Advantages of gas turbine engines

• Very high power-to-weight ratio, compared to reciprocating engines.

• Smaller than most reciprocating engines of the same power rating.

• Moves in one direction only, with far less vibration than a reciprocating engine.

• Fewer moving parts than reciprocating engines.

• Greater reliability, particularly in applications where sustained high power output is required.

• Waste heat is dissipated almost entirely in the exhaust. This results in a high temperature exhaust stream that is very usable for boiling water in a combined cycle, or for cogeneration.

• Low operating pressures.

• High operation speeds.

• Low lubricating oil cost and consumption.

• Can run on a wide variety of fuels.

• Very low toxic emissions of CO and HC due to excess air, complete combustion and no "quench" of the flame on cold surfaces.

Disadvantages of gas turbine engines

• Cost is very high.

• Less efficient than reciprocating engines at idle speed.

• Longer startup than reciprocating engines.

• Less responsive to changes in power demand compared with reciprocating engines.

• Characteristic whine can be hard to suppress.

From http://en.wikipedia.org/wiki/Gas_turbine

Exercise 16, p. 75.

How Do Piston Aircraft & Turboprops Compare?

Price

From a manufacturing and engineering perspective, the reciprocating engines found in piston aircraft are far less complex than their turboprop counterparts. This is primarily due to the high temperatures and forces unique to turboprop engine operation, which must be accommodated both in materials and engine design – and which come at a price. For this reason, piston aircraft almost always offer a lower cost of entry.

Maintenance

While piston engines are indeed a more simple design, turboprop engines have far fewer moving parts and the smooth, vibration-free operation of a turboprop engine typically offers greater reliability – and longer time between overhaul (TBO) – than a piston aircraft. In other words you can generally log more hours on your turboprop before you need to bring it in for inspection.

The typical TBO for a turboprop engine is 3,000 hours while TBO for a piston aircraft is generally 2,000 hours. So the higher upfront cost of a turboprop aircraft may be somewhat offset by lower maintenance costs over time.

Performance

The power of a turbine engine almost always allows turboprop aircraft to travel at higher speeds than piston aircraft. And as turboprop aircraft cabins are typically pressurized these planes also commonly fly at higher altitudes.

Turboprop aircraft are generally most efficient at altitudes of 20,000 to 30,000 feet and at average speeds of 250 to 300 ktas, while piston aircraft, which are typically not pressurized, are usually restricted to altitudes of 12,000 feet or less (unless an oxygen system is used). And as piston engines are less powerful than turboprops engines, piston aircraft speeds are generally limited to about 200 ktas.

Distance

Piston aircraft are generally smaller aircraft, seating no more than six passengers, and are well suited for relatively short missions of 300 miles or less, while turboprops tend to be larger aircraft with greater passenger capacity – and more fuel on-board – and are more likely to be found flying distances of up to 1,000 miles.

Both piston engine aircraft and small turboprop aircraft are right at home accessing smaller airports with shorter runways, making them the ideal way to reach many desirable final destinations, where larger aircraft simply cannot land.

Ultimately, there are many factors to consider when investing in an aircraft, but giving careful thought to the types of missions you intend to fly and understanding which aircraft will best support your intended use – while accommodating your budget – will help you arrive at the right choice!

From http://www.shorelineaviation.net/news---events/bid/50442/Piston-Engine-Aircraft-vs-Turboprop-Engine-Aircraft

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