured by the Germans but escaped by jumping out of a train.
On foot, he hid in the woods during the daytime then walked more than one hundred miles over eight nights to the safety of Switzerland.
Between the wars he was the world's finest polo player.
He became equally determined to be a fighter pilot in the Second World War and served in the USAAF as a Lieutenant Colonel. He was assigned as an assistant air attaché to the US Embassy in London and arrived in Britain in April 1942, just in time to observe the mating of the Merlin to a Mustang.
Hitchcock first flew a Merlin-Mustang on November 6th, 1942.
Later in the war he was assigned to a staff position in the Ninth Air Force. He learned how to fly the Mustang and felt compelled to learn more about its stability problems, when it was fitted with a new fuselage fuel tank giving the aircraft a rear center of gravity. On April 12th, 1944, during a test flight he was unable to Pull out of a dive and died in the crash.
Tommy was the right man in the right place to promote the Merlin-Mustang to disbelievers in America. Witold Chanter, Rolls-Royce's Performance Engineer at Hucknall and a Polish exile, began furnishing statistics and graphs starting on June 8th, 1942 which demonstrated that for both the Spitfire V and the Mustang Mk. I to fly at 350 mph it took 260 more horsepower for the Spitfire to achieve the same speed.
Challier said a Mustang fitted with a Merlin 61 would have a speed close to 440 mph at 27,800 feet and (would have) a plus-20 mph advantage over the Spitfire IX.
The Mustang was predicted to be one of the fastest, highest-flying fighters in the world, if re-engined with a two-stage Merlin. By the middle of June, Challiers' facts astounded one Rolls-Royce engineer who said the Mustang "Has a very low drag, for which, so far, there is no very definite explanation."
On July 27th, 1942, 16 RAF Mustang Mk Is undertook their first long-range reconnaissance mission over Germany, which made the Mustang the first single-engined aircraft to penetrate German airspace from Britain.
Given notice of its very long range Maj. Hitchcock passed on to his superiors in the US all the data on Mustang operations and conferences and the penetration of German airspace should have been noted by officers at Materiel.
Word of Challiers predictions reached General Arnold who cabled Ambassador John Winant in London to say he was “...having an immediate investigation made as to the possibility of converting Merlin 28 production to Merlin 61s, with a view of installation in Mustangs if it works out."
CTI-710 ordered a prototype P-51 equipped with a Merlin 61. Tommy Hitchcock would have been informed of Arnold's cable.
The redesigned Spitfire XIV appeared in late 1943. Officials were aware in 1942 that there could be a gap between the Mks IX and XIV and interest in the Merlin-Mustang became acute. Because both the Spitfire IX and XIV were high-altitude fighters, re-engining of the Mustang was to be revised to use the Merlin 65, a medium-altitude engine.
At the very end of June, 1942, Hives was depressed about the fighter position, both in this country and the USA, but he added that “...we are sold completely on the Mustang. The Merlin 61 goes into it with no alteration to the engine cowling or to the radiator cowling".
Hives was so hopeful that the Merlin-Mustang would prove to be a good fighter for the RAF that he wanted 250 Mustang airframes shipped from America for mating with Merlins.
Sir Wilfried Freeman offered to get 500 Merlin-Mustangs were being test-flown at Hucknall in June.
Starting in July, Hives and other British officials invited Brig. Gen. Frank O’D. Hunter to participate in discussions so that British excitement would be carried back to Wright Field. The AAF doubted British claims for the Merlin-Mustang and asked Dr. Edward Warner to travel to Britain in August to examine the conversion and assess Challier's figures. Challier put out some new estimates in which he stated the Mustang with a Merlin 61 would have a service ceiling of 40,100 ft and full throttle height would be 25,000 ft!
These predictions astounded believers on one side of the Atlantic and were viewed with skepticism on the other side.
On June 23rd, 1942 the AAF had initiated a contract for 1,200 Mustangs but it was not signed until August 23rd, and did not mention a Merlin-Mustang!
