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SuperSTOL with Catto Prop

PostPosted: Mon Feb 13, 2017 12:17 pm
by Augustus
I am wondering if the minimum RPM for the Rotax engine (with the 2.43:1 gearbox in mind) is the ideal RPM just after touchdown for a SuperSTOL. I'm thinking that it might not be.
This is my thinking and please spank me soundly if you disagree!

My minimum RPM is set at 1,950 (which is what I use for touch down). That means my MONSTER Catto prop is churning @ 802 rpm. That's waaay to fast.

What do you aviators think?

Re: SuperSTOL with Catto Prop

PostPosted: Mon Feb 13, 2017 12:33 pm
by kenryan
Rotax manual says 1400 for minimum idle rpm. Can you set it at that, and use some throttle on start and warm up if necessary?

Re: SuperSTOL with Catto Prop

PostPosted: Mon Feb 13, 2017 1:01 pm
by Augustus
Ouch Ken. Will check it out. 576 rpm sounds quite a bit better at touchdown.
Still adjusting things after two years. Thanks.

Re: SuperSTOL with Catto Prop

PostPosted: Mon Feb 13, 2017 1:06 pm
by kenryan
I have heard that idling low can be hard on the gearbox. Maybe that only applies on the ground? Would be a good question for the Rotax Forum:

http://www.rotax-owner.com/en/rotax-forum/3-4-stroke-technical-questions

Re: SuperSTOL with Catto Prop

PostPosted: Mon Feb 13, 2017 7:38 pm
by dkshow
I can't remember what mine idles at but I'm sure it's more than 1400. I know they don't like to run slow. I think mine idles somewhere near 1750-1800

Re: SuperSTOL with Catto Prop

PostPosted: Mon Feb 13, 2017 11:56 pm
by AV8R Paul
Mine Rotax idles at 1600 to 1700 RPM just fine.

Re: SuperSTOL with Catto Prop

PostPosted: Thu May 04, 2017 9:46 am
by Augustus
Thanks for the info folks. Here's an update: In the interim from my original post, I had one of my OEM floats decide to not float. It's a good thing that I did not adjust the idle. It would have resulted in much head scratching about how I just messed up my engine. It was pretty much an easy diagnosis and fix to replace the floats in one of the carbs. Thanks again to Ronnie and South MS Light Aircraft, Inc.
I did reduce my idle to around 1600 RPM and it was EXACTLY what the doctor ordered. I increase the idle up to about 1900 after I land but that few seconds where it is at 1600 makes a big difference -- especially on a hard runway with a downward slope.

Re: SuperSTOL with Catto Prop

PostPosted: Thu May 04, 2017 10:41 am
by FlyerChief
Chasing the Perfect Idle Speed

There is a response to the idle speed question on the Rotax Forum...
http://www.rotax-owner.com/en/rotax-blog/item/44-912-idle-rpm

My 912 uls will idle smoothly as low as 1300 rpm, so I find myself having to adjust it up every flight with the throttle to keep it around 2200 for warm up. Being able to turn the idle down to to 1300 appears to give me smoother shutdowns, but it's way too slow to idle a 912 uls for any length of time.

Dan