VAF Forums

VAF Forums (http://www.vansairforce.com/community/index.php)
-   Electronic Ignition Systems (http://www.vansairforce.com/community/forumdisplay.php?f=103)
-   -   Custom Timing Curve for Legacy EFII Ignition (http://www.vansairforce.com/community/showthread.php?t=157647)

crabandy 02-09-2018 10:34 PM

Custom Timing Curve for Legacy EFII Ignition
 
I have a "Legacy" EFII Dual Ignition only (no injection) on my Parallel valve standard 8.5 compression O-360 with a fixed pitch Catto Prop. I've flown almost 300 hours behind the canned ignition curve with no problems per say, but I don't believe it is optimum for my situation.
I generally takeoff full power 2100 static RPM and climb at full power ROP and 130 KIAS. After level, accelerate and CHT's below 400 I pull power below 65% and adjust the mixture to LOP. I have to manipulate the throttle somewhat to achieve an EGT spread within 80*. I also burn 91 Mogas in 1 tank during cruise when available.

Here is my canned ignition curve super imposed in purple on Nigel Speedy's graph from his article in KitPlanes Magazine "The effects of ignition advance on cylinder heat temperature, speed and efficiency."



I'm thinking my canned timing curve is a bit aggressive with the oversquare condition with my fixed pitch prop during climb resulting in higher engine temps. I would appreciate any input on my proposed timing curve anyone has to offer. I have spoke to and appreciate Robert of EFII who has consistently fielded/answered my numerous questions via phone and email for the past several years.

My current ignition curve is currently controlled by RPM and Manifold Pressure together.

The current RPM curve is shown in the shaded yellow column 30 degrees above 1250 RPM, my proposed timing curve keeps timing at 25 degrees BTDC above 1250 RPM.



My current ignition curve uses a 4 degree retard at higher manifold pressures tapering down to 0 retard at 24.1, set timing as 30 degrees BTDC above 1250 RPM. With my proposed timing curve of 25 degrees BTDC I would start an ignition advance similar to Nigel Speedy's compromise timing curve shown in the first graph. 1 degree advance starts at 24.6 inches manifold pressure and levels off at 6 degrees of advance at 22.3 inches of manifold pressure for a total of 31 degrees of ignition advance. I'm initially limiting the advance close to what I've been flying the last 290ish hours.



Robert suggested a value at the low end of the manifold pressure range in case of a manifold pressure sensor failure, I picked 0 degrees to keep timing at 25 degrees.



Thoughts, suggestions and ideas appreciated!

DanH 02-10-2018 06:31 AM

Quote:

Originally Posted by crabandy (Post 1238385)
With my proposed timing curve of 25 degrees BTDC I would start an ignition advance similar to Nigel Speedy's compromise timing curve shown in the first graph. 1 degree advance starts at 24.6 inches manifold pressure and levels off at 6 degrees of advance at 22.3 inches of manifold pressure for a total of 31 degrees of ignition advance. I'm initially limiting the advance close to what I've been flying the last 290ish hours.

Andy, consider manifold pressure to be a proxy for altitude, then think about where you typically cruise. In general, flying higher is more efficient, plus the benefits of a LOP advance are more pronounced. Sadly, far too many RV'ers don't routinely climb high (say 9500-12500) because they are fighting CHT all the way up.

I would suggest 23 degree base timing for your parallel valve, then start adding advance at 24.6"MP. You're carbed, so that would probably be 4500 feet or so, WOT and leaning in the climb to maintain best power mixture. Now stretch out the ramp so it doesn't arrive at 31 degrees until a much lower MP, say 20" or less. That should put you pretty close to a best power ROP timing all the way up into the 9.5-12.5K altitude (i.e. least time to climb), after which you go LOP.

23 degrees base is obviously conservative, but I note you have auto fuel on board, and run a fixed pitch prop. It would buy a little detonation margin while oversquare, in case you picked the wrong tank on a hot day, and it will lower CHT without significant power loss (in any). Later, after establishing a baseline, shift the entire map 2 degrees more advanced (25 base) and see if you can tell any difference. I'll bet you can't.

