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  #11  
Old 06-13-2017, 06:47 AM
JBPILOT JBPILOT is offline
 
Join Date: Nov 2007
Location: Jesup, Iowa
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Default Just another comment - -

Are you using the OEM supplied stronger throttle springs on the carbs ? Lighter duty springs may not be pulling the same and makes it harder to adjust at various ranges.
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  #12  
Old 06-13-2017, 09:24 AM
Jolly Jolly is offline
 
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Location: San Francisco, CA
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A mechanical sync is done first and all it does is get you in the ballpark to do the pneumatic sync. Once done it usually doesn't have to be done again for subsequent syncs unless you remove carbs or cables and need to start from scratch. If you keep up on the sync at every annual/100 hr. inspection then the cabs should only need a tweak to keep them synced.
The reason to use 3300-3500 rpm over the recommended 2500 rpm is that 2500 rpm is still too far down into the idle circuit using only the idle jets which are out of play at higher rpms and because it flows little fuel and air. Even though we don't fly at 3500 rpm it is more representative of air and fuel flow and it is getting off the idle circuit into the main jet side. If you only balance at 2500 rpm and then advance the throttle you are much more likely to get your gauge needles to split again. If you sync at higher rpms that usually isn't the case unless you have another problem. Syncing too low an rpm is like using a torque wrench at its top or bottom 10% of its range. It isn't recommend.
The reason to set the high rpm sync first is because if you set the idle first you will most likely have to do the idle again after youturn the Bowden cable adjuster for the higher rpm sync.
You can set the idle at 1600-1800 rpm if you want. Pick your own rpm. We should all know that you should never just shut and idle at low rpms under 1800 and for that matter you are always better of at 2000 rpm or higher. It is much easier on the gearbox and engine components due to the engine's high compression. The only reason to have a lower idle rpm is for shut down only. When you pull all the way back and the idle is dropping to let's say your 1700 idle rpm then shut down the engine.
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  #13  
Old 06-13-2017, 09:48 AM
rvbuilder2002 rvbuilder2002 is offline
 
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Location: Hubbard Oregon
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Quote:
Originally Posted by Jolly View Post
The only reason to have a lower idle rpm is for shut down only.
Not so Roger

As has been discussed and debated here in the past, an idle speed set at 1800 RPM (or higher) will have a pronounced impact on landing performance of an RV-12.

I strongly recommend owners follow the recommendations of the RV-12 maint. manual regarding idle speed adjustment, and then operate the engine within Rotax's recommendations by manually positioning the throttle so that the engine is never idling below the green range.
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  #14  
Old 06-13-2017, 09:51 AM
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DaleB DaleB is offline
 
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Quote:
Originally Posted by Jolly View Post
You can set the idle at 1600-1800 rpm if you want. Pick your own rpm. We should all know that you should never just shut and idle at low rpms under 1800 and for that matter you are always better of at 2000 rpm or higher. It is much easier on the gearbox and engine components due to the engine's high compression. The only reason to have a lower idle rpm is for shut down only. When you pull all the way back and the idle is dropping to let's say your 1700 idle rpm then shut down the engine.
Where would one find a reference for this information? I've always pulled the throttle to 1800 (I think it is -- the bottom of the green arc on the tach) and shut down. I have my idle set to roughly 1600, because otherwise it can be a challenge to get slow enough on final.
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  #15  
Old 06-13-2017, 11:24 AM
Jolly Jolly is offline
 
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Location: San Francisco, CA
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The stick controls air speed on approach and landing and the throttle altitude or glide slope. All these articles say the same. There are hundreds more.
Landing in your chosen idle rpm speed is controlled by the stick and the nose attitude.

http://www.boldmethod.com/learn-to-f...-a-glideslope/


https://www.pilotworkshop.com/tips/f...oach_speed.htm

http://www.110knots.com/airspeed-and...ls-of-thought/

http://flycasey.com/landing-pitch-and-power/

Quote from Beyond PPL book on flying:

