F-16C, F-16E vs F-14D

Agreed, it will never be a fair fight but how would the F-16 match up against the ... ?
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f-16adf

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Unread post26 Aug 2017, 14:06

You guys might want to get Quicksilver's opinion on fighting the two. He flew against Tomcats and Eagles at NFWS, I believe.
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hummingbird

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Unread post26 Aug 2017, 18:33

Eloise wrote:But if you look at the maneuver devices charts, when you reduce the altitude, clearly the wing sweep back sooner, maneuver flaps are also retracted at slower velocity, up to 0.3M different between sea level and 35k ft


The maneuver flaps have speed restrictions due to pressure concerns, i.e. any speed above x mach @ x altitude will cause damage, thus when operating these you have to keep within the envelope, the CADC doing this automatically. i.e. said envelope has nothing to do with wing sweep, where on auto there are 2 fixed channels with a variable in between. By comparison the slats are entirely dependant on AoA vs speed out to M 0.85 irrespectice of altitude.

Eloise wrote:The flight test data doesn't give me lines above 6.5G curve, so to extrapolate over G values like you wanted i need to find CLmax.


The charts stretch to 7.5 G's and the lift curve does not change in shape between the two fixed sweep schedules for <14 kft & >20 kft, it is just moved back or forth with the points of flap & slat extension/retraction being a mere 0.03 mach apart.

Also I should note that looking at the 5 kft, 10 kft, 15 kft, 25 kft and 35 kft lift & Ps charts I see no change in the lift curve until mach .85.
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Unread post26 Aug 2017, 19:51

hummingbird wrote:Also I should note that looking at the 5 kft, 10 kft, 15 kft, 25 kft and 35 kft lift & Ps charts I see no change in the lift curve until mach .85.

I'm sorry, but here you are flat out wrong. Calculating CLmax is very easy with the charts you have provided. It is a straightforward thing with effectively no room for error. I have already plotted CLmax for the tomcat at 35,000 using the chart you provided and have proved that CLmax does indeed drop as speed increases the entire time, not just where the flaps stop working. If CLmax was the same then at twice the speed needed for 1G there would be 4G available, but there isn't. The max CL is steadily declining which is why it looks to you as though it is not changing. Run the numbers and you will see.

Since you are one of those "body lift" types then just use Lift Area (lift coefficient * area) LA

Lift=Weight*G=.5*.002377*sigma(ratio of density over sea level density)*(Mach*speed of sound in feet per second)^2*LA

Looking at how G changes with Mach (as everything else is constant) you can see how LA decreases as speed increases at any point on the 35,000ft chart.

Oh and to help out, at 35,000ft sigma is 0.309875 and the speed of sound is 972.885 feet per second.

I have not run the numbers on the lower altitudes, but at 35,000ft the maximum lift coefficient is dropping.

And please stop using the term "lift curve" here as it is incorrect. lift curve refers to the CL vs AoA chart.

Using the V-N diagram (gee vs speed) I made the CLmax vs speed chart. I then used that to make a Turn Rate vs Mach chart. Then someone posted an actual turn rate vs Mach chart, and what do you know, the math holds up to a reasonable margin, enough to be human error is grabbing the second or third significant digit from the V-N chart.
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madrat

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Unread post26 Aug 2017, 21:40

What makes the lift drop off so much at .85 mach?
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hummingbird

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Unread post27 Aug 2017, 06:53

sprstdlyscottsmn wrote:
hummingbird wrote:Also I should note that looking at the 5 kft, 10 kft, 15 kft, 25 kft and 35 kft lift & Ps charts I see no change in the lift curve until mach .85.

I'm sorry, but here you are flat out wrong. Calculating CLmax is very easy with the charts you have provided. It is a straightforward thing with effectively no room for error. I have already plotted CLmax for the tomcat at 35,000 using the chart you provided and have proved that CLmax does indeed drop as speed increases the entire time, not just where the flaps stop working. If CLmax was the same then at twice the speed needed for 1G there would be 4G available, but there isn't. The max CL is steadily declining which is why it looks to you as though it is not changing. Run the numbers and you will see.


