TYPE: Business jet.
PROGRAMME: Learjet 31 introduced September 1987; first flight of aerodynamic prototype 11 May 1987; first production aircraft (N311DF) used as systems testbed; FAA certification 12 August 1988. Learjet 31A and 31A/ER announced October 1990 to replace Learjet 31 from June 1991.
VARIANTS: Learjet 31A/ER: Optional extended range version with 2,597 litres (686 US gallons; 571 Imp gallons) fuel with higher max T-O weight.
CUSTOMERS: Total 15 Learjet 31s delivered during 1990.
COSTS: Standard Learjet 3lA price $4,275,000 (April 1991); Learjet 31A/ER $4,392,600 (April 1991).
DESIGN FEATURES: Learjet 31 combined fuselage/cabin/power plant of Learjet 35A/36A with wing of Learjet 55; Delta Fins added to eliminate Dutch roll, stabilise aircraft at high airspeeds, induce docile stall and reduce approach speeds and field lengths; stick pusher/puller and dual yaw dampers no longer required for departure; slick shaker and single yaw damper retained for comfort.
Additional features of Learjet 31A include cruise Mach number up to 12,500 m (41,000 ft) increased four per cent to 0.81 and VMO increased from 300 knots (556 km/h; 345 mph) to 325 knots (602 km/h; 374 mph). Increases mainly benefit descent from high altitudes Learjet 31A also features integrated digital avionics package.
FLYING CONTROLS: All control surfaces mechanically actuated; ailerons have brush seals and geared tabs; electrically actuated trim tab on port aileron. Electrically actuated tailplane incidence control has separate motors for pilot and co-pilot and single-fault survival protection; aircraft can be manually controlled following tailplane runaway and landed with reduced flap. Rudder has electric trim tab; automatic electric rudder assist servo operates automatically if rudder pedal loads exceed 22.6 kg (50 lb). Full-chord fences bracket the ailerons; airflow between fences corrected by arrowhead energisers on leading-edge, row of round-head screws aft of leading-edge and two rows of energiser strips near ailerons. Single spoiler panel in each wing used as airbrake and lift dumper. Hydraulically actuated flaps extend to 40°. Optional drag parachute mounted on inside of baggage hatch under tail.
STRUCTURE: Multi-spar wing with machined skins.
LANDING GEAR: Retractable tricycle gear; main legs retract inward, nose leg forward; twin mainwheels with anti-skid disc brakes; nosewheel has full-time digital steer-by-wire replacing speed-limited steering of Learjet 31. Max airspeed with gear extended 260 knots (481 km/h; 299 mph); tyre limiting speed 183 knots (339 km/h; 210 mph).
POWER PLANT: Two 15.56 kN (3,500 lb st) Garrett TFE731-2 turbofans with digital electronic engine controller giving automatic retention of power settings above 4,570 m (15,000 ft) and special idling control for descent from 15,545 m (51,000 ft). Engine synchroniser fitted. Optional Dee Howard 4000 thrust reverser system weighs 109 kg (240 lb). One integral fuel tank in each wing holds 641 kg (1,413 lb); standard fuselage tank 608 kg (1,340 lb); ER fuselage tank 804 kg (1,773 lb); fuselage fuel transferred by pilots by gravity or pump; single-point pressure refuelling optional.
ACCOMMODATION: Cabin furnishings include a three-seat divan, four Erda 10-way adjustable individual seats, side facing seat with toilet, two folding tables, refreshment cabinet with ice chest, baggage compartment, coffee warmer, water dispenser, cup and miscellaneous storage, coat rod, forward privacy curtain, overhead panels with reading lights, indirect lighting, air vents and oxygen masks, and passenger lifejackets.
SYSTEMS: Hydraulic system operates flaps, landing gear, airbrake, wheelbrakes and thrust reversers; system pressure 68.95-120.6 bars (1,000-1,750 lb/sq in); pneumatic standby for gear extension and wheelbrakes. Normal cabin pressure differential 0.64 bar (9.4 lb/sq in) with automatic flood engine bleed if cabin altitude exceeds 2,820 m (9,250 ft); pop-out emergency oxygen for passengers and masks for crew. Electrical system based on two starter/generators, two nickel-cadmium batteries and two inverters; both buses can run from one engine; electrics operate tailplane incidence, rudder assister and nosewheel steering. De-icing by bleed air for wing, engine intakes and windscreen; tailplane electrically heated; fin not protected. Alcohol spray for radome to stop shed ice entering engines; controls prevent internal ice and condensation during long descents. Single engine at idle, burning 15.9 kg (35 lb) fuel every 10 minutes, acts as APU.
AVOINCS: Bendix/King integrated digital avionics package.
EQUIPMENT: Throttle-mounted landing gear warning mute and go-around switches, nacelle heat annunciator, engine synchroniser and synchroscope, recognition light, wing ice light, emergency press override switches, transponder ident switch in pilot's control wheel, engine synchroniser and synchroscope, flap preselect, crew lifejackets, cockpit dome lights, cockpit speakers, crew oxygen masks and fire extinguisher are standard.