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2.18.7 T he First Engine Run.
2.18.7.1 The first start of the engine is always a critical operation. The engine should be pre-oiled using the manufacturer’s instructions. For aircraft using other than FAA-approved oil pressure and temperature gauges, the FAA recommends attaching an external calibrated oil temperature and pressure gauge to calibrate the engine instruments. After priming the engine and completing the starting engine checklist items, the first concern is to get an oil pressure reading within the first 20 to 30 seconds after engine start. If there is no oil pressure reading, shut down the engine.
2.18.7.2 There are three common problems that would cause low or fluctuating oil pressure.
1. Air in the oil pressure gauge line. This is easily fixed by loosening the line connection near the oil pressure gauge and squirting oil into the line until full. Another option is to use a pre-oiler to provide the pressure and carefully bleed the air out of the line near the oil gauge by loosening the B-nut connecting the oil line to the gauge.
2. A misadjusted oil pressure relief valve. Cleaning the pressure relief ball, checking for the proper number of washers, correcting spring tension, and re-adjusting the setting could solve the problem.
3. An internal problem within the engine, most likely the oil pump. An engine tear down would be required.
2.18.7.3 With good oil pressure/temperature readings and the engine running smoothly, ensure that the engine oil pressure and temperature gauges in the cockpit match the calibrated oil pressure and temperature gauges attached to the aircraft for the first run. Do not overlook this test. It is critical to determine the accuracy of the cockpit engine gauges not only for the ground engine run-in period, but also for in-flight engine cooling tests.
2.18.7.4 Work through the engine manufacturer’s run-in schedule. Most engine manufacturers recommend a series of engine runs from low rpm to maximum rpm. Each run usually incorporates a 200-rpm increase and lasts no longer than 10 minutes. The secret to a successful engine run is not to let the engine temperatures exceed manufacturer’s limits during engine runs.
Note: Engines with chrome cylinders or chrome rings require different high power run-in programs. Follow the manufacturer’s run-in instructions to ensure the engine will perform satisfactorily over its lifetime.
2.18.8 E ngine Cooldown. After a ground run, the cooling off period takes approximately an hour. This is because a newly overhauled engine needs time for the internal parts, such as rings, cylinders, valves, bearings, and gear faces, to expand and contract several times to obtain a smooth surface that retains its “memory.” This is a lengthy process even when done right, but it is important not to skip any of the recommended runs. You risk
2-38 increasing oil consumption and reducing overall engine performance, reliability, and engine life span—which could be costly in the long-term—if you skip any of the runs.
2.18.9 Record the Engine Run-In Data. During the engine run, monitor the CHTs, oil temperature, and oil pressure. Record the readings and adjustments for future reference.
If the CHTs are rising close to the red line, reduce power and stop the test. Some causes of high CHTs include:
• Using spark plugs with the improper heat range;
• CHT gauges installed on the wrong cylinder;
• Missing or badly designed cylinder head cooling baffles;
• Partially plugged fuel nozzles (applicable to fuel injected engines);
• Fuel lines of improper internal diameter (creates lean mixtures);
• Engine improperly timed either mechanically and/or electrically; and
• The carburetor fuel mixture set excessively lean.
2.18.10 Selecting Adjustments. Narrow down what adjustments need to be made by recording the change and its resulting effects. The record of the change and its effects are then used for making a logical decision for follow-on adjustments as needed to reach the proper engine performance parameters. Two ways of recording the engine performance parameters are:
2.18.10.1 Keeping a detailed paper log of each applicable engine instrument on each run-up.
2.18.10.2 Using an EFIS to record all engine performance indications for all engine runs in their entirety. EFIS for experimental aircraft may consist of either a standalone system or be connected to a multifunction display (MFD).