Take a minute before you respond next time because you obviously didn't correctly interpret what I wrote. What I was talking about was the difference between the lift limit curve at different altitudes, specifically at the boundary of the flap/slat operating envelope, not wether or not the CLmax changes with speed which ofcourse it does as the wing gradually sweeps back changing the planform. In short what I was trying point out was that there's only a 0.03 mach difference at the point of flap/slat deactivation between the two CADC schedules for below 14kft and above 20 kft, i.e. basically none. That's it. How you read that as me saying the CLmax doesn't change, I don't know.

Since you are one of those "body lift" types then just use Lift Area (lift coefficient * area) LA

Lift=Weight*G=.5*.002377*sigma(ratio of density over sea level density)*(Mach*speed of sound in feet per second)^2*LA

Looking at how G changes with Mach (as everything else is constant) you can see how LA decreases as speed increases at any point on the 35,000ft chart.

Oh and to help out, at 35,000ft sigma is 0.309875 and the speed of sound is 972.885 feet per second.

I have not run the numbers on the lower altitudes, but at 35,000ft the maximum lift coefficient is dropping.


Again no disagreement regarding the fact that the CLmax drops, ofcourse it does.

And please stop using the term "lift curve" here as it is incorrect. lift curve refers to the CL vs AoA chart.


I am talking about the max lift limit curve, I just called it a lift curve out of convenience. We can call it a lift limit curve or IT load factor curve instead if that suits you better.
Last edited by hummingbird on 27 Aug 2017, 07:20, edited 3 times in total.
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Unread post27 Aug 2017, 07:09

madrat wrote:What makes the lift drop off so much at .85 mach?


The retraction of the maneuver slats & flaps.

Here's the 35,000 ft chart for when the maneuvering devices are not operating vs when they are (note the sharp dink to the Ps curve as well at the point of retraction):

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eloise

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Unread post27 Aug 2017, 09:37

hummingbird wrote:The charts stretch to 7.5 G's

The Ps curve doesn't touch 7.5 G
hummingbird wrote:the lift curve does not change in shape between the two fixed sweep schedules for <14 kft & >20 kft, it is just moved back or forth with the points of flap & slat extension/retraction being a mere 0.03 mach apart

The slats are extended and retracted at a fixed speed at all altitudes and you can say 10° of wing sweep differences will not affect Clmax considerably but the maneuver flaps retraction point has approximately 0.35 Mach differences between sea level and 35k ft. That can not be ignored.


hummingbird wrote:Also I should note that looking at the 5 kft, 10 kft, 15 kft, 25 kft and 35 kft lift & Ps charts I see no change in the lift curve until mach .85.

The lift-speed chart at 15kft is cut flat at 0.67M due to G limit, you will not know about CLmax fluctuations after that point.
F-14 lift 15kft.png


I think we can know lift curve change without even without running the Maths because Clmax on Em diagrams are curves instead of straight lines
10k ftEM chart.png

F-14 EM 10k.jpg
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eloise

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Unread post27 Aug 2017, 13:49

madrat wrote:What makes the lift drop off so much at .85 mach?

When sweep angle of the wing increase, the steepness of CL/AoA curve is reduced. But higher sweep wing will stall at higher AoA, so CLmax doesn't reduce as much as Cl/Cd ratio. In short, higher sweep reduce sustain turn rate more than it does to instantaneous turn rate.
With speed between @0.6M - @0.85M, F-14 uses higher AoA to compensate for a more gentle lift curve.
However @ 0.85M @35k ft both slats and flaps of F-14 are retracted, that reduce stall AoA. Stall AoA reduced =>Clmax will decrease => lift will drop.

edit: according to the manual, F-14 started to sweep the wing back after 0.45M, but @14k ft between 0.45M - 0.6M the wing only sweep back by 1°, while it sweep back by 47° between 0.6M-0.85M so i ignored effect of the initial sweep.
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Unread post27 Aug 2017, 19:52

eloise wrote:The Ps curve doesn't touch 7.5 G


We were talking about ITR, not STR. It was the max lift limit curve (or ITR curve) that I said would reach 9 G's before the that on the F-16, not the Ps (or STR) curve past M 0.65 where the F-16 is definitely ahead.

