|Jan 06, 2010, 02:53 PM|
Sorry, DanL, I was not clear. I had no concerns for safety due to permanent barrel bulge. I meant that all barrels will bulge a little bit when fired, and then return to original diameter. If they are stressed within the elastic limit of the metal there is no permanent distortion, nor, for ductile metals like copper, brass, and steel, permanent damage. btw, the same is not true of aluminum, every distortion causes damage, I've read. It was the temporary bulge of the brass barrel, pushing against a tight, friction-fit resin outer carronade that was my interest. Some plastics can take it, witness Glock pistols, and some plastics can't. I was thinking that if the plastic used for the carronades was of the 2nd type, it might crack and then fail - probably just causing cosmetic problems, though I guess it might possibly send bits of plastic flying, depending on the failure mode.
Easy enough to test, just fire several times and then look for plastic cracks.
Plastic is also subject to heat damage; whether the temp of the barrels would cause any is unknown to me. Again, testing could find out :-). Or maybe you already know - at this point you are the world's expert on small scale, multi-material gun barrels :-).
|Jan 06, 2010, 04:29 PM|
Resin barrel carronade
Brooks, I built this 1/12th scale carronade with a brass inner barrel and then cast epoxy around that barrel to get the scale profile. The inner barrel is shortened to keep the low L/D ratio. The muzzle bore is 1/2" to reflect the appearance of the 6.25" bore of the prototype, but the bore diameter drops to about 5/16" for most of its length.
The model is not cannon grade, and I don't fire it as such. I do fire it with a small charge of BP and a soft wad, no projectile. It fires by remote control (Rx and batts in the base) from a distance.
There has been no sign of barrel cracking, bulging etc.
Again, if a plastic soda straw doesn't split after numerous firings, heat and pressure surely don't seem to be an issue at this charge size and operating scale. A Baretta develops super pressure - what the heck bullet mass is it accelerating to supersonic speed within milliseconds? Holy cow! My foam wads travel 3 to 5 feet (and they rarely show even a scorch mark)
The 1/12th carronade goes Whoof!, not Bang!
|Jan 07, 2010, 08:06 AM|
Gun tackle - scale size
In preparation for the rigging of the new scale carronades, prototype gun, block and line size info is needed.
Philip@SC&H provided excellent details in previous posts. I've taken the liberty of copying and pasting to this thread the information he provided.
On gun bore sizes:
"6 lb cannons, available for all ships, are approximately 9/64” (3.6mm) Ø bore. This equates to 3.5” in real life.
18 lb carronades, which are used only on the Prince, are approximately 7/32” (5.6mm) Ø bore. This equates to 5.2” in real life.
32 lb carronades, available on the brigs and HMS Surprise (the carronade that Dan is working with), are approximately 17/64” (6.7mm) Ø bore. This equates to 6.35” in real life."
On gun tackle:
"Rope sizes were given in circumference in those days..."
"I quote from Brian Lavery "The Arming and Fitting of English Ships of War 1600-1815":
In 1716 breech ropes were 6in in circumference for guns of 24 pounds or more, 5in for guns from 12 to 18 pounds, and 4in for 9- and 6-pounders. They tended to become thicker over the years. In 1749 it was recommended that the breech ropes of 42- and 32-pounders should be increased by 1in in circumference, and that they should be long enough to let the guns run back to the hatch coamings without touching them. By the 1780's 7in ropes were used for 32- and 42-pounders, and 5-1/2in ropes for 12- and 18-pounders.
Normally a breech rope was three times the length of the gun.
This implies the breech rope for your 18lb carronades should be 0.073" Ø and for your 6lb long guns you can't be far wrong at .053" Ø. All tackle for your guns should be 0.026" Ø, although you could probably go down to 0.021" Ø for the long guns."
"... the sizes you came up with (for 18lb carronades) are a touch under but close enough:
.073" = 1.85mm (breech line)
.053" = 1.35mm (gun tackle)
I think ordering the 1.75mm and 1.25mm would be good. The 0.1mm difference is a small amount (a piece of standard copy paper is almost this thick (0.085mm))."
So, for the 32lb carronades on Syren:
Breech lines = 7" circumference or D= 2.2" (56mm). At 1/24scale, D= 2.3mm
Gun tackle = 0.026" (0.66mm) diameter at 1/24 scale. (this seems too light, so likely will go to about 1mm (about 1" full scale)).
Blocks will be 6" or 7" long, or in the 1/24 scale range of 6.5 to 7.5mm long, depending on available sizes.
|Jan 08, 2010, 08:57 AM|
Rotary switch currrent rating
Yep, it would be...for maybe a single use.
The switch you show is rated at 0.3A. Each gun pulls nearly 10A (circuit blows 8A fuses - a 10A is used) as the nichrome very rapidly heats. The very rapid contact cycle (wear) and high amps would be too much for standard rotary switches.
A high current model like the attached pic is $30 or more for a single pole 11 contact switch. I have less than $2 in the switch I built, and the switch build is fast and easy.
Also, the switch I built has 18 contacts, fired in two separate groups of 9, with only 180 degree rotation of the activating servo - a pretty customized design.
You are right, though - there are proper switches available commercially, but likely at a high price.
|Jan 09, 2010, 04:56 PM|
Dan: These are absolutely great. It appears that you have the igniter coil really working well.
|Jan 13, 2010, 05:07 PM|
Schematic for Firing Carronades
The rotary switch, deck plugs, wiring, brass barrels and ignitors are done. Waiting for the mold to be completed to resin cast the back halves of the carronades.
Need to make 9 more slides, hooks, and twisted line, get 72 7mm double blocks and then attach and rig all the gun bases on deck.
Attached: the schematic layout of the gun firing system. The new nichrome igniters are made to heat very fast - they pull a measured 7.5-8.5 amps at 2.6V from two NiMH 10Ah 'D' cells (the highest capacity "D" cells I've ever seen).
|Feb 26, 2010, 04:35 PM|
Siren in Clive Cussler's Corsair
I picked up a copy of Corsair by Clive Cussler to read on vacation, and the whole first chapter is about the Syren's participation in the Tripolitan war. The very first sentence bring her in!
He spells it Siren, but at that time she was still Syren. The spelling did change, but a couple years later I think.
Anyway, way cool.
|Feb 27, 2010, 03:02 PM|
Aerominded--you are quite right--but he can't sail for beans. His crew tried to board a SUPERIOR vessel last summer only to be crippled and run aground.
We'll see how things go with the upcoming gunfight this spring.
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