4 Fuel Tanks with Rotax 912

[Martin Pohl(Guest)]

I am installing a Dynon EMS-120 in my Rotax 912ULS equipped Zodiac XL.

Question: I have 4 fuel tanks (though need GP2 and GP3 for the outer tank fuel sensors). Is it possible to connect the Rotax CHT to the 25-PIN harness (where normally the CHT is connected to) instead of GP2/3? Or can I change the Rotax CHT probes to the ones used on the Lycoming and then connect them to the normal CHT-inputs?

Any idea of how to solve the problem otherwise?

And when do you think I can display Coolant temperature?

Looking forward to hearing from you.

Rgds
Martin

 

[dynonsupport]

The CHTs which come preinstalled on the Rotax engine can not be hooked up to the 25 pin thermocouple wires as they are not thermocouples. You could, however, source appropriately sized ring terminal type CHT probes. These are mounted behind the spark plugs. They would need to be type J thermocouples, and the wire that goes between them and the 25 pin harness needs to be thermocouple wire as well.

Coolant temperature support should be coming soon, though we're not exactly sure when. This will likely use one of the GP inputs though, which it sounds like you will not have available. However, this site has an interesting article on why CHTs may be more interesting to you than the coolant temperature: http://www.rotaxservice.com/rotax_tips/engine_instruments.htm (scroll down to the 4 stroke section)

 

[Martin Pohl(Guest)]

Thank you for your answer.

I asked the german representative for Rotax engines about J-thermocouples for the spark plugs. He wrote that they do not provide engine limitation data for the cylinder temperatures at the spark plugs and therefore they do not recommend this kind of installation. He also said that most probably temperatures at the spark plugs are different to the temperatures measured at the "normal" Rotax CHT probes.

Well, as it looks like, I will have to connect the Rotax-CHT-probes to the EMS and install 2 additional fuel gauges for the 2 outer tanks...

What do you think about a switch that either connects the inner tanks OR the outer tanks to the EMS? I would do the fuel sensor calibration in the EMS for the inner (main) tanks. The outer tanks are exactly of the same size and shape as the inner tanks and have the same sensor installed.

Regards
Martin Pohl
Zodiac XL, Switzerland

 

[dynonsupport]

There's no electrical reason why your tank switch idea wouldn't work, but any variation in the float senders' output, the shape of the fuel tanks, etc may impact the accuracy of the second set of senders accuracy.

 

[Martin Pohl(Guest)]

Thx. I will install a switch that allows switching between inner and outer tanks. This switch additionally opens/closes one of the external contacts so that it is clear on the EMS which tanks are displayed (e.g. "OUTR".

Rgds
Martin

 

[Krzyzewski]

CHT measurement on Rotax 912/914

If you want to keep the GP inputs for other functions rather than for measuring CHT with the Rotax supplied CHT sensers an alternative is to replace the fitted Rotax CHT senders with Westac J thermocouples. They supply a metric threaded version that fits into the Rotax pre threaded holes and changing them over is really easy.

Once you have done this you can use the standard CHT inputs on the EMS and keep the general purpose inputs for other functions.

Tony

 

[A321Flyer]

Tony

Thx for the good hint! What kind of thread do I need for the Rotax-sender replacement? Do you have a P/N for the sender?

Martin

 

[A321Flyer]

I don't have my Rotax engine yet. It will be a 912ULS. What thread do the CHT sensors have?

Martin

 

[dynonsupport]

See this post for info on replacement CHT probes for the Rotax 912