Temp Sensor on a TT39

[forjer]

Has anyone put a temp sensor on a Thunder Tiger .39 engine? If so, got any pics?

I'm installing a Carb Smart and I'm not sure where to install the temp sensor. Sure...near the compression chamber, but it's a bit different when comparing to an OS 50. This head does not have the full radial fins and it doesn't look like there's a great spot for the sensor. The cast head shows a parting line which I believe is just above where the compression chamber is, but there's not a wall directly below to mount the sensor up against as this is the junction between the jug and the head. This probably doesn't describe well enough without pics of the underside of the head.

[vandelescrow]

I was surprised on the finless bob video that the sensor he mouned was actually on the head, I figured the combustion chamber would be just below that.

If no one else responds, can you get one of those temp sonsors (I think venom makes them) that record the temp in flight? This way you can move it around and find there the highest temp is on the engine. I think on these the sensor part is a loop that goes around the engine, not a probe like on the carbsmart.

[forjer]

The combustion chamber is virtually entirely in the head (if it's anything like a motorcycle engine). The piston will rise to TDC which is anywhere from .030" under the top of the cylinder as shown in the attached image, to flush or even slightly above the cylinder into the gasket area for higher compression ratios. Since this is where all the "go" action occurs, it stands to be the hottest part of the engine.

I ended up mounting it to the top of the head near the plug as shown in the other attached image. I didn't have access to any thermal adhesive, but I did manage to find some thermally conductive gap filling material made by Bergquist which they call GF1000 (Gap Filler 1000). I'm not sure how well it'll hold up adhesion wise as it doesn't get very hard. It ends up curing to a soft, thermally conductive, vibration dampening, gel-like modulus. Hopefully it'll hold up to fuel.

I haven't flown it yet...maybe today. It's only 40 deg F. I'm not so sure that the the sensor needs to be on the hottest part of the head as it will work equally well on relative temperatures elsewhere. It would, however, be beneficial to have the sensor on the part of the head that will see / transmit the change in temperature the quickest.

[vandelescrow]

I just asked a few guys at the field and they said right next to the glow plug would be the hotest so where you mounted it in the pics looks like the best place.

Brr, 40 degrees toward the end of April! Well I guess when I'm baking in August you will still be nice and comfortable.

[forjer]

...Brr, 40 degrees toward the end of April! Well I guess when I'm baking in August you will still be nice and comfortable.
Not really...I believe the average temp here in MN for August is 85-90 which is nice...until you add the 60 - 70% humidity.

No luck with the Carb Smart today for the first run. I had the main set at 2 turns out center servo. After a couple minutes, the servo had moved to full rich. I adjusted another half turn out. Another couple minutes and it was full rich again. I went to 3 turns out. Before getting off the ground I could see the servo heading towards the rich end again. WTF! I pulled the linkage, backed out the needle put it back to 3 turns out and hooked it up again. Went back to full rich. The temp didn't seem hot using the finger-backplate test.

I parked it and flew the Rex.

By the way...it was 37 deg F so I hope it wasn't getting hot at 3 turns out.

I need new rubber for the engine. Anyone know who carries a gasket/o-ring set?

So I got home and turned on the Tx and Rx. The CS servo moved full lean (like it's supposed to) and then steadily went full rich. Cycled it off and on again with the same result. I then messed with the gain pot.

Full clockwise the servo went full lean.
At about 40% counterclockwise the servo went full rich.
At full counterclockwise the servo went center.I then dialed the gain to the point where the servo returned to full lean and hit the button to go to 110 deg...the servo went full rich. Dialed down the gain a little more and the servo returned to full lean. Hit the button for 120 deg and the servo returned to full rich like before. Sound right? Something seems fishy.

So I dropped the engine and something didn't look right there either. Looks like the sensor was bleeding. Kinda like when you get pricked by a needle.

Any thoughts? Anyone? Bueller?

[forjer]

I pulled the sensor. It didn't look like this when I installed it. The white particles are what I installed it with. So...is it because of the Finless epoxy mod? The GF1000 I installed it with? That it got too hot? That it was a defective sensor? Operator error?

[vandelescrow]

Now mind you I don't have a carb smart, I'm reading what other people are experiencing with it and so far, waiting till CSM improves the durability of the sensor. R/C heli mag said they ruined 2 sensors trying to install it for there review.

But with that said, FinlessBob said in his video he epoxied it so it wouldn't short out against the head.

Hope this helps