The 500 A-36s were absorbed in the contract, but Echols did not specify what was to follow them. It was at this juncture that two USAAF camps formed, one favoring the Mustang and one criticizing it. Few officers prior to June 23rd would have gambled their careers to support the P-51 and many after that date continued to disparage the British project. General Arnold had initiated formal reengining of the Mustang in the US but the job was overseen without enthusiasm or alacrity on the part of some key officers.
Nevertheless, NAA, awaiting a real Merlin 61, proceeded with re-engining immediately using a mock-up.
Brig. Gen. Fairchild pointedly remarked to Echols that directive has been issued by the Materiel Command as to what production will follow the A-36.” Fairchild wanted P-51s produced as part of the contract for 1,200 Mustangs and said -...the Merlin should be introduced.
Despite Echols’ disinterest, Brig. Gen. Franklin O. Carroll, Chief of Experimental Engineering, was not intimidated and on August 14th he told the Technical Executive: “...we are proceeding full blast with the installation of the Merlin 61 (VI650-3) engine in two P-51 airplanes. North American has estimated that the first airplane will be ready for flight by October 1, 1942, contingent upon receipt of the engine by September 7th.”
Meanwhile, in the ETO, during the disastrous Dieppe raid on August 19th, 1942, four British and Canadian Mustang squadrons, including No. 26 Squadron, saw action covering the assault on the ground. That day, an American pilot flying in the Canadian Squadron, F/O Hollis Hills, became the very first P-51 Mustang pilot credited with an aerial victory.
In May and June 1942, Rolls-Royce received and reengined several Mustangs (serials AM121, AM208, AL975, AM203 and AL963) with Merlin 65s and four months later, rolled out the first of them for ground running. The British prototypes were designated Mark X. None of the 5 Mustangs were exactly the same as engineers were trying out different techniques and solutions to the new installation.
First flight came in October 1942, one month before NAA’s modified Mustangs flew. Rolls-Royce, not as much concerned with aerodynamics as would be an airframe manufacturer, built a deep chin scoop under the spinner of the re-engined Mustang X, degrading directional stability and requiring fin fillets.
NAA received authorasition on July 25th to go ahead with the conversion. They pulled 2 aircraft aside, 41-37352 and 41-37421, and re-engined the Mustangs. In contast to the British, NAA carefully redesigned the airframe, retaining the familiar Mustang profile.
NAA’s Bob Chilton made the first flight on November 30th, 1942.The re-engined Mustang briefly was designated XP-78 but the AAF soon reverted to XP-51B, the original designation.
One of Rolls-Royce’s conversions - a Mustang X, serial number AM 121 - was handed to the USAAF’s Eighth Fighter Command at RAF Bovingdon on June 26th, 1943. USAAF markings and call letters VQ-R were applied.
The XP-51B had to be strengthened for the added power and a new propeller by Hamilton Standard was designed.
The Merlin 61 V-12 with its two-stage compressor really cooked the air before it entered the carburetor. An intercooler had to be installed to cool the intake air. The Brittish installed the intercooler under the engine near the intake trunk of the Mustang X. The Americans put the intercooler in the doghouse assembly with the coolant radiator under the fuselage. This reduced the size of the cowlings around the new engine but increased the size of the belly scoop area.
The first flight by Bob Chilton was on November 30, 1942. NAA was very pleased with the results (might have been some jumping up and down with excitment). The new Mustang reached 441 mph at 29,000 plus feet. At this altitude, the XP-51B would simply run away from an Allison Mustang that was nearly 100 mph slower.
Orders for the new P-51B were placed in August of 1942, months before the test flights. P-51A production was cut short to make room for the new Merlin powered Mustangs. During this time period Packard was working with Rolls Royce to build their Merlin series V-12s in the U.S. The negotiations were successful and Packard began the produce V-1650-3 Merlins for the new P-51B.
A government-imposed system of priorities
emerged out of necessity in late 1942.
