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 post16 Nov 2019, 12:14

sprstdlyscottsmn wrote:
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.


Spot on.

Entering and staying in a purely horizontal turn fight is playing the Tomcats fiddle for no good reason, esp. when you're in the rocket ship that is the F-16. Use the vertical in the F-16 and the Tomcat will soon start to struggle.

Hence like Okie has said, given a choice between the two aircraft in a dogfight, I would generally choose the F-16. It's just a much easier aircraft to get max performance out of, and any screw up (which is less likely to happen due to the carefree handling) can more easily be saved due to the higher level acceleration & climb rate.

IMO the F-16 is the ultimate dogfighter of the teen series fighters, an absolute monster in overall performance, outturning anything it can't outclimb or outrun, and outclimbing or outrunning anything it can't outturn, and it wasn't beat until the arrival of the eurocanards & F-22.
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Unread post16 Nov 2019, 12:37

f-16adf wrote: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.


Again, the F-14 pilot can simply choose to match the F-16's instantanous rate and lose less energy as well. The F-14 pilot has the option of pulling a higher ITR & tighter radius if he so wishes. At 5 kft the 55,600 lbs loaded F-14 can pull a 1300 ft level turn if he wants, something the 26,000 lbs loaded Viper simply cannot match.

In short, in purely horizontal fight all the F-14 pilot has to do is to match the F-16's ITR (which is lower than the F-14's) until both aircraft drop to ~0.6 mach, at which point the F-14 is now better able to hold its rate than the F-16 and can thus sustain a tighter & higher rate turn.

But again, why would the Viper pilot ever engage in such a foolish game? If I was the Viper pilot I would stay way above 0.6 mach at all times, and instead quickly climb up over the F-14 and maintain a nice max STR circle above him at around 0.75-0.8 mac. Then when I see the F-14 try to come up to follow me I would gradually tighten the turn until I see his nose start to drop in his effort to pull lead in the climbing turn, then roll over and slide right down in behind him.
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Unread post16 Nov 2019, 15:09

Spurts, this is my point about so called ITR.

I have done an experiment with the Mirage 2000's 15,000ft chart. Now obviously the Mirage has a better ITR than the B Tomcat. And I believe, it at that altitude and 9G, bleeds slightly less energy too or they are similar if you were to equalized war loads for both jets (50% gas and 2-AIM-9). My top bleed for the Mirage 2000 and 9G is at -1600Ps. Estimated for the Tomcat nearly -1600Ps. I remember you estimated a -2200Ps bleed at 10,000ft for it a while back -granted with 8AAMs.


Now this is what I did, I took the Mirage 2000 numbers. I started off with -1000Ps @.8mach, -1400Ps @.7mach, -1600Ps @.65mach, -1400Ps @.6mach, -1000Ps @ .5mach, and -450Ps @ .4mach.

Here is an exmaple of first problem.
-1000fps @.8mach
.8 (1056)= 844.8 , I used 1056 as speed of sound at 15,000ft. I took 720*5280/3600 = 1056
-1000fps/844.8=1.18
1.18 (32.2) = 38.0
38.0/1056 = .0360


So each successive figure:

.0576 for -1400
.0710 -1600
.0674 -1400
.0576 -1000
.0326 -450



I came up with

44.08 degrees of turn in 2.14 sec
17.82 degrees of turn in .78 sec
16.7 degrees of turn in .73 sec
32 degrees of turn in 1.6 sec
38.5 degrees of turn in 2.2 sec


Total of 149.1 degrees of turn in 7.45 sec from .8mach to .4mach, and with an average of 20.01dps turn rate.



Please look at my numbers and see if I made any errors. I have no problems being corrected.


So if these figures are in fact correct, the Mirage 2000, a jet with a great 9G ITR, high lift curve; Doesn't even make it to half of the turn before he is basically at 200KCAS (.4IMN) and out of airspeed/decreasing if he so wishes to ride this curve. And that is why you never see the jet attempt to perform in fact such a maneuver. I would imagine the like for the F-14. They don't even make it to 180, so no pilots of these jets are dumb enough to attempt this high ITR or not.



I also have another question to ask you about computing this.
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Unread post16 Nov 2019, 16:11

Comparing the M2000 with the F-14 is where you're making your first mistake, the former being a pure delta wing will loose a lot more energy in the turn than the variable sweep F-14 due to the much higher lift induced drag penalty of the low AR delta planform.
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Unread post16 Nov 2019, 16:17

True, it's a delta. No argument there. But, As I said, very high -Ps are a bad thing. And the Tomcat's Ps spike is surrounded by them, that is if you indeed want to draw it out to 9G. So lets let the person with the Aerospace Engineering Degrees answer this one.
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Unread post16 Nov 2019, 17:55

Assumptions: Speed of sound at 15,000ft is 1,056ft/s, I’m seeing 1,057ft/s from https://www.digitaldutch.com/atmoscalc/ . Assumed value is within any future rounding error of actual value.
.0360 is M/sec deceleration
You averaged 0.0360M/s and 0.0576M/s decelerations between 0.8 and 0.7M to get your time of 2.14s.
I assume you also averaged the turn rates between these two based on the Mirage chart to get degrees turned in the unit of time.
That is my understanding of your analysis. If that is correct, then I see no mathematical errors and your answer should be within an expected margin of error from reality.

I will do a few DCS Tomcat tests, one at 50% fuel 2 AIM-9s at 15,000ft, another at 5,000ft 8AAM “chart matching”, another SL clean “airshow” test. I will turn blackout off and turn unlimited fuel on so my weight stays constant to perform multiple tests.
What I expect to see is two fold, it will be hard to maintain a given G or AoA as there is no limiter for me to hold against, and I will decelerate rapidly during hard pulls.

Oh, and a few G onset rate tests.

Followup, I saw G onset rates from 3-7G/s depending on speed. It is near impossible to do "x G to y AoA at steady altitude" test in real life in the Tomcat. I either end up slowly building G or overshooting the AoA and stalling out even at .7M.
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Unread post17 Nov 2019, 04:57

I can get onset rates of 20+ G/s in the DCS Tomcat quite easily by just janking the stick back. Just be prepared to lose your wings if you're going too fast.

At 55,600 lbs w/ 4xAIM7 + 4xAIM9 @ 5 kft the DCS F-14B matches the real life F-14B/D EM charts to within 0.05 G in sustainable load factor. Peak STR is reached at 5.6 G's @ 0.56 Mach, and peak sustainable load factor is 7.3 G's @ 0.88 mach.

It's the same story for the DCS F-15C, it matches the real life EM charts very well, and G-onset rate is near instant. The DCS F/A-18 also has a lightning fast onset rate (20+ G/s), despite of thos however it is almost instantly halted by the FLCS at the G limit, a 0.5 G overshoot being the most I've seen.

The DCS F-16 is the only one of the teen fighters so far with a comparatively low G-onset rate and a sort of hesitation to increase the load factor above 8.5 G, the onset rate being slowed much earlier, and as a result it has a hard time reaching 9 G's at its corner speed plateau unless going much faster to begin with. This is not what you see in BMS or can observe on HUD footage, here the F-16 seems to build up G's very rapidly and reaches 9+ G's (9.3) very fast & without any hesitation. Hence this is my biggest gripe with the DCS F-16 atm, as this lack of onset rate makes it feel very sluggish in pitch as compared with the other fighters.
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