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An AT-6C Texan in flight in 1944.

The North American AT-6 Texan (USAAC/USAAF pre-1962 designation) was an American single engine trainer. First developed in 1937, it would go on to become the most produced training aircraft in history. It was identified as SNJ by the US Navy and Harvard by Commonwealth nations. In 1962, the Air Force designation was changed to T-6.[1]

History

Origins

The story goes back even before North American Aviation put its name on its aircraft but served as the parent to General Aviation at Dundalk. Maryland, where types GA-l to GA-15 wars created. In late 1934 the US Army issued a requirement for a new basic trainer; the next type encountered by pupil pilots after they had encountered the lower powered primary trainer. The General Aviation design team, under vice-president J. Lee Atwood, quickly produced a cantilever low-wing monoplane with all-metal structure (including a wing skinned with flush riveted stressed skin, though the rest of the aircraft was mainly fabric covered), fixed cantilever main legs, a 400-hp (298-kW) Wright R-975 Whirlwind engine and modern open cockpits. Instead of becoming the GA-16 it was styled as the NA-16, reflecting the company's change of name.

The NA-16 was flown at Dundalk in April 1935, with civil registration X-2080. The US Army pilots at Wright Field thought it the best design submitted and the nearest approach to a tactical aircraft then achieved in a trainer, but requested several changes. This classic prototype thus became the NA-18 with enclosed cockpits (covered by tandem sliding canopies), a faired landing gear and the 600-hp (448-kW) Pratt 81 Whitney R-1340 Wasp engine. This aircraft was later sold to Argentina, but in late 1935 the US Army adopted the NAA trainer and placed an order for 42, with the designation BT-9. On the strength of this, the company moved to sunny California, paying a $600 annual rental for a site at Inglewood (on what is today Los Angeles International Airport) and building a completely new factory with 150 employees (nine years later the payroll had reached 91,000).[2]

BT-9 deliveries

The BT-9s were delivered in training colours of blue fuselage and chrome-yellow wings and tail, with blue/red/white-striped rudder. Most BT-9s had fixed slats on the outer wings and were used as unarmed pilot trainers, fitted with flaps pumped down by a manual hydraulic system. These were probably the first flapped basic trainers, and flaps were provided on all subsequent models. The R-975 Whirlwind was fitted to most of the fixed-gear versions, except for the US Navy NA-1 and a batch for China, was of smaller diameter than the Pratt & Whitney Wasp used on the much more numerous retractable-gear models, and resulted in a slightly better forward view. Main gears were far forward making nosing over difficult, and on most of fhesc variants the exhaust was collected at the trout of the engine and discharged through the right side of the cowl. Many sub-types including the first two big orders for France, had the original curved wingtips and rudder; but the NA-57 for France had the new wing and tail, first flown on the NA-54, which was structurally better and easier to produce. Large numbers of the Fnriner type had Et.2 (Entraincment biplace) or P2 (Perfectionnement hiplace) in black on their striped rudders, and they were put to various uses by the Vichy Forces and Luftwaffe. Aircraft of the second batch were diverted to become Yales in Canada, mostly with the exhaust stack extended back over the right wing roof. Export sales came thick and fast, no two batches being exactly alike but all having the R-975 or R-1340 engines, except for wartime licence-built Swedish Sk l4 versions which had to use an Italian Piaggio engine, and the Imperial Japanese Navy models which had a Kofobuki engine driving a wooden propeller. The Japanese variants, designated K10W and K5Yl, had many local modifications, notably to the canopy, rear fuselage and vertical tail.[2]

Attack trainer

The real mainstream began with the US Army Air Corps competition in 1937 for a BC (basic combat) trainer, able to undertake pilot instruction whilst at the same time simulating the handling and cockpit conditions of a combat type, with the option of being able to mount fixed and movable guns and carry bombs if necessary so that one type could almost turn out a fully-fledged combat pilot or gunner, The same NA-16 was taken as the starting point, but it was fitted with a big Wasp engine, driving a Hamilton variable-pitch propeller and a hydraulic pump feeding 2| 1,000-lb/sq in (70.3-kg/cm’) system which worked the flaps and also the new retractable main landing gears, which folded inwards ahead of the span with the wheels in compartments causing unwed projections ahead of the wing roots. This NA-Z6 prototype of 1937 won the competition, and the first production model was the U5 Army's BC-l, some of which were the first specially designed instrument trainers, designated BC-11. Further changes brought in stressed-skin fuselages, integral wing tanks (soon followed by removable aluminum wing tanks), and the new angular wingtips and rudder. In 1940 the BC category was superseded by AT (advanced trainer, a category dormant for 13 years), the NAA aircraft becoming the AT-6.