One of the systems in need of change was the awesome
power of the Materiel Command. Coincidental with
government’s changes to Materiel was a rising chorus of
people opposing Echols’ wait-and-see attitude affecting the
contract for 1,200 Mustangs and the
Merlin-Mustang. Arnold, Fairchild,
Kindelberger, Atwood, Schmued, Warner,
Hives, Hitchcock, and others disagreed
with slow acceptance of the Merlin-
Mustang. When the government made its
sweeping changes, Echols’ power was
diminished. He relented and shortly
afterward agreed to produce the P-5 IB.
The XP-51B had to be strengthened for the added power and a new propeller by Hamilton Standard was designed.
The Merlin 61 V-12 with its two-stage compressor really cooked the air before it entered the carburetor. An intercooler had to be installed to cool the intake air. The Brittish installed the intercooler under the engine near the intake trunk of the Mustang X. The Americans put the intercooler in the doghouse assembly with the coolant radiator under the fuselage. This reduced the size of the cowlings around the new engine but increased the size of the belly scoop area.
The first flight by Bob Chilton was on November 30, 1942. NAA was very pleased with the results (might have been some jumping up and down with excitment). The new Mustang reached 441 mph at 29,000 plus feet. At this altitude, the XP-51B would simply run away from an Allison Mustang that was nearly 100 mph slower.
Orders for the new P-51B were placed in August of 1942, months before the test flights. P-51A production was cut short to make room for the new Merlin powered Mustangs. During this time period Packard was working with Rolls Royce to build their Merlin series V-12s in the U.S. The negotiations were successful and Packard began the produce V-1650-3 Merlins for the new P-51B.
A government-imposed system of priorities
emerged out of necessity in late 1942.
One of the systems in need of change was the awesome
power of the Materiel Command. Coincidental with
government’s changes to Materiel was a rising chorus of
people opposing Echols’ wait-and-see attitude affecting the
contract for 1,200 Mustangs and the
Merlin-Mustang. Arnold, Fairchild,
Kindelberger, Atwood, Schmued, Warner,
Hives, Hitchcock, and others disagreed
with slow acceptance of the Merlin-
Mustang. When the government made its
sweeping changes, Echols’ power was
diminished. He relented and shortly
afterward agreed to produce the P-5 IB.
Edgar Schmued was born in Germany in 1899. He was fond of mechanics and aviation and started working as a student in a small engine factory in
Germany. At a later age he started studying aeronautics and enlisted in the Austro-Hungarian Flying Service at the outbreak of WW1.
After the war his brothers immigrated to a German community in Sao Paulo, Brazil. Edgar would follow their example in 1925 and found a job with General Motors automotive division. GM held stock in several other companies at that time, including Fokker Aircraft Company. They were impressed by Schmued and helped him to immigrate into the US in 1929, where he held a position at Fokker in Teterboro, NJ.
In 1929, NAA took over the Fokker Aircraft Corporation and Schmued, who worked for GM as a field service manager in Brazil, moved to the USA to work with aircraft - something he had always wanted to do, with his training as a mechanical engineer.
Fokker soon became General Aviation, but the Airmail Act of 1934 forced airmail carriers to rid themselves of holdings that controlled aircraft construction. This meant that GM had to get rid of NAA which, in turn, took over General Aircraft. Kindelberger had come from Douglas Aircraft a year earlier, and was now president of the 'new' NAA. 'Dutch' moved the company west and asked Schmued to join him, but Schmued's wife did not want to move to California so the designer joined the firm of Bellanca - a decision he soon regretted.
However, 'Dutch' had kept the job offer open, and Schmued and his family finally moved west in 1936. However, just 100 miles from Los Angeles, the family was involved in a serious car accident which killed Schmued's wife and left the designer seriously injured - it took him until February 1936 to recover.
The successful design of the new fighter was the work of a dedicated team (L-R): aerodynamics specialist Larry "Louis" L. Waite, NAA chief Engineer Raymond H. Rice and chief-designer: Edgar Schmued.
