# How do Aircraft Carrier Steam Catapults work? **URL:** \ **Category:** Factual Questions\ **Created:** [May 4, 2002, 1:35pm UTC](https://boards.straightdope.com/t/how-do-aircraft-carrier-steam-catapults-work/107245 "2002-05-04T13:35:33Z")\ **Posts on this page:** 17\ **Page:** 2
**Author:** ![bman45acp](https://avatars.discourse-cdn.com/v4/letter/b/dc4da7/32.png) [@bman45acp](https://boards.straightdope.com/u/bman45acp)\ **Post date:** [September 6, 2014, 1:44pm UTC](https://boards.straightdope.com/t/how-do-aircraft-carrier-steam-catapults-work/107245/21 "2014-09-06T13:44:34Z")
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. ---
**Author:** ![Redfishhunter930](https://avatars.discourse-cdn.com/v4/letter/r/df705f/32.png) [@Redfishhunter930](https://boards.straightdope.com/u/Redfishhunter930)\ **Post date:** [September 6, 2014, 2:19pm UTC](https://boards.straightdope.com/t/how-do-aircraft-carrier-steam-catapults-work/107245/22 "2014-09-06T14:19:52Z")
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 ---
**Author:** ![Xema](https://avatars.discourse-cdn.com/v4/letter/x/9de053/32.png) [@Xema](https://boards.straightdope.com/u/Xema)\ **Post date:** [September 6, 2014, 3:33pm UTC](https://boards.straightdope.com/t/how-do-aircraft-carrier-steam-catapults-work/107245/23 "2014-09-06T15:33:13Z")
If anyone is still interested in this zombie thread, here’s a [PDF](http://www.globalsecurity.org/military/library/policy/navy/nrtc/14310_ch4.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. ---
**Author:** ![SanDiegoTim](https://avatars.discourse-cdn.com/v4/letter/s/85e7bf/32.png) [@SanDiegoTim](https://boards.straightdope.com/u/SanDiegoTim)\ **Post date:** [September 6, 2014, 11:55pm UTC](https://boards.straightdope.com/t/how-do-aircraft-carrier-steam-catapults-work/107245/24 "2014-09-06T23:55:30Z")
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. ---
**Author:** ![Reply](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/reply/32/15952_2.png) [@Reply](https://boards.straightdope.com/u/Reply)\ **Post date:** [September 7, 2014, 1:12am UTC](https://boards.straightdope.com/t/how-do-aircraft-carrier-steam-catapults-work/107245/25 "2014-09-07T01:12:10Z")
… ---
**Author:** ![Oddball\_92](https://avatars.discourse-cdn.com/v4/letter/o/b3f665/32.png) [@Oddball\_92](https://boards.straightdope.com/u/Oddball_92)\ **Post date:** [September 7, 2014, 1:30am UTC](https://boards.straightdope.com/t/how-do-aircraft-carrier-steam-catapults-work/107245/26 "2014-09-07T01:30:11Z")
> [@Redfishhunter930](#): > > 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 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. ---
**Author:** ![Zakalwe](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/zakalwe/32/270_2.png) [@Zakalwe](https://boards.straightdope.com/u/Zakalwe)\ **Post date:** [September 7, 2014, 2:04pm UTC](https://boards.straightdope.com/t/how-do-aircraft-carrier-steam-catapults-work/107245/27 "2014-09-07T14:04:38Z")
> [@Oddball\_92](#): > > We called them holdback pins. Different sizes for different aircraft types. I was on 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) ---
**Author:** ![Snnipe\_70E](https://avatars.discourse-cdn.com/v4/letter/s/b5a626/32.png) [@Snnipe\_70E](https://boards.straightdope.com/u/Snnipe_70E)\ **Post date:** [September 7, 2014, 4:20pm UTC](https://boards.straightdope.com/t/how-do-aircraft-carrier-steam-catapults-work/107245/28 "2014-09-07T16:20:22Z")
> [@Tranquilis](#): > > Bear in mind that the steam system for the cats is _seperate_ from main propulsion steam. There’s still a need for a seperate system (and cosequently, extra steps), else your available steam pressure for flight ops would change with every change of bell. Can’t have a change in the throttles affect steam pressure just as the trigger is pulled… That would be _bad_. 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. ---
**Author:** ![SanDiegoTim](https://avatars.discourse-cdn.com/v4/letter/s/85e7bf/32.png) [@SanDiegoTim](https://boards.straightdope.com/u/SanDiegoTim)\ **Post date:** [September 7, 2014, 9:23pm UTC](https://boards.straightdope.com/t/how-do-aircraft-carrier-steam-catapults-work/107245/29 "2014-09-07T21:23:34Z")
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? ---
