F-16.net

Last edited by KXY on Jul 02, 2008 - 11:45 PM; edited 3 times in total

We all know the Viper is a "9-g aircraft". I've been wondering about the limits/norms of other jets. Couldn't really find anything on Google, so I think it would be nice to compile a list of the world's modern military jets and their respective g limits , normal manuevering g loads, ect..

Consider the aircraft in "airshow trim". No external stores, and about 1/4-1/2 a tank of internal fuel. Include both instantaneous and sustained in ideal conditions, altitude and airspeed wise.

Feel free to add on,
In no particular order:
F-4
F-14A/B/C/D
F-15A/B/C/D/E
F-16A/B/C/D
F-117
F/A-18A/B/C (legacy Hornets)
F/A-18E/F (Super Hornets)
F-111
A-10
AV-8B
F-22
F-35

Panavia Tornado
Rafale
Mirage F-1
Mirage 2000
EF200 Eurofighter
Jas-39 Gripen

Mig25
Mig29
Mig31
Mig35
Su-27
Su-30
Su-33
Su-34
Su-35[/b]

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Veteran Joined: Dec 15, 2006 Posts: 439

Real-life is not a video game or a oversimplified textbook. G limits are not a constant. The G. limit of an aircraft can vary widely depending on the (payload) load out, amount of fuel, etc…

My fault, should've clarified that - Edited at the top - Say, airshow trim. No external stores, and half a tank of gas.

Elite Joined: Apr 26, 2004 Posts: 1175 Status: Offline

ATFS is 100% correct. You can over "G" a 16 with 4 g's .....it's depends on how it is configured and where the fuel is. If you have 370 tanks full and pull 7 G's you would be lucky to still have wings..........

Purple

Elite Joined: May 26, 2005 Posts: 1093

No matter what, it's not just a number, max G depends on airspeed and altitude. Also are you talking about instantaneous or sustained G? Not a simple question by any means.

Guysmiley wrote:

No matter what, it's not just a number, max G depends on airspeed and altitude. Also are you talking about instantaneous or sustained G? Not a simple question by any means.

Ughh. Edited at the top again.

After having failed miserably with the engine fan blade discussion, I’m going to take this on anyway. The G limit question is both complex and simple at the same.

If you are talking aircraft “performance”, then G limits are a function of many of the previously described factors, primarily configuration and weight. But generally, the aircraft wing will be capable of a specific maximum G available at or above a particular calibrated airspeed. The more speed you’ve got, the more G available. Basically, it doesn’t matter what’s hanging on the airplane, if you have the speed, you’ve got the G available. It may not be a good idea to use it, because it is possible for things to come off of the airplane, including the wings.

“Performance” for a particular amount of structural G allowable is a function of how low a speed you can attain the G and Boyd’s “P sub s”, i.e., in what geometric plane you can or can't sustain it.

But on the simple side, there is only one “maximum” G limit under whatever the optimum conditions for that aircraft to achieve this limit happen to be (air-show config?). Clean configuration, lower gross weights, symmetrical application of control inputs, etc., all contribute to the “biggest” number.

U.S. aircraft prior to the F-15 (with one exception) were generally limited to 7.33 G, which is 2/3’s of 11 G which is the structural fatigue limit that was spec’d and tested for those aircraft. After the F-15, they advertised them as 9 G aircraft. I don’t know if they raised the structural fatigue spec to 13.5 G or lowered the buffer to 9/11’s of 11 G.

I’m not familiar with the European aircraft, but I suspect structural limits for a particular manufacturing process are probably global.

I don’t know the later models, but the F-16A used to have a switch in the cockpit with two positions: Cat 1 & Cat 3. For a given side-stick input, Cat 1 would give you a full up 9 G airplane regardless of weight or configuration. Cat 3 was to be selected in certain configurations that had more restrictive G limitations and the FCC would prevent the pilot from over-stressing the aircraft. It also, evidently, prevented a particular pilot from being able to pull out prior to impact on the Wildcat Range in Utah, because he was following the recommended procedures. I never flew in anything but Cat 1.

I always wondered what happened to Cat 2.

regards, O.L.

Veteran Joined: Mar 24, 2007 Posts: 379 Status: Offline

I'm going to step on a few toes here, so get ready. There is so much mis-information on this thread it is hard to believe.