NAA was unable to meet demand, even with an Inglewood plant whose floor areas had expanded from 159,000 sq ft (14,770 m) to almost 2,000,00 sq ft (185,800 ml)! A new factory was therefore built in Dallas, Texas (others were built elsewhere for other NAA types), and from 1942 the AT-6 was accordingly named Texan.[2]

Since 1938 the name Harvard had taken firm hold in the British Commonwealth for the NA-16/BC-1. British industry had been totally unable to meet the RAF's need for aircraft in 1938, because orders had not been placed in time, and a great outcry went up when foreign aircraft were ordered. The NAA trainer was the first, soon followed by the Lockheed Hudson and Consolidated Catalina. The Harvard Mk I was a BC-1 with British instruments and radio, and bucket seats tailored to the seat pack parachutes. The first of 400 entered service in December 1938 at No. 3 FTS, Grantham, camouflaged on top and down to the mid-line of the fuselage, and yellow below. Subsequently the RAF received about half of the 4,768 Harvards supplied from NAA or from Noorduyn on US Lend-Lease contract, a further 1,380 Harvards being supplied direct From Noorduyn and (post-war) from Canadian Car and Foundry, as well as 285 post-war T-6Js for European air forces fimdcd under the MDAP.[3]

Massive production

Almost all the gigantic wartime contracts were for the AT-6A, AT—6C and AT-6D, and the corresponding US Navy SNJ-3, SNJ-4 and SNJ-5, which were externally similar with the straight-edged airframe, stressed-skin fuselage and provision for a hand-aimed gun in the rear cockpit, the usual canopy having a rear fairing which rocked up and forward as the main section was slid open. On most earlier versions the rear fairing was fixed. Structurally the big exception was launched by the NA-88 of 11 April 1941, when production was already on a massive scale even though the United States was still neutral. There was a fear that aluminum would run out, and in this model NAA redesigned the aircraft to have a basic wing structure, flaps, fin and all control surfaces of spotwelded low-alloy steel. and the forward fuselage side panels‘ whole rear fuselage, cockpit fluur and tailplane of plywood. This saved 1,246 lb (565 kg) aluminium or light alloy per aircraft, with a surprisingly modest weight penalty and nor much difference in manufacturing cost.

Designations were AT-6C, SNJ-4 and Harvard Mk IIA, but after a while it was accepted that there would he no shortage of aluminum and the original structure was restored (still as the NA-88) in the AT-6D, SNJ-5 and Harvard Mk Ill, though these introduced 24-volt electrics.

One of the electric items much appreciated by ground crew was the starter. Of the inertia type, the flywheel was spun by the pilot depressing his heel on a treadle in the floor between the rudder pedals. A healthy rising whine ensued, and when the pitch was high enough the pilot would instead depress his toe, rocking the treadle and engaging the flywheel. Other familiar terms included Ki-Gass manual engine priming, a wobble pump for building up fluid pressure before starting, a manual selector for building up hydraulic pressure, and massive diecast trim wheels and levers for the landing gear and flaps. Every example was pleasant to fly and of course fully aerobatic but if harshly handled would flick dangerously through 270" and a landing with excessive vigorous stick pressure would likewise result in violent wing-drop which, at the very least, would break the spars and often caused a write-off. Thus, the NAA trainers fulfilled the requirement in not being so easy that pilots did not have to fly correctly.[3]

Service

United States

Great Britain

With war imminent, it was apparent that Britain would be unable to meet its own aircraft requirements, and home production would be largely concentrated on operational types. Accordingly, orders were placed with American manufacturers to fill the gap. A pressing need was for a modern advanced trainer. and hopes had been pinned on the de Havilland Don, but this had turned out to be a failure. lt's place would be taken by the Miles Kestrel, developed as the Master, but this was unlikely to be available for some time, and as a stop-gap an order was placed for an adaptation of the North American BC-1, a robust machine already supplied to the US Army Air Corps. Ironically, the Harvard as it became with the RAF, long outlasted the Master.[4]

Powered by a Pratt and Whitney Wasp R-l34O-S3l-ll engine, the initial order was for 200 machines, and the deliveries commenced in December 1938. The first machine (N7000) was sent to Martlesham Heath for testing, but was lost when it dived into the ground at Eyke. Suffolk on 16 February 1939. Testing continued with N7001 and N70l3, however, and a report was made at the end of the year. The report made two main criticisms. Visibility forward from the front seat was below .average, a severe handicap for a training aircraft, especially for taxiing, take-off and landing. It was even worse from the rear seat due to the strong-point between the seats. The view in other directions was good, however. A lever fitted on later aircraft enabled the front seat to be raised, which helped the pupil, but it increased the problems of the instructor in the back seat, who now had to lean sideways to get much of a view.

