Building a submarine

[FC4]

Hey again,
good to see so many of you helping us out. In response to Entropy's post (#21) we assume the craft must be underwater throughout the run but in terms of steering the craft is allowed to bump its way along the sides.
In response to the "rocket" fans out there: the project is marked considering the complexity of the design, especially the engine.
Thanks for that prop. link akitene and others who've posted about props. A design limitation I forgot to share is that we have a day to actually build the thing so we must rapid prototype most parts and keep machining to a minimum to save time. Also we'll use a stock propeller.

 

[Tin Falcon]

A design limitation I forgot to share is that we have a day to actually build the thing so we must rapid prototype most parts and keep machining to a minimum to save time. Also we'll use a stock propeller.

An important detail you left out . That does add to the challenge.
IMHO a preassigned and proven CO2 engine will help insure success. does the engine need to be made as well in that time frame. If you can use a commercial product look the airhog toys. I have an old aircraft fuselage and engine they also made buggy's find one of those at a yard sale and you have a power plant design that could be rp manufactured. .

 

[lensman57]

Hey again,
good to see so many of you helping us out. In response to Entropy's post (#21) we assume the craft must be underwater throughout the run but in terms of steering the craft is allowed to bump its way along the sides.
In response to the "rocket" fans out there: the project is marked considering the complexity of the design, especially the engine.
Thanks for that prop. link akitene and others who've posted about props. A design limitation I forgot to share is that we have a day to actually build the thing so we must rapid prototype most parts and keep machining to a minimum to save time. Also we'll use a stock propeller.

Hi FC4,

One day to complete is not very long to start building engines and propellers, if the design brief allows it why not just use a direct discharge of the gas through a varible nozzle or control valve if need be. If you go down this route, allow for the loss of the gas weight to control the buoyancy.

A.G

 

[TorontoBuilder]

TB : as far as double action vs single and multiple cylinder I would think stokes per minute should cover all engines except for multiple expansion then one would have to calculate each cylinder seperately and add the totals.
Tin

Thanks Tin... you are absolutely correct.

After reviewing Greeley's formula I see that he did use number of strokes for the value "N".

I apologize to everyone for causing some confusion here. I was thinking Greeley used rpm for N rather than strokes. Greeley simply expressed N using the root calculation i.e. N = RPM x 2, with 2 being the factor to account for the double power stroke per engine revolution.

Tin was correct that N covers all engines except for multiple expansion engines. I blame Harris for my momentary confusion... because his statement "N = number of stokes per minute in a double acting engine" is actually misleading. It is number of strokes per minute in any engine!

I was however on the right track, since I was stating that the formula required a factor for the # of cylinders and action of the engine... which is the case.

So for anyone else like me who has less experience with the power formula, if you need a reminder of how N is actually calculated, the root calculation is engine RPM x # of cylinders x # of power strokes per revolution.

For the following engine types the calculations are as follows:

single acting single cylinder engine (N = rpm x 1);
double acting single cylinder (N = rpm x 2);
single acting multiple cylinder (N = rpm x # of cylinders):
double acting multiple cylinder (N = rpm x 2 x # of cylinders).

My brain is so much happier when it understands all factors required for a calculation... now I can finally let this go and bookmark this page in case I ever need a reminder.

 

[TorontoBuilder]

Hi FC4,

One day to complete is not very long to start building engines and propellers, if the design brief allows it why not just use a direct discharge of the gas through a varible nozzle or control valve if need be. If you go down this route, allow for the loss of the gas weight to control the buoyancy.

A.G

I concur with A.G. given those times constraints I'd use a gas nozzle design... unless the rules permit you to purchase or build an engine prior to the competition.

I am a huge fan of junk yard wars, and having tried similar types of projects I know for a fact how difficult it is to even complete a project that can meet all the goals of the challenge. KISS principles usually win out under such conditions.


Addendum...
But if you can pre-purchase components, I'd go turbine direct connected to one of the Raboesch 6 bladed brass props I mentioned, using their prop shafts.

