The SR-71 aircraft had “aerospikes” at the front if its engines to manage the airflow during Mach 3+ flight. Modern fighter aircraft (F-22, F-18, etc.) do not appear to have such accoutrements, and yet they are capable of supersonic flight. How do the engines on these aircraft cope with supersonic air inlet speeds?
They use intake ramps to slow and compress the intake air.
[nitpick]
Fighter aircraft like the F-22, F-18, etc. do not use gas turbine engines, they use true jet engines. They generate forward thrust via high power combustion exhaust, whereas gas turbines primarily generate rotational torque (similar to reciprocating or ‘piston’ engines) thru high power combustion connected to an output shaft and, for fixed wing aircraft, a propeller i.e. a turbo-prop or, for helicopters, a gearbox and main rotor or, for tanks, a transmissions.
No, no suggestion they use “gas turbines” but they do use “turbojets”. The turbo referring to the turbine that drives the compressor prior to combustion.
Have you bought this nitpick up before?
A gas turbine is a general term that includes turbojets.
I thought so, you brought up the same nitpick here, but it’s wrong. A turbojet and a turbofan are both types of gas turbine. A turboprop is also a type of gas turbine. In case it’s not clear, the turbine section is present in a turbojet and turbofan but it is used to drive the compressor stages only whereas on a turboprop it is also used to drive the prop.
One thing about the SR-71/A-12 was that it was not just supersonic, but seriously fast supersonic. The spike didn’t unlatch and become a specific part of the control mechanism for engine airflow until Mach 1.6, against a maximum speed of Mach 3.2 (or actually 3.5 plus before all sorts of other problems became apparent.). Concorde maxed out at about Mach 2, Raptor is 2.2. One might assume that the highly troublesome spike was simply not needed for the other designs. The very wide range of speeds the blackbird operated over would have made intake ramps a lot harder make work as the shockwave geometry would have varied over a much longer length.
hell, a turbocharger is a gas turbine, just one without its own gas generator.
What do you consider a true jet? Nothing but ramjets and rockets? All of the things now categorized as jet engines work on the same principle, high velocity fluid is ejected from an aperture to provide thrust. How the gas gets that way is irrelevant. Even ducted fans powered by non-turbine enginee are no different than a turbo-jet in the principle of operation.
What is colloquially referred to as a ‘jet engine’ means, for me, either a turbo-fan (airliner) or turbo-jet (fighter). I hate it when someone refers to a helicopter or tank etc. as having a ‘jet engine’ when they just have a gas turbine engine. The key difference being one generates thrust, the other generates torque (turbo-fans both).
Technically gas turbines include all of them, but I don’t know of a separate name for a torque-generating gas turbine engine so when I hear ‘gas turbine’ that’s all I think of.
No, I disagree. A ducted fan is just a propeller, i.e. it moves air by swinging a bunch of little barn doors. A turbo-jet moves air by mixing fuel with it and combusting it. The turbine in a turbo-jet is not akin to a Cessna’s prop, it’s akin to a high speed fuel pump.
A turbo-fan jet engine is just a type of ducted fan that uses a turbine engine to drive a fan (which is a variation of a propellor). Both produce a directed airflow using a stator and a nozzle. Airline turbofans produce the majority of all thrust from the fans. All turbo-jets exhaust a lot of cooling air no matter how much combustion exhaust is used for thrust.
Did the engines of the SR-71 not transition to the ramjet mode after reaching a certain airspeed, because the turbines created too much drag? As I recall, that was when the cones were needed to control the flow of air into the engines. Or is my memory faulty?
The SR71 engines at all supersonic speeds were ramjets with a turbo jet in the middle. At subsonic speeds the turbo-jet provided thrust and compression for the ram jet operation. At supersonic speeds the spikes created a shock wave in the inlet that compressed the intake air. At some point shock wave compression was all that was needed to maintain ram jet operation, but I thought the turbines continued to operate to provide electricity and hydraulic pressure.
A torque generating gas turbine is a turbo-shaft. When people use gas turbine to refer to a turbo-jet or turbo-fan they are being quite correct. It sounds like the problem is that you incorrectly associate “gas turbine” with a turbo-shaft.
we are in agreement here.
yes, they’re all gas turbines. If you need specificity, just call it the type of engine it is (turbojet, turbofan, etc.) Saying a turbojet engine is “not a gas turbine” is just plain wrong. Just like that guy who claimed externally-scavenged two-stroke piston engines weren’t “true two-strokes.”
wrong again. A propeller’s blades are airfoils, and generate “lift” just like the aircraft’s wings except the “lift” they generate is parallel to the ground. A ducted fan is a fan (duh) which generates thrust by forcing air through the duct and expelling it out the rear. So a ducted fan is a jet regardless of what kind of engine is driving the fan.
you don’t get to make up your own terms for things and expect everyone else to adhere to them.
Aha! That sounds right, but at that point I’d imagine most of the airflow was channeled around the turbojet to reduce drag. The Blackbird was one complicated beast…
You think ducted fan blades aren’t airfoils? He’s right; a ducted fan is just a type of propeller. FWIW, Wikipedia agrees.
Also, a fan is a type of propeller, with the only difference in that fans tend to have more blades.
That said, “propeller” is a bit ambiguous and may be used to refer specifically to an unducted, low blade count propeller (the Wiki page does this, also).
You’d better send a nastygram to Textron-Bell, and make them rename their JetRanger. 
Turboshafts generate thrust. Sometimes it is used to augment the thrust generated by the prop.
Think of it this way: A turbojet engine is a gas turbine engine that generates thrust with exhaust gasses. A turbofan is a gas turbine engine that generates thrust by turning a large fan, and augments it with thrust with exhaust gasses. A turboshaft engine is a gas turbine engine that is connected to a transmission that is in turn connected to a propeller, rotor system, or wheels, and which may augment the forward force with exhaust gasses.
A turbine-powered helicopter is a gas turbine-powered helicopter is a jet helicopter.
Yeah. There must have been some complicated intermediate modes of operation. And I recall something about the difficulty in maintaining the proper inlet conditions for a turbo-jet running inside of a ramjet.
Yes, a turbo-shaft was the term I was looking for! Will not confuse the two again.
No, that’s not really the point I was trying to make, airfoil vs paddle wheel. The point was that in a ducted fan the turbine-ish fan blades are directly generating thrust, similar to a standard propeller. In a true turbo-jet the turbines primarily serve to feed compressed air into the combustion chamber where it’s mixed with fuel, ignited, and thrust is created from this combustion.
The point is some people think that fighter jets are being ‘pulled’ or ‘sucked’ thru the air by the high speed turbine like a propeller, and this is not the case. The turbines are merely part of the air/fuel delivery system, closer in analogy to the high speed fuel/LOX pumps on a rocket engine.