Originally Posted by b377
....the cognitive problem when talking about 'intake' produced thrust....
You're hitting the nail on the head. It's a
cognitive problem.
Nearly all that is taught about jet propulsion (or aircraft propulsion in general) treats the engine, or rather the propulsive system, as a "black box", with mass going in, energy being added by the fuel, and basically the same mass coming out with added momentum.
Yes, in that case Mr Newton has the correct description of what's going on.
F= m x a !
The simplistic thrust formula T = m' x (Vo - Vi) is just another way of stating the same thing.
It's when you start looking in detail of what happens
inside that "black box" that the "cognitive problems" start.
You're now suddenly dealing with a far more complex description of how and where the momentum exchange happens.
The basic F= m x a, while globally still perfectly valid, is no longer much use when you try to "get your head around" what exactly happens inside that "black box".
Inside the "black box", thinking in terms of pressure distribution, and in particular the forward components of those pressures, is an easier way of understanding what is going on.
I'm not a "propulsion" engineer, and I'm the first to admit when I first saw "the intake produces 75% of the thrust", that my first reaction was "huh"??? too.
And yes, it did take me more than a moment to work out what I now tried to say just above.
Luckily, the structural design engineers that designed the engine nacelle, and more specifically the intake, knew about this.
Because indeed, at Mach 2, those 75% of the actual propulsive force of the "engine system" was transferred to the wing structure and from there to the rest of the aircraft... by the intakes.
Just as well they were bolted on properly....
CJ