13

Powerplant Controls And Instruments

airplane should not cause a change in control setting sufficient to affect seriously its operation. Moreover, the controls should be provided with adequate means to assure that they will be positively held in their flight settings without slipping out of position The engine control linkages should be designed so as to resist vibration and place no bending on threaded sections. Bolts and nuts should be

POWERPLANT CONTROLS Powerplant controls are linkages or mechanisms by which the powerplant and its components are operated and regulated. Such regulation or control is usually from the pilot's compartment, with duplicate used even in shear connections controls being provided, as the necrather than clevis pins and cotters, essity demands, for various crew members. Controls in all cases con- since cotter pins acting as a sole means of securing controls are sist of the following three elements: considered poor practice. Bolts in (a) A handle, lever, rod, cable, the system should preferably not or switch to be operated by the be used in a cantilever manner pilot. (b) A suitable means of con- but should be symetrically loaded. Cable controls should be provided nection, such as rods, cables, flexiwith suitable support for all pulleys ble wire in conduit, hydraulic or and fairleads, and should be arpneumatic lines, or electric wires. ranged so that they will operate These may be supplemented by bell with a minimum of backlash and cranks, levers, fairleads, hydraulic friction in the system. Carburetorpumps, selsyn or autosyn transair-intake controls and controls for mitters and motors, values, boair shutters in the cooling and oil osters, relays, etc. systems should be sufficiently (c) An actuating part or mechstrong to permit their operation anism which operates the unit to under icing conditions. be controlled. This element may be a rod end, cable end, lever, gearing THROTTLE CONTROLS: Throttle controls should afford a positive hyraulic pump or motor, electric and immediately responsive means solenoid, motor, or selsyn or autosyn for controlling the engine. A formotor. ward movement should open the The choice of the means of conthrottle. The control should be control depends on the importance of structed of suitable material and the control to continued engine opbe capable of withstanding vieration whether positive positionbration and the loads which may ing is required, the distance to be imposed by the pilot, and should the part to be controlled, accessibprovide a friction lock, or equivaility for control elements, and the lent, to keep it from creeping in forces required. flight. Flexible-type, throttle-conRods (or tubing) and cables are trol units, if used, should be of an favored for such critical applicaapproved type Regardless of the tions as throttle, mixture and protype throttle control used, it is peller controls. Such elements lend desireable that the system be arthemselves to positive positioning ranged with a spring at the carburwith little chance of malfunctionetor so that any breakage in the ing. Of these, rods or tubes may be system wi'i cause the throttle valve favored since they are capable of to go to an open position cortransmitting push, pull, and torque. responding to cruising power. On the other hand, cable controls offer convenience for long-disMIXTURE CONTROLS: The mixtance control or where many bends ture control should require forare required to reach the part to be ward movement for "rich mixture" controlled. Control linkages of these The control handle should not be types may require supports at inlocated close to any other fretervals throughout their length to quently operated control (such as prevent them from vibrating. preheat, etc) of similar appearance since a pilot may inadvertently Flexible-wire in conduit type of place the mixture in the lean pocontrols are used for many controls, sition when carelessly intending to particularly on small installations. operate the other control These controls are relatively easy PROPELLER CONTROLS The to install due to their ability to propeller-pitch should have equivmake moderate bends without the alent air-worthiness to the throttle use of bell cranks or pulleys. Sharp control. A forward movement bends should be avoided since they should increase the rpm. The control increase operating loads and acshould be conveniently located as cellerate wear. Such controls should close to the throttle as possible. The be carefully supported at close inpitch should remain in any set tervals to prevent distortion under position and, if it is of the constant load. The adequate support of bends rpm controlling type, it is recomis particularly important. mended that it be given approxiINSTALLATION OF POWERmately the same movement range PLANT CONTROLS. All controls as the throttle. The positive stops should be readily accessible to the for controllable propellers should pilot, and should be plainly marked be located in the propeller itself as to identity and direction of opand not governed by a positive erations. All cockpit controls constop on the propeller pitch control nected to the engine should give in the cockpit. full travel of the control at the FUEL SYSTEM CONTROLS. The engine, and any normal movement fuel-system controls should be of the engine as installed in the

