Cessna 318 / A-37 / T-37
Late in 1952 the USAF formulated a requirement for a jet trainer which would econ-omically permit student indoctrination at an early stage in the training curriculum. Specified design requirements included an empty weight of 4,000 lb (1814 kg) in order to limit both cost and complexity of the aircraft; the ability to undertake twenty take-offs and landings within a two-hour period; flight handling characteristics matching those of the most modern operational fighters; a 35,000 ft (10668 m) cruise ceiling with sufficient high altitude manoeuvrability to wholly orientate students, and a maximum traffic pattern speed of 113 knots (209 km/h) to assure good low-speed handling characteristics. Side-by-side seating for the student and instructor was favoured. The Marbore II became the Continental J69 and the Cessna company designed their Model 318 around two J69s. This aircraft was a basic jet trainer. In the ensuing design contest, Cessna's Model 318 was designated the victor early in 1953, and as XT-37s, three prototypes (54-716 to 54-718) were ordered.
The first of these flew on October 12, 1954, (piloted by Bob Hagen), powered by two Continental YJ69‑T‑9s (licence built Turbomeca Mabore IIs) with 920 lbf (4.1 kN) thrust each, by which time its manufacturers had been awarded a $5 million contract for eleven pre-production T-37A trainers (54-2729 to 54-2739), the first of which flew on September 27, 1955. One of the XT-37 prototypes was lost in a flat spin; the pilot baled successfully. Some strengthening of the wing centre section was found to be necessary, the cockpit layout had to be revised, and field trials with the pre-production machines were accompanied by minor teething troubles, among these being the fuel system of the Continental J69 turbojets-licence-built Turbomeca Marbore IIs, but these were soon overcome, and by the early spring of 1956, contracts had been placed for twenty (55-4302 to 55-4321) and 127 (56-3464 to 56-3590) production T-37A trainers, a contract for a further 123 machines (57-2230 to 57-2352) following shortly afterwards, and the 200th T-37A rolling off the assembly line on July 23, 1958. 534 were built under successive contracts, but were slow in entering service as a result of the need for a number of changes and modifications before they were considered acceptable for training purposes.
The T-37A was delivered to the U.S. Air Force beginning in June 1956. In the spring of 1957, the first training courses on the T-37A had begun at Waco, Texas, the first class of twenty students receiving 150 hours on the new jet trainer after forty hours on the piston-engined Beech T-34A primary trainer. The second group of students at Waco had only twenty hours on the T-34A as the next stage in evolving an all-jet curriculum.
In April 1961 all-through jet training was initiated, the pupil flying from the very beginning of his training on T-37 aircraft which had a speed range of 138-684km/h. No catastrophic accident rate resulted, as had been feared by many, but one point which had not been fully considered was the much higher training cost using jet aircraft. There is inevitably a varying pupil rejection rate at the end of primary training, and it was decided in 1964 to revert to light piston-engine trainers, which are much cheaper to operate, for this primary phase, so that T-37 pupils were those left after the first weeding-out.
The T-37A was powered by the 920 lb.s.t. (417 kgp) J69-T-9 turbojet, but during 1959, after the delivery of 416 aircraft of this type, production switched to the T-37B with 1,025 lb.s.t. (465 kgp) J69-T-25 turbojets, and new Onini and UHF equipment, the first of the improved trainers being accepted by the USAF on November 6, 1959. Subsequently, all T-37As passed through a modification programme to bring them up to 'B' standards. The first T-37A was completed in September 1955 and flew later that year.
For the training role, Cessna chose straight wings, twin wing root-mounted engines and side-by-side seating. The original 417-kg (920-lb) thrust Continental J69-9 engines, built under licence from Turbomeca, were not calculated to make the American type a startling performer.
