DIY EGT setup

[Bruce Tuncks]

Would it be possible to measure EGT's by simply clamping thermocouple wire to the outside of the exhaust pipe?

 

This would of course only give the exhaust pipe temperature, but maybe this is good enough.

 

My plan is to put 4 sender wires, one on each exhaust pipe, at about 2" from the flange. Just twitch up the thermocouple wires and put them under a hose-clamp. ( or maybe touch the twisted end with a welder first ?)

 

Then use a 4 way rotary switch and one gauge. This setup works fine for the CHT's on the 2200 Jab engine.

 

The engine has run well for more than 10 years now, but only 500 hours, but the last time I took the spark-plugs out, one of them seemed a little whiter than the others. So maybe an "exhaust pipe temperature" would help to see if the cylinders were even or not.

 

 

[fly_tornado]

have you spoken to Bundaberg about doing this?

 

 

[Jaba-who]

The short answer is "no, probably".

 

The gas temperature inside the exhaust pipe varies in a concentric ring from centre of column to the outside. The outside "ring" is cooler than the inside core column.

 

The outside of the exhaust pipe is in an environment of its own. Depending on the air flow inside the cowl the outside of the pipes will be cooler than the gas inside the pipe.

 

Also the numbers change rapidly with engine settings etc so I would have thought the differential temps from inside to out will also be significantly changed or variable at different operating temps. And there is not certainty that the temp differences will change linearly either. You may get accuracy at some temps but not others

 

(I moved my CHT probes to the new centre position and tested them and they were accurate to 80 degrees C but then got more inaccurate as temps went up to real operating temps while flying. Then they were as much as 20 degrees lower. So moved them all back to under the rings. As annoying as that is.)

 

Now presume you do as you suggest and you get a bunch of numbers - you are then left comparing them to a bunch of numbers derived by Jabiru by putting a probe of a known length into a flow of gas a known depth and measuring that temperature. When you use a set of your numbers to decide if your engine is doing OK you have to know if your numbers correlate to the test derived numbers. If they do, then fine but if they don't then you need to know what formula you could use to convert your number to comparable correctly derived numbers.

 

So the "No" in my answer is that you are going to be unsure where your outside temp is in comparison to the desired inside temp.

 

The "Probably" is because you could do some testing comparing it to a properly placed probe to see where your outside probe temp is compared to the inside temp.

 

But this begs the question ....Why not do it right and stick a proper positioned probe in?

 

It seems like you are going to have probes there so why not drill the holes. It's pretty straight forward.

 

As for the switching of the probes. It works. I have a glass cockpit but all the round gauges as well for backup. As the engine only has one oil pressure and one oil temp sender I have two switches that send the pressure and oil data to either the dynon or the round gauges. They work fine. I think I had some dodginess in one of them once and it was because of corrosion on the contacts and I replaced the switch and all has been fine since. If I can give any advice get good quality switches so you don't get any resistance across the contacts otherwise you'll get wrong readings.

 

 

[Bruce Tuncks]

Thanks Jaba-who, that's really useful info.

 

I gather that the probes end at the pipe centre, and they only need a hole drilled at a precise place in the pipe, and this precise spot is available from the factory. Do they supply the probes?

 

Do the probes have a gasket which seals the pipe when clamped by the hose-clamp? I have only seen ones which need a welded nut.

 

Now if I do install these EGT probes properly, will the information turn out to be worth the effort and cost? For example, if one cylinder is running a bit hotter, is it possible to fix?

 

 

[Jaba-who]

Thanks Jaba-who, that's really useful info.I gather that the probes end at the pipe centre, and they only need a hole drilled at a precise place in the pipe, and this precise spot is available from the factory. Do they supply the probes?

Do the probes have a gasket which seals the pipe when clamped by the hose-clamp? I have only seen ones which need a welded nut.

 

Now if I do install these EGT probes properly, will the information turn out to be worth the effort and cost? For example, if one cylinder is running a bit hotter, is it possible to fix?

The probes are about 1.0 - 1.5 cm long as best I recall. That would put the tip of the probe close if not all the way into the centre of the pipe.

 

The probe comes with a hose clamp which has a hole drilled in it with the probe going through the hole. The probe has a flange which sits under the hose clamp and is sandwiched outside the the pipe. You drill a hole in the pipe (pretty easy to do) at 100 mm from the exhaust outlet flange on the pipe. Make the hole exact size for probe and with the hose clamp it doesn't leak.

 

I bought mine from Jabiru when I bought the aircraft kit along with the Dynon. I think they still sell them. Otherwise aircraft spruce sells everything. I buy stuff direct from the USA. There is a Brisbane distributor but they are very poor on the service when I did try them. Stuff never got sent till I chased them up several times and once I ordered stuff from both USA Aircraft Spruce and from Brisbane at the same time (had to get Torque Seal from here because its a dangerous goods and a $2 tube from there was going to $102 from the US) ) and the stuff from the USA arrived first!!

 

Once they are giving you readings you can tell if there's a cylinder running lean or rich.

 

Then you can do several tricks like change the cobrahead (the fibreglass tube (after the SCAT hose ) at the carby intake) and install baffles to change the air swirling in the plenum chamber. Or tilt the carby top toward the hot side - same situation.

 

Or change the jet sizes if they are all running lean.

 

After that - if its just one cylinder running lean then you may need to talk to Jabiru as that's starting to get more tricky. I know some people have changed the aerofoil divider in the plenum chamber to a cylindrical post. But I'm not sure about that. never tried that.

 

 

[Kyle Communications]

http://www.lightflying.com.au/Stratomaster%20Pages/StratoProbes.htm

 

look here Bruce about halfway down

 

 

[jetjr]

You will get a spread of temps and theres not much you can do except manage the engine for the hottest one. Knowing this EGT info is very important.

 

Spruce have some 4 and 6 way switches to do exactly as you want.

 

Pretty sure you can buy the right ones direct from Dynon in USA. Jabiru have very small pipes as engines go so getting ones small enough is tricky

 

 

[Old Koreelah]

With a delicate engine like the Jab why muck about with dodgy instruments? I had a single EGT and four CHTs run thru a rotary switch into a single analog guage. Was blissfully unaware of how bad my temps were until I replaced the lot with some good long probes from CAMit and an MGL digital guage. A lot of attention to airflow and sealing the engine bay reduced my CHTs by 24 degrees C.

 

 

[Jaba-who]

I am inclined to agree with OK on this ( despite my previous statement that switches work) the ideal is to have all the temps displayed continuously so you see them so often you get to learn what the temps vary like with various power settings and the like. Occasional switching to view them will leave you with a gap in really knowing your engine.

 

MGL sell a round gauge style display for only a couple of hundred dollars. A mate of mine has one says they work very well.

 

 

[Bruce Tuncks]

Thanks guys

 

Here's a picture of the possibly lean-running sparkplug, together with one of the other 3. It looks worse ( more white) in the photo than in real life for some reason.

 

Now the factory has the clamp-type senders, which they say are to go with the Dynon display. They have K-type thermocouple wire. Would these go with the MGL display?

 

 

 

[fly_tornado]

the white balance is wrong in your camera