Engine Controls and Rigging

8-10 To prevent injury to the crew or damage to the aircraft or engine, be sure that the engine is steadied when moving the hoist frame. Engine nacelles are rarely designed for the engine to be fitted and bolted into place as though it were being mounted on a bare wall. The engine must be guided into position and mated with its various connections, such as the mounting bolt holes and the exhaust tailpipe. This must be done despite such obstacles as the nacelle framework, ducts, or firewall connections and without leaving a trail of broken and bent parts, scratched paint, or crushed fingers. When the engine has been aligned correctly in the nacelle, insert the mounting bolts into their holes and start all of the nuts on them. Always use the type of bolt and nut recommended by the manufacturer. Never use an unauthorized substitution of a different type or specification of nut and bolt than that prescribed.

The nuts on the engine mount bolts must be tightened to the torque recommended by the aircraft manufacturer. While the nuts are being tightened, the hoist should support the engine weight sufficiently to allow alignment of the mounting bolts. If the engine is permitted to exert upward or downward pressure on the bolts, it is necessary for the nuts to pull the engine into proper alignment. This results in nuts being tightened to the proper torque value without actually holding the engine securely to the aircraft. The applicable manufacturer’s instructions outline the sequence for tightening the mounting bolts to ensure security of fastening. After the nuts are safetied and the engine sling and hoist are removed, bonding strips should be connected across each engine mount to provide an electrical path from the mount to the airframe.

Mounting the engine in the nacelle is, of course, only the beginning. All the ducts, electrical leads, controls, tubes, and conduits must be connected before the engine can be operated. Connections & Adjustments There are no hard-and-fast rules that direct the order in which units or systems should be connected to the engine. Each maintenance organization normally supplies a worksheet or checklist to be followed during this procedure. This list is based upon past engine installations on each particular aircraft. If this is followed carefully, it serves as a guide for an efficient installation. The following instructions are not a sequence of procedures but a discussion of correct methods for completing an engine installation.

The system of ducts for routing air to the engine varies with all types of aircraft. In connecting them, the goal is to fit the ducts closely at all points of disconnect so that the air they route does not escape its intended path. The duct systems of some aircraft must be pressure checked for leaks. This is done by blocking the system at one end, supplying compressed air at a specified pressure at the other end, and then checking the rate of leakage. The filters in the air induction system must be cleaned to ensure an unrestricted flow of clean air to the engine and its units. Because methods for cleaning air filters vary with the materials used in the filtering element, clean them in accordance with the technical instructions for the aircraft being serviced.

The exhaust system should also be carefully connected to prevent the escape of hot gases into the nacelle. When assembling the exhaust system, check all clamps, nuts, and bolts, and replace any in doubtful condition. During assembly, the nuts should be gradually and progressively tightened to the correct torque. The clamps should be tapped with a rawhide mallet as they are being tightened to prevent binding at any point. On some systems, a ball joint connects the stationary portion of the exhaust system to the portion that is attached to the engine. This ball joint absorbs the normal engine movement caused by the unbalanced forces of the engine operation. Ball joints must be installed with the specified clearance to prevent binding when expanded by hot exhaust gases.

Hoses used inside low-pressure systems are generally fastened into place with clamps. Before using a hose clamp, inspect it for security of welding or riveting and for smooth operation of the adjusting screw. A clamp that is badly distorted or materially defective should be rejected. Material defects include extremely brittle or soft areas that may easily break or stretch when the clamp is tightened. After a hose is installed in a system, it should be supported with rubber-lined supporting clamps at regular intervals. Before installing metal tubing with threaded fittings, ensure the threads are clean and in good condition. Apply sealing compound, of the correct specification for the system, to the threads of the fittings before installing them. While connecting metal tubing, follow the same careful procedure for connecting hose fittings to prevent cross-threading and to ensure correct torque.

