Thinking things throu, carronade carriages

[Izzy Madd]

Just silly me asking again.

As the gun is fixed to the upper carriage, and the elevation screw is rsting on a metal plate fixed on this same upper carriage, where does this enormous lateral force on the screw come from? I would understand if gun and screw were not fised to the same carriage, but like it is...?

Could the wedge be someting like a convenience article? There is quite a load on the screw, which makes it difficult (and slow) in turning. Getting of part of the load would make it easier to lower the elevation.

Jan

With the force of the recoil going back and nowhere for it to go energy has to be released. So either the gun explodes or the force goes down through the pin because of the straightening of the ropes. The for May not be so much lateral as compression with only one choice as to what happens next. It bends

[amateur]

I know that recoil has somewhere to go. But everything fixed to the gun willgo together with the gun. So the whole upper carriage willgo aft, putting stress on the connecting bolt between lower an dupper carriage, but i fail to see why recoil will put stress on this screw. Perhaps i need some more thinking...

 

Jan

Edited March 22, 2015 by amateur

[Izzy Madd]

More engineering calculations:

 

Based on the data in http://www.thenrg.org/resources/articles/The%20carronade.pdf, the muzzle velocity of a 32 lb carronade is 750 ft/sec.  Assuming that the explosive force, and therefore the acceleration, is constant, then the average muzzle force is 70,000 lbs.   A lot of this force will go to accelerating the mass of the barrel, but for the moment assume all of this force has to be counter-acted by the elevation screw (which would happen is the slide stuck, or the breech rope were too long and the fighting pin hits the end of the slot).   From the geometry of the 1812 design I described above, then the load on the elevation screw is about 25,500 lbs.  The drawings specify a root diameter of the screw as 1.25" (outside diameter = 2.125"), resulting in a stress of 20,000 psi.  The yield strength of wrought iron is in the range of 23,000 to 32,000 psi. It they used a heat treatable (hardenable) or cold worked steel, which was available, the the yield strength is in the 60,000 psi range.  

 

Since I've greatly over-estimated the load, a screw could survive with a good safety margin in "regular" use.  

 

Bruce

I think this relies on the none existent QC in the manufacturing as well as the very big IF margin. As it is well documented that bosses didn't care if it worked just that they got payed.

 

A prime example was the so called colonial musket rifle. Which was safest if you stood about ten foot in front of when it was fired. As it was most likely to blow the head of the person holding it.

 

And as you very well described data relies on it being heat treated AND a good sound material AND a 32 pounder AND these were 68 pounders. Then I'd still want to be a long way back.

[Izzy Madd]

I know that recoil has somewhere to go. But everything fixed to the gun willgo together with the gun. So the whole upper carriage willgo aft, putting stress on the connecting bolt between lower an dupper carriage, but i fail to see why recoil will put stress on this screw. Perhaps i need some more thinking...

Jan

The way the ropes are rigged above the bolt they would pull the back end of the barrel down this force would be on to the pin.

[Izzy Madd]

Just by luck discovered this small detail on the Vic replica ...

 

IMG_2220.JPG

 

... just a small twist for the story ...

 

XXXDAn

Like I said just because the plans don't have them doesn't stop a canny old sea dog using them. Especially when it his life on the line...

[Izzy Madd]

Good questions, Izzy.

 

I would think that if the "wedge" or quoin were used it would have shown up on the plans and drawings for these guns.  Or in the list of equipment as quoins do show up for cannon.   They do show in the drawings/lists for gunnades which were cannonades on the wheeled carriages.   Most puzzling.

Only if it was officially there not if it was a thing that was used because the crew wanted to be sure...

[amateur]

Thanks, now I see.

 

Jan

[jud]

Little more than the weight of the rear of the gun on the screw, before, during and after firing. The initial beginning load on the screw will vary a bit at different elevations of the gun tube and roll of the ship. Don't forget that a recoil system is intended to spread the force of recoil over time and distance, the carrage with it's slide is a recoil system and the line running through the block and tackels is another part of that system. The breaching is a safety device to keep the gun in the area it is intended to be and seldom even has the slack taken out of it by the forces of recoil. The block and tackle at the side of a gun are used as dampers on the recoil as well as used to pull the gun back into battery and also used as an aiming device. The screw only controls the elevation of the vertical part of aiming the gun and supports the static weight of the gun. That screw being ridigly secured to the breach end of the gun by a threaded hole is free to move with the threads, the bottom end, unless provisions are made, just drags back and forth on whatever it is resting on  when the gun elevation is changed. Gun tube rotates and everything secured to it moves with it around the trunnion. This is a good discussion about a small but important part of those historical guns.

jud

[Lieste]

While a 32lb carronade is only using 1/4 of the powder charge of the 'distant' charge of the 32lb gun, it is also considerably lighter. A consequence of this is that recoil velocity is higher than for the gun, and the recoil distance available/required is less. Recoil energy for the 17.25cwt carronade is a *bit* lower than the maximum for the gun, but is similar to that of the 'middling' charge of the 55cwt gun. All this combines to give a much 'sharper' check on the breeching, elevation screw and carriage than the large guns. Compared to the small calibre guns, which have much more metal per pound of shot/powder this 'same calibre' difference is even more marked.

A 32lb carronade will have around 4 times the recoil energy of a 9lb gun, and will be absorbing it over a shorter distance. (While a carronade is 'pushing' material limits (and later got a brass bushing in the breech to avoid failure of the threads), and it wasn't generally permitted to double shot them for regular use to save the breechings, fittings on the hull framing, and the carriage, the guns had a lot more leeway for using double shot with it's higher recoil - similar recoil is seen with a double shot and half charges, and distant charge and single shot, and middling charge and double shot is only around a third more.

[Lieste]

Looking again at the discussion of the elevation screw, I think too attention is being placed on the screw itself, which is a strong forged piece. The original fitting was into a screw thread cut into the cast iron of the gun/carronade. This relatively soft/brittle material would degrade and/or fail particularly if the gun was abused (double charges, from loading mishap, or double shot, even with the appropriate reduced charges), the use of a quoin could either delay this failure (IMO less likely, as the space is cramped), or keep the gun in action after the thread stripped/casting broke away (IMO more likely as the elevation screw would be missing post failure, freeing up space for the quoin to adjust for elevation by being inserted/withdrawn).

A later change was a larger casting, drilled and a brass fitting inserted to take the 'female' screw thread.

The 'Quoin patch' was seen on many intermediate date jointed carronades, but not all of the earliest ones, nor all of the latest ones, and was the location for the foundry data for carronades so fitted.

 

[allanyed]

Quote: I think this relies on the none existent QC in the manufacturing as well as the very big IF margin. As it is well documented that bosses didn't care if it worked just that they got payed.

 

Izzy

Your comment about Quality Control being nonexistent is interesting.   I wonder if Melville and Carron tested this kind of thing (recoil) when designing then building the carronade or, as you said, they did not care as long as they got paid.  I love the research before a build and would love to see the well documented information that you mention.  I have no doubt there were cheats out there but have never had the chance to hear about specifics and not just on carronades.

Thanks in advance

 

 

[bruce d]

1 hour ago, allanyed said:

I wonder if Melville and Carron tested this kind of thing (recoil) when designing then building the carronade

My understanding is that the Carron company presented demonstrations of their new product and sought feedback. It had good selling points, such as lower crew requirement and faster rate of fire, and I recall nothing (it has been a while since I read up on it) concerning problems caused by recoil. Before long, Captains wanted this weapon on their vessels.

Izzy, can you share the documentation that specifically relates to the Carron policy?