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  #21  
Old 02-09-2013, 05:26 AM
pierre smith's Avatar
pierre smith pierre smith is offline
 
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Default

David, any reason why the lower D-180 doesn't show LOP? When I select "Lean" mode on my D-120, a little box appears with -20 or similar, after the EGT peaks..the big numbers (1425) disappear.

Best,
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  #22  
Old 02-09-2013, 08:59 AM
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db8 db8 is offline
 
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Jon. That makes it real easy based on the formula. Just to make sure I have this correct: if I have a 193 HP 4 cyl 360, as long as my FF is less than 9.7 GPH (or use 9.5 to be on the safe side), I will never be above 75% HP at any altitude? 9.7 x 14.9/193 = 74.9%

Therefore, you should never be able to hurt the engine by leaning too much below this FF (again, no matter what alt)?
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  #23  
Old 02-09-2013, 11:28 AM
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hevansrv7a hevansrv7a is offline
 
Join Date: Jul 2005
Location: Detroit, MI
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Default Safe Leaning

Quote:
Originally Posted by db8 View Post
Jon. That makes it real easy based on the formula. Just to make sure I have this correct: if I have a 193 HP 4 cyl 360, as long as my FF is less than 9.7 GPH (or use 9.5 to be on the safe side), I will never be above 75% HP at any altitude? 9.7 x 14.9/193 = 74.9%

Therefore, you should never be able to hurt the engine by leaning too much below this FF (again, no matter what alt)?
That multiplier is only correct when LOP. However, the correct, if unknown multiplier for richer mixtures is lower. For that reason, you should be safe.

HOWEVER, the Advanced Pilot folks also have a recommendation for determining the "target EGT" so that you can begin leaning at lower altitudes and during a climb. I have mine labeled right next to my EFIS. It is a number you determine experimentally for your individual airplane. That seems to me to be a good safety concept for the engine.
I don't want to try to explain their stuff, but it was on their website the last time I looked.
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  #24  
Old 02-09-2013, 04:00 PM
Bob Redman Bob Redman is offline
 
Join Date: May 2006
Location: Newcastle NSW Australia
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Default RESPONSE TO POST #10

Thanks for the graph David, it seems broadly consistent with the Lycoming graph. The subtle differences are in the detail, as usual.

Thanks to all the posters, particularly for the reminder of the fuel flow multiplier - if I stay below 34 Litres/Hr (9.1 USG/Hr) I should be below 75% regardless of the Dynon display. Our indicated fuel flow seems accurate when compared to fuel dip/added.

My response to David's comment:

a. When operating my preference is to cruise at full throttle, set my preferred RPM, and lean, usually at 8.5 to 9.5K alt. I have been leaning to leanest cylinder not beyond 30C/54F LOP. After seeing your graph, I will use leanest cylinder not beyond 25C/45F LOP. Note that I am limited to a maximum of 22" manifold air pressure (MAP) when below 2350RPM because of electronic ignition.

b. For the results listed in post #9, I could not collect data above 6.5K alt. Also, I was not sure whether or not I would have to adjust throttle to maintain a constant MAP. So I decided to reduce throttle for the 5 data points, but did not need to adjust either throttle or RPM.

c. In any case, from time to time I have needed to, & will need to again, cruise at less than wide open throttle (WOT), so the data is useful.

For interest, here is more (winter) cruise data (all observed):

a. At 8.5K alt (DA 9K), WOT, 22.5"/2360RPM, 66%, peak EGT, 30 Litres/hr (7.9 USG/Hr), 138KIAS (141KCAS) 158KTAS, 86C/187F oil temp, CHTs 150/162/170/164C (302/324/338/327F).

b. At 9.5K alt (DA 10K), WOT, 21.6"/2200RPM, 60%, peak EGT, 27 Litres/Hr (7.1 USG/Hr), 129KIAS (132KCAS) 150KTAS, 86C/187F oil temp, CHTs 138/149/160/152C (280/300/320/306F).
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  #25  
Old 02-09-2013, 04:30 PM
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RV10inOz RV10inOz is offline
 
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Default

Pierre,

I assume you mean the %age power and the ROP LOP indicator? If so your D120 needs to be connected to an AOT source, via a D100 and DSAB, and altitude etc will be as well.

Then go to the engine setup page in the D120, and input the HP rating etc.

Download a D120 manual and it will be explained.

One other critical thing to note here for all viewers. The latency in probes and subtle variations often mean if you lean past peak, from the rich side you get a different peak number every time.

