Rather a long post here but hopefully the pictures will also speak for themselves.
Over the weekend I tried a number of experiments regarding simulating gunfire. The basics are quite simple using a home-made smoke generator (Nichrome wire wrapped round a wick resting in a small bath of fog fluid) and blowing air and smoke/fog out of a barrel. Fundamentally this follows the principles I have been working on with Iron Duke but I wanted to re-validate the proposed system and process to see if there were areas for improvement.
First experiment.Single barrel with a small container not much larger than the barrel containing the smoke generator air supply is just blowing gently down a tube. The concept was to see if such a simple arrangement would produce a smoke cloud. Could it be that simple that vaporising the fog fluid in a relatively confined space would work? When it exits the barrel would it immediately mix with the surrounding air and provide the volume needed? I blew down the tube and smoke certainly exited but the volume was disappointing. A longer heat time did not improve matters.
Second experimentBasically the same as the first but this time with a larger smoke container something in the region of three times the volume. The results were a significant increase in smoke volume so this would seem to be the way to go and may be sufficient to contain all within the turret structure. If the turret was airtight the whole interior of the turret could be used? This has some possibilities?
Third ExperimentI used the barbette under the turret itself as the smoke container which has greater volume still and this produced the volume of smoke as shown in the picture which I believe is adequate to simulate gun fire. I used a 15mm copper elbow feeding into a 15mm/8mm adaptor which was taped to a plastic barrel. The barbette is sealed and air blown through plastic tube. The pressure required is not high and may well work with a fish tank air pump.
I deliberately did not put any valve at the base of the gun. I wanted to see if this was really needed as maybe the smoke would stay inside until blown out. My conclusion is a valve is required as otherwise before firing the smoke tends to drift out which would spoil the effect.
Conclusions:1)
I think this is a viable approach and produces sufficient smoke and sufficient shots.
2)
A puff of air is better than a gentle blow the effect is more sudden.
3)
A valve of some kind is needed at the barrel to stop smoke drift.
4)
Current consumption is 5 amps on 12v. Three generators = 15 amps.
5)
I need a single smoke generator on for about 8 seconds to generate sufficient smoke
6)
Whilst the current consumption is quite high this needs to be set against 3,600 seconds in an hour so nominally 450 shots! (Assuming the battery can discharge at 5 amps). Its not that simple in practice due to efficiency losses but the potential numbers are certainly attractive.
7)
The smoke definitely needs space to form properly in the consistency needed but importantly the volume needed is nowhere as large as early trials had suggested, which means it can be smaller.
The barbette is about 3 wide by 2 high plastic drain pipe connector.
9)
After firing about 10/12 times the copper elbow was hot to touch, so more heat than anticipated, but I think this is manageable and no damage was caused to the plastic barrel which remained cool during the experiments. I think the copper was hot as it was directly over the element.
10)
Using the barbette as the smoke container meant I could have a 15mm hole off center for the smoke to exit. Condensation on the copper proved negligible although some drops were formed at the end of the barrel. If the barrel is elevated then this may be reduced and just run back into the fog fluid bath.
One of the problems is to design an efficient valve that will seal at very low pressure and be easy to operate and sufficiently small. I have tried sliding valves (A plate with a hole in it which slides sideways to permit smoke flow through) and disc valves (A circular disk with a hole such as it rotates it aligns with a hole and again permits smoke to flow through). These worked to a degree but were complex to manufacture and prone to leakage and installation problems.
I have now decided to go a piston valve route basically a brass tube with a hole drilled through one side to the other with another brass tube inside. If the inner tube is slid it will open a passage for the smoke to pass through. Experiments with this show they should be easy to build and operate and be quite gas tight.
The plan is to build a shared smoke tank underneath A and B turrets, one under Q and the other under X and Y with the piston valve(s) at the top of all three tanks all of which will be fixed to the underside of the deck thus simplifying smoke transfer to the rotating turret and barrel. Air supply will be through a single powerful fan blowing into a distribution pipe through ½ diameter plastic pipe to each of the smoke boxes again with a piston valve to prevent back flow.
Some thought will show this has to be an entirely separate part and installed in the hull albeit this will depend on the particular ship characteristics. The air connectors will be cone shaped and push through latex sheet with a hole in it thus providing an air tight seal to the smoke box. This method means only a single more powerful fan will be needed which could be easily modified dependent on system characteristics.
Operation will then be:
1)
Smoke units on for 8 seconds
2)
Open fan valve and switch on fan
3)
Simultaneously switch off smoke generator and open gun valve for 2 seconds to eject puff of smoke from all five turrets, so a proper broadside.
4)
Switch of fan and close both valves
5)
Repeat as required.
I plan to use a slow cam to operate various micro switches in sequence and believe the whole system to be fairly simple to build and maintain.
Simplistically if I have three generators working at once they will draw 15 amps. Assuming the battery can supply this current drain how many shots will it give us? If I have a total battery capacity of 15 amps/hour this is 15 amps for 1 hour or 1 amp for 15 hours. 15 amps per hour = 3,600 seconds. Divided by 28 (3 generators x 8 seconds = 24 seconds equivalent duration) = 150 broadsides. If battery capacity is doubled then we get 300 broadsides. Again simplistically if we then times this by 50% for loss of efficiency etc we get 75 broadsides or 150 broadsides respectively. Modern batteries should readily be able to provide the current requirements for those of you who are better at batteries do please comment if this is generally correct. Single shots from A & B and Q and X & Y could extend the effect considerably.
I hope to have this ready for Iron Duke for Wicksteed Park in May if all goes well.
The end point is to create a system which can be readily built and operated with no pyrotechnics and importantly can produce a high number of shots.
Sorry, a long post here but thought the gunfire developments may be of interest.
Cheers
Geoff
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Topic: Gunfire (Read 38480 times)