2.18.11 After Shut-Down.
2.18.11.1 After each engine run, check for fuel and oil leaks, loose connections, and hot spots on cylinders, which can be indicated by burnt paint. The FAA recommends draining the oil and removing the oil screen/filter within the first 2 hours of running the engine. Check the screen/filter for ferrous metal with a magnet. Wash and inspect the screen/filter for non-ferrous metal like brass, bronze, or aluminum.
2.18.11.2 A very small quantity of metal in the screen is not uncommon in a new or newly overhauled engine. It is part of the painful process of “running-in.” If subsequent oil screen checks—2 hours apart—show the engine is “making metal,” this indicates a problem inside the engine and a tear down inspection is required.
2.18.11.3 The FAA also recommends all fuel sumps, filters, and gascolators should be checked for debris after each engine run. Special attention should be given to
2-39 the fuel system by builders who use composite or fiberglass fuel tanks.
Composite and fiberglass strands can be very fine, making visual detection difficult. Frequent cleaning of the fuel filters and screens early in the flight testing phase will avoid a gradual buildup of loose composite fibers, which would reduce or stop the flow of fuel to the engine.
SECTION 11. ADDITIONAL ENGINE TESTS
2.19 Objective. All of the engine and fuel system tests and inspections should be listed and recorded on a checklist designed for that purpose. That document should note the completion of each of the above tests with information obtained during that test. Record the fuel flow, compression test, magneto timing, idle speed, oil pressure, hot and cold, etc. These checks will determine if the engine supply of fuel is adequate at all angles of attack.
2.19.1 Mi xture and Idle Speed Check . After completing the initial engine “run-in” tests, check the idle speed and mixture settings. To determine if the mixture setting is correct, perform the following:
2.19.1.1 W arm up the engine until all readings are normal.
2.19.1.2 Adjust the engine rpm to the recommended idle rpm.
2.19.1.3 Slowly pull the mixture control back to idle cut-off.
2.19.1.4 Just before the engine quits, the engine rpm should rise about 50 rpm if the mixture is properly adjusted. If the rpm drops off without any increase in rpm,
2-40 the idle mixture is set too lean. If the rpm increases more than 50 rpm, the idle mixture is set too rich.
2.19.1.5 Because most air-cooled aircraft engines need excessively rich fuel air mixtures to provide cooling for full-throttle operation, the condition should be confirmed. This is most easily accomplished by running the engine at full throttle (with the aircraft properly secured), manually leaning the mixture, and observing an increase in EGTs and in some cases an actual rise in rpm. While the amount of EGT rise is variable, the important aspect is that there is a rise of 25 to 50 degrees Fahrenheit (°F) or more. This will help alleviate engine overheating situations during the first few hours of inflight operation.
Note: Some amateur builders, after properly setting the idle mixture/rpm to the manufacturer’s specification, increase the engine idle rpm by 100 rpm for the first 10-plus hours of flight testing. This is to ensure that the engine will not quit when the throttle is pulled back too rapidly, or when power is reduced on the final approach to landing.
Be aware that in some situations, particularly with light wing loading or low drag types of aircraft, adding 100 rpm to the idle speed could cause the landing distance to be increased significantly and also have an unexpected adverse effect on landing behavior.
2.19.2 Mag neto Check.
2.19.2.1 The magneto checks should be smooth and the difference between both magnetos rpm drops should average about 50 rpm. The builder also should perform a “hot mag” check, to prevent unexpected engine self-starts. To perform this check, run up the aircraft until the engine is warm. At idle rpm, turn the magneto switch off, the engine should stop running. If the engine continues to run, one or both of the magnetos is not grounded, or “hot.”
2.19.2.2 The usual causes for a hot magneto are a broken “P” lead coming out of the magneto or a bad magneto switch. THIS IS AN IMMEDIATE THREAT TO
THE PERSONAL SAFETY OF ANYONE NEAR THE AIRPLANE AND SHOULD BE REPAIRED AT ONCE.
