Thrust and Speed

[TheWanderer]

A simple experiment:

1. Steady level flight at FL100, speed 250 KIAS.
   Increase speed to 300 KIAS while maintaining level, 0 fpm rate of climb.
   => Thrust needs to be increased to increase speed. If you change pitch, you start descending or climbing.
2. Steady stable climb with 250 KIAS and 500 fpm rate of climb.
   Increase speed to 300 KIAS while maintaining 500 fpm rate of climb.
   => thrust needs to be increased to increase speed. If you change pitch, the the rate of climb changes.
3. Steady stable climb with 300 KIAS and 500 fpm rate of climb.
   Reduce speed to 250 KIAS while maintaining 500 fpm rate of climb.
   => Thrust needs to be reduced to decelerate. If you change pitch, rate of climb changes.
4. Steady level flight with 300 KIAS. Reduce speed to 250 KIAS, keep 0 ft rate of climb.
   => Thrust needs to be reduced to reduce speed while maintaining level flight.
5. Steady decent with 250 KIAS, 500 fpm rate of decent.
   Increase speed to 300 KIAS.
   => Thrust needs to be increased to accelerate. Change of pitch changes rate of decent.
6. Steady descent with 300 KIAS, rate of decent 500 fpm.
   Slow down to 250 KIAS while maintaining 500 fpm rate of decent.
   => Thrust needs to be decreased to slow down. Change of pitch changes rate of decent.

Conclusion: Thrust controls speed and pitch controls rate of climb or decent.


Special cases

1. Transition from level flight to climb:
   Potential energy is added, additional thrust is required to deliver this additional energy requirement.
2. Transition from level flight to decent:
   Potential energy is used up to overcome drag, less thrust is required to maintain constant speed.