Northrop YF-17 WHIF

[KJ_Lesnick]

Evan,

NIH = Not Invented Here

'Tis all too common a mental ailment.

So, the insight would have had to come from some guy near or at the top?

[elmayerle]

Either that or someone in the "right" department within Engineering.  the Preliminary Design/Advanced Design folk don't always listen too well to suggestions/comments from the production-model or field service engineering folk.

[KJ_Lesnick]

So if the Preliminary Design or Advanced Design people came up with it, it would be accepted?

[elmayerle]

Well, it would have more chance of being accepted.  Personalities and personal foibles can still play a part. 

[KJ_Lesnick]

Evan,

I have two additional questions,

1.)  Why did the USAF insist that one LWF design would have one engine, and the other would have two?  Why didn't they just go for a one-engined design?

2.)  Was there anything they could have done to the shape of the F-16's LERX to have prevented the deep-stall without any hits, or at least serious hits in instantaneous and sustained G capability?  (Guesses will do if you don't have an exact answer)


KJ Lesnick

[elmayerle]

1) As originally envisioned, they were testbeds only and the USAF wanted to evaluate as many variables as possible.

2) I honestly don't know and I've not dealt with the aerodynamics side of things in a long enough time (I've been more on teh detailed design side of things) that I don't feel comfortable speculating.  I do, though, remember an AW&ST article from the 1990s where the folks responsible for the F-5's sharknose had left Northrop to form their own company and were proposing some alterations to the F-16's LERX to enhance manuevering performance.  I don't believe, though, that any metal was ever cut on the idea.

[KJ_Lesnick]

Evan,

1) As originally envisioned, they were testbeds only and the USAF wanted to evaluate as many variables as possible.

That sort of makes sense.  Still you'd think a light-weight design wouldn't need any more than one engine. 

2.) I honestly don't know and I've not dealt with the aerodynamics side of things in a long enough time (I've been more on teh detailed design side of things) that I don't feel comfortable speculating.

As I understand the deep-stall that occurs with the F-16, is the result of the chines producing relatively more lift at high AoA (50-60 degrees as I remember) compared to the rest of the wing producing a strong nose-up tendency (more than the stabilators can counter) and also a reduction in directional control.

One thing I can think of would be to round off the chine a bit at the front more so.  It would prevent excessively powerful vortices from forming and keep the lift levels up front from getting too high.  I don't know though if it would reduce instantaneous agility and sustained agility. 

I do, though, remember an AW&ST article from the 1990s where the folks responsible for the F-5's sharknose had left Northrop to form their own company and were proposing some alterations to the F-16's LERX to enhance manuevering performance.

If I recall correctly they wanted to add small surfaces on the chine and on the front of the leading-edge flap that were either flexible, aeroelastic controlled, or computer controlled, that would better control the vortices and possibly provide increased lift through camber changes.  I'm not entirely sure as it's been awhile since I've read anything about this (Can you find the article?)

The idea was that it would be used to further optimize the LERx at lower AoA's which would increase instantaneous agility, and either

-reduce vortex intensity on the strake
-increase vortex intensity on the wing
-some combination of both
   
Allowing them to take it over 50 to 60 degrees AoA without a loss of pitch control.  The plane as I understand it would be able to have done cobra-maneuvers if that obstacle was out of the way.  They also wanted to use a larger wing like the Agile Falcon design which would restore the wing-loading to that of the F-16A.
 

I don't believe, though, that any metal was ever cut on the idea.

I don't think so either.


KJ Lesnick

[KJ_Lesnick]

Evan,

Do you have any further information about that F-16 LERX modification to improve maneuverability and prevent deep-stall?  I can't find the article online and I'm quite certain I don't remember the full details of it

[elmayerle]

Evan,

Do you have any further information about that F-16 LERX modification to improve maneuverability and prevent deep-stall?  I can't find the article online and I'm quite certain I don't remember the full details of it

Nope, 'twas 15-20 years ago and I really don't remember too much at this remove.  I do seem to remember that where the LERX met the nose went from the smoothly curved planform of the stock F-16 to something more like how the F-18's LERX join with it's fuselage.

[KJ_Lesnick]

Evan,

Nope, 'twas 15-20 years ago and I really don't remember too much at this remove.  I do seem to remember that where the LERX met the nose went from the smoothly curved planform of the stock F-16 to something more like how the F-18's LERX join with it's fuselage.

So, the chine was rounded off more at the front of the chine?


KJ Lesnick

[elmayerle]

As I remember, yes,  The edge of the chine came in nearly normal to the fuselage with their trim.

[KJ_Lesnick]

Evan,

As I remember, yes,  The edge of the chine came in nearly normal to the fuselage with their trim.

Did the plane still retain the heavy blending between the LERX/wing and the fuselage?


KJ Lesnick

[elmayerle]

As I remember, yes; just that the chine was cut back for better vortex control coming off the chine/fuselage intersection.

[KJ_Lesnick]

Evan,

As I remember, yes; just that the chine was cut back for better vortex control coming off the chine/fuselage intersection.

Just out of curiosity, since you said the chine was more like the F/A-18.  I assume you mean the F/A-18 -A through -D right?  Or do you mean the YF-17 or F/A-18E/F?


KJ Lesnick

[elmayerle]

Actually, the interesection of chine and fuselage is probably close to that of any of the F-18 variants, the sharp edge of the chine coming in, from a tight turn, normal, or nearly so, to the fuselage at that station.