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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hummingbird

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Unread post13 Nov 2019, 05:44

johnwill wrote:Not true. In an F-16, if the airplane is trimmed for 1g in level flight and a pure roll command (no change in pitch command) is applied, the airplane will roll, but the g command and actual g is still 1g, not 0g. If you roll 90 deg or if you roll 180 deg or 360 deg, the airplane will still be at 1g.


Well I am talking aircraft in general, where if you quickly roll left or right from level flight to immediately afterward engage in a horizontal turn, then the G's should briefly drop to near 0 in the horizontal plane before you start pulling back or the aircraft simply settles at that bank angle. I know the F-16 is 1 G trimmed, but if you roll quickly it shouldn't have time to command 1 G before you start the subsequent pull, i.e. it should also depend on the speed of the roll, otherwise the aircraft would be doing a 1 G barrel roll if you just roll the aircraft - and based on BMS or DCS it doesn't trim to 1 G that fast.
Last edited by hummingbird on 13 Nov 2019, 06:19, edited 3 times in total.
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Unread post13 Nov 2019, 06:05

f-16adf wrote:Well, on this one i'm going to have to disagree. I have flown many upon many hard turns (near the Utility Category limit) in Cessna 172's and Cherokee Archer's and upon rolling into the turn I have never experienced zero G. (A Coordinated turn ie. keeping the ball centered with rudder) When I have experienced zero or negative G ---is pulling the yoke back for a few moments and then pushing it forward.


With a sufficiently fast roll where you start level with 1 G in the vertical, you should briefly experience 0 G in the horizontal before you pull pitch in the turn - that is unless you barrel roll into a turn.

If you only roll say 30 deg and then just let the aircraft settle in the bank without further stick input, the aircraft will start turning on its own and you will be experiencing G somewhere in between horizontal & vertical depending on your bank angle, speed & trim. But it will happen gradually, not at an instant, hence why I'm saying that in fast 90 deg roll you will be briefly at or close to 0 G before lift is applied in the horizontal, either on its own or by the pilot via pitch command.

Regarding the Gripen video, https://www.youtube.com/watch?v=eXaPfUs6sQw at about 5:33 his G meter is at 1G and stays positive all throughout turn commencement. His turn to hit 9G takes about 1.16 Seconds nearly matching what the Swedish poster said on this forum about its onset rate. viewtopic.php?f=30&t=1029
The jet simply never hits 9G at 1 second or before.


I never said it did, what I did say was that it is definitely noticably above 6 G/s, which it also is. Hence 6 G/s is not the max G-onset rate of the Gripen, not at all.

Now as far as the F-16 is concerned, and as what the Colonel said in the article I posted: 3G at high altitude (and only bettered by the Raptor). Dropping down from 30-35,000ft to SL, is the question here. I simply am not going to believe unless told by an actual Pilot that you are going to gain approx. 7G/sec in onset rate from that altitude loss.


As has already been mentioned the aircraft doesn't lack control surface effectiveness to reach far beyond even 10 G/s if that's what the designers wanted, the designers deliberately make it so it won't pull that quickly. Hence you can't take a figure for 35 kft and then just linearly scale it for SL.

10 G/s centrifuge profiles would also make zero sense if the Viper wasn't actually capable of such an onset rate.
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Unread post13 Nov 2019, 06:28

What is "aircraft in general" supposed to mean? For a purely mechanical control airplane (is that an aircraft in general?), in level flight, the pitch command holds the horizontal tail at an angle that trims angle of attack so as to develop lift equal to the weight of the airplane. That is called 1g flight. If the pilot commands a roll without changing the pitch command, the airplane rolls and the tail angle remains the same, and the AoA remains the same, and the lift remains the same, and g remains the same, 1g. "g" is load factor, which equals lift/weight.

So, can you explain what in your world makes the "aircraft in general" go to 0 g? Remember 0 g means zero lift. How did the lift manage to disappear? It doesn't matter how quickly you command the roll, the airplane is already at 1 g, so it doesn't need any time to get back to 1 g. The lift vector you have before the roll, rotates with the airplane to maintain 1 g, no matter how fast you command the roll.

Not that it matters.
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Unread post13 Nov 2019, 09:41

I agree that it doesn't matter to our discussion, but allow me to demonstrate what I mean:


As you can see even with the F-16, which automatically trims to 1 G, it takes a tiny bit of time before it trims out to 1 G after a fast 90 deg roll.

As for aircraft without the automatic 1 G trim, this happens:
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Unread post13 Nov 2019, 14:51

"10 G/s centrifuge profiles would also make zero sense if the Viper wasn't actually capable of such an onset rate."