If you want to spend some time poking around, do a BMP (big Mixture Pull) and sneak up to peak from the Lean side. Results are sometimes more consistent and its less effort finding the what was last to peak (now first) and then go from there. It is also less stressful when at high power on the engine to find peal from the lean side.
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  #26  
Old 02-09-2013, 04:40 PM
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RV10inOz RV10inOz is offline
 
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Hi Bob,
Quote:
it seems broadly consistent with the Lycoming graph.
The APS graph was carefully constructed from real Dyno values, to get the relationships very accurate. I know your penchant for manufacturers data, but depending on which graph you look at the Lyc data can be rough or accurate. So I would say that the Lyc stuff is bradly consistent

Quote:
a. When operating my preference is to cruise at full throttle, set my preferred RPM, and lean, usually at 8.5 to 9.5K alt. I have been leaning to leanest cylinder not beyond 30C/54F LOP. After seeing your graph, I will use leanest cylinder not beyond 25C/45F LOP. Note that I am limited to a maximum of 22" manifold air pressure (MAP) when below 2350RPM because of electronic ignition.
I would say, try this, at 8-10K' WOT, 2400-2500 RPM, and the last cylinder to peak from the rich side, or first to peak from the Lean side, set at 10dF LOP. Anything else is a compromise.

Quote:
c. In any case, from time to time I have needed to, & will need to again, cruise at less than wide open throttle (WOT), so the data is useful.
Not sure when that might be, but lets assume you are in a WOT cruise, and you want to slow down quite a bit (ATC maybe...or just the view, or flying with a Cessna) once you have the mixture set just pull MP back, the Bendix fuel system is pretty good at keep the F/A ratio consistent.

This is why on descent from even in the FL's I rarely touch the mixture until the hangar door, apart from maybe a tweak. Refer the Airsport article back in JUN or there abouts.

Have you considered bribing your daughter and shifting the wedding plans a month or so.
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  #27  
Old 02-09-2013, 05:44 PM
vjdslk vjdslk is offline
 
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Location: Rocklin, CA
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Default

Quote:
Originally Posted by db8 View Post
Jon. That makes it real easy based on the formula. Just to make sure I have this correct: if I have a 193 HP 4 cyl 360, as long as my FF is less than 9.7 GPH (or use 9.5 to be on the safe side), I will never be above 75% HP at any altitude? 9.7 x 14.9/193 = 74.9%

Therefore, you should never be able to hurt the engine by leaning too much below this FF (again, no matter what alt)?
Dave, your math is correct provided you are LOP at that FF regardless of altitude. Remember, the only time you do damage to your engine is when you lean too far while still ROP and get into the red box, or you don't lean far enough once you are LOP and are still in the red box. Once you are LOP, you can't do any damage by leaning too much. The engine will eventually just stop running from an excessively lean mixture, but you won't do any damage to it.

Jon D.
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  #28  
Old 02-09-2013, 06:10 PM
justplanecrazy justplanecrazy is offline
 
Join Date: Mar 2008
Location: Perth, Western Australia
Posts: 30
Default Mixture Variation Testing

To add some real data to the discussion, below (I hope as I have never inserted external links) is some data from recent testing varying only mixture settings.



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  #29  
Old 02-09-2013, 06:17 PM
justplanecrazy justplanecrazy is offline
 
Join Date: Mar 2008
Location: Perth, Western Australia
Posts: 30
Default Another Attempt at Attaching Links

https://dl.dropbox.com/u/75643362/VH...%20Testing.pdf

https://dl.dropbox.com/u/75643362/VH...%20Testing.pdf
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  #30  
Old 02-09-2013, 06:19 PM
jetdriven jetdriven is offline
 
Join Date: May 2012
Location: Houston tx
Posts: 124
Default

Quote:
Originally Posted by RV10inOz View Post
Hi Bob,


The APS graph was carefully constructed from real Dyno values, to get the relationships very accurate. I know your penchant for manufacturers data, but depending on which graph you look at the Lyc data can be rough or accurate. So I would say that the Lyc stuff is bradly consistent

I would say, try this, at 8-10K' WOT, 2400-2500 RPM, and the last cylinder to peak from the rich side, or first to peak from the Lean side, set at 10dF LOP. Anything else is a compromise.

Not sure when that might be, but lets assume you are in a WOT cruise, and you want to slow down quite a bit (ATC maybe...or just the view, or flying with a Cessna) once you have the mixture set just pull MP back, the Bendix fuel system is pretty good at keep the F/A ratio consistent.

This is why on descent from even in the FL's I rarely touch the mixture until the hangar door, apart from maybe a tweak. Refer the Airsport article back in JUN or there abouts.

Have you considered bribing your daughter and shifting the wedding plans a month or so.
I have noticed my new Precision RSA-5 makes quite a drop in fuel flow from full throttle to about 90% throttle. You have to reset the mixture then, it gets too lean. Below that, say from 40-90% throttle, it stays pretty consistent. There must be an additional WOT fuel circuit, like an economizer in a carburetor. I dont think our old Bendix RSA-5 unit did that as much.
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