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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.
3-1 CHAPTER 3. TAXI TESTS SECTION 1. LOW-SPEED TAXI TESTS
3.1 Ob jective. Ensure that the aircraft “tracks” straight and there is adequate directional control at 20 percent below the anticipated takeoff speed. Determine if the aircraft’s engine cooling and the brake system are adequate. Predict the flight trim of the aircraft and its handling characteristics during takeoff and landings. Enable the pilot to become proficient with the handling and braking characteristics of the aircraft.
Note: You should conduct a low- or high-speed taxi test as if it were the first flight. The pilot should be wearing the proper clothing, seatbelt/shoulder harness, and helmet and be mentally and physically prepared for the possibility of flight.
3.2 Taxi Tests.
3.2.1 Preparation. Before taxi tests in a conventional, or tailwheel, aircraft, the tail should be physically raised until the aircraft is just about in the takeoff position. The pilot should spend an hour or more in the cockpit to become accustomed to the aircraft’s takeoff position. This small but important aspect of training will help the pilot avoid overreacting to an unexpected deck angle on the first flight. Now is the time for the pilot at the controls to have identified all the controls and devices necessary to fly the aircraft. The checklist should be in an advanced state of development, the seating and seatbelts fully fitted, and the seat height position established. Seating the pilot too low is a major problem in properly identifying pitch attitude during operation.
Note: A minimum of one other f light test team member should always be monitoring taxi tests. This team member can watch for evidence of fire/smoke or other problems the pilot can’t see.
3.2.2 Beginning the Test. The taxi tests should begin with a taxi speed no faster than a walk.
The pilot should spend this time getting acquainted with the aircraft’s low speed handling
3-2 characteristics by practicing 90-, 180-, and 360-degree turns and braking action. The pilot should also remember the importance of monitoring the oil pressure, oil temperature, and CHT, and maintaining them within limits, and should not overlook these checks.
Note: Some aircraft brake manufacturers have specific brake lining conditioning procedures (break-in) for metallic and non-asbestos organic linings. You should complete proper brake lining conditioning before starting the low- and high-speed taxi tests. If not properly conditioned, the brake lining will wear quickly and give poor braking action at higher speeds.
3.2.3 I nstrument Check. The pilot should check the flight instruments for operation each time the pilot taxies the aircraft. The compass should match the direction in which the aircraft is pointed, such as the magnetic heading of the runway or taxiway. When making a right hand turn, the turn coordinator/turn and bank should indicate a right turn but the ball should skid to the left. The vertical speed indicator should read zero and the artificial horizon should indicate level.
3.2.4 After Taxi Run. A fter each taxi run, inspect the aircraft for oil and brake fluid leaks. You should not consider a leak as a minor problem, but repair every leak and service the system before the next taxi test.
SECTION 2. HIGH-S PEED TAXI TESTS
3.3 Objective. Determine the aircraft’s high-speed handling and braking parameters.
3.3.1 D irection of Rotation . Propeller rotation will determine which rudder pedal you press to compensate for the asymmetrical thrust of the propeller blades. For example, when viewed from the cockpit, a Volkswagen automotive engine mounted in a tractor configuration will rotate the propeller counterclockwise. In this case, the pilot would use the left rudder pedal for high-speed taxi and takeoff. For a propeller turning clockwise, you would apply right rudder pedal.
3.3.2 Follow the Flight Test Plan. A s with every part of the flight testing program, the high-speed taxi tests should follow the flight test plan. Start slowly and do not progress to the next step until the flight test team is thoroughly satisfied with the aircraft and the team’s performance.
3.3.3 Increasing Taxi Speed. E ach taxi run should be 5 mph faster than the last run until the aircraft is within 80 percent of the predicted stall speed. Prior to reaching the predicted stall speed, the pilot should test aileron effectiveness by attempting to rock the wings slightly. As taxi speeds increase, the rudder becomes more responsive and directional control will improve.
3.3.3.1 I n a nose gear aircraft, the pilot should be able to raise the nose of the aircraft at 80 percent of the predicted stall speed. If the nose cannot be raised at this speed, the W&B and CG range should be rechecked. Most likely, there is a forward CG problem or the main gear is too far aft.
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3.3.3.2 In a tailwheel aircraft at 80 percent of stall speed, the pilot should be able to lift the tail and assume a takeoff position. Again, if the tail cannot be raised, recheck the W&B and CG range. Most likely, there is a rearward CG problem or the main gear is too far forward.
Caution: Heavy braking action at high speeds in tailwheel aircraft may cause directional problems, such as ground loops or nose overs.
3.3.4 T axi with Flaps. If runway conditions permit, duplicate each taxi test with the flaps in the takeoff and landing configuration. Record the flap effects on directional control and insert the information in the draft copy of the AOH.
3.3.5 Lift-O ff Point. Estimate the point on the runway where lift-off will occur and mark it with a green flag if no other existing reference is available.
3.3.6 Braking Distance.
3.3.6.1 Determine how much runway the pilot will need if it becomes necessary to abort the takeoff. This is usually accomplished by accelerating to 80 percent of lift-off speed, bringing the engine back to idle, and applying heavy braking action to bring the aircraft to a full stop. After a takeoff/abort test, give the brakes time to cool down. The brake lining should be examined carefully and replaced if necessary.
3.3.6.2 After determining the distance required to come to a full stop after aborting, add 30 percent to the distance. Measure that distance from the opposite end of the active runway. If no existing reference is available, mark it with a red flag.
The taxi tests are completed when the test pilot is satisfied with both the aircraft’s and the test pilot’s individual performance. Before the first flight, you should thoroughly inspect the aircraft and give special attention to the landing gear, brake system, engine, and propeller.
3.3.7 R epairs. During this inspection, ensure all discrepancies have been corrected. Examine the screens/filters for metal, flush the fuel system, and clean all the screens/filters.
Perform a leak check on the engine and the fuel system by running-up the engine.
Note 1: T he first high -speed taxi tests should be made in a no wind or a light headwind condition. The pilot should ensure that the tests will not interfere with the normal airport operations or create a safety hazard for other aircraft.
Note 2: Pilots of tailwheel aircraft should always be aware that ground loops are possible at any speed. This is true especially if the main landing gear is located too far forward of the aircraft’s CG.
4-1 CHAPTER 4. THE FIRST FLIGHT S ECTION 1. GENERAL
4.1 Objective. Take every precaution to ensure that the first test flight is an uneventful one.
4.2 General.
4.2.1 The first flight is an important event for you. As important as it is, it should not be turned into a social occasion. This puts enormous peer pressure on the pilot to fly an aircraft that may not be airworthy or to conduct the flight in inclement weather.
4.2.2 A professional will avoid this trap by following the flight test plan and inviting only those members of the crew needed to perform specialized tasks when testing the aircraft.
4.2.3 The first flight should be flown a thousand times: the first 500 on paper, the next 499 flights in the test pilot’s mind, and once in actuality. The first flight test should be so well-rehearsed by the test pilot and ground crew that the first flight is a non-event.
4.3 Recommendations.
4.3.1 The best time to test fly an aircraft is usually in the early morning when the winds are calm, and the pilot is well rested.
4.3.2 In addition to a pilot’s kneeboard, a small portable tape recorder or video camera properly mounted to the aircraft is an excellent way to record data.
4.3.3 Good communication with the ground is essential for data exchange and safety.