When connecting the starter, generator, or various other electrical units within the nacelle, make sure that all lead connections are clean and properly secured. On leads that are fastened to a threaded terminal with a nut, a lock washer is usually inserted under the nut to prevent the lead from 8-11 A B C D E F G H J K A B C D E F G H J KSerrated throttle control arm Control rod Adjustable rod ends Cable drum Tensiometer Cushion movement Quadrant locking pin Cable turnbuckle Cable drum locking pin Throttle stop working loose. When required, connector plugs can be safetied with steel wire to hold the knurled nut in the full- tight position.

Electrical leads within the engine nacelle are usually passed through either flexible or rigid conduit. The conduit must be anchored, as necessary, to provide a secure installation and bonded when required. All engine controls must be accurately adjusted to ensure instantaneous response to the control setting. For flexibility, the engine controls are usually a combination of rods and cables. Since these controls are tailored to the model of aircraft in which they are installed, their adjustment must follow exactly the step-by-step procedure outlined in the manufacturer’s instructions for each particular model of aircraft.

throttle control system for a reciprocating aircraft engine. Follow a general procedure for adjusting throttle controls. First, loosen the serrated throttle control arm at the carburetor and back off the throttle stop until the throttle valve is in the fully closed position. After locking the cable drum into position with the locking pin, adjust the control rod to a specified length. Then, attach one end of the control rod to the locked cable drum, and reinstall the throttle control arm on the carburetor in the serrations that allow the other end of the control rod to be attached to it. This correctly connects the control arm to the cable drum.

Now, loosen the cable turnbuckles until the throttle control can be locked at the quadrant with the locking pin. Then, with both locking pins in place, adjust the cables to the correct tension as measured with a tensiometer. Remove the locking pins from the cable drum and quadrant. Next, adjust the throttle control so that it has a slight cushion action at two positions on the throttle quadrant: one when the carburetor throttle valve is in the full-open position and the other when it is closed to the idle position (stop to stop). Adjust the cushion by turning the cable turnbuckles equally in opposite directions until the throttle control cushion is correct at the full-open position of the throttle valve. Then, when the throttle arm stop is adjusted to the correct idle speed 8-12 setting, the amount of cushion should be within tolerance at the idle speed position of the throttle valve. The presence of this cushion ensures that the travel of the throttle valve is not limited by the stops on the throttle control quadrant, but that they are opening fully and closing to the correct idle speed as determined by the throttle arm stop.

Adjustment of the engine controls is basically the same on all aircraft regarding the linkage adjustment to a predetermined length for a specific setting of the unit to be controlled. Then adjust cables, if used in the control system, to a specific tension with the control system locked. Finally, the full travel of the unit to be controlled is ensured by establishing the correct cushion in the controls. In general, the same basic procedure is used to connect the linkage of the remaining engine controls. After rigging the engine controls, safety the turnbuckles and castle nuts, and make certain the jam nuts on all control rods are tightened.

On multiengine aircraft, the amount of cushion of all engine controls on each quadrant must be equal so that all are aligned at any specific setting chosen. This eliminates the necessity of setting each control individually to synchronize engine operations. After the engine has been installed, it is necessary to adjust the cowl flaps, if installed, so that the passage of the cooling air over the engine can be regulated accurately. Operate the system and recheck for opening and closing to the specified limits. Also, check the cowl flap position indicators, if installed, to ensure that they indicate the true position of the cowl flaps. Cowl flaps are doors at the bottom of the rear cowling that are used to control air flow through the cowling.

The oil cooler doors are adjusted in a manner similar to that used to adjust the cowl flaps. In some cases, the procedure is reversed in so far as the door is first adjusted to retract to a specified point, and the limit switch on the motor is set to cut out at this point. Then, the jackscrew is adjusted to permit the door to open only a specified distance, and the open limit switch is set to stop the motor when this point is reached. After the engine has been completely installed and connected, install the propeller on the aircraft. Before doing so, the thrust bearing retaining nut should be checked for correct torque. If required, the propeller shaft must be coated with light engine oil before the propeller is installed; the propeller governor and anti-icing system must be connected according to applicable manufacturer’s instructions.

