F-16 DFLCS control law & G-onset rate

Always wondered why the F-16 has a tailhook, or how big a bigmouth F-16's mouth really is ? Find it out here !
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sprstdlyscottsmn

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Unread post14 Nov 2019, 17:16

f-16adf wrote: Additionally, there exists absolutely zero videos of the B Tomcat pulling off Sea Level turns in under 19.6 seconds (And with zero armament). The 14.7 second 360 degree decelerated turn of Solo Turk Block 40 has nearly a 5 second advantage over it.

Just remember, all demo pilots have to keep under 5.5G due to peacetime NATOPS limits.
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f-16adf

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Unread post14 Nov 2019, 17:28

Don't you mean 6.5G?
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Unread post14 Nov 2019, 17:39

I do not. 6.5G was the "wartime" NATOPS restriction and 5.5G was the "peacetime" NATOPS restriction.
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f-16adf

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Unread post14 Nov 2019, 17:56

Ok, cool, then I learned something. But, if we are going to estimate SL turn rates. Even if it is say 19.7DPS that theoretically still falls below the 6.5G line. If it is 5.5G, still turn rate is near upper 18's. My point is, either of those figures pale in comparison with Solo Turks. And after 6.5G, turn rates on the Tomcat go down according to data.

Also, as stated by Nance he in fact did hit 7-8G as a Tomcat demo pilot on occasion.
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Unread post15 Nov 2019, 13:36

F/A-18 G-onset rates vs speed:
Image

That's up to 27 G/s for the F/A-18C. Also note that at 0.6 Mach it's 3 G/s @ 40 kft and 19 G/s @ SL, that's a ratio of 6.33 to 1 for that altitude difference. So if the F-16 is capable of 3 G/s at 35 kft, I would be surprised if it couldn't hit at least 9 G/s at SL, a 3 to 1 ratio.

Hence why I say it wouldn't make much sense if designers wouldn't have allowed for the F-16 to attain 10 G/s via the FLCS when other relaxed static stability fighters with similar AoA & G limitations were allowed that much. The control surfaces are certainly capable of providing the necessary force.




As for the subject of measuing turn times at demos, first of all I find that quite unscientific because there are way too many unknowns, and also keep in mind that a max rate turn limited to 5.5 G is quite a handicap for the F-14.

To achieve the 14 sec 360 turn that you claim a Solo Turk did you would have to hit atleast ~9 G's of instantanous load factor, max ITR, something no F-14 was allowed to do in a demo eventhough it could easily take it. So the 19 sec turn around for the F-14 in a demo is pretty damn impressive if the pilot wasn't even allowed to pull max ITR or go above 5.5 G's sustained. (Note: Loaded F-14 hits ~6 G's at its max STR @ 5 kft, at SL it would be over 7 G's)

That said we don't have to guess regarding turn rates, we have the official performance charts for both the F-14 & F-16, and we know that if both are maxed out performance wise (with similar load out), and with no regard for G limits, then below ~0.65 mach the F-14 wins in ITR or STR, whilst above that speed the F-16 wins STR wise. Again this is assuming the F-14 pilot doesn't give two sh*ts about the 6.5 G limit ofcourse, which in peace time they certainly did, whilst they obviously wouldn't so much in combat with as much as 11 G's having been reached by Tomcat pilots without any damage to the airframe.
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Unread post15 Nov 2019, 16:09

Solo Turk is achieving his average rate of 24.5DPS becasue he is Decelerating throughout his turn. He is coming in at 9G and probably around .62-.63mach and basically flying -250Ps throughout his turn. And he is finishing his turn at around 5G's and probably . 4mach. He is not flying a Sustained Turn, and notice going from 9G on down his turn radius is decreasing. And most importantly he is not losing any vertical feet.

You seem to think that a -Ps means you are solely losing vertical feet, no, it's an acceleration/deceleration value. For instance, take a 5.56 round and fire it out of a rifle (say an AR). At the muzzle it may have around 2900F/Ps in velocity, while 300 meters down range it might be around 1900F/Ps in velocity. Meaning in another words it has slowed down, i.e. lost energy.


