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    the hermetically sealed class 206A submarine

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    Hermann
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    the hermetically sealed class 206A submarine

    Post  Hermann on Wed Feb 25, 2015 9:52 pm

    Hi friends,

    among my papers I have found an article that I had written in 1995 for a German ship modeller Magazine. As it may be of some interest for you I have started to translate it into English (please excuse my poor English) and will post it time by time.
    Here is the first item:


    The Hermatically Sealed Model Submarine

    Story of a model submarine of the German class 206A submarine S195 / U16


    Preface

    This is the story of an unusual model submarine that I started to build in 1976, rebuilding it in the early 1990ies and that is "in service" since 1994 up to now. As the title claims it is hermetically tight by its design concept - we will see later what this means in details. This model is one of the first submarine models with an electronically commutated ("brushless"), wet running DC motor (if not the very first) and is the precursor of my aluminium model S182 / U32 of the recent class 212A of the German Navy that was described in a guest article in one of the latest issues of the AMS "In Depth" magazine.


    How it begun...

    The story begun in 1975 when a ship modeller friend showed me a poster of one of the first  class 205 submarines of the German Navy. As I already had had the wish to build a model submarine but did not like the World War II types very much I just made up my mind to build this (at this time still modern) type.
    The class 205 was the first submarine type of the young Federal German Navy to be built in greater numbers and it were the first to be built with hulls made of non magnetic (stainless) steel to enable them to operate also in shallow waters where mines meant even more a potential danger. In the cold war in these times the were intended mainly to operate in the Baltic Sea. The were rather small, about 500 tons displacement but carrying 8 torpedo tubes in the bow.
    The first batch became a disaster soon - although extended investigations on nonmagnetic steel had been made before building, the steel of the hulls began to corrode internally (as later detected as inter- crystalline stress rupture corrosion). So after a few years the submarines were decommisioned for safety reasons. Some years later in the mid 1970ies, the type 206 was built, now with better and corrosion-resistant steel. This class, modernised at the end of the 1980ies as class 206A, was in service for more than 30 years until they were replaced by the class 212A with air independent propulsion system by fuel cells . The rather small class 206A submarines, about 500 tons displacement, 48 metres in length and with a crew of 22, were the first German submarines that crossed the Atlantic Ocean again to join NATO exercises in the Caribbean Sea and to make goodwill visits to the US.      

    Another reason to build a model of the class 205 was that it was well suited to be built with a plastic tube as pressure hull and a technics rack insert for radio control, propulsion system and diving system and the batteries. Bow and stern sections could be made of GRP laminates, the conning tower of polystyrene plastic sheet material. This design offered a splendid access to the interior and provided a good structure stability of the hull as well as good conditions for pressure tightness by only a few O-ring seals.
    I had seen submarine models with their hulls covered by hatches with "thousands of screws" and I wanted to avoid this design with its inherent drawbacks under all circumstances.
    To get sufficient space inside I planned to use a plastic sewers tube of 160mm outside diameter. To fit into the boot of my car I drove as a student those days (a FIAT 127 , I still have this car preserved as a classic car now) the model should not be longer than 125 centimetres so the proportions would be a little compressed.
    I designed the internal technics rack as a framework of three 10mm x 10mm steel rods hard solderer together with ring ribs made of 10mm x 2mm flat steel. This framework should extend from the end of the stern with the propeller tube up to the bow bulkhead where the cylindrical section ends. The conical rear section of the hull should be fixed to the frame and the tube should be shifted over the frame just to the beginning of the conical section. There an O-ring seal should provide tightness. The front end of the tube should be covered with a circular aluminium bulkhead plate also equipped with an O-ring seal. Tube and bulkhead should be screwed to the frame by a screw penetrating the bulkhead in the centre and sealed there and going further into a thread in the frame. The bow should be free flooded and attached to the bulkhead. The rudders were designed to be made of brass sheet material and the diving system should consist of a ballast tank made of brass sheet metal to be filled by a hose pipe roller pump.

    ....(to be continued)

    As the model looks today...




    Last edited by Hermann on Wed Feb 25, 2015 9:53 pm; edited 1 time in total (Reason for editing : adding a picture)
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    Hermann
    AMS member

    Posts : 105
    Join date : 2011-07-03
    Location : at home, near Bremen (Germany)

    Re: the hermetically sealed class 206A submarine

    Post  Hermann on Thu Mar 05, 2015 8:39 pm

    here the Story continues


    Starting to build...

    Just after the design considerations had settled in my mind I started to build the model. Main source of material were several DIY markets where I got the sewers tube, steel rods, sheet brass and so on. I was a student in those days and my working conditions in my small student's flat in the town of my university away from home were very limited (as well as time). By occasion I got access to a (very old)  lathe and could make several things that needed to be turned (e.g. the case and some other parts of my ballast water pump, the front bulkhead and others). By the time I made progress and eventually the model, although being not ready, was at least able to swim and submerge for the first trials.

    The first experience did not really satisfy me - the model did run well, the diving system worked as intended but due to the rudder arrangement like that of the original early class 205 submarines (two steering rudders besides the stern section and not in the propeller thrust) the model had a very bad maneuverability, especially when surfaced. With rudders full in port or starboard direction the model needed a circle of nearly 20 metres to turn (in this case it behaved like the original ones which needed tug assistance in harbour very often). It did not make fun to control it with this bad maneuverability
    And - what I disliked most - was the fact that the seals for the propeller shaft and for the rudder shafts were not really water tight. After submerging in depths up to 3 metres for a couple of minutes I found some drops of water having penetrated the seals. Due to my limited workshop abilities bearings and the surface of the shafts had been made not so precisely as they should have been and so the leakage occurred. So I thought about improvements...