Preparation of Engine for Ground & Flight Testing Pre-Oiling Before the new engine is flight tested, it must undergo a thorough ground check. Before this ground check can be made, several operations are usually performed on the engine. To prevent failure of the engine bearings during the initial start, the engine should be pre-oiled. When an engine has been idle for an extended period of time, its internal bearing surfaces are likely to become dry at points where the corrosion-preventive mixture has dried out or drained away from the bearings. Hence, it is necessary to force oil throughout the entire engine oil system. If the bearings are dry when the engine is started, the friction at high rpm destroys the bearings before lubricating oil from the engine-driven oil pump can reach them.

There are several methods of pre-oiling an engine. The method selected should provide an expeditious and adequate pre-oiling service. Before using any pre-oiling method, remove one spark plug from each cylinder to allow the engine to be turned over more easily with the starter. Also, connect an external source of electrical power (auxiliary power unit) to the aircraft electrical system to prevent an excessive drain on the aircraft battery. In using some types of pre-oilers, such as that shown in driven oil pump must be disconnected to permit the pre-oiler tank to be connected at this point. Then, a line must be disconnected, or an opening made in the oil system at the nose of the engine, to allow oil to flow out of the engine.

Oil flowing out of the engine indicates the completion of the pre-oiling operation, since the oil has now passed through the entire system. 8-13 In order to force oil from the pre-oiler tank through the engine, apply air pressure to the oil in the tank while the engine is being turned through with the starter. When this action has forced oil through the disconnection at the nose of the engine, stop cranking the engine and disconnect the pre-oiler tank. A motor-driven oil pump can also be used to pump oil through the engine during the pre-oiling operation. When no external means of pre-oiling an engine are available, the engine oil pump may be used. Fill the engine oil tank, or crankcase, to the proper level. Then, with the mixture in the idle cutoff position (reciprocating engine), the fuel shutoff valve and ignition switches in the off position, and the throttles fully open, crank the engine with the starter until the oil pressure gauge mounted on the instrument panel indicates oil pressure.

After the engine has been pre-oiled, replace the spark plugs and connect the oil system. Generally, the engine should be operated within 4 hours of being pre-oiled; otherwise, the pre-oiling procedure normally must be repeated. Fuel System Bleeding To purge the fuel system of air locks, and to aid in flushing any traces of preservative oil from a pressure carburetor, fuel injector unit, or fuel control (turbine), remove the drain plug in the fuel unit chamber that is farthest from the fuel inlet to the fuel unit. In its place, screw a threaded fitting to a length of hose leading to a suitable container. Then, set the fuel control unit to flow fuel so that fuel is permitted to flow through the system. After ensuring the fuel shutoff and main fuel tank valves are open, turn on the fuel boost pump until there are no traces of preservative oil in the fuel being pumped through the system. The passage of air is indicated by the absence of air mixed in the fuel emerging from the end of the hose submerged in the container of fuel. Air trapped in the system should not be confused with the numerous small air bubbles that may appear as a result of the velocity of the fuel being ejected from the engine’s fuel unit. Usually, after approximately a gallon of fuel has been bled off, the system can be considered safe for operation. After completing the bleeding operation, return all switches and controls to their normal, or off, position, and replace and safety all fuel unit connections disturbed.

Propeller Check The propeller, if equipped, must be checked before, during, and after the engine has been ground operated. The propeller should be checked for proper torque on the mounting bolts, leaks, vibration, and for correct safety. A propeller whose pitch-changing mechanism is electrically actuated may be checked before the engine is operated. Propellers whose pitch-changing mechanisms are oil actuated must be checked during engine operation after the normal operating oil temperature has been reached. In addition to checking the increase or decrease in rpm, the feathering cycle of the propeller should also be checked.

Checks & Adjustments After Engine Runup & Operation After the engine has been ground operated, and again after flight test, operational factors must be adjusted, as necessary, and the entire installation given a thorough visual inspection. These adjustments often include fuel pressure and oil pressure, as well as rechecks of such factors as ignition timing, valve clearances, and idle speed and mixture. If these rechecks are indicated by the manner in which the engine performs. After both the initial ground runup and the test flight, remove the oil sump plugs and screens and inspect for metal particles.

