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  #1  
Old 06-30-2021, 10:18 PM
fehdxl fehdxl is offline
 
Join Date: Mar 2005
Location: Bellevue, NE
Posts: 704
Default RV-12iS throttle position for start

The RV-12iS POH provided by Van’s says the throttle should be at 50% +/-5%… why is this? Seems way too much power for start…and it prevents watching Gen A take over the load from Gen B. I’ve been opening it 1/16” to 1/8” and it starts just fine and at about 1800rpm. Looking to learn the why behind 50%. Thanks! -Jim
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  #2  
Old 07-01-2021, 12:07 AM
NinerBikes NinerBikes is offline
 
Join Date: Dec 2018
Location: Granada Hills
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Quote:
Originally Posted by fehdxl View Post
The RV-12iS POH provided by Van’s says the throttle should be at 50% +/-5%… why is this? Seems way too much power for start…and it prevents watching Gen A take over the load from Gen B. I’ve been opening it 1/16” to 1/8” and it starts just fine and at about 1800rpm. Looking to learn the why behind 50%. Thanks! -Jim
Do you see where it says 2500 rpm for 5 seconds in the POH? Probably to excite the fields on the alternators /generators so that they start recharging the battery and generate positive amperage to handle the electrical load of the fuel pumps.

Did you know that Rotax wants you to maintain 2500 rpms until oil temp is at or above 120F for run up, to minimize wear to the clutch and gearbox dogs in the gearbox?

So it seems that 2500 rpms is not excessive, instead, it's necessary.
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Last edited by NinerBikes : 07-01-2021 at 10:19 AM.
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  #3  
Old 07-01-2021, 02:43 AM
Karl Kistler Karl Kistler is offline
 
Join Date: Oct 2017
Location: Fehraltorf, Switzerland
Posts: 26
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I set 42%, gives about 2500RPM, then i can increase to 2600 RPM to see the switchover of Gen and observe the loading increase and Batt voltage.
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  #4  
Old 07-01-2021, 10:23 AM
fehdxl fehdxl is offline
 
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Location: Bellevue, NE
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That’s all true. But starting too high and you won’t see GEN B come on line, then when above 2500 for 5 seconds watch GEN A take over the load. It’s an electric airplane…need to ensure both GEN B and A are working. Starting at 50% doesn’t allow the check of both.

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Originally Posted by NinerBikes View Post
Do you see where it says 2500 rpm for 5 seconds in the POH? Probably to excite the fields on the alternators /generators so that they start recharging the battery and generate positive amperage to handle the electrical load of the fuel pumps.

Did you know that Rotax wants you to maintain 2500 rpms until oil temp is at or above 120F for run up, to minimize wear to the clutch and gearbox dogs in the gearbox?

So it seems that 2500 rpms is not excessive, instead, it's necessary.
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  #5  
Old 07-01-2021, 10:24 AM
fehdxl fehdxl is offline
 
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Karl, What are you physically looking at or setting to make that happen? Maybe I need to just draw a line where 2200-2300 rpm is, and start it with the throttle at that line. Thx.

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Originally Posted by Karl Kistler View Post
I set 42%, gives about 2500RPM, then i can increase to 2600 RPM to see the switchover of Gen and observe the loading increase and Batt voltage.
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  #6  
Old 07-01-2021, 11:10 AM
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rvbuilder2002 rvbuilder2002 is offline
 
Join Date: Jul 2005
Location: Hubbard Oregon
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The percent throttle value is specifically that. A % value of the how much the throttle plate is opened.
It should not be confused with percent power. Throttle position of 50% is way less than 50% power.

Having said that, in many instances, using 50% throttle position for engine start is way too much in my opinion.
The RV-12iS POH lists that value because that is what Rotax specifies in there generic engine operation check list.
We have found that in warmer ambient temps, 35-40 percent works well to get a nice smooth start that doesn't jump to an excessively high RPM. In that condition, with an engine that has recently run, 35% seems to work very well.

During the winter, particularly in very cold conditions, it will generally need 50+%
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  #7  
Old 07-01-2021, 12:12 PM
Karl Kistler Karl Kistler is offline
 
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Quote:
Originally Posted by fehdxl View Post
Karl, What are you physically looking at or setting to make that happen? Maybe I need to just draw a line where 2200-2300 rpm is, and start it with the throttle at that line. Thx.
42% throttle position
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  #8  
Old 07-01-2021, 04:17 PM
fehdxl fehdxl is offline
 
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Quote:
Originally Posted by Karl Kistler View Post
42% throttle position
Thanks, how could I have missed the big 42% right there? I see it now.
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  #9  
Old 07-01-2021, 10:24 PM
Karl Kistler Karl Kistler is offline
 
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Quote:
Originally Posted by fehdxl View Post
Thanks, how could I have missed the big 42% right there? I see it now.
https://share.icloud.com/photos/0zlQ...Ezw#Fehraltorf
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  #10  
Old 07-02-2021, 08:26 AM
NinerBikes NinerBikes is offline
 
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Location: Granada Hills
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Quote:
Originally Posted by Karl Kistler View Post
Is that on display on both Dynon and Garmin glass EFIS's?
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