Toobuilder 02-10-2018 09:06 AM

I think you are on the right track Andy, but in situ test is the quickest way to get what you want. Two things right off: If you dont have a way to adjust timing in flight, call Ross and see if you can get the dual board programmer. Second, see if your box can be reprogrammed to use the LOP function. This is a VERY handy feature for your application.

With that capability in place, go out and burn some gas looking for some key test points. As a minimum you want to find your "best" performance at:

Cruise altitude, best power mixture
Cruise altitude, LOP
Sea level power, Full rich
Idle

At ROP cruise it's pretty simple to sweep the advance 10 degrees around your current "known good" setting to find your peak TAS. Dont expect to find a very sharp peak when ROP, but you should be able to distinguish a "hump". LOP is the same technique, except the peak is going to be a lot more distinct.

With the full power setting, you are using a similar technique, but you re not looking for a peak, you are looking for the point where retarding the ignition causes the TAS to drop. So in this case, go fast and record the TAS as a baseline. Then start pulling timing OUT and watch the TAS. Once you get a drop in speed, record your ignition setting, add one more degree to get your former speed back, and this is now your new 100% power setting. My guess is it will be a lot less than even the data plate value your engine has from the factory. Using the minimum advance here assures you are not losing any power, but have as much detonation magin in the bank as you can.

Idle timing is just a nice to have. In my experience, the Lycoming likes a lot of advance. I accomplish this by relying pretty heavily on MP as a controling function. This differs from your scheme in that you are primarily RPM driven with the MP as only a minor correction. For example, I start at a baseline of 15 degrees until 1000 RPM, then ramp up to 25 degrees by 2000, where it remains flat. I've also been zeroing out the MP advance for the lowest few "slots" on the window to guard against sensor failure, but the first usable setting is a whopping 15 degrees advance. This advance reduces as the MP increases and is shaped to intercept my typical 100%, cruise, and idle/taxi power setting (in my case, my engine "likes" ~ 34 degrees). The advance continues coming out until it zeroes, and then goes negative at about 25 inches MP, ultimately retarding 6 degrees at 30 inches MP.

If you were to follow this scheme, you would tailor your MP curve to hit your engines "happy points" at idle, cruise and also at 100% power. your curve would look different from mine, but the methodology is the same.

I have a flight test worksheet made up which will help you gather and organize this data. If you want a copy, send me a PM with your email and I'll get it out to you.

crabandy 02-11-2018 10:05 PM

Thanks Dan and Michael for the responses!

Michael, I woukd love a look at your test cards.

I’m guessing I have the older boards with the older software with only 250 RPM adjustability, I’ll eventually have to dissect my boxes and see for sure. For now I have 1 programmer and no way to easily swap ECU’s in Flight, I could buy another cable and swap the programmer to individual boxes but kinda combersome.

I thought about in Flight changing the timing on just one ignition kinda like a single EI and Mag setup but I think that would skew my results once both ignitions were using the same timing.

My engine idles very smoothly at 500 RPM even with the Catto on the current timing, once I dial in the upper MP curves I’ll have to spend some time dialing in the lower RPM/MP timing.

Dan, I Fly 9-13K as much as possible. Doesn’t take long to get there and I like the performance and other options the extra altitude allows, no level offs needed but I will always exceed 400 CHT after a hot quick turn.
Your suggested curve does make sense, pretty easy to change 1 base timing value on the ground from 23 to 25 and test fly. I’m thinking of using your suggested 23 degree base timing and this advance schedule, I started the advance at 25" MP and kept it easy roughly advancing 1 degree/1" MP. I leveled off the advance at 7 degrees at 19"MP-7"MP. I assume less than 7" MP the engine isn't running or a manifold pressure sensor failure. This also gives me similar timing to what I have run previously in the lower MP range.