Once British interest in the new fighter design had become more solidified, the problem of creating a new airframe around the Allison V-1710 was the type of challenge enjoyed by Schmued. The inline V-12 required a large radiator for cooling, and its placement could greatly affect performance, both to the positive or negative.
Having a liquid cooled engine meant installing a coolant radiator. On the Spitfire, coolant radiators were installed underneath the wings. This design had a few drawbacks: firstly, when on the ground, the intake of the radiator was partially blocked by the undercarriage which caused temperature problems while running the engine on the ground. Secondly, if a stray bullet went through the radiator, the engine would overheat which lead to a forced landing.
Atwood would claim he came up with the idea of placing the radiator on the new fighter design behind the pilot. However, Atwood's claim was rebuffed by several other surviving NAA employees from the time period, who stated that the location was the obvious choice.
The Meredith effect is a phenomenon whereby the aerodynamic drag produced by a cooling radiator may be offset by careful design of the cooling duct such that useful thrust is produced. The effect was discovered in the 1930s and became more important as the speeds of piston-engined aircraft increased over the next decade.
The Meredith effect occurs where air flowing through a duct is heated by a heat-exchanger or radiator containing a hot working fluid such as ethylene glycol. Typically the fluid is a coolant carrying waste heat from an internal combustion engine.
For the effect to occur, the duct must be travelling at a significant speed with respect to the air. Air flowing into the duct meets drag resistance from the radiator surface and is compressed due to the ram air effect.
As the air flows through the radiator it is heated, adding heat energy to the air and further increasing its volume. The hot, pressurised air then exits through the exhaust duct which is shaped to be convergent, i.e. to narrow towards the rear. This accelerates the air backwards and the reaction of this acceleration against the installation provides a small forward thrust.[2] The thrust obtainable depends upon the pressure difference between the inside and outside of the duct.[1] The air expands and cools as it passes along the duct, before emerging to join the external air flow.
F. W. Meredith was a British engineer working at the Royal Aircraft Establishment (RAE), Farnborough
It was estimated that around 90 per cent of the cooling system drag would be eliminated by the efficient thrust of the exiting air. NA-73X was designed to have the coolant radiator installed underneath the fuselage, behind and below the cockpit. Putting the scoop (which provided cooling air for glycol and oil cooling) under the fuselage was mainly done to preserve the streamlined design of the fighter.
The drawback of such an arrangement was the extra weight and combat vulnerability of the long pipes that led to and from the engine. Having its own intake and exhaust system however proved to be a welcome bonus to the design. The hot air from the coolant radiator actually created additional thrust as the hot air exited at a greater velocity than it entered. As a result, a controllable flap was made at the rear of the housing, so this thrust could be regulated.
Another design feat that would ensure the NA-73X was an extremely fast fighter was the use of a brand new wing design: the laminar flow wing. Edgar Schmued recalled that, "We had planned to use an NACA-23 series airfoil and then heard NACA had developed a laminar-flow airfoil. That airfoil was specifically adapted by Ed Horkey, our first and only aerodynamicist and his assistants, who developed the ordinates of the laminar-flow airfoil.”
A laminar flow wing reduces drag considerably because the wing is thinner than the previously used conventional wings.
The leading edge of the wing is more pointy and the upper and lower half of the wing are almost identical to each other. The thickest part of a laminar wing occurs at 50% chord while in the conventional design maximum thickness is at about a fifth of the way across the wing from the leading edge.
As a result, drag is significantly reduced because the wing takes considerably less effort to cut through the air. This was a very bold step especially considering the timeline promised.
On the Mustang, the smooth flow can theoretically continue more than halfway back along the airfoil before transitioning to turbulent flow, creating far less drag.
Kindelberger was concerned that this new wing might not work, but Edgar assured him that he would design and build another wing in just one month. Regarding the wing, Ed Horkey later wrote, “Our concern was that we didn’t get all of the great laminar flow projected, since 20 percent would be too thick an airfoil, even in those days. It was decided to lay out new airfoils, which were around 16 percent thick at the root and 11 percent thick at the tip...
