WARNING – XXX 2: State of the Union movie spoilers follow:
(But dont worry, the movie sucked anyway)
After laughing our way through most of the new XXX movie, we came to a part that we cant agree on. There is a scene where he attaches a Bradley Fighting Vehicle (Or some foreign equivalent) to the deck catapult on an aircraft carrier.
Not only did it move the Bradley, but it launched that thing pretty damn fast – almost jet fighter fast, and sent it slamming into an M1 MBT (or some strange contraption that looked like an M1 but had a dual 50 cal and three large cannons and shoots the SLOWEST 105mm round I’ve ever seen… WTF was that about??).
Anyway, there are a couple people I know who say the catapult is definitely strong enough to launch a Bradley. One guy (the “expert”), says that when he was in the Navy, they used to launch old cars and stuff with the catapult.
Even if that’s true, the car has WHEELS and is no where near the 20 something TONS a Bradley weighs. And though the Bradley has tracks, I think it’s more comparable to dead weight, like a block of steel, than to an object with wheels.
So I want to ask the TM and find out the Straight Dope. I know you guys will come through with power specifics on the catapult, weight of a Bradley, coefficient of friction of the Carrier Deck and all that stuff. You guys know everything!
So what do you say? Could a Bradley be launched off the deck of an Aircraft Carrier using the catapult alone and with the Bradley facing the path of motion (so the tracks are facing the right way). And if it “could” launch the Bradley, how fast would it move?
I think “hell no”, but I’ve been wrong before. . .
Well according to the army, the Bradley weighs 50,000 pounds unloaded and 67,000 pounds combat-ready.
And according to the navy, the F-14 Tomcat weighs 43,600 pounds. It doesn’t say whether that weight includes the missiles and stuff that the plane carries.
If the Bradley is unloaded, the difference in weight is not that great, really.
The real difference, of course, is that when the aircraft is launched it is not merely the power of the catapult that causes it to fly off the end of the ship. Presumably (and i know nothing about military aircraft or flying) at the same time that the catapult is pushing the plane, the pilot is also gunning those two “F110-GE400 Afterburning Turbofans with over 54,000 lb Total Thrust.” I reckon that might make a bit of difference.
That is an empty weright for an F-14. Typical gross takeoff weight is in the neighborhood of 64,000lbs. Yes, the engines do contriubte but let’s put things in perspective. F-14 weighs 64,000lb and the thrust is less, 54,000lb as you say, than that so the acceleration from engines alone is somewhat less than that of gravity, about about 27feet/second[sup]2[/sup]. It takes less than two seconds for the cat to launch an airplane. In that time the engines will get the plane moving to 54feet/second or about 36 miles per hour. In that same time the catapult gets the plane moving to about 150 knots, 165 miles per hour. I roughly calculate about 190,000lbs of force from the catapult to achieve that speed.
I once saw a takeoff incident where the pilot, my squadron XO at the time, forgot to release the parking brake for takeoff. 32 tons of metal and wheels that won’t turn. The cat launched the plane to the same airspeed as if the wheels had been turning. Note that the main tires on an F-14 are about three feet tall and for carrier use are inflated to 300psi. This is how the XO earned the nickname “Boom-Boom Bertsch.” He was okay. Although he could have trapped with two blown tires everyone decided it was safer to bingo to the beach.
IANAE but I think the biggest problem in launching improvised objects from a catapult is having an attachment point that isn’t torn off from the force. The launch bar on modern carrier planes is intergral to the nose gear which is designed to take the massive loads and of course the same applies to the tail hook.
I snort derisively at your parking brake. Greater surface area then the F-14 example matters not because the pressure per area unit is an inverse function so total friction will be similar. I think a carrier catapult could toss a Bradley a good distance before splashdown.
The two weights are close enough that you could expect the catapult to accelerate the Bradley to quite a respectable speed, even if not quite that needed to launch the F-14. The engines of the jet are indeed powerful, but given the very short duration of a cat shot (and the low airspeed during much of it), they don’t contribute a high percentage of the launch energy.
A practical problem when launching the Bradley would be how to attach it to the catapult in a way that would accept the very high forces without breaking something. (It was probably not designed with this in mind.)
But while mhendo has a point about the thrust generated by the engines on the aircraft, that’s not sufficient to get the aircraft up to flight speeds in the time that the plane would have on the flight deck. In fact, for many people who have to fly off a carrier on a COD flight - the most unnerving part is that after the plane leaves the catapult it drops… so that the passengers are looking out and UP at the flight deck. I’m mentioning this to point out that the actual effect of the plane’s thrust really doesn’t become a factor until after the plane is at flight speed.
I’m going to go with those who are saying, as long as the Brad was in neutral, it would accellerate fairly well, and go off the flight deck. How FAR it remain in the air is another question altogether. While the steam catapult gets the an F-14 up to about 150-175 mph, I would expect that the Bradley only gets up to 120-140 mph.
Nuh-uh. The F-14 does not have a greater than 1:1 thrust to weight ratio. The F-14 cannot fly straight up on engine thrust alone as can an F-16.
Grumman says the GE engines have 27,948lb afterburner thrust each which is pretty close to what I calculated.
Note that the approach speed is listed at 125knots instead of the 165knots I quoted for takeoff. The plane must be much lighter on landing so stall speed is significantly slower than for takeoff. Landing an F-14 on a carrier with full fuel tanks would structurally damage the airframe.
The aerodynamics of a Bradley are also somewhat important, at least as far as predicting how far it will go and on which side it will land. I can well imagine a Bradley getting launched and tumbling all over the place, until it smacks down hard.
Aha. I was reading this on the Navy site: “(2) F110-GE400 Afterburning Turbofans with over 54,000 lb Total Thrust” as meaning that the engines produced 54klbs each. Apologies.
I can confirm this, as I had to endure this once. I had to test a bunch of gear on the USS John C. Stennis, and was then flown off on a C-2.
They strap you in in seats facing backwards, and when the catapults are engaged, you’re thrown against the harnesses. You then have a wonderful sinking feeling and you really do think you’re going to plow into the drink right in front of a masive ship bearing down on you at high speed.
Then you lift up, and the rest of the flight is uneventful.
I’m happy to have had the experience, but I don’t want to make this a habit.
Yes, it has to be or they may easily destory lighter airplanes or launch heavier ones below stall speed and send them in the drink. An insufficiently powerful launch is called a cold cat shot and is one of the many hazards in carrier flight. The same is true of arresting gear and I once saw an F-14 go in the drink due to improper settings.
I have nothing to contribute, other than my opinion that an aircraft catapult will launch just about anything sideways, and a picture of a car that no amount of “I think I can!” is gonna save.
He was okay. Although he could have trapped with two blown tires everyone decided it was safer to bingo to the beach.