A quick explanation of CatI/Cat III (Stores Config)
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I see quite a few people on these forums who seem to be a bit confused about what the STORES CONFIG switch does. Hopefully this quick note will shed some light on the subject.
First off, we need a small history lesson. (Uh-oh, there goes Toad again…) Since the invention of the airplane, and the subsequent use of it in military applications, more pilots have been killed in training accidents than have been killed in battle. In fact way more. And the single biggest cause of those accidents is what is known as a “departure”, otherwise known in civilian aviation as a “stall”. A “departure” occurs when the critical angle of attack is exceeded. It is not a direct function of speed, but a direct function of the angle at which the relative wind strikes the wing chord line. The wing chord line is a theoretical line going straight from the leading edge of the wing to the trailing edge of the wing. Here’s a drawing of it:
When the critical angle of attack (AOA) is exceeded, the air flowing over the top of the wing becomes disturbed, circling in vertical eddys or vortices above the wing rather than flowing smoothly across the top surface, and this greatly reduces the lift the wing can produce. Basically the wing stops holding the airplane up. Now in normal airplanes, this is not necessarily deadly…stalls and spins and recoveries are taught regularly. But fighter airplanes are designed to be less stable than their civilian counterparts. This means that the center of gravity is closer to the center of lift. (In fact that’s pretty much all that means, but that’s another discussion…;) ). So stalls or departures are more difficult to recover from in fighters than in, say, a Cessna 172.
So military pilots must be extra careful not to depart their airplanes. But in the heat of battle, or even the heat of training for battle, guys want to yank and bank their airplanes to get the advantage over their opponent. So the engineers who designed the F-16 created the FLCS (Flight Control System). One of the jobs for the FLCS is to try to prevent the pilot from departing the airplane. (Ah!)
The FLCS limits the AOA that the pilot can put the airplane into. It does also limit the G that the pilot can induce, but this is dependent on airspeed, and is usually 9 G. Here is an excerpt from the F-16 C/D Block 50/52 “Dash One” manual:
_CATEGORY I LOADINGS
The FLCS minimizes the possibility of departures or spins. Roll rate inputs command flaperons and horizontal tails for roll power to provide a relatively constant roll response. Maximum command 360-degree rolls at subsonic speeds may cause a slight g reduction on termination. At supersonic speeds, maximum roll rates may cause a slight increase in g. AT high AOA and low airspeed conditions, roll performance is reduced by the FLCS to minimize pitch/rool coupling. Aft CG’s, open speedbrakes, asymmetric missiles, or centerline stores decrease departure resistance.
CATEGORY III LOADINGS
Aircraft response with most category III loadings remains similar to that of the clean aircraft; however, large stores significantly increase total aircraft drag and reduce performance. Light buffeting may occur during level flight at approximately 0.92 mach. In addition, surging may occur near the store limit airspeed, especially at low altitude. Neither condition requires specific action.
With STORES CONFIG switch in CAT III, the AOA/g limiter provides departure resistance for all category loadings. Except for the requirement to avoid structural overstress, pilot workload is reduced to a level comparable to that with category I loadings._
And here is a copy of the STORES CONFIG switch limitations:
CAT I
Max AOA = 25°
AOA and roll rate are limited when AOA is between 15 - 25 degrees and airspeed is <250kts
CAT III
Max AOA = 16°-18° dep. on GW
AOA begins to be limited starting at 7°AOA/100kts through 15°AOA/420kts, depending on AOA and airspeed
9g is available until 15° AOA; max g decreases as a function of AOA/airspeed
Max roll rate is limited to approx. 60% of CAT I roll rateWith the STORES CONFIG switch in CAT I, it’s very simple. G is limited to 9, and AOA is limited to 25’. But with the switch in CAT III, the behavior changes. At very low speeds (100 knots) AOA is limited to 7’. As airspeed increases, so does the maximum AOA until you get 15’ at 420 knots. 9 g is available at AOA lower than 15’. So, if you go fast enough, you can pull 9 g in CAT III. In fact it’s pretty easy to do.
