Chapter 11
Light-Sport Aircraft Engines
Propeller gearbox torque examples
Linear form: Example of minimum torque: F × L = 20 N × 0.76 m = 15 Nm. Example of maximum torque: F × L = 59 N × 0.76 m = 45 Nm.
by the dog gears in the torsional shock absorption unit.
Turn the propeller by hand back and forth between ramps, taking into consideration the friction torque. No odd noises or irregular resistance must be noticeable during this movement. Attach a calibrated spring scale to the propeller at a certain distance (L) from the center of the propeller. Measure the force required to pull the propeller through the 15 or 30 degree range of free rotation. Calculate friction torque Nm by multiplying the force Newton’s (N) or pounds (lb) obtained on the spring scale by the distance the scale is attached from the center of the propeller (L). The distance measurement and torque measurement must be in the same units either standard or metric and cannot be mixed up. The friction torque must be between a minimum of 25 Nm and maximum of 60 Nm (18.5 to 44.3 ft/lb). A calculation example is as follows:
Friction torque worked example
Linear form: Friction Torque (FT) = Length (meters) × Torque (Newtons); FT = 0.5 meters × 60 Newtons; FT = 30 Nm
Source note: The formula box prints 'Torque (Newtons),' while the surrounding paragraph identifies the measured quantity as force and the units shown are newtons. The printed formula wording is preserved here without correction.
Remove crankshaft locking pin and reinstall plug with new gasket. Reconnect negative terminal of aircraft battery. If the above mentioned friction torque is not achieved, inspect, repair, or overhaul the gearbox in accordance with the manufacturer’s instructions for continued airworthiness. Testing the propeller flange is not normal maintenance but can be carried out if defects or cracks are suspected.
Daily Maintenance Checks
The following checklist should be used for daily maintenance checks. Repair, as necessary, all discrepancies before flight.
- Verify ignition OFF.
- Drain water from fuel tank sump and/or water trap (if fitted).
- Inspect carburetor rubber socket or flange for cracks and verify secure attachment.
- Inspect carburetor float chamber for water and dirt.
- Verify security and condition of intake silencer and air filter.
- Verify security of radiator mounting. Inspect radiators for damage and leaks.
- Verify coolant level in overflow bottle and security of cap.
- Verify coolant hoses for security, and inspect for leaks and chafing.
- Inspect engine for coolant leaks (cylinder head, cylinder base, and water pump).
- Verify oil content for rotary valve gear lubrication and security of oil cap.
- Verify oil hoses for security, and inspect for leaks and chafing (rotary valve gear lubrication system and oil injection system).
- Verify ignition coils/electronic boxes for secure mounting, and check ignition leads and all electrical wiring for secure connections and chafing.
- Verify electric starter for secure mounting, and inspect cover for cracks.
- Verify engine to airframe mounting for security and inspect cracks.
- Verify fuel pump mounting for security, and inspect all fuel hose connections (filters, primer bulbs, and taps for security, leakage, chafing and kinks).
- Verify fuel pump impulse hose for secure connections, and inspect for chafing and kinks.
- Verify safety wiring of gearbox drain and level plugs.
- Inspect rubber coupling for damage and aging (C type gearbox only).
- Rotate engine by hand and listen for unusual noises (first, double verify ignition OFF).
- Check propeller shaft bearing for clearance by rocking propeller.
- Inspect throttle choke and oil pump lever cables for damage (end fittings, outer casing, and kinks).
Pre-flight Checks
The following checklist should be performed for all preflight checks. Repair, as necessary, all discrepancies and shortcoming before flight.
- Verify ignition OFF.
- Check fuel content.
- Inspect for coolant leaks.
- Verify oil tank content (oil injection engines).
- Verify spark plug connectors for security.
- Inspect engine and gearbox for oil leaks.
- Inspect engine and gearbox for loose or missing nuts, bolts, and screws, and verify security of gearbox to engine mounting.
- Inspect propeller for splits and chips. If any damage, repair and/or rebalance before use.
- Verify security of propeller mounting.
- Check throttle, oil injection pump, and choke actuation for free and full movement.
- Verify that cooling fan turns when engine is rotated (air-cooled engines).
- Inspect exhaust for cracks, security of mounting, springs, and hooks for breakage and wear, and verify safety wiring of springs.
- Start engine after assuring that area is clear of bystanders.
- Single ignition engines: check operation of ignition switch (flick ignition off and on again at idling).
- Dual ignition engines: check operation of both ignition circuits.
- Check operation of all engine instruments during warm up.
- If possible, visually check engine and exhaust for excessive vibration during warm up (indicates propeller out of balance).
- Verify that engine reaches full power rpm during takeoff roll.
Troubleshooting & Abnormal Operation
The information in this section is for training purposes and should never be used for maintenance on the actual aircraft. Only qualified personnel (experienced two-stroke technicians) trained on this particular type of engine are allowed to carry out maintenance and repair work. If the following information regarding the remedy of the malfunction does not solve the malfunction, contact an authorized facility. The engine must not be returned to service until the malfunction is rectified. As described earlier in the text, engines require basically two essentials to run: spark and correct air-fuel mixture. The majority of problems quite often are a simple lack of one or the other.
Troubleshooting
Follow an organized method of troubleshooting. This facilitates the identification of discrepancies or malfunctions.
- Fuel—start by checking the supply (tank), fittings (loose), filter (plugged), and float chamber (fouled).
- Spark—check for spark at the spark plugs.
Problems of a more complex nature are best left to an engine technician. The following are examples of engine troubles and potential fixes.
Engine Keeps Running With Ignition OFF
Possible cause: Overheating of engine.