Listed Max-G figures vs Actual Max-G figures

KJ_Lesnick

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I was thinking about the maximum-G figures for a lot of cold-war aircraft. Many of them were hugely inaccurate or actually fudged for one reason or another.

The MiG-15 was officially listed at 5-G's, however the design could probably physically pull 7-G's or more, the F8U/F-8 was listed as having a maximum-G capability of 6.5 G's, as was the F-4. It's obvious both can pull in the ballpark of 9G's or even a little bit over that.

Since these aircraft are all ancient and there would be no secrecy behind their maneuvering capability, I'm wondering what the actual max-G capabilities are for planes such as...

The Me-262, The F-80 Shooting Star, the FH Phantom, the F2H Banshee, the F-84 Thunderjet/Thunderstreak, the FJ-1 Fury, the F-86 (and FJ-2/3/4 Fury) Sabre, the F7U Cutlass, the F9F Panther/Cougar, The F4D Skyray, the F3H Demon, the F-100 Super-Sabre, the F-101 Voodoo, the F-102A, the F-104 and the F-108 Rapier.

I know many WW2 planes were capable of around 9-G's max. I don't know about the F-80, F-84, and F-86 type planes. I think they were officially listed in the 5G range, but I would assume them to be far more maneuverable. I do remember hearing 7.33G's max for the F-86, which does appear to make sense as the MiG-15 was said to be able to do in excess of 7G's, however why would they not be able to do 9 like the propeller planes?

I don't recall hearing any serious problems regarding G-limits on the F-100 so I assume it was pretty good though no figures. The F-101 I do remember hearing it didn't have as high a max-G capability as desired and was later strengthened, officially the initial figures were 5.33 and it was strengthened to 6.25, but that sounds kind of low considering WW2 and Korean War era fighters could pull more. The F-102 instinctively I figure would be about the same as the F-106 as, well quite simply, they were similar designs and allegedly they had the same wings, but I'm not 100% sure of that.

The F-104, while it ended up being developed as an interceptor, did have it's roots as a fighter.

The F-108 was a large aircraft, but I do remember hearing somewhere that the Air Defense Command wanted a max-G capability of 5.33 G's. Now granted it's a big aircraft, but there were other aircraft with G-figures listed as 5.33 and could almost certainly pull a great deal more than that.


I'm wondering if anybody knows anything further


KJ Lesnick
 

TomS

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In many cases, the listed figure is the designed G rating for the aircraft structure. The aerodynamics will allow the plane to pull harder than that, but doing so will "over-g" the airframe, necessitating all sorts of inspections before it can be flown again.
 

KJ_Lesnick

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TomS,

Uhm, the P-51 was rated for like +10/-4G's IIRC. And the F-4 Phantom routinely pulled 8 or 9 G's...
 

GTX

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KJ,

I think you missed Tom's point - the actual achievable doesn't really matter in a practical sense. The max factor is a design/safety/operational limit imposed. True, this will be less than max actually able to be pulled (and sometimes actually done), but exceeding this limit results in serious maintenance inspections as there is a chance that the airframe etc may be over stressed resulting in failure at a later point or increased fatigue life being accrued (the same goes for hard landings). Sure, in a life or death dogfight, the pilot may exceed these limits (and there are cases of this documented, with resulting aircraft damage also documented), but in general this will not be done,

Regards,

Greg
 

KJ_Lesnick

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Yeah, but I was under the impression that in Vietnam 8-9G's was do-able with F-8's and F-4's without damage...
 

Weasel Pilot

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I flew F-4s (D, E & G) so let me take a stab at this. The F-4's maximum rated g - right out of the flight manual page 5-7: " Acceleration of 8.5 G is permissible only for symmetrical maneuvers with gross weight below 37,500 pounds and airspeed below Mach 0.72." Did guys exceed this? Yes. Did some of them die because the airplane came unglued? Yes (An small percentage) but those that lived to tell the tale probably broke the engine mounts and were lucky to get home. Note that this limit was hard to achieve due to various reasons: 1. Operating weight (No fuel or stores) was 33.5, er...33,500 pounds. This gave you only 4,000 pounds to play with, not much, especially with the burners cooking.
2. Stores limits - Oh, yeah then knock off 2.5 g cause you're carrying empty wing tanks (6.0 g max, symmetrical). Anything else hanging out there? You're not only going to eat up your 4.0 in weight, (which means even LESS gas) but you're gonna add additional restrictions.