The T-37B is basically a low-wing cantilever monoplane of all-metal construction, and has its twin J69-T-25 turbojets mounted in the thickened wing roots, their inboard location creating a negligible change in directional control with one engine inoperative, and facilitating the demonstration of single-engine procedures. A single-stage, centrifugal compressor engine, the J69-T-25 has a fully automatic altitude compensating fuel control, and the two power plants draw their fuel from the main fuselage tank immediately aft of the cockpit, this being fed from six inter-connecting rubber-cell fuel tanks in each wing, the total usable capacity of these being 257 Imp. gal. (1 168 lt). Engine-driven pumps and submerged booster pumps drive the automatic fuel transfer system, but in the event of a fuel proportioner or electrical system malfunction, fuel is auto-matically supplied to the engines by the gravity system.
The low 'sit' of the T-37B on the ground eliminates the need for cockpit entrance ladders, flush steps in the fuselage 24 in (61 cm) above the ground providing easy entrance from either side of the aircraft. The cockpit itself is ideally situated, well forward of the wing, and, with the backward-folding, jettisonable clam-shell type canopy offers excellent visibility. The panel itself is a relatively simple and straightforward approach to current requirements. The primary instruments are duplicated for instructor and student, all instruments may be monitored, and all operating controls and switches are easily accessible from either seat. Positioned to port on the student's side are the navigational and flight instruments, including directional and attitude indicators, altimeter, turn-and-bank, rate-of-climb and airspeed indicators, and course indicator. In front of the instruc-tor on the starboard side but within reach of the student are the radio controls, circuit breaker, etc., and the engine instruments mounted over the central quadrant include tachometers, fuel flow and exhaust temperature indicators, fuel and oil pressure gauges, loadmeters and accelerometer. The stick grips and throttle quadrants are of fighter type.
A 1,500 psi (105.5 kg/sq.cm) hydraulic system is installed. Two engine-driven, constant-displacement hydraulic pumps are used to drive the landing gear and doors, speed brake and thrust attenuators, nosewheel steering system, flaps and stall spoilers. The hydraulically-operated brakes are independent of this system. The electrical system comprises two 200-amp. starter-generators, one 24-volt, 36-amp hour battery and associated control equipment. No ancillary starting equipment is necessary, the battery being sufficient to provide engine starts for all normal training operations.
Structurally, the T-37B comprises a semi-monocoque fuselage, a two-spar aluminium alloy wing of NACA 2418 section at the root and NACA 2412 section at the tip, and a normal cantilever monoplane type tail assembly of which the fin is integral with the fuselage, and the tailplane is mounted one-third of the way up the fin. Hydraulically-operated high-lift slotted flaps with a total area of 15.1 sq ft (1.4 sq.m) are mounted inboard of the ailerons which have a total area of 11.3 sq. ft. (1.05 sq.m), and all movable tail surfaces have electrically-operated trim tabs. Because of its low drag characteristics, an hydraulically-actuated speed brake is located on the underside of the fuselage nose section, aft of the nosewheel well. This brake works in conjunction with thrust attenuators which deflect the exhaust blast and permit higher rpm during landing approaches. When the attenuators are extended, the resultant effective thrust is reduced by more than forty per cent. Both attenuators and speed brake are controlled by the speed brake switch when the throttles are below seventy per cent rpm. The thrust attenuators automatically retract when the throttles are advanced above seventy per cent rpm.
The undercarriage has two extension systems, the primary system being hydraulically actuated and the secondary system being pneumatically powered. The wheel brakes are, as previ-ously mentioned, operated by a separate hydraulic system controlled by dual rudder and brake pedals, and the wide track of the main members (14 ft 0.5 in.- 4.28 m) results in an unusually high degree of ground stability.
The T-37B demonstrates good stability in all configurations and conditions of flight. Extremely effective control surfaces result in instant response, and light forces, well balanced between the three controls, make all manoeuvres easily co-ordinated. Spins are mild and recovery by use of standard procedure is positive. The excellent stall characteristics are well defined with lateral control effective at all times, and good stall warning is provided for all flight configurations. Landings are accomplished equally well from either scat, and no abrupt pitch or directional trim change results when power is added for another circuit of the field.
