AGM-88 in Cat I/III mode

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ender

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Unread post06 Mar 2009, 12:19

Hi

I have a question with AGM-88 Cat configuration.
If 2 HARMs are loaded, it's allowed to fly in CAT I mode or it's mandatory to select CAT III mode?

Understand HARM isn't considered as a heavy weapon but I not sure.

Thanks!!
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Butcher

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Unread post06 Mar 2009, 16:57

When carrying A-G weapons and/or wing tanks they must be in CAT III mode. Even when you have a centerline, the F-16 can go CAT I but the Gs it can pull is slightly limited. Only when you have A-A and no centerline (a jammer will do), you can go CAT I (9Gs).
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johnwill

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Unread post06 Mar 2009, 18:47

As Gums would say, "back when the Earth was still cooling", external wing tanks with A-A were Cat II. The only difference between Cat I and Cat II is bank angle change for full stick rolls. Since that is a pilot-observed limit, there are no control law differences between I and II. Also remember that Cat designation has nothing to do with g limit.

When you have a centerline, that's Cat I as you say, but again g-limits have nothing to do with Cat. With fuel in the centerline, it's g-limit is 6.5, and when empty, it is 9.

In the thirty years that have passed since external store Categories and g-limits were assigned, all this may have changed.
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ender

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Unread post06 Mar 2009, 19:31

Yes, all the things you've said are true, but I asked this because weapons like AGM-88 and AGM-65 shouldn't be considered like heavy weapons.

If you read the AIR FORCE INSTRUCTION 11-2F-16,VOLUME 3 in 3.7.4. section, you can see that is not allowed to make takeoff formations if you are loading live munitions EXCLUDING AGM-88, AGM-65 and others.(see 3.7.4.4)

The first question was refered to this. This is because theese weapons are considered Light weapons, so you can flight with in CAT I, or this exception is to avoid posible explosions in the runway if colision happens?

Thanks
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Magnum

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Unread post07 Mar 2009, 03:21

I don't have a -1-1 in front of me but we ALWAYS flew with it in CAT 3. Pretty sure its a CAT 3 config.

Butcher:

Your statement is incorrect. You can have wing tanks and still be CAT 1. Also, a centerline tank with just A-A loadout is CAT1. I can pull 9g with a centerline tank just fine.
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johnwill

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Unread post07 Mar 2009, 05:43

The AGM-88 is Cat III because it is air to ground, not because it's heavy. Category III has nothing to do with g limits. Category limits are related to handling qualities, g limits are related to strength.

Here's what Cat III does to control laws
1. Reduced AoA limit
2. Reduced roll rates
3. Reduced pilot rudder command limit
Note it does NOT reduce g limit.

Here's why they are needed. At high AoA, roll-pitch coupling can cause loss of control through excessive AoA. This condition is made worse when you have an unbalanced store load, as after firing one AGM-88.

Most A-G stores have a 5.5g (symmetric) limit, but the AGM-65 is 6.5g. If someone wanted to pay to raise the AGM-88 g limit, it proably could be raised, but it would still be Cat III. As I said, g limits are structural. The limiting structure may be the pylon, the wing, or the store itself. The AGM-88 may be relatively light, so it may not overload the pylon or wing, but its g limit may be due to the limit on the weapon itself.

Another thing involved in setting g limits is cost. If each and every store loading (including normal downloads) were analyzed and flight tested to it actual limit, it would be prohibitively expensive. In practice it is much more practical to clear stores to a nominal limit (like 5.5g), analyzing many loadings, flight testing a few loadings, and clearing the rest by "similarity".

g limits are always a compromise between cost, simplicity, and capability. I've already mentioned cost, but what about simplicity? You could for example, have different g limits for every gross weight, every speed, every altitude, every store download, every roll rate, etc. The g limit would constantly be changing and no pilot could keep up with it. A digital flight control computer could easily keep up, but the utility of such a variable limit is questionable at best. So g limits are set to handle the worst worst worst condition. Worst weight, worst speed, worst altitude, etc. At all other conditions the limits are conservative.

In the same way, Cat limits are set by worst worst worst conditions. AGM-88 loadings might be able to handle Cat I above 350 kt for example, but evidently the cost of clearing that is not worth it.
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geogen

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Unread post07 Mar 2009, 07:45

Very interesting read.. Johnwill and Magnum, while on topic... just curious about the G-limits with A-A config, and those Vipers with CFT tanks (no other external fuel)? 6.5 G full CFT fuel? No limits w/empty CFT? Thanks in advance!
The Super-Viper has not yet begun to concede.
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johnwill

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Unread post07 Mar 2009, 16:42

geogen,
Sorry I can't help there. CFT showed up many years after I left the F-16 program. Just guessing, I'd say the limits would be the same as for other externals, 6.5 with any fuel, 9 empty. More than likely, the weapon limit would be lower anyway.
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clown_shoes

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Unread post07 Mar 2009, 17:55

g-limits for block 40 and 50 a/c are 7 g's with gas in the tanks, not 6.5
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mckenzy7

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Unread post07 Mar 2009, 18:46

You need to consult your 1F-16()-1-2, it will give you all the limitations for the carriage of the AGM-88.
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SnakeHandler

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Unread post07 Mar 2009, 20:26

CFTs are rated to 9Gs. Also, while the jet may be CAT III, it isn't necessary to put the CAT switch in the right place. Just go easy on the jet at slow speeds and high AOA. The advantage to leaving the switch in CAT I all the time is that it is one less thing you need to do after jetting your stores when threat reacting or going to a less than offensive merge.
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skicountry

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Unread post07 Mar 2009, 21:35

Good discussion all.

