ARCUS M. Engine ups and downs !

[Rod Witter]

May I introduce myself to the forum ?

            My special interest is in the ARCUS M.   I am a fan of Schemp Hirth.  I think I am on my 10th glider from SH. I had an ARCUS T (G-RCUS) for some time (no 28).

I now have ARCUS M no: 106 at Lleweni Parc, north Wales (UK) – which will soon be transferred to Nympsfield in the care of Dan Welch.  I have had the new M (106 is G-ILEW) since December 2014.

        It is clear that the M version is a very complex bit of kit and, with the greatest respect to Schemp Hirth, it may be that the Forum and its exchanged wisdom can be a significant source of problem solving, providing a useful addition to the assistance available from a busy factory service department.

 

So here is my first post:  The engine spindle updrive proximity switch failed in the first two weeks - and I am now awaiting a new one from the factory. I am hoping it is the switch that has failed and not the control box.  Has anyone on the forum , having experienced up proximity switch failure, been unable to solve the problem by switch replacement ?

 

Now to the down limit switch: It is noticeable that , immediately after the limit switch in the engine box operates (and gives a solid green “down” indication on the panel) a trip switch (it sounds like) also operates within the spindle drive.  This sounds like a loud click, and I wonder whether there is some internal thermal protection for overload in this direction ? (as opposed to the panel mounted 12 amp CB – which does not “pop” in this situation )

 

The maintenance manual is silent on the subject.   Can anyone throw light on the matter. ?  Does anyone know who makes the spindle drive, and where one can see an exploded view ?

[Simon Waddell]

Dear Rod

The proximity switch failed on our Arcus after about 6 engine hours.  It is a very fragile device and I understand SH are looking for an alternative solution.

Changing the switch fixed the solved the problem.  Because of the restricted access, changing it is a bastard. The worst part is adjusting it so there is the right amount of slack in the engine restraining/traction wire: because of the geometry of the pylon, moving the switch 1mm results in almost a 10mm change in slack.  Although I tackled the job alone, it's really a two-man job.

We have had no issues with the limit switch in the engine compartment.

I don't know if there is a thermal overload switch in the spindle drive itself.  I do know that once the proximity switch failed, the pylon would extend to the vertical position and then the C/B would blow almost immediately under the stalled load - no noise from the spindle drive itself.

I hope this is of some assistance.

Simon

Arcus M HB-2503 T42, s/n 79 

On Friday, 16 January 2015 15:29:57 UTC+1, Rod Witter wrote:

May I introduce myself to the forum ?

            My special interest is in thDeae ARCUS M.   I am a fan of Schemp Hirth.  I think I am on my 10th glider from SH. I had an ARCUS T (G-RCUS) for some time (no 28).

[Rod Witter]

Thank you simon.
I think the cable lenght is critical (to the extent that it could do with a bottle screw adjuster - the 20 mm tolerance quoted in the maintenance manual seems excessive) surely the designer intended all the engine thrust to go thru the wire ?
Full power prop thrust will of the order of 100Kgf, which equates to 1 tonne thru the rubber bush (leverage looks like 10 to 1) which surely cannot take that load and will split.
The key is perhaps to ensure the wire is ALMOST tight at trip switch moment, thus thrust goes onto wire with only modest distortion of rubber bush to ensure taut wire? What do you think ?
I hope to get the new switch in a few days and reset all the dimensions. Does it come with trailing wire back to connector block ?

[Simon Waddell]

Hello Rod

I have to say that I slavishly followed the instructions in the maintenance manual.  Thinking about you comment/question, I would say the thrust has to be taken by the two engine mounts and the cable rather than the rubber bush which is probably just there to provide a degree of compliance in the system. Any force on the bush will pass into the spindle drive and I am not convinced it is designed or installed to take a load of one tonne.

As I recollect, when the switch trips there must be 10-15mm of slack along the axis of the cable; this is taken up when the pylon moves forward under thrust from the propeller.  The amount of slack is critical; I would say that if there is too much, the load WILL be taken by the spindle drive rather than the cable and that is not good!  But I am commenting from memory.

The switch comes with a pigtail but I recollect that I had to transfer the AMP Faston connector from the broken unit: cue soldering, heat-shrink sleeving etc. You will also need a small amount of silicon caulking - I found some in the local DIY store in a pressurised can which was much easier to use than the usual cartridge which would be a challenge to use in the confined space.

Good luck!

Simon   

[b.aro...@home.se]

Hello Rod,

 

Regarding the adjustment of the cable and spindle drive stop position, I have got following description from Walter Binder, who is the designer of the engine installation  (I have had one of the first gliders with this system, an ASH25 with Rotax 463 engine, since 1999): The cable should have about 15-20mm slack in the extended position.  This way, the thrust load transfer to the fuselage structure is shared between the cable, pivot point and the spindle drive, in order to reduce the vibration transfer. He pointed out it was important not to have the cable tight.

When our Arcus M s/n 38 was delivered in August 2012, the slack was less than 10mm. At that time there was no maintenance manual available, but I readjusted the limit switch to just below 20mm slack. We had no problems with the limit switches so far (40h engine time).

Regarding the click sound in the spindle drive, I have not noticed that, and I don’t know the internal design of the unit. But in the spindle drive units of some older SLGs like the Janus cM and DG-400 I know there is an internal brake, which is released by magnetic forces when the current starts to flow to the engine. In these drives a click sound is heard when the brake applies after the current is switched off, maybe there is a brake also in this unit.

Bengt Aronsson

[Mark]

If there is a brake on the spindle drive that is elecromagnetically operated then if you either raised or lowered the motor a small amount with the mast

[Mark]

My post got cut off. User error.

But if you manually opersted the mast then ad soon as you stopped the mast in any pisition if there is a click associated with a brake then that shoulf be repeatable.

[Jorgen Thomsen]

Hello Rod

In November 2013 I had to install a new spindle drive.
After installation I discovered that the up proximity switch did not work. I found one of the sensor wires in the 4 lead connector disconnected.
After fixing this, the proximity switch still didn't work, and the spindle motor continued to mechanical stop.
I found that the sensor is sensitive to the position on the spindle drive shaft.
When I turned the proximity switch slightly on the shaft, it worked fine. I has worked fine since.

You may have the same problem.

I have experienced an internal break in the 4 lead connector, that sits on the spindle drive shaft. This caused the spindle drive to stop, as the lost connection was one of the main power leads.
Vibration is the problem. I have filled the connectors with silicone, and made sure, that all cabling is tied tight to the spindle drive shaft.

Before this season, I have reduced the cable tolerance by 10 mm, so the play is now slightly under 15 mm. I believe no significant force should be on the spindle shaft during engine operation.

Kindly
Jorgen

[Rod Witter]

Thank you to all for helpful suggestions.

                                    The replacement proximity switch did not fix the problem but fortunately (before changing the spindle drive or control box) I spotted a break in the wiring at the four way connector plug. (the signal plug is very small and vulnerable)   Repairing this has fixed the problem.

Now to set up the adjustment and get flying again.

[Simon Waddell]

Hello Rod

My friend Heini Schaffner had exactly the same problem; should be the first thing to check in case of failure.  I didn't but, luckily(?), it was a switch failure. An AMP-FASTON connector for small signal wires like that is a poor choice: there is little protection against vibration fatigue in the soldered connection to the pins.

Simon

HB-2503 s/n 79