Why are turbines more expensive than recip ?

[mstram]

Just started reading some basics about turbine engines.

They seem to be much simpler than recips ???

Why are they more expensive ?

(and how much more expensive are they ? ... I briefly looked for prices on the web, didnt find anything yet).

Aside from the cost, do recips have *any* advantage over turbines ?

Mike

[429 CJ]

Because turbines (such as the PT-6 group of turboprops) spin so fast internally, they have to have an extrodinarily well engineered and strong bearings and other internal components. They also operate under very high temps and pressures so therefore have to be manufactured out of exotic materials such as titanium etc (read expensive to replace) to much more exacting tolerances. Sure, the turbine engines can go a long way further in regards to TBO, but they can just as quickly go u/s when they are not cared for properly (maintainence and operating proceedures).

"Recips" as you put it, are very much like the engine in your car, but your car doesn't have a swept volume of up to 720ci for the "flat" (or IO as some call them) motors, and many, many times that size for some of the big radials that have graced our skies in days gone by. They are around 1/10 the cost to overhaul than a turbine engine(generally speaking) and weigh much more than a turbine.

Besides, a turboprop can develop many more times the shaft horsepower than an equivelent weighing reciprocating engine. Imagine an engine for an aeroplane that is basically the same size as a 40lt steel drum, can run on some very different types of fuels, light enough for one strong man to be able to carry, and develops up to 1500shp up to a level much higher than a piston a/c. Now, to extract the same sort of horsepower out of a piston, you would find yourself with a massive engine that had many, many rows of cylinders, was difficult to tune properly, chewed through unbelievable amounts of fuel, and weighed around the same as a medium car. I kid you not.

Hope that helps.

[ 10 August 2001: Message edited by: 429 CJ ]

[411A]

You must remember also that a turbine engine has life-limited parts, unlike recip engines which can be maintained on-condition.
With the FAA, this extends to the airframe of a turbine engine powered aircraft as well, phase checks (calendar and cycle limited) are required, not just annual inspections, as on recips.
Deep pockets are required.