Tying in to the asymmetrical stores and the F-16 issue.

Having sat through my fair share of briefings/sales pitches by all the major fighter manufacturers, the one thing I recall the Boeing boys always doing was to jab the F-16s "lousy" asymmetrical flying qualities (compared to the F/A-18). They'd post up a chart of an ADF Viper and Hornet in nominal A-A configuration of two AIM-7s and two AIM-9s and then note that with one Sparrow expended, the ADF Viper's handling qualities compared quite unfavorably to the Hornet's, which remained restriction-free.

Is the F-16 design particularly sensitive to asymmetrical configurations? Certainly, over the past decade, it has been carrying mildly asymmetrical A-A and A-G loadouts but nothing like the Hornet's crazy bag and weapons configurations.

Your thoughts?

Skicountry
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skwabie

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Unread post07 Mar 2009, 22:45

johnwill wrote:g limits are always a compromise between cost, simplicity, and capability. I've already mentioned cost, but what about simplicity? You could for example, have different g limits for every gross weight, every speed, every altitude, every store download, every roll rate, etc. The g limit would constantly be changing and no pilot could keep up with it. A digital flight control computer could easily keep up, but the utility of such a variable limit is questionable at best. So g limits are set to handle the worst worst worst condition. Worst weight, worst speed, worst altitude, etc. At all other conditions the limits are conservative.


Hi Johnwill,
very nice post.
But I thought the F-18's FLCS calculates the planes's maximum G limit factoring fuel, loading etc.
Remember it pretty well coz t'was the first time I realized how much advanced the F-18's avionics is compared to the 16.
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deadseal

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Unread post08 Mar 2009, 02:28

2 bags is not cat 3....harms can be cat 1 or 3 depending on the rest of your stores. The only reason that you can do a form takeoff with mavs or harms is they r (forward flying i.e missles). Form takeoffs are based on Your TOLD. (and potentially ruining your wingie's day by dropping a couple of -38's on the runway for him to run over)
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johnwill

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Unread post08 Mar 2009, 07:47

skicountry wrote: They'd post up a chart of an ADF Viper and Hornet in nominal A-A configuration of two AIM-7s and two AIM-9s and then note that with one Sparrow expended, the ADF Viper's handling qualities compared quite unfavorably to the Hornet's, which remained restriction-free.

Is the F-16 design particularly sensitive to asymmetrical configurations?


Naturally, you can depend on competitors showing the competition is the worst possible light. The F-16 was not designed to carry the AIM-7, but it was scabbed on before the AMRAAM was ready. Seems pretty obvious to me that when you expend one weapon from a small airplane, it will be affected more than when the weapon is expended from a significantly larger airplane. DUH! (That's directed at Boeing/MAC, not skicountry)

As far as unsymmetric loadings on the F-16 go, keep your speed over 350 and you'll have no problems. In FSD flight test, we flew GBU-8 (2200 lb) on station 3 (maybe it was 7) without any problem, using normal control laws (this was before Cat I/III came along). If you turn away from the store while taxiing, you want to slow down a lot or you'll lift the main gear on the inside. Unsymmetric loadings are the reason Cat III was developed. That's another case of a limiter being set for a worst case condition (unsymmetric stores), leaving the symmetric store case with a somewhat conservative limiter.

Keep in mind that the things which make the F-18 have better low speed handling than the F-16 (forward cg, two vertical tails, etc) also make it have less speed, range, and sustained g capability. Can't have everything (unless you have an F-22).


skwabie wrote: But I thought the F-18's FLCS calculates the planes's maximum G limit factoring fuel, loading etc.
Remember it pretty well coz t'was the first time I realized how much advanced the F-18's avionics is compared to the 16.


I'm not familiar with F-18, but as I said earlier, a digital FLCS can easily do it. That'a where the pre-block 40 F-16 analog FLCS was lacking. Can you tell me if the F-18 unit provided an automatic variable limiter or just an indication of a variable limit? For most A-A loadings, the F-16 did not need a variable g limiter, since it could handle 9g anywhere, any weight. The F-18 however, could handle only 7.5g at its worst A-A case, so a variable g limit might give them a little more capability at non-critical conditions.

And speaking of variable limiters, our YF-16 had a variable g limiter, based only on speed and altitude, not fuel load. The YF was designed for 6.5g at the worst case, but when we got enough flight test data, the flight control boys wired up a special board with a mapped g limiter we structures types gave them. It allowed 9g over about 90% of the flight envelope at any fuel load.
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