Cat III Limits AOA
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The CAT III system is a g-command system with only an AOA feedback. It won’t take your loadout configurations or Gross Weight into account. You are able to pull 9G at low AOA. But as soon as the AOA reaches 15.5°-15.8°, max G command is reduced to 1G in order to prevent any AOA excursions. (According to T.O.1F-16CM-1-2, each type of configurations has its own G limits. And pilots are responsible for keeping the jet below the limits. FLCS will not do that for you.)
The concept is, by limiting the AOA, the available Gs will be reduced. (pure physics). Let’s take an HAF F-16C Block52+ flying at 0.4Mach and 10000Ft with a Gross Weight of 34000lbs for instance. Under CAT I configuration, you can pull to a max 2.3G. But with CAT III, the load factor reduced to 1.6G. This is because the aircraft requires higher AOA to produce enough lift in order to reach a higher load factor (under a certain Gross Weight/Airspeed conditions).
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… The concept is, by limiting the AOA, the available Gs will be reduced. (pure physics)…
Don’t get it yet. If the maximum G is 9+, and you can get 9+ with the CAT III limiter, how does limiting the AOA to 15.5°-15.8° reduce the available Gs? And a AOA larger than 15.8° reduces Gs anyway.
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Because G is the acceleration due to lift on the aircraft in the direction of the normal axis.
What causes lift? A complex question. However, for the alpha values within the limiters on the F-16, as you increase alpha you increase lift. On a conventional aircraft, this holds true until some critical alpha, which is termed a stall.
at high subsonic speeds in the F-16, it attains 1G flight with about 3° alpha. It gets more G with more alpha. You pull back on the stick, it raises the nose, increasing the alpha, and the G correspondingly.
You can see then, that limiting the available alpha does limit the available G. As the alpha gets to 16°, the FLCS limits the available G command to prevent the alpha increasing further.
AoA/G Limiter
Refer to Figure 1-58. In cruise gains, the AOA/g limiter reduces the positive g available as a function of AOA. The negative g available is a function of airspeed. Below 15 degrees AOA, the maximum positive g available is +9g. As AOA increases, the maximum a,llowable positive g decreases. The positive g limit and maximum AOA depend on the position of the STORES CONFIG switch . In CAT I, positive g decreases to a value of 1g at 25 degrees AOA. Maximum commanded AOA is approximately 25.5 degrees. In CAT III, maximum AOA varies from approximately 16-18 degrees as a function of GW and g. The negative g available above approximately 250 knots is - 3g. Below 250 knots, the available negative g varies between -3g and zero g as a function of airspeed, altitude, and AOA.In takeoff and landing gains, the STORES CONFIG switch has no effect on limiting or gains. Maximum positive g is a function of airspeed and AOA. The negative g command limit is not a function of airspeed. It is a fixed limit. The maximum AOA for 1g is approximately 21 degrees. In inverted or upright departures, the AOA/g limiter will override stick pitch commands if the MPO is not engaged. The MPO can always override the negative g fu nction of the limiter. It can also override the AOA function of the limiter when the AOA exceeds 35 degrees. Refer to MANUAL PITCH OVERRIDE (MPO) SWITCH, this section.
According to T.O.1F-16CM-1-2, each type of configurations has its own G limits. And pilots are responsible for keeping the jet below the limits. FLCS will not do that for you.
The G limits imposed by the STORES CAT switch are only there to protect the airframe from departures, and are only ‘secondary’ limits due to the actual limit, which is limiting the alpha (as you do state).
Additionally to the effects of the STORES CAT switch, many stores the F-16 can carry are not flight tested as rigorously as the aircraft - or ARE tested so rigorously, and found to fail before the aircraft does. As such, many stores have their own associated operating limitations, found in the appropriate -1-2 to the jet you are operating. For instance, sidewinders carriage airspeed limits are up to the aircraft limit airspeed of 800kts/M2.05, whereas centerline fuel tanks have a max carriage limit airspeed of 600kts/M1.5.
The key thing to note there is that the FLCS provides no protection to stores from over-G. It is as Peregrine says above, that the pilot is responsible for staying within the stores limitations for the loadout he (or she) is flying.
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I see in that one you ALSO linked to a previous thread XD
How deep does the rabbit hole go??
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The CAT III system is a g-command system with only an AOA feedback. It won’t take your loadout configurations or Gross Weight into account. You are able to pull 9G at low AOA. But as soon as the AOA reaches 15.5°-15.8°, max G command is reduced to 1G in order to prevent any AOA excursions. (According to T.O.1F-16CM-1-2, each type of configurations has its own G limits. And pilots are responsible for keeping the jet below the limits. FLCS will not do that for you.)
