VAF Forums

VAF Forums (https://vansairforce.net/community/index.php)
-   RV General Discussion/News (https://vansairforce.net/community/forumdisplay.php?f=2)
-   -   Climb power and CHT?s (https://vansairforce.net/community/showthread.php?t=158758)

Raymo 03-19-2018 10:40 AM

Quote:

Originally Posted by N941WR (Post 1246973)
That is exactly how I configured Tim's P-mag's. (See my post above.)

Regarding your RPM limit, I would raise that up one notch to just over 3,000 RPM. It is easy to hit 2816 and when you do, the ignitions will stop firing, dumping raw fuel into the exhaust. When the prop slows down and the ignition starts firing again, that raw fuel in the exhaust will light off with a LOUD bang. That causes the pilot to need to change their underpants as soon as they land.

Thanks. Missed our post, somehow. We set the Max RPM per Brad's recommendation and 2600 RPM limit of the prop but I understand the concern.

N941WR 03-19-2018 10:56 AM

Quote:

Originally Posted by Raymo (Post 1246982)
Thanks. Missed our post, somehow. We set the Max RPM per Brad's recommendation and 2600 RPM limit of the prop but I understand the concern.

If your FP prop is pitched correctly, the only way you are going to hit the 2800 RPM Rev limiter is by getting the nose down and not retarding the throttle, which a good bump can do in a hurry. That's why mine is now one setting higher, as is Tim's who has a CS prop. It will still save him from an overhaul.

lr172 03-19-2018 11:03 AM

Quote:

Originally Posted by scard (Post 1246964)
This thread was started with respect to an O320 that probably has a MA-4 carb which operates quite differently than the carb that you would expect to see on a O360. With the MA-4spa, it is my understanding that throttle position doesn't effect the "enrichment" circuit as it does on the larger carbs.

I have a 320 and my research a few years ago showed some of the MA-4SPA models having an economizer and some didn't. The economizer reduces flow through the main jet at lower MAP levels. While not technically a WOT enrichment, it provides the same function - higher than designed fuel flow at high MAP levels, usually associated with WOT condition. I don't know the cutoff points, but would speculate around 26.

Larry

YellowJacket RV9 03-19-2018 11:53 AM

Quote:

Originally Posted by N941WR (Post 1246976)
I'm not convinced it is a fuel delivery issue. If that was it, then all four cylinders would run hot, not just one.

Not necessarily. The poor fuel distribution can cause some cylinders to run much leaner than others at different throttle settings. It certainly does on mine.

Chris

lr172 03-19-2018 10:33 PM

Quote:

Originally Posted by N941WR (Post 1246894)
Tim is based about eight miles from me and when he installed the P-mags, I used the EICAD program from E-mag to set the Advance Shift to a -1.4 degrees on both his P-mags (I also lowered his Max Advance by 1.4 degrees), which puts them at 25.2 degrees for takeoff. As with any custom configuration on the P-mags, do you not install "the jumper".

After talking with Tim on the drive in this morning, I do not believe his issue is with the P-mag or fuel delivery. The reason being is that if either were the issue, then all the CHT's would be high due to bad timing or a lean mixture. If he was injected, I would imagine it is possible that a jet could be clogged forcing #3 to run lean.

That brings us to two possible issues, either a baffle seal around that cylinder or a leak on the intake tube for #3. He is going to inspect the intake tube gaskets and hopefully install the cowling and inspect the seals with his borescope. (His prop is out for an inspection, so no flying for a week or two.)

I will also stop by his hangar later this week and verify the P-mag timing is correct. It was correct when we left the hangar after I set them but it never hurts to verify such things.

A thought for all of you installing P-mags but are not planning on an EICommander; Tim does not have an EIC but he did bring the connections for one into his cockpit and terminated them with two female DB9 connectors under his panel. This allows for easy adjustment with the EICAD program. Should he ever buy an EIC, he can simply make a Y cable that goes from both DB9 connectors to the EIC's DB15 connector.

