3 Operating Figures

Question 1

Which elements produce negative thrust?

Answer 1

turbine, nozzle

Question 2

explain with two equations where the need for a large bypass ratio comes from?

Answer 2

thrust equation, propulsive efficiency equation. thrust equation says high mass flow rate and large flow acceleration for high thrust but high flow acceleration decreases propulsive efficiency so large mass flow rate accelerated little is best (high propulsive efficiency)

Question 3

discuss the repercussions of the range equation

Answer 3

-best range at high subsonic
-linear engine and aerodynamics dominate nonlinear weight with LONG range aircraft -as important for short range aircraft
(for weight and range, think of long range and short range as defined by the fuel proportion)

Question 4

which graphs (why) is the best range values at high subsonic speeds?

Answer 4

overall efficiency of engine is increasing with mach number

L/d cuts in half at sonic

eta * l/d is max at ~0.8

(sl p 65)

Question 5

describe how the ram effect and the velocity effect have decreasing effects on thrust produced with increasing mach number.

Answer 5

ram effect: up mach number increases flight velocity which increases mass flow (ram effect)

velocity effect:
up mach number decreases difference of velocities which increases drag.