26.10 Piston Engines - general

26.10.2 Explain the fundamental difference between piston and gas turbine (jet) engines.

The working cycle of a turbine engine and a piston engine. 

Gas Turbine Engine

• combustion occurs at a constant pressure
• induction, compression, combustion and exhaust occur continuously
• continuous action and is not enclosed so pressure is constant and volume increases
• no peak or fluctuation pressures
• requires light fabricated combustion chambers
• low octane fuels

Piston Engine

• occurs at a constant volume
• induction, compression, combustion and exhaust occur intermittently
• only one stroke is utilized in the production of power
• no continuous action and is enclosed so pressure rises and volume is constant
• peak pressures in excess of 1,000 lb. per sq. in.
• requires cylinders of heavy construction
• high octane fuels

The comparative advantages of turbine engines versus piston engines for aircraft propulsion. 

Gas turbine engines

• have the ability to develop more power for a given size.
• are  lighter weight (better power to weight ratio).
• are more compact, meaning less drag.
• are more reliable, and
• can use cheaper fuel (kerosene).

26.10.4 Distinguish between the basic types of piston aircraft engine.