Clean the screens before reinstalling them. Check all lines for leakage and security of attachment. Especially, check the oil system hose clamps for security as evidenced by oil leakage at the hose connections. Also, inspect the cylinder holddown nuts or cap screws for security and safety. This check should also be performed after the flight immediately succeeding the test flight. Rigging, Inspections, & Adjustments The following instructions cover some of the basic inspections and procedures for rigging and adjusting fuel controls, fuel selectors, and fuel shutoff valves. 1. Inspect all bellcranks for looseness, cracks, or corrosion.

2. Inspect rod ends for damaged threads and the number of threads remaining after final adjustment. 3. Inspect cable drums for wear and cableguards for proper position and tension. While rigging the fuel selector, power controls, and shutoff valve linkages, follow the manufacturer’s step-by-step procedure for the particular aircraft model being rigged. The cables should be rigged with the proper tension with the rigging pins installed. The pins should be free to be removed without any binding; if they are hard to remove, the cables are not rigged properly and should be rechecked. The power lever should have the proper cushion at the idle and full-power positions. The pointers, or indicators, on the fuel control should be within limits. The fuel selectors must be rigged so that they have the proper travel and do not restrict the fuel flow to the engines.

8-14 Pylon and nacelle control Power levers Control rods Wing front span Center console Rigging Power Controls Many older conventional turbofan engines use various power lever control systems. One of the common types is the cable and rod system. This system uses bellcranks, push-pull rods, drums, fairleads, flexible cables, and pulleys. All of these components make up the control system and must be adjusted or rigged from time to time. On single-engine aircraft, the rigging of the power lever controls is not very difficult. The basic requirement is to have the desired travel on the power lever and correct travel at the fuel control. On multiengine turbojet aircraft, the power levers must be rigged so that they are aligned at all power settings.

Most computer controlled engines have an electronic connection from the flight deck to the engine. This eliminates the need for any type of cable or linkages. In the computer controlled system, the computer sends electronic information through wires or buses to the fuel control to command it to follow pilot inputs from the flight deck. On older style aircraft the power lever control cables and push-pull rods in the airframe system to the pylon and nacelle are not usually disturbed at engine change time and usually no rigging is required, except when some component has been changed. The control system from the pylon to the engine must be rigged after each engine change and fuel control change. Figure 8-13 shows the control system from the bellcrank in the upper pylon to the fuel control.

Before adjusting the power controls at the engine, be sure that the power lever is free from binding and the controls have full throw on the console. If they do not have full throw or are binding, the airframe system should be checked, and the discrepancies repaired. After all adjustments have been made, move the power levers through their complete range, carefully inspecting for adequate clearance between the various push-pull rods and tubes. Secure all locknuts, cotter pins, and safety as required. Adjusting the Fuel Control The fuel control unit of the typical turbofan on older aircraft can be a hydromechanical device that schedules the quantity of fuel flowing to the engine so that the desired amount of thrust can be obtained. The amount of thrust is dictated by the position of the power lever in the flight deck and the particular operation of the engine. Thus, the thrust of the engine and the consequent rpm of its turbine are scheduled by fuel flow.

The fuel control unit of the engine is adjusted to trim the engine to obtain maximum thrust output of the engine when desired. The engine must be retrimmed after a fuel control unit is replaced, the engine does not develop maximum thrust, engine change, or excessive throttle stagger. After trimming the engine, the idle rpm can be adjusted. The idle rpm is adjusted by turning the INC. IDLE screw an eighth of a turn at a time, allowing sufficient time for the rpm to stabilize between adjustments. Retard the power lever to idle and recheck the idle rpm. If wind velocity is a factor, the aircraft should be headed into the wind while trimming or checking the trim on an engine. Since trimming accuracy decreases as windspeed and moisture content increase, the most accurate trimming is obtained under conditions of no wind and clear, moisture-free air. Do not trim when there is a tailwind because hot exhaust gases may be reingested. As a practical matter, the engine should never be trimmed when icing conditions exist because of the adverse effects on trimming accuracy. To obtain the most accurate results, the aircraft should always be headed into the wind while the engine is being trimmed.

