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Old 04-06-2018, 05:03 AM   #16
Funksammler
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I was comparing the Lz12 with the K4 autopilot (a very scientific process, also known as "playing") when I discovered that the automatic synchronisation "Kreiselüberwachung" on the K4 was no longer working. The "Kurskreisel" is supposed to receive a small electrical signal from the Patin PFK/3 compass indicator but this signal was absent, an unwelcome defect.

This meant opening up the PFK/3 instrument to see what the problem was:



What you see is a "caged" section which contains two potentiometers: the top one with three runners forms part of the desynn mechanism that turns the scale of the instrument; the bottom one with a single runner is the "relay" that provides the synchronisation signal. This runner connects to one of the sliding contacts lower down on the axle which connects it to the output contacts on top of the axle. It turned out the the electrical connection between this runner and the output contact was lost.

The thin electrical sliding contacts (four in case of the PFK/3) carry the signals from the rotating part to the static part of the instrument. The sliding contact of the relay potentiometer is the top one and was found to be defective.

The connections to the contact rings are a common weak point on Patin repeater compasses. Extremely thin wires run along the axis under this contact section, the insulation of these wires contains lactose. Under influence of moisture and age, this lactose forms lactic acid, which eats through the thin wires. The wires are literally destroyed by their own insulation material....

Unfortunately ii is virtually impossible to repair, it would require the whole instrument to be dismantled to replace the contact rings and wires, an extremely high risk operation on such a delicate instrument.

The only saving grace in this case was that the faulty contact was the top one, so a new wire could be fitted to the external surface of the contact ring and connect to the relay potentiometer runner without crossing any of the other contacts.

I managed to loop a thin copper wire around the edge of the contact ring and solder it in place:



This wire was led to the potentiometer runner and soldered to it in parallel to the failed wire. The sliding contact was set a fraction lower so that it would not touch the new wire. The new wire is barely visible on the photograph so you can imagine it was a fidgety job...

In any case, the fix restored the synchronisation function of the instrument and after proper aignment of the relay potentiometer, the K4 autopilot is once again fully functional.

regards,

Funksammler
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Old 04-06-2018, 09:11 AM   #17
whsammler
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Really enjoying this thread. Seeing this type of work & experimenting/testing is fantastic!!!!

Glen
Collector of Wehrmacht Ordnance, Optics & Field Equipment.


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Old 04-08-2018, 06:35 AM   #18
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Back to the Lz12.... One of the more difficult jobs was the restoration of the autopilot's main switch. In itself the switch is a simple on-off switch, connected to the steering unit by Bowden cables. I did manage to find a switch many years ago, this was probably a ground dug example which had been poorly "restored" Although the mechanism to operate the Bowden cables was fortunately present, the mechanism to lock the switch in the "ein" and "aus" positions was completely missing.

This locking mechanism in the switch is essential, as the levers operated by the Bowden cables are spring loaded, without the locking mechanism the switch would simple return to the "aus" position when released.

It took be about a month and several tries to reconstruct the locking mechanism, the space in which to build this is very tight and I had to try a few options before it worked to my satisfaction.

I also had to make a bracket to mount the switch:



Also missing was one of the aluminium cable flanges, so I had to do a bit of miniature turning on my lathe. So hopefully the switch will be fully functional again. I have not yet received the materials to make the Bowden cables, so I have to wait a bit more to find out if it works as intended.



The switch was positioned under the main panel of the autopilot model:



This position reflects the way the the main switch was fitted on the Ju52 (in the Ju52 the bracket was even larger, also holding the vacuum regulator switch) and should just allow me to route the Bowden cables between the various instruments.

So now I await delivery of the Bowden cables so I can finish the installation of the main switch and add some more functionality to the Lz12 autopilot.

regards,

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Old 04-14-2018, 05:28 AM   #19
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Another intermezzo while waiting on the Bowden cable materials gave me a chance to have a look at some US compasses. The American equivalent of the Patin remote compass was the "Magnesynn" compass. The Magnesynn differs from the Desynn system used by Patin in that it uses a 400Hz AC voltage. This uses a permanent magnet as a rotor so there is no need for contacts between the static and rotating parts of the instrument. This also means that in the transmitter, the magnetic rotor can be housed in a separated liquid filled compartment from the electronic parts. The Magnesynn compass was widely used in US aircraft, waterproofed versions were also used by the navy, for example in landing craft.