Purplehaze - there is no loading on the F-16 which is over-g at 4g (symmetric maneuver). The limit with full 370s is 6.5g. Considering that all g limits have a 150% design factor, 7g would not cause any structural failure. Plus the only time you have full 370s is just as you drop off of a tanker. The only 4g limits I ever saw were for 600 gallon tanks with fuel and for gear down.

Guysmiley - On some airplanes, g limit may depend on airspeed and altitude (not the F-16), but there is still only one max g for an airplane.

outlaw162 -
(1) We are not talking about "available" g here, which is determined by AoA, weight, and airspeed. g limit refers to structural g limit, above which some part of the airplane exceeds limit load. That part is not necessarily the wing, recalling the forward fuselage failure on the F-15 several months ago.
(2) The 7.33g you mention for the F-15 is in fact 2/3 of 11g, but 11g has nothing to do with a "fatigue" limit. 7.33g is called the design load factor and 11g is called the ultimate load factor. That means the structure was designed to fail at the most critical 11g condition, considering fuel load, weapon load, airspeed, and altitude. The 9g / 13.5g relation is the same. Fatigue is the effect of reduced strength due to many repeated loads.
(3) Your intrepretation of the effect of the Cat 3 limiter is entirely wrong. The Cat 3 switch position did not change the FCC g limiter, only the maximum roll command, the AoA limiter, and manual rudder command limits. Cat 3 was SUPPOSED to be used with external store loadings with 5.5g or 6.5g, but those were supposed to be pilot-observed limits. The pilot who sadly couldn't pull out prior to impact was not inhibited by a lower Cat 3 g limiter, but could have been done in by the Cat 3 AoA limiter if he was at a too low airspeed. A lot of people (me included) spent a lot of time (and taxpayer money) developing the Cat 3 limiter in an attempt to keep you safe. Too bad you decided on your own to not to use it. Did you just ignore the configuration caution light?
(4) Categories 1, 2, and 3 were developed for various sets of external store loadings. Cat 1 was essentially air to air without underwing tanks, Cat 2 was air to air with underwing tanks, and Cat 3 was air to ground (and ferry with three tanks). Cat 1 used full FCC capability with 360 degree rolls, Cat 3 (as stated) used reduced AoA limit, reduced max roll command, reduced manual rudder command, and 180 degree rolls. Cat 2 used the same FCC control laws as Cat 1, but was limited to 180 degree rolls. If you had studied the External Stores Limitations chart in Section 5 of your -1, you would have known that.

Since their inception on the F-16, flight control limiters have been controversial, precisely because of situations like outlaw162 mentioned. The basic question is do you limit the airplane to prevent overload (g limiter) or departure (AoA limiter) or do you allow over-loading the airplane or risk departure and give the pilot the capability to avoid a sudden impact with the ground or another airplane? USAF decided for the limiters, obviously.

The first limiters were primitive due to limited computer power. Today's limiters are more capable but the controversy remains.

Elite Joined: Aug 30, 2005 Posts: 663 Status: Offline

John,

Great post, the key is that sustained loads are always specified in terms of symmetric maneuvers.

A good example of an airframe having a structural overload within the normal maneuver envelope is the American Airlines A300 crash in New York.

FAR part 23 states "... limit loads are the maximum loads to be expected in service [i.e. the highest load expected in normal operations] and ultimate loads are limit loads multiplied by a safety factor [of 1.5]. The structure must be able to support limit loads without detrimental, permanent deformation. At any load up to limit loads, the deformation may not interfere with safe operation. The structure must be able to support ultimate loads without failure for at least three seconds ..."

In the case of the A300 the rudder induced loads were sufficient to overload the fin while operating within the published airframe envelope. We had a similar incident with a S3 at Pax. River many years ago.

Can anyone put aside ego and answer the question? We are all very impressed with how much all of you know about Gs, G Loading, and all the other stuff. I dont think its too far of a streach to assume KXY was trying to word the question as "under IDEAL circuimstances". Or we can go back to seeing who knows the most about givin subject...... Just a thought,

Elite Joined: Dec 14, 2005 Posts: 687 Status: Offline

outlaw162 wrote:

After having failed miserably with the engine fan blade discussion...