Given that this problem appeared immediately after the installation of the Pmags (please correct me if not accurate), it would be difficult to assume the problem is unrelated to the installation. I imagine it is possible that the owner disturbed the intake gaskets or something else during the installation. However, given the immediate onset of the problem, it seems logical to focus on what has changed. I'm sure he could improve the baffles, but what are the odds they just started leaking the day he installed the pmags. Same with fuel flow. If the temps were normal before the installation, I can't imagine drilling a jet is going to fix the new problem on #3.

I would spend some time thinking about everything that I touched when I did the install. Have you had the cowl off since? Maybe a baffle seal was kinked or out of position, maybe a rag was left on top of the cylinder, etc. Has someone confirmed that the timing was set properly. It wouldn't be the first time that someone timed the ignition incorrectly on a Lycoming. Did you confirm that each sparkplug was tightened, etc. Also, I don't believe you are looking for a lean condition on #3. Lean cylinders don't show these types of disparities. If the other three cylinders are under 400 and let's say 100* ROP, you won't see a 50 degree increase in CHT by leaning to peak from 100 ROP (Peak CHTs occur at approx 80 ROP and will fall on either side of it). I don't know what the typical CHT spread is between 250 ROP and 80 ROP, but I can't imagine it is 50*. Maybe someone else can chime it, I don't ever run that rich. Detonation is a more likely culplrit for this type of spread. Detonation is most often caused by timing issues, going back to what has just changed.

Good luck,

Larry

N941WR 03-20-2018 05:40 AM

Quote:

Originally Posted by lr172 (Post 1247182)
Given that this problem appeared immediately after the installation of the Pmags (please correct me if not accurate), it would be difficult to assume the problem is unrelated to the installation. I imagine it is possible that the owner disturbed the intake gaskets or something else during the installation. However, given the immediate onset of the problem, it seems logical to focus on what has changed. I'm sure he could improve the baffles, but what are the odds they just started leaking the day he installed the pmags. Same with fuel flow. If the temps were normal before the installation, I can't imagine drilling a jet is going to fix the new problem on #3.

I would spend some time thinking about everything that I touched when I did the install. Have you had the cowl off since? Maybe a baffle seal was kinked or out of position, maybe a rag was left on top of the cylinder, etc. Has someone confirmed that the timing was set properly. It wouldn't be the first time that someone timed the ignition incorrectly on a Lycoming. Did you confirm that each sparkplug was tightened, etc. Also, I don't believe you are looking for a lean condition on #3. Lean cylinders don't show these types of disparities. If the other three cylinders are under 400 and let's say 100* ROP, you won't see a 50 degree increase in CHT by leaning to peak from 100 ROP (Peak CHTs occur at approx 80 ROP and will fall on either side of it). I don't know what the typical CHT spread is between 250 ROP and 80 ROP, but I can't imagine it is 50*. Maybe someone else can chime it, I don't ever run that rich. Detonation is a more likely culplrit for this type of spread. Detonation is most often caused by timing issues, going back to what has just changed.

Good luck,

Larry

Larry, here is why I don't believe it is a timing issue:

1. The P-mafs fire two cylinder at the same time. If there was a timing issue and one coil pack failed, at a minimum, two cylinders would show high CHT's, not just one.
2. I was there when Tim set his timing to TDC and we verified each other. If the timing was off, all four cylinders would have high CHT's, not just one.
3. I configured the standard timing setup down 1.4 degrees, as I recommend, and emailed Tim screen shots of both configurations for his records.

No, I can't think of any way Tim's issue is related to the P-mags but I would love to be proven wrong.

N941WR 03-20-2018 05:52 AM

Tim just called and I found out two things.

1. He had never performed a climb like the one that prompted this thread with his old ignition so it is not possible to say his high CHT is a result of the new ignitions or if the issue was always there.

2. He does not have the deflectors in front of his #1 and #2 cylinders to push the cooling air up over the front cylinders and help cool the rear ones.

He was not the builder but since the plane came from Canada, the original builder put plate nuts in to make the deflectors removable. We are going to start with aluminum tape to see if that helps and then will make a set of deflectors. (I also made mine removable, so we already have a pattern.)


All times are GMT -6. The time now is 09:22 AM.