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914 CHT

 
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willydewey



Joined: 24 Sep 2014
Posts: 53
Location: Guildford Surrey United Kingdom

PostPosted: Thu May 09, 2019 2:59 am    Post subject: 914 CHT Reply with quote

HI Guys
I bought a 2004 Europa XS (914) from a UK builder who was a computer expert. Unfortunately he suffered a stroke and cannot converse on how he wired up the circuit. Recently the Grand Rapids EIS has been warning of a fault which has been traced to the CHT probes. These have been removed. The port side CHT is a probe in a dry socket. I believe this is a thermistor type. The starboard CHT is a 10mm washer type, probably a K style thermocouple 10mm dia fixed with a bolt.
I dont understand why there is this variation and I would be grateful for advice what is correct and if possible the part numbers involved.
Talking around I have been told that these CHT probes should be wired to the Rotax control box? but I can find no evidence of this.
In the meantime I have disconnected the CHTs but run the risk of overheating should I loose the coolant. So help would be much appreciated.
Regards to all
Bill Dewey G-IANI


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paul.the.aviator(at)gmail
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PostPosted: Thu May 09, 2019 8:28 am    Post subject: 914 CHT Reply with quote

Hi Bill,
It's been a long time time I have wired mine so forgive me if I lead you astray.  Could you clarify a few things.

  • Has the standard Rotax probe been removed on one side or both?
  • Are you monitoring all the head temperatures with the 10mm washer, or do you have a combination of the standard probe + 10mm washer type.

If you are using a combination then I would expect them to be different, one sits deeper into the head, the other sits on top of the head. I always thought that it was off that Rotax only provided for monitoring 2 heads.

The sensors are thermistors but I do not recall they type. I know that Grand Rapids used to sell the 10mm washer type at one time and Greg did tell me what they were but I have forgotten (sucks to get old).  GRT used to be fairly responsive so if you do want to know what type of thermister it is you might try contacting them.
Paul
On Thu, May 9, 2019 at 6:02 AM willydewey <willydewey(at)gmail.com (willydewey(at)gmail.com)> wrote:

Quote:
--> Europa-List message posted by: "willydewey" <willydewey(at)gmail.com (willydewey(at)gmail.com)>

HI Guys
I bought a 2004 Europa XS (914) from a UK builder who was a computer expert. Unfortunately he suffered a stroke and cannot converse on how he wired up the circuit. Recently the Grand Rapids EIS has been warning of a fault which has been traced to the CHT probes. These have been removed. The port side CHT is a probe in a dry socket. I believe this is a transistor type. The starboard CHT is a 10mm washer type, probably a K style thermistor 10mm dia fixed with a bolt.
I dont understand why there is this variation and I would be grateful for advice what is correct and if possible the part numbers involved.
Talking around I have been told that these CHT probes should be wired to the Rotax control  box? but I can find no evidence of this.
In the meantime I have disconnected the CHTs but run the risk of overheating should I loose the coolant. So help would be much appreciated.
Regards to all
Bill Dewey  G-IANI

--------
Give a wise man knowledge and he will be yet wiser





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SPURPURA



Joined: 04 Apr 2015
Posts: 66
Location: KAPV

PostPosted: Thu May 09, 2019 1:15 pm    Post subject: Re: 914 CHT Reply with quote

The GRT EIS uses a 10mm bolt in place of the Rotax CHT probe.

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h&jeuropa



Joined: 07 Nov 2006
Posts: 634

PostPosted: Fri May 10, 2019 5:14 am    Post subject: Re: 914 CHT Reply with quote

Hi Bill,

GRT EIS has several dedicated inputs: CHT, EGT, Oil Temp, Oil Press, Volts, RPM, Carb Temp, OAT, Coolant Temp and Fuel Flow. By dedicated I mean the software is programmed to expect those inputs if sensors are attached. You do not have to define them to the software. Likewise you do not have to use them either.

Oil Temp and Oil Press use the VDO sensors supplied with the engine. Volts is measured internally from the power input. RPM uses the Rotax supplied tach signal. The others are optional and use sensors available from GRT (most of which are VDO sensors). When you purchase a sensor from GRT it will come with data specifying what the Scale Factor and Offset for that sensor should be set at.

CHT requires Type J thermocouples and EGT requires Type K thermocouples. GRT supplies CHT thermocouples that are ring style P/N CHT 10-01. Rotax supplies the engine with VDO resistive CHT probes that thread into the cylinder head. These will NOT work for GRT CHT. You can use them to secure the GRT ring thermocouple or remove them and secure the thermocouple with a M10 bolt.

Any Type J thermocouple will work and you may be able to obtain them locally. I'm sure GRT has them available and shipping should be reasonable. Be sure to use thermocouple extension wire (not common electrical wire) if needed.

The VDO sensor currently in port cylinder head is the same as the one used for oil temp. These have become quite expensive lately, so be sure to keep it for possible future use.

GRT EIS gives you six inputs you can define and use as you wish. Most have sensors available from GRT. In my case I use my inputs for Port fuel qty, Stbd fuel qty, Man press, differential fuel press, amps and cowl flap position.

