Some Tips on Ultralight Pre-flight/Maintenance

A well-maintained Rotax carburetor system can often have unexpected visitors; note the open vent line (arrow). Although necessary for correct operation of the carburetor, this is an inviting place for a worm or insect to nest. If one of these critters gets in there it can shut off the carburetor air balance and stop the engine. This is an important area to check during a pre-flight if the aircraft has not flown for an extended period.

The pencil points to the rubber collar on the Rotax 912 carburetor attachment. This collar should be inspected frequently for cracks as it must be in good condition to seal the mixture flowing to the engine. Any cracks will allow air to suck through and lean the mixture, with corresponding engine performance degradation.

Additionally, the seal or collar on a two-stroke Rotax must be fastened securely because it holds the entire carburetor in position. Although many ultralights have two carburetors, both are required to balance the fuel flow to the cylinders. A failed carburetor on a two-stroke engine can starve half the engine of oil, as in this case, where a bearing failure in flight occurred (arrow points to bearing failure). In addition, the lean fuel/oil mixture causes an immediate rise in cylinder head temperature and often leads to piston seizure.

Cracks in the exhaust system become "breakaway components" very quickly during flight, and this can play havoc with the propeller if the aircraft is a pusher type. Always conduct a careful pre-flight for such indications. Note the finger pointing to a crack initiation.	Brake disc fasteners left unlocked can work out and damage the brake-puck housing. If you are unable to use lockwire, use star washers or some other locking device. Remember: if it can come out, it will come out.

Some ultralight kits were delivered with very light aluminum alloy wheels to save weight. These types often fail in sideloads, so they must be monitored for signs of pre-cracking, particularly if operating off rough fields. The catastrophic failure of a wheel or axle usually results in severe damage to the undercarriage and a wing.	Speaking of broken axles or undercarriage legs, as this photo indicates, they can, and do, break from metal fatigue, particularly on rough-field operations and under conditions of excessive flexing over a period of time.