2.19.3 C old Cylinder Check.
2.19.3.1 The builder should perform a cold cylinder check if the engine is running rough and an ignition system problem could be contributing. A cold cylinder can be detected easily by switching magnetos and reading modern EGT monitors (if equipped) or by aiming a handheld laser thermometer at each exhaust stack. If you have neither one, perform the following:
1. Run the engine on the bad magneto for about 30 seconds at 1,200 rpm.
Without switching the mag switch back to “both,” shut off the engine.
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2. One of the test crew should quickly use a grease pencil to mark an area of the exhaust stacks approximately an inch from the flange that attaches the stacks to the cylinders.
3. Check the marks on the stacks. If one or more of the exhaust stacks with a grease mark has NOT been burned to a grayish-white color and the mark on the stack still retains most of the original color of the grease pencil, the “cold cylinder” has been identified.
2.19.3.2 Probable causes of the cold cylinder problem are: (1) defective spark plugs,
(2) ignition leads, or (3) a cracked distributor in one of the magnetos. To detect if the spark plugs are bad, switch both plugs to another cylinder. If the grease pencil proves the problem moved to the new cylinder, the spark plugs are bad. If the problem remains with the original cylinder, the ignition lead or magneto is bad.
2.19.4 Carburetor Heat.
2.19.4.1 The FAA strongly recommends that all amateur builders using a carbureted engine install a carburetor heat, or “carb heat,” system that complies with the engine manufacturer’s recommendation. If no recommendation is available, we suggest a carb heat system for a sea-level engine. A conventional venturi should be designed so that it will provide a 90 °F increase in the venturi at 75 percent power. For altitude engines using a conventional venturi carburetor, 120 °F increase in venturi temperature at 75 percent power will prevent or eliminate icing. Remember: Too little carb heat will have no effect on carburetor icing, and too much carb heat will cause an overly rich mixture which will reduce power and may shut down the engine.
2.19.4.2 During the engine tests, make numerous checks of the carb heat system. To avoid overly rich mixtures from oversized carb heat ducts, ensure that the carb heat duct is the same size as the inlet of the carburetor.
2.19.4.3 Be certain there is a positive reduction in rpm each time “carb heat” is applied. If there is no reduction, or the rpm drop is less than expected, check the carb heat control in the cockpit and on the carb heat air box for full travel.
Also, check for air leaks in the “scat tube” connecting the heat muff to the carburetor air box.
2.19.5 Fuel Flow. A fuel flow and unusable fuel check is a field test to ensure the aircraft engine will get enough fuel to run properly, even if the aircraft is in a steep climb or stall attitude, and is accomplished in the following manner:
2.19.5.1 Place the aircraft’s nose at an angle 5 degrees above the highest anticipated climb angle. The easiest and safest way to do this with a conventional gear aircraft is to dig a hole and place the aircraft’s tail in it. For a nose gear aircraft, build a ramp to raise the nose gear to the proper angle.
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2.19.5.2 Make sure the aircraft is tied-down and chocked. With minimum fuel in the tanks, disconnect the fuel line to the carburetor. The fuel flow with a gravity flow system should be 150 percent of the fuel consumption of the engine at full throttle. With a fuel system that is pressurized, the fuel flow should be at least 125 percent. When the fuel stops flowing, the remaining fuel is the “unusable fuel” quantity.
2.19.5.3 The formula for fuel flow rate for a gravity-feed fuel system is 0.55 times engine horsepower (hp) times 1.50. This gives a fuel flow rate in pounds of fuel per hour. Divide the pounds-per-hour number by 60 to calculate pounds per minute, and divide again by 6 to calculate gallons per minute. To get gallons per hour for Avgas divide pounds per hour by 6; or multiply gallons per minute by 60. For a pressurized system, substitute 1.25 for 1.50 to calculate the fuel flow rate.
