Saturday, March 12, 2005

Pullin' 30 Gees

I was watching the latest episode of Battlestar Galactica last night. They had some good stuff about Starbuck not being able to fly with a bad knee because of the g-forces and how she wouldn't be able to keep the thruster pedal down. Commander Adama noted that Starbuck would need to be able to hold the pedal down while pulling 6 gees, which is 6 times normal gravity for the unitiated, meaning everything is 6 times heavier than normal -- including the blood in your head, which becomes too heavy at high gees for your blood pressure to keep it in your head, so it drains into your body and you pass out from lack of oxygen to the brain.

6 gees is a lot. But it isn't as much as F-16 pilots sometimes have to pull. They sometimes go up to 9 gees, beyond which almost everyone passes out. Most pass out before 9 gees. It varies from person to person.

But that's a human limitation, not a mechanical one. The F-16 is fully capable of pulling maneuvers that will make the pilot black out almost instantly. If the pilot just pulls the stick as hard as he can, the plane will execute the maneuver just fine, but the pilot won't be awake to see it.

Now, let's talk about the maneuvers we see Vipers doing. Specifically, in last night's episode, Apollo, while flying at what appears to be pretty much full out, whips his Viper around in the space of perhaps five ship lengths reverses his thrust and heads out in the other direction.

An F-16 is about 49 feet from tip to tail. Vipers look to be a bit smaller, but we'll go with that. That means that in perhaps the space of 250 feet or so, Apollo spun around, decelerated* from flying full-out, and began accelerating the other way.

Was Apollo pulling 6 gees? Uh, no. I could calculate how many gees he was pulling -- my guess would be something like 20 gees -- but I don't really need to. As I noted above, the F-16 is easily capable of pulling maneuvers that exceed the human factors limit of 9 gees, and it can't do anything even close to what Apollo's Viper did in that scene. In fact, he would have passed out just from the spin move, flying straight into a canyon wall, even if his decelerating and then blasting off in the other direction weren't enough to put his lights out all by themselves.

This isn't a serious complaint about the show. I like the fact that the Vipers now have directional thrusters along the fuselage that allow them to do cool maneuvers, even though almost every maneuver they are used for would knock the pilot out faster than a bottle of ether. And I like the fact that the show actually takes stuff like g-forces into account, even though they vastly underestimate the forces the pilots would be pulling. No "intertial dampers" like in Star Trek and Star Wars. Not that intertial dampers weren't a cool idea to explain the maneuvers Enterprise could do despite having long nacelles held on by thin little supports. But it's become an overused convention in SF television, I think.

Just don't think that fighters like Vipers, having those cool directional thrusters, could really work. Well, they could work, as long as they are operated by remote control or the pilot isn't human. But the human body is the limiting factor on these things, not engineering. The Air Force's new F-22 "Raptor" is actually more maneuverable than the F-16. Even planes operating under the limitations of gravity and an atmosphere can already perform maneuvers well in excess of what the human body can tolerate. Technology isn't the issue. Human physiology is.

* "Decelerate" is not the appropriate term from the physics standpoint, of course. Since acceleration is a vector, having both a value (speed) and a direction, Apollo was technically still accelerating as he slowed down. He was just accelerating in the direction opposite his current direction of travel.


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