We can't all be 'engine guys'... Cheers

If we were there wouldn't be any Crew Chiefs to pick on... Poke

...or pilots to keep us ALL employed... Doh

Keep 'em flyin' Thumb

TEG

That was an excellent post johnwill.

vertical

Veteran Joined: Mar 24, 2007 Posts: 379 Status: Offline

Unwin, sorry you feel correcting mis-conceptions is wrong. Most people seem to think sharing knowledge is a good thing. I assure you, my ego does not need stroking.

Asiatrails, good example with the A-300. I think I read somewhere there was no limitation on A-300 rudder application and that is what lead to the failure. The first officer applied large repeated opposite rudder commands in attempt to stop the motion cause by wake encounter. Sadly, the application frequency coupled with the natural frequency of the airplane caused the sideslip to diverge and overload the tail. Oddly enough, that same phenomenon was the reason for the only structural prohibited maneuver in the original F-16 handbook in 1979. "No repeated rudder reversals .....".

You are right that g capability is usually specified in terms of symmetric maneuvers, meaning zero roll rate, zero sideslip. But the handbooks always specify g limit symmetric and g limit with max roll. For example, F-16 limits are +9/-3 sym and +6/-1 max roll. What then are g limits for a half command roll? No one knows, because the USAF didn't pay for that information. I tried for years to get the USAF to let us install a g/roll limiter which varied the g limit according to the roll commanded, but no luck. They let us put one on F-16XL (actually they did not know it was there), and the Korean T-50 has one which works fine. I am completely out of that business now, so other airplanes probably have it by now.

To help make Unwin happy, here is my contribution to the original question,

F-111A/D/E/F 7.33g
F-111B 6.5g
F-111C 6.5g

F-16 all 9g

Veteran Joined: Dec 15, 2006 Posts: 439

With all due respect john will, by the military book you’re probably correct. However some of the people that you are criticizing may have some points from an engineering or real world or field perspective.

Perhaps Purplehaze is not addressing the structural limits of the aircraft itself, but the limitations of some of the hard points or weapons themselves. Perhaps the limitations on the aircraft are not from the aircraft itself but from the stores or hard points as a given combination is only as strong as its weakest link.

I seem to remember a story ( I’m not sure if it’s true or not) of an F-15 that ripped off some stores on climb out turn after takeoff. I think it may have been a newly approved loadout for the Iraq war but the burning climbing turn may have exceeded the hard point or store limitations. The rumor I heard is that it was at only about three or four Gs. Perhaps it was just a yarn?

Unwin wrote:

Can anyone put aside ego and answer the question?

As engineers often joke, it depends on the variables. (it’s funny and true, unfortunately the typical laymen doesn’t get it).

Though to the layman it may look like a simple question; in reality it is about 40 questions wrapped into one, and as others have alluded to there is no simple answer to each one. There can even be differences between serial numbers which may have different strength or weight issues. Sometimes a retrofit can change the specifications, and of course there can be a fair amount of difference between different types of electronic packages that can affect weight and distribution. Also not every aircraft has the same fuel capacity, and it may be somewhat opinion or perspective as to what is half fuel loading.

Sometimes for air shows nonessential warfare equipment is removed to enhance performance.

Also some of these aircraft specifications are somewhat security sensitive, I think some of the weight, G ratings and fuel capacities are not public knowledge on some of these aircraft.

If you want some pretty good ballpark figures that are fairly simple, I suggest you buy a Jane’s all the world aircraft set and try to figure out the answer yourself.

A lot of the public figures are just ballpark figures/estimates and sometimes they may even be misinformation. Some of these aircraft haven’t even made it to military service yet, so some of the figures may be revised with design revisions.

You seem to want a simple answer, for something there is no simple answer and that in some cases may be a lot of work and not suitable for public knowledge.

Even if it was all suitable for public knowledge, I question that professionals would go to such an effort on so many different aircraft for something that is just likely to be used for shallow fodder for message board arguments (urinating contests).

Veteran Joined: Apr 25, 2004 Posts: 385 Status: Offline

johnwill wrote:

F-111A/D/E/F 7.33g
F-111B 6.5g
F-111C 6.5g

F-16 all 9g

In the operational world, and according to the booklets, the F-16A will allow up to 9.5 for a short while. If it ever happens I don't know, but the FLCC is not cosidered to have failed if it allows 9.5G. If the HUD indicates that 9.8G has been pulled a structural check must be performed. I saw 9.9G, so the rest of the day was ruined. It later turned out that this was an indication fault on the HUD.

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Aircraft G Limits