Fuel Consumption

Question 1

Jet SFC =

Answer 1

fuel flow / thrust (mass of fuel burnt per unit of thrust)

Question 2

Jet SAR =

Answer 2

TAS / fuel flow (air distance flown for each unit of fuel)

Question 3

For jet aircraft the SFC … with altitude up to the tropopause after which it …

Answer 3

reduces

remains constant

Question 4

SAR improves with … as the increase in … adds to the benefit of reducing …

Answer 4

height

TAS at altitude

SFC

Question 5

Prop SFC =

Answer 5

fuel flow / power (fuel burnt for each unit of power)

Question 6

Piston aircraft have a reducing … with altitude up to … after which it increases

Answer 6

SFC

the full throttle height

Question 7

What is full throttle height?

Answer 7

Piston engines give their best SFC when the intake pressure is high, RPM low and the throttle wide open. This would give too much power at low level but as height is increased you will reach point where the power required to fly at the best range speed is achieved with the throttle fully open, weak mixture set and cruise RPM selected. This is what is called the full throttle height and is where you will get best piston SAR