Van's Air Force
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Overload clutch?
- Thread starter kritsher
- Start date
Slipper clutch
Hi Kritsher,
Do not do the overload test as this can and does bend engine mounts. You want to do the slipper clutch in the gearbox. I don't think you meant the overload clutch, but just for future reference.
The gearbox slipper clutch should be checked during the 25 hr. inspection and all 100 hr. and Annuals. It only takes about 5 min. All 912ULS engine that enter the US has the gearbox slipper clutch. Most 912UL's do not, but it can be installed or ordered that way.
This slipper clutch test is an easy procedure.
You will need that little Allen head 1 3/4" screw called the crankshaft locking pin that came with your engine usually found in the orange plastic tool pouch. Don't loose this pin. Just above the magnetic oil plug you will see a gold colored screw with an allen head. Remove this. You can remove one spark plug per cylinder if you want to turn the prop a little easier or leave them in, it doesn't matter. The easiest way for a new person to find the notch that the pin will seat into is to take a flashlight and look into the hole you just took the screw out of. Rotate the prop with your free hand while looking in the screw hole. You will be looking at a lobe inside rotating and it is shaped somewhat like an ear and not fully round. As you rotate the prop and look in the hole you may see nothing, but blackness or you may see a shinny oil covered surface. The shinny surface is what you are looking for. As you continue to rotate the prop watching the shinny surface you will eventually see a "V" notch cut into the smooth surface. Stop there. You can move the prop back and forth to get it centered. The pin you have will now screw down into the hole and seat into that "V" notch. The pin screws down into the notch and has about 3/4" still sticking out when seated. If it goes in farther than this, stop and lock for the notch again because you missed it. If it sticks way out much farther you missed the notch and you are on top of the shinny surfaced lobe. The pin in the notch locks the crankshaft.
WORD OF WARNING:
DO NOT put the pin into the blank black space in the gearbox and try and rotate the prop and bend the pin (it's hard to do, but a couple of people managed it) and do not forget it in the notch and try to start the engine. If you bend this pin and it can't be unscrewed then the case has to be split to remove it. Don't let this scare you this is an easy procedure.
Now you can not turn the crank, but the prop can still move 30 degrees with some friction. We are going to measure this friction.
Next measure out from the prop hub center along a blade and put a mark some where between 26"-30". This number can be anything, but much shorter and it's hard to turn the prop smoothly and most people don't have blades that allow much longer. Let's use 28" out from the hub center for now. Attach a string and a fish scale. I prefer the digital scale and they cost around $20-$30. Put the string on your 28" mark and pull the prop through that 30 degree arc while watching the scale to get a reading. Let's say you get 17 lbs on the scale.
That's ft/lbs and we want to convert it to in/lbs for your reading. So multiply your 28" x 17 lbs = 476 in/lbs. This is a good reading and you can write it down in the Rotax Line Maint. check List that I hope your using for your 25 hr. inspection and keeping it for your records and for every 100 hr. and Annual Condition Inspection from now on.
Most measurements I see are from 420-490 in/lbs and the higher the better, but any where along there is good. This is the measure of the 3 Belville washers pressure in the gearbox system. When they become weak and the measurements become too low then these get tossed and new ones installed, but that for you is a long ways away.
I hope this helps.
Hi Kritsher,
Do not do the overload test as this can and does bend engine mounts. You want to do the slipper clutch in the gearbox. I don't think you meant the overload clutch, but just for future reference.
The gearbox slipper clutch should be checked during the 25 hr. inspection and all 100 hr. and Annuals. It only takes about 5 min. All 912ULS engine that enter the US has the gearbox slipper clutch. Most 912UL's do not, but it can be installed or ordered that way.
This slipper clutch test is an easy procedure.
You will need that little Allen head 1 3/4" screw called the crankshaft locking pin that came with your engine usually found in the orange plastic tool pouch. Don't loose this pin. Just above the magnetic oil plug you will see a gold colored screw with an allen head. Remove this. You can remove one spark plug per cylinder if you want to turn the prop a little easier or leave them in, it doesn't matter. The easiest way for a new person to find the notch that the pin will seat into is to take a flashlight and look into the hole you just took the screw out of. Rotate the prop with your free hand while looking in the screw hole. You will be looking at a lobe inside rotating and it is shaped somewhat like an ear and not fully round. As you rotate the prop and look in the hole you may see nothing, but blackness or you may see a shinny oil covered surface. The shinny surface is what you are looking for. As you continue to rotate the prop watching the shinny surface you will eventually see a "V" notch cut into the smooth surface. Stop there. You can move the prop back and forth to get it centered. The pin you have will now screw down into the hole and seat into that "V" notch. The pin screws down into the notch and has about 3/4" still sticking out when seated. If it goes in farther than this, stop and lock for the notch again because you missed it. If it sticks way out much farther you missed the notch and you are on top of the shinny surfaced lobe. The pin in the notch locks the crankshaft.