In other words, what we did is pick the pressure distribution we wanted. Then we drew an airfoil shape, and... we could check our pressure distributions. If it didn’t match, we could make a change to the airfoil contour, then go back and recalculate the pressure distribution.” This spirit of gaining knowledge and working together were key elements in creating the NA-73X.
Schmued wrote, “We discovered that when the wing was very thin, the aileron control system had to be extremely well designed to fit into the small space that was available. We used some rather unorthodox systems for the aileron control by using a wobble plate. That is a term for a special form of mechanism which we used that was very successful.
Further major design features were:
Special attention was paid to features which would make the aircraft easy and inexpensive to manufacture and at the same time to get the highest performance possible. 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.
The design also allowed a bomb or other store to be carried on a single pylon under each wing.
The small NAA engineering department issued drawings to the fabrication shops in a never-ending stream that included 16-hour working days, seven days a week. Dutch and his team were aiming for a delivery date of a complete airframe in January 1941.
Incredibly, on September 9th, 1940, just 102 days after their promise made to the British, the North American Aircraft company delivered. NA-73X was rolled out of the NAA factory at Mines Field in LA (remember, this was a tall order at the time for a company that had never build a fighter aircraft before, although incomplete in some details and sitting on tires and wheels from the Harvard production line. It had no armament installed and also had no engine…
Allison had not delivered the engine on time and it would be another 20 days before the V-12 arrived to be mated to the airframe. When they finally got the Allison, it had been modified from the drawings and NAA had to build new motor mounts. The sleek firewall forward design was courtesy of race pilot Art Chester (“Since Art was about the right size, I designed the cockpit around him,” said Schmued).
NAA would later record that the company had expended 78,000 man-hours engineering on the NA-73X.
Allison engineers had rated the F3R (civilian designation for the V-1710-39) at 1,100 hp, but had fixed the critical altitude at 11,000 feet, and here lays the inherent weakness of the engine. This critical altitude figure meant that the performance of the fighter would start to fall off at any altitude over 11,000 feet, thus giving a critical advantage to enemy fighters with powerplants that had a higher altitude rating.
Front and rear view of the Allison V-1710-39 engine
In a contract approved on September 20th , 1940, it was agreed that the fourth and tenth production NA-73s would be the planes diverted to the Army.
They were given the designation XP-51.
NAA hired freelance test pilot Vance Breese, a colorful and often outspoken personality, to do the first test flight. At the time, several freelance pilots vied for such test work (and there was a lot of it), and the pay was often very lucrative and much more than a pilot on the company payroll would make. NAA had previously used Breese to test fly Schmued’s NA-35 trainer.
It was the morning of October 26th, 1940. NA-73X with registration NX 19998 was parked on the ramp as Breese, who wore his usual double-breasted suit, climbed into the cockpit to start the flight that would lift NAA to new horizons. After mentally going over the checklist he hit the starter. The Curtiss-built propeller jerked a few times and the Allison burst into full staccato life, with just a hint of smoke dissipating from the exhaust stacks. The powerplant had been warmed up by the mechanics earlier that morning.
Breese began to taxi the prototype, the long nose obscured forward vision on the ground, which made S-turning mandatory. Pointing the nose into the wind and standing on the brakes, Breese gave the Allison a thorough run-up. Once satisfied, the pilot took the active runway and moved the throttle smartly forward. After rolling 100 feet, he brought the engine up to full power and pointed the nose down the centerline of the runway, shoving in right rudder to counteract the rapidly increasing torque.
The lightly loaded NA-73X (weights were 6278 lbs empty and 7965 lbs normal loaded) was quickly airborne, but the first flight was a rather sedate affair, Breese keeping within gliding distance of Mines Field. After flying for about five minutes, he came back to land. He went over initial handling data with Schmued and others, and then Breese went off for his second flight, which was about 10 minutes in length. He found that the gleaming craft exceeded initial performance estimates. Throttling back, he brought the NA-73X in for a smooth landing.
