8178,
I always thought the Sabre had a US made copy of the Rolls Royce Nene just like the Mig 15 did, guess I was wrong on that point!

Like I said earlier maintaining the pressures inside a turbine is a precarious balancing act and if something isn't right it all goes south pretty quickly. On all of the older and even some of the current designs, there is a metal strap that is wrapped around the engine at the aft end of the compressor section. This strap covers a series of slots and is held tight to seal those slots off and prevent air from flowing out of them. The bart is referred to as a bleed band and is used to dump excess pressure when the pilot rolls off the throttle quickly. Since the compresor is spooled up to a very high rpm at full throttle it carries a great deal of energy and takes a few seconds to sspool down. Consequently since the compressor drum is still turning it is still making pressure, excess unneeded pressure when your attempting to power down, in this case. The band was controlled by the fuel control or, in the case of the J-79 or F-100 in the Phantom or Eagle, was controlled via the engine ECU. When the FC or ECU senses the lower power demand it opens the band to dump excess pressure from the compressor outboard before it can build and create a stalling condition.

I have always wondered how the small model turbines deal with this issue and I can only guess that it's because of this that they are somewhat slower to spool up(or down) than we would like them to be(turbine lagg as it were). The ECU that controls a models turbine has an incredible amount of number crunching to do and I suspect that by varying the fuel flow to maintain rpm, and thus pressures, it's all done in the programming.

Just remember, if something changes....like an air leak in a fuel line, your turbine is goign to have problems because the system isn't programmed to compensate for such things. For a model turbine to function correctly everything has to be just right.