ORIGINAL: Sport_Pilot
Jets and fans, on the other hand, increase their thrust as speed
Not sure about jets but ducted fans have higher thrust when on the ground. The difference is that they generally have less thrust on the ground than a prop, but more thrust than a prop at speed, but they still have more thrust on the ground than when in the air. F=MA is still at work, the air is accelerated to a higher delta V when on the ground which is more mass to create the higher thrust on the ground. F=MA is easier to calulate with fans and jets because almost all of the air goes straight back. With a prop some of it goes to the side near the tips, and some wraps around in a vortice at the tip, some is lost against the cowl, and some is lost with frictional losses against the fuse.
No calculations are really needed - jets are reaction devices
inlet air is heated and accelerated.
Fan jets are props running at extremely high pitch and speed -which also produces a fast flow - but soon, the drag exceds the thrust -even tho the theoretical prop speeds are much higher.
Neither increase thrust as the craft increases in speed.
As altitude increases, prop efficiency decreases and reaction engine efficiency increases
In zero atmosphere - even a tiny reaction device will continue to accelerate the vehicle ( (ion drive as an example)