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  #11  
Old 11-24-2021, 11:01 AM
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DanH DanH is offline
 
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Quote:
Originally Posted by Walt View Post
Angle valve engine, base was set at 20 and max advance I believe set to 9 degrees.
Walt, is it possible to confirm the 9 degree figure, and the MP/RPM/CHT at which the subject began leaning?

Quote:
Originally Posted by 00Dan View Post
This is a curious topic. Has testing been published anywhere regarding advance levels on high compression engines?
...high compression angle valve engines..

The angle valve IO-540 K is the NA Lycoming used for detonation studies. Given enough heat and MP it can be pushed into detonation at will, with the stock 8.7 compression ratio and stock timing. Not specific to 10:1 CR, but there is a huge quantity of data running typical and minimum spec 100LL in the FAA's Swift fuel study. Search AR0853.
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  #12  
Old 11-24-2021, 11:14 AM
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Quote:
Originally Posted by DanH View Post
Walt, is it possible to confirm the 9 degree figure, and the MP/RPM/CHT at which the subject began leaning?
I checked with him, max was set to 29 deg, full throttle/2400 rpm 8000 ft.
CHT around 375 until the event which then went to around 460-470 from his recollection.
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EXP Aircraft Services LLC
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Last edited by Walt : 11-24-2021 at 11:17 AM.
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  #13  
Old 11-24-2021, 11:20 AM
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rv6ejguy rv6ejguy is offline
 
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Quote:
Originally Posted by Walt View Post
I checked with him, max was set to 29 deg, full throttle/2400 rpm 8000 ft.
CHT under 400 until the event which then went to around 460-470 from his recollection.
Too much timing for this engine and CR running ROP and even LOP. Results predictable.
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Ross Farnham, Calgary, Alberta
Turbo Subaru EJ22, SDS EFI, Marcotte M-300, IVO, Shorai- RV6A C-GVZX flying from CYBW since 2003- 450.6 hrs. on the Hobbs,
RV10 95% built- Sold 2016
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  #14  
Old 11-24-2021, 12:01 PM
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jliltd jliltd is offline
 
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I always set fixed timing. Especially with an angle valve. I am not looking to save 1 gallon per hour. I am looking for effortless hot starts while avoiding mechanical impulse couplers. I am way too slow to make ignition timing theory a full time hobby.
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  #15  
Old 11-24-2021, 03:37 PM
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Toobuilder Toobuilder is offline
 
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Quote:
Originally Posted by rv6ejguy View Post
Too much timing for this engine and CR running ROP and even LOP. Results predictable.
Indeed. On both counts.

Plenty of info on this site alone that shows that.

You can lead a horse....
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WARNING! Incorrect design and/or fabrication of aircraft and/or components may result in injury or death. Information presented in this post is based on my own experience - Reader has sole responsibility for determining accuracy or suitability for use.

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  #16  
Old 11-25-2021, 07:00 AM
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FWIW, the 6-cylinder's current Mode Switch function is poorly considered.

From the manual:

Start engine with Mode Switch set to VAR (plugs will not fire at cranking speeds in FIX Mode).

It means every operating cycle begins with the ignition in advancing mode. If a conservative fixed timing mode is desired, the pilot must remember to change the switch position to fixed mode after start. Humans being human, it's not going to happen 100% of the time.

I suspect the fixed mode requirement, if demanded by certification, was treated as an unnecessary ornament. That's obviously not true, give the Glasair example illustrated here. We'll probably see a fixed timing mode switch on the 4-cyl versions in due course. If so, let's hope they change the switching scheme to "one or the other", all the time.

FWIW, my own ignition is configured with fixed timing mode as the default, as the mode switch is located in a row with the aux pump, lights, etc. Advancing mode is enabled by moving the switch to a physical position perceived as an obvious ON, in accord with all the other switches in the row. And yes, it starts in either mode.
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Last edited by DanH : 11-25-2021 at 12:09 PM.
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  #17  
Old 11-25-2021, 08:44 AM
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Snowflake Snowflake is offline
 
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Quote:
Originally Posted by DanH View Post
It means every operating cycle begins with the ignition in advancing mode. If a conservative fixed timing mode is desired, the pilot must remember to change the switch position to fixed mode after start. Humans being human, it's not going to happen 100% of the time.
Perhaps that could be mitigated with a DPDT start switch, one side of which engages the starter and the other side of which switches the PMag between VAR mode and FIX mode?
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  #18  
Old 11-29-2021, 02:59 PM
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rvmills rvmills is offline
 
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Great discussion, to which I'd like to add a couple questions for Walt, Ross, Michael, Dan and anyone that may have data/experience to add, plus some experience from my ROP/LOP testing. No intent to hijack, and hope this is value added.

