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Dynamic Propeller Balance Question

Invicto89

I'm New Here
I haven't done this before, so please excuse my naiveté.

I have reviewed the SL-00024 Rev 1, MM R3.7, and PAP Rev 2.4 and searched the forum but haven't found the answer to this question:

For an RV-12iS, when conducting a dynamic propeller balance procedure, is the lower cowl supposed to be left on?

I am concerned about the lower cowl flexing during full throttle / high RPM ground run introducing weird harmonic resonance issues that then are no longer there when, with the upper cowl installed, the flying configuration structure allows much less flexing.

If the lower cowl is supposed to be removed, then should I just secure/zip tie the induction hose/air filter/IAT assembly?

I just had my Sensenich 2 blade prop blades factory refurbished and statically balanced and will be using a Dynavibe Classic balancer device.

I have already reviewed the procedures for reinstallation, pitch matching, blade tracking, etc. prior to the dynamic balance procedure.

Thank you in advance for any help, tips, or cautions.

Steve

PP/LSRM-I
'22 Donation made
2020 RV-12iS Dynon 120482
TBD RV-8A 81635
 
When I loan out my Dynavibe for rv-12'ers to do their prop balancing, I have a tip sheet that recommends removing the cowl completely. There are two main reasons:

  1. The forward/top part of the lower cowl can vibrate and move in the wind and the spinner's backplate can scratch it.
  2. It is more difficult to attach the Dynavibe vibration sensor to the side of the gearbox.

I have run the engine with no air filter during these runs. A calculated risk for sure, and I inspect the local area to be sure that the intake won't suck in any zip ties, fabric, nuts, etc. Gnats and other tiny insects.. maybe will get in, but I'm not concerned. Potentially, you could connect the air filter directly to the intake.. or via the scat tube.. and make sure its all ziptied safely in place. I always connect the engine intake temperature sensor as well (with zipties) to make the ECU happy.. as it needs to know the temperature in order to calculate the proper fuel/air mixture.

The pitch matching is very important.. better to spend the extra time to get that right.. otherwise you'll waste your entire day trying to dynamically balance it.

I can send you the tip sheet if you're interested.
 
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Since I am to balance an RV-12 prop using the Dynavibe Classic, I am seeking to understand your comments.

When the lower cowl is removed, how does this effect the oil cooler since it was attached to the lower cowling?

Why do you remove the air cleaner?

Also, I would like to see your cheat sheet.

Thanks.

Brett H
Columbus, IN
 
The OP posts an interesting question.... I wonder how "balanced" the prop is in actual flight with aircraft suspended in air and smooth airflow over cowling? I would imagine aircraft sitting on huge immovable object (the ground) and prop pulses reverberating against the tarmac is a different resonance than flight regime....
 
I have performed a balance with and without the lower cowl - no difference was detected. As Walt does, I tie the forward end of the cowl away from the spinner.

Brett, on the iS, the engine air filter is attached to the lower cowl, not the oil cooler. The oil cooler is suspended from the engine. That was Rob’s comment about not having the air filter attached to the throttle body when testing without the lower cowl in place.
 
A little un related to the post...I've done a few pitch adjustments on my 2 blade prop and always had trouble getting both blades at the same pitch after tightening the bolts. I made a blade wrench out of 5/8" plywood that I slide down the blade. It allows me to get a much more accurate adjustment as I now can have the blades a bit more snug while twisting. I have the Dyna Vibe Classic and leave the lower cowl on (non 12is) ...I have gotten my vibes down to .03 the smoothness is noticeable.
 
Many thanks to all that responded.

Rob - I appreciate the tip sheet offer and have sent you PM.

Steve

PP/LSRM-I
'22 Donation made
2020 RV-12iS Dynon 120482
TBD RV-8A 81635
 
Since we are on this subject i have one question.. On the process of balancing in reference of this sheet. to figure out the angle do we do as we are looking at the pro (puts in counter clock rotation ) or do we reference form the pilot view (clock wise)
If you see on this picture you need to know clockwise or counter. I am assuming we would use the counter clock direction for the angle find. am i Correct?
 

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