Engine Adjustment and Post-Installation Checks

8-16 Barometer (inches of mercury) DAT °F (°C) Trim targets 12 (−11) 16 (−9) 20 (−7) MIN IDLE (%N2) APP IDLE (%N2) 2.5 BLEED OPEN INC (%N1) 2.5 BLEED CLOSED INC (%N1) TAKEOFF (EPR) 95% TAKEOFF THRUST (EPR) 90% THRUST CHANGE DECEL (EPR) MIN IDLE (%N2) APP IDLE (%N2) 2.5 BLEED OPEN INC (%N1) 2.5 BLEED CLOSED INC (%N1) TAKEOFF (EPR) 95% TAKEOFF THRUST (EPR) 90% THRUST CHANGE DECEL (EPR) MIN IDLE (%N2) APP IDLE (%N2) 2.5 BLEED OPEN INC (%N1) 2.5 BLEED CLOSED INC (%N1) TAKEOFF (EPR) 95% TAKEOFF THRUST (EPR) 90% THRUST CHANGE DECEL (EPR) 31.0 30.0 29.0 28.0 27.0 26.0 25.0 24.0 23.0 22.0 57.6 67.5 60.4 63.5 1.45 1.42 1.03 57.9 67.8 60.6 63.8 1.45 1.42 1.03 58.1 68.1 60.9 64.0 1.45 1.42 1.03 57.6 67.5 60.4 63.5 1.48 1.45 1.03 57.9 67.8 60.6 63.8 1.48 1.45 1.03 58.1 68.1 60.9 64.0 1.48 1.45 1.03 57.7 67.6 60.4 63.5 1.50 1.46 1.04 58.0 67.9 60.6 63.8 1.50 1.46 1.04 58.2 68.2 60.9 64.0 1.50 1.46 1.04 58.0 67.7 60.4 63.5 1.51 1.47 1.04 58.2 68.0 60.6 63.8 1.51 1.47 1.04 58.5 68.3 60.9 64.0 1.51 1.47 1.04 58.3 67.8 60.4 63.5 1.53 1.48 1.04 58.5 68.1 60.6 63.8 1.53 1.48 1.04 58.8 68.3 60.9 64.0 1.53 1.48 1.04 58.6 67.9 60.4 63.5 1.54 1.50 1.04 58.8 68.2 60.6 63.8 1.54 1.50 1.04 59.1 68.5 60.9 64.0 1.54 1.50 1.04 58.9 68.0 60.4 63.5 1.56 1.51 1.04 59.2 68.3 60.6 63.8 1.56 1.51 1.04 59.4 68.6 60.9 64.0 1.56 1.52 1.04 59.5 68.3 60.4 63.5 1.57 1.52 1.04 59.8 68.6 60.6 63.8 1.57 1.52 1.04 60.0 68.9 60.9 64.0 1.57 1.52 1.04 60.2 68.8 60.4 63.5 1.59 1.53 1.04 60.4 68.9 60.6 63.8 1.59 1.53 1.04 60.7 69.2 60.9 64.0 1.59 1.53 1.04 60.9 69.0 60.4 63.5 1.61 1.54 1.04 61.2 69.3 60.6 63.8 1.61 1.54 1.04 61.4 69.6 60.9 64.0 1.61 1.54 1.04 ASSUME 1. Ambient temperature: OAT = 12 °F 2. Barometric pressure = 29.0 inches of mercury SELECT TRIM TARGETS FOR THE FOLLOWING 1. Minimum idle (%N2) is 57.7 (+1.5/−0.5)%N2 2. Approach idle (%N2) is 67.6 ±0.5 %N2 3. 2.5 bleed open inc (%N1) 60.4 ±0.5 %N1 4. 2.5 bleed closed inc (%N1) is 63.5 ±0.5 %N1 5. Takeoff (EPR) is 1.50 +0.01/−0.00 EPR 6. 95% takeoff thrust (EPR) is 1.46 EPR 7. 90% thrust change deceleration (EPR) is 1.04 EPR Removal of Helicopter QECA Prior to removing the helicopter QECA, the engine should be preserved if it is possible to do so. Then, shut off the fuel supply to the engine and drain the oil. Make the disconnections necessary to remove the QECA, and then perform the following steps: 1. Attach the engine lifting sling to a hoist of at least a two-ton capacity.

