18 5/24/95AC 90-89A SECTION 9. PAPERWORK ‘‘It is harder to write a lie in a logbook than tell one, because your eyes see it and your fingers feel it.’’ Bob Moorman, Ultralight Instructor (1994)
1. OBJECTIVE. To have the proper documentation and paperwork to conduct the flight test.
a. Weight and Balance: The weight and balance for the aircraft should be carefully done. The gross weight and CG range should be determined prior to every flight.
b. Airworthiness/Registration/Operating Limitations/Placards/Weight and Balance: Must be on board, or the aircraft is not legal to be operated.
c. Checklists: In addition to the assembly/airworthiness checklist previously discussed in section 7, the builder should prepare the following checklists: preflight; take-off/cruise; before starting;
descent/before landing; starting the engine; after landing; before takeoff; securing the aircraft; and emergency procedures. A checklist to cover the above procedures may seem a tedious task, but it will only be the size of a 5x8 card -- similar to a checklist for a Cessna 150 or a Piper PA-28-140.
NOTE: The amateur-builder should anticipate several revisions to the checklists.
d. Flight Manual: It is imperative a flight manual describing the anticipated performance of the aircraft be written by the aircraft builder/kit manufacturer. The manual will be revised several times during the flight test phase until it accurately reports the aircraft’s performance.
e. Maintenance Records (logbooks): Operators of amateur-built aircraft are required to only record the yearly condition inspections in accordance with the aircraft’s operating limitations. The FAA recommends, however, that every amateur-built aircraft/ultralight owner record in the aircraft’s logbooks all inspections and maintenance performed.
This will create an aircraft’s maintenance history and will be invaluable in spotting trends.
19 SECTION 10. POWERPLANT TESTS ‘‘Don’t short-change the engine tests or you won’t be around to give your grandkids a ride.’’ Dick Koehler, A&P Instructor (1994)
1. OBJECTIVE. To ensure that the engine has been properly run-in and is safe to operate in all rpm ranges.
a. An engine pre-oil and cold compression test can be conducted as follows:
(1) Remove the rocker-box covers and one spark plug from each cylinder.
(2) Using an external oil pump, or by rotating the propeller in the direction of rotation, pump a substantial supply of oil up from the sump into the rocker arms.
(3) When the engine is pre-oiled, run a cold compression test of each cylinder.
(4) The results will serve only as an initial bench mark for comparing other compression tests taken after the engine has been run-up to operating temperature.
b. New/newly overhauled engine run-in procedures:
(1) Most amateur-builders start with a new or newly overhauled engine and proceed to ‘‘run it in’’ on the airframe. This practice is followed due to lack of access to a test cell or a special ‘‘club’’ propeller that is specifically designed to aid in engine cooling during run-in. There are pros and cons to using an airframe to run in an engine, but the best advice has always been to follow the engine manufacturer’s instructions. These instructions are found either in the manufacturer’s overhaul manuals, service bulletins, or service letters. Following the manufacturer’s instructions is especially important if the engine has chrome cylinders which require special run-in procedures.
(2) Also, before running-up the engine, be certain that it has the proper grade oil in the sump.
Some new and newly overhauled engines are shipped with a special preservative oil to prevent corrosion.
20 5/24/95AC 90-89A Drain this out and reservice the engine with the correct oil before starting.
c. Used engine run-in procedures: Some amateur-builders install a used engine from a flyable aircraft. The same checks and adjustments used on a new or newly overhauled engine should be conducted. New and used engines require special attention to engine cylinder baffling to ensure cylinder cooling is within the engine manufacturer’s cylinder head temperature specifications.
d. Pre run-in checks:
(1) Before beginning the powerplant tests, inspect the engine and propeller carefully. All fuel and oil line connections should be tight. Check the torque on the engine mount attaching bolts. Be certain that there are no tools, hardware, or rags laying between the cylinders or under the magnetos.
(2) Check for the proper amount of oil in the engine and that the dip stick gives an accurate reading of the oil quantity. Be advised that some engines were mounted on an angle in type certificated aircraft. These engines have a special part number oil dip stick, which corrects for the different angle of oil in the crankcase. The same engine, mounted level in a amateur-built aircraft with the original dip stick, will not show the correct oil quantity.
e. Test and Support Equipment:
(1) A cylinder head temperature gauge (CHT) is needed to ensure that all cylinders are receiving the proper flow of cooling air.
(2) On the newer aircraft engines, the cylinders are drilled and tapped to accept a bayonet type of CHT thermocouple probes. For older engines, the thermocouple is designed like a spark plug washer and fits under a spark plug. It can be installed in any cylinder, either under the top or bottom spark plug.
