Learjet 25

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Learjet 25 is a twin-engine, twin-jet corporate aeroplane with ten seats (two crews and eight passengers), produced by Learjet. This is a straight line variant of the Learjet 24. Learjet 25 is similar to model 24, but is 1.27 metres (4 feet 2 in) longer and can carry three extra people.

The Learjet 25B was manufactured in 1970 together with the Learjet 25C in the same year. Electric revolution counter comprises a motorized sensor and a display in the middle of the dashboard. The marks on the dials refer to the percentage of the max. permissible motor revolutions.

Large marks are graded in 2% steps from 0% to 100% and the small scale in 1% steps from 0% to 10% to allow more accurate rpm adjustments by drivers. EPR (Engine pressure ratio) allows the driver to maintain the necessary level of output to achieve certificated aeroplane output without going beyond motor restrictions.

Intake and exhaust pressure from the motor supercharger turbines are detected by the EPR emitter and converted into an electric pulse that is sent to the EPR display. Gasoline flows are indicated by a gasoline system. Fuelling flows through a rotary vane of each motor causing the vane to rotate and a pick-up spool to give impulses as the vane passes the spool area.

Averaging of the pulsing DC current is transmitted to the selected mode dial and to the tank level gauge. For the 25-061 to 25-180 airplanes, the motor-driven hydraulics deliver the liquid under a system head of 1500 pips and are held at 1250 to 1500 pips by a regulators. For airplanes 25-181 and later, the motorized volumetric circulator circulates liquid under a 1450 pressurized airspeed to the system and maintains steady air at 1500 to 1550 pressurized airspeed.

An overpressure is avoided by a solenoid control which opens at 1700ppsi. Precharged batteries dampen and absorb water hammer. In case of an accident, two motor-driven shut-off vents stop the power supply to the motor-driven electric motors. However, on aeroplanes fitted with an assist hydraulics plunger, the hydraulics plunger situated in the lower middle of the dashboard will activate the assist hydraulics plunger to supply hydraulics in stand-by mode.

There is a push button that activates the dispenser when the hydraulics are below a pre-set value and stops the dispenser when the pressures return to normality. Conventionally three-wheeled, the chassis can be retracted by hydraulics and is equipped with an air-hydraulic snubber and primary undercarriage. Nosewheel has a special shaped tyre to avoid spray of liquid into the engine.

The front wheels are steered via the electronic control surfaces according to the synchronization system. Hydraulics to retract and extend the transmission are transferred through a system of tubes, pipes and actuators and electrically operated by end stops and magnetic valve. In case of breakdown of the hydraulics or electric system, the alarm can be extended by pneumatic means.

Bow undercarriage flaps are mechanical with rods fixed to the front undercarriage damper brace. Learjet 25 uses wheeled braking as the main way to reduce airspeed after land. Braking system uses hydraulics to increase performance. There are two changeover solenoids in the discharge pipes to avoid liquid return between the pilot's and co-pilot's footpads.

Variable speed drives in each major axel produce an AC current at the DC inlet proportional to the rpm of the vehicle as they are powered by the rims. In the event of a deviation, it triggers a small momentary-action motor in the affected steering solenoid that directs the brake fluid to the reverse via a steering solenoid.

By accelerating the wheelspeed to standard tolerances, the standard brake pressures are re-established. In general, the Learjet 25 has five petrol canisters. With two wingtanks, one trunk and two wingtipanks. Every wingtank stretches from the outer central bulkhead to the wingtip and supplies each powerplant with its own independent gas.

There is a transversal throttle to avoid transferring gas between the wingtanks. Non-return poppet style flappers, situated in the various fins of the wings, allow free internal passage of fuels but limit external outflow. In every wingedank near the middle bulkhead, there is a jettison and an electric booster pumps fitted to feed the pressurized fluid to the relevant power plant system.

Tilting tanktanks offer extra filling space to allow longer periods at height. There is a nozzle injector in every tilting container that delivers the fluid to the wingtanks. You can also use the non-return flaps to feed your propellant into the wingedanks, but the lower half of the propellant in the tiltinganks must be pumped by the nozzle pumps.

The majority of Learjet 25 airplanes were equipped with a single hold bulkhead. It can be refilled from the high-pressure vane feeders via the delivery line and the oil transmission valves. Once the reservoir is full, a floating selector switches off the vane booster motors and shuts off the valves. While transferring gasoline, the trunk gas injection unit is pumping gas into the two wingedanks.

AC (alternating current) and DC (direct current) electric system are installed in the airplane. The DC system is powered by two 24-volt battery packs in stand-by mode, which are used to start the motor. A number of airplanes have a 1000 VA booster converter which is used as an optional extra system capacitance. The nose wheels are steered by electric control via the control surface foot switches.

Traditional butterfly valves are used to enhance flight performance at low velocities and decrease approach and departure velocities. Peel over alarm system uses a peel over alarm plate on each side of the nostril. A pitch sensor provides a stress in proportion to the pitch of the airplane. If the airspeed is 7% above the barn, the barn alarm activates a steering pedestal jogger that generates a low frequent buffer tone through the steering pedestal to alert the team.

