Aero-Tips!

A good pilot is always learning -- how many times have you heard this old standard throughout your flying career? There is no truer statement in all of flying (well, with the possible exception of "there are no old, bold pilots.")

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Aero-Tips 11.11.06

More and more airplanes in the general aviation fleet have fuel injected engines. One of the lessons pilots need to learn about starting fuel injected engines is how to start them when they are hot -- how to prevail in the dreaded "hot start".

Note: a "hot start" in turbine engines is a completely different situation, with a far more critical outcome. Today's we'll stick to our fuel-injected piston topic.

Why hot starts are an issue

Fuel injected engines depend on liquid fuel in the lines all the way to fuel injector nozzles, which combine air and fuel just before it enters the cylinders for combustion. Any vapor in the fuel lines interrupts flow, and may form a "vapor lock" that prevents fuel delivery altogether. Fuel vapor results from undissipated heat, usually in an engine-driven fuel pump but sometimes elsewhere in the fuel injection system.

Hot start

The procedure to perform a hot start differs based on the engine/airframe combination and, significantly, the type of fuel injection system involved, but all hot start procedures have one thing in common: replacing fuel vapor with liquid fuel. This can be accomplished in several ways:

• Running a boost pump while the mixture control is in the idle cutoff position.
• Attempting start with the mixture in idle cutoff, and advancing the mixture when the engine fires (note; this is the normal start procedure in some fuel-injected engines).
• Purposely flooding the engine (by running the a boost pump with the mixture set to rich), then performing the Flooded Start procedure.
• Performing the normal start with the throttle set more open than normal, hoping the engine-driven fuel pump pushes vapor out of the lines.

Put 20 pilots in a room and you'll probably come up with about 18 different ways to hot-start a fuel injected engine. Any may work on any given day, but generally there's one technique that works best for a specific engine/airframe combination. Some options (like intentionally flooding) may result in a damaging backfire or, in extreme cases, an engine-warping liquid lock in the cylinders.

Aero-tip of the day: Ask engine experts (user groups, manufacturers, etc.) to learn a safe, dependable way to hot start the fuel injected engines you fly.

FMI: Aero-Tips