**Author:** ![Really\_Not\_All\_That\_Bright](https://avatars.discourse-cdn.com/v4/letter/r/e8c25b/32.png) [@Really\_Not\_All\_That\_Bright](https://boards.straightdope.com/u/Really_Not_All_That_Bright)\ **Post date:** [September 9, 2014, 5:08pm UTC](https://boards.straightdope.com/t/how-do-aircraft-carrier-steam-catapults-work/107245/30 "2014-09-09T17:08:52Z")
> [@bman45acp](#): > > 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. 148 seconds or less, since a carrier with four catapults can launch one aircraft [every 37 seconds](http://www.navy.mil/navydata/ships/carriers/powerhouse/powerhouse.asp). ---
**Author:** ![Cushmandoug](https://avatars.discourse-cdn.com/v4/letter/c/a9a28c/32.png) [@Cushmandoug](https://boards.straightdope.com/u/Cushmandoug)\ **Post date:** [January 25, 2016, 9:47pm UTC](https://boards.straightdope.com/t/how-do-aircraft-carrier-steam-catapults-work/107245/31 "2016-01-25T21:47:02Z")
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? ---
**Author:** ![bob\_2](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bob_2/32/3341_2.png) [@bob\_2](https://boards.straightdope.com/u/bob_2)\ **Post date:** [January 25, 2016, 10:20pm UTC](https://boards.straightdope.com/t/how-do-aircraft-carrier-steam-catapults-work/107245/32 "2016-01-25T22:20:35Z")
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 > **[How Aircraft Carriers Work](https://science.howstuffworks.com/aircraft-carrier3.htm)** > > Catapults use pressurized steam to boost planes off of an aircraft carrier’s limited runway space. Learn how catapults quickly propel planes to high speeds. ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [January 26, 2016, 1:36am UTC](https://boards.straightdope.com/t/how-do-aircraft-carrier-steam-catapults-work/107245/33 "2016-01-26T01:36:36Z")
> [@Cushmandoug](#): > > … 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?.. 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. ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [January 26, 2016, 1:43am UTC](https://boards.straightdope.com/t/how-do-aircraft-carrier-steam-catapults-work/107245/34 "2016-01-26T01:43:32Z")
Late add. Be sure to read the PDF linked in post #23. The info there is both excellent and official. ---
**Author:** ![Snnipe\_70E](https://avatars.discourse-cdn.com/v4/letter/s/b5a626/32.png) [@Snnipe\_70E](https://boards.straightdope.com/u/Snnipe_70E)\ **Post date:** [January 26, 2016, 5:05am UTC](https://boards.straightdope.com/t/how-do-aircraft-carrier-steam-catapults-work/107245/35 "2016-01-26T05:05:42Z")
> [@Tranquilis](#): > > Bear in mind that the steam system for the cats is _seperate_ from main propulsion steam. There’s still a need for a seperate system (and cosequently, extra steps), else your available steam pressure for flight ops would change with every change of bell. Can’t have a change in the throttles affect steam pressure just as the trigger is pulled… That would be _bad_. 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. ---
**Author:** ![Xema](https://avatars.discourse-cdn.com/v4/letter/x/9de053/32.png) [@Xema](https://boards.straightdope.com/u/Xema)\ **Post date:** [January 26, 2016, 2:49pm UTC](https://boards.straightdope.com/t/how-do-aircraft-carrier-steam-catapults-work/107245/36 "2016-01-26T14:49:03Z")
> [@Snnipe\_70E](#): > > I doubt that there is much extra room to have a separate boiler for the cats. 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”. ---
**Author:** ![mlees](https://avatars.discourse-cdn.com/v4/letter/m/ba8739/32.png) [@mlees](https://boards.straightdope.com/u/mlees)\ **Post date:** [January 26, 2016, 2:51pm UTC](https://boards.straightdope.com/t/how-do-aircraft-carrier-steam-catapults-work/107245/37 "2016-01-26T14:51:07Z")
> [@LSLGuy](#): > > 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. Water, according to this multipage link: [http://navyaviation.tpub.com/14001/css/14001\_139.htm](http://navyaviation.tpub.com/14001/css/14001_139.htm) [Previous page](https://boards.straightdope.com/t/how-do-aircraft-carrier-steam-catapults-work/107245.md?page=1)