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February 03, 2007

Comments

Fodder

Why on earth would Windows Vista agree the pilot needed to eject? The big yellow ring is vestigial unit, like a turn signal arm.

Morenuancedthanyou

I may be the skunk at the picnic here, but I think 2/3 of a billion dollars for a single plane is obscene. We can spend our money better some other way... like paying down our current debt. Closing the border. Or not spend it at all.

Chris Byrne

Actually, now that I think about iy, there were a couple of incidents of uncontrolled full stabilator deflection (the F16, like almost all other modern fighters has a vully flying stabilator nto an elevator) resulting in uncontrolled descent into terrain. However these were failures of the trim system, and the control actuators; not failures of the control system as a whole.

Chris Byrne

Jim, for mission ciritical components, when possible military aviation typically uses a two by two, or a three by three system.

Each component has a primary and an identical backup internal to it, with possibly a final failsafe backup to give minimal functionality.

Then there are two identical components for each system, with possibly a third failsafe component to give minimal functionality.

Thus, a total failure would require four, six, or even nine failures. The degree of redundacy is determined by the criticality of the subsystem in event of failure, and the weight, space, and cost taken up wy the redundant systems.

The initial acceptance standards for such systems are ridiculously high, with MTBFS far beyond the normal expected lifetime of the platfrom. Unfortunately these sytems do degrade somewhat over time, and maintenance isn't always 100% It's generally very good, but eventually with such complx systems, things do get missed.

One of the main reason why the space shuttle costs so much to fly it, is because they tear each shuttle down to the bones and rebuild it and retest it from the ground up, as if new, after every mission. You can't exactly do that with a fighter aricraft.

The risk is so vanishingly small in comaprison to other risks of miltiary aviation, that it is considered by all involved to be acceptable.

To my knowledge, in 30 years there have been less than a dozen losses of F16s (the first totally unstable fly by wire design fielded by the US) to major control system failure; and none of them have broken up in flight, or had uncontrolled attitude excursions due to control system failure. Mostly it was them running out of elevator or rudder authority and flying controlled into terrain.

Jim

It's like Chris said. Even if there was a rod & cable connection to the hydraulics (which there isn't), the plane couldn't be flown without computer intervention.

What'd be interesting (but have no OpSec need-to-know), is how many layers of redundancy exisit in those systems, how far apart are the various 'puters physically isolated throughout the airframe, and is there some rudimentary, "get-home" capability, even if all warfighting attributes are lost.

And finally, let's hope that there's some other computer in there which knows to utterly self-anhiliate the plane upon the pilot's ejection or other airframe catastrophe. Don't need another (relatively) intact Gary Power's U-2 in some smoking pile on the soil of an unfriendly in this cruel world.


Jim
Sloop New Dawn
Galveston, TX

og

hey, I'm a fan of technology, but you sometimes still need analog.

Chris Byrne

Huh... most all glass airplanes have at least one backup powered attitude indicator, and comnpass, jsut in case. I don't see that here.

Of course in the event of total electrical failure, the F22 is an inherently unstable aircraft (in fact, it has a high negative stability, and thus deviations will accelerate rather than damp out), and the pilot will be blacked out or dead from rapid uncontrolled attitude changes within seconds anyway. Most likely before he could punch out. Even if he could stay awake, said uncontrolled excursions would make safe ejection impossible.

Mel

...and said pilot would give his right nut for a whiskey compass, an altimeter, and an attitude gyro - - or is it all fly-by-wire, too?

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