If you use the F-14B Specific Energy Charts and plot for Sea Level, his Max sustained turn rate will still occur prior to 6.5G. It occurs somewhere between 6.5G and 5G. Notice that when going from 25K to 15K to 10K to 5K there is an average increase of around 2-2.1DPS. So at SL I would expect the generally the same. At 5K it is 16.1-2. At SL, with using the SEP charts, and the near 2.1DPS gain it probably will be around 18.3-4, and that is with the 8 AAMS and 50% fuel. Again, seeing that with the SL SEP numbers the nature of the curve is still nearly identical to the 5K chart. Meaning it should bow upwards a little between 5G and 6.5G. Now strip off the weapons which weight basically is close to but less than 3,700lbs Notice that from going from 59,695lbs to 55,620lbs a difference of 4,075lbs turn rate only increases maybe max by 1.4DPS. So even using that liberal figure, lets add that to 18.3, so now we are at 19.7DPS. Again, a liberal figure. That still falls slightly below 6.5G. Now lets say he does come in fast at SL and at 9G, He at 9G would be bleeding near twice the -Ps in energy than the Turkish Viper. The F-16, according to the Block 30 big inlet chart, bleeds a little over -400Ps at 9G and near -500 at 8G. Look at the Tomcats 5K chart, if you were to draw out a 9G line he would be losing over -1600Ps. And even from explicit data from the chart, with it at just 6.5G he is already at near -1000Ps. So a theoritical SL 9G Tomcat turn, means he probably will see a 27.5-28PDS ITR, but at a fleeting instant, then after losing energy at copious amounts.


So there is basically no way for any F-14 to match the time of Solo Turk, and he is flying a Block 40. If he were in a Block 30 it would be even faster since he is around 700lbs lighter. The only jets that can come close to his time are the "striped down" Anatoly Kwotschur (Kvotchur) Su-27 or another GE powered F-16.


It should be noted as well, Keith "Okie" Nance in his Aircrew Interview Q&A explicitly said (at 1:27:20) he flew many airshow demos at 7-8G.
And the words of an email from an F-14 pilot to me from years back: "In training, it was not unusual to go beyond 6.5 Gs accidentally. This would be written up in the logbook and an inspection would be made. A pilot would not get into trouble by exceeding the G-limits, unless he made a habit of it; did not write it up, or overstressed the aircraft causing significant damage. I believe I may have hit 8Gs a time or two, and certainly a number of times over 7Gs. It happens."

Now you can believe it or not, I don't really care-




Solo Turks time (at 2:40) is not a claim, it is reality. Time it, see with what you come up with. The F-14's time is not anywhere even close.
https://www.youtube.com/watch?v=q36JblL7IRg
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Unread post15 Nov 2019, 18:43

hummingbird wrote:Hence why I say it wouldn't make much sense if designers wouldn't have allowed for the F-16 to attain 10 G/s via the FLCS when other relaxed static stability fighters with similar AoA & G limitations were allowed that much. The control surfaces are certainly capable of providing the necessary force.


The F-16 has negative static stability under most subsonic conditions. The control surfaces actually do not have to provide the force to generate G-onset -- if they stop moving, the aircraft will immediately depart controlled flight, either pitching up or down something greater than +/-60 AOA, generating G loads of +/- 10 to 15 Gs depending on airspeed, and basically stopping forward flight. The tailplanes are actively working to keep the pointy end facing forward at all times. And once the pilot gives a G command with the sidestick, the tailplanes move enough to start the increase of AOA in the desired direction, then are actively moving the other way to slow and stop the increase in AOA as the commanded G is reached. So the FLCS is actually working to manage the G-onset rate below what the airframe is capable of subsonically.

Early in the F-16 operations, there were a few events where FLCS lost electrical power, the tailplanes froze in their neutral rig position, and the aircraft departed with a -15 G pitch down and crashed. The immediate response was a TCTO to re-rig the horizontals so that the aircraft would pitch up instead in that condition, but it was still going to be a 15 G departure with loss of all flying speed. There was some debate as to whether this re-rig was a good thing, but the pilot community was reflexively against the nose down departure - can't say I blame them.