(3) Each type of CHT design can have multiple thermocouples which are connected to a selector switch in the cockpit. The pilot then selects the cylinder he wants to monitor. This also is an excellent troubleshooting tool for identifying fouled plugs and bad ignition leads.
(4) If there is only one CHT thermocouple, attach it to the rearmost cylinder on the right side of the engine (as viewed from the cockpit) and runup the engine. Run the same test on the opposite rearmost cylinder to be certain the hottest running cylinder was selected. Calibrated oil pressure and oil temperature gauges also are needed to test the accuracy of the engine instruments installed in the aircraft.
(5) The following support equipment is needed: 50 feet or more of tie-down rope, tie-down stakes, two chocks for each wheel, fire extinguisher, assorted hand tools, safety-wire, cotter-pins, ear and eye protection, grease pencils, logbooks, clip board, pen and paper, a watch to time the tests, rags, and manufacturer’s instructions.
f. Safety Precautions: Before the first engine run, ensure the aircraft is tied down, brakes on, and the wheels are chocked. The builder and flight test team should wear ear and eye protection. All flight test participants should be checked out on fire extinguisher use and operation. During engine runs, do not allow anyone to stand beside the engine, or inline or close to the propeller. Making minor adjustments to a running engine, such as idle and mixture settings, is a very dangerous procedure and should be done with great care by experienced individuals.
g. The First Engine Run:
(1) The first start of the engine is always a critical operation. The engine should be pre-oiled in accordance with 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 the 4 cycle engine in order 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. If there is no oil pressure reading -- shut down.
(2) There are three common problems that would cause low or fluctuating oil pressure.
(i) 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 preoiler to provide the pressure and carefully bleed the air out of the line near the oil gauge by loosening the B-nut that connects the oil line to the gauge.
(ii) 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.
(iii) An internal problem within the engine (most likely the oil pump): An engine tear down would be required.
(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, which were 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 runin period, but for in-flight engine cooling tests.
(4) Work through the engine manufacturer’s run-in schedule. The majority of the 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 manufacture’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.
h. Engine Cool Down: 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 (e.g., 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 to save time. To do so is to risk increasing oil consumption and reducing overall engine performance, reliability, and engine life span -- which could be costly in the long-term.
i. Record the engine run-in data: During the engine run, monitor the cylinder head temperatures, oil temperature, and oil pressure. Record the readings and adjustments for future reference. If the cylinder head temperatures are rising close to the red line, reduce power and stop the test. Some causes of high cylinder head temperatures include using spark plugs with the improper heat range; cylinder head temperature 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.
j. After shut-down:
(1) After each engine run, check for fuel and oil leaks, loose connections, and hot spots on cylinders (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) 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.
(3) It also is recommended all fuel sumps, filters, and gasolators be checked for debris after each engine run. Special attention should be given to the fuel system by the builder who constructed fuel tanks out of composite or fiberglass materials.
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 build up of loose composite fibers, which would reduce or stop the flow of fuel to the engine.
22 5/24/95AC 90-89A SECTION 11. ADDITIONAL ENGINE TESTS ‘‘Always go with the best fix not the cheapest fix.’’ Bill Deeth, Master Mechanic (1994)
1. OBJECTIVE. To determine if the engine supply of fuel is adequate at all angles of attack.
a. Mixture 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:
(1) Warm up the engine until all readings are normal
(2) Adjust the engine rpm to the recommended idle rpm
(3) Slowly pull the mixture control back to idle cut-off
(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, the idle mixture is set too lean. If the rpm increases more than 50 rpm, the idle mixture is set too rich.
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 + 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.
b. Magneto Check:
(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 ensure against the engine, on its own, deciding when and where to start. To perform a hot mag 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 hot (not grounded).
(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 ANY-
ONE NEAR THE AIRPLANE AND MUST BE REPAIRED AT ONCE.
c. Cold Cylinder Check:
(1) If the engine is running rough and the builder determines it may be an ignition problem, perform the following check:
(i) Run the engine on the bad magneto for about 30 seconds at 1200 rpm. Without switching the mag switch back to ‘‘both,’’ shut off the engine.
(ii) 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.
(iii) 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) Probable causes of the cold cylinder problem are defective spark plugs, ignition leads, or 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.
d. Carburetor Heat:
(1) It is strongly recommended that all amateur-builders install a carburetor heat system that complies with the engine manufacturer’s recommendation. If no recommendation is available, the FAA suggests a carburetor heat system for a sealevel engine and a conventional venturi should be designed so that it will provide a 90 degrees F increase in the venturi at 75 percent power. For altitude engines using a conventional venturi carburetor, 120 degrees F increase in venturi temperature at 75 percent power will prevent or eliminate icing.