2. Raise the hoist to apply a slight lift to the QECA. Loosen both engine mount lower attachment bolt nuts before leaving the upper attachment bolts. 3. Remove the bolts from the sway braces and remove both engine upper attachment bolts. Then, remove both engine mount lower attachment bolts and remove the QECA from the helicopter. Mount the power package in a suitable workstand and remove the sling. Installation, Rigging, & Adjustment of Helicopter QECA The installation of a new or an overhauled engine is in reverse of the removal procedure. The manufacturer’s instructions for the helicopter must be consulted to ascertain the correct interchange of parts from the old engine to the new engine.

The applicable maintenance instructions should be followed. Refer to the Maintenance Instructions Manual and associated technical publications for detailed information concerning rigging the throttle, mixture control, cable tensions, and related data. Testing the Engine Installation Normal engine run-in procedures must be followed in accordance with the manufacturer’s instructions. A flight test is usually performed after the engine has been installed and the engine controls have been adjusted. Engine Mounts Mounts for Reciprocating Engines Most aircraft equipped with reciprocating engines use an engine mount structure made of welded steel tubing. The mount is constructed in one or more sections that incorporate the engine mount ring, bracing members (V-struts), and fittings for attaching the mount to the wing nacelle.

8-17 The engine mounts are usually secured to the aircraft by special heat-treated steel bolts. The importance of using only these special bolts can be readily appreciated, since they alone support the entire weight of, and withstand all, the stresses imposed by the engine and propeller in flight. The upper bolts support the weight of the engine while the aircraft is on the ground, but when the aircraft is airborne another stress is added. This stress is torsional and affects all bolts, not just the top bolts. A typical engine mount ring shown in at four positions on the engine mount structure. Each fitting houses a dynamic engine mount.

The section of an engine mount where the engine is attached is known as the engine mount ring. It is usually constructed of steel tubing having a larger diameter than the rest of the mount structure. It is circular in shape so that it can surround the engine, which is near the point of balance for the engine. The engine is usually attached to the mount by dynafocal mounts, attached to the engine at the point of balance forward of the mount ring. Other types of mounting devices are also used to secure the different engines to their mount rings. As aircraft engines became larger and produced more power, some method was needed to absorb their vibration. This demand led to the development of the rubber and steel engine- suspension units called shock mounts. This combination permits restricted engine movement in all directions. These vibration isolators are commonly known as flexible, or elastic, shock mounts. An interesting feature common to most shock mounts is that the rubber and metal parts are arranged so that, under normal conditions, rubber alone supports the engine.

Of course, if the engine is subjected to abnormal shocks or loads, the metal snubbers limit excessive movement of the engine. Dynafocal engine mounts, or vibration isolators, are units that give directional support to the engines. Dynafocal engine mounts have the mounting pad angled to point to the CG of the engines mass. [Figure 8-16] Mounts for Turbofan Engines The engine mounts on most turbofan engines perform the same basic functions of supporting the engine and transmitting the loads imposed by the engine to the aircraft structure. Most turbine engine mounts are made of stainless steel and are typically located as illustrated in Figure 8-17. Some engine mounting systems use two mounts to support the forward end of the engine and a single mount at the rear end.

Turbine Vibration Isolation Engine Mounts The vibration isolator engine mounts support the power plants and isolate the airplane structure from adverse engine vibrations. Each power plant is generally supported by forward vibration isolator mounts and an aft vibration isolator mount. The forward vibration isolator engine mounts carry vertical, side, and axial (thrust) loads and allow engine growth due to thermal expansion. The aft mounts take only vertical and side loads; however, they will also accommodate thermal expansion of the engine without applying axial loads to the engine flanges. 8-18 The vibration isolators consist of a resilient material permanently enclosed in a metal case. As an engine vibrates, the resilient material deforms slightly, thereby dampening the vibrations before they reach the airplane structure. If complete failure or loss of the resilient material occurs, the isolators will continue to support the engine.

Preservation & Storage of Engines An engine awaiting overhaul or return to service after overhaul must be given careful attention. It does not receive the daily care and attention necessary to detect and correct early stages of corrosion. For this reason, some definite action must be taken to prevent corrosion from affecting the engine. Engines that are not flown regularly may not achieve normal service life because of corrosion in and around the cylinders. The normal combustion process creates moisture and corrosive by-products that attack the unprotected surfaces of the cylinder walls, valves, and any other exposed areas that are unprotected. In engines that have accumulated 50 hours or more time in service in a short period, the cylinder walls have acquired a varnish that tends to protect them from corrosive action; engines under favorable atmospheric conditions can remain inactive for several weeks without evidence of damage by corrosion. This is the best-case scenario, but aircraft that operate close to oceans, lakes, rivers, and humid regions have a greater need for engine preservation than engines operated in dry low humid areas.