The original FLCS power source was the main aircraft Constant Speed Drive Generator, with little Ni-Cad batteries (of unknown charge state or condition) in the FLCS computers as backup. Via TCTO, a trickle charge from the main aircraft battery to the FLCS batteries was added to ensure they were fully charged, and then a Variable Speed / Constant Frequency PMG generator dedicated to provide 100% reliable power to the FLCS system was developed and retrofitted to fix the problem for good.
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Unread post15 Nov 2019, 20:22

f-16adf wrote:Solo Turk is achieving his average rate of 24.5DPS becasue he is Decelerating throughout his turn. He is coming in at 9G and probably around .62-.63mach and basically flying -250Ps throughout his turn. And he is finishing his turn at around 5G's and probably . 4mach. He is not flying a Sustained Turn, and notice going from 9G on down his turn radius is decreasing. And most importantly he is not losing any vertical feet.

You seem to think that a -Ps means you are solely losing vertical feet, no, it's an acceleration/deceleration value. For instance, take a 5.56 round and fire it out of a rifle (say an AR). At the muzzle it may have around 2900F/Ps in velocity, while 300 meters down range it might be around 1900F/Ps in velocity. Meaning in another words it has slowed down, i.e. lost energy.


I know solo turk didn't achieve a 14 sec 360 via STR f-16adf, that's what I was trying to tell you, that he had to hit max ITR, which means riding the max lift curve from start to finish. The F-14 wasn't ever allowed to do that at demos as it would bring it way above the 5.5 or even 6.5 G limit.
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Unread post15 Nov 2019, 20:40

And I pointed out to you that, say if it did, it wouldn't have the available Ps to complete the turn in that time since it in fact is bleeding near twice the -Ps at 9G vs the F-16C. Theoretically, if i'm at 9G I certainly would rather be in the jet that bleeds -500Ps vs the jet that bleeds -1000Ps.
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Unread post15 Nov 2019, 20:54

f-16adf wrote:And I pointed out to you that, say if it did, it wouldn't have the available Ps to complete the turn in that time since it in fact is bleeding near twice the -Ps at 9G vs the F-16C. Theoretically, if i'm at 9G I certainly would rather be in the jet that bleeds -500Ps vs the jet that bleeds -1000Ps.


You don't seem to understand that the F-14 doesn't need to hit 9 G's to beat the F-16 round a turn. It can beat it round the turn with a lower G, which is the point you're entirely missing.

A few facts here:
1) The F-14 has a higher ITR than the F-16 across the board (no limiter)
2) F-14 has a higher STR than the F-16 below 0.6 Mach, and importantly almost exactly the same max STR. (within 0.1 dps)

In short your mistake is assuming that the F-14 pilot goes to his max ITR (28 dps) or tries to match the F16 in G's pulled, but he doesn't need to, he can simply match the F-16's rate, lowering his speed loss as well, until speed drops to 0.6 mach, at which point the F-14 can now maintain a higher rate than the F-16. And same rate at a lower speed = smaller radius = eventual gun solution.

It's pretty simple.
Last edited by hummingbird on 15 Nov 2019, 21:02, edited 1 time in total.
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Unread post15 Nov 2019, 21:01

f119doctor wrote:
hummingbird wrote:Hence why I say it wouldn't make much sense if designers wouldn't have allowed for the F-16 to attain 10 G/s via the FLCS when other relaxed static stability fighters with similar AoA & G limitations were allowed that much. The control surfaces are certainly capable of providing the necessary force.


The F-16 has negative static stability under most subsonic conditions. The control surfaces actually do not have to provide the force to generate G-onset -- if they stop moving, the aircraft will immediately depart controlled flight, either pitching up or down something greater than +/-60 AOA, generating G loads of +/- 10 to 15 Gs depending on airspeed, and basically stopping forward flight. The tailplanes are actively working to keep the pointy end facing forward at all times. And once the pilot gives a G command with the sidestick, the tailplanes move enough to start the increase of AOA in the desired direction, then are actively moving the other way to slow and stop the increase in AOA as the commanded G is reached. So the FLCS is actually working to manage the G-onset rate below what the airframe is capable of subsonically.

