BA 77,
At high altitudes the total thrust produced by the engines will be less. Altitude will not affect the 75% ratio of thrust produced by bypass.
However the airspeed will affect it. At high airspeeds the high bypass turbo fans experience more MOMENTUM DRAG than the rise in thrust due to RAM EFFECT.
whereas low bypass engines at high speeds still can impart much more additional velocity to air, as compared to high bypass whose fan can't accelerate air to velocities,the inner jet engine can.
So for a low bypass engine the thrust remains almost constant at all speeds whereas a high bypass engine produces less thrust at high airspeeds.
So i guess the Percentage for high bypass turbofans decreases with airspeed.
Vicky