Six more functional test flights took place (31 October and 4,8,11,12 and 13 November). These were made by Breese to fulfill his contract obligations and he was then on to other testing projects after putting some 3 hours 30 minutes on the airframe.
However, Breese had numerous complaints about the aircraft and it required time to correct them. Breese, an excellent self-promoter, was pretty much a very good seat-of-the-pants pilot. What the NA-73X needed, however, was an engineering test pilot.
NAA was fortunate in having access to an excellent wind tunnel facility at the California Institute of Technology where extensive tests were undertaken to prove various NAA concepts.
Vance Breese in NA-73X after first 5 min test flight Oct 26th 1940
Back at Mines Field, Paul Balfour (commercial pilot certificate number 12596) was hired by the company in 1936 and eventually assigned the post of chief test pilot for the NA-73X. Before his death in the early 1970s, Breese stated that he had bet money with NAA officials that Balfour would crash the aircraft on his first flight. Breese won.
On the morning of 20 November 1941, the ground crew prepared the NA-73X for Balfour’s flight. Schmued would later recall, Before this flight, I asked Balfour to get into the airplane and go through the routine of a takeoff and flight. He responded that one airplane is like the other and he would not need the routine check out.”
Balfour’s first flight was also scheduled to be a high-speed test run for the NA-73X. The pilot took off at approximately 0710. Mechanic Olaf T. Anderson later stated that the engine had run fine on the ground and, “at about 0540, I warmed the engine up as is the usual procedure before the flight. Oil and Prestone temperatures were normal (oil 65 degrees C; Prestone 95 degrees C). Oil pressure was 80 pounds and fuel, 13 pounds. The engine was mn for five minutes and then shut down. When I started the engine for Mr.Balfour before takeoff, it was a little hard to start (the Allison representative said their engines have a tendency to do such).
As Balfour pulled the gleaming fighter up after about 12 minutes flying time, the Allison suddenly stopped running. Checking the instruments, nothing seemed amiss. However, executing a wide sweeping turn caused the NA-73X to lose altitude and Balfour quickly realized he was not going to make the runway. During the last portion of the turn, he dumped landing gear and flaps as he directed the stricken prototype toward a plowed field just west of Lincoln Boulevard. The now-glider whistled down in a correct landing attitude, but as soon as the tires touched the soft plowed soil (at approximately 0723), the NA-73X violently flipped over. The built-up structure behind the pilot saved Balfour from being crushed, and the pilot scrambled for safety' from the movable side window.
The reason of the crash is a much debated one.
The official report stated that Balfour did not change the fuel selector switch and this the engine starved by the lack of fuel. But why did a seasoned test pilot, even though sources claim he took a casual approach to the test flight, make such a rookie mistake?
When NA-73X was rebuilt, the air-inlet-scoop was moved as far forward as possible. It was noted that, at high angles of attack the airflow was cut-off, thus starving the engine of air.
Some state that there is a possibility that NAA did not want to risk the project because of the design and “blamed” Balfour for the crash?
There is a report of an eye witness to the crash (an NAA employee) who stated
that the crash happened shortly after take-off and that, upon examination of the fuel tanks, fuel was in the auxiliary and right tank, but there was no fuel left in the left tank. If that is true and the crash happened shortly after take-off, the aircraft was given to Balfour with little fuel in the left tank. That fuel would have been used up during taxi, run-up and take-off (Either Balfour wasn't told correctly about the fuel status, he selected the wrong tank or ground personnel did not fill as instructed)
Balfour was killed on November 10th, 1951 while test flying a modified CB-25J for NAA.