With the aircraft headed into the wind, verify that the exhaust area is clear. Install an engine trim gauge to the T-fitting in the turbine discharge pressure line. Start the engine and allow it to stabilize for 5 minutes before attempting to adjust the fuel control. Refer to the applicable manufacturer’s instructions for correct trim values. Compensate for temperature and pressure during the trimming process. If a hydromechanical fuel control is not within limits, turn the INC. MAX screw [Figure 8-14] about one-eighth turn in the appropriate direction. Repeat, if necessary, until the desired value is attained. If the aircraft is equipped with a pressure ratio gauge, set it to the correct value.

An example of a trim check using an electronic controlled fuel control must take into account temperature and pressure 8-15 IDLE MAX INC INC RPM adjustment 0.125 hex socket 0.1875 hex socket for each parameter measured. The parameters checked can include: 1. Minimum idle (percent N2). 2. Approach idle (percent N2). 3. 2.5 bleed open (percent N1). 4. 2.5 bleed closed (percent N1). 5. Takeoff engine pressure ratio (EPR). 6. 95 percent takeoff thrust (EPR). 7. 90 percent thrust change decal (EPR). The actual trim check would be done based on a temperature and pressure, such as the example in Figure 8-15. For these given temperature and pressures, the target parameter values can be derived from a chart in the manufacturer’s manual.

The engine is run up, and these values are checked against the tolerances given in the manual. Turboprop Powerplant Removal & Installation Since most turboprop powerplant removal and installation instructions are developed for QECA, the following procedures reflect those used for a typical QECA. The procedures for turboprop engine removal and installation are similar to those presented in the section of this chapter for turbojet engines, except for those systems related to the turboprop propeller. Open the engine side panels and remove the nacelle access panels. Disconnect the engine thermocouple leads at the terminal board. Before disconnecting any lines, make sure that all fuel, oil, and hydraulic fluid valves are closed. Plug all lines as they are disconnected to prevent entrance of foreign material.

Remove the clamps securing the bleed-air ducts at the firewall. Then, disconnect the electrical connector plugs, engine breather and vent lines, and fuel, oil, and hydraulic lines. Disconnect the engine power lever and propeller control rods or cables. Remove the covers from the QECA lift points, attach the QECA sling, and remove slack from the cables using a suitable hoist. The sling must be adjusted to position the hoisting eye over the QECA CG. Failure to do so may result in engine damage. Remove the engine mount bolts. The QECA is then ready to be removed. Recheck all of the disconnect points to make certain they are all disconnected prior to moving the engine.

Move the engine forward, out of the nacelle structure, until it clears the aircraft. Lower the QECA into position on the QECA stand and secure it prior to removing the engine sling. The installation procedures are essentially the reverse of the removal procedures. Move the QECA straight back into the nacelle structure and align the mount bolt holes and the firewall. Start all the bolts before torqueing. With all the bolts started, and using the correct torque wrench adapter, tighten the mount bolts to their proper torque. Remove the sling and install the access covers at the lift point. Using the reverse of the removal procedures, connect the various lines and connectors. New O-ring seals should be used.

The manufacturer’s instructions should be consulted for the proper torque limits for the various clamps and bolts. After installation, an engine runup should be made. In general, the runup consists of checking proper operation of the powerplant and related systems. Several functional tests are performed to evaluate each phase of engine operation. The tests and procedures outlined by the engine or airframe manufacturers should be followed. Reciprocating Helicopter Engine & QECA The engine is installed facing aft with the propeller shaft approximately 39° above horizontal. The engine is supported by the engine mount, which is bolted to the fuselage structure.

The installation of the engine provides for ease of maintenance by allowing easy access to all accessories and components when the engine access doors are opened. The QECA contains the engine, engine mount, engine accessories, engine controls, fuel system, lubrication system, ignition system, cooling system, and hydromechanical clutch and fan assembly.