Another torpedo thread?

[cstranc]

Well it's been a little

Well it's been a little while since my last post. I am in panic mode trying to figure out the fewest things I can put into the Sierra and still get to take it to Carmel...

Due to the tight space constraints between the torpedoes and the front dive planes I found that I had to construct the torpedo assembly to ensure that it would not interfere with the dive planes. So let's rewind just a little...

For my 1/60 scale Sierra the torpedoes will be about 6" long. I had planned on using an aluminum tube for the body, then I found this styrene...

Ok so I have a few concerns that it will hold the propell and react nicely to gluing. Why do I bother with the plastic?

The gas trapped in that tube will be the floatation for the torpedo. If the weight of the nose and tail assemblies and pickup tube exceed that floatation you will be searching for your torpedoe at the bottom of the lake.

By taping the ends of the tubes and dropping them into water you can see the aluminum tube does float. Probably well enough to support fairly light nose and tail assembly, but I would be cautious... Because the styrene is so much lighter there is lot's of excess floatation. In fact you might want to take care it does not float too much or it will not look realistic.

I'm not 100% sure which material I shall use yet. But I do know what it will look like:

Working from bottom to top you can see two prototype torpedoes. Next is the caddy. The caddy has is open at one end, then other end is sealed except for a 1/8" hole that the filling tube on the tail of the torpedo will stick out of. Looking a little higher in the picture you can see my mock torpedo with it's filling tube in place and the valve assembly. The valve assembly is described earlier in this thread.

When you put a torpedo in a caddy and then push the filling valve on the 1/8" tube it looks like this.

A neatly packaged torpedo. Stand it on it's end, apply propell through the valve and you are good to go. Except the pressure in the filling valve will cause the torpedo to slip free of the o-ring in the valve assembly after 10 seconds and "self fire"... I don't want to be the cause for WW3 so I need to positive restraint on the loaded torpedo. That is one of the jobs for the torpedo assembly.

The loaded torpedo caddies get dropped into place on the torpedo assembly. You can see the filling valve has a washer built into it. This indexed into a groove on the assembly preventing the valve from sliding away from the torpedo.

From the front you can see each tube has it's own little door restraining the torpedo from moving forward. Nice and safe with no false launches.

So let's take the torpedo assembly appart and see what it is made of.

Top left is the base plate with all stationary bits attached to it. I have green masking tape on it during construction so I can draw lines on it. When it is ready it will be just the plexiglass. The aluminum channel on the right of the base holds the fill valves in place. The aluminum channel on the left of the base plate steadies the front of the caddy, the 2 screws that hold the left aluminum channel also hold a plexiglass bar that extends to the right. This plexiglass is a guide for the aluminum channel in the center, allowing it to slide left to right.

Below the base plate are the four torpedo caddy sliders. These operate individually, the caddy will (eventually) have a ring on it that will index into the slots on these sliders allowing us to move the caddy left to right, firing the torpedo at the appropriate time.

You can also see the torpedo doors to the left of the sliders.

Assembling the sliders to the base it looks like this. Also you can see the brass arms that are all tied to the motion of a single servo. The brass arms run next to the sliders and are held in place by a plexiglass flange.


Looking from the side you can see how the slider has a little arm on it that can latch into the servo arm. When the slider arm is latched the movement of the servo is translated into a movement of the slider. When the arm is not latched the servo motion goes un-noticed by the slider.


So if all the arms are latched and you pull the servo fully in one direction it look like this...

At the right the brass plate has moved 3/4" this motion has pulled the caddy sliders over. The little arms that go from the caddy sliders to the torpedo doors have also been retracted.

As the arms retract back they no longer engage the tab on the torpedo door allowing the door to fall open. Ready to fire.

As I mentioned earlier. Each caddy should have a ring on it. When the slider is in the fully retracted position this ring should drop into a groove and engage with the slider. When this happens and the slider is then driven forward (left) it will push the caddy off the valve assembly and fire the torpedo.