If the rules permitted pre-purchased components, I'd also try a stamp basic processor, a gyroscope input, rear rudder and forward bow planes and write a basic stabilization program... this will allow your sub to run straight and compensate for the discharge of gas by adjusting the bow planes.

 

[sunworksco]

Before you go down the wrong path, you may want to register on the www.subcommittee.com submarine forum. Everything there is tried and true.

 

[rpledm]

Nothing scales directly so this group needs a bit more info.
First: Is this to be a scale sub or does anything go?
Second: What are you using as a control? Micro-controller? R/C? Clockwork?
Third: How much help is your Prof allowing you to have?
A lot of other questions and suggestions will follow as a result of these questions and answers. You should also ask yourself, "Is this my Prof?"

 

[mrehmus]

Exhaust the gas from the engine to outside the hull. Set it up correctly and you will get a bit of jet propulsion.

How are you going to control depth? Basic and primary question of every submarine sailor.

Remember, there are only two kinds of ships, Submarines and targets.

 

[Lakc]

Turning liquid co2 to a useable gas for an engine is an extremely endothermic reaction. Using the most of the gas you can get at a high enough pressure looks to be the key. At large flow rates, your pressure will drop very quickly.

 

[FC4]

Nothing scales directly so this group needs a bit more info.
First: Is this to be a scale sub or does anything go?
Second: What are you using as a control? Micro-controller? R/C? Clockwork?
Third: How much help is your Prof allowing you to have?
A lot of other questions and suggestions will follow as a result of these questions and answers. You should also ask yourself, "Is this my Prof?"

1) The project is for a miniature sub: it won't be scaled up.

2) There are no electronic control systems in it seeing as we only have 8 hours to build the thing, so we are planning to design it to have neutral buoyancy and steering-wise we've got an impeller-style design like a torpedo so fins drive the thing in a straight line. At the moment we've got a one-way crank attached to the piston so the prop rotates the right way. Also our design is a SINGLE cylinder oscillating engine. Most commentators on this thread have mentioned a double cylinder system: is it imperative we have two?

3) Regarding help from you guys; I consider this research and we will or have actually design(ed) each part so our Prof. should be fine with it.
Another point: we are allowed to buy parts but I think that is limited to, say, ball bearings and gears and tubing, rather than complete engine systems which we could then tune for our needs.

Hope that helps you help me,
Alex

 

[GerryB]

G.Day Alex,
I think your project for building a Submarine should be looked at from a different angle.
What you are expected to build is to put it blindly is a Torpedo.
A Torpedo is nothing more than an unmanned Submarine.
Designed to go a distance to the target,submerged to a certain depth,as fast as possible.
During the first years of the IIWorld War,Torpedo's were powered by compressed gasses,later by electric batteries.
It was the use of Gas that gave away the telltale approach of a Torpedo as it was ejected from Motor exhaust.
I have built two Submarines (Submersibles) Both over 6ft long,Radio Controled
and i can tell you that there is more to getting them to work correctly other than the propulsion system.
Hope this is of use,best of luck with your project.
GerryB

 

[FC4]

Yes our design is essentially that of a torpedo. The original design was self-levelling and had other eccentricities but given the short build period we have to keep it simple.

 

[mrehmus]

...
During the first years of the IIWorld War,Torpedo's were powered by compressed gasses,later by electric batteries.
It was the use of Gas that gave away the telltale approach of a Torpedo as it was ejected from Motor exhaust.
...
GerryB[/QUOTE]

No compressed gas propulsion in U.S. torpedos. All the Mk 14's we fired in the 60's were steam powered using compressed air and methanol to heat water.

The Mk 14 was the main torpedo in WWII and was introduced in 1941. We used Mk 14s in the 1960's on both nuclear-powered Fast Attack and Missile subs on which I served.

The Mk 10, introduced in 1915, which the Mk 14 replaced, was also steam powered, generated by burning methanol. The Mk 10 was also used during WWII.

The Mk 18, which was battery-powered was introduced late in WWII but did not replace the Mk 14. It took the Mk 37 and then the Mk 45 to do that.

http://en.wikipedia.org/wiki/Mark_14_torpedo for more information.