At the time of the accident, the prototype had accumulated just 3 hours 20 minutes of flying time (Balfour had logged 2,298.40 hours of solo tune at this point). The Civil Aeronautics Authority Air Safety Board listed damage to the aircraft as “engine housing broken, both wingtips damaged, tail surfaces damaged, top of fuselage damaged, and other miscellaneous damage.”
Investigation of the crash revealed that the Allison had run dry when the selected fuel tank had been allowed to be completely depleted. NAA and the British both agreed that, in spite of the crash, they had a winning aircraft and the accident was no way the fault of the design.
Some aviation historians have recorded that the prototype was scrapped after the accident, but this was not the case. Actually, the prototype was carefully raised out of the bean field by crane and transported back to NAA where it was stripped apart and rebuilt in a very short time. However, to increase the pace of flight testing, the first RAF machine was completed and joined in the flight program. NA-73X would fly again in January, 1940. Since the NA-73X encountered very few problems during following tests, production for the RAF begun almost immediately.
The first Mustang that left the production line, serial AG345 for the RAF, was added to the test program and made its first test flight in April of 1941, with Louis Waite at the controls.
Meanwhile, following the arrival of this official British Purchasing Commission communique at NAA on 12 December 1940, the NA-73 officially became known as the Mustang:
Robert C. “Bob” Chilton was hired as chief test pilot to replace the unfortunate Balfour, and a study of Bob’s logbooks indicates he flew the rebuilt NA-73X on 3 April 1941 for a 1-hour familiarization flight from Mines Field. Chilton also recalled that the NA-73X had made between five and six flights with another pilot immediately after its rebuild. Chilton went on to make at least a dozen more flights with the aircraft.
Bob later remarked, “The NA-73X was a clean-flying aircraft with no bad vices. It was quite pleasant in the air and handled very similar to the later production articles.”
Chilton had accrued considerable fighter experience in the Air Corps before going to NAA, flying the Boeing P-12 and P-26, the Curtiss P-36, and other fighter types. His expertise in the fighter field enabled the engineers to incorporate changes that would be beneficial to the combat pilot.
“I recall that the NA-73X was just pushed to the side after it had been retired from its last flight,” stated Chilton. “It probably ended up on the company’s junk pile, but I do not recall seeing it there. The NA-73X was a very attractive aircraft and its aluminum skin glowed with constant waxing by George Mountain Bear, an American Indian whose duty was to keep the airframe as clean as possible to pick up those few vital miles per hour.”
With the first RAF aircraft coming off the production line, NAA and the British decided to use these airframes for continued testing. “The ‘old’ NA-73X was no longer representative of the design,” said Chilton. “We had orders on our hands for hundreds of new fighters and the NA-73X had served its purpose. It had established the trend for what I believe was the finest propeller-driven fighter ever built by any country.”
Research indicates that the NA-73X, stripped of useable components, may have been donated to a local trade school.
NA-73X | ||
Production Number | 1 | |
Dimensions | ||
Length | 32.25 ft - 9.83 m | |
Height | 12.20 ft - 3.72 m | |
Width | 37.04 ft - 11.28 m | |
Weight | ||
Empty | 6278 lbs - 2848 kg | |
Normal takeoff | 7965 lbs - 3613 kg | |
Maximum gross | n/a | |
Powerplant | ||
Manufacturer | Allison V-1710-F3R | |
CID (Cubic Inch Displacement) | 1710 | |
Normal takeoff HP | 1150 | |
War Emergency HP (WEP) | n/a | |
Performance | ||
Maximum speed | 382 mph - 614.77 km/h | |
Normal cruise speed | n/a | |
Climb to 20,000ft | n/a | |
Service ceiling | n/a | |
Fuel capacity | 180 US gallon - 681.37 liters | |
Fuel capacity with drop tanks | n/a | |
Combat range (internal fuel) | n/a | |
Combat range (with drop tanks) | n/a | |
Armament | ||
Machine guns | n/a | |
Rounds available | n/a | |
Bombs (lb) | n/a | |
Other | n/a |
NA-73X | ||
US Serial Number | NX19998 | |
