F-20 Tigershark - no artificial limiters like the F-16

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delta2014

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Unread post15 Oct 2017, 23:09

I was watching this video regarding the F-20 Tigershark:

https://www.youtube.com/watch?v=6BDgQwlfHII

At 5:50 - 5:55 the narrator says:

"It has no restrictions or limiters on angle of attack, roll rate or yaw."

Is it possible to turn off the artificial limiters in the F-16? Or is that absolutely not possible, and the F-16 must always fly with restrictions and limiters on angle of attack, roll rate and yaw?

Thanks,

Delta
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jbgator

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Unread post15 Oct 2017, 23:51

The answer is no. But let me ask you, do you think the F-20 could do any angle of attack, any roll rate, and any yaw rate the pilot wanted? If you say yes.....I say NO. Do you have any idea how dangerous a departure can be even in training, much less in combat when you become an uncontrollable grape? The bottom line is an F-20 pilot would need to know the limits of his jet and observe them. Since they vary over the flight regime and loading of the jet he would need to be able to do some serious cranial calculations to determine how far he could go in current conditions (Alt, AS, AOA, load out, etc.). Obviously he would have to WAG (wild a$$ guess) and conservatively apply his inputs to not exceed the limits thereby not maximizing his jet's capability. I never worried about that and always got 100% what the jet could do without a departure. So you guys give up this "limiters are a limitation" BS. Pull as hard as you want....no over G, no AOA departure. Yaw all you want, no yaw departure or, more importantly, roll all you want, no roll-coupled departure. All this in a jet with relaxed static stability...F-20...fogettabout it.
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basher54321

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Unread post16 Oct 2017, 00:18

The cause of both F-20s that were lost (with their pilots) seem to be attributed to GLOC with the information I have.

Technically they can change the F-16 limits - was done for the MATV program - but no reason to do it for the standard production jets.
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litzj

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Unread post25 Aug 2018, 11:47

Is there any performance chart like EM chart for F-20?
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Gums

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Unread post25 Aug 2018, 16:30

Salute!

JB has it nailed.

I flew 50 to 100 hours in the F-20 sim at Hawthorne back in 1984 to 1985 as part of the McAir vs Northop lawsuit.

No limiters I could see!!!

My actual flight in the jet was cancelled the night before I was scheduled, and after I and another pilot had gone thru the cockpit check and such at Edwards that day. Lawyers did not want the McAir "expert witnesses" to fly the thing and legal "discovery" processes would have demanded that their guys fly it as well. I think the bird at Edwards was the one that crashed OTW to Europe that spring. OTOH, it could have been the "original" test article. So I cannot comment about buffet and handling for the "real thing".

The g-loc explanation seems O.K. for at least one of the crashes.

Finally, be advised that the Vipers I flew did not limit gees versus roll rates/stick force inputs. John Will could comment here, but I think we had a 5.x gee limit for max roll commands. I do not have my manuals here at the fishing cabin, or could provide a definitive answer.

Gums sends...
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"God in your guts, good men at your back, wings that stay on - and Tally Ho!"
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johnwill

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Unread post25 Aug 2018, 22:10

Gum, you are close. Limit g for max roll commands was 6.0 for air to air loadings.
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Gums

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Unread post26 Aug 2018, 01:40

Salute!

Thanks, John-Boy ( aka John Will, structural engineer extraordinaire).

I also think we had some new limits when the Cat III FLCS was implemented. And if I recall correctly, first good deep stall was an assymetric load and roll to depart the sucker.

The biggie for this old pilot was that the leading edge flaps and other enhancements made for very smooth high AoA maneuvers. Up to then we had really good buffet and wing rock and all kindsa "clues" that we were at the edge of the envelope.

Gums sends....
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FlightDreamz

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Unread post26 Aug 2018, 03:08

basher54321The cause of both F-20s that were lost (with their pilots) seem to be attributed to GLOC

That's the way I remember it as well (recall reading about it in Aviation Week & Space Technology at the local library).
A quick Google search turned up https://theaviationgeekclub.com/impress ... prototype/ ,"..following investigation cleared the F-20 of mechanical or design issues..it concluded that Cornell had blacked out due to excessive G-forces....the second prototype of the F-20 (serial number 82-0063..) crashed in May 1985..killing Northrop pilot Dave Barnes..practicing for the Paris Air Show. Again the crash was blamed on G-LOC."
See also http://www.thecid.com/f20a/f20crash.htm
If I recall correctly they crashed two (out of three prototypes built) performing at Airshows. Farnborough International Airshow was one of them I think
A fighter without a gun . . . is like an airplane without a wing.— Brigadier General Robin Olds, USAF.
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basher54321

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Unread post26 Aug 2018, 14:20

Yes I think that is right the last one (pre-production I thought not prototype) is hanging up in California Science centre and the fourth was never finished.

https://californiasciencecenter.org/exh ... tigershark
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johnwill

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Unread post26 Aug 2018, 21:07

Gums wrote:
I also think we had some new limits when the Cat III FLCS was implemented. And if I recall correctly, first good deep stall was an assymetric load and roll to depart the sucker.



