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  #41  
Old 10-23-2018, 11:32 AM
lr172 lr172 is offline
 
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Quote:
Originally Posted by Carl Froehlich View Post
Not exactly.

A MP increase by ram air is the same as adding throttle to increase MP. Your servo will add more fuel. Effect on mixture will be in the grass (assuming constant altitude).

Carl
From my experience, the servo doesn't compensate in a linear fashion when manually leaned with the mixture control. Next time you are in cruise, add a bit of throttle. You'll notice that you get leaner and leaner the more you add. The mixture adjustment is not linear with air flow based fuel control in the servo. Increases in throttle or MP seem to require enriching the mixture to maintain the same AFR.
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Last edited by lr172 : 10-23-2018 at 12:03 PM.
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  #42  
Old 10-23-2018, 01:46 PM
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DanH DanH is offline
 
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Originally Posted by Paddy View Post
This is intuitive, however I believe you may have empirical manometer data from your excellent exploration of cowl exit design that would support the numerical relationship between MP and plenum pressure.
Actually, I directly measured average bleed air deltas about two weeks ago, and expect to measure on a per cycle basis in the near future. The differential pressure transducer got here last Wednesday, but this past weekend I was sidetracked by experiments involving balloons and Jameson.
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  #43  
Old 10-23-2018, 02:31 PM
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Originally Posted by DanH View Post
I was sidetracked by experiments involving balloons and Jameson.
I'm with you Dan, having grown up not 10 miles from the distillery in Dublin, I applaud your sense of priority!
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  #44  
Old 10-23-2018, 02:53 PM
scsmith scsmith is offline
 
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Quote:
Originally Posted by Carl Froehlich View Post
Not exactly.

A MP increase by ram air is the same as adding throttle to increase MP. Your servo will add more fuel. Effect on mixture will be in the grass (assuming constant altitude).

Carl
I think that is true when ROP, but my observation of the Bendix servo behavior when LOP is that it does not change fuel flow to match changes in MP in a way that keeps mixture even approximately constant.
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  #45  
Old 10-23-2018, 09:07 PM
MConner MConner is offline
 
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I run a carbeurated O-540 (250 hp) and see about the same numbers as the OP. I add another 1/2 gph and cruise at 160 knots at 10.5 gph. Our claim to fame is the low drag airframe. I can still get 160 true at almost 20,000í DA making less than 50% power. I have tried it as high as 22,000í DA and was at 154 KTAS enjoying a 40 knot tailwind burning 8.7gph.
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  #46  
Old 10-24-2018, 09:16 PM
Kellym Kellym is offline
 
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Originally Posted by tim2542 View Post
I donít believe % power indications from an engine monitor will be accurate when LOP, at least the GRTís use a Lycoming % power table that goes out the window when LOP.
15.7 x fuel flow / rated HP works when LOP.
Edit: that works with 8.5:1 compression ratio, I donít know the number for others C/Rís
Tim Andres
Actually the number for 8.5 to 1 is 15.0 x FF= HP, HP/rated power equals % power. For 200 hp IO360 that is 10gph when LOP for 75%. For 260HP IO540 that is 13 gph =195 hp = 75%.
It looks to me like Dynon is using a FF ratio to MAP and RPM to determine % power. I had a problem with my fuel flow, indicating much higher than actual, and it wouldn't show LOP when so lean engine was stumbling and losing power. Now that I fixed the FF, the LOP/ROP indications appear to match the above calcs. You can't hurt a normally aspirated engine at any mixture setting if you have RPM and MAP where they fit the 65% setting. Once you have achieved LOP with a fuel injected engine, you can add throttle to WOT and you will still be LOP regardless of power generated.
For climb I just roughly adjust mixture to maintain EGTs between 1200 and 1300 until I level off and lean to LOP.
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  #47  
Old 10-24-2018, 10:57 PM
bob888 bob888 is offline
 
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Just to add another data point, I get 171 kt TAS at 9500 ft PA, 5 degC, 21.5 in MP, 2300 rpm and 10.7 gph. I think my instrumentation is accurate and the speed is confirmed by GPS speed check.
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  #48  
Old 10-24-2018, 11:24 PM
tim2542 tim2542 is offline
 
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Kelly, do you have a source for that? Not arguing, just want to know which is correct. Iíve seen 15.7 quoted for years, never seen a multiplyer for other CRís.
Tim Andres



Quote:
Originally Posted by Kellym View Post
Actually the number for 8.5 to 1 is 15.0 x FF= HP, HP/rated power equals % power. For 200 hp IO360 that is 10gph when LOP for 75%. For 260HP IO540 that is 13 gph =195 hp = 75%.
It looks to me like Dynon is using a FF ratio to MAP and RPM to determine % power. I had a problem with my fuel flow, indicating much higher than actual, and it wouldn't show LOP when so lean engine was stumbling and losing power. Now that I fixed the FF, the LOP/ROP indications appear to match the above calcs. You can't hurt a normally aspirated engine at any mixture setting if you have RPM and MAP where they fit the 65% setting. Once you have achieved LOP with a fuel injected engine, you can add throttle to WOT and you will still be LOP regardless of power generated.
For climb I just roughly adjust mixture to maintain EGTs between 1200 and 1300 until I level off and lean to LOP.
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  #49  
Old 10-27-2018, 10:51 AM
Kellym Kellym is offline
 
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Quote:
Originally Posted by tim2542 View Post
Kelly, do you have a source for that? Not arguing, just want to know which is correct. Iíve seen 15.7 quoted for years, never seen a multiplyer for other CRís.
Tim Andres
Yes...Gami/Advanced Pilot Seminars. I've only seen 14.9 or 15.0 for our compression ratio. Have used that figure reliably for around 18 years, or shortly after John Deakin did his Pelican's Perch articles.
Turbo-charged with around 7:1 compression use 13.7 multiplier.
I have been searching to get you the actual reference. Taking longer than expected.
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