How long does it take to reset a steam catapult from a launch. I read that the new electromagnetic launch system can reset in 45 seconds. I wonder how the two compare.
I have a question for you Navy people.
How big are the holding bolts? Are they threaded? What happens to the two pieces when it breaks? (FOD) Whose the person that replaces the bolts. Are they small enough that the person can just carry them around in a sack. Like a carpenter
If anyone is still interested in this zombie thread, here’s a PDF that describes the design of a steam catapult in great (excessive?) detail.
The “sealing strip”, which limits the escape of steam, is described on page 16.
The “bolts” I believe you are referencing are known as “dogbones.” They are not threaded. The size/tensile strength of the dogbone depends on the weight/type of aircraft. Half of the bone goes with the aircraft and is disposed of when the aircraft returns. The half left behind (in the hold-back bar) was simply thrown overboard.
W/regard steam, the Midway (and I’m sure other carriers) generated both superheated and saturated steam. The former was used on the cats.
Don’t think anyone inquired, but 50-60 gallons of water were expended with each cat shot.
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We called them holdback pins. Different sizes for different aircraft types. I was on FORRESTAL and we flew F-4J aricraft…early 70’s. The holdback pins are cylinders about 9" long and about 2" in diameter with a thinner section in the middle. It was this thinner section that sheared. Half of the pin went with the aircraft and was removed later. The other half was left on the deck inside a receiver device. It was discarded.
“Discarded” in this case being a euphemism for “chucked over the side to the bottom of the ocean” (as noted by SanDiego Tim) unless kept by somebody for a souvenir.*
- I worked on the Lexington which was where most aviation candidates did their first carrier landings/shots (in that order) and the squadrons would often send a guy up to the cats to retrieve the holdback pin to give to the aviator in some sort of secret ceremony later. I didn’t want to know, aviators are fucking crazy people.
Zakalwe
ABE3 (Aviation Boatswain’s Mate - Launching & Recovering Equipment)
Also a bell change does not affect the boiler pressure. You should have the same pressure with a stop of dead slow bell as with a Full Bell.
Speaking of items tossed overboard, how about the cross-deck pendants, otherwise known as arresting cables? They were discarded at 100 arrests, unless otherwise damaged. Anyone know if this (tossing overboard) is still the practice?
148 seconds or less, since a carrier with four catapults can launch one aircraft every 37 seconds.
The aircraft carrier catapult is actually two (2) horizontal steam cylinders, one each side of the slot with a saddle bogie between the two. The zipper seal is in fact made of metal and as the bogie slides down the deck (both ways) the metal piece reseals in front of and behind the “Shoe” as it is called. The shoe straddles both cylinders to make sure there could never be a failure to completely launch the aircraft. The two things I do not understand is how and where does the shoe stop and how does it release the aircraft drag arm at the end off the launch sequence? Also, how does the surge stop that is fastened to the backside of the front landing gear, towards the rear of the aircraft to restrain the launch, until such time as the aircraft can come up to full power and the “shooter” releases the plane for launch?
I don’t know why all the old links above don’t work, but here is a simple description of how a steam catapult works
At the end of the catapult expansion stroke there’s some distance left to decelerate the shoe and piston assembly. It’s a ton of metal going 150+mph so it has to be slowed in a controlled manner; it won’t be done by just slamming into a fixed stop.
Whether it’s a water brake or counter steam pressure I do not know. But it’s a pretty obvious design either way. I’m pretty sure I’ve seen a water brake in one manual or another for at least one model of US catapult.
Which is also the key to how the aircraft drag arm releases. The drag arm has a T-shaped knob on its end and is spring loaded upwards. Before launch the drag arm was pushed down by hand and the end was inserted into a matching inverted T-shaped slot in the top of the shoe.
Then the whole catapult plus aircraft is first placed in tension, then fired to launch the aircraft. A the end of the cat stroke the shoe starts to slow down. The aircraft doesn’t.
So the aircraft begins to pull ahead of the shoe. After a couple-few inches of differential travel the end of the drag arm gets to the end of the T-slot & springs up and out of the shoe. The aircraft is now free of the shoe & continues accelerating down the deck those last few feet to the edge.
I couldn’t parse a second question out of your last sentence; the one I didn’t quote above. Try again and somebody can answer.
Late add. Be sure to read the PDF linked in post #23. The info there is both excellent and official.
stop to emergency full ahead the steam pressure should be the same, the firing rate will change. On a M type the temperature can be different.
I worked with an Ex BT.He said every time the cats launched a plain it sucked the boiler pressure down. Made steading firing a boiler a pain.
I doubt that there is much extra room to have a separate boiler for the cats. Plus with out a steady flow of steam through the boiler it would not be possible to superheat the steam.
The PDF linked in post #23 makes it clear that the catapult steam comes from the propulsion boilers, and is held in an accumulator ready for the next “shot”.
Water, according to this multipage link: