Originally Posted by HN39
What you call "momentum reduction (...) experienced as a braking force" is what I would call "intake momentum drag", and others "ram drag". The term "inlet drag" is somewhat ambiguous, because it could refer to the skin friction or pressure forces acting on the intake duct.
Well, so there's yet another new term: "inlet momentum drag". It's a shame we can't find vocabulary on which we can agree, and to which we can stick.
Some of the air passing outside the duct will encounter reverser air, become quite slowed in the negative-x direction and thereby contribute to momentum reduction. I wouldn't want to call that "intake..." or "inlet..." anything.
Originally Posted by HN39
forces 'produced' by engine internal components that you quote from J.D. Anderson's book. Without an explanation of how they are derived, these figures don't mean anything to me.
I think they should. My point in citing them is as follows. If you include all the forces from inlet up to turbine, there is still a net forward force (positive-x). So since thrust reverse generates a net backward force, there is a fair bet, to understate the case, that some of those forces will be significantly different in the reverse-thrust configuration. If they are significantly different, then saying "thrust is this-minus-that; take away this; you're left with minus-that" is a misleading way to try to explain the braking effect caused by reverse thrust.
Originally Posted by HN39
Now that we agree on the intake side, let's turn to the exhaust side of the engine, which to me seems to be slightly 'under-exposed' in your account.
I wouldn't yet say that we agree on the intake side. But I am quite willing (obviously - one can check!) to agree that I haven't really addressed what happens with the exhaust.
There are various ways to slice the pie when talking about the contributions of various architectural components of an engine to the braking effect under reverse thrust. I think the contributions of the components to load mostly change. The difference between the normal-thrust contribution of a component at a given RPM and the reverse-thrust contribution of that component at the same RPM could be called the "drag due to <the component> when in reverse-thrust". I note that the total momentum-reduction will be larger than the sum of the drags due to the components when in reverse-thrust. That is why I resist giving the entire momentum-reduction phenomenon a name which suggests it has to do with a specific engine component such as the intake or the inlet.
PBL