"In days of yore, instructors always taught that on the approach you should control airspeed with pitch and maintain the correct glide slope with the throttle.
The technique taught was (and still is) a good device for getting students to co-ordinate properly their applications of pitch and throttle."
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  #16  
Old 06-13-2017, 11:49 AM
rvbuilder2002 rvbuilder2002 is offline
 
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Location: Hubbard Oregon
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Quote:
Originally Posted by Jolly View Post
The stick controls air speed on approach and landing and the throttle altitude or glide slope. All these articles say the same. There are hundreds more.
Landing in your chosen idle rpm speed is controlled by the stick and the nose attitude.

http://www.boldmethod.com/learn-to-f...-a-glideslope/


https://www.pilotworkshop.com/tips/f...oach_speed.htm

http://www.110knots.com/airspeed-and...ls-of-thought/

http://flycasey.com/landing-pitch-and-power/

Quote from Beyond PPL book on flying:

"In days of yore, instructors always taught that on the approach you should control airspeed with pitch and maintain the correct glide slope with the throttle.
The technique taught was (and still is) a good device for getting students to co-ordinate properly their applications of pitch and throttle."
Roger (Pretenting to be someone else because of previously being banned),
Please don't start this debate all over again (for those interested there is a lot of discussion in the forum archives on this)

Bottom line.... I agree that Roger is on the Rotax engines but on at least this one point ignore what he says.
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  #17  
Old 06-13-2017, 12:15 PM
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Phantom30 Phantom30 is offline
 
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Quote:
Originally Posted by DaleB View Post
Where would one find a reference for this information? I've always pulled the throttle to 1800 (I think it is -- the bottom of the green arc on the tach) and shut down. I have my idle set to roughly 1600, because otherwise it can be a challenge to get slow enough on final.
Dale...there has, for some time, not sure how long; various views regarding "correct" idle rpm (and landing rpm's)....I would follow Scott's advice.

I, personally like a lower idle rpm (1550), and I go there only for engine shut down. Landing, I use around 2000 rpm, as I like to use a higher approach speed fly onto the runway. I pull back to idle just before main wheels contact; then to 1900 for run out/taxi...just my way.

Jolly's sync procedure is right on....use them! And you will be happy.
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  #18  
Old 06-13-2017, 12:48 PM
rvbuilder2002 rvbuilder2002 is offline
 
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Just to clarify (even though it has been covered numerous times and is in the archives)

Even if you use 1600 RPM for an idle setting, with the throttle pulled to idle in a glide for landing, the engine will not be idling at 1600 RPM.
Because of relative wind the prop is unloaded and the engine will be turning at more like 1900.
Only when you come to a complete stop will the engine idle down to 1600 RPM and at that point the pilot should advance the throttle and get the RPM back in the green range
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  #19  
Old 06-13-2017, 01:49 PM
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DaleB DaleB is offline
 
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Quote:
Originally Posted by rvbuilder2002 View Post
Just to clarify (even though it has been covered numerous times and is in the archives)

Even if you use 1600 RPM for an idle setting, with the throttle pulled to idle in a glide for landing, the engine will not be idling at 1600 RPM.
Because of relative wind the prop is unloaded and the engine will be turning at more like 1900.
Only when you come to a complete stop will the engine idle down to 1600 RPM and at that point the pilot should advance the throttle and get the RPM back in the green range
Yes, I'm aware of that. I honestly couldn't tell you what my actual RPM is on final -- I pay no attention to it until rolling out. Throttle is all the way out and my eyeballs are over the nose with an occasional glance at airspeed until the AoA starts beeping. I have the idle set for 1600 or very slightly above on the ground.
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  #20  
Old 06-13-2017, 08:41 PM
DaveWelch DaveWelch is offline
 
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Thank-you John,
I remember noticing that difference before and had forgotten.
I'll pay more careful attention during my third, hopefully final, mechanical sync!
Clear Skies,
dave
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