You are right. Danish Maj. Sven Hjort (you probably know him) was also at low airspeed to make things worse. Cat III reduced max AoA, roll rates, and rudder motion, and gave a 200 kt low airspeed warning, but did not change g limits. I'm sure you remember air to ground g limits were pilot observed, not automatic.
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Unread post26 Aug 2018, 22:54

Salute!

Thanks for some confirmation, John.

Lottsa folks do not realize that we did not have symmetrical gee limits in most cases. So I could pull 9 gees once fast enuf.

In Cat III, our gee versus AoA function was slightly different, and I think it was about 18 degrees max AoA, but I am still in the mountains and don't have the manuals.

As instructors we would use the Cat III laws to simulate a well-known adversary jet.

Gums sends...
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"God in your guts, good men at your back, wings that stay on - and Tally Ho!"
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johnwill

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Unread post27 Aug 2018, 07:10

Gums wrote:Salute!

Thanks for some confirmation, John.

Lottsa folks do not realize that we did not have symmetrical gee limits in most cases. So I could pull 9 gees once fast enuf.

In Cat III, our gee versus AoA function was slightly different, and I think it was about 18 degrees max AoA, but I am still in the mountains and don't have the manuals.

As instructors we would use the Cat III laws to simulate a well-known adversary jet.

Gums sends...


The Cat III AoA limiter I saw varied between 16 and 18 degrees, depending on g and airspeed. Your memory is still good, even at your advanced age. I am allowed to say that because I'm even older by a few years. :shock:
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outlaw162

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Unread post27 Aug 2018, 19:34

With all respect JW, 'AOA limiter' is still a euphemism for 'G' limiter until you get up to the 9G airspeed for CAT III, which is somewhat above the CAT I 9G speed. At any given speed below this, whether you call it an AOA limiter or not, it is also a 'G' limiter. The only reason I could imagine for flying in CAT III would be to simulate an aircraft with 'less overall performance capability'. You could turn an F-4D with an F-16 in CAT III in the speed range a turning fight would end up.

I wonder how AGCAS handles CAT III ? Does it override it, or takeover/pull early ?

Hope you're doing well. :D

(BTW, I was told that Rich Rose, F-106/A-1/A-7, RIP, from the 162nd, actually got a flight in the F-20. Is this correct?)
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johnwill

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Unread post27 Aug 2018, 22:48

Outlaw, of course you are right about the "limiter" being a g/alpha limiter. Thinking about AGCAS in Cat III, pilot-observed g limits are around 5.5g, so unless the limit is greatly exceeded, I wouldn't think GLOC would occur. If it did, AGCAS levels the wings and commands a 5g pull up. Only at lower airspeeds would the AoA part of the g/alpha limiter be approached at 5g. I don't have a clue if AGCAS can override the Cat III AoA limit.

I understand pilots sometimes use Cat III with air to air loadings to simulate other airplanes, so in that case GLOC could occur. I suppose the same situation could also apply to Cat I at its higher AoA limit.

I'm doing well, not even a headache in at least ten years. CAVU.
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Unread post28 Aug 2018, 04:08

Salute!

I can't post the AoA vs Gee control law for the Cat I FLCS because I am in the mountains and all my mnuals are back in Florida.

However, make a simple graph with AoA as the x-axis and Gee for the y-axis. Then just draw a straight horizontal line at "9" on Y-axis until reaching "15" degrees on the X-axis (the AoA). Then draw almost a st line from there to "1" on the Y-axis and "27" on the x-axis. Dat;s the plot, no kidding.

So until slow enuf to hit 15 deg AoA with max aft stick, you could pull 9 friggin' gees. As you got slower you rode the "curve" down until at 27 deg AoA and all you could get was 1 gee.

I always thot of the Viper limiter as an AoA doofer versus gee limiter. The FLCS plot looks like the engineers had an EM diagram in front of them and tried to optimize what we pilots could command. My VooDoo was a no sierra AoA limiter and also had a pitch rate "stick pusher' that would activate if you yanked too hard or tried to get past the "command signal limiter". The Sluf could get to max gee if going real fast, otherwise hit AoA limits well before gee limits, and a plot of gee versus AoA would look like the Viper plot, but lower gee and higher AoA.

We used the Cat III mode to simulate a Flogger and maybe another plane. And let all here know that the Cat I versus Cat III switch position was a pilot choice.

Gums sends...
Gums
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"God in your guts, good men at your back, wings that stay on - and Tally Ho!"
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