Static RPM

Experimental amphibious aircraft with a reported 170 hours on engine. I don't characterize it is intermittent as much as "variable". 

Robert,

I don’t know much about Warp Drive props, but I did notice that the 3-blade Warp Drive manual does not list the 72” 3-blade as an approved combination on the 912 ULS. 60”-70” look to be the approved sizes. Of course the combination may work fine, but it might be worth talking with Warp Drive about your issues.  

Thanks for noticing. I'll double-check my measurements. Maybe it's a 70". 

I cannot imagine how I can get 2400RPM on that prop at 5200RPM engine speed unless I don't have the 2.43 reduction ratio. I wonder if it's possible I have the 2.27 gearbox on this 100HP 912ULS. The aircraft had the 912UL at one point. Is it even possible to mount the 2.27 to the 100HP engine?

Before going off the beaten path, verify that your tach is reading correctly by using a TruTach to measure the prop rpm then multiply by 2.43

My Aviasport/Rotax tach was reading way low. I'm told that this eventually happens to all of them. The experimental version can be tweaked via screwdrive, but the official Rotax is sealed and must be replaced. Heck with that, I replaced mine with a much better one from UMA.

Thanks Jeff. I have a cheap RC portable tach. I’ll try that or see if someone around has a TruTach. Looks like you were off 300rpm. By my calculation, I could be off 500-600 rpm!

I see something that might be an adjustment screw in the middle of the back of my Rotax tach.

I remeasured and think I have 70inch. I’ll confirm with Warp based on SN.