Overstress

Mon – January 26, 2004

An overstress is when a pilot pull’s more “g” than the aircraft is rated for. While it’s true that there is an engineering pad attached to the g-limit, the pad is inelastic – in other words, each overstress event will to a greater or lesser degree reduce long-term airframe integrity and service life.

Overstressing a jet is considered bad form, but it’s also something that will happen from time to time. I wouldn’t trust a fighter pilot who’d never overstressed his aircraft. It either meant he didn’t trust himself, or that he wasn’t trying hard enough to fly up against the performance limits, the “edge of the envelope.” But it’s also true that you just wouldn’t want to try to make a career out of overstressing aircraft.

For one thing, it really makes the maintenance guys unhappy. An overstressed jet is down until inspected, and nothing makes a maintainer angrier than giving a pilot a perfectly good airplane, and having him go out and break it, horsing around. And routinely overstressing aircraft takes you out of the category of “aggressive” (a good thing) and places you in the category of “ham-handed,” (get working on your resume).

The FA-18 is a relatively difficult jet to overstress – it is possible (I have done it!), but for the most part, over-g in the FA-18 is attached to a phenomenon known as transonic pitch-up. The dynamics of this phenomenon are beyond the scope of this text (read: I can’t remember – just kidding, Lamont), but suffice it to say that the engineers at McDonnell-Douglas did a pretty good job of making the jet pilot-proof.

The F-16, on the other hand, is less so.

Which brings me to (wait for it): The Worst Overstress I Ever Had.

Part of the reason is that the Viper is just faster than the Hornet. G-available  correlates to indicated airspeed (I will spare both of my readers the fine distinctions between indicated, true and calibrated airspeed for now – but don’t make me mad, or so help me…). The faster you’re going, the more g you get.

And so it came to pass one day that I, in an F-16N, and my wingman, in an F-5E, were fragged for a 2v2 sweep mission against a pair of Homestead Air Force Base F-16s. Long story short, we gained an offensive advantage at medium range, and our adversaries were forced to run away, which the F-16 does wonderfully well.

And I attempted to catch them, which the F-16 does equally well. Leaving my F-5 wingman panting in the dust, I gained radar locked on a guy several miles away, hauling the mail and going for the deck. He was out of range for a missile attack, but I could hear him and his wingman chattering on the radio. They had lost visual mutual support, and were attempting to regain situational awareness and formation.

I was going 800 knots, which was as fast as you were allowed to go. If my man turned so much as 30 degrees or so to rejoin with his wingie, I would be all over him like a cheap suit. Like white on rice. Like a bad rash. Like… you get the picture.

So yeah, I was bringing the heat.

It’s a lot of fun to go that fast, down low, with your adversary right there in front of you, totally defensive and your finger on the trigger. There is a buzzing sound in the inlet, and your canopy howls with the dynamic stress of the airflow. The wave tops below flash by like the trestles on a high-speed train.

At that speed, you are unconcerned with virtually anything but that which is right in front of you. Things behind you will not be a factor (unless you turn, oh please turn) and things beside you will soon be behind you.

The fighter’s wingie called on the radio and said he was right three o’clock, one mile. The lead called “blind,” meaning he didn’t see him.

“HAH!” thought I, “not only is he defensive, but he is blind as a bat!”

“RIGHT THREE O’CLOCK, WINGFLASH!” the wingie emphasized his position call by rocking up on his wing, at ninety degrees to the horizon – showing himself in planform for his lead – a wingflash.

“Blind!”

And that sort of put me to thinking. Even Elmer Fudd should have been able to see an F-16 in plane form from 1 mile away.

So if the wingie was flying along beside an F-16, and that F-16 was not his lead, then who could he be flying next to?

A quick glance to my right three o’clock told me who.

Apparently the same notion worked its way through the wingie’s wetware, since as I began my rapid windup break turn into him, he began to turn into me.

At least I’m pretty sure he did. Because that’s when the lights went low.

The F-16N was rated for 9 g’s. You could easily get more, at 800 knots. I did.

At very high g, and especially at high g-onset rates, the blood drains from your head to your lower extremities. Your optic nerves are especially sensitive to blood loss, so your vision progressively narrows until it looks like you’re peering at the world through soda straws – all peripheral vision is lost. And if you keep it up, pretty soon the lights go out, and sometimes when that happens you lose consciousness. When that happens, your limp hands fall from the controls until you regain consciousness. Sometimes you wake up dead.

Your g-suit is specifically designed to combat that tendency, by forcing air into it’s bladders from a weighted (and g-sensitive) valve, the blood is forced back into your upper torso, where by galvanic contortions (not unlike dealing with the worst case of constipation in medical history), you attempt to move it a little higher. And all the while, your average 175-pound pilot feels the apparent weight of 1960 pounds pushing him down in his seat. His ten-pound head will feel like it weighs 110 pounds (and gets kind of hard to move around).

That’s at 11.2 g’s.

I don’t know if I’ve mentioned before that this hurts. A lot. In a really, really good way, normally. You live for pulling g’s, as a fighter pilot.

But 11.2 g’s isn’t normal.

Somehow my new adversary and I manage to blunder into a merge without clacking into one another. I ease g for a moment at the merge to check his intentions, and see him going vertical.

Which is a good thing, because that means you’ll lose airspeed, even in an F-16. And I don’t want any more airspeed. I want to make the bad thing stop.

So I join him in the vertical, still pulling hard for a while, because you don’t lose 800 knots right away. We get into a particularly violent and thankfully, short fight, in which I emerged victorious (hey, it’s my story). Shortly after that, his lead shot me like a coward, in the back, from my six o’clock, and unobserved.

But that’s his story. And that’s all I have to say, about that.

Good clean fun, and I’m off to the field with my wingman in tow. On the way back, I’ve got to call maintenance and confess my fault (“forgive me, base, for I have sinned.”)

“620 five minutes out, down jet.”

“What are you down for?”

“Overstress.” Here’s where I might get lucky. Maybe they don’t ask me how bad the overstress was – I’d only ever heard of one overstress worse than that. Maybe all the ready-room cowboys lining the wall around the SDO desk won’t get to hear what a plumber Lex is.

“How much?” the maintainer’s voice asks, tiredly.

Ah, well. It was fun while it lasted.

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2 Comments

Filed under Best of Neptunus Lex, Uncategorized

2 responses to “Overstress

  1. Old AF Sarge

    Heh. Fun while it lasted…

  2. Pingback: Index – The Best of Neptunus Lex | The Lexicans

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