Viper Centrifuge ROR's all have a 6G/sec onset rate. I have already posted the documents that prove it. Yes, certain centrifuges can go much higher. But the ROR's just are not flown at those levels. And if they are please show me a DOCUMENT stating specifically so. Meaning true real life empirical evidence vs anecdotal evidence.

You seriously need to throw out this vicarious flight sim life that you seem to buttress all your premises around. Those sims all have errors and they keep correcting them over time or at least try to, with successive "patches". So what does that tell you? When I see F-18's having superior turn rates above .8 mach or see Tomcats with 32 degree per second ITR, or 21-23DPS sustained turns even at SL, and Mirage 2000's not having the best initial turn, or the designers not seemingly understanding decelerated level turns aka -PS ---yes I laugh.



Any evidence of the Gripen having a 7.5G/sec higher onset rate? Even with the Swedish poster (with the link I provided) divide out all his math. And from the 9G turn in the video, both nearly 7G/sec. 10G/sec seems fantasy land levels.



And as far as the F-16 achieving a 10G/sec ROR, I am seriously going to need something other than your word to believe it as so.
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Unread post13 Nov 2019, 14:57

https://www.wpafb.af.mil/Welcome/Fact-S ... ed-centri/


"Aircrew acceleration training and research/testing missions are conducted in the centrifuge, which is capable of producing 20 times the force of gravity, or G's, and can accelerate up to 15 G's in one second."


Now does that mean just because the Centrifuge at Wright-Pat is capable of 15G/sec onset rates, that the F-16 or F-15 or F-22 for that matter all have 15G/sec onset rates?





F-16 Centrifuge training vid, once again not anywhere near 10G/sec onset rate. Kinda can connect the dots here....
https://www.youtube.com/watch?v=yeIDvevEYuw
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Unread post13 Nov 2019, 22:37

What document have you posted that proves all F-16 profiles are 6 G/s ? Up until now I've got atleast 3 Viper pilots telling me that they've done 10 G/s profiles. So I know what you're claiming isn't true. 6 G/s might be the std. ROR profile for the USAF, but 10 G/s ones exist.

Also I've yet to hear a single Viper pilot claim that the centrifuges can match the onset rate of the real aircraft, on the contrary all who have ever spoken on that subject have said the exact opposite, i.e. the centrifuges are nowhere near as brutal as the real aircraft.

Also in this very thread you've got actual SME's saying that 6 G/s is "definitely on the low side".

Furthermore the EF Typhoon which features similar AoA limitations as the F-16 is capable of 10 G/s, as designed. Why would F-16 designers limit the Viper to a lower G onset rate than this? Are you going to claim that the F-16's control surfaces can't generate the lift needed for 10 G/s ?
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Unread post13 Nov 2019, 22:58

https://static.e-publishing.af.mil/prod ... 11-404.pdf
"Type 2 Aircraft—Aircraft capable of rapid G-onset rates greater than 6.0 G/sec and sustained
G-loading greater than 5 seconds above 7.5 G. Examples of USAF military aircraft meeting this
definition are the F-15 C/D, F-16, and F-22A."
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Unread post13 Nov 2019, 23:33

Read that doc carefully, it is saying that they are: "Aircraft capable of rapid G-onset rates greater than 6.0G and sustained G-loading greater than 5 seconds above 7.5G.

This proves absolutely nothing because I have always said that the onset rates are above 6G/sec. But you seem to think that >6G/sec = 10G/sec onsets which it certainly does not. If anything it further proves my point that the ROR's are all flown with 6G/sec onsets. Which I have already stated numerous times.

So a jet that is supposedly capable of 10G/sec onsets, yet the pilots are only exposed to training with 6G/sec onsets, All the while the centrifuge they train in can do 15G/sec onsets. Hmmm, that makes a lot of sense.......



Finally, I never said that the G loading was not greater than 6G. What I said for the Viper is that it probably is like the Gripen aka 6.7 to maybe 7G/sec. Since when does a 6.7/6.8G/sec or even 7G/sec onset equal to the far off figures that you are postulating aka 10G/sec for the Viper?
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Unread post13 Nov 2019, 23:41

http://www.airforcemag.com/MagazineArch ... glock.aspx


and


"After pilots complete the GOR run, they proceed to the ROR exposures. These consist of onset rates of six Gs per second up to plateaus of ten to fifteen seconds duration at levels ranging from +5Gz to +9Gz. Because fighter Pilots spend a lot of time looking over their shoulders, they are given the opportunity in training to take rapid onset runs while in the "check six" position. These ROR, high-G runs are the brass rings of the training program. On successful completion of this program, the pilot is well trained and confident of his ability to cope with eight or nine Gs in his aircraft. The success of this program has been demonstrated by the marked drop over the past three years in the rate of pilot losses to G-LOC."