The following photograph shows the transmitter and the indicator on top of a test unit:



After a bit of fiddling, the Magnesynn system came back to life. It provides a nice comparison to the German Patin compass.

A more complex compass is the Gyrosynn compass, this is one of the world's first flux gate compasses. The Gyrosynn compass was used in all heavy bombers like the B-17 to give increased accuracy that could be used for long distance navigation. It was also used in Canadian build Lancaster bombers, as these used a lot of US designed navigational and radar equipment.

Instead of taking a reading from a moving compass needle, the Gyrosynn reads the direction of the earth's magnetic field directly in a flux gate. This uses the saturation properties of the magnetic material to generate a tiny electronic signals. The advantage of this direct measurement is that the compass does not have the instabilities and swings of a magnetic compass, a disadvantage is that it requires electronic amplification to process the tiny electronic signals.

The next picture shows the master unit of the Gyrosynn compass:



The flux gate is held horizontally by a gyroscope. So sensitive is the sensor that it would be influenced by the tilt of earth's magnetic field so care must be taken that it only measures the horizontal component. The initial erection of the gyroscope is done by locking the gyroscope straight in relation to the compass housing (this should be done while the aircraft is in it's normal horizontal flight position), after that the gyroscope uses the typical "rotating ball" mechanism used in the USA to keep the gyroscope in the horizontal position. The erection of the gyroscope could be done remotely with a special motor unit:



It cost me some head scratching to get this unit to work properly. The motor unit contains a cam driving a breaking contact to stop the motor after a certain number of revolutions. It contains a second breaking contact to light up a signal lamp in the control unit. The challenge was to make the lamp light up while the contact was broken, some sort of inverting circuit was needed for that and it just was not present in the equipment. I suspect that at some point, a capacitor had been fitted instead of a resistor in the unit as the only way I could make it work was to change the circuitry to include a resistor. Without any original circuit diagrams to hand I can only guess...

The other elements of the compass are shown on the next picture:



To the left is the oscillator/amplifier unit. It contains a rectifier to supply the anode voltage for the valves, two oscillators and a three stage amplifier. The unit needed a bit of TLC as it probably has not worked since the end of WW2. I had to do a bit of a search to find replacement tubes, in the end the rectifier tube was found to be defective. Although a circuit diagram was printed on the bottom cover of the amplifier, the schematics are poorly drawn making it challenging to fault find without a full service manual.

The large instrument on the right is the main indicator. Because the electronic signal from the master compass is too weak to drive a magnesynn directly, the magnesynn receiver inside the main indicator has a coil instead of a permanent magnet as a rotor, the signal from this coil is amplified by the amplifier and fed to a motor that turns the instrument. When the instrument is aligned with the signal from the master compass, the signal in coil is zero and the motor stops turning the instrument. This system resembles the system used in the Patin "Funkbeschicker" and PKT-p2 (again the Germans used an electromechanical DC system while the Americans used an electronic AC system) so again it provides an interesting comparison.

The main instrument can be compensated for any errors in the magnetic system while the scale can be shifted to compensate for magnetic variation (the magnetic North Pole is constantly moving, so the navigators carried variation tables so that the compass system could be set to point to the "true north".

The main indicator contains a Magnesynn transmitter so the compensated signal can be sent to up to six "slave" indicators. With the variation properly set by the navigator, the pilot would get an accurate display of the true course flown.

Apart from the mechanical drive between the erection motor and the master compass, the system is now up an running again. I will probably build a small "Navigator's Panel" to set up a permanent demonstration of the system.

