Plane & Pilot
Tuesday, June 4, 2013

Hot Starts

Fuel injection is a wonderful feature—most of the time. In hot-weather restarts, however…

When was the last time you drove down to 7-Eleven on a sizzling-hot summer afternoon to buy a Lotto ticket, came back with what you hoped were the winning numbers, and your car refused to start because of the heat?

Chances are, never, unless you drive a fairly antiquated machine. Any auto newer than about 1990 is almost inevitably fitted with electronic ignition that senses exactly what's needed for a civilized start and fires up consistently in the first three seconds.

If you had to fly to that 7-Eleven to buy a Lotto ticket, however, you might be in for a very different experience. The majority of aircraft engines (excluding those few fitted with FADEC systems) don't have computers to control every aspect of start, full-throttle operation, cruise and idle. That's perhaps all the more ironic considering that a typical aircraft engine costs about five times the tab for a 300 hp V6 in an Infiniti or Lexus.

What if you combined a proven automobile engine with an iconic airframe? Back in the late 1980s, someone tried exactly that. Porsche and Mooney (Airplane Company) collaborated on the M20L, a stretched Mooney 231 fitted with a highly modified, geared, Porsche 911 engine. A guaranteed winner, right? Wrong. The airplane didn't sell well—it was more of a marketing problem than anything else, and with a dozen or more airplanes sitting in the grass at Kerrville, Mooney loaned me one of the new PFM 3200-powered Mooneys in 1988.

I had the airplane for three months and flew it all over the West. I operated in the late-winter cold of Montana and the early summer heat of Las Vegas, and with the benefit of Porsche's automotive technology, the engine started in about five blades in every possible temperature condition. (Mooney discontinued the model in 1989 after 41 airplanes had been built, but that's another story.)

My luck with dedicated fuel-injected aircraft engines hasn't been so impressive. I'm not sure how many times I've been embarrassed by not being able to restart a fuel-injected engine, but I'd bet it's at least four hands' worth of fingers. Fuel injection results in more even fuel delivery between cylinders, but it also can play havoc with hot starts, specifically because the pilot usually has full manual control of the start process.

Carbureted engines also can present starting problems in extreme hot weather, but fuel-injected powerplants are the most problematic. Restarting problems after being heat-soaked cut across virtually all models and sizes of injected piston engines.

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