These characteristics are ideal for a training aircraft but they also result in an excellent weapons platform, and supplanting the T-37B trainer on the Wichita assembly line as the T-37C which has underwing attachment points for offensive stores or drop tanks and is intended primarily for supply to the smaller nations militarily aligned with the USA. With a gun sight mounted in the cockpit, underwing racks can carry bombs or rocket, gun or photographic pods for internal security duties, and the T-37C served with such coun-tries as Portugal (30) and Vietnam. Mission range may be increased to more than 1,100 nautical miles (2 040 km) by the addition of wingtip tanks which, each containing 54 Imp gal. (246 lt), increase the total fuel capacity to 366 Imp gal. (1664 lt). Fuel is transferred from the tip tanks to the wing tanks by inline booster pumps, utilizing the existing internal fuel system, and provision is made for jettisoning.
When production ended in 1977 a total of 1,268 T-37s had been built for the USAF and for export.
During 1962 two Cessna T-37B trainers were evaluated by the USAF's Special Air Warfare Center to consider their suitability for deployment in the counter-insurgency (COIN) role. These were first tested with their original powerplant of two 465kg thrust Continental J69-T-25 turbojets, at a take-off weight of 3946kg, almost 33% above the normal maximum take-off weight. Subsequently the airframes were modified to accept two 1089kg thrust General Electric J85-GE-5 turbojets. This increase in power made it possible for the aircraft, then designated YAT-37D, to be flown at steadily increasing take-off weights until a safe upper limit of 6350kg was reached.
After successful trials Cessna were requested to convert 39 T-37B trainers from the production line to a light-strike configuration, a contract being awarded in 1966. Designated A-37A, they were delivered, only being withdrawn from service ten years later in 1974. The new model was based on the earlier experiments with the two YAT-37Ds, and equipped with eight underwing hard-points, provided with wingtip tanks to increase fuel capacity and powered by derated General Electric J85-GE-5 turbojets.
Delivery to the USAF began on 2 May 1967, and during the latter half of that year a squadron numbering 25 of these aircraft underwent a four-month operational evaluation in South Vietnam. Following this investigation they were transferred for operational duty with the 604th Air Commando Squadron at Bien Hoa, and in 1970 they were assigned to the South Vietnamese air force.
This led to the conversion of a number of T-37Bs to A-37A Dragonfly status for operational evaluation in Vietnam and followed with development of the much more dedicated A-37B. Production of 577 started in 1968, featuring the General Electric J85 turbojet, airframe stressed to 6g, much-increased fuel capacity and eight underwing hardpoints.
Various improvements to the avionics, upgrading of the turbines, the addition of wingtip fuel tanks, and provision for weapons saw the trainer develop into an attack version, and new aircraft were still being delivered for export in late 1977. Featuring side by side seating, the lightjet powered by two General Electric turbojets each rated in excess of 2800 lb static thrust had a range of some 1050 miles on a tankage of 1100 litres. Armed with a mini-gun in the nose and with four pylons on each wing for ordinance and stores, the A-37 could feature a typical delivery of four 8701b bombs, two 600 lb bombs and two 500 lb bombs. A load could consist of an assortment of fire bombs, demolition bombs, canister clusters, flares or rockets. The aircraft could, it is claimed, carry their own weight in stores.
During this period, Cessna had built the Model 318E prototype of a purpose-designated light-strike aircraft based on the T-37 and this flew for the first time in September 1967.
The initial production batch of this A-37B was started quickly enough for the first deliveries to begin in May 1968.
The A-37B differed in construction from the prototype YAT-37D, its airframe stressed for 6g loading, maximum internal fuel capacity increased to 1920 litres with the ability to carry four auxiliary tanks having a combined capacity of 1516 litres, and with provision for flight-refuelling.
The engines were changed to two General Electric J85-GE-17A turbojets of 2585 kg (5700 lb) total installed thrust. The tip tanks became stan-dard, a GAU-2B/A 7.62mm Minigun was installed, and eight underwing hardpoints. The two inner of these can each carry 395 kg (870 lb), the intermediate ones 272 kg (600 lb) and the outers up to 227 kg (500 lb) although the maximum weapon load is 2576 kg (5680 lb) with a maximum takeoff weight of 6350 kg (14000 lb).
For the assessment of results both gun and strike cameras were carried, and some armour protection for the crew of two was provided by the inclusion of layered nylon flak-curtains installed around the cockpit.
