i will be pretty happy if someone answer the why, behind JFT being able to do or not do supercruise...
It is a combination of things, not of any one thing.
talking about design not allowing it seems not logical to an amateur because the same aircrft can go to supersonic speed using afterburns? so why not without after burns..? only reason to an amateur is lack of engine power,which the current engine seems to address situation?
There is a difference between a 'supersonic dash' versus a 'supersonic cruise'.
Afterburner or reheat is a barely directed/controlled explosion, to put it simply. What we do is simply dump a large quantity of fuel directly into the exhaust stream of a turbine and let that fuel quantity explode. The result is a powerful push or thrust in the opposite direction and if we sustain this barely directed/controlled explosion long enough, thrust will also be sustained and we will reach Mach.
Which begs the questions of why do we need to dump fuel in the exhaust? What is the difference between burning fuel in the exhaust versus burning fuel
INSIDE the engine? After all, is it not burning fuel inside the engine gave us the exhaust in the first place?
Reasonable questions...
A turbine or 'jet' engine is essentially an internal combustion engine. Same as the one we use for our cars. But the differences between the two types on how each process or burn the fuel are crucial to the understanding of why we need a feature call 'afterburner' or 'reheat' for the turbine engine.
Take a liter of fuel be it kerosene or gasoline or even cooking oil. You should understand that this quantity of fuel is a packet of energy, or one form of energy. In this form -- liquid -- the most efficient exploitation of this quantity is to break it down into smaller and smaller and smaller packets
BEFORE we ignite or burn it. We break it down by pressurizing it and force it through a physical structure. The method is called 'atomization' and we see it in carburetors and fuel injectors in our cars...
Carb Class: Basic Principals of Carburetor Operation
...the process of mixing air with fuel is atomization. Atomization is where things get tricky and some black magic comes to play; carburetor manufacturers, modifiers and other fuel system related companies are always searching for more efficient ways to atomize fuel and air.
The 'atomization' process attempts to break any quantity of fuel down to the molecular level in order to maximize its explosive power in both time and strength.
MSD Ignition
...finely atomized air/fuel molecules in a cylinder being ignited by a single, small spark produced by a stock ignition.
Note: We will never be able to achieve %100 efficiency.
But essentially, the more 'fine' the fuel/air atomization process, the better the fuel conservation with the more power produced at any moment. The MSD source above have basic illustrations on fuel atomization that are helpful enough in visualization of the process.
The internal combustion engine in our cars is the 'reciprocal' type...
Reciprocating engine - Wikipedia, the free encyclopedia
A reciprocating engine, also often known as a piston engine, is a heat engine that uses one or more reciprocating pistons to convert pressure into a rotating motion.
A turbine or 'jet' engine is technically also an internal combustion engine but it is how each burn, not atomize the fuel/air mixture, that forced us to have a feature call 'afterburner'.
In the reciprocating infernal combustion engine, air flow and fuel/air atomized mixture delivery are in pulses, not continuous, and this mean maximum temperatures are in spikes, not a plateau (flat), and this mean metals have 'rest' or cooling periods between maximum temperature stresses.
It is the opposite with the turbine infernal combustion engine where air flow is continuous. Its dependency on the most efficient fuel/air atomization process is no different than the reciprocating design, except unlike the reciprocating design, the fuel/air mixture delivery must also be continuous instead of periodic pulses. This mean maximum temperature is quickly reached and it
STAYED THERE like a plateau (flat). The engine core must stay this way literally for hours and this is probably the most hellish environment that Engineering -- as a discipline -- have yet produced.
Do not look at the engine face fan. It is the core that is out of sight that matters. Materials Science have had extreme difficulties in producing alloys for the core and because of this limitation, exhaust power produced by the core have not been able to take an aircraft into Mach and keep it there. Hence the need for the terribly inefficient and wasteful but powerful enough 'afterburner' feature. Even the Concorde and SR-71 requires afterburners to reach Mach and it is only their optimized aerodynamics for long duration Mach are they able to supercruise once they reached Mach, which lead us to aerodynamics and airframe designs.
Post 41 correctly pointed out that most aircrafts, particularly the ones for multi-purpose use, are not good for supercruise but only for supersonic dashes. The Concorde and the SR-71 can supercruise but they cannot maneuver or carry cargo the way we want. Their aerodynamics are for as low drag/resistance as possible to maximum exploitation of any engine thrust, afterburn or not. Fighters, not even the F-22, are not very efficient out of utility. The fighter aircraft must make radical attitude changes, carry at least one human being, carry weights (missiles) whose presence can disappear abruptly (launch), unlike fuel where its presence progressively decreases and can be replaced, and must be able to repeat in as short time as possible in a 24hr period. So structurally speaking, in terms of robustness, most fighters, including the F-22, are
ALREADY NON-CONDUCIVE for supercruise. But because the USAF want the feature, an engine must be designed to make it possible.
It is a combination of aerodynamics, airframe structure, utility, and propulsion that will enable any design, including the JFT, on whether the fighter can supercruise or not. When an aircraft is on paper, everything must be weighted and as the American experience have demonstrated, one thing can outweigh another that would force a major redesign when a contract is underway. So the reality is that as the JFT as is, is it possible to give it the supercruise capability assuming an engine is available.
but what benefit does supercruise has in real combact
Fuel economy. Simple as that. A supesonic dash can get you out of trouble when you are in a fight. A supersonic cruise can get you into a trouble spot when you are needed. Either way, the more fuel you have via efficient fuel management, the longer you can contribute to the war effort.