Bottom line is, the pilot still has to be careful about how he flies the jet with stores on. Remember it’s still just an airplane, it’s not magic.
Hanging thousands of pounds of stuff from your wings has a very big effect, and that effect must be taken into consideration. -
Thanks Toad, I posted this as a blog entry, hopefully will also port it to the new wiki page that is in the works…
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Great informative post Toad, thanx.
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Thanks. Where does the name come from?
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Excellent post Toad, thanks.
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It does also limit the G that the pilot can induce, but this is dependent on airspeed, and is usually 9 G. Here is an excerpt from the F-16 C/D Block 50/52 “Dash One” manual:
With the STORES CONFIG switch in CAT I, it’s very simple. G is limited to 9, and AOA is limited to 25’. But with the switch in CAT III, the behavior changes. At very low speeds (100 knots) AOA is limited to 7’. As airspeed increases, so does the maximum AOA until you get 15’ at 420 knots. 9 g is available at AOA lower than 15’. So, if you go fast enough, you can pull 9 g in CAT III. In fact it’s pretty easy to do.
Very nice post
I would like only to make a small illucidate if you permit me, so our friends dont misunderstand the words CATIII = G limiter
From my knoledge we can not say (is wrong) that CATIII reduce the G’s. But as a result of the rest that you explained AOA indirect afect’s the the G’s.For the history of CAT limiter
In the first models A&B was analog in the new one C&D is digital (rapide and accurate)If Iam wrong please tell me so to del this post so wee dont confuse the rest
Thank you for your nice post.
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one of the main purpose of cat switch is to decrease roll rate performances in order to avoid roll departures
read FLCS2article on website
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I think Toad’s post must be added to Falcon 4 BMS Wiki.
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I think Toad’s post must be added to Falcon 4 BMS Wiki.
Already on its way … Toad will be writing for the WIKI… YAY
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There is also another thread in here about the same subject, and some posters there have provided good and accurate information.
https://www.benchmarksims.org/forum/showthread.php?5599-SMS-Jetison-problem-and-CAT-1-CAT-III-issues
This (present) thread is good anyway, has all the info in one place.
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Excellent explanation, very clear. Thank you very much!!
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In the first models A&B was analog in the new one C&D is digital (rapide and accurate)
If Iam wrong please tell me so to del this post so wee dont confuse the rest
You are a bit wrong here:
F-16A/B/C/D/AM/BM/K=blocks 1 to 32=analog FLCS.
F-16CG/DG/CJ/DJ/I/S/U=blocks 40 to 60=digital FLCS. -
had an interesting read on this yesterday…
salute gums…!
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had an interesting read on this yesterday…
salute gums…!
Interesting reading…
I work/worked on blocks 10,15,30,40,52+ so I know for sure DFLCS started with block 40. -
In short CAT III with A/G stores
CAT I for A/A of after having jettisoned or used A/G stores
Correct? -
Thanks
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Hello guys, I liked to much the CatI / Cat III notes from 72nd_Toad, So I decided to translate it to Spanish for people who need it.
The translated notes you can download from here.
Enjoy!
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Great post! Thanks Toad!
BTW, I’ve been always curious about the number. We have CAT I and III. What happens to CAT II ? Is there any historical background to missing CAT II ?
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Cat II loading distinction did exist for small horizontal tail models (old, like block 10 A). It is in between I and III. With switch in Cat III you could do anything, with switch in Cat I you had to be careful about how big a max roll rate roll you did (full turn max at low AOA, half turn max at high AOA).
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Its been mentioned a couple times on F-16.net. apparently CAT I applied to air to air loadouts, and CAT III was A-G loadouts with wing tanks… And now I cant recall whether CAT II was to be AA plus wing tanks or AG without tanks…