2 Test flights, first at 23 degrees base timing and the second at 25 degrees. Flights performed as close together as possible for similar atmospheric conditions.
-warm airplane up flying for 15 minutes
- land
-record OAT/altimeter setting/CHT/oil temp
-takeoff full throttle climb out 100 KIAS and 100 ROP to 10K
-Record time to climb/CHT/Oil Temp
-set 20” man pressure and LOP and record KTAS/CHT

Toobuilder 02-11-2018 10:13 PM

You might be only a software upgrade away from "current" EM-5 functionality. The biggest bang for the buck is the LOP function - makes changes in a flight test scenario essentially risk free. Send me a PM with your email and I'll get the worksheet out to you.

M McGraw 02-12-2018 04:45 AM

Test flights
 
Hello Andy,
It might be easier if instead of recording altimeter you just set the altimeter to 29.92. I do all my test flights at pressure altitude and record the OAT. That allows me to easily convert all my data to density altitude. It may not matter if your able to make all comparisons on the same day, but the advantage is you can better compare data over the life of the aircraft.

In case you need it the simplest formula for Density altitude:

DA = PA + [120 x (OAT - ISA Temp)] and ISA Temp = 15 - [(PA / 1000)] x 2

DA - Density Altitude
PA - Pressure Altitude
OAT - Air Temp in degrees C
ISA Temp - standard atmospheric temp at altitude in degrees C

NOTE: These formulas do not account for relative humidity, but they will get you the same results as your trusty old E6B.
Marvin

RV10inOz 02-12-2018 05:08 AM

Dan,

Great post. From the GAMI dyno I can suggest that the 23 degrees you speak of is equivalent to what a magneto produces at the spark plug. So, in saying that, with a magneto being a compromise, it could be another degree or so, especially on a fuel with less latency.

You may want to take that number down a bit. Pressure sensors are the way to go, but it is expensive to test.

As a guided guess you are on the right track, but could be a bit more conservative.

All the best.

DanH 02-12-2018 08:53 AM

Quote:

Originally Posted by crabandy (Post 1238832)
Dan, I fly 9-13K as much as possible. Doesn’t take long to get there and I like the performance and other options the extra altitude allows, no level offs needed but I will always exceed 400 CHT after a hot quick turn.

Yep, that's why I suggest delaying the addition of advance until a lower MP, and then ramping it in more slowly. The current timing map (in purple, displayed in your first post) starts advancing too early, and hits 30 BTDC while you're still in a climbing flight phase where best power is desired.

Why would a vendor deliver the system with advance cranked up to 30 BTDC at 24"? I'll speculate, and say it's hot-rodder thinking (i.e. power before all else). Power claims sell the merchandise. In reality we should be more interested in the "all else" part.

Let's look at dyno numbers from a good high performance engine shop

Yep, 30 BTDC was the best timing for max power...at an RPM suitable for Reno, or Red Bull.

BTDC HP-RPM

20 217 @3050

25 228 @3082

30 232 @3082

33 223 @3004

At 2700 RPM? No power difference between 25 and 30 degree timing. Running 30 just added mechanical stress, and higher CHT.

BTDC HP

20 200

25 210

30 210

32 205

Here's the good part. Take a look at 25 BTDC vs 30 in the RPM range (underlined red) where a fella might operate while climbing with a fixed pitch prop. Below 2500 RPM, less timing makes more power.



BTW, I've not posted it here, but power at 20 BTDC timing wasn't a lot less than 25 in the 2000 to 2500 RPM bracket.

Anyway, that's the theory. Go fly and get us some data.

crabandy 02-12-2018 10:48 AM

Thanks Marvin, I’ve done my previous test at pressure alt as well using 29.92. In my “mind” seems easier for airspeed to pre-calculate Density Alt and and fly all test at the same DA, but PA it is.

Thanks for the graphs/explanation DanH.

Another question......Wondering if burning oil (3-5hrs per at) retards timing?

M McGraw 02-12-2018 11:07 AM

DA vs PA
 
Actually,
If your precalculating and saving your data in DA, that is a good way to do a comparison.


All times are GMT -6. The time now is 09:42 PM.