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Prop Clocking, vibration?

edclee

Well Known Member
Patron
I recently had the prop off my RV-9A IO-320 for my condition inspection and I decided to check to see what Sensenich had to say about it. They have an instruction published that says to set #1 to TDC on the compression stroke and put #1 blade at 11 oclock. I did that and now it seems I have a vibration around 2200 rpm that I did not have before. There are no balance weights on the hub or spinner. Has anyone any words of wisdom on this? Any idea why Sensenich advises this clocking?
Ed
 
First, make sure you have the correct bushings in the right holes. They actually drive the prop, the bolts only hold the prop on the bushings. Second, check static balance, don't chase your tail. Then perhaps dyno balance, remember, there is a #1 blade and a #2 blade. Both should be identical, but it is a way to remove and replace the propeller in the same place, not 180 degrees out. Sometimes, go figure, besides my RV, I have a Scout. The manufacture says with the prop stopping at the 12:00 position, that is how the FAA certified the aircraft. I really want to replace / move bushings per the Lycoming service instruction 1098Q to allow a stop at the 10/2 position, but without an STC, that would void my insurance. Also, I recommend a 60 degree spread on weights when dyno balancing, helps with the different orders of vibration.

Regards,

DAR Gary
 
Also, I recommend a 60 degree spread on weights when dyno balancing, helps with the different orders of vibration.

Regards,

DAR Gary

Not sure where the above recommendation comes from, splitting weights is sometimes the only way to effectively accomplish the balance and actually zero in on the the ideal balance location. It has nothing to do with changing the magnitude of harmonic vibrations.
 
A question, please

I obviously can't know all of the details/variables. The prop OEM probably made the suggestion for clocking probably based upon "standard" assumptions; fixed timing I.A.W. engine OEM nameplate, standard compression rations, etc. The aforementioned would surely effect the related dynamics of the rotating mass. What is your current engine config? Was any balance optimization done for it's previously clocked position? I'm assuming you'll need to take it back to parade rest and start again. Please let us know what you find and ultimately do.
 
Update on Vibration/Clocking

Well, nothing special about the configuration. Standard Sensenich metal prop and I took it off this morning to check out the bushing thing. I also downloaded Lycoming SL1098Q, which addresses various engines and their flanges and their bushing configurations. When I took mine off I verified that the prop can, in fact be clocked in any of six positions. All the bushings are tight and are fitted properly for my engine. The nose of the bushings are all identical, only the diameter that fits into the bore of the flange is larger on one of the bushings. The two types in use are 72066-s and 72067-S. Why Lycoming fit one bushing different I don't know.

Anyway, I put it back like I just had it and did a dynamic balance. It was not too far off. I measured 0.18 ips to start with and after balancing weights were added, got it to about 0.03 and it seems smooth. I guess there is not a problem except that I still cant figure out the Sensenich instructions to mount the prop with blade 1 at 11:00 with #1 at TDC on compression stroke.
Ed
 
For my benefit

For my benefit, did the prop have any balance moves done while in its old/current again position? Changing clocking after balancing (even 180 deg) would certainly have an effect. Let us know if you don't mind.
 
Clocking worked for me

After replacing my hollow crankshaft (Superior AD) with a solid crank, I did a successful dynamic balance (.02 IPS) on my whirlwind GA prop, but still had a noticeable vibration at 2500 rpm, my preferred cruise rpm, in the air. I then adjusted prop pitch so I could hit 2500 rpm on the ground and tried it again. After readjusting the prop for cruise I still sensed a vibration at 2500 in the air. I then re-clocked the prop from 11:00 - 5:00 to 9:00 - 3:00, and rebalanced the prop for the third time. Perseverance paid off, vibration now acceptable at all rpm settings.