Mr Optimistic
The high pressure in an engine or jet would tend to push the back end off: nothing to do with drag force on the nozzle surface,
I agree that most (but not all) of the rearward force on the nozzle is produced by the pressure in the jet pipe. But that does not mean that we cannot call it drag. Isn't Form drag caused by pressure acting on the forward facing surfaces of an aircraft?
I used the term DRAG because the force on the nozzle acts rearwards. If you prefer to use another word then you are free to specify one.
But the important point as far as this discussion goes is the fact that the force on the nozzle acts reawwards.
just pressure acting on the rear surface.
The pressure is actually acting on the forward facing surfaces of the nozzle. That's why it tends to push it rearwards.
Nozzle turns pressure into flow speed.
Agrred, but does not answer the question.
Blow up a balloon, turn it around so it faces away from you and let go of the untied end. Would it fly away from you owing to drag over the aperture or into your face because of the thrust ?
Agreed, but still does not answer the question. IE. On what part of the engine does the thrust force that has been produced by accelearting gas through the nozzle act.
Put a weak joint between the nozzle of a rocket motor and the case and see what happens (owing to the pressure inside the case) - from half a mile away that is.
The nozzle would probably fly rearwards. The exception would be the a condi nozzle in which case the direction would depend on the relative magnitudes of the forward forces acting on that part of the nozzle downstream of the throat, and rearward acting forces on the part upstream of the throat. My vote would go for it flying reaward in most cases.
And the adiabatic expansion or compression on flow through a cone would cause no discernable heating or cooling (convergent at subsonic speeds would in any case heat).
I do not agree.
Don't need de laval nozzle theory here. NB look at most rocket plumes, they bulge out ie exit pressure is still above ambient. Small drag losses in a nozzle
I said that we don't neeed to consider a condi nozzle. You are correct that the pressure downstraem of the throat is greater than ambient. That is why it creates thrust on that part of the nozzle that is downstream of the throat.
I suspect are just accounted for by an 'engineering factor' in practice.
Agreed. That "engineering factor" would include ensuring that the attachment of the nozzle was strong enough to stop it being torn off and thrown rearward.
But none of your post addresses the question at hand. On waht part of teh engien does the thrust caused by acceleration of air thropugh the nozzle actually act?