Prop Balance

[68niou1]

How can you tell if your prop is out of balance? Would you notice it more at higher rpm vs. lower rpm? The reason I ask is because I am at a dead end. I have performed everything I can think of but my 80hp Rotax UL still idles rough and makes massive gearbox ratcheting noises below 2500 rpm. I am wondering if my prop is out of balance/and or bent. However- It runs smooth from 2500 on up all the way to 5200, so in my mind I am thinking if the prop was bad it would get worse at higher rpm- not better. I had the gearcase rebuilt so that takes it out of the equation, and the engine only has 150 hours since new. I know the original owner ground looped the plane so I have a lot of unanswered questions. Any input would be appreciated-

Thanks,

Scott

[DesertFox4]

I know the original owner ground looped the plane so I have a lot of unanswered questions.

Was there any mention of a prop strike in this engine's history?

[68niou1]

None in the logs. I was not told about the ground loop when I bought the plane- I found out about it from the grand old interweb when the builder of the plane(the original owner commissioned him to build it) mentioned in another forum how he had to go rescue the owner when he(the owner)ground looped it. A couple of posts later there is a picture of my plane so no question about whether or not it actually happened. Also I found a bent rim in the trailer- and there is scarring on the tail-further evidence

[Av8r3400]

I haven't commented on my progress lately because I haven't finished, yet. I will (hopefully) be doing a test run today.

But...

1. How many hours do you have on the motor? Check.
2. Do you know if Kitfox service bulletin # 54A has been complied with?
3. Has the gearbox ever been serviced? Check.
4. How about the prop?


Does the motor move easily in the rubber mounts? Mine did. Complying with the bulletin helped that a lot. I have not run it yet to see if that cured or helped the problem.

[68niou1]

I haven't commented on my progress lately because I haven't finished, yet. I will (hopefully) be doing a test run today.

But...

1. How many hours do you have on the motor? Check.
2. Do you know if Kitfox service bulletin # 54A has been complied with?
3. Has the gearbox ever been serviced? Check.
4. How about the prop?


Does the motor move easily in the rubber mounts? Mine did. Complying with the bulletin helped that a lot. I have not run it yet to see if that cured or helped the problem.

1. Engine only has 150 hours on it.
2. SB 54A Has been done.
3. Gearbox was just done by Aircore Aviation.
4. Prop has never been messed with as far as I can tell.

I have been chasing this same problem since I got the plane in July- I did not have much Rotax experience- so did not know what was "normal". Since then I have listened to quite a few and mine is not right compared to everyone else. That only leaves the prop- or I am wondering if there is too much spacing in the gears in the gearbox???

[Dorsal]

One quick question is does it change much on one ignition or the other?

[Slyfox]

I am going to throw this out here. there is always one side when checking the mags that is always a little rougher.

next, when starting these things if you choke a slightest bit to much, you WILL have a low end roughness. to choke mine I have mags off , pull throttle all the way off, with choke on crank for a count of 3 or 3 cycles, can here it (compression) . I than stop release choke, turn on mags, start engine. after start up I go to 3000 rpm. the rotax manual actually says to run at High rpm until it smooths out. I generally keep it above 2500 all the way out to the runway. After my flight and land, the low rpm is nice and smooth.

Now with that said, I have choked it just a little to much, like count of six, that thing will not run at low idle for nothing. At least until I pull the plugs and clean them, than It's back to normal.

these engine hate too much fuel. I've flown behind the ul and uls for 1800 hours now, rich starts always affects the low end.

[68niou1]

One quick question is does it change much on one ignition or the other?

Does not change on either side. Both ignitions are within 50 rpm of each other at drop- and I do not use the choke to start it.

[68niou1]

I am going to throw this out here. there is always one side when checking the mags that is always a little rougher.

next, when starting these things if you choke a slightest bit to much, you WILL have a low end roughness. to choke mine I have mags off , pull throttle all the way off, with choke on crank for a count of 3 or 3 cycles, can here it (compression) . I than stop release choke, turn on mags, start engine. after start up I go to 3000 rpm. the rotax manual actually says to run at High rpm until it smooths out. I generally keep it above 2500 all the way out to the runway. After my flight and land, the low rpm is nice and smooth.

Now with that said, I have choked it just a little to much, like count of six, that thing will not run at low idle for nothing. At least until I pull the plugs and clean them, than It's back to normal.

these engine hate too much fuel. I've flown behind the ul and uls for 1800 hours now, rich starts always affects the low end.

Slyfox I need you to stop by and listen to it. Brendon is right behind me and I have listened to his- Chad's and Kelly's, none of them sound like mine. Let me know when you are available-

[Slyfox]

are you back out at felts? what times are you generally there? You can also take the plugs out and look at them. chances are the front plugs I believe might be black, that's not good. although it can be normall, for these generally are darker than the others. If need be I have a spark plug cleaner. quick clean and back in. Do you have a key switch for mags, or flip switches. I have flip switches and I feel that's the only way to go on the 912.

The other day when doing a check over, I found my cable slipped out at the carb for the choke, that can kick the choke on just a little. the fix is to put a wire from the carb to the wire to keep it in place.