By Rotax control box I assume you mean TCU, turbo control unit? It does not have any provision for CHT input. It comes with a harness from Rotax with connections to the airbox, throttle position sensor, ambient pressure and air box pressure. The TCU operates the servo motor which in turn operates the wastegate of the turbo.

I hope this helps. Manuals are online at GRT and I can answer most questions (I wrote several of the manuals).

Jim Butcher


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budyerly(at)msn.com
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PostPosted: Sun May 12, 2019 8:44 am    Post subject: 914 CHT Reply with quote

Bill,
Flying with no engine monitoring of the CHT is not only not recommended it violates government regulations on required engine monitoring.

I can’t emphasize enough to read the GRT EIS manual.
Any info is there on the operation. The EIS always is the input to the GRT displays (Horizon, Mini, etc.).

Opinions are like butt holes, everyone has one.  2nd hand owners who choose to do their own maintenance must become familiar, in fact, pro’s at the installation and maintenance of each system. Flying is fun, improper maintenance or lack of it can and will lead to mishaps. Download your manuals for the aircraft. (I have mine on the cloud and can refer to them off my cell phone) Study the system, and for sure ask questions. We all had questions on installation. If the previous builder did not provide wiring documentation, you will have to make up your own to understand how things work. That is why I have my 2nd hand owners spend a week in doing a nose to tail on the plane so they know where to look and I can tell what their maintenance limitations are. Even certified airplane mechanics that have no experimental aircraft experience are often times put into questionable airworthiness decisions without proper documentation.

The GRT EIS is designed not to use CHT ring terminals of the J type. Do not use the Rotax cylinder probes as the CHT input on the EIS 25 pin CHT/EGT D sub.

Facts on GRT CHT is it is a thermocouple ring terminal not a resistive type. Do not operate the EIS without the ring terminal CHT probe. Inspect and test the CHT ring terminal at least annually. Normally any failure in a ring terminal CHT is either age and the nichrome wire at the crimp point has failed (or was cut by an improper crimp). Buy a new one. The next problem is simply a connection error. The EIS sends out 5 volts to the CHT ring via a thermistor wire. That wire (normally a red for the +5 and white for the return signal on a J type thermocouple) is somewhat fragile. GRT and other manuals say any extension also has to be the same type wire. Not really over a short distance.

In my observations of many aircraft I’ve inspected and assisted on, any error in reading is usually wear, owner operator installation or programing. I have had one bad EIS box in 20 years of installs.

Don’ts:
Wrap your CHT wires all around the heads or exhaust pipes.
Cut or trim your CHT wires shorter. Changing the connector at the end is basically OK but normally use a Spade connector connecting your CHT J wires to extend them into the panel.
Allow the CHT wires to be routed directly above exhaust pipe connection as leaks have a huge affect on readings.
Reliability of H2O probes in the coolant line is not a primary source of information due to poor grounding unless tested and properly grounded.
Crimp or severely kink the thermocouple wires.

Do’s:
From the CHT ring, use standoffs and hang the wires away from other heat sources to the transition plug or instrument itself.
Use proper spade connectors from the termination to any firewall transition plug. GRT recommends using CHT Thermocouple extensions for the wire if necessary to the EIS plug.
Protect your Thermocouple wires as the nylon wound insulation is easily damaged. Heat shrink works fine.
Coil excess wire rather than cutting it.
Use quality connectors and proper sized wires in completing your wiring.
Check your EIS output on the 25 pin CHT/EGT connector is putting out 5 volts.
I recommend you use the H2O input for the #3 CHT input as a cross reference to CHT.

Note: The #3 cylinder is in close proximity to the exhaust pipe and oil tank. Probes on #3 tend to run high because of this.
See Cooling 101 on my website www.customflightcreations.com Techniques section.

Enjoy your reading. If you need one I have copies of the older GRT EIS Model 4000 I can send you.

Best Regards,
Bud Yerly
Custom Flight Creations

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willydewey



Joined: 24 Sep 2014
Posts: 53
Location: Guildford Surrey United Kingdom

PostPosted: Sun May 19, 2019 7:33 am    Post subject: Re: 914 CHT Reply with quote

Hi Paul, Bud, Spurpura, H&J, AS well as Jim
Thanks Guys for your replies, all are much appreciated.
I raised the question because the GR EIS was misbehaving and found a thermistor probe and a K type on opposite sides of the engine. I have now, with the assistance of a friend shorted out the probe type thermocouple and repositioned the ring bolted type K style. Result problem solved.
Thanks once more I am now able once again to aviate!!!
Regards to all
Bill Dewey


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h&jeuropa



Joined: 07 Nov 2006
Posts: 634

PostPosted: Sun May 19, 2019 8:27 am    Post subject: Re: 914 CHT Reply with quote

Bill,

Glad you've solved the problem.

Just to be certain, the CHT are Type J thermocouples, red and white wires and 50 microvolt / deg C while EGT are Type K thermocouples, red and yellow wires and 40 microvolt / deg C.

While either will work, to have accurate CHT readings they need to be Type J.

Jim Butcher


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