Jet Engines: Beasts of Burden
I noticed the planes my airline flys only sit on the ground a few minutes and they are back in the air over and over again all day long! How can this be good for them? Doesn't it make them break more often? How can they hold up?
Let's use a car analogy. Imagine if your car worked for a taxi company.... It would be running pretty much constantly for three or four years. It would get an oil change every week because, in a week, it has gone 6000 miles. In a year, the engine would be replaced because it had 300,000 miles on it. (White Horse Limos in Raleigh/Durham N.C. has Chevy Suburbans with 430,000 miles on them! THE SAME ENGINE!)
Do you think you'd get 300,000 miles out of your engine? Probably not. Wonder why? Machines like to work. The hardest thing you can do to your car engine is to start it up in the morning after it has cooled off. The temperature stress is terrible to the motor. Oil has dribbled down to the pan and has to be pumped back up to coat and protect the working parts as the engine starts. For a few seconds during start the engine is almost dry (that's why you should never rev your car engine right after a cold start -give it five seconds to get up to oil pressure. Warm starts are fine: The engine internal parts are all dripping with oil from when you turned it off 30 minutes ago.)
Pratt & Whitney makes jet engines used on the older 737 and MD-80 series aircraft. These engines are also used on oil rigs in the Gulf of Mexico to generate electrical power for the rig. The engines on those rigs run off natural gas, which is plentiful and usually run for 90 days (that's 24/7!!!) before another "power pack" is brought on line. The depowered pack is then shipped back to land to be inspected and rebuilt. What they found amazed them when they got the first motor back on land: It was like brand new! Jet engines on airliners are the same way. Keep them warm from running them and they like it. Oil seals stay sealed longer; bearings stay tight longer; and fluids stay in better shape. Another analogy is exercising the human body. Regular exercise keeps your system working better than infrequent bouts on the treadmill or bike.
I have done exterior inspections in Providence in winter where the engine covers are placed on the cowling openings to keep snow and gook from collecting in the engine. Upon opening the covers, the engine was still warm from when it flew six hours ago--even though the outside air temperature was below freezing!
SECRET PILOT STUFF--Oddly, jet motors start so slowly and have so few moving parts, they don't see the stress that a car engine sees on start up. They use synthetic 10W oil--very much like sewing machine oil--WAY thinner than the oil in your car. And, jet engines never get their oil changed. Oil slowly gets burned as it seeps past the oil seals, and Maintenance just adds oil periodically as the Pilots see the gauges in the cockpit reach a certain point. Scheduled maintenance inspections are done on a very strict timetable as specified by the manufacturer and the FAA.