The avionics is limited to comprehensive but basic navigation/com-munications and a non-computing gunsight. A Forward Air Control variant existed as the OA-37B.
By the time production ended in 1977, 577 A-37Bs had been delivered. The Cessna Model 318E Dragonfly (A-37B) is equipped with two General Electric J85-17A turbojets, giving it almost double the takeoff power (each rated in excess of 2,800 lbs static thrust), and subsequently double the takeoff weight, over that of the T-37. Increasing the number of and strengthening the hard points, enables the A-37B to carry close to its own empty weight in armament (around 5000 lb).
The US Government supplied 254 Cessna A37B Dragonfly's to the Vietnam Air Force (VNAF) during the Vietnam War. After the fall of South Vietnam in 1975, ninety-five VNAF A37B aircraft were captured and incorporated into the Vietnamese People’s Air Force. Many were transferred to the US Air National Guard.
More than 600 were delivered at home and abroad, including sales to Brazil, Chile, Guatemala, Honduras, Peru, Thailand.
The last T-37B was officially retired from active USAF service on 31 July 2009.
Military Users: (All models) Brazil, Cambodia, Chile, Columbia, Ecuador, Guatemala, Greece, Honduras, South Korea, Pakistan, Peru, Portugal, Thailand, Turkey, South Vietnam, Vietnam, USAF (and Luftwaffe via US training programme).
Three prototypes of the Model 318, first flown October 12, 1954. Powered by two Continental YJ69-T-9s (licence built Turbomeca Mabore IIs).
Pre-production batch of eleven airframes. All subsequently redesignated as T-37A-CEs.
Cessna Model 318A, production standard. Two Continental T69-T-9s. Production came to 444 units, survivors up-graded to T-37W CE. Single example to JT-37A-CE for special test. T-37 universally known as the Tweety Bird or Tweet in USAF service.
Further improved production standard, improved radio/navigation installation and J69-T-25s. Model 318B, 552 built.
Version of T-37B-CE for Military Assistance Program countries. Provision for underwing pylons and tip tanks optional. 198 built.
Two T-37C-CEs converted to counter-insurgency aircraft with six underwing hardpoints and two General Electric J85-GE-5s. Both redesignated YA-37A-CE. Cessna Model 318D.
'Production' version of YA-37A-CE with eight underwing hardpoints and 7.62mm Minigun in nose. 39 T-37B-CE converted.
New-build version, as A-37A-CE but with J85-GE-17A, increased fuel, provision for in-flight refuelling and strengthened airframe. 577 built of which one was termed YA-37B-CE for development work.
At least 122 A-37Bs redesignated for use by Air National Guard units in the Forward Air Controller role.
Engines: Two Continental T69-T-9
Wing span: 33.78 ft ( 10.3 m).
Overall length: 29.25 ft ( 8.9 m).
Height: 9.17 ft ( 2.8 m).
Wing area: 183.9 sq.ft ( 17.1 sq.m).
Wing aspect ratio: 6.20.
Empty wt: 4056 lb ( 1841 kg).
Normal T/O wt: 6574 lb ( 2984 kg).
MTOW: 6574 lb ( 2984 kg).
Internal fuel cap: 257 Imp.Gal. (1168 lt).
External fuel cap: 108 Imp.Gal. (490 lt).
Wing loading: 35.7 lb/sq.ft ( 174 kg/sq.m).
Pwr loading: 3.7 lb/lbst ( 3.7 kg/kgst).
Max speed: 452 mph ( 727 kph).
Initial ROC: 3000 fpm ( 15 m/sec).
TO dist 50 ft: 2025 ft ( 617 m).
Range: 935 sm ( 1500 km).
Engine: 2 x Continental J69-T-25 turbojets, 1,025 lbs.t. (465 kgp).
Span, 33 ft 9.5 in (10.3 m)
Length, 29 ft 3 in (8.93 m)
Height: 9.19ft (2.80m)
Wing area, 183.9 sq.ft (17.09 sq.m).
Gross weight: 6,574 lb-2 982 kg
Empty wt: 4,056 lb (1840 kg).