See, you were saying that centrifuge training uses 10G/sec onsets, which it once again, does not.
download/file.php?id=31745&mode=view




Also, I don't claim to be anything. But I can read a flight manual. So where does the F-14 get a 21-23DPS SL STR? Why does a Shaw Block 50 weigh the same empty as a Greek Block 50? How come the Block 50 isn't doing 17 second complete 360 degree turns as the jet does in real life? Why is the Hornet on steroids past .8Mach? Why did they dummy down the Mirage 2000?
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Unread post14 Nov 2019, 00:55

Again this isn't about std. USAF ROR profiles (esp. since different countrys AFs use different ROR profiles), it's about the max g-onset rate that the real aircraft is capable of, and I've seen nothing that would indicate it should be below at least 8 G/s, and I'm confident it's capable of even more.

Off Topic: Why are you all of a sudden talking about the F-14? Do you feel it is overperforming in DCS? I can tell you for a fact that it isn't. Flying with everything set to auto, as you should, the DCS F-14 is matching the real life performance charts precisely. To achieve anything like 20 dps STR at SL you will need a completely clean aircraft with about half fuel. (Unless you're talking about a few people "cheating" and dropping full flaps not caring they will jam in order to achieve a higher rate ofcourse, but that has actually patched recently)

Same goes for the DCS F-15C btw, it closely matches the real life performance charts for the jet.

As for the DCS F-16, I can do a sub 17 sec 360 turn in it no problem. My three only problems with the DCS F-16 FM atm is the oddly low G-onset rate (much lower than in BMS which by comparison feels right), the too low full mil thrust and finally the inability to apply more than -2 G's, where'as HUD footage shows -3 G sustained negative loops.
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Unread post14 Nov 2019, 02:28

It's really simple to find its turn rate at Sea Level, ie standard day. Reference Figure 9-2. Specific Excess Power Diagrams (Sheets 2,3,4 of 12). 3G at SL happens at about .33 mach. 5G at SL at about .46 mach, and 6.5G at SL at .62 mach. Now Superimpose those on the diagram and with the generally same upward curving arch it, should top off at about 18.2 or 18.3 DPS. That is with 4 Sparrow, 4 Sidewinder. Tear off those missiles and 2 pylons and a good, or more realistic number is now about 19.3-19.4DPS. at SL w/50% fuel.

For the Hornet, there are published numbers telling that after .7mach its turn rates go down. Although I will say that there are CF-18 demos from the mid 1980's showing it completing a 360 in under 18 seconds. I have a book that says its max STR is slightly over 20DPS. But not happening at .8 or .9 mach-

It is well known that the Mirage has the best initial turn of all those jets. SL it is around 29DPS. or a little over.



As far as the F-16 there are Solo Turk demos of him completing 360 degree turns, though not at Ps=0 (but above), in crazy minimum times of 14-15 seconds. And he is in a Block 40. Starting at about 2:35 mark https://www.youtube.com/watch?v=q36JblL7IRg

And I'm sure the Block 50 isn't too far off that insane turn figure.


So that is my take on it-





As far as the G onset, (and it's getting to the point of absurdity here). Here is the report of GLOC of Thunderbird jet and his maneuvers. Now I'm certainly not implying max onset is 5.8 as in that one column. But the guy was flying a clean jet, and there are no figures at or around 10G/sec as far as initial onset rates in this report. Or even in pilot error to accidentally induce or go past 6. Although, the maneuver may have not required anything above 6 to get it started. Yet, unfortunately, there was still a fatality here going from -G to +G, i.e Push/Pull. But I'm still sticking to my estimate of 6.7-7G/sec, or until an actual F-16 driver does in fact tell me I'm wrong.
F-16 Thunderbird pg.jpg



From this report:
https://www.acc.af.mil/Portals/92/AIB/1 ... 132501-787
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Unread post14 Nov 2019, 09:50

Said fatality report obviously doesn't show us the max onset rate the aircraft is capable of, it just shows us the onset rates typical for that demo routine. G-LOC fatalities, just like that one, also typically happen after having sustained a high amount of Gs for a prolonged time, not a milisec rapid onset pull / jerk. A report on human physiological limitations concludes that 12 G/s can be pulled unstrained for 1.5 sec before G-loc, as the brain has enough reserve oxygen to last for that long without any blood flow before it starts shutting down.