Sounds simple. I sure hope it works...

Rewinding a little bit. Each caddy / slider operates individually moving, or not moving with the servo only if the slider arm is latched. With the caddies removed you can see how it would be configured when we first set sail.

Torpedo 1 is at the bottom, torpedo 4 is at the top. Torpedo 1 is engaged already. Torpedoes 2,3,4 are not engaged. The arm has been lifted and the slider moved 1/4" to the left .

Now when the servo starts retracting it begins to look like this...

The slider for torpedo 1 immediately moves to the right. The slider for torpedo 1 has a pin on it that will eventually start pushing the slider for torpedo 2 to the right. So if we move the servo 1/2 way back torpedo 1 will nudge torpedo 2 a little so that when the servo returns to the left / home position the arm for torpedo 2 is now engaged. We have latched our second torpedo, but because we only went 1/2 of the servo travel the caddy for torpedo 1 did not engage the slider and the door for torpedo 1 did not open.

You can see where this is going.

If you start out and move the servo fully over and back it will: engage the next torpedo, open the torpedo door and then push the torpedo off the valve to launch it.

This way you can launch each torpedo individually.

If you have got painfully close to your target you can retract the servo to the 1/2 way mark 3 times to engage tubes 2,3,4 and then fire all at the same time.

Or any combination in between.

In theory. In practice I am sure there are things that can go wrong. With all four tubes latched the servo force might be an issue. We shall see.

In terms of integrating this into the Sierra, I shall be mounting the assembly onto the bottom hull. I will design the mount so I can adjust it accurately. The torpedoes will actually launch from holes in the top hull, so I will need to ensure good alignment between the assembly and the exit tubes mounted permanently into the upper hull.

I had wanted to have outer torpedo doors, but I had to give up on those for simplicity and expedience. I want to be sailing this in Carmel (this year).

Another night I shall go into the construction of the assembly. That was fun. Believe me these pictures are not my first attempt at this...

I am a little worried about the weight of all this hardware so close to the waterline. Shall have to see what that does to the stability.

And if anyone has a simple, elegant design for firing 4 tubes please shoot me now, or better yet, let me buy us a couple of beers in Carmel and then tell me what I should have done...

Chris

[mylo]

Chris,

In all honestly, I

Chris,

In all honestly, I don't understand everything you've done there, but I'm guessing that to see it in the flesh would clarify.

.....none the less,

...the idea of being able to operate 4 tubes individually ..OR.. together as a salvo by using one servo (channel) is fantastic. I love it.


Later,

Mylo

[cstranc]

Well, summer came and went

Well, summer came and went and was busy in many respects. Now let me be a lesson to you all: always post as soon as you can, or else you forget, or you don't have the right picture...

I did not get a lot of quite time this summer, but whenever I could I would sneak away and work on my Sierra. In particular the torpedoes and launching tubes. This is a choppy recollection of what transpired...

I found that thin wall plastic tubing. That was meant to solve any torpedo weight problems....

Good thing I did not invest much time on that, and was wearing gloves and glasses when I filled it with Propell.

Mental note: stay with aluminum, unless you are big enough to go with brass.

So my next lesson: weight matters, even tiny little bits of it.

Here you can see a few generations of torpedoes. After the plastic fiasco I decided to make a torpedo out of that tent peg from so long ago. I know it was not quite scale, and not quite the right taper, but it probably had a lesson or two to teach me.

As you can see version #1 likes to rest at the bottom of my simulated lake. Version #2 I was a lot more carefull with weight allocation, meaning the tube was cut to length, the nose fitted, then sealed with tape, with the brass filling tube inside and floated. This time I kept drilling more and more out of the aluminum nose peice until the torpedo floated.