If both blades of the tilt reach 5% above the stable, the elevator servos will move an airplane leading edge down. Forces exerted downwards towards the nostril are 80 lbs on the steering gear. If the blades of the blade inclination sink below the stable point, the instruction Nose Down is remote.

Conversion of signal from pull-over alarm system into visible indication of airplane pull-over alarm position by means of pull-over alarm signal, allowing crews to observe close range of pull-over alarm area. Needle reacts to the dynamical force of the head to the nasal cavity. Traditional flight velocity scales are gauged in nodes and the Mach scales are gauged in percent of Mach and associated with an aeroid that agitates the scales to balance changes in head.

The motor exhaust is led to a recuperator via a current regulation solenoid valves. Booth temp. is regulated by controlling the temp. of the pressurized exhaust ventilation that passes through the booth. Cold-storage systems are used for chilling and dehumidifying while the airplane is on the floor or operated at an altitude below 18,000ft.

Learjet 25 pressurised stateroom for high altitudes without additional aeration. Car pressurization is generated by the air-conditioned exhaust gas, which enters the car through the manifold channels and is regulated by modulation of the amount of exhaust gas from the car. A magnet restricts the difference in pressures to 0.25psil during floor operation to maintain proper operation of the doors and escape.

Air head at ultimate cruise level is kept at 8.7 passenger per second air head to cab height ratio. Normally the fail-safe action opens at 8.9 persi and the fail-safe action opens at 9.2 persi, which is the max. permissible fail-safe action.

Oxigen is present in a pressurised flask inside the back flipper of the airplane. Air burst discs release air from the air when the air tank pressures reach 2700 to 3000ppsi. Extinguishing system is a continual system and gives a fire alarm to the crews if the back gondola range temperatures exceed 510 °C or if the front gondola range temperatures exceed 480 C. The fire alarm system is a permanent system.

The content of two ball-shaped fire extinguishers can be transferred to both engines. Non-return valves prevent backflow between the canisters. There are two disc-shaped displays fitted below the motor on the right. In the event of breakage of the amber disk, either one or both tanks have been unloaded into the motorgondola. One or both vessels have been unloaded above board when the glass breaks, because an overheating state leads to excess internal overpressure.

Some Learjet 25 aircrafts are equipped with a tow shaft. In case of an accidental release during the flight, the towing shaft is fixed to the airplane with a connection system which detaches it from the airplane. Fasten the fastener to the airplane at the front end of the tail cone opening gate.

The point is close to the center of mass of the airplane and reduces the weather vanes when using the slide in crosswinds. Taxis are driven with front wheels with electric control. However, the guidance system in aeroplanes without varying authorities demands that the driver selects the either main or secondary guidance modes.

Prismatic steer modes allow up to 45 degree rotation and are designed for slower speeds and aggression. For aeroplanes having adjustable authoritative control, the tax authorities vary according to surface velocity. In the Learjet 25, the CJ610-6 power plants have a very low moment of inertia as well as fast acceleration. The power of a stand-alone powerplant is good with a climbing capacity of about 1700 ft per min, a total mass at altitude and a maximum servicing limit of about 21500 ft.

For windmill motors, the best sliding path is achieved with a neat aeroplane layout and a sliding velocity of 160 to 170 kn. The Learjet 25 slides about 26 sea mile per 10000 ft height drop at this rate. Compared to most General Aircraft planes and more advanced lightweight planes, the Learjet 25 is a sophisticated one.

Pilots have a high working pressure and the approaches, landings and take-off rates of civil aircrafts are above all high. Learjet 25 also needs long take-off and landings at great heights or environmental temperatures. With 6000 ft height, 50 degree Fahrenheit and an avarage of 5 passenger loads, the Learjet 25B will need about 8000 ft take-off and runway.

Learjet 25 provides an excellent high-speed passenger transportation system for six to eight people. Flight levels typically range from flight level 390 to flight level 430, which means that the Learjet 25 is able to overfly most meteorological regimes and overloaded air space. At a cruise velocity of about Mach 0.76, travelers arrive at their destinations on schedule.

Because of the simple conversion of the cabins, the Learjet 25 has found a recess as a plane for flying Gold Standard. Although the Learjet is used at lower elevations and is small undercarriage, it can be landed on dirt tracks if provided with a dedicated "gravel set". Today, many Learjet 25s are still in normal service, particularly in the United States, Mexico and Canada.

Learjet 25 is specifically entered in the Federal Register 78 FR 39576. Learjet airliners which have not been altered by the installation of noise-compliant level 3 power plants or which have not been fitted with noncompliant engine "hushkits" shall not be allowed to operate in adjacent 48 States after 31 December 2015.

LJ25 is the identifier of International Civil Aviation Organization (ICAO) used in the schedules of all Learjet 25s. Enhanced model with increased tank capacities. Taylor, John W. R. Jane's All The World'scraft 1976-77. Taylor, Michael J.H. (1999) Brassey's Worldcraft & Systems Directory 1999/2000. The Wikimedia Commons has published articles related to the Learjet 25.