Q's:

- Walt, do you have MP numbers for the test? I know you said WOT at about 8,000' in response to Dan's query, but knowing the MP would be a good data point. Seeing the trend and rate of increase in CHT vs Fuel Flow would be good too.

- Does a max increase of 9 on a base of 20 in the P-mag mean 29 is the max advance? (I know that may sound like a dumb question, but I also know the P-mag curves are proprietary, and we may not know where his timing actually was...that's not a shot at P-mags at all, just a data question).

- Does your friend by any chance have an O2 sensor installed, with a lambda or AFR readout? More good data if available.

- What type of spark plugs is your friend running, auto or aircraft? Is the heat range of the plugs correct?

- What type of fuel was he running? 100LL hopefully, but want to be sure it wasn't MoGas.

- Walt, Ross and Michael, you guys indicate this was almost an expected result. Is that because it's an angle valve engine with 10:1? Or because it's an AV/10:1 with Pmags? Interested in why you feel this way, and if it has applicability to parallel valve motors with 10:1.

Here's my semi-selfish reasons for asking all this (along with trying to add to the discussion here, and help find root causes of a damaged engine)

Background: I have a Lycon IO-540 CB45 (narrow deck, parallel valve) with 10:1 CR. One mag (I've had both Bendix and Slick over the years), one Electroair EI. I run REM37BY massive electrode plugs on all cylinders, gapped for the mag on the bottom, and the EI on the top. Much of my testing was done with the mag timed at 25 and the EI at stock delivery setting (which is about 23). I have an EI timing readout and an AFR readout. My engine monitor is an older VM-1000, with no data logging, so LOP testing and injector balancing is quite the 20th century analog/slide-rule-ish process, with lot's of hand-written log sheets transferred into spreadsheets along the way.

I've done quite a bit of LOP testing and injector balancing over the past 10 years, most of which was done on X-C flights up at 10.5K to 13.5K. I've always been concerned about detonation "red zone", especially with my 10:1 engine, so higher altitude testing has been my norm (its where I like to cruise on X-C's too). Typical power settings have been WOT/2100 to WOT/2300 (2200-2300 is where most of my data is). WOT at those altitudes has been 19-21 or 22" MAP. With the mag at 25 and the EI MAP sensor on, and EI advance reading in the mid to high 30's, I'd never seen runaways or CHTs over 400 during any of the tests. I've felt that I had safe margins from detonation. Cylinders 2 and 5 used to peak first, and run a bit hotter than the rest (CHT), but over time, I made injector restrictor body changes that balanced things out nicely.

Flash forward to now, after an upgrade from a Bendix RSA-5 to an AFP FM300B fuel injection servo (a couple years ago). I hadn't done any recent LOP tests, and Steve Smith and I discussed that at Reno this year, as we chased cylinder cooling with a new nitrous system and water spray system installed. Our goal was to adjust external water spray to keep 1, 2, 5 and 6 cool, and bring up 3 and 4, while I slowly leaned towards best power for racing with nitrous (about 11.8 to 12.0 AFR). We just about had it nailed when my fuel pressure transducer failed on Sunday taxiing out...didn't get to test our last adjustment. 2 was the last cylinder to stay hot, and we didn't know if it was the governor blocking air, another airflow issue, a water issue, or a leaning issue. So Steve encouraged me to do some LOP testing on the way home to check that aspect, which I did.

While I was looking to see how 2 was acting on those recent post-Reno '21 tests, it seemed to fall back into line, and 5 became my hot spot. On one test, at 11,500/21.5"/2300RPM, it slowly crept to 425-430, but cooled right back to 380 on the lean side. 6 got to 400, and the others were all 395 and below. Concerned about that 430, we did a compression check and borescoped the engine, and saw no indication of damage. In fact, my airpark neighbors (builders and mechanics) were impressed with the condition of my 2000 hour motor (and compressions were in the 73-77 range, 5 being the 73). I also cleaned all the plugs and injectors.

One thing I'll fess up to is that I found all of my plugs (top and bottom) gapped for the EI. Dammit...that's too much gap for my mag plugs! I messed that up, and must have raced that way...probably left some power on the table. Hopefully I've not damaged my brand new mag! So far no indication of that.

