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Inlet spike


DaveRindner
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In Wings Of Red Star : Mig-21. It is stated, with heavy fake Russian accent by Peter Ustinov, that getting the inlet spike was a challenge, and like with SR-71 inlet, there had to be a program to push in/out the inlet spike to prevent inlet stalls. Though not stated in program inlet stall could and often did lead to unstarts. Basically a shock ring that travels through the compressor with great violence and can flame out the motor. So curious, for Mig21 testers, is spike program , manual, or automatic (i.e. no user control implemented). In Col. Rich Graham's AWESOME SR-71 book, those Mach 2+ unstarts were bane of SR-71 program. They were never really solved. Ben Rich spend 25 years managing the program and it was never really solved, only made less common, and easier to deal with in 1980's, when inlet spike got digital control.

They way I understand inlet stalls and unstarts is it starts with a rumble near or near, at, or above Mach2, like a stick shaker for stalls, then there is a large bang, then aircraft pitches or yaws. The pilot has to ride it out judge when unstart has passed, bring aircraft under control quickly, or risk high speed stall/spin. All 2nd and 3rd gen Mach2+ aircraft with inlet spike are susceptible.

I am curious where this sim stands, if they simulate the motor accurately. Does that mean that air behavior inside inlet is also modeled.

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Check this: http://www.twitch.tv/graywo1f/b/564620064

 

Apparently there's a bug in the version which he recorded with, the SPRDs keep on giving thrust so eventually he can't even slow down to land the plane. But this is the only instance I've seen so far around Mach 2 - and he has had it more than once that the engine just stalled at those high speeds. I was already suspecting that this is due to the nose cone and Mach shocks that prevent from sufficient air flow at the intake. So at least that is modelled :)

dcsdashie-hb-ed.jpg

 

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They way I understand inlet stalls and unstarts is it starts with a rumble near or near, at, or above Mach2, like a stick shaker for stalls, then there is a large bang, then aircraft pitches or yaws. The pilot has to ride it out judge when unstart has passed, bring aircraft under control quickly, or risk high speed stall/spin. All 2nd and 3rd gen Mach2+ aircraft with inlet spike are susceptible.
There is no reason that a flame out would cause the MiG-21 to lose control under normal circumstances since the jet engine is on the centerline. With multi-engine airplanes you would suddenly have a big yawing moment from asymmetric thrust if one of the engines suddenly stopped. That is where the losing control thing comes from.
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[sIGPIC][/sIGPIC]

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