2.19.5.4 The fuel consumption rate of most modern engines is about 0.55 pounds per hour per brake hp. Figure 2-8, 100 Hp Fuel Flow Rate Chart, illustrates the results of this calculation for a 100 hp engine:
Figure 2-8. 100 Hp Fuel Flow Rate Chart If your fuel is… Then the fuel flow rate for a 100 hp engine is… Pounds per hour Pounds per minute Gallons per hour Gravity feed 82.5 1.38* 13.75 Pressurized 68.75 1.15* 11.49* *-rounded to the nearest 100th.
2.19.6 Changing Fuel Flow or Pressure. If the aircraft’s fuel flow rate is less than planned, there is a volume or pressure problem. An increase in the fuel flow volume may necessitate installation of larger fuel line fittings on the fuel tanks, fuel selector, and carburetor in addition to larger internal diameter fuel lines. To increase fuel pressure, install an electrically driven or engine-driven mechanical fuel pump prior to the first flight.
2.19.7 C ompression Check . When the engine run-in procedures have been completed, perform an additional differential compression check on the engine and record the findings. If a cylinder has less than a 60/80 reading on the differential test gauges on a hot engine, that cylinder is suspect. Have someone hold the propeller at the weak cylinder’s top dead center and with compressed air applied, listen. If air is heard coming out of the exhaust pipe, the exhaust valve is not seating properly. If air is heard coming out of the air cleaner/carb heat air box, the intake valve is bad. When the oil dipstick is removed and air rushes out, the piston rings are the problem.
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2.19.8 L ast Check. Drain the oil and replace the oil filter, if applicable. Check the oil and screens for metal, visually inspect the engine, and do a run-up in preparation for the taxi tests. Do not fly the aircraft if anything is wrong, no matter how small or how insignificant. The sky, like the sea, is an unforgiving and uncompromising environment.
SECTION 12. PROPELLER INSPECTION
2.20 Objective. Help you develop an inspection program to maintain your propeller.
2.20.1 P ropeller Designs . There are three kinds of propeller designs: metal, wood, and composite. Because of weight considerations, metal propellers are used more on amateur-built aircraft than ultralight vehicles. Wood and composite propellers are the overwhelming choice for ultralight vehicles. Wood propellers are light, reliable, and inexpensive but require frequent inspections. Composite carbon-graphite material props are more expensive than wood, but are stronger and require less maintenance.
2.20.2 Choosing a Propeller. All types of propellers have one thing in common: they are constantly under high levels of vibration, torque, thrust, bending loads, and rotational stress. Even small nicks in the leading edge of the blade can very quickly lead to a crack, followed by blade separation. Propeller tip failure and a subsequent violent, out of balance situation can cause the propeller, engine, and its mounts to be pulled from the airframe in less than 5 seconds. Choose your make and model of propeller carefully. A propeller with the wrong size and pitch will give a poor rate of climb, cruise, or could cause the engine to “overspeed.” Always follow the manufacturer’s recommendations.
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2.21 Recommendations for All Propellers.
1. Never approach the vicinity of the propeller unless the ignition switches have been confirmed to be in the OFF position and the key is removed.
2. Never use a propeller for a tow bar when moving the aircraft.
3. Never stand in front of or in-line of a rotating propeller.
4. Never hand prop an engine on uneven or wet/snow covered ground.
5. Always inspect the propeller before and after a flight.
6. When working on a propeller, make sure the ignition is off first.
7. Always maintain the propeller to manufacturer’s instructions.
8. To avoid nicks and cuts, do not perform run-ups near gravel or loose stones.
9. Apply a coat of automotive wax once a month to protect the finish and keep out moisture.
10. Assume a propeller is unairworthy if it has suffered any kind of impact or ground strike.
11. After any repair or repainting, or if vibration or roughness is noted, re-balance the propeller.
12. Propeller blades should be balanced within 1 gram of each other to avoid over stressing the gear reduction system and propeller shaft.
13. A propeller should be re-torqued as per the propeller manufacturer’s recommendations. If there are no manufacturer’s recommendations available, check the bolt torque on all newly installed propellers every hour of operation for the first 10 hours and once every 5 hours thereafter.
