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Slipper Clutch

bernsbm

Active Member
Friend
Doing there 25 hour inspection on my RV12iS E-LSA equipped with the Rotax 912iS engine and noticed there is no slipper clutch (unlike my previous 912ULS equipped RV12). Not sure the reason for this. Anyone know? Thanks
 
Really? Have you tried locking the crankshaft with special 8mm bolt and then turn the prop shaft?

Hard to believe Van's would eliminate the slipper clutch...
 
Locked the crankshaft and pulled really hard on the prop... no movement. Nothing like my previous ULS.
 
The slipper clutch is related to the torsional needs of the engine/gearbox/prop combination. Pretty sure Vans would follow the recommendations provided by Rotax.
 
You can go here... https://www.rotax-owner.com/en/gene...otax-engine-manufacture-date?start=140#p27724 and provide your engine SN. These good folks will tell you exactly how your engine is configured from the factory.

I asked about my engine and got this reply:
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5652766 was produced 25-Feb-2009

Engine Type:ROTAX 912 ULS
Engine Version: 912 ULS2
Model Number:309120110
Original Factory Configuration:

with fuel lines
UL2 I=2,43 with clutch
without vacuum pump
with green valve covers
without mech. tachom. pick up
without external generator
without air guide baffle
with std. temperatur sensors
with screw connection UNF
with expansion tank
without air box
bent sockets for engine truss
starter large
 
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The newer IS models were tearing up gearboxes in short order.

Rotax made some changes to the gearbox configuration, including adding an oil squirter to the housing that lubes the clutch while in use.

There may have been other modifications made also, such as perhaps higher Belville washer tension on the springs, making the clutch more difficult to develop any play.

Talk to Rotax about it, and what, if any, the new specs might be. Van's doesn't build the motors, Rotax does, so contact Rotax.
 
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For a time reference, I received my 912iS Powerplant kit from Van’s end of May 2019 and it’s got the clutch.
 
Thanks everyone, appreciate the comments. Putting the suggestions together, I think I understand where I was getting confused.

I checked Rotax-owner.com and confirmed my engine has the overload clutch. I also found an interesting discussion of prop play with the crankshaft locked, comparing ULS and iS engines.

The ULS engine gearbox has 30 degrees of play between the dog ears of the gear and hub. The force needed to move across this 30 degrees is the friction torque, which is measured at regular maintenance intervals. I was trying to do the same on my iS engine. Apparently, there is no slippage/30 degrees of movement in the iS gearbox. Hence no friction torque measurement. I should have suspected the gearboxes were different; unlike the 912ULS MML the 912iS MML does not include a section on measurement of friction torque! Anyways, will put in a call to Rotax on Monday to confirm my assumptions are correct.
 
Doing there 25 hour inspection on my RV12iS E-LSA equipped with the Rotax 912iS engine and noticed there is no slipper clutch (unlike my previous 912ULS equipped RV12). Not sure the reason for this. Anyone know? Thanks

From Lockwood

"While both engines have an overload clutch, they have different dog hubs. The ULS has what’s called a 30° hub. If you lock the crankshaft, there is still 30° freedom of movement on the propeller shaft. That is what you’re measuring on the friction torque test. The iS has what’s called a 0° hub. If you lock the crankshaft, there is no freedom of movement on the propeller shaft. There is, therefore, no friction torque to measure and, hence, no specification for it in the 912iS manuals."
 
Thanks for posting. This confirms what I read on the Rotax Owner's forum. I had assumed the ULS and iS engines were the same, other than the fuel system. Lesson learned!
 
From Lockwood

"While both engines have an overload clutch, they have different dog hubs. The ULS has what’s called a 30° hub. If you lock the crankshaft, there is still 30° freedom of movement on the propeller shaft. That is what you’re measuring on the friction torque test. The iS has what’s called a 0° hub. If you lock the crankshaft, there is no freedom of movement on the propeller shaft. There is, therefore, no friction torque to measure and, hence, no specification for it in the 912iS manuals."

Is the 0 degree hub a newer model and a retrofit to the older ULS if the 30 degree dog hub fails at higher hours? Does it also require the newer style external housing with oiler?
 
The downside to the 0 degree overload clutch is you cannot do the "fish scale" clutch inspection. So iS engines require a 600 hour gearbox inspection, even if operated 100% on mogas.
 
I never could see the point in testing the overload (the actual test of the dogs). Seems to me that the overload function is only important in a prop strike, and if you get a prop strike you still have to check the crank shaft angle. I’ve always thought the small likelihood of a prop strike when operating off paved runways did not justify the actual clutch overload test that requires taking the engine off the mount. Am I missing something?
 
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