Take-off dist to 50-ft. (15 m): 2,025 ft. (617 m).
ROC S/L Military RPM: 3370 fpm (17 m/sec).
Service Ceiling-Military RPM: 38,700 ft (11 796 m).
Single-engine Service Ceiling- ½ Fuel Military RPM: 25,000 ft (7 620 m).
Cruise speed-Normal rated power, ½ fuel at 35,000 ft (10 668 m): 320 kts (593 kph).
Max speed ½ fuel Military RPM at 20,000 ft (6 096 m): 369 kts (684 kph)
Range-at 35,000 ft (10 668 m) at 289 kts (535 kph): 692 nm (1282 km).
Max range-5% reserve at 35,000 ft (10 668 m) at 289 kts (535 kph): 809 nm (1 499 km).
Range-at normal RPM with 5% reserves at 35,000 ft (10 668 m) at 313 kts (580 kph): 755 nm (1390 km).
Landing Distance from 50ft (15 m): 2,600 ft (792 m).
Stalling speed-gross weight, SL: 74 kts (137 kph).
Engine: 2 x Continental J69-T-25 turbojets, 1,025 lbs.t. (465 kgp).
Span, 33 ft 9.5 in (10.3 m)
Length, 29 ft 3 in (8.93 m)
Height: 9.19ft (2.80m)
Wing area, 183.9 sq.ft (17.09 sq.m).
Armament: 2 x 250lb Iron Bombs
Rate-of-Climb: 3,370ft/min (1,027m/min)
Service Ceiling: 39,199ft (11,948m; 7.4miles)
Engine: 2 x General Electric J85-GE-5 turbojet, 2,400 lb.s.t. (1 088.6 kgp).
Gross weight: 10,500 lb. (4 763 kg).
Take-off dist: 1,000-1,700 ft (305-518 m).
Ordnance: 3,000 lb. (1361 kg).
Max speed: 475 mph (764 km/h) clean
Max speed: 320 mph (515 km/h) max external ordnance and wingtip tanks.
A 37 Dragonfly
Engine: 2 x Continental J69-T-25, 4562 N / 465 kp
Length: 29.298 ft / 8.93 m
Height: 9.35 ft / 2.85 m
Wingspan: 33.793 ft / 10.3 m
Max take off weight: 6401.1 lb / 2903.0 kg
Max. speed: 370 kts / 686 km/h
Service ceiling: 38714 ft / 11800 m
Range: 1150 nm / 2130 km
Cessna A37B Dragonfly
Engines: Two General Electric J85-17A Axial Flow turbojets, 2,850 lbs (1293kg)
Wingspan: 10.93 m / 35 ft 10 in over tip-tanks
Wing Area: 193.5 sq. ft / 17.98 sq. m
Length: 8.62 m / 28 ft 3 in
Height: 2.71 m / 8 ft 11 in
Empty weight: 6,254 lb / 2,843 kg
Maximum Takeoff weight: 14,000 lb / 6,364 kg
Maximum landing weight: 6350 kg (14 000 lb)
Wing Tank Capacity: 2 x 83 Imperial Gallons / 376 Litres / 99 U.S. Gallons
Fuselage Tank Capacity: 2 x 66 Imperial Gallons / 299 Litres / 79 U.S. Gallons
Wingtip Tank Capacity: 2 x 75 Imperial Gallons / 341 Litres / 90 U.S. Gallons
Pylon Tank Capacity: 4 x 81 Imperial Gallons / 367 Litres / 97 U.S. Gallons
Maximum Speed: 420 knots / 483 mph / 778 km/h
Cruise Speed: 265 knots / 305 mph / 491 km/h
Cruise at 25,000 ft: 489 mph (787 km/h).
Rate-of-Climb: 6,990ft/min (2,131m/min)
Service Ceiling: 41,762ft / 12,729m
Range w/max.fuel: 1629 km / 1012 miles
Range w/max.payload: 740 km / 460 miles
Take off run: 1740 ft.
Landing dist: 1710 feet.
Armament: One GAU-2B/A 7.62mm Minigun