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  #31  
Old 01-26-2019, 09:24 PM
N941WR's Avatar
N941WR N941WR is offline
 
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Quote:
Originally Posted by Fred.Stucklen View Post
I've been running the "B curve" timing on my IO-360B engine for the last 1620 Hrs. The only times I've seen high CHT's is when I try to do aggressive full power climbs at gross weight on a hot day (or after taxing for too long, then taking off)….
A couple of questions for you:
1. Is this a 180 hp parallel valve engine or 200 hp angle valve?
2. What compression ratio are you running?
3. What is the manufacturer's recommended timing setting?
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Bill R.
RV-9 (Yes, it's a dragon tail)
O-360 w/ dual P-mags
Build the plane you want, not the plane others want you to build!
SC86 - Easley, SC
www.repucci.com/bill/baf.html

Last edited by N941WR : 01-26-2019 at 09:27 PM.
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  #32  
Old 01-27-2019, 06:19 AM
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DanH DanH is offline
 
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Quote:
Originally Posted by Fred.Stucklen View Post
I've been running the "B curve" timing on my IO-360B engine for the last 1620 Hrs. The only times I've seen high CHT's is when I try to do aggressive full power climbs at gross weight on a hot day (or after taxing for too long, then taking off).

So after I read this tread, I decided to try running the engine with the timing set to the "A curve - jumper in". Note that I'm running the Sensenich metal cruise prop (85 pitch). Here is what I noted as differences:

• The CHT’s definitely ran lower by 25*-30*. Max temps in cruise was under 300* (high 290’s). We did not see any CHT overheating on climb out today (at the same full load point), but the outside temps were only in the mid 50’s, so it probably wouldn’t have happened anyway.
Climb CHT reduction is probably the #1 reason to retard timing, lower mechanical stress (avoid high stress due to higher gas pressure at TDC) being #2.

Quote:
• The EGT’s were definitely higher at about 100* hotter, or around the low 1400* temp point (engine leaned). This is an indication that there is fuel still burning when the exhaust valve opens. I noted that during the slow leaning process, the EGT’s went well over 1500*….
This is a p-V (pressure -volume) diagram for a research engine at 1200 RPM, borrowed from Taylor's Internal Combustion... The X-axis is cylinder volume, with TDC on the left. The Y-axis is cylinder pressure. I've added some notes; the only variable is ignition timing.



Note that when ignition is delayed, peak pressure is indeed reduced, as noted above. Pressure later in the stroke, around exhaust valve opening, is higher. Cylinder volume is the same at exhaust valve opening for any ignition timing, so higher pressure means higher gas temperature.

Pressure and temperature are proportional when temperature is expressed in degrees Kelvin. Here the reported EGT increase was 100 F. Given a jump from 1400F to 1500F, or from 1033K to 1083K, the required pressure increase at valve opening is only about 5%.

Quote:
• Fuel burn was higher by about .5 gal/Hr. I was not able to get the same RPM’s at the “B curve” gal/Hr. leaning point. An indication of less power??
Just to clarify, fuel burn became higher when the mixture knob was adjusted to get the same RPM you would have expected with more advanced timing? That too would be an expected result.

Quote:
• Take off RPM was only 2290 RPM, a bit lower than when the “B curve” timing was used. I interpret this as an indication of less available power.
Good data point. How much lower?

Quote:
• The engine did idle at a lower RPM, almost stalling and definitely below the PMAG power output RPM (which then required ship power to keep them running).
Expected, but that's just a stop screw adjustment.

Quote:
So, overall, I’d say that there was a loss of performance for the lower CHT's. Tomorrow I’m going to remove the jumper and take some more numbers… I might also try retarding the timing manually somewhere in between the two PMAG curves.
It's all a matter of weighted compromise.

My compliments sir. Keep bringing that data.
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Last edited by DanH : 08-01-2019 at 06:21 PM.
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  #33  
Old 01-27-2019, 06:55 AM
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Fred.Stucklen Fred.Stucklen is offline
 
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Default PMAG Timing

Quote:
Originally Posted by N941WR View Post
A couple of questions for you:
1. Is this a 180 hp parallel valve engine or 200 hp angle valve?
2. What compression ratio are you running?
3. What is the manufacturer's recommended timing setting?
1. 180 hp parallel valve engine
2. 8.5:1
3 25* BTDC
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  #34  
Old 01-27-2019, 07:15 AM
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Fred.Stucklen Fred.Stucklen is offline
 
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Default PMAG Timing

Quote:
Originally Posted by DanH View Post
Climb CHT reduction is probably the #1 reason to retard timing, lower mechanical stress (due to higher gas pressure at TDC) being #2.

........


It's all a matter of weighted compromise.

