I'll try to elloborate regarding the V1
min ,
max and
optimum in easy words.
When doing a takeoff calculation some objectives need to be achieved:
- Not run out of runway
- Be able to stop on remaining runway at V1
- Be able to clear all obstacles airborne
To calculate the first two, it is a simple accelerate-stop scenario.
The brake capability, therefore the deceleration rate, is known by the performance engineers.
The acceleration however depends on thrust availability which is of course a variable due to potential of derated thrust and assumed temperature methods or flex methods to reduce engine thrust at takeoff, designed to extend engine on wing lifetime.
Due to the variable in takeoff thrust availability, the acceleration thus varies.
The least amount of thrust required to achieve liftoff and still reach V2 and achieve screen height and obstacle clearance can then be calculated.
Due to the now reduced thrust availability the aircraft now however does not climb as well as it would with full rated thrust and bleeds off, the xxK rated engine thrust limit.
Therefore obstacle clearance may not be achieved, so in order to achieve that weight must be reduced at this trust setting
or additional thrust may be required to achieve these clearances.
It now becomes an issue of finding the minimum speed which will at a predefined thrust availability:
- allow you to still get airborne on the runway length available and clear the obstacles in your path
- be able to stop in the ruway distance remaining
Look closely at the example I posted from a calculation output.
You will see a relationship between different areas of assessment, runway length, obstacles, brake energy, ...
Optimum merely defines a calculation midpoint between the
max and
min as predefined by the software in the Operations IT department using a set of criteria, like i said using a scalar, or additive of difference between
max and
min added to the V
min.