Early in the F-16 operations, there were a few events where FLCS lost electrical power, the tailplanes froze in their neutral rig position, and the aircraft departed with a -15 G pitch down and crashed. The immediate response was a TCTO to re-rig the horizontals so that the aircraft would pitch up instead in that condition, but it was still going to be a 15 G departure with loss of all flying speed. There was some debate as to whether this re-rig was a good thing, but the pilot community was reflexively against the nose down departure - can't say I blame them.

The original FLCS power source was the main aircraft Constant Speed Drive Generator, with little Ni-Cad batteries (of unknown charge state or condition) in the FLCS computers as backup. Via TCTO, a trickle charge from the main aircraft battery to the FLCS batteries was added to ensure they were fully charged, and then a Variable Speed / Constant Frequency PMG generator dedicated to provide 100% reliable power to the FLCS system was developed and retrofitted to fix the problem for good.


Yep, in other words if they wished the designers could've given the F-16 the ability to pull over 20 G/sec in onset rate, but that just wouldn't be in anyway useful to the pilots or worth the risk in terms of G overshoots. Hence I believe they probably stuck to ~10 G/s as max commandable onset rate, same as the EF designers did.
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Unread post15 Nov 2019, 21:40

f-16adf wrote:Theoretically, if i'm at 9G I certainly would rather be in the jet that bleeds -500Ps vs the jet that bleeds -1000Ps.

Theoretically, if BOTH planes are starting a 9G pull from the same speed (lets say .9M for the sake of discussion), the F-16 will lose speed slower (retain more speed) but the F-14 will turn quicker and tighter because by decelerating it is moving "left" up the 9G line faster to higher DPS and smaller radii, and since the max lift line of the F-14 is "to the left" of the F-16 then there will be a time where the lift limited Tomcat is still turning with higher DPS and a smaller radius.

Now, only an idiot Viper driver would keep playing this turning game once he saw the Tomcat go from wings back to wings forward in mere seconds. He should then take his game vertical while still holding G. This will tighten the horizontal radius and give a definitive position advantage against the F-14.

In this setup, the F-14 would have dropped from .9M to .7M in the first 90 degrees of turn or so, while the F-16 is still at .8M. If the F-16 pilot goes vertical here while still turning at 9G, he will lose speed, but he has speed to lose. The F-14 pilot is now stuck with a bad choice, reduce G to try and save speed, go vertical at the expense of more speed, or both.
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Unread post15 Nov 2019, 21:52

If the Tomcat pilot wants to stay at Ps=0, and .55-.65mach, fine. As JbGator said, the F-16 can be at -Ps. So lets say the F-14 pilot drills around in circles at Sea Level at .55-6IMN. So he would still have a turn rate as I said at SL of (and going by charted info from the manual ---the Specific Excess Power sheets, for 3G, 5G, 6.5G) around 19.7DPS. And a radius of 1600ft. Now lets take Solo Turk He comes in at 9G and .64 Mach starting radius of about 1800ft. By the time he is done with the turn (at around 5G, his ending radius is now about a little over a 1100ft.) It doesn't take a genius to figure out who wins here. The F-16 is flying with basically the same turn radius while at a far higher turn rate. All throughout this maneuver the Viper's turn circle is shrinking. Look at the video it shows the exact same thing.
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Unread post15 Nov 2019, 21:56

Spurts, I am fully aware of that. The question is (and I had the numbers) since the F-14 is at blazing high -Ps, throughout this turn, does he even ever finish or get close to finishing that turn before he is basically down to landing speeds. We have already seen what Solo Turk can do.


Use that formula for what you did with the F-16 v Gripen thread. I plugged in estimated numbers, using that formula. That is what I'm inferring here.
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Unread post15 Nov 2019, 22:23

I see. In my (admittedly DCS) experience, no. If I ever start at 9G and hold through max lift AoA then I will either black out or be down to .4M within one turn. Best bet is to hold around .55-.6M and 15 "units" AoA. I can't look at the G meter when doing this because of where it is located and the HUD does not provide any ADC info.

That is a bit off topic for this thread though, as that has little to do with onset rates and control laws.
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