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Details of Some Components Used for Subsidiary Services in Aircraft Mars Pump and Ground Power Unit The Solar Mars gas turbine unit was recently demonstrated in operation as a fire pump and as a ground power unit for starting jet engines in aircraft. A description of a Mars auxiliary power unit in service with the U.S. Air Force was published in AIRCRAFT ENGINEERING, March 1955. The Mars gas turbine is a small portable plant developing 40 to 75 h.p. and operating at a speed of approximately 40,000 r.p.m. on natural gas or any distillate fuel. It weighs less than 100 lb. and is smaller than a two-foot cube. Starting may be by manual or electrical means. The fire fighting unit is hand started, and delivers 415 Imperial gallons per minute at a pressure of 100 lb./sq. in. with a 16 ft. suction lift. Fuel is diesel, petrol or kerosene; fuel consumption at full load is electrode and an outer earth return electrode separated A means of rapidly evaluating thrust at all altitudes 104 lb./hr. Two seven-gallon portable tanks provide by a ceramic tube. The end of the tube has a semi- and temperatures is provided by the jet engine gross sufficient fuel for one hour's sustained running at full conductive coating fired on. When an initial electrical thrust system, designed for both fixed and variable load. During operation the tank in use is mounted on impulse is received from the high energy unit a path exit area installations. The indicator gives a direct the tubular frame of the unit, and connected by a is ionized (through the carbon deposit if present) reading of the thrust in pounds or a percentage of the short flexible pipe with a self-sealing coupling which across the surface of the ceramic, which has a negative designed or rated thrust. The pressure differential allows the tank to be replenished during operation temperature coefficient. The resistance of the path principle is used with tailpipe pressures and aero without interrupting the fuel flow. The unit is very therefore drops with the increase in temperature and plane static pressure as inputs. In variable exit area well governed, and rapid changes of load have no the voltage in the high energy unit is discharged in an engines, corrections for exit area are automatically noticeable effect on turbine speed. are across the face of the igniter. entered. Speed reduction between the power unit and the A Mach number and airspeed control system gives water pump is accomplished by a single train 9·1: 1 electrical outputs which control indicated airspeeds or Industrial Gas Turbine spiral bevel gear. The complete pump unit, exclusive Mach numbers at a value manually preset. The posi A small industrial gas turbine engine is now being of fuel tanks, weighs 175 lb. tion of a double-throw switch determines whether produced by Rover Gas Turbines Ltd. a subsidiary of The ground power unit is used for starting jet air indicated airspeed or Mach number is the controlling the Rover Co. Ltd. The engine can be used in its craft engines and for operating aircraft electrical function. In indicated airspeed control, the signal generating set form as a ground starter for aircraft systems on the ground. The unit consists of the Mars from an airspeed synchrotel transmitter is sent to the engines or as an auxiliary power unit to supply engine, one large d.c. generator for starting power, stator of an airspeed setting synchro. The rotor, electrical power for testing aircraft instrument systems one small d.c. generator for service power, electrical which is manually set for the desired indicated air without using the main engines. It can also be used as controls, fuel tank and battery for starting. Normal speed, gives the control signal. In Mach number a source of power for ground radio and radar installa continuous output ratings at 28·5 V d.c. are 650 amps control, the signal from the transmitter is applied tions, and for driving pumps and air compressors. starting power plus 250 amps service power, or 700 to the stator of a Mach number differential synchro. The engine has a continuous power rating of 60 amps service power. Overload ratings are 800 amps The rotor is manually set to the required Mach b.h.p. and a total weight of 130 lb. The consumption for two minutes for starting, plus 300 amps for number setting, and the signal from it applied to the of liquid fuel is approximately 9 gallons per hour. A 25 minutes service power, or 1,100 amps for two stator of an altitude synchrotel transmitter. The wide range of distillate fuels and gases can be used. minutes starting and service power. Controls are rotor output gives the Mach number control signal. automatic, with push button starting. For both functions of the control system a phase Kollsman Instruments Rated engine speed of the gas turbine is 38,200 reversing zero appears when the control point is r.p.m., and reduction gear ratio is 8·5 : 1. Fuel con reached. The Kollsman Instrument Corporation, Elmhurst, sumption at rated load is 1·95 lb./hr./h.p. Weight New York, intends to produce in the near future a The master air data computer gives true airspeed of the ground power unit is 700 lb. number of new devices for special specific appli and Mach number, pressure altitude and absolute Mars gas turbines will shortly be manufactured in cations. pressure, true air temperature, relative air density this country by Sugg Solar Ltd. of Crawley, Sussex, and true altitude variation. The static pressure compensator has been designed a subsidiary of William Sugg and Co. Ltd. to rectify errors in instruments using static pressure. Another development is a self-powered pressure When a condition exists which would cause inac switch for applications where an electrical pulse is High Energy Igniter curacy in static pressure readings, an electrical error required at a predetermined pressure altitude after A new igniter system to overcome the difficulties of signal is transmitted from a computer to the static having first passed through another predetermined the starting and relighting of jet engines has been pressure corrector, which is situated in the static pressure altitude above the trigger altitude. No devised by K.L.G. Ltd. A high energy electrical pressure line and automatically corrects this pressure external power is required. source operating at a controlled breakdown voltage so that its output is true static pressure. A multiple pressure switch assembly consists of ensures that a predetermined amount of electrical A fore and aft acceleration switching system has a combination of up to four standard pressure energy will be delivered to the igniter plug regardless been developed to de-energize electrically a gyro switches. Units have been designed for sequence of external conditions, i.e. the system is not altitude erection system when acceleration reaches a pre-set operation in various combinations. Switches can be of sensitive. value. A conventional Machmeter or true airspeed the manually operated direct setting type or the remote The plug is a surface discharge type instead of the transmitter is followed by a conventional servo sys setting type. conventional gap type. It consists of an inner, live tem, so that the follow-up motor position is linear A dual pressure switch has been designed for dif with true airspeed and its velocity is proportional to ferential pressure or absolute pressure switching. Two the rate of change of airspeed. The voltage output diaphragms balanced against each other carry on of the generator coupled to the motor is proportional their common balancing lever the two contact points to acceleration. This output is compared with the which complete the circuit. Both diaphragms must supply voltage in a relay, which is actuated when the move the set distance before the circuit is complete, output reaches a pre-set value. so that there is no possibility of premature contact. The mechanism has a high natural frequency and no An improved cabin pressure control system has bearings or sliding parts. only two controls to be set by the operator, one for the desired cabin altitude, the other for the rate at In an altitude synchrotel transmitter, pressureswitch- which cabin altitude will be reached. The pressure ing is done by a synchrotel transmitter. The instrument switches with open-close contacts have been replaced sends altitude information to a control transformer by pressure monitors using induced voltages for con synchro whose rotor is set to give desired signal trol. A transistor type amplifier can be supplied. The altitude. This output, fed to a magnetic amplifier, cabin is automatically depressurized at a comfortable actuates a relay when zero is received. rate when the plane lands. Rapid vertical motions and gradual changes in alti A jet engine pressure ratio computer system operates tude are both shown on the instantaneous vertical by means of two absolute pressure monitors. The speed indicator. Rapid changes of altitude are meas signals from these sensing devices are amplified and ured by integrating the output of a vertical accelera drive positioning motors in a computer mechanism. tion monitor, while gradual changes are measured by The computer places in position potentiometers which a vertical speed monitor. These electrical signals give give the output signal. readings on a common dial. Aircraft Engineering
Aircraft Engineering and Aerospace Technology – Emerald Publishing
Published: Aug 1, 1955
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