It is very satisfying to see this 75 year old technology at work again, such a stark contrast to the rubbish produced today that hardly lasts five years....

regards,

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Old 04-15-2018, 04:21 AM   #20
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The Bowden cable stuff arrived, so I could get to work on the final details of the Lz12 autopilot. I first had to make a few adapters to fit the M6 cable tensioners to the M10 threaded bracket on the control unit. After that the Bowden cables had to be cut to length and the end fittings soldered to the cable. This took a lot of measuring, test assembly and disassembly, but in the end it all came together:



You can see the two cables connected to the levers of the control box. Unfortunately the rotating sleeve is missing from the left cable holder, but the ball shaped cable end fitting sits snugly in the recess without any risk of it coming loose without the sleeve.

The cables runs as low as possible over the top of the autopilot, fitted to the support bracket of the rudder assembly:



Finally, the cables are routed between the instruments on the front panel to the switch mounted just below:



It all just about fits together making the area behind the panel quite busy with electrical cables, pneumatic lines, drive axles and Bowden cables. It gives an idea what a nightmare a full instrument panel must have been to design and fit out.

After a bit of fiddling to get the correct cable tension the output valve on the control unit can now be remotely operated from the main switch under the panel. The locking mechanism in the switch works perfectly, keeping the unit locked in the "off" or "on" position as required. The operation is actually lighter than I anticipated so I am well pleased with the end result.

So now the Lz12 autopilot is fully operational (although an electrical "Kursmotor" could be added if I manage to find the correct one....).

So here is a sequence of photographs to demonstrate a demo startup procedure of the Lz12 autopilot.

We start with the autopilot switched off; all the switches are set to "Aus" and the gyrocompass is locked, there is no pneumatic pressure yet so all the indicators are "dead":



The pneumatic pump is now started. The first thing that starts working is the pneumatic compass indicator, this has now moved into the right corner:



At the same time, the two gyroscopes are starting to run up. I now adjust the compass setting to bring the indicator to the centre, the top scale of the gyrocompass will turn in time:



The bottom scale of the gyrocompass is now set using the bottom knob, once it is aligned the knob is pulled out to uncage the gyroscope:



After a few minutes of running up the autopilot can be switched on (the Lz12 takes quite a long time to run up, much slower than the later electrically driven autopilots):



As a final step, the "Überwachungschalter" is switched on. This will ensure that the magnetic compass keeps the gyrocompass properly aligned. A bit difficult to see due to the camera's flash, but the white indicator on the top left of the gyrocompass is indicating that the "Überwachung" is switched on:



The autopilot is now working. At the start it swings a bit from side to side but as the gyroscopes reach their full speed the course holds steady (you can see very slow rudder movements showing that the autopilot is at work). If the turntable is pushed to the side, the Lz12 reacts with some huffing and puffing, giving full opposite rudder to counter the movement. The movement of the turntable is stopped and reversed, causing the rudder to move towards the opposite side to stop the rotation. Now the rudder gives small deflections to slowly move the turntable back to the set course. When it reaches the set course, the rudder swings slightly opposite to stop the movement before resettling into a stable state.

The autopilot deals with larger deflections with ease, very small deflections cause some oscillation and it takes a while to settle. This is because of the nature of the Lz12 autopilot (dynamic, second order as discussed in a earlier section of this thread). The later Askania Lztz 14 autopilot added a third order measurement (angular acceleration) to the mix to address this issue. These lessons were later carried over into the Patin autopilots.

The Lz12 may have been outdated at the start of the war, but the story is not yet over. Elements of the system were later adapted to create the autopilot of the V1 flying bomb but that story will have a wait....

regards,

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Old 04-16-2018, 06:20 AM   #21
IK5QLO
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This thread makes me feel horny...

Outstanding Job, Funksammler, please keep it going!
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Old 04-27-2018, 12:27 PM   #22
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Back in post #19 on the USAAF equipment I mentioned that the erection mechanism of the Flux gate compass caused some head scratching. Turns out that there were two types of control boxes: the first type with a two-position toggle switch and a later type with a push button. The two are not compatible, no wonder I had troubles to make it work. It turned out that my motor unit was designed to work with the toggle type switch:



The old type control box requires the operator to flick the switch to the "cage" position for at least 5 seconds after which the switch can be returned to the "Uncage" position. The light stays on as long as the switch is set to the "cage" position.

Oh well, another mystery solved....

regards,

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