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-   -   Increasing CHTs (https://vansairforce.net/community/showthread.php?t=139588)

scard 07-17-2016 06:49 PM

After a steak dinner, Test flight #2 results just in. "Could not have been any happier." It is good to have a built-in test pilot on staff to accelerate testing.

I'm sorry for the lack of engineering detail, but it is by design. When my CHT is 385 and we absolutely know from the last 9yrs that it should be 355-360, it is way out of whack for us. The important reference is Change. Listen to the machine.

Weasel 07-17-2016 07:53 PM

Quote:

Originally Posted by scard (Post 1095983)

(That sure is one ugly failure mode of the Lightspeed!)

Definantly not good!! I have the timing output signal from the Lightspeed Plasma III going to an open input on the EFIS so that the degrees timing is logged in with the datalog file.

This also provides a visual display for troublshooting and managing advance with various fuels.

DennisRhodes 07-17-2016 08:13 PM

I have noticed gradual similar CHT increases say 25 to 30 Deg on my O- 320 D2J with a non impulse Slick mag on the left and a LS Plasma II plus on the right . I tried the "Run only on the LS plasma" for about 3 or 4 minutes today at about 80% power and noticed a substantial drop in CHT on all four also in the neighborhood of 30 deg On return to both all the CHT increased back up to the 390 range. Decided to go to mag only and saw a decrease in power . Not sure what thats tell me but the mags got about 350 hours on it and I believe I will check the timing and plugs on both in a couple of days.

flybill7 07-18-2016 08:19 AM

Quote:

Originally Posted by scard (Post 1095983)
Definitely a Lightspeed Plasma II+ failure stuck at approx 43deg timing any way you cut it. A new replacement is installed and behaves exactly as it should. We shot it with the timing light and, yeah, this is the way it should be. A test flight agrees that we have the airplane we know so well back, no matter if it is hot out. CHTs and oil temp are back where they should be.

Hi Scott, I've been having the same high CHT issues with my TMX-360. When you say a new replacement is installed, does that mean you replaced the Lightspeed brainbox? ... Bill

scard 07-18-2016 09:00 AM

Quote:

Originally Posted by flybill7 (Post 1096112)
Hi Scott, I've been having the same high CHT issues with my TMX-360. When you say a new replacement is installed, does that mean you replaced the Lightspeed brainbox? ... Bill

Yes. Simply because it's base timing was obviously messed up. It was stuck at full advance no matter what.

We went through log books last night and were able to determine roughly when this occurred and that we could count the total number of hours flown until resolution on one hand.

DanH 07-18-2016 09:33 AM

Quote:

Originally Posted by scard (Post 1095983)
(That sure is one ugly failure mode of the Lightspeed!)

Yes, and it may explain some past issues with other engines. A high compression engine, running WOT and leaned to best power, will detonate heavily given an ignition failure mode that defaults to 43 degrees.

Most MP sensors are three wire, 5V power, ground, and signal. The typical signal varies from a bit less than one volt at high manifold suction (low MP gauge pressure) to something near 5 volts at low manifold suction (wide open throttle). Low output voltage tells the control system to add advance. Thus it appears an open or high resistance circuit, either on the power side or the output voltage side, could default the system to max advance.

I don't know for sure, but I theorize that current OEM automobile code flags MPS output less than the expected lowest output voltage, turns on the check engine light, and switches operation to a pre-programmed default value. That's certainly what an aircraft system should do.

I'll look into the EDIS system I'm currently flying. Ross, can you comment on the new CPS system? And it would be interesting to hear from Electroair.

flybill7 07-18-2016 09:36 AM

High CHTs
 
Thanks Scott, I am envious that you were able to troubleshoot and resolve so quickly. This one has been a real bear for me. ... Bill

rv6ejguy 07-18-2016 10:25 AM

Quote:

Originally Posted by DanH (Post 1096149)
Yes, and it may explain some past issues with other engines. A high compression engine, running WOT and leaned to best power, will detonate heavily given an ignition failure mode that defaults to 43 degrees.

Most MP sensors are three wire, 5V power, ground, and signal. The typical signal varies from a bit less than one volt at high manifold suction (low MP gauge pressure) to something near 5 volts at low manifold suction (wide open throttle). Low output voltage tells the control system to add advance. Thus it appears an open or high resistance circuit, either on the power side or the output voltage side, could default the system to max advance.

I don't know for sure, but I theorize that current OEM automobile code flags MPS output less than the expected lowest output voltage, turns on the check engine light, and switches operation to a pre-programmed default value. That's certainly what an aircraft system should do.

I'll look into the EDIS system I'm currently flying. Ross, can you comment on the new CPS system? And it would be interesting to hear from Electroair.

With the CPI or EM-5 we can default the extreme ends of the MAP scale (shorted or open failures) to 0 MAP advance so you'd only have the base RPM setting of around 25 degrees total. The CPI uses an integral sensor. We have supplied over 600 of these in EIC, XIC and CPI units over the last 17 years. Zero MAP sensor failures. The CPI has a gauge mode to show current total timing as well.

The EM-5 uses an external MAP sensor and will show an error code in the programmer and turn on the check engine light if there is a open or shorted sensor. We have heard of about 8-10 MAP sensors failures in the last 22 years over many thousands of systems sold. Most of these can be attributed to people not mounting the sensors with the vacuum port down as the instructions state or substituting their own El Cheapo brand of sensor.

I'm not sure why any manufacturer would have 43 degrees programmed in on a Lycoming EI or why it would be designed in such a way to advance if the MAP signal is lost. Scary IMO.

RVbySDI 07-18-2016 10:44 AM

Has there been any communication from Klaus on this failure? I would be curious to hear from him. All be it, having had conversations in the past with him, I can just imagine the tone of the conversation.

scard 07-18-2016 11:01 AM

Quote:

Originally Posted by RVbySDI (Post 1096177)
Has there been any communication from Klaus on this failure? I would be curious to hear from him. All be it, having had conversations in the past with him, I can just imagine the tone of the conversation.

No there has not. We're not wasting the brain cells on it right now as I imagine the same conversation as you do :). Something to deal with after OSH.

Ross, thanks for your comment. I was intending on asking you how you deal with this.


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