So after assessing the engine, cleaning (and re-gapping) my plugs and cleaning my injectors, I set out to do some more LOP/injector balance testing. After a discussion with Don at AFP and Steve about race CHT and my recent LOP testing, I did a cruise power leaning test (10.5K/22.1" MP/2300 RPM) on one day, and a 75% (ish) test (8.5K/24.2" MP/2400 RPM) on another day. Mag and EI had been set at 21 for racing (MAP sensor off for racing with nitrous), but I reset both to 22.5 for these tests, and had MAP sensor on. EI readout was 30 on the first test, and 29 on the second).

Test 1 showed #5 got to 396 CHT with all others in the 360's/370's. #6 has been trending slightly lean of the others, and is the first injector body swap that I will try next.

Test 2 showed #5 got to 405 CHT with all others in the 380's and 390's. Similar delta to #5 from the rest.

Don recommended this comparative test, to see if at higher power, the richest and leanest cylinders were changing. I see a clear trend that 6 is leaner than the rest, and a less clear trend that 5 richens at higher power.

I need more testing to establish more clear trends, but seeing this thread has my attention about doing LOP testing at 24 squared. That brings my post full circle, and thanks for bearing with me on all the above.

Is the experience of Walt's friend a "10:1 Angle Valve with P-Mag" issue?
Does his result translate to a 10:1 Parallel Valve engine with a mag and an EI?

Asking for a friend (my engine)!

Cheers,
Bob
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Last edited by rvmills : 11-29-2021 at 04:14 PM.
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  #19  
Old 11-29-2021, 05:13 PM
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rv6ejguy rv6ejguy is offline
 
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It appears that the AV engine needs 3-5 less degrees of ignition timing compared to a PV engine to make max power.

You can run 3-5 degrees more timing when 50 LOP because of the much slower burn rate compared to ROP which delays the point of peak cylinder pressure (PCP) in relation to crank angle.

The lower the MAP, the more timing you can run before encountering detonation due to lower charge density.

With a 10 to 1 AV running at high MAP, ROP (fast burn) and 29+ deg of timing, you almost certainly will get detonation and the severity and propensity increases with high CHT and IATs.

Lower RPM has the tendency to increase detonation through both decreased chamber turbulence and the slower piston speed in relation to combustion speed, effectively advancing the point the point of PCP.

A slow lean pull isn't the best idea as you pass through a more dangerous zone, slightly to the rich side of peak.

If you look at the Lycoming dyno test data from their fuel testing, you'll see that a bit more timing does almost nothing for power but does increase CHTs and likelihood of detonation. It isn't worth it in my view to split hairs. Lys are not cheap to repair these days.
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Turbo Subaru EJ22, SDS EFI, Marcotte M-300, IVO, Shorai- RV6A C-GVZX flying from CYBW since 2003- 450.6 hrs. on the Hobbs,
RV10 95% built- Sold 2016
http://www.sdsefi.com/aircraft.html
https://www.youtube.com/channel/UCiy...g2GvQfelECCGoQ



Last edited by rv6ejguy : 11-29-2021 at 05:19 PM.
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  #20  
Old 12-01-2021, 12:55 AM
scsmith scsmith is offline
 
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Quote:
Originally Posted by rv6ejguy View Post
It appears that the AV engine needs 3-5 less degrees of ignition timing compared to a PV engine to make max power.

You can run 3-5 degrees more timing when 50 LOP because of the much slower burn rate compared to ROP which delays the point of peak cylinder pressure (PCP) in relation to crank angle.

.
Ross, why is there a difference between AV and PV for the same CR? I'm guessing there is a different combustion chamber shape that goes along with the different valve orientation? And the combustion chamber shape has a lot to do with the way the combustion event progresses, as well as whether it enhances mixing, so it has a significant effect on propensity for detonation?

It is a tricky issue for us LOP proponents. We need the spark advance to get good LOP performance, but don't want the advance when ROP. So when MAP is moderately high (24") it is good to pull fast to the LOP position and not dwell near peak. BUT...

What Bob Mills was trying to describe is a series of our observations that the GAMI spread of the engine seems to be rather RPM dependent, or at least fuel-flow dependent. One wonders if the flow divider characteristics change the distribution at higher fuel flow rates? So, for example, at typical high altitude LOP operations, there may be very little or no GAMI spread, because we have tuned all the injectors there, but at race power, where we would like all the cylinders to be running at the same air-fuel ratio, they may not be. It seems possible that at 2700+ RPM and WOT race power, Bob's cyl #2 may be leaning sooner than the others (and getting higher CHT), whereas at his typical cruise conditions, it is #6 that is leaning first (only slightly). But how do we test safely at those conditions? I suppose we could install 6 individual air:fuel ratio sensors.


One take-away is that we should probably confine our higher MAP testing to times when we have purple gas.
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