Tuesday, June 4, 2013
Fuel injection is a wonderful feature—most of the time. In hot-weather restarts, however…
Contrary to what you might imagine, there's not always consistency in the remedy for such problems, either, even for engines of exactly the same horsepower and model designation. Quite often, the design of cowlings, cowl flaps, exhaust pipe exits and enclosures for retractable nosewheels can change the cooling characteristics of an engine such that hot-start procedures may vary significantly from one airplane to another, even on aircraft equipped with the same model engine.
To no one's surprise, start procedures in hot weather are almost exactly the opposite of those in cold weather. In extreme cold conditions, it's almost impossible to overprime most engines. (Once, at Grand Canyon in winter at about 0 degrees F, I had a local pilot tell me to start my turbocharged single by turning on the fuel pump with the mixture full rich, "Then, go to lunch." I didn't take his advice literally, but I did run the pump for a full minute at full rich, hit the starter, and the engine lit almost immediately.)
The obvious risk of overpriming in cold weather is that you could pool fuel beneath the cowling and ignite it accidentally. I once watched a beautiful Cessna T-210 in Fargo, N.D., burn to a crisp on a frigid January day when the pilot overprimed the engine and leaped out to fight the resulting fire, only to discover he had a dead fire extinguisher.
Conversely, in very hot conditions, you may need no prime at all, or at least very little. One pilot living in Phoenix told me if he's restarting after a half-hour shutdown, he leaves mixture and throttle at idle, turns on the fuel pump to clear the lines of hot air and begins cranking. He claimed the engine usually starts within 10 seconds.
If you're flying into a potential hot-start situation, prevention is often easier and safer than correction. There are some simple ways to short-stop an engine from vapor locking or at least diminish the problem of restarting. If you know you'll be firing back up within an hour or so, make it a point to park the airplane pointed into whatever wind there is. That may not always make the line boy happy, but insist on it if it doesn't totally disrupt his ramp.
If there's a covered tiedown space available to put the airplane in shade, opt for that, even if it costs you a few bucks more. (During a July stop in Tucson several few years ago, I watched a pilot attach a miniature battery-powered fan to the cowling air intake. The owner told me it provided about an hour's worth of fan power to evacuate the hot air and cool the engine. Clever idea, so clever that the owner said he had already had three of the fans stolen.)
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