F-16 Sustained Turn Performance

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delta2014

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Unread post19 Jan 2015, 21:04

Hello to all,

I recently came across this message board post from 2003 (not a post on this forum). The man who posted this said he flew the F-16. Here is what he said:

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There is no fighter out there that can sustain a 9g turn indefinitely. I fly F-16s, and we can sustain a high g turn better than just about any aircraft in the world, including the F-15. In a clean configuration going into a max g turn at 500 knots in full afterburner, we can only sustain 9g's for a few seconds, then the g's rapidly begin to bleed off as your airspeed decreases. Like someone mentioned above, your instantaneous g will be much higher than your sustained g. Some fighters, have very good instantaneous turn rates, but crappy sustained rates (delta wing aircraft are like that). Others are terrible in both rates (Mig 23 and 25 for example). The F-16 is good in both regimes which is why it generally has an advantage over most fighters in a turning fight.
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In particular, I am interested to know your thoughts regarding this statement:

"In a clean configuration going into a max g turn at 500 knots in full afterburner, we can only sustain 9g's for a few seconds, then the g's rapidly begin to bleed off as your airspeed decreases."

Thanks very much,

Delta2014
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sprstdlyscottsmn

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Unread post19 Jan 2015, 23:40

The key points to know are altitude, initial airspeed, and if this is a max pull. In the described scenario if he had been going 50-75kt faster, and in full AB, he would begin accelerating. No one WANTS to turn under those conditions as your rate is lower and your radius is larger. You always want to be in your "corner" which for the F-16 is between 350 and 450 knots indicated. A more gentle pull can generate a phenomenal sustained turn rate and a hard pull can generate a great instantaneous turn rate. The F-16 at 9G will bleed speed at a slower rate than say an F/A-18 at 7.5G, but it will still bleed off 100 knots in a few quick seconds. Anyway, that is the short answer.
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smsgtmac

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Unread post20 Jan 2015, 06:01

Spurts' speaks the truth of it.

Perhaps a chart covering one altitude will add to the point?
F-16Blk15 at 15k.jpg
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delta2014

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Unread post18 Jul 2015, 00:10

At 350 knots at low altitude, would the F-16 be able to sustain a 6 G level turn at full afterburner power?

Thanks,

Delta
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basher54321

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Unread post18 Jul 2015, 13:42

delta2014 wrote:At 350 knots at low altitude, would the F-16 be able to sustain a 6 G level turn at full afterburner power?

Thanks,

Delta


Yes - e.g. Sea Level / light - actual figure may differ per variant some what.
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Gums

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Unread post20 Jul 2015, 02:39

Salute!

At slightly above 350 IAS and below 5K our early jets would hold 9 gees in burner.

Don't know where this rapid bleed of 100 knots comes from, and I never saw it below 10K or so on a break turn. Hell, in mil power we could turn for 3 or 4 seconds at the limiter before losing little, if any speed.

Guess the later versions grew in weight and even the bigger motors could not compensate for the increased induced drag and such.

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sferrin

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Unread post22 Jul 2015, 18:48

Gums wrote:Salute!

At slightly above 350 IAS and below 5K our early jets would hold 9 gees in burner..


So, on the runway at Hill? :P
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jbgator

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Unread post22 Jul 2015, 19:56

It is important to note that no US pilot is allowed to do BFM at or below 5000' in training. 5K' AGL is the floor for training BFM in USAF and is the same or higher for the other services. So BFM engagements usually start at 18-25K' depending on the elevation below the airspace. So when you hear a USAF pilot talking about what the jet can sustain in BFM they are talking about the 15 and 20K EM diagrams like the one posted by SMSgtMac above. Clearly many on the forum do not know how to read one so a little primer before I go on.

The lines going from lower left to upper right are turn radius in feet. The lines curving down from top left to lower right are G (load factor). The dark and dashed lines that go up from lower left, peak in the middle, and then descend down the right side are the aircraft performance envelope. The left most dark line is the lift-limit line describing the maximum aerodynamic performance of the jet. The upper right descending line is the G-limit line (notice just over 9 Gs). The lines in between are called P-Sub-S lines (Ps) and describe the energy sustained or lost for the given airspeed and G with solid lines indicating Positive Ps (gaining energy) and the dashed lines indicating Negative Ps (losing energy). The bottom scale is obvious as Mach and CAS. The left scale is turn rate in degrees per second. This is a F100-PW220 diagram. I don't recall the differences but I know the Big Lip Blk 30 has better Ps than this (sorry Gums it's better than the A-model). Suspect Blk 50 is too. The F-18A-D is not as good. Don't know about SH. This is for level turn. Climbing or descending turns change the situation.

