The explanations about this matter have never satisfied me completely.
Thanks for your post, Pb.
We all seem to know the basic principles, work, power. Of course anything that produces force or work produces power. But I have difficulties in grasping why the difference between them is better visualised labelling them as "power producing" and "thrust producing" engines, respectively.
I always thought it had to do with the way energy was put into the engine, either in strokes or continuously, which made FF to be proportional to power output in pistons and to thrust in jets.
But in the end the fuel flow is pretty continuous in both engines.
Besides if fuel is energy then fuel flow is power. Since fuel is the source of energy of powerplants, the power achieved by any vehicle powered by an engine is limited by its fuel flow and its efficiency (thermal, mechanical and propulsive). All engines are "power producing". So why cannot we properly compare jet and piston airplanes?
Answered:
On the one hand, the behaviour of thrust with speed with a fixed throttle/thrust lever: in the pistons it decreases noticeably with speed whereas in the jets it is approximately constant.
On the other hand, the difficulties in measuring thrust in piston engines (or power in jet engines).
I guess we can always compare fuel flows, although taking into account efficiency and fuel heat power.
By the way, I have read somewhere that the A380 has Thrust gauges, along with the usual N1 or EPR ones. Does anyone know how they calculate thrust? Does its thrust lever angle demands N1, EPR or thrust? I would love to have them in my airplane.