Originally Posted by
stilton
That answers my question in the clearest most understandable manner, now it all makes sense !
Thanks for that
OK, that's the answer for comparing old and new engine at same density altitude. That assumes that the performance was
engine limited. Often it is not, and the maximum power allowed is limited by gearbox, rotor head of other airframe limitations. In that case, the increased power cannot be used. (Well, you practically
can use the additional powers, but you are discouraged by one of the other means from making use of the additional available power. And sometimes you should have regardless, but that belongs to another thread.)
Consider however the following: An engine delivers its nominal power only at sea lever and standard atmospheric conditions. Take the engine up to some altitude (density altitude, to be more specific) it might now only produce half of its nominal horses. (See also here:
Reduction in Max Continuous Power in turbine helicopter with increase in altitude?)
Solution:
- Double nominal engine horse power
- Tell pilots (see above) to please not use the now available additional horsepower at low DA
- When at that altitude contemplated above, the new engine - at half of its nominal power - still delivers what the old engine did at sea level
No changes to speed or MTOW, just the same documented performance available at higher DA