Corrosion-Preventive Materials An engine in service is in a sense self-purging of moisture, since the heat of combustion evaporates the moisture in and around the engine, and the lubricating oil circulated through the engine temporarily forms a protective coating on the metal it contacts. If the operation of an engine in service is limited or suspended for a period of time, the engine is preserved to a varying extent, depending upon how long it is to be inoperative. There are three types of engine storage: active engine, temporary, and indefinite. An engine in active storage is defined as having at least one continuous hour of operation with an oil temperature of at least 165 °F to 200 °F and storage time not to exceed 30 days. Temporary storage describes an aircraft and engine that is not flown for 30 to 90 days, and indefinite storage is for an aircraft not to be flown for over 90 days or is removed from the aircraft for extended time.

Corrosion-Preventive Compounds The preservation materials discussed are used for all types of engine storage. Corrosion-preventive compounds are petroleum-based products that form a wax-like film over the metal to which they are applied. Several types of corrosion- preventive compounds are manufactured according to different specifications to fit the various aviation needs. The type mixed with engine oil to form a corrosion-preventive mixture is a relatively light compound that readily blends with engine oil when the mixture is heated to the proper temperature. The light mixture is available in three forms: MIL-C-6529C type I, type II, or type III. Type I is a concentrate and must be blended with three parts of MIL-L-22851 or MIL-L-6082C (SAE J1966) grade 1100 oil to one part of concentrate. Type II is a ready-mixed material with MIL-L-22851 or grade 1100 oil and does not require dilution. Type III is a ready-mixed material with grade 1010 oil for use in turbine engines only.

The light mixture is intended for use when a preserved engine is to remain inactive for less than 30 days. It is also used to spray cylinders and other designated areas. The desired proportions of lubricating oil, and either heavy or light corrosion-preventive compound, must not be obtained by adding the compound to the oil already in the engine. The mixture must be prepared separately before applying to the engine or placing in an oil tank. A heavy compound is used for the dip treating of metal parts and surfaces. It must be heated to a high temperature to be sufficiently liquid to effectively coat the objects to be preserved. A commercial solvent, or kerosene spray, is used to remove corrosion-preventive compounds from the engine or parts when they are being prepared for return to service.

Although corrosion-preventive compounds act as an insulator from moisture, in the presence of excessive moisture, they eventually break down and corrosion begins. Also, the compounds eventually dry because their oil base gradually evaporates. This allows moisture to contact the engine’s metal and aids in corroding it. Therefore, when an engine is stored in a shipping case or container, some dehydrating (moisture removing) agent must be used to remove the moisture from the air in and around the engine. Dehydrating Agents There are a number of substances (referred to as desiccants) that can absorb moisture from the atmosphere in sufficient quantities to be useful as dehydrators. One of these is silica gel. This gel is an ideal dehydrating agent since it does not dissolve when saturated.

As a corrosion preventive, bags of silica gel are placed around and inside various accessible parts of a stored engine. It is also used in clear plastic plugs, called dehydrator plugs, that can be screwed into engine openings, such as the spark plug holes. Cobalt chloride is added to the silica gel used in dehydrator plugs. This additive makes it possible 8-19 (Sacramento Sky Ranch). for the plugs to indicate the moisture content, or relative humidity, of the air surrounding the engine. The cobalt- chloride-treated silica gel remains a bright blue color with low relative humidity; as the relative humidity increases, the shade of the blue becomes progressively lighter, becoming lavender at 30 percent relative humidity and fading through the various shades of pink [Figure 8-18], until at 60 percent relative humidity it is a natural or white color. Some types of dehydrator plugs can be dried by removing the silica gel and heating the gel to dry it out, returning it to its original blue color. [Figure 8-19] When the relative humidity is less than 30 percent, corrosion does not normally take place.

Therefore, if the dehydrator plugs are bright blue, the air in the engine has so little moisture that internal corrosion is held to a minimum. This same cobalt-chloride-treated silica gel is used in humidity indicator envelopes. These envelopes can be fastened to the stored engine so that they can be inspected through a small window in the shipping case or metal engine container. All desiccants are sealed in containers to prevent their becoming saturated with moisture before they are used. Care should be taken never to leave the container open or improperly closed. Engine Preservation & Return to Service Before an engine is placed in temporary or indefinite storage, it should be operated and filled with a corrosion-preventive oil mixture added in the oil system to retard corrosion by coating the engine’s internal parts. Drain the normal lubricating oil from the sump or system and replace with a preservative oil mixture according to the manufacturer’s instructions. Operate the engine until normal operating temperatures are obtained for at least one hour.