Remember: Too little carburetor heat will have no effect on carburetor icing, and too much carburetor heat will cause a overly rich mixture which will reduce power and may shut down the engine.
(2) During the engine tests, make numerous checks of the carburetor heat system. To avoid overly rich mixtures from oversized carburetor heat ducts, ensure that the carburetor heat duct is the same size as the inlet of the carburetor.
(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’’ that connects the heat muff to the carburetor air box.
e. Fuel Flow and Unusable Fuel Check: This 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.
(1) First, 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.
(2) Make sure the aircraft is tied-down and chocked. With minimum fuel in the tanks, disconnect the fuel line to 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.
(3) Since the fuel consumption of most modern engines is approximately .55 pounds per brake horsepower per hour for a 100 horsepower engine, the test fuel flow should be 82.5 pounds (13.7 gallons) per hour for gravity feed, or 68.75 pounds
(11.5 gallons) per hour for a pressurized system. The pounds per hour divided by 60 equals 1.4 pounds and 1.15 pounds per minute fuel rate respectively.
NOTE: Formula for fuel flow rate gravity feed is .55 x engine horsepower x 1.50 = pounds of fuel per hour divided by 60 to get pounds per minute, divided by 6 to get gallons per minute. For a pressurized system, substitute 1.25 for 1.50 to determine fuel flow rate.
f. Changing Fuel Flow or Pressure: If the aircraft’s fuel flow rate is less than planned, there
24 5/24/95AC 90-89A 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.
g. Compression Check: When the engine runin procedures have been completed, perform an additional differential compression check on the engine and record the findings. If a cylinder has less than 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 still being 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 dip stick is removed and air rushes out, the piston rings are the problem.
h. Last 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 runup 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.
25 SECTION 12. PROPELLER INSPECTION ‘‘A tough decision is what a man makes when he cannot form a committee to share the blame’’ George Lutz, Col. U.S. Air Force, Retired (1994)
1. OBJECTIVE. To help the amateur-builder/ ultralight aircraft owner develop an inspection program to maintain his/her propeller.
a. There are three kinds of propeller designs:
metal, wood, and composite.
(1) Because of weight considerations, metal propellers are used more on amateur-built aircraft than ultralight aircraft. This makes wood and composite propellers the overwhelming choice for ultralight aircraft.
(2) Wood propellers are light, reliable, and inexpensive but require frequent inspections.
(3) Composite carbon-graphite material props are more expensive than wood, but are stronger and require less maintenance.
b. 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.
c. It is essential that the make and model propeller is carefully chosen. Always follow the manufacturer’s recommendations.
d. Exercise caution if experimenting with different makes and models propellers. A propeller with the wrong size and pitch will give a poor rate of climb, cruise, or could cause the engine to ‘‘overrev.’’
2. RECOMMENDATIONS FOR ALL PROPELLERS.
a. Never use a propeller for a tow bar when moving the aircraft.
b. Never stand in front of or in-line of a rotating propeller.
26 5/24/95AC 90-89A
c. Never ‘‘PROP’’ an engine on uneven or wet/snow covered ground.
d. Always inspect the propeller before and after a flight.
e. When working on a propeller, make sure the ignition is off first.
f. Always maintain the propeller to manufacturer’s instructions.
g. To avoid nicks and cuts, do not perform run-ups near gravel/loose stones.
h. Apply a coat of automotive wax once a month to protect the finish and keep out moisture.
i. Assume a propeller is unairworthy if it has suffered any kind of impact or ground strike.
j. After any repair or repainting, or if vibration or roughness is noted, re-balance the propeller.
k. Propeller blades should be balanced within 1 gram of each other to avoid over stressing the gear reduction system and propeller shaft.
l. Check the bolt torque on all newly installed propellers every hour of operation for the first 10 hours and once every 5 hours thereafter.
m. After torquing the propeller, track the blades.
FIGURE 5 - Propeller Tracking
3. PROPELLER TRACKING CHECK.
a. Ensuring good powerplant operation first starts with a properly installed propeller. Each propeller should be checked for proper tracking (blades rotating in the same plane of rotation). The following procedure is simple and takes less than 30 minutes:
(1) Chock 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 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). Each blade should be within 1⁄16’’ from one another.
b. If the propeller is out of track, it may be due to one or more propeller blades that are bent, a bent propeller flange, or propeller mounting bolts that are 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.
4. METAL PROPELLER INSPECTION Perhaps the two biggest problems affecting the airworthiness of metal propellers are corrosion and nicks on the leading edge.
a. Identifying Corrosion.
