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True first gen jet fighters generally had very SHORT jet pipes! Think ME262, Gloster meteor, De Havilland Vampire. It was a deliberate part of the designs to mount the jets on the wings or within the nacelle of the twin boom to keep that jet pipe as short as possible to limit thrust loss. The aircraft already had marginal power as it was.If one looks at drawings of first generation jet fighters with the engine mounted internally in the fuselage, like the F-86, one thing that strikes me a bit strange is that the engine is mounted quite centrally, with a long exhaust pipe going from the back of the engine to the tail of the aircraft. View attachment 742025
Similar for same generation USSR fighters like Mig-15 and Mig-17.
Or a very early French prototype using Jumo 004 engine: View attachment 742026
One could argue this is for balance, but, well, just move the wings backward? Which is what happened for the next generation, like Mig-21 or Mirage III: View attachment 742027
I'm not sure I understand the point about incomplete expansion? If you want to change the expansion of the jet stream, you need a divergent or convergent nozzle. A straight pipe like on the F-86 does nothing except eats thrust via skin friction, no? Or well, given the engine is where it is, it prevents the tail of the plane from catching on fire, which one presumes is useful.Jumo 004
View attachment 742041
R13-300 (MiG-21MF engine)
View attachment 742042
AFAIK, long exhaust nozzles were necessary to prevent incomplete expansion of the jet stream. The exhaust nozzle of the R13-300 looks quite long, by the way. Compare with the non-afterburn modification (R95Sh):
View attachment 742043
Yes, but it seems while the next generation fighters had engines with significantly improved thrust/weight, they didn't use this improvement to install lighter weight engines, but rather to go faster. If you compare the weight of the engine as a fraction of gross weight of the plane, you'll see it's fairly similar in F-86, Mig-21 and Mirage III (I didn't do an exhaustive check, just a few representative aircraft). Still the later two aircraft managed to place the engines at the rear end of the airframe (well, they had afterburners so the engines were longer than the F-86 one, but still..).First generation jet engines had a much lower thrust-to-weight ratio, so they had to be mounted where it would benefit the aircraft's CoG.
Even the He178 had it's HeS3 mounted near the center of the airframe.
With the advent of more powerful engines, the engineers were able to move the engines further back.
As I noted earlier, the first-gen jet engines dictated a narrow area where they could be mounted in order to preserve CoG. Even the Me262 required modifications to it's wings in order to keep the weight of the Jumos within that zone.
The technology of Aerodynamics, Thermodynamics, Materials, Structures and Design etc, etc only progresses at a certain rate. Critical to Fast-Jet development has been the development of higher power to weight engines that allow the development of all the other design features and performance.
It is a bit like saying, why didn't George Stevenson build The Flying Scotsman instead of the Rocket, after all, it's just another steam engine.
Eng
As I said, I think the greater power-to-weight engines made the development of rear mounted engines configuration possible and advantageous, but only as the technology of the whole machine became available.Yes, that is exactly my question. Why did they need to place the engine close to the middle of the fuselage with a long jet pipe, instead of at the rear end like later ones? What understanding aerodynamics or something else prevented that?
Clearly they were aware of the disadvantages of a long jet pipe, see e.g. the quote above about the slightly peculiar layout of the Vampire.
I'm not asking why the F-86 didn't reach Mach 2 with a 130 kN engine like the F-16.
I don't understand how more powerful engines would allow you to disregard CoG considerations.
The Blackburn Buccaneer designed in the 1950s had the engines mounted ahead of the wing spar with exhaust at the rear of the wing.
View attachment 742207
View attachment 742208
Lack of all-flying tails? With the CoG and CoL so close to the elevators, they don't get much of a lever advantage. For aircraft without hydraulic boost, this would be even more if a problem.If one looks at drawings of first generation jet fighters with the engine mounted internally in the fuselage, like the F-86, one thing that strikes me a bit strange is that the engine is mounted quite centrally, with a long exhaust pipe going from the back of the engine to the tail of the aircraft.
One could argue this is for balance, but, well, just move the wings backward? Which is what happened for the next generation, like Mig-21 or Mirage III: