Forum: F-16 Design & Construction

IIRC the suit has channels that contain the liquid. The actual body area covered by the liquid isn't that large, just enough IMO to cover key blood pathways.

As an aside, I believe the liquid used is potable so it would supplement water supplies in case the pilot had to bail out over inhospitable terrain.

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The F-16 was designed for 9g because that's what the USAF wanted. GD would have designed it for anything they wanted, short term and long term strength.

But there is always more to the story. The YF-16 was designed for 6.5g at any speed and altitude with about half fuselage fuel, and up to 9g at non-critical conditions (lower fuel, different speed/altitude). For example, at .95/10k, the airplane could reach limit wing load at 6.5g, but at 1.2/30k, the 9g wing load was less than the first example. Then when the F-16 came along the spec was 7.33g at at all speeds and altitudes with full fuselage fuel. GD did a trade study to determine what the weight penalty would be if it designed for 9g at all speeds and altitudes. The penalty was 22 pounds, so the AF said, great, give us 9g everywhere.

Why 9g? My opinion is g-loc concerns, which turned out to be valid. The structure can be designed for any g level, but weight is an issue.

Thanks for the replies. Thumb

As Gums mentioned there have been quite a few occasions in which pilots have pulled more than 9g, granted it was only for a few seconds but they suffered no ill effects. Of course the greater the g pulled the less time it can be sustained so that is another thing to consider. Perhaps the design tradeoff wasn't worth it?

johnwill wrote:

GD did a trade study to determine what the weight penalty would be if it designed for 9g at all speeds and altitudes. The penalty was 22 pounds, so the AF said, great, give us 9g everywhere.

Why 9g? My opinion is g-loc concerns, which turned out to be valid. The structure can be designed for any g level, but weight is an issue.

The weight penalty is virtually nothing. In terms of one off cost, I wonder how much additionally it would add to the price tag of each airframe? If we could increase the airframe g limit to 12 but program the FCS for 9 then the life of the airframes would increase by quite a large margin I would imagine. I guess that the weight increase per g may be exponential so it will start to have a serious impact on performance.
Anyway I'm sure GD looked at all the tradeoffs and came to the most sensible decision.

Obi

Forum Veteran Joined: Dec 15, 2006 - 12:28 AM Posts: 760

cywolf32 wrote:

Actually, a liquid cannot be compressed, only a gas can.

That’s not true. For the most part it may be true for the context of this thread. For the most part it may be true with most regular earthbound physics. However under extreme conditions some liquids can be ever so slightly compressed.

Under extreme physics such as in astrophysics liquids can be compressed significantly. The gravity within a black hole is so intense it can compressed liquids.

It does't make sense to push an airframe beyond the pilots limits. Anyhow, HOBS and and other systems negate this. If I can look at it, I can kill it pretty much. Let's not forget that I can see behind and below as well. Game changer all around!!

Obi_Offiah wrote:

My understanding is that modern g-suits and accessories such as the Combat Edge vest allow pilots to handle greater loads?

G-suits will only give you an extra G or two of tolerance. Combat Sweat doesn't give you much more, but maybe another G and a half.

Anyway, a G-suit and full Combat Edge are not designed to take one past 9 Gs. Rather, it's designed to help prevent you from blacking out and/or G-LOC'ing. If someone blacks out at 7 Gs, guess what? Combat Edge really won't help that person reach 9 all that much.

Actually, if C.E. gave that same person any more protection, it would likely just help him black out at 8 or 9 Gs instead of 7. But, really, if the pilot was just going to black out anyway, then what have you solved with the extra equipment? Nothing. That's why your body needs to be prepared for higher G before you fly. A good diet, exercise, plenty of rest, and some good G warm up maneuvers are the key.

Like Gums said, if you yank back on the stick, you can knock yourself out pretty quickly. Instead, if you gradually build up the Gs, you can help yourself out, and possibly give yourself that extra G or two.

Around the time I was leaving ACLS (now known as Aircrew Flight Equipment), some fighter units had already stopped using the vest. I know the Raptor guys still wear the vests, but I'm not sure about other units. I've seen Viper guys come in transient not wearing the vest, so make of that what you will.

9 Gs for the Viper is, like others have said before, a combination of human tolerances and maintenance-related reasons.

Tinito_16 wrote:

cywolf32 wrote:

http://www.scientificamerican.com/article.cfm?id=0009B40B-48D2-1CC6-B4A8809EC588EEDF

Actually, a liquid cannot be compressed, only a gas can.

Can't open the link for some reason, but anyways, I heard in a discovery channel program that seawater @ many hundreds of feet below the surface is denser (because of compression) than the surface water. If I'm not mistaken a liquid CAN be compressed but not anywhere near the level you see with air. You won't have any appreciable degree of compression in the amount of water you'd use for the bladders in a G-suit. The G-Suit (let alone the pilot wearing it) wouldn't be able to withstand that kind of pressure anyways, I'm talking about many atmospheres worth, the kind you find in the deepest ocean trenches. The program was about deep sea fish I think. Anyways my point was that the air pressure would be felt differently than liquid pressure, because liquids cannot be compressed much (very very little) compared to air. This might be more painful and very hard for a pilot to adapt to.

The water at deeper depths is more dense because it is colder, not because it is compressible. Liquids are incompressible, no matter what.

Enthusiast Joined: Jun 10, 2010 - 02:44 AM Posts: 44

VPRGUY wrote:

9G isn't necessarily the human threshold - modern aerobatic aircraft routinely go to 10-12G in many maneuvers without a g suit, although they don't sustain that kind of G load for more than a few moments. 9 may simply be what 'human factors' engineers decided the average 'conditioned' person could sustain through use of a g suit and proper technique.

I had a Saudi IP that said he pulled 12G in a training mission as a student pilot...his IP at the time was NOT very happy with him.

Quote:

vcq09
I had a Saudi IP that said he pulled 12G in a training mission as a student pilot...his IP at the time was NOT very happy with him.

Something tells me that jet's maintenance crew didn't exactly put him on their Christmas card list either! Wink

Wonder how long it took to inspect that bird and what kind of damage the over-G caused?

I would ask some questions regarding the 12G. There are very few, if any circumstance that would allow the pilot to make a move like that. The one time I had to work on a jet that indicated 9.9G on the HUD turned out to be the G sensor that feeds the HUD that had failed, while the flight control system had done the job to keep him under 9.9G. It took all Friday afternoon with all hands on deck to do the G-check afterwards.

While there have been cases of false high G indications in the HUD, there have also been cases of actual high G events in the F-16 (i.e. slightly above 10) even with the FLCS G-limiter working normally. So it doesn't surprise me that 12 G could be reached in a Saudi jet (F-15?) without a G limiter.

lamoey wrote:

I would ask some questions regarding the 12G. There are very few, if any circumstance that would allow the pilot to make a move like that. The one time I had to work on a jet that indicated 9.9G on the HUD turned out to be the G sensor that feeds the HUD that had failed, while the flight control system had done the job to keep him under 9.9G. It took all Friday afternoon with all hands on deck to do the G-check afterwards.

I remember hearing something about incident (Edwards maybe?) where a F-16 had a transient flight control problem (electrical) and temporarily departed controlled flight. During this transient, it was over 10Gs. The pilot regain control, and the jet landed safely.

Even without any FLCS problems, there is something about crossing that transsonic boundary that can lead to an over G.
fisk

In the case I mentioned the viper pilot had broken the day’s rules of engagement, or whatever it is called, which stated no closer than 1000 feet. I guess the pilot Cool

got carried away when he got the upper hand on a US F-15 and practically climbed up the augmenter of the Eagle, then got shaken pretty badly by the turbulence behind the Eagle.

Forum: F-16 Design & Construction

Why does 9g seem to be the design aim?