Gates Lear 35 / C-21
Development by Garrett of the TFE731 turbofan engine, promising lower noise levels and greater fuel economy than the General Electric CJ610 turbojet which had been the standard Learjet engine, led to the Learjet 35 and Learjet 36 introduced in 1973. It had been intended originally to develop additional versions of the Learjet 25 as the Learjet 25B-GF (Garrett fan) and Learjet 25C-GF. A Learjet 25 served as, the engine test-bed, with a 1588kg thrust TFE731-2 engine in the starboard nacelle and the CJ610 retained on the port side. It was flown on 19 May 1971 followed by a second Learjet 25 with two TFE731-2s on 19 May 1971and, on 22 August 1973, the first Learjet 35 took to the air.
The 35 is a model 25B with a fuselage stretch (13 inches in the cabin), 0.61m increased wingspan outboard of the ailerons and the Garrett (Honeywell) TFE-731-2C engines (certified in 1974), with the 35A having a redesigned wing for better short field and low speed handling. The Model 35A incorporates wing-tip fuel tanks with an overall length of 48 ft 8 in (14,83 m). The engines are 3,500 lb st (15,6 kN) Garrett TFE731-2-211 turbofans.
The 35 and 36 differed in fuel/seating capacity, the Learjet 35 carrying a maximum of eight passengers and, with reduced payload, having transcontinental range; and the Learjet 36 seating up to six passengers but with the ability to trade two of them for the extra fuel to give non-stop capability across the North Atlantic. Certification was gained and the first deliveries made in 1974.
Gates Learjet expanded the slow-speed boundaries of their entire bizjet line by certificating their Century III wing leading edge and flight control system modification. Aircraft with the modification bear the designation "A" following their model numbers. The Century III modifications on model 35s and 36s reduced the stalling speed and gave better low-speed flying qualities. With the exception of the aerodynamic improvements to the Learjet wing, the new models introduced in 1976 did not represent profound applications of new technology. Rather, they were predictable examples of evolutionary changes.
The US Air Force leased 83 Model 35As as operational support aircraft between 1984-85 and bought them outright in 1986. These six-to eight-seat light jets are designated C-21A and were joined by four more in 1987, replacing T-39 Sabreliners.
Gates offers a wide range of special-mission aircraft for military applications, based on the Learjet 35A/36A corporate jet. The principal versions are the RC-35A for aerial survey, photography, and reconnaissance with Lorop cameras and Slar; the EC-35A for electronic warfare training, weapons simulation, and operational ECM/ESM duties; and the utility UC-35A.
In 1979 Gates unveiled a Sea Patrol model of the Lear 35A. Only two airframe mods were necessary to convert the 35A to the Special Missions role. A large belly radome has been fitted, housing the Litton 360 sea surveillance radar, while standard NATO underwing hardpoints have been attached, capable of carrying up to 500 lbs of external stores - sonobuoys, flares, smoke markers or rescue pods. These, plus the vast array of surveillance equipment fitted, has upped the aircraft’s empty weight some 1,300 lbs. APS weight is now 11,600 lb, maximum take-off weight 18,000 lbs. The maximum speed and altitude are down, from 0.83M to 0.79M, and about 5,000 feet from the stock 35A’s 41,000 ceiling, while fuel flow is up about 100 lb/hr.
With intercept dash speeds of 480 knots, and long-range patrol cruise of 0.74 Mach (say 430 knots at 31,000ft), the manufacturers claim the Sea Patrol Lear can cover nearly twice the amount of ocean as a slower turboprop. With 6,238 pounds fuel capacity and a typical 1,200 lb/hr consumption from the Garrett turbofans, 4½ hours safe endurance is available at altitude (effectively 2,000 nm), while patrol range at wavetop height is still 1,000 miles.
Gates Learjet Corporation reached a major milestone on 28 March 1980 when it delivered the 1,000th Learjet - a Century III 35A.
In September 1986 the USAF announced that the 80 C-2lAs (Learjet 35As) leased from Gates in 1983 as the second element of the Operational Support Aircraft (OSA) programme, were to be purchased outright. The aircraft were delivered between March 1984 and October 1985 to replace CT-39 Sabreliners in the high-priority-transport and other support roles.
By 1991 around 750 Learjet Model . 35/36 variants had been sold, including approximately 200 special mission versions to 20 customers around the world.
Engines: 2 x Garrett TFE 731-2C.
MTOW: 17,000 lb.
LR-35A Learjet Century III 35A
First built: 1974.
Engines: 2 x Garrett TFE 731-2-2B, 3500 lbs thrust.
Length: 48.7 ft.
Height: 12.3 ft.
Wingspan: 39.5 ft.
Wing area: 253 sq.ft.
Wing aspect ratio: 6.2.
Maximum ramp weight: 17,250 lbs.
Maximum takeoff weight: 17,000 lbs.
Standard empty weight: 9971 lbs.
Maximum useful load: 7279 lbs.
Zero-fuel weight: 13,500 lbs.
Maximum landing weight: 15,300 lbs.
Wing loading: 67.2 lbs/sq.ft.
Power loading: 2.4 lbs/lb.
Maximum usable fuel: 6238 lbs.
Best rate of climb: 4760.
Certificated ceiling: 45,000 ft.
Max pressurisation differential: 9.4 psi.
6500 ft cabin alt @: 45,000 ft.
Maximum single-engine rate of climb: 1470 fpm @ 200 kts.
Single-engine climb gradient: 441 fpm.
Single-engine ceiling: 25,300 ft.
Maximum speed: 471 kts.
Normal cruise @ 41,000ft: 459 kts.
Fuel flow @ normal cruise: 889 pph.
Stalling speed gear/flaps down: 99 kts.
Balanced field length 4,224 ft