marked in a conventional fashion and when special fuels or sequences of fuel tank use are necessery the markings should include these instructions. For instance, when fuel of two grades or octane numbers is provided, the fuel control instructions should list which fuel is to be used under each flight condition. The fuel-system marking should also specify the tank or tanks to be used for take-off, when special operating instructions are necessary. Values of the type which have their "on" position with the handle in line with the fitting or lines can be marked by providing a plate or painting "on" and "off" positions on adjacent surfaces. Fuel-system controls should preferably be arranged with the handle down when the valve is "on" so that gravity will tend to keep the valve on. In single-tank airplanes it is recommended that the fuel shut-off control be lightly safetied "one" so it will only be used in an emergency. If the control is not safetied, care should be taken not to locate it close to any other frequently operated control of similar appearance since this may

gine mount, care should be taken to ensure that all paint is removed and a clean, metal-to-metal contact is made at the ground connection to the structure. In addition where the engine is mounted on rubber or other insulating, shockabsorbing material, the engine should be bonded to the engine mount. POWERPLANT INSTRUMENTS: The following instrument should be provided from each engine: (a) Fuel-quantity indicator (b) Oil-pressure indicator (c) Oil-temperature indicator

(d) Tachometer (e) Oil-quantity indicator (,f) Fuel-pressure Indicator (if pump-fed engines used) (g) Manifold-pressure indicator (if altitude engines used). Those powerplant instruments which are essential to safety in

flight such as the tachometer and

manifold pressure gauge, should be so installed as to be easily visible to the pilot with a minimum practical deviation from his normal position and line of vision when he is looking out and forward along the flight path. Other powerplant instruments should be mounted so result in careless closing of the as to be visible to the pilot in fuel valve while intending to opflight but may, because of their erate the other control. function, be in a less prominent Special care should be taken to position. arrange the fuel valve control so POWERPLANT INSTRUMENT that the fuel valve cannot inadvertINSTALLATION Powerplant-inently be knocked over to the "off strument lines should be installed position, by the pilot. The "off" with the same precautions as recoposition should be obvious to the mmended and uses for fuel-system pilot and within his direct view. lines and fittings. In addition, gauPREHEAT CONTROLS. The car- ges or instruments which require buretor-heat control should prefthe use of fuel, oil, or other inerably be in a location apart from flammable-fluid lines, under presother engine controls, such as sure, should have restrictions inmixture and fuel shut-off valves, corporated into the line so that so as to preclude inadvertent operline failure will not permit large ation due to confusion resulting quantities of the fluid to be supfrom clo>e proximity and similar plied in the engine compartment or appearance. cockpit. Such restrictions should be installed as close to the source as IGNITION SWITCHES. It should possible and the orifice or opening be possible to shut off all ignition should not be larger than approxwith one hand without requiring imately a number 60 drill size the pilot to divert his attention (.040 inch). from controlling the airplane, and INSTRUMENT MARKINGS. In the the switches should be so located marking of instruments it is conwith respect to other controls or sidered desireable to use standarstructure that the possibility of dized markings so as to avoid contheir inadvertent operation when fusion or inadvertent hazards due the pilot wears a heavy glove will to erroneous readings which may be remote. The practice sometimes result if the pilot switches from one adopted of providing two separate plane to another where instruments switches in single-engine installare not marked or are marked in ations equipped for dual ignition a different manner. The standard is not without hazard to ground marking practice adopted by the personnel when starting the engine aircraft industry, and which is due to the fact that one switch recommended is as follows: may inadvertently be left in the (a) Green arc representing nor"one" position Such switch instalmal operating range. lations should be located in full (b) Yellow arc representing view of the pilot to avoid possible precautionary range (between maxhazards. A single, dual-ignition imum continuous and take-off) switch is preferred. (c) Red radial line representing Particular care should be taken maximum or minimum limits. in the grounding of magneto (d) Red arc representing a proswitches to ensure a good ground contact. Otherwise operating per- hibited range for other than momentary operation. sonnel may be exposed to a danThe marking should be accompgerous hazard from this source when starting the engine. The lished by any other method desired so long as the marking cannot be switches should preferably be changed in flight and is readily grounded to the engine. When discernible and durable switches are grounded to the en-