For context F-15 pilots for example were found to conciously rarely apply onset rates of more than a smooth 4 G/s during ACM training, eventhough said aircraft features no limiter and can go way above 10 G/s. The qouted reason being that they felt if they started applying anything above 5 G/s they no longer felt confident they could reliably stay within the 7 G limit they usually operated under by feel. In short they were self regulating their stick inputs in order to stay both comfortable and safely within the limits. In real combat however they always had the ability to jerk out a way faster onset rate should they need it.

As for the F-16, it has massive control surfaces for its size, hence if the designers wanted it they could have set the g-onset rate way beyond what any pilot would find usable or safe. But since 9-10 G/s was deemed applicable in the EF 2000 there's no reason to believe that the F-16 isn't similar in this regard, esp. since too low an accessible G-onset rate can be deciding disadvantage in a dogfight, as the fighter that can reach a certain G the fastest will have a head start in any angles fight.


As for the DCS F14 again:
Remove the 4x AIM7's + 4xAIM9's plus their glove pylons and I see no reason the F-14B shouldn't be capable of 20 dps at SL - a figure that quickly rises as the F-14 burns through its fuel.

We tested the F-14B @ 55,600 lbs w/ 4xAIM7 + 4xAIM9 and unlimited fuel (50%) and it matched the performance charts to within -/+0.05 G in sustainable load factor. (we dont measure dps as there's no reliable way of doing this for dcs except calculating it from the load factor reached. And using tacview is a big no no)


Btw the F-15C is capable of 18.5 dps at SL with the same load out as pr. its performance charts, and since it's in general ~0.5 dps lower than the F-14 in max STR I'd expect about 18.7-19.2 dps for the F-14B with afforementioned load out at SL. Remove the drag & weight of the missiles and pylons and you're at 20+ dps easy.


As for the DCS F/A-18 we agree, something is off with its FM, it shouldn't be outrating the F-16, esp. not above 400 knots, but I believe this stems of ED lacking actual EM charts for this aircraft.
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Unread post14 Nov 2019, 11:05

Also in the RAF the std. ROR centrifuge profile for EF pilots is 9 G reached at 6 G/s and sustained for 15 sec (NATO standard), despite the aircraft itself being capable of 9-10 G/s, hence a 10 G/s profile is made available by the new Thales centrifuges in the UK, and an onset rate capability of atleast 10 G/s is recommended for all new centrifuges constructed in NATO countries (the Poles recommended this in the early 2000's).
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Unread post14 Nov 2019, 15:33

If the onset is truly 8G/sec, yes, that seems more believable than 10G/sec. But as I said earlier, it would not make too much sense if the Centrifuge at Wright Patterson AFB can attain 15G/sec, while the Jet is capable of 10G/sec onset, yet (as all the docs/videos say) F-16 pilots are only trained to about 6G/sec onsets in their ROR's. But, you do bring up a good point about what the Brits do with the EF.



Concerning the Tomcat, I have taken those SL SEP chart numbers from the manual, and I come up with ~.5DPS (give or take) lower than what you come up with. I figure it out to be in the mid 19's (again-give or take) with a clean jet at 50% fuel, SL. I extrapolated the weight of the 8 missiles and their effect on performance/ differences from the other 57,193 and 59,695lb load out charts. Losing that weight/drag from 8 AAMs/pylons is going to effect it less since it is a giant airplane to begin with. But either 19.4 or 19.5, or as you say maybe near 20 is not a big deal. My issue is watching some vids of it going beyond that. For instance I witnessed slightly over a 32 degree TRT. Yes, at an instant (and tac view or not). But even with Flaps down (and we must remember lowering flaps increase lift, BUT, beyond a point it also starts to increase drag) and the temp down to -15. That figure seems like an embellishment (lift limit out to 9G or not). The only jets that can attain near 32 degrees or slightly over are the F-22 and the Rafale/possibly Typhoon. The Gripen is 30 degrees and change. And the Mirage 2000's is slightly over 29 degrees. 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.




The reason why the YF-17 failed the LWF competition was because it, at .7 mach and beyond, was outperformed by the YF-16 (together with other issues -- Acceleration, Fuel, etc). And from what I read- by an increasing margin. Conversely, .7mach and under the YF-17 did best the YF-16, but not by a large amount. There is also a chart posted on the net, of it having an approx 2DPS disadvantage to the F-16A at .9mach and 15,000ft. The F-16 is about 14.3, Hornet is about 12.3. And a book from the mid 1990s says near the same, that at .8-.9mach the F-16 out turns it by increasingly larger margins. According to WAJ and IAC, the Hornet does in fact have a STR a little over 20DPS, but not at .8-.9IMN.





Other than that, some of these sims don't seem too bad. I guess the guys that attempt to develop them try their best as far as you can attain with VR.
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