Always take the appropriate precautions when turning or working around a propeller. After the flight, remove all the spark plug leads and the top spark plugs. To prevent corrosion, spray each cylinder interior with corrosion-preventive mixture to prevent moisture and oxygen from contacting the deposits left by combustion. Spray the cylinders by inserting the nozzle of the spray gun into each spark plug hole and playing the gun to cover as much area as possible. Before spraying, each cylinder to be treated should be at the bottom center position and the oil at room temperature. This allows the entire inside of the cylinder to become coated with corrosion-preventive mixture. After spraying each engine cylinder at bottom center, respray each cylinder while the crankshaft is stationary with none of the cylinder’s pistons at top dead center.

The crankshaft must not be moved after this final spraying, or the seal of corrosion-preventive mixture between the pistons and cylinder walls are broken. Air can then enter past the pistons into the engine. Also, the coating of corrosion- preventive mixture on the cylinder walls is scraped away, exposing the bare metal to possible corrosion. The engine should have a sign attached similar to the following: “DO NOT TURN CRANKSHAFT—ENGINE PRESERVED PRESERV ATION DATE ____________.” When preparing the engine for storage, dehydrator plugs are 8-20 Ventilator plug screwed into the spark plug opening of each cylinder. If the engine is to be stored in a wooden shipping case, the ignition harness leads are attached to the dehydrator plugs with lead supports. [Figure 8-20] Special ventilatory plugs are installed in the spark plug holes of an engine stored horizontally in a storage container. Any engine being prepared for storage must receive thorough treatment around the exhaust ports. Because the residue of exhaust gases is potentially very corrosive, a corrosion-preventive mixture must be sprayed into each exhaust port, including the exhaust valve. After the exhaust ports have been thoroughly coated, a moisture-proof and oil-proof gasket backed by a metal or wooden plate should be secured over the exhaust ports using the exhaust stack mounting studs and nuts. These covers form a seal to prevent moisture from entering the interior of the engine through the exhaust ports. Engines stored in metal containers usually have special ventilatory covers. Another point at which the engine must be sealed is the intake manifold. If the carburetor is to remain on the engine during storage, the throttle valve should be wired open and a seal installed over the air inlet.

But, if the carburetor is removed and stored separately, the seal is made at the carburetor mounting pad. The seal used in either instance can be an oil-proof and moisture-proof gasket, backed by a wooden or metal plate securely bolted into place. Silica gel should be placed in the intake manifold to absorb moisture. The silica gel bags are usually suspended from the cover plate. This eliminates the possibility of forgetting to remove the silica gel bags when the engine is eventually removed from storage. A ventilatory cover, without silica gel bags attached, can be used when the engine is stored in a metal container.

After the following details have been taken care of, the engine is ready to be packed into its container. If the engine has not been spray coated with corrosion-preventive mixture, the propeller shaft and propeller shaft thrust bearing must be coated with the compound. Then, a plastic sleeve, or moisture-proof paper, is secured around the shaft, and a threaded protector cap is screwed onto the propeller retaining nut threads. All engine openings into which dehydrator plugs (or ventilatory plugs if the engine is stored in a metal container) have not been fitted must be sealed. At points where corrosion-preventive mixture can seep from the interior of the engine, such as the oil inlet and outlet, oil-proof and moisture-proof gasket material backed by a metal or wooden plate should be used. At other points moisture-proof tape can be used if it is carefully installed.

Before its installation in a shipping container, the engine should be carefully inspected to determine if the following accessories, which are not a part of the basic engine, have been removed: spark plugs and spark plug thermocouples, remote fuel pump adapters (if applicable), propeller hub attaching bolts (if applicable), starters, generators, vacuum pumps, hydraulic pumps, propeller governors, and engine- driven fuel pumps. 1. Remove seals and all desiccant bags. 2. Remove cylinder dehydrators and plugs or spark plugs from upper and lower spark plug holes. 3. Remove oil sump drain plug and drain the corrosion preventive mixture. Replace drain plug, torque and safety. Remove oil filter. Install new oil filter, torque and safety. Service the engine with oil in accordance with the manufacturer’s instructions.

Warning: To prevent serious bodily injury or death, accomplish the following before moving the propeller: a. Disconnect all spark plug leads. b. Verify that magneto switches are connected to magnetos and that they are in the off position and P-leads are grounded. c. Throttle position CLOSED. d. Mixture control IDLE-CUT-OFF. e. Set brakes and block aircraft wheels. Ensure that aircraft tiedowns are installed and verify that the cabin door latch is open. f. Do not stand within the arc of the propeller blades while turning the propeller. 4. Rotate propeller by hand several revolutions to remove preservative oil.

