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I want to compare piston engines and turbofans on a maintenance basis. Let's say both engines are capable of 100 kN of thrust. Let's say both engines fly for 10,000 hours.

Over that time, what kind of maintenance can we expect from those engines. In particular:

  • How many times will the engine need major servicing?

  • How many man-hours does that servicing require?

  • About how much does it cost to do that servicing?

Major servicing for a piston engine would be something more than an oil change. For a turbofan it would be an overhaul.

Come to think of it, I don't know exactly what kind of servicing goes on for a piston engine other than an oil change. Is it like an overhaul where you dissasemble it and make sure everything fits together properly?

In case you're wondering, I'm envisioning these engines in a commercial cargo role. So no excessive dirtiness or hard throttling.

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  • $\begingroup$ Most piston engines need an overhaul (complete tear down and rebuild) every 1800 to 2400 hours on average for GA engines. When you get into the thrust you are talking about you are really out of the typical range of piston engines and moving towards a turboprop. It is also hard to compare engines just using thrust numbers, piston engines rely greatly on prop design to produce thrust, so there is more than the engine to consider. $\endgroup$ – Ron Beyer Jan 6 '17 at 5:20
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    $\begingroup$ Is there any piston engine capable of 100 kN of thrust? $\endgroup$ – vasin1987 Jan 6 '17 at 5:44
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    $\begingroup$ @vasin1987 The largest production piston, the Pratt & Whitney Wasp produced 3800 rated HP. The largest one made (2) was the Lycoming XR-7755, which produced 5000 HP. The GE90 produces 110,000 HP and outputs up to 510kn of thrust...I'm not sure that even with an ideal propeller setup that 100kn is possible out of a piston, living or dead. $\endgroup$ – Ron Beyer Jan 6 '17 at 5:56
  • $\begingroup$ @RonBeyer I would question the overhaul frequency that you cite. Those times may reflect the manufacturers recommended times between overhaul, but—legal requirements for certain operations notwithstanding—a well operated engine will exceed that time by 50-100% or more before a full teardown is required. At my old operation we routinely took engines to 3000-5000 hours and beyond before sending them in for rebuild, and then often merely as a precautionary measure, not out of need. $\endgroup$ – J Walters Jan 6 '17 at 16:38
  • $\begingroup$ @JonathanWalters "need" wasn't the right word, I should have used "recommend", I wrote an answer on that (oddly enough you commented on :) ) a while ago that pretty much says what you said, I'll just chalk it up to it being late when I wrote the comment. But yes, you are right, some engines are very happy flying long beyond TBO. $\endgroup$ – Ron Beyer Jan 6 '17 at 18:56
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Your question has some areas that depend on circumstances, models, etc. but to answer in general:

  • Piston engines are generally fully overhauled every 1200 to 2000 hours or so. Time to overhaul one varies with the engine model, and where the overhaul is done, as it can be done at the factory, at a repair shop, or by a qualified A&P/IA (a field overhaul). A piston engine overhaul can cost as much as $25,000 or more.
  • Turbofan engines will likely not require major service during those 10,000 hours. Most turbofan engines are inspected regularly and continue to operate on condition unless manufacturer recommended time periods are reached or exceeded. Time to overhaul varies greatly by engine model. Costs vary greatly as well, but in the case of turbofans you're talking in the hundreds of thousands of dollars.
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    $\begingroup$ Any clue why a turbofan overhaul would be much more expensive than a piston overhaul? AFAIK, overhaul is just disassembling all the parts, measuring them with laser precision, then putting them back together. Turbofan should just be unscrewing each blade from the disk. If anything, piston should be worse due to many special moving parts like the crankshaft, gearbox, those timing valves, carbeurator, etc. Maybe you were comparing a very large turbofan with a very small piston, since most pistons go on small GAs and most turbofans go on large commercial jets. $\endgroup$ – DrZ214 Sep 3 '18 at 19:15
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    $\begingroup$ I'm not a specialist in this field, but I can tell you as someone who works on vehicle (piston) engines the main cost is labor and any "specialist" labor like repairing a transmission is very expensive. Turbo fans are built to extremely tight tolerances that need a lot of modern tech which piston engines aren't. Yes piston engines require decent tolerance but there's a reason the term "backyard mechanic" exists. $\endgroup$ – YAHsaves Sep 3 '18 at 21:08
  • $\begingroup$ @DrZ214 There is a difference between inspection, which is mostly labor, and the replacement of life-limited parts. Those parts are usually anything that moves/rotates. The law requires manufacturers to list which parts of the engine are life-limited (law.cornell.edu/cfr/text/14/33.70). The limits are not normally expressed in hours for turbine engines, they are based on cycles (starts). The cost of manufacturing those parts, as well as the labor to R&R them correctly, is what adds up to hundreds, if not millions of dollars, on some engines. $\endgroup$ – Juan Jimenez Sep 4 '18 at 10:41

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