(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) 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.
(3) Inter-granular 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 had a ground strike and have been straightened.
(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 20-37D, ‘‘Aircraft, Metal Propeller Maintenance,’’ for additional maintenance information and corrective actions.
b. Nicks and Metal Blades.
(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 crack 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) 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 must be marked unserviceable and discarded.
c. 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.
5. PROPELLER INSPECTION.
a. 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, which are caused by UV radiation
(7) The charring around the mating surface of the prop and the engine flange -- both indications of a loose propeller
b. A word about torque: A new, wooden propeller should have the mounting bolts checked
28 5/24/95AC 90-89A for proper torque within the first hour of flight and every hour for 10 operational hours thereafter.
(1) After 10 hours, check the bolt torque every 5 hours thereafter. The mounting bolt torque also should be checked prior to flight if the aircraft has been in storage for a long period of time (3 to 6 months).
(2) If the bolts need to be torqued, it is suggested 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 chapter 1, section 7) as the bolts are torqued down.
The torqued bolts should be safety wired in pairs.
(3) If nylon/fiber insert type nuts are used, they should be changed every time the propeller bolts are re-torqued. They should never be used with a bolt with a cotter key hole in the threaded area because 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 pass the nylon/fiber insert after torquing.
(4) If any of the following damage is found, a wood propeller should be removed from the aircraft and sent back to the manufacturer for repair. If the propeller cannot be saved, it should be marked unserviceable.
(i) Any cracks in the blades or hub
(ii) Deep cuts across the wood grain
(iii) Blade track that exceeds 1⁄16’’ limits after attempts to repair
(iv) Any warpage or obvious defect
(v) Extreme wear (leading edge erosion, bolt hole elongation)
(vi) 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 it’s entire span rather than concentrating the moisture (weight) in the low blade and creating a vibration problem.
6. COMPOSITE PROPELLERS INSPECTION.
a. There are generally two types of composite propellers: thermo-plastic injection molded propeller and the carbon/graphite fiber composite propeller.
(1) The thermo-plastic injection molded propeller is a low cost, thin bladed propeller used on engines of 80 horsepower or less. Propeller inspection is straight forward, by examining the 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 of an inch or less can be dressed out and filled using a two-part epoxy.
(2) Carbon/graphite composite propellers are primarily used on engines of 40 horsepower and more. One should inspect for small hair line cracks in the gel coat. These spider cracks are usually caused by vibration generated by a mismatch of the engine and propeller combination. If a crack in the base material of the propeller other than the gel coat is found, do not fly until the manufacturer inspects the propeller.
(i) Nicks of 1⁄2 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 (looks like a fiberglass wire bundle) that runs hub to tip on the leading and trailing edge, do not fly. The propeller has been severely damaged and must be sent back to the factory for inspection and repair.
(ii) Before making even small repairs on a composite propeller, check with the manufacturer first. Larger nicks must go back to the factory for inspection and repair.
29 CHAPTER 2. TAXI TESTS SECTION 1. LOW SPEED TAXI TESTS ‘‘Yelling ’Clear the Prop!’ before you start an aircraft is the first of a series of well planned, choreographed steps to make you a professional.’’ Jack Crawford, Pilot, Mechanic, Airport Operator (1994)
1. OBJECTIVES. The objectives of the taxi tests are fourfold:
a. To ensure that the aircraft ‘‘tracks’’ straight and there is adequate directional control at 20 percent below the anticipated take-off speed.
b. To determine if the aircraft’s engine cooling and the brake system are adequate.
c. To predict the flight trim of the aircraft and its handling characteristics during take off and landings.
d. To allow the pilot to become proficient with the handling and braking characteristics of the aircraft.
NOTE: All taxi tests, low and high speed, should be made as if it were the first flight.
The pilot should be wearing the proper clothing, seat belt/shoulder harness and helmet and be mentally and physically prepared for the possibility of flight.
2. TAXI TESTS.
a. Prior to beginning taxi tests in a conventional (tail dragger) aircraft, the tail should be raised until the aircraft is in the approximate take-off 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.
NOTE: All taxi tests should always be monitored by a minimum of one other member of the flight test team, who will watch for evidence of fire/smoke or other problems not visible to the pilot.
b. The taxi tests should begin with a taxi speed no faster than a man can walk. The pilot should spend this time getting acquainted with the aircraft’s low speed handling characteristics by practicing 90, 180, and 360 degree turns and braking action. The pilot should also remember that monitoring the oil pressure, oil temperature, cylinder head temperature, and maintaining them within limits is a critical function that must not be overlooked.