Gates Lear 55
At the 1977 Paris air show Gates Learjet announced details of its new Learjet 50 series. This was intended to comprise the Learjet 54, Learjet 55 and Learjet 56 with longer and larger cabins, all powered by twin Garrett AiResearch fanjets. The 55 was to have advanced wings incorporating NASA-developed winglets and this last feature gave rise to the name Longhorn.
The larger wing incorporating near-vertical winglets that have replaced the traditional Learjet tiptanks. The wing’s increased aspect ratio and super-critical winglets provide substantial aerodynamic improvements that in turn produce greater fuel efficiency and improved flight performance at high and low altitudes. The wing also has been responsible for significantly improved short-field performance. The balanced field length is 3,520 feet for the 54/55/56 series.
Only the Longhorn 55 has been developed, construction of the first airframe starting in April 1978 after successful testing of an aerodynamic prototype of the wing on a Learjet 25. The first of two Learjet 55 prototypes was flown initially on 19 April, 1979, and certification and delivery of the first production aircraft were recorded on 18 March 1981 and 30 April 1981 respectively.
The Model 55 followed the same overall configuration as earlier members of the Learjet family, and accommodated a crew of two on a separate flight deck and up to 10 passengers in the main cabin. In September 1986 the company announced the Model 55B, offering a new interior, 'glass' cockpit, improved take-off performance and increased range, all of which increased the aircraft's operational flexibility. One year later, the Model 55C was revealed, fitted with rear underfuselage 'Delta Fins' giving improved directional stability at all speeds and reducing the landing speed, and thus removed the need for a stick puller/pusher.
Launched in 1987 was the Model 55C, which has a longer fuselage and deeper cabin than the 31. The engines were more powerful 3,700 lb st (16,46 kN) units and winglets and Delta-Fins were also standard.
Later versions are the 55C/ER extended-range version fitted with an extra tank holding 1175kg of fuel in the tailcone, and the Model 55C/LR giving even-longer-range through the installation of a further 322-litre fuel cell behind the standard fuselage tank. Typical configuration of this version is two crew and seven passengers. Around 150 Model 55 variants had been built by the end of 1990 and the version is to be superseded by the Learjet 60 during 1992.
LR-55 Learjet Longhorn 55
Engines: 2 x Garrett TFE 731-3A-2B, 3700 lbs thrust.
Length: 55.1 ft.
Height: 14.7 ft.
Wingspan: 43.8 ft.
Wing area: 265 sq.ft.
Wing aspect ratio: 7.2.
Maximum ramp weight: 20,750 lbs.
Maximum takeoff weight: 20,500 lbs.
Standard empty weight: 12,530 lbs.
Maximum useful load: 8220 lbs.
Zero-fuel weight: 15,000 lbs.
Maximum landing weight: 17,000 lbs.
Wing loading: 73.7 lbs/sq.ft.
Power loading: 2.6 lbs/lb.
Maximum usable fuel: 6682 lbs.
Best rate of climb: 4380 fpm.
Certificated ceiling: 51,000 ft.
Max pressurisation differential: 9.4 psi.
8000 ft cabin alt @: 51,000 ft.
Maximum single-engine rate of climb: 1250 fpm @ 200 kts.
Single-engine climb gradient: 379 ft/nm.
Maximum speed: 483 kts.
Normal cruise @ 41,000ft: 456 kts.
Fuel flow @ normal cruise: 1014 pph.
Stalling speed gear/flaps down: 103 kts.
Balanced field length 3,900 ft
Engines: 2 x Garrett TFE731-3A-2B turbofans, 1678kg
Max take-off weight: 9525 kg / 20999 lb
Empty weight: 5832 kg / 12857 lb
Wingspan: 13.35 m / 43 ft 10 in
Length: 16.80 m / 55 ft 1 in
Height: 4.48 m / 14 ft 8 in
Wing area: 24.57 sq.m / 264.47 sq ft
Max. speed: 884 km/h / 549 mph
Cruise speed: 744 km/h / 462 mph
Ceiling: 15545 m / 51000 ft