So looking at the diagram you can see where the quoted USAF pilot is coming from in that at all speeds at 15K in a level turn the F-16A PW220 is in a negative Ps situation and will lose energy. It will slow down at 9G till it gets to about 420 KCAS at which time the aerodynamic limits (AOA limiter in this case) take over from the G limiter and the G drops off down to about 8 G at 350 KCAS and if he keeps pulling max aft stick it will continue to slide down the aero line to about 150 KCAS where it hits Ps zero. If starting at 450 KCAS the jet will be doing an instantaneous rate of about 18 increasing to almost 20 at 420 CAS, holding that till about 350 CAS then dropping off rapidly to just over 10 at 150 CAS. An impressive average turn rate but not the way you would actually turn unless you were defensive against a really capable adversary and, even then, not the best way to respond. Defensively you would max perform the jet till you knew a missile was no longer on the way. This was usually a max performance break turn but not in AB so you slowed down a lot. But 18-20 degrees per second and chaff/flares quickly decided the matter...either you were dead or the adversary comes off to maneuver for a follow up shot or guns. Ease off the G a little, plug in AB, and stuff it in his face. Not 9G, but right to that great plateau only the Viper has between 350-450 CAS at about 6-7 G where the Ps is zero, turn rate is about 14, and radius is 3-4K feet. You can feel it because it is light buffet as the LEFs are just barely programming. Hold that till he cashes in all his chips to get the gun shot and then use all that excess energy to jump right back up to about 18-20 degrees per second, make him overshoot, and reverse to kill.

If offensive, accelerate to the turn circle, go right to 9G to get an impressive circle entry from 500 CAS down to about 350 CAS in AB averaging 18-20 degrees, then same thing. Ease off to the light buffet (6-7 G at 350-450) to herd him around the sky and when he cashes in, you have more, modulate the throttle, vary between lead and lag to get to his control zone, and gun his brains out.

None of this takes into account the vertical component that you use to your advantage to maintain or expend energy as you need to to accomplish your offensive or defensive objective. (kill or survive)

Neutral engagements are mostly like the offensive set up as you expend energy to gain a positional advantage but go to preserve mode in between to maximize performance versus energy loss. The dumb pilot pulls on the pole till he is at 150 CAS and out of options. Flying a Viper or a Hornet.

If you overlay this EM diagram with other jets like the Hornet you will see their impressive nose rates as G/aero spikes to high turn rates but even higher negative Ps. So they have one good turn and then they are slow ducks. The smart pilot flying these jets knows the same strategy I described above and only uses that for specific advantage gain and then goes to energy conservative modes. But the F-16 has what we call a Plateau not a spike. See how the Ps lines level off in the 300-500 CAS range? No other jet has such a large region of high performing yet preservative capability. They have spikes. That is how an F-16 wins and a poorly flown F-16 loses. Yes, sustained 9G at 5K is possible, but not at 15K. Deal is, your adversary is up there with you feeling the same loss of performance and usually more loss than the Viper.

I have heard much about nose pointing with new HOBs missiles. I caution the FNGs that simulated missiles in training BFM using shot criteria is a lot different than real missiles in real situations. Cashing in all your energy to get the quick kill when the missile might not produce expected results is dangerous. If WSEP results are showing that kind of Pk then go for it, but fighter pilots who live to be old fighter pilots usually will not put all their eggs in the Pk basket of one missile. Early on fighting the Hornet in the late 80s they often called kills with AIM-7 and AIM-9M at very high AOA and lots of look up as they would be below the Viper, out of speed, but able to get a vertical auto-lock with their radar and shoot. Later WSEP proved these shots were very low Pk as the missile pitches into the relative wind and exceeds gymbal limits for the missile. Obviously AIM-9X and newer missile with TV will be better but till we have lots of shots in those regimes I wouldn't bet my life on it. Never flew against the MiG-29 but always wanted to see all the WSEP type shots to prove the missile could really do what the HMS and tone seemed to imply. To my knowledge no such massive shot testing ever occurred on those missiles. So SLEM all you want but till I see the data I'm not expecting most of those shots to be effective.

Like Gums, the old guy opines. Take it or leave it. JB
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fulcrumflyer

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Unread post23 Jul 2015, 17:53

Having flown hundreds of sorties with the Russian HMS and AA-11 Archer I can say the combination works very well. The one limitation is that the MiG-29 pilot can't tell exactly what the Archer is tracking once it automatically goes into self-track. In the Spring/Summer of 2003 we (53rd Test and Evaluation Group and 53rd Weapons Evaluation Group) did a missile/aircraft exploitation at Eglin using seven German MiG-29s and fired several AA-11s and AA-10A Alamos provided by the Germans at full and subscale drones. The exploitation was called Project Grace. We initially called it Project Lusty after a WW 2 program to exploit captured Luftwaffe equipment. Lusty was an acronym for Luftwaffe Secret Technology and it seemed appropriate since we were using German MiGs and missiles. Unfortunately, after briefing Gen Jumper, the then USAF Chief of Staff, to get permission to proceed with the exploitation, one of his staffers decided "Lusty" was inappropriate, so we had to change the name. Most of the shots were instrumented so we could capture telemetry data. Within its kinematic envelope the Archer proved to be very effective and eye watering to say the least. I do agree with JBgator's statement; pulling the black out of the stick to be the first one to get to a HOBS WEZ and not having any energy for follow-on maneuvering can prove to be an unwise move. Missiles don't always work and can be defeated by countermeasures and defensive maneuvers.
If you've got access to the classified test report, it's an interesting read.
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sprstdlyscottsmn

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Unread post23 Jul 2015, 18:47

Thanks for the input
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popcorn

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Unread post24 Jul 2015, 00:25

More of what fulcrumflyer speaks of here....http://www.airspacemag.com/military-avi ... 03/?page=1
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