    But in the following time other themes should keep me away from working on the model - finishing my studies, marriage, entering my profession, building a home and founding a family.

    Nevertheless I was thinking how to improve the model from time by time but it would last several years until I became able to do it...


    (to be continued)

    Picture of my model as class 205 submarine U6, bevor rebuilding as class 206 submarine

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    david f
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    Re: the hermetically sealed class 206A submarine

    Post  david f on Sat Mar 07, 2015 7:59 am

    Interesting account of the development. Slightly leaky shafts and a poor turning circle are common experiences. Look forward to seeing how you sort them out.

    David
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    Hermann
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    Re: the hermetically sealed class 206A submarine

    Post  Hermann on Sun Apr 12, 2015 8:43 pm

    Hi David,
    the bad experience with leaky shafts made me think about a completel different solution (just like Monty Python: "And now for something completely different..."), just see:



    New ideas...

    Of course improvements would have been possible to achieve by better material of shaft seals and a less "eccentric" running and furthermore polished stainless steel shaft, also for the rudder shafts and also more precise workmanship than I had been able to do in the time when I had been a student. But an idea arose in my head whether it wouldn't be possible to make a complete different approach and avoid sliding seals at all (to quote Billy Joel: "I don't know why I go to extremes..."). A device not being necessary and not being present couldn't be a source of leakage at all. So it was the challenge to design solutions for propulsion and steering. The previous diving system that worked with the hose pipe roller pump was already well suited as the pump was already a hermetically sealed system by principle without any sliding seals or valves.
    At the end of the 1980ees I resumed my work on the model.
    For the propulsion system I thought first about a magnetic coupling where an inner rotor driven by a conventional motor and equipped with a number of permanent magnets would couple through the pressure hull wall to an outer complementary rotor with magnets that would be attached to the propeller shaft in the free flooding outer area. This would give a perfect hermetical separation between the interior of the pressure hull and the outside water. Only a little later another idea came into my mind: Why using a conventional motor with magnet rotor to drive the outside rotor? A stator system with coils controlled by switching transistors just depending upon the momentary rotor position would do the job even better! In fact such an arrangement would even be an electronically commutated DC motor with hermetically separated mechanical output, or, as we would also say today, a wet running brushless DC motor! So I started my design by making sketches of the mechanics and the commutation electronics, nowadays called as "motor controller". But this was in 1992 and brushless motors were not so common as today...
    As the approach for my wet running brushless motor was a completely different one my design was also different to the designs you will see today, in mechanical design as well as concerning the motor electronics. My motor is a sensor controlled motor with block commutation and the motor electronics incorporates an overlay PWM (pulse width modulation) for speed control as well as reverse rotation function. The motor electronics has a direct connection to the servo output of the RC receiver that is galvanically isolated and it provides also a current limiting so that the motor cannot burn off even when stalled. The motor electronics is mounted to the motor casing so it forms one unit.
    Designing and building the motor took more than a year...

    (to be continued)
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    merriman
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    Re: the hermetically sealed class 206A submarine

    Post  merriman on Sun Apr 12, 2015 9:58 pm

    Hermann wrote:Hi David,
    the bad experience with leaky shafts made me think about a completel different solution (just like Monty Python: "And now for something completely different..."), just see:



    New ideas...

    Of course improvements would have been possible to achieve by better material of shaft seals and a less "eccentric" running and furthermore polished stainless steel shaft, also for the rudder shafts and also more precise workmanship than I had been able to do in the time when I had been a student. But an idea arose in my head whether it wouldn't be possible to make a complete different approach and avoid sliding seals at all (to quote Billy Joel: "I don't know why I go to extremes..."). A device not being necessary and not being present couldn't be a source of leakage at all. So it was the challenge to design solutions for propulsion and steering. The previous diving system that worked with the hose pipe roller pump was already well suited as the pump was already a hermetically sealed system by principle without any sliding seals or valves.
    At the end of the 1980ees I resumed my work on the model.
    For the propulsion system I thought first about a magnetic coupling where an inner rotor driven by a conventional motor and equipped with a number of permanent magnets would couple through the pressure hull wall to an outer complementary rotor with magnets that would be attached to the propeller shaft in the free flooding outer area. This would give a perfect hermetical separation between the interior of the pressure hull and the outside water. Only a little later another idea came into my mind: Why using a conventional motor with magnet rotor to drive the outside rotor? A stator system with coils controlled by switching transistors just depending upon the momentary rotor position would do the job even better! In fact such an arrangement would even be an electronically commutated DC motor with hermetically separated mechanical output, or, as we would also say today, a wet running brushless DC motor! So I started my design by making sketches of the mechanics and the commutation electronics, nowadays called as "motor controller". But this was in 1992 and brushless motors were not so common as today...
    As the approach for my wet running brushless motor was a completely different one my design was also different to the designs you will see today, in mechanical design as well as concerning the motor electronics. My motor is a sensor controlled motor with block commutation and the motor electronics incorporates an overlay PWM (pulse width modulation) for speed control as well as reverse rotation function. The motor electronics has a direct connection to the servo output of the RC receiver that is galvanically isolated and it provides also a current limiting so that the motor cannot burn off even when stalled. The motor electronics is mounted to the motor casing so it forms one unit.
    Designing and building the motor took more than a year...

    (to be continued)

    Some ideas that will help you magnetically isolate the internal control surface linkages from the external linkages:



    David

    Dr.Schmidt
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    Re: the hermetically sealed class 206A submarine

    Post  Dr.Schmidt on Mon Apr 13, 2015 11:36 am

    I actually like that approach allot!

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