Reverse understanding of the reality... This is like saying wet roads cause rain. One wants as low jet velocity as possible because thrust is the momentum added to the air and momentum scales linearly with both speed and velocity. The same energy added to more mass means more momentum. Adding energy to a bigger mass of air is always better. It is impossible for an engine to not generate a jet faster than the incoming flow anyway.
Man this is wrong on so many levels.
Firstly when talking about how thrust interacts with stuff that’s flying you need to consider momentum not energy.
Secondly since the part about engine choice and jet velocity part makes absolutely no sense whatsoever I’ll try to explain. The reason you want different engines for different speed regimes boils down very roughly into “having as much mass flow as possible while maintaining adequate exhaust velocity”. Propulsive efficiency is higher for engines with high mass flow than with high exhaust velocity, all else being equal, but in reality bypass air in turbofans (especially high bpr ones) have difficulty accelerating enough for high Mach number operations which is why you see turbojets and ACEs being developed that operates as basically a turbojet at high Mach numbers. No you don’t need the jet speed to be equal to the forward motion of the plane and I don’t see how that even works unless your engine’s mass flow rate equals the plane’s mass (in which case P=mv kicks in and ensures the momentum from the exhaust equals the momentum of the aircraft except it’s still not correct because the freestream velocity hasn’t been taken into account which leads to a bunch of reference frame shenanigans).
Pretty much exactly what I said explained in terms of momentum. I just took energy as a constant and used energy to make the analogy due to the fact that excess jet speeds produce residual kinetic energy that interacts with the freestream and produces losses. Its not like the the thrust comes from unicorns. It comes from the propelling nozzle ejecting molecules carrying kinetic energy. Jet velocity vs maf. Same thing.
On top of that I fail to see how the rubbing between the engine exhaust jet and the freestream is part of this conversation as once the jet leaves the exhaust the force (and by extension moment) is imparted onto the jet and what happens after is none of the jet’s business (that is unless you want to go into under and over expansion and how that messes with the pressure field behind the nozzle and how that in turn affects the nozzle behavior but again that’s off-topic).
This is literally part of the definition of propulsive energy that you just explained. This difference in air speeds produces losses in the form of wake that consume fuel and don't contribute to propulsion at all. This difference has to exist due to having to overcome drag, but too much of it means you are using the wrong engine for the job.
Also the fact that (for an actual working engine) the jet velocity is higher than the freestream has nothing to do with drag and everything to do with if it’s not exiting at a higher speed then it’s simply not creating any thrust and at that point you might as well build a glider for all the good that engine will do.
And why do you need thrust during cruise? Only to overcome drag. Even lift imparts only lift induced drag in the horizontal component. Total drag is the only force acting on the plane in the horizontal component. For a plane to travel at constant speed and altitude, the only force it has to overcome is total drag. That is the only reason jet velocity needs to be slightly higher than the freestream velocity.
No you don’t need the jet speed to be equal to the forward motion of the plane and I don’t see how that even works unless your engine’s mass flow rate equals the plane’s mass (in which case P=mv kicks in and ensures the momentum from the exhaust equals the momentum of the aircraft except it’s still not correct because the freestream velocity hasn’t been taken into account which leads to a bunch of reference frame shenanigans).
Mass isn't considered at constant speeds and level flight, only lift induced drag.
Thinking that jet engines need to have a stationary jet velocity above M2 to reach M2 is Reddit understanding. There is no jet velocity matching in aerospace engineering.
So are you saying the engine can produce a jet velocity below M2 while the plane travels above M2?
None of these are relevant to the (already very off) topic and they address nothing too. You are trying to nitpick the semantics of my writing. Go look at the thrust and wing area of the F-15 and other 4th gens and compare them to the previous aircraft of the similar MTOW. A strawman argument is exaggerating or distorting peoples' statements and then arguing against that version. Which is exactly what you attempted with Mach 5 and the CFM-56 examples.
I twisted nothing. You said it is too draggy and brought in the Cold War then brought in claims made in advertisements, so I told you the fact that it can do over M2.4 runs counter to what you are saying. It is probably draggy in the subsonic regime, but like I explained before, subsonic drag requires planes to look clean and heavily streamlined, while supersonic drag requires a different kind of streamlining that deals with compressible flow.
The WS-15 is probably isn't rated for a lower pressure or temp than engines from 50 years ago
This part is why I made the CFM example. It has to do with bpr and maf and the airframe. We are talking about the configuration of the engine and at what point it operates at maximum efficiency, which can only be one single point regardless of temp limits, opr, epr etc. Of course the WS-15 will have all the bells and whistles of a modern engine, but you can't make it push any jet velocity you want without taking the core and reconfiguring things around it.
???????? Air defenses those countries had were indeed defeated and EW was a part of it. The US sent the F-117s to bomb Baghdat right at the start during the Gulf War. This was mentioned on this thread previously in other contexts.
They sent in Special Forces and CIA into the country and convinced most of the Iraqi military to lay down their arms and the whole country fell down in a couple of weeks. Iraq was surrounded by enemies, landlocked, and blockaded for decades and corruption was running rampant. Calling it a highly contested airspace is just not a serious argument. In a real war like the Ukraine war, we clearly see objects getting shot down all the time unless long range standoff missiles and ship launched missiles are used.
