A ``rubber'' jet engine is used, i.e. we assume that if there is no engine fitting the requirements, we will have one constructed and built exclusively to this aircraft. To make assumptions on what the engine data will be, data from an existing engine is scaled using statistical and historical fractions. If we have a new engine produced, a good guess is that it will be more effective than the data from the ``old'' existing engine. Typically this can be calculated:
For this aircraft we rescaled the A4-1 engine, which produces 
thrust.
This aircraft will need 
of thrust, which will be achieved using 2
engines weighing 
each.