F-16 LERX / Deep-Stall Question

KJ_Lesnick

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This is kind of an academic question, but what geometric changes would have been necessary to have prevented the F-16 from having the deep-stall tendency?

I have intended to ask this question, in fact I tried on Airliners.net but I couldn't get any answer as I was simply explained that the deep-stall problem could be recovered from -- I already knew this -- I wanted to know from a simply hypothetical standpoint what physical characteristics would have kept the chine from developing such an extreme pitch-up tendency around 50-60 degrees alpha (I was told that some other high alpha airplanes had an advantage in their wider rear fuselages, though the F-16's rear fuselage with the chine-shelves seem wider than the F-18's).

The only thing I could think of is for the chines to have been slightly rounded-off in the front (look at the F/A-18's chine vs the F-16's chine)...


KJ Lesnick
 

aim9xray

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IIRC, Eidetics did some studies in the early 90s, I think, on trimming and reshaping the LERX/chine/whatever. The customer did not take the project to flight test.
 

KJ_Lesnick

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If you could find any further information on that, I'd like to see it (assuming it's not classified or anything)

KJ Lesnick
 

aim9xray

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Sorry Kendra - that's your homework assignment. Please report back to the board with what you have found via Google, Yahoo, etc. I await your contribution...
 

KJ_Lesnick

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Apparently they thought of some means of using some kind of pneumatic device, or some kind of small flap like device placed on the chine and the LED's to control the vortex -- the flap on the strake thing allegedly offered improvements in instantaneous agility as well actually. Other proposals also included putting a bigger wing on the design to allow the F-16C to achieve the wing-loading the F-16A did.

Still, I'm surprised they didn't round off the front of the chine a tiny bit. It sounds like it would deal with excessive amount of lift produced at high alphas (this sounds bad but the deep-stall of the F-16 is caused by the chines apparently producing such a large amount of lift at about 50-60 degrees of alpha that it shift's the center of pressure too far forward to the point that full down stabilator cannot make the nose drop -- if at those alphas the lift did not get so high you wouldn't get the pitch-up), the rest of the chine could still generate a sizeable vortex I would presume -- the F/A-18 has a rounded off chine at the front and it can fly at extremely high-alphas, it however doesn't have a deep-stall problem that the F-16 has.


KJ
 

overscan (PaulMM)

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My patience is finally at an end. Like aim9xray said, go find out the answer yourself, read some books, contact Harry Hillaker via a ouija board and ask him.
 

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