Since version #2 floated I actually used it. That taught me another lesson. A "subtle" rotation on the fins to get the torpedo to rotate as it moves forward is not enough. I had a 1/16" offset from the tip of the fins to the tail, with whatever inperfections in it's alignment (which was not bad) it had a turning circle of 10 feet. Perfect if you want to sink you own sub.

But I jump ahead. One trick I really liked with this prototype was drilling the 1/8" hole for the filling tube.

I did not have my micro lathe yet, so I was challenged. In the end I cut 1 inch lengths of brass tubing. Sizes from 1/8" up to the OD of the torpedo. The drill goes in the middle, you press it down and it self aligns. I did grind a flat area before I started drilling.
(sorry about the picture).

In this next pic you can see the 1/8" tube and what went inside it. I drilled a small (smallest micro drill I had, and I broke a few of them) hole in the inner rod. I thought the staggered sizes would be as close as I would get to a nozzle. Also just in case it got water inside all I have to do is pressurize, hold it vertical, and out the water comes.


So how did it work? A little hard to say. That 10 foot turning radius happened to point it to the bottom of a dark lake. It ran quickly on the surface for about 10 feet, and then left this trail of bubbles from the depth. Thankfully it ran out of propell (5 seconds run time?) then floated to the surface to fly another day.

But lesson learned. Version #3 will have significant rotation on the fins. This time it was going to be scale for my model. This works out to a 7/16" tube and about 6" long. I chose to make the masters for the nose and tail pieces out of resin so that I could test the bouyancy every step of the way.

You can see I removed a lot of the resin by drilling a 3/16" hole into both pieces.

Glueing the fins on was fun. They are made of styren strip that I cut and sanded. Actually I cut and sanded twice as many as I needed then selected the best four. I wanted to get a consistent result when I attached them to the tail peice, but they can be soo touchy.

That's the jig I used. First tape the torpedo at the right angle, the Xacto blades are stuck down with double sided tape to give me 2 reference points. The fin gets stuck to a little tape and placed so that it contacts the blades. Tripple check all alignment and apply CA.

This is the end view. Note that I predrilled a slight 1/8" countersink on the end of the tail piece. This will make it simple when I have to drill out for the 1/8" filling tube.

Sorry I did not take pictures of the silicone mold and resin for making numerous nose & tail pieces.

And here they are together Versions 2 & 3.

You can see the difference in the angle on the scale one. I have not tried to put a nice finish on the large one yet. I would like to see how it runs first. The world froze (at least the lakes around here) before I could test fire it. Have to find an indoor pool.

With this torpedo I used a more conventional 5" long 1/16" aluminum pickup tube. I have enough nose and tail parts, I should be able to experiment with different lengths of tube, etc. That should be fun.

Speeking of fun - launching torpedoes is fun. Earlier in the post I had created a mechanical monstrosity. I was not happy with it, so I took the things I liked and moved on...


I liked the compact and simple valve to allow filling, and having a "caddy tube" to hold the torpedo.


That is the assembled torpedo in the caddy with the valve assembly attached. At this point you stand it vertically and fill it with liquid Propell, then drop it into the launcher:


This is my single launcher prototype.

The caddy sits in a 5" length of 5/8" aluminum C channel. This is attached to the cylinder below via a slot in the plexiglass base.

The valve sits in a 1" long 5/8" C channel but this is fixed, so as the caddy slides forward the torpedo is pulled out of the valve.

It is a little hard to see but at the left end the front of the caddy tube is blocked by a door.

The cylinder has 1" travel. as it starts...

The block of plexiglass on the end of the cylinder forces the door to retract down below the level of the caddy. While the piston moves forward the 5" aluminum C channel does also, but because the caddy has 1/2" play in it's slot it stays still.


As it passes the 1/2" travel the caddy starts to get pulled forward...


Until the torpedo is on it's way.

Then when the cylinder retracts the caddy is pulled back, and the door closes.

This is what it lookes like from above:


I shall take some pictures of the 4 tube launcher. I like it. but it is a little heavy. I hope it does not sink the Sierra...