Torpedo Questions

[ramius-ii]

Hi All,
Question 1: The Typhoon uses torpedo with a number of 65-76 "KIT" (Whale) from what I can discover, this torpedo is 650mm in diameter and 9.14 meters long. At a scale of 1/100 the results would be 6.5mm (1/4") by .0914m (3.59") long. Seems small. Is this correct?

Question 2: What is the pressure (PSI) of aero-duster or propel?

Question 3: is there a good picture of this torpedo?

Thanks, Ed

[Wheelerdealer]

Re: Torpedo Questions

[quote]Hi All,
Question 1]

Hi Ed, Some of those 650mm torps carried by the Typhoon were 11m long, still just 11cm at 1:100. I think propel is stored at 50-60psi.

[ramius-ii]

Thanks

Thanks Ramesh!
You have always been a good friend. I called the manufacturer of Aero-Duster, MS-222N (Miller Stephenson) and their engineer said they load the cans to 40 grams of product or 78 PSI.

It was just helpful to know what pressure I am working with so I could set my compressor for testing. It is also useful when selecting materials to know their "burst" pressure.

The picture part of the question was to calculate the correct taper angle for the rear fins.

Best, Ed

[mike dory]

Guy's -- Just remerber the

Guy's -- Just remerber the pressure of Super duster or Propel will change with the outside temperature. the 78 LBS. The super duster people are quoting is at 68 F. At 90F drgees, it will be well over 120 Lbs. This can cause torpedoes to "cook off". The pressure inside the torpedo can exceed the friction holding the torpedo in the tube. This is why many of us always put our boats in the water just as soon as there loaded. Never leave them loaded sitting out in the hot sun. It's not nice to have to go over and ask for your torpedo back after it's landed in someone's lunch, or worse. Best Wishes Mike Dory

[cstranc]

I was playing with a

I was playing with a test torpedo this weekend. I fired it a few times. Let's just say it did not go straight... In fact, if it had been fired from my model it would have self-terminated maybe 4 or 5 times...

I guess the rotation caused by those fins is quite important.

I am using a 1/32" hole in the pickup tube. On my last run the torpedo stopped, then sank. I recovered it from the shallows, dropped it back into it's test launch tube and turned to for shore. Now it turns out the propell expands a lot and that causes it to cool a lot and that can cause ice to form. That caused my torpedo to stop while still "loaded". 30 seconds later it did a vertical liftoff from the tube and continued to seek targets in the lake.

Unrelated subject. I did not want to cast my own tubes for the torpedo body. I was going to use aluminum, that is just a litle bouyant. Then I bumped into

at a hobby store. It comes in many sizes, has a 50% reserve bouyancy, so you can offset the weight of the nose and tail mouldings.

I got it locally but you can see available tube sizes (3/32" to 1/2") at: http://www.cchobbies.com/catalog/rodevergreen.htm

I sure hope it can withstand the required pressure....

One other thing from this weekend. My test torpedo is only 5" long. Thin aluminum body. Besides going in circles (no fins to rotate it) it also drove to the surface - half out of the water - while running and then sank when complete.

I am hoping the 6" long 7/16" OD real torpedo will ride in the water better, and not sink after . You sure get an appreciation all the things that have to go right to make this work...

[aeroengineer1]

There are a few things

There are a few things to consider here. The first is that these torpedoes are traveling at a rather high speed and there for are going to require some stability and control analysis. Remember, these things are just like model rockets and hence they should have the same elements.

http://exploration.grc.nasa.gov/educati ... tstab.html

This is a link that describes the stability and control of a rocket. There is a model rocket handbook if I remember right that was a product of estes. Usually it can be found in many libraries. It goes through the criteria for rocket stability, but the basic thing is that it is best to have the center of gravity further toward the front and the center of pressure behind that. So as to simplify the discussion, we are going to say that this produces forces magically to stabilize the rocket. Think of an arrow or javelin. If the weight was not on the front would it fly well?

The next thing to consider is material strength and the operating conditions. I have not looked it up, but I do know that styrene plastic is rather brittle. This could be bad. If it were to have a small defect in the material, it would not take a stretch then rupture in a small hole, but the failure mode would probably be more like a bomb effect. This could be further complicated by the cold temperature of the propel gas. One might want to consider if the material breaks down in propane and those other gases that are in the propel gas. There are some websites that list chemical venerability of materials.

I am not trying to sink anybodies boat, but I do want to make sure that we as a modeling community do things safely. Having torpedoes go off errantly could be bad for all of us. Yeah, yeah, I know perhaps I am being to cautious as an engineer.

Adam

[tmsmalley]

Thanks for your safety reminders

Thanks for your safety reminders Mike and Adam. We can't be too careful with our hobby - there are enough restrictions in our lives as it is!

[mylo]

Could the speed of the

Could the speed of the model torp not be controlled by the size of the exhaust hole when we are talking about propelling it by the release of compressed gasses ? To bring the model torp closer to scale speed, have that hole quite tiny ? This hole of course has to be BANG ON in the center if you are to have any hopes of the torp going straight.

Has anyone had success with electric torps ? My understanding is that the torque of the elec motor spins the torp as opposed to the prop, resulting in a torp sitting in one place, spinning away.

Mylo

[cstranc]

Adam,
A big thanks from

Adam,
A big thanks from me for highlighting the safety concern. I shall think about that very carefully and maybe test a little in a very controlled environment.

So does this mean that people generally use aluminum or resin for the torpedo body?

If resin does it have better failure characteristics?

Milo,
As for electric torpedoes -> counter rotating props on co-axial shafts. But my fingers are to big for that type of work.

I suppose you could bend the fins to generate a counter torque while under way. They would not counter the prop totally, but that's ok because you do want the torpedo to rotate as it runs. Actually the entire side surface area of the fins will provide a resistance that will counter the rotation due to the prop.

Chris