Hello everyone,

I’m a french 22-years student in engineering school. I speak just a few words of german this is why I choose to write in English.

I’m really interested in submarine models. I’m working on a pressluft Upholder class. I present my project in details on a french forum: http://www.forumsousmarin.fr/forum/view ... f=6&t=2390

A few CAD-views of my submarine:





I was really happy to discover that pressluftjunkies forum was back because even if in France there are submarine modellers, not a lot use pressluft systems. This is why I’ve a few questions about your models.

Best regards

Pierre Germanaud

Hi Pierre,

thanks for your introdution. It's absolutely no problem to write in English over here.

Nice Project btw, I like the Upholder class. So if you have any questions or want to share your project, go ahead. I'm pretty sure there are someone who is able to help.

Best regards

Andy

Hi Andy,

For the moment my main question is about condensation. When you compress air, water contained in condense. On industrial compressors there are specific components to trap water. Do you use something similar on your models against it?
I think it can damage components in air circuit (solenoid valve, pneumatic connection...) if there is some water in the circuit. Moreover if some water stay in the tank, it can rust and weaken...

Thank you for your help,

Pierre

Good question. The trick is to install the air line for blowing the main Ballast tank on the lowest Position of the air tank. When you emerge the sub, all condensed water will blow into the main ballast tank. Other air lines are installed at a higher position (i.e. scopes and valves).
This works in several subs since years.

But you should use stainless steel or something similar for the air tank to avoid rust.

Best Regards

Andy

Currently on my drawings the input and the output of the tank are in the same height, in the tank's symetry axis. Because of the curved shape of the ends of the tank, I found it more logical to install the pneumatic connection on the axis.

I plan to build my tank with a tube and two pressed steel shields. Two CAD views of my tank and the real parts:







Of course it could be better with stainless steel but I don’t have it for the moment...
Maybe if i strip down my tank to dry it after using it, it could be ok for the rust... But it's not ideal...

Well, you should consider to switch to stainless from the beginning. I'm pretty sure that you will run in a problem because of condensed water. I can see that you are using small plates to thicken the wall for the connectors. That’s fine. But try to attach one of these also on the tubes on the outer wall of the tube (check the picture). And use this connection for blowing the tank only.

Thank you for your help and sorry for my response time...

I’ve a new question, this time about the compressor.

I’ve noticed that in a lot of pressluft submarine there are special pipes connected to the compressors (black, with fibers). Then they are joined via a Y to the tank with classical polyurethane pneumatic tubing.
Why such a polyurethane tube is not used directly on the compressor? With a 6 x 4 Legris tube, the size seems to be right for the compressor’s end-piece. Is it because of the temperature reached?

I will have other questions about the interference suppressor for the compressors but i have many time before solving this problem!

Hi,

yes you are right! The Problem is the temperature. The tube will dissolve from the compressor nozzle. The black fibre tube is fuel tube or brake hose.

Btw. WELCOME!

Next question please

regards

Sascha

Hi,

there are also check valves between the Y connector and the compressors to prevent the back flow from the tank. You should use 2 of them, 1 for each compressor.

Regards

Andy

Hi,

Thank you Sasha and nice to virtually meet you! Maybe one day in real... I would like to go to the Kaiserlautern meeting. According to Simon Rohou it’s a really nice time and his photos make want to come!

To prevent the back flow from the tank to the compressors i won’t use check valves but a 3/2-way valve. The two compressors are joined to the entry (via a Y) of the valve, one exhaust is joined to the tank and the other to an exhaust silencer.

This valve serves in the role of check valve to prevent the back flow, but it also permits to start the compressor without pressure and then join it to the tank. Finally it permits to relieve pressure in the compressors when the tank is full, like in big compressors systems.

Hello Pierre,
to your first question. For my planned Type 209 i will take brass for the pressure tank. Soldered with silver solder. You can find such parts here:
http://www.modellbau-hartmann.de/produc ... 90-mm.html
http://www.modellbau-hartmann.de/produc ... -0-mm.html
greetings Hans-Jürgen

Hi Hans, and thank you for the links. I have a similar copper tube, i can maybe use it for my tank.