There was a 1st TFW DO (Deputy Commander for Operations) many years back that got vertigo during a dogfight and was screaming straight down at the Atlantic, doing "mach-snot". His SA returned at the last possible moment and he put something like 10 g on the jet in the (less than 200 foot ASL) recovery. It got him home but was a Class B accident, there was so much damage to the jet. (He was in a pre-MSIP C model - I think - which was a 7.33 g jet)

When you're gonna die anyway (dodging SAMs, or the rapidly approaching Atlantic) go ahead and over-g the jet, ya got nothing to lose, but don't think that guys went out and typically exceeded the flight manual limitations. Unlike speeding, running a stop sign or other "tho shalt nots," ignoring flight manual/NATOPs guidance has severe consequences!
 

Lauge

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Weasel Pilot said:
Unlike speeding, running a stop sign or other "tho shalt nots," ignoring flight manual/NATOPs guidance has severe consequences!

Well said. If it's you and your aircraft on one side, versus gravity on the other side, you and your aircraft are never going to win! The best you can hope for is a draw..... :p

Regards,

Thomas L. Nielsen
Denmark
 

Abraham Gubler

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A common engineering standard is to build for 1.5 times listed maximum peacetime G. So if the G Limit is 5 Gs it can actually take 7.5 G before the wing snaps off. As to proofing all this, determining just how much G the aircraft can take and what effect high G has on its fatigue life is why new designs are put through such stringent testing, including test to destruction.

Here is some great History Channel video showing part of the F-14 testing, including destruction test (not max G test but), also inverted climb with full stores.

http://www.youtube.com/watch?v=8RXdQKF2wB0
 

doolyii

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I always wondered about real operational limitation of the airframe structure (great weasel pilot posting). Indeed as Mr. Gubler mentioned, typical structure (airframe) is designed for, limit loading, ultimate load (1.5 x limit), fatigue, damage tolerance and corrosion (mostly) plus discrete event (bird strike, ballistics, hard landing etc) and all the rest of flutter restriction (structural divergence). Actual operational restriction will be also limited by controllability (thanks for the describing experience !), I remember that all too often, stability and control are the most limiting factor before aircraft reaches its structural limitation, but not sure about that...

Propulsion system will have same requirements plus vibration/acoustics related requirements (resonance, HCF, LCF) with significant thermal requirements.

but each design step, and meeting each requirements, all engineers would like to add just a bit more conservatism in it..mostly for wife and kids...I suspect that's why aircraft don't evaporate at 1.5000001 x limit load factor, and redundancies in design...but then again, recently (2007 or 2008 ?) F-15 forward fuselage literally blew off during flight (crack divergence)..

I do not think it's possible to clearly define how far aircraft can exceed more than operational limitation ?
 

r16

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as it has already been mentioned on the posts above mine it is 1.5 times the limit , in this context engineers would "expect" an P-40 or F-86 to stay in one piece at 12 and 10.5 G respectively . There have been cases where the limit were exceeded , ı was recently reading about F-86s and a g-meter on one showed 12G but ı think no body would count on the performance delivered across the fleet of any type .
 

KJ_Lesnick

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Why was the F-86 not as capable of as high a G-load as earlier planes? I'm just curious why a P-40 and P-51 could pull a higher load than an F-86
 

r16

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it seems faster speeds call for thinner structures which might tend to be weaker weight for weight . An engineer will no doubt give a better answer but to have maximum performance , say F-86 , desiners could have chosen to cut corners . ı have read that MiG-25 is limited to 4.5G as the steel structure would have been far heavier if stressed for higher values .
 

mz

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IIRC, with some approximations, when you keep the weight similar but double the thickness, the stiffness grows eight fold.
 

Weasel Pilot

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Note that the MiG-25's g limit - like that of most fighters varried according to the situation. While the "maximum maximum" (thank you, don Rumsfeld) was 4.5, this dropped to a mere 2.2 g with full fuel!
 

norseman

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There was a case of a Russian pilot pulling close on 10g in a Mig 25 once and even managed to limp home but the aircraft was close on written off if I remember rightly, will have to track down the article again.
 

norseman

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They are very sturdy aircraft (unsophisticated in many respects even for the year) but can be pushed above and beyond their limits by quite some margin if you don't mind carrying out some pretty major repairs afterwards, just like the occasional Mach 3+ sorties which required an engine rebuild afterwards. Seemingly the 10g aircraft suffered some pretty major warping damage.
 

HeavyG

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Aren't listed max-G figures generally the result extensive airframe stress testing? I would figure those numbers would change as an aircraft went through actual flight testing and change even more as it went through regular service.
 

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