5. Service and install spark plugs and ignition leads in accordance with the manufacturer’s instructions. 6. Service engine and aircraft in accordance with the manufacturer’s instruction. 8-21 Engine attachments Cover Base 7. Thoroughly clean the aircraft and engine. Perform visual inspection. 8. Correct any discrepancies. 9. Conduct a normal engine start. 10. Perform operational test in accordance with operational inspection of the applicable Maintenance Manual. 11. Correct any discrepancies. 12 Perform a test flight in accordance with airframe manufacturer’s instructions. 13. Correct any discrepancies prior to returning aircraft to service.

14. Change oil and filter after 25 hours of operation. Engine Shipping Containers For protection, engines are sealed in plastic or foil envelopes and can be packed in a wooden shipping case or in pressurized metal containers. The engine is lowered into the shipping container so that the mounting plate can be bolted into position. The protective envelope is attached directly to the base of the shipping case. Then, the engine is lowered vertically onto the base and bolted directly to it. A carburetor not mounted on its reciprocating engine (or no provision is made to seal it in a small container to be placed inside the shipping case) can, in some cases, be fastened to a specially constructed platform bolted to the engine.

Before the protective envelope is sealed, silica gel should be placed around the engine to dehydrate the air sealed into the envelope. The amount of silica gel used is determined by the size of the engine. The protective envelope is then carefully gathered around the engine and partially sealed, leaving an opening at one end from which as much air as possible is exhausted. A vacuum applied to the container is very useful for this purpose and is also an aid in detecting any leaks in the envelope. The envelope is then completely sealed, usually by pressing the edges together and fusing them with heat.

Before lowering the shipping case cover over the engine, a quick inventory should be made. Be sure the humidity indicator card is placed so that it can be seen through the inspection window and that everything required is enclosed in the container. While lowering the wooden shipping case cover into position, be careful that it does not twist and tear the protective envelope. Secure the cover and stencil or mark the date of preservation on the case. Also, indicate whether the engine is repairable or serviceable. There are several types of shipping containers in use. [Figure 8-21] Another type allows horizontal installation of an engine, thus eliminating the need for an extra hoist.

The engine is simply lowered onto the base portion of the container and secured. Then, silica gel bags are packed into the container, usually in a special section. The amount of silica gel required in a metal container is generally greater than that needed in a wooden shipping case, since the volume of air in the metal container is much greater than that in the protective envelope installed around an engine in a wooden shipping case. Also, in the metal container the silica gel bags must dehydrate the interior of the engine, since ventilatory plugs are normally installed in the engine openings in place of dehydrator plugs. All records of the engine should be enclosed inside the shipping container or on the outside for accessibility. A humidity indicator should be fastened inside the containers with an inspection window provided. Then, the rubber seal between the base and the top of the container must be carefully inspected. This seal is usually suitable for re-use several times. After the top of the container has been lowered into position and fastened to the base of the container, dehydrated air at approximately 5 pounds per square inch (psi) pressure is forced into the container. The container should be checked for leaks by occasional rechecks of the air pressure, since radical changes in temperature affect the air pressure in the container.

Inspection of Stored Engines Most maintenance shops provide a scheduled inspection system for engines in storage. Normally, the humidity indicators on engines stored in shipping cases are inspected every 30 days. When the protective envelope must be opened to inspect the humidity indicator, the inspection period may be extended to once every 90 days, if local conditions permit. The humidity indicator of a metal container is inspected every 180 days under normal conditions. If the humidity indicator in a wooden shipping case shows by its color that more than 30 percent relative humidity is present in the air around the engine, all desiccants should be replaced. If more than half the dehydrator plugs installed in the spark plug holes indicate the presence of excessive moisture, the interior of the cylinders should be resprayed.

If the humidity indicator in a metal container gives a safe blue indication, but air pressure has dropped below 1 psi, the container needs only to be brought to the proper pressure with 8-22 dehydrated air. However, if the humidity indicator shows an unsafe (pink) condition, the engine should be represerved. Preservation & Depreservation of Gas Turbine Engines The procedures for preserving and depreserving gas turbine engines vary depending upon the length of inactivity, the type of preservative used, and whether or not the engine may be rotated during the inactive period. Much of the basic information on corrosion control presented in the section on reciprocating engines is applicable to gas turbine engines.

However, the requirements for the types of preservatives and their use are normally different. The lubrication system is usually drained and may or may not be flushed with preservative oil. The engine fuel system is generally filled with preservative oil, including the fuel control. Before the engine can be returned to service, the preservative oil must be completely flushed from the fuel system by motoring the engine and bleeding the fuel system. Always follow the manufacturer’s instructions when performing any preservation or depreservation of gas turbine engines.