WORD OF WARNING:
DO NOT put the pin into the blank black space in the gearbox and try and rotate the prop and bend the pin (it's hard to do, but a couple of people managed it) and do not forget it in the notch and try to start the engine. If you bend this pin and it can't be unscrewed then the case has to be split to remove it. Don't let this scare you this is an easy procedure.
Now you can not turn the crank, but the prop can still move 30 degrees with some friction. We are going to measure this friction.
Next measure out from the prop hub center along a blade and put a mark some where between 26"-30". This number can be anything, but much shorter and it's hard to turn the prop smoothly and most people don't have blades that allow much longer. Let's use 28" out from the hub center for now. Attach a string and a fish scale. I prefer the digital scale and they cost around $20-$30. Put the string on your 28" mark and pull the prop through that 30 degree arc while watching the scale to get a reading. Let's say you get 17 lbs on the scale.
That's ft/lbs and we want to convert it to in/lbs for your reading. So multiply your 28" x 17 lbs = 476 in/lbs. This is a good reading and you can write it down in the Rotax Line Maint. check List that I hope your using for your 25 hr. inspection and keeping it for your records and for every 100 hr. and Annual Condition Inspection from now on.
Most measurements I see are from 420-490 in/lbs and the higher the better, but any where along there is good. This is the measure of the 3 Belville washers pressure in the gearbox system. When they become weak and the measurements become too low then these get tossed and new ones installed, but that for you is a long ways away.
I hope this helps.
Last edited:
RFSchaller
Well Known Member
From a practical standpoint I don't see any value in the overload clutch test (the one that tests the dog slippage and takes extreme torque). The purpose of the clutch is to protect the engine as much as possible from a prop strike. I prefer plan A: don't get a prop strike.
Am I missing something?
Am I missing something?
overload and slipper clutch
The overload and slipper clutch are two different things. They are shown in the Rotax Line Maint. manual. The slipper clutch (gearbox) you should do. If the slipper torque value gets too low you get unwanted vibrations and even some times when it test high enough a re-shim of the gearbox can fix the vibration. Testing the overload clutch puts so much torque on the engine it can and has bent the airframe.
The overload and slipper clutch are two different things. They are shown in the Rotax Line Maint. manual. The slipper clutch (gearbox) you should do. If the slipper torque value gets too low you get unwanted vibrations and even some times when it test high enough a re-shim of the gearbox can fix the vibration. Testing the overload clutch puts so much torque on the engine it can and has bent the airframe.
RFSchaller
Well Known Member
Roger,
Do you see any practical value in the overload test? Seems like a lot of effort for not much return.
Rich
Do you see any practical value in the overload test? Seems like a lot of effort for not much return.
Rich
Hi Rich,
I personally don't do the overload clutch test just for routine maint. checks. Rotax doesn't seem to have any heartache over this. Many were even warned not do it in Rotax class because it bent frames and you need to add bracing so you don't tweak your frame. Not all frames from aircraft Mfg's are the same and some bend more easily and some people get too carried away with all the torque it takes to do it.
I rarely ever do an overload test unless there are special circumstances so I don't do the test just to do it.
I do the gearbox slipper clutch test every 25 hr, 100 Hr. and Annual Condition inspection. That's non destructive and only takes a few minutes.
I personally don't do the overload clutch test just for routine maint. checks. Rotax doesn't seem to have any heartache over this. Many were even warned not do it in Rotax class because it bent frames and you need to add bracing so you don't tweak your frame. Not all frames from aircraft Mfg's are the same and some bend more easily and some people get too carried away with all the torque it takes to do it.
I rarely ever do an overload test unless there are special circumstances so I don't do the test just to do it.
I do the gearbox slipper clutch test every 25 hr, 100 Hr. and Annual Condition inspection. That's non destructive and only takes a few minutes.