14. After torqueing the propeller, track the blades.
2-45 Figure 2-9. Propeller Tracking
2.22 Propeller Tracking Check.
2.22.1 In stallation . Ensuring good powerplant operation starts with a properly installed propeller. You should check the propeller for proper tracking—the blades rotating in the same plane of rotation. The following procedure is simple and takes less than 30 minutes:
1. C hock the aircraft so it cannot be moved. Remove one sparkplug from each cylinder—this will make the propeller easier and safer to turn.
2. Rotate the blade so it is pointing straight down.
3. Place a solid object (e.g., a heavy wooden block that is at least a couple of inches higher off the ground than the distance between the propeller tip and the ground) next to the propeller tip so it just touches.
4. Rotate the propeller slowly to see if the next blade “tracks” through the same point (touches the block, see Figure 2-9). Each blade should be within 1⁄16 inch from one another.
2.22.2 T racking. If the propeller is out of track, one or more propeller blades may be bent, a propeller flange may be bent, or propeller mounting bolts may be over or under torqued.
An out-of-track propeller will cause vibration and stress to the engine and airframe and may cause premature propeller failure.
2.23 Met al Propeller Inspection. Perhaps the two biggest problems affecting the airworthiness of metal propellers are corrosion and nicks on the leading edge.
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2.23.1 Identifying Corrosion.
2.23.1.1 Surface corrosion can occur on the surface of metal blades due to a chemical or electrochemical action. The oxidation product usually appears on the surface of the metal as a white powder.
2.23.1.2 Pitting corrosion causes small cavities or pits extending into the metal surface.
This is an advanced form of corrosion, appearing as small dark holes that usually form under decals or blade overlays.
2.23.1.3 Intergranular corrosion, rare and difficult to detect in propellers, is the most dangerous form of corrosion. It attacks the boundary layers of the metal, creating patches of lifted metal and white/gray exfoliation on the surface of the propeller. It is sometimes found in propellers that have had a ground strike and have been straightened.
2.23.1.4 If any of these signs of corrosion are found, do NOT fly the aircraft. Refer to the manufacturer’s maintenance manual for corrosion limits and repairs or AC 43-4, Corrosion Control for Aircraft, and AC 20-37, Aircraft Propeller Maintenance, for additional maintenance information and corrective actions.
2.23.2 N icks and Metal Blades.
2.23.2.1 Nicks in the leading and trailing edge of a metal blade are usually V-shaped.
They are caused by high-speed impact between the propeller and a stone or piece of gravel. Properly trained individuals can “dress out” the nick or pit if the nick is not too wide and/or deep. Before each nick is dressed out, each nick and surrounding area should be inspected with a 10-power magnifying glass for cracks. If an area looks suspicious, inspect the area again using the propeller manufacturer’s approved dye penetrant or fluorescent penetrant method.
2.23.2.2 If the nick is left unattended, the high propeller operational stresses will be concentrated at the bottom of the nick’s V and, in time, will generate a crack.
The crack can migrate across the blade until the blade fails, producing a massive imbalance between the propeller and the engine, ultimately causing structural failure. Cracks in metal blades cannot be repaired. A cracked propeller is marked unserviceable and discarded.
Warning: Metal propellers are matched/tuned to the engine and airframe resonant frequency by being manufactured with a particular diameter to minimize vibration. DO NOT SHORTEN METAL BLADES for any reason unless the manufacturer specifically permits this major alteration.
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2.24 Wood Propeller Inspection.
2.24.1 Inspection Frequency. Wood propellers should be inspected before and immediately after a flight. Inspect to ensure the following:
1. The drain holes are open on metal edged blade tips.
2. The metal/composite leading edge is secured and serviceable.
3. The blades, hub, and leading edge have no scars or bruises.
4. The mounting bolt torque and safety wire or cotter pins are secure.
5. There are no cracks on the propeller spinner (if applicable), and the safety wire is secure.
6. There are no small cracks in the protective coating on the propeller. Ultraviolet radiation can cause these cracks.
7. There is no charring around either the mating surface of the prop and engine flange.
Charring in either location indicates a loose propeller.