The slats are extended and retracted at a fixed speed at all altitudes and you can say 10° of wing sweep differences will not affect Clmax considerably but the maneuver flaps retraction point has approximately 0.35 Mach differences between sea level and 35k ft. That can not be ignored.


And it isn't, everything is on the charts.

The lift-speed chart at 15kft is cut flat at 0.67M due to G limit, you will not know about CLmax fluctuations after that point.


That is true, but I still have the curve for both with and without maneuver devices operating, thus I can draw the line from the point of maneuver device deactivation with the 2nd set of curves where they are not operating.

I think we can know lift curve change without even without running the Maths because Clmax on Em diagrams are curves instead of straight line


That is the max lift limit curve, same as on the other chart, the doghouse plot for operational use just only goes to the navy limit of 6.5 G's.
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Unread post28 Aug 2017, 12:23

I always wondered why it added sweep at high altitudes when the air thinned out. I would think it would benefit from less sweep as altitude increased. I can see torsion twisting being an issue at lower altitude, but not so much at 36,000 feet. Too bad we never got to see some of that wing engineering that went into the F-111 program make its way into the F-14 program.

Having ordnance under the wing and away from wing fences probably would have added some safety. Then again, the wings probably would have become fragile...
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Unread post28 Aug 2017, 15:43

hummingbird wrote:We were talking about ITR, not STR. It was the max lift limit curve (or ITR curve) that I said would reach 9 G's before the that on the F-16, not the Ps (or STR) curve past M 0.65 where the F-16 is definitely ahead.

I was actually comparing it with F-15.
F-16 has a hard aoa limiter so it never reach Clmax, i don't expect F-16 instantaneous turn rate to be good

hummingbird wrote:And it isn't, everything is on the charts.
That is true, but I still have the curve for both with and without maneuver devices operating, thus I can draw the line from the point of maneuver device deactivation with the 2nd set of curves where they are not operating.

It is a lot easier and more accurate if you just calculate Clmax with the diagrams value then put it in excel to draw the curve.
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Unread post28 Aug 2017, 15:45

madrat wrote:I always wondered why it added sweep at high altitudes when the air thinned out. I would think it would benefit from less sweep as altitude increased

The sweep is smaller at high altitude.
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Unread post28 Aug 2017, 22:23

eloise wrote:I was actually comparing it with F-15.


But why the sudden focus on Ps? We litterally have all the data for Ps since the F-14 is incapable of sustaining 9 G's, thus the 7.5 G limit never inhibits precise observation of the Ps curve.

F-16 has a hard aoa limiter so it never reach Clmax, i don't expect F-16 instantaneous turn rate to be good


The F-16 has a very good ITR despite of this, the FCS being AoA biased towards a high L/Dmax for best STR but still allowing for 9 G's ITR to be reached as soon as possible without risking a deep stall, hence the F-16's decreasing limit from 25 to 20 and finally 15 deg AoA.

hummingbird wrote:It is a lot easier and more accurate if you just calculate Clmax with the diagrams value then put it in excel to draw the curve.


Maybe, I wouldn't know as I don't use excel :P
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Unread post03 Sep 2017, 17:37

I am not a NFWS alum, but have fought Eagles and Tomcats many, many times. I learned BFM when it was G/H/P 'winders and exclusively LCOS gunsights. Lotsa maneuvering for envelope management that simply doesnt exist in the same context today.

'A' model Tomcat a much different BFM adversary than a B/D Tomcat, accepting for the moment an assumption of similar pilot proficiency (a big assumption...). The difference, of course, was the engines -- vastly different Ps and freedom to maneuver without fear of stalling the engine. TF-30 shortcomings in the 'A' are extensively documented in the public domain.

Eagle generally a tougher BFM opponent, but there were periods of time where pilots were getting less BFM exposure (cyclic budget stuff that affects everyone from time to time) and it was apparent in the apparent BFM proficiency of Eagle guys. You've got X number of sorties per month; do you spend it on BFM or BVR stuff? Always a delicate balance that COs/OpsOs/TrainingOs had/have to balance.

I know it's fun to compare the charts and the numbers but, in my experience, the quantifiable differences were always subordinate to pilot ability/experience -- always. That was then, this is now and things have changed.
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