My compliments sir. Keep bringing that data.
Dan,
Good explanation. I've been toying with the idea of installing an EI Commander so that I can get better real time data, and be able to more quickly making timing changes. I've got an extra 3.125" hole in the panel just for that device. Maybe Bill can chime in and tell me which device would be better in that location.
Running the engine on the "B curve" yesterday gave me the distinct impression that there was less power overall. The take-off RPM on the "B curve" was 2290 RPM, and about 2350 running on the "A curve", so, with a fixed pitch prop, to me that is showing less power.
Can't fly today as the weather here is terrible. I'll try and get a few more data points during the week.
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RV-7A N924RV Flying (2000 Hrs & counting)
RV-6A N926RV 875 Hrs (Sold)
RV-6A N925RV 2008 Hrs (Sold)
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  #35  
Old 01-27-2019, 07:58 AM
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Quote:
Originally Posted by Fred.Stucklen View Post
The take-off RPM on the "B curve" was 2290 RPM, and about 2350 running on the "A curve", so, with a fixed pitch prop, to me that is showing less power.
Agree, about 4 HP less. I suspect you can get it back if you lean just a little.
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  #36  
Old 01-27-2019, 05:35 PM
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N941WR N941WR is offline
 
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Quote:
Originally Posted by Fred.Stucklen View Post
Dan,
Good explanation. I've been toying with the idea of installing an EI Commander so that I can get better real time data, and be able to more quickly making timing changes. I've got an extra 3.125" hole in the panel just for that device. Maybe Bill can chime in and tell me which device would be better in that location.
Running the engine on the "B curve" yesterday gave me the distinct impression that there was less power overall. The take-off RPM on the "B curve" was 2290 RPM, and about 2350 running on the "A curve", so, with a fixed pitch prop, to me that is showing less power.
Can't fly today as the weather here is terrible. I'll try and get a few more data points during the week.
Fred, the EIC is designed for the 2-1/4" hole, so you will need to buy an adapter. Putting it on your panel will allow you to make adjustments, preferably on the ground.

The no jumper "B curve" starts firing at 30.8 degrees, which is a good amount more advance than your engine was designed for.

The jumper in "A Curve" starts at 26.6 degrees, which is still a bit more advance.

You must have some really efficient baffles, or bad CHT probes. Most (I)O-360's in a Van's cowl tend to run very close to 400 degrees at full power, if not over 400 in climb and only cool down in level flight.

A number of our customers, myself included, have experienced lower CHT's and slightly higher speeds by lowering the "A curve" by 1.4 degrees. This means that their P-mags will fire at 25.2 degrees for take off and a max advance of 33.6 degrees in cruise.

I am surprised that your cylinders run as cool as they do.
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RV-9 (Yes, it's a dragon tail)
O-360 w/ dual P-mags
Build the plane you want, not the plane others want you to build!
SC86 - Easley, SC
www.repucci.com/bill/baf.html
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  #37  
Old 01-27-2019, 06:18 PM
Bavafa Bavafa is offline
 
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Quote:
Originally Posted by Fred.Stucklen View Post
Dan,
Running the engine on the "B curve" yesterday gave me the distinct impression that there was less power overall. The take-off RPM on the "B curve" was 2290 RPM, and about 2350 running on the "A curve", so, with a fixed pitch prop, to me that is showing less power.
Can't fly today as the weather here is terrible. I'll try and get a few more data points during the week.
Am I miss reading this post or your earlier post? Your earlier post, at least the way I read it, indicates a lower RPM of 2290 with the A curve and a higher RPM with the B curve.

I did experiment some with the A and B curve and some custom curves as well with my IO360-M1B in a 7A and found the difference between the A and B curve was little and not worth the higher CHT. The B curve was a bit better up high and the penalty down low was a bit higher CHT which would push my CHT to 400 and above if I kept climbing at full power. Like the above post, I am impressed with your CHT numbers. My baffles weren't anything like DanH work but I would say much above average.
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N825SM RV7A - IO360M1B - SOLD
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  #38  
Old 01-27-2019, 06:32 PM
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N941WR N941WR is offline
 
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Mehrdad,

Just to be clear, are you talking about the parallel valve engine in your -7A, which you have since sold?

The angle valve engine in your -14A seems to cool much better than the parallel valve engines for some reason and that engine requires 20 degree timing. Since you have an EIC in your 14A, creating a custom configuration that sets the timing correctly should be fairly easy.
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Bill R.
RV-9 (Yes, it's a dragon tail)
O-360 w/ dual P-mags
Build the plane you want, not the plane others want you to build!
SC86 - Easley, SC
www.repucci.com/bill/baf.html
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  #39  
Old 01-27-2019, 06:42 PM
Bavafa Bavafa is offline
 
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Hi Bill,
That is correct and I am planning on experimenting with different curves with my new IO390. Currently I am using the "A" curve without any modifications but I have set the timing with about 5 degrees retard of TDC on the flywheel when I set the timing on the PMAG which brings it to the manufacture suggested 20 degree.
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N825SM RV7A - IO360M1B - SOLD
N825MS RV14A - IO390 - SOLD
N258SM RV14A - IO390EXP119 - Out of Paint shop & flying
Dues paid
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  #40  
Old 01-27-2019, 06:51 PM
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N941WR N941WR is offline
 
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Quote:
Originally Posted by Bavafa View Post
Hi Bill,
That is correct and I am planning on experimenting with different curves with my new IO390. Currently I am using the "A" curve without any modifications but I have set the timing with about 5 degrees retard of TDC on the flywheel when I set the timing on the PMAG which brings it to the manufacture suggested 20 degree.
Great! I just wanted to make sure you were not damaging your engine.

Since you have the EIC, it is really easy to create custom configurations and send them to the P-mags, as you know.

Feel free to call, if you have any questions.
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RV-9 (Yes, it's a dragon tail)
O-360 w/ dual P-mags
Build the plane you want, not the plane others want you to build!
SC86 - Easley, SC
www.repucci.com/bill/baf.html
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