2.24.2 Torque Check. You should check for proper torque on the mounting bolts of a new, wooden propeller within the first hour of flight and every hour for 10 operational hours thereafter per the propeller manufacturer’s recommendations.
2.24.2.1 Refer to the manufacturer’s recommendations for re-torque procedures and intervals. If there are no manufacturer’s recommendations, after 10 hours, check the bolt torque after every 5 hours of operation. You should also check the mounting bolt torque before flight if the aircraft has been in storage for 3 to 6 months.
2.24.2.2 If you need to torque the bolts, we suggest that all the bolts be loosened for an hour to allow the wood to relax. “Finger tighten” the bolts until snug and tighten the attaching bolts in small increments, moving diagonally across the bolt circle. It is good practice to check the propeller track (see paragraph 2.22) as the bolts are torqued down. The torqued bolts should be safety wired in pairs. Check the blade track in accordance with the manufacturer’s recommendations when a re-torque is accomplished on wood propellers.
AC 43.13-1, Acceptable Methods, Techniques, and Practices—Aircraft Inspection and Repair, Chapter 8, Engines, Fuel, Exhaust, and Propellers, contains information to assist the aircraft owner in properly maintaining and inspecting the propeller installation.
2.24.2.3 If nylon/fiber insert type nuts are used, you should change them every time you re-torque the propeller bolts. Never match this type of nut to a bolt with a cotter key hole in its threaded area—the sharp edges around the hole will cut the nylon/fiber insert and reduce the fastener’s effectiveness. All self-locking nuts should have at least two bolt threads visible past the nylon/fiber insert after torqueing.
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2.24.3 W ood Propeller Repairs. You should remove a wood propeller from an aircraft and send it either back to the manufacturer or to an appropriately certificated FAA Repair Station for repair if any of the following damage is found:
1. A ny cracks in the blades or hub;
2. Deep cuts across the wood grain;
3. Blade track that exceeds 1⁄16 inch limits after attempts to repair;
4. Any warpage or obvious defect;
5. Extreme wear such as leading edge erosion or bolt hole elongation; and
6. Any separation between lamination.
Note: When parking the aircraft, always leave the wood propeller in the horizontal position. This position will allow the wood to absorb small amounts of moisture evenly across its entire span rather than concentrating the moisture (weight) in the low blade and creating a vibration problem.
2.25 Composite Propeller Inspection. There are generally two types of composite propellers:
thermoplastic injection-molded propellers and carbon/graphite fiber composite propellers.
2.25.1 T hermoplastic. The thermoplastic injection -molded propeller is a low cost, thin bladed propeller used on engines of 80 hp or less. Propeller inspection is straightforward:
examine blades and hub for cracks and nicks. If a crack is found, do not fly until the propeller is replaced. Small nicks of 3⁄16 inch or less can be dressed out and filled with a two-part epoxy.
2.25.2 Carbon/Graphite. The carbon/graphite composite propellers are generally used on engines of 40 hp and more. You should look for hairline cracks in the gel coat. Spider cracks are usually caused by vibration generated by a mismatch of the engine and propeller combination. If you find a crack in the base material of the propeller—other than the gel coat—do not fly until the manufacturer or other appropriately certificated entity/person inspects the propeller.
2.25.2.1 N icks of ½ inch or less in the leading or trailing edges of carbon/graphite propellers can be dressed out and filled using a two-part epoxy. But if the nick has severed the fiberglass roving—which looks like a fiberglass wire bundle—that runs hub to tip on the leading and trailing edge, do not fly. The propeller has severe damage and is sent back to the manufacturer or other appropriately certificated entity/person for inspection and repair.
2.25.2.2 Before making even small repairs on a composite propeller, check with the manufacturer.