I am going to work on the propeller and the drivetrain in a student project.

I have a few questions about it:

My propeller will be about 105mm diameter (7 bladed propeller). What is the right turning speed for such a propeller? A French modeller advises me about 2000 rpm, is it right according to you?

For the moment i have a classical brushed DC motor:


I have to study this motor, in particular to know the rotation speed and its consumption. I project to use a classical toothed-belt drive to adapt the rotation speed and increase torque.

I also study the opportunity to use a brushless engine. Andy i know you use such a motor on your Beluga, and it seems to be really powerful, maybe a bit too much as we can see on your video! I’m really interested by your feedback about it and by the fact that you have used the two solutions.

I’ve read this subject where you write about it but i don’t understand everything because i’m a very bad german speaker...: viewtopic.php?f=21&t=944&hilit=brushless&start=100

I don’t know this type of engine very well but i think that they have really high rotation speed. But i have noticed that you use a direct drive (no reduction).
The HXT63-74 from Egon is a 200kv engine, so if you use a 24V power it runs about 4800 rpm, which is really too much for a 7 bladed propeller, isn’t it?
Is this computed speed the maximum speed or the rated speed? Of course i think that you can reduce speed with the controller but is it still interesting to use a brushless engine in terms of energy efficiency?

Moreover the power difference between the two solutions is crazy: 120W for the Dunker GR 63/55 and 2000W for the Egon HXT 63-74! Why haven’t you chosen a brushless motor in the same power range? You projected to use two Danker motors so about 250W. So why don’t you choose a brushless in this power range?

Thank you for your help!

Pierre

Hi,

I prefer brushless for more than one reason. First of all because of the effectiveness. It's possible to reduce the turns by Remote Control. My adjustment for the big Brushless Motor is about 30% which works really fine. But, it is absolutely necessary to measure the current at full load to prevent damage on the circuits and lines.

Another advantage is the obsolete gear and the current consumption.

The biggest problem are the turns per volt. Small motors are mostly build with a high rpm at 24V which is not very suitable for our purpose. That’s the reason why I choose such a big motor.

If you want to stick in a Dunker, I have one with controller to sell.

Andy

Hi,

Thank you Andy for your rapid response.

I understand why you choose such a big motor for the kv problem!

I will study the price of each solution. A brushless and its adapted controller is more expensive than a classical brushed motor and its controller. But if i need to buy a complete toothed-belt drive for the brushed solution it is also expensive. If my current brushed motor is adapted, i would maybe keep it as a first solution.

In this case i will just have to buy the toothed-belt drive and the controller. It will be the less expensive solution.

A last question about it; what is the right rotation speed range for such a propeller (7 bladed propeller; 105mm diameter)?

I really thank you for your help!

Pierre

I think it depends on the pitch of the propeller. I recommend to find it out by measuring the current consumption at full throttle (in the water). You should not exceed the limits. With brushed motors, you also should be able to drive at full speed. It the sub is to fast or undriveable, change the gear. If you drive with half speed for a longer time, the controller gets hot. This is the advantage of the brushless system.

Also think about needed speed, available battery power and the time you want to play without loading the batteries. All that counts in. Calculation? Well, trial and error is imho the easiest way.

Andy

I note the influence of all those settings.

I’m agree with you that no calculation can replace a real test. But i design this part of my submarine with a few collegues in the case of a student project in connection with my engineering school, in fluid mechanics teaching. This is why i have to compute the different parameters and follow a scientific approach. So i have a more theorical approach than in classical modelism. For example, we are going to compute the submarine's Cx with a calculator, it’s not really essential but this is an opportunity to learn to use this powerful tool.

Of course different intermediate tests will check the computed results!

For the power electrical design, i will follow a classical way.

Hello Pierre
I know that there is a calculation tool for airplane props:

I found different tools for Big Boats, but the main problem is, to find the correct value for the slip.

Regards Nils