The concept is, by limiting the AOA, the available Gs will be reduced. (pure physics). Let’s take an HAF F-16C Block52+ flying at 0.4Mach with a Gross Weight of 34000lbs for instance. Under CAT I configuration, you can pull to a max 4.8G. But with CAT III, the load factor reduced to 3.8G. This is because the aircraft requires higher AOA to produce enough lift in order to reach a higher load factor (under a certain Gross Weight/Airspeed conditions)…
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You can see then, that limiting the available alpha does limit the available G. As the alpha gets to 16°, the FLCS limits the available G command to prevent the alpha increasing further…So I put 34089 pounds of bombs on the jet and CAT III was automatically set. And took off. Using the chart Peregrine provided, at 10,000 feet what kind of feedback from the jet instruments, or the jet itself, should I look for at mach .4, mach .63, and higher mach as I attempt to pull Gs?
Edit: Just saw Toad’s post, but may I get a response here anyway?
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If you make a limiter pull with a GW of 34K lbs, in CAT III at 10K ft and M0.4, in a block 52 jet, you will get 3.66G. If you first switch to CAT I, you will get 4.8G instead. If you accelerate to M1.0 first you will get 9.0G instead.
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the purpose of CAT limiter has never been to control G’s or protect stations from overG
point beeing you can pull 9G easily in cat3
the purpose of the CAT limiter is to restrain AOA / G couple and roll rate to limit the roll depatures in case of loads.
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You can see then, that limiting the available alpha does limit the available G. As the alpha gets to 16°, the FLCS limits the available G command to prevent the alpha increasing further.There was a chart in the original post. How do you read that chart?
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Yeah, we goofed it up actually.
Enter the bottom of the chart with mach number, and follow it vertically until you intercept the altitude reference line. Follow that across to the baseline on the left panel. Enter the panel at the bottom with gross weight and follow that vertically upward. Then from the original entry at the baseline, draw a line parallel to the curve to the second line drawn from GW, then go horizontally left to read available G. I think.
Its all in the dash, but I dont have it to hand at the moment, so thats guessing really.
The goof was that the chart has a sample entry in green and red, showing two speeds (M0.4 and M0.66), but it doesnt use the correct baseline and I think overestimates allowable G due to that. Would have to check the dash to be sure.
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Yeah, we goofed it up actually.
I don’t think you goofed that chart up. It shows the correct baseline at 34,000 pounds for CAT I and CAT III, and the Gs for 10,000 Altitude and mach .4 and .6. Anyway, here are the instructions from T.O. GR1F-16CJ-1-1
Actually, the chart I was asking about was the chart you included in your post yesterday at 01:30, the 4th post in this thread. How do you read that one?
Edit:
I read Flight Model (FM) Developer’s Notes Part 4, “Revealing the Dark Side of the F-16-FLCS”, pages 16-17 but I’m still not sure how to interpret those dashed lines. -
Oh. Well, that one is a lot easier - or simpler perhaps is the better word.
Conditions to the left of the appropriate line are valid. Conditions to the right of the appropriate line are outside the FLCS limits.
At 15 degrees alpha, you can get 9G if you are going fast enough, regardless of CAT switch position. At 25 degrees alpha, you can only get 1G flight - and then only in CAT I. Switch to CAT III at that moment and it would command nose down to lower the AoA to somewhere around 15.5 degrees alpha.
As for the other chart, I didnt goof it up in my last post, but the one prior, and the colors highlighting an example, are goofed at the part where the two lines meet. It does mean that the numbers I quoted are incorrectly high.
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…Conditions to the left of the appropriate line are valid. Conditions to the right of the appropriate line are outside the FLCS limits.
At 15 degrees alpha, you can get 9G if you are going fast enough, regardless of CAT switch position. At 25 degrees alpha, you can only get 1G flight - and then only in CAT I. Switch to CAT III at that moment and it would command nose down to lower the AoA to somewhere around 15.5 degrees alpha.
Thanks for this explanation of the dashed lines in the chart in post #4 of this thread.
As for the other chart, I didnt goof it up in my last post, but the one prior, and the colors highlighting an example, are goofed at the part where the two lines meet. It does mean that the numbers I quoted are incorrectly high.
You got my head spinning on this. When you say “my last post, but the one prior” which post are you talking about? The chart in post #2 in this thread looks OK. If possible, could you show the chart that you say is incorrect and then show a corrected version of that chart?
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The chart is correct - the green and red lines overlayed on that chart show an invalid solution.
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Sry my fault. Corrected:
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Here’s the corrected….
okay, Im too slow.
Here’s my version XD