The other problem was noise. An electric intercom was fitted, but this only proved satisfactory at low speed as the microphones picked up considerable external noise, and it was impossible to hear properly while taking off or climbing, or when flying at high cruising speeds or above. The raucous sound of the Harvard was very noticeable externally. It was easily distinguishable from other aircraft, this feature being diagnosed as due to the high tip speed of the direct-drive airscrew, the pitch of the resulting note, rather than its volume, being instinctively seized by the ear. This noise reached its peak in the plane of the aircraft, and the problem was never eliminated, as can be readily heard on surviving Harvards.

Following the initial delivery, a further 200 Mark ls were ordered, many of which served in Southern Rhodesia. These were followed by the Mark ll, based on the AT-6 for the USAAF, with squared off wing tips and a triangular fin and rudder, these features being retained on subsequent versions. The rear fuselage was of a light alloy monocoque, in place of the earlier fabric covered steel tubing. Some Mark lls also went to Rhodesia, but the majority were retained in Canada for schools set up under the British Commonwealth Air Training Plan.

One of the few Mark IIs to reach the United Kingdom was BD134, which in January 1941 took part in comparative tests with the Mark I at the Aeroplane and Armament Experimental Establishment at Boscombe Down. Its handling characteristics were found to be similar to those of the Mkl. It behaved satisfactorily in a dive, and recovery from a spin was certain. Behavior in the stall was essentially the same, though there had been no improvement in the large height loss which occurred in this manoeuvre. During climb, both the cylinder and oil inlet temperatures were within permissible limits for tropical summer conditions, but the oil tended to run hot in level flight. this did not matter in normal English summer conditions, but was likely to cause difficulties in Rhodesia.

The next version to appear was the AT-6C, which became the Harvard IIA in RAF parlance, this having a plywood rear fuselage. The Wasp R-1340-S3Hl of the earlier marks was replaced by the Wasp R-1340-ANl, having only a short exhaust stub on the starboard side, as opposed to the long one of the Mk.ll. A batch of 747 of these went mainly to the Middle East, Rhodesia and New Zealand. They were followed by the Mark IIB, the equivalent of the American AT-6A, built in large numbers under licence in Canada by the Noorduyn company, and used not only by the RAF but by all Commonwealth countries participating in the training plan. The final RAF version was the Mark III, corresponding to the AT-6D, all these American versions being known as Texans in the USAAF. Total production for the RAF and BCATP was 4905 machines.

The Harvard was a very strong machine, but could be dangerous if not properly handled. Pupils graduating from elementary machines could have great difficulty controlling it initially, lt could flick suddenly, without warning, and would flick stall if looped too fast. Landings could be disastrous if the tail was held too high, and pupils were instructed not to throttle back until both main wheels were firmly on the ground. Even when the tail had come down it was not safe to relax, as the aircraft was‘ prone to ground looping.[5]

The flap and undercarriage levers were immediately next to each other, thus presenting the distinct danger of selecting flap instead of undercarriage and vice versa. To avoid this, whenever one moved the undercarriage lever, it was always with a clenched fist, but when handling the flap selector lever, one grasped it. So you had the clenched fist and grasping syndrome, which definitely helped to avoid wrong selection.

Don March, a wartime Air Training Corps cadet who learnt to fly on Harvards post war.[5]

References

  1. http://www.daveswarbirds.com/usplanes/american.htm
  2. 2.0 2.1 2.2 World Aircraft Information Files Aviation Partwork. Midsummer Books Ltd. File 232 Sheet 1 (World Military Aircraft:North American T-6 family - Flying classrooms.
  3. 3.0 3.1 WAIF File 232 Sheet 2 (World Military Aircraft:North American T-6 family - Sixty plus years of service.
  4. Sturtivant, Ray. The History of Britain's Military Training Aircraft. Haynes Publishing group. 1987. ISBN 0 85429 579 8. Page 119
  5. 5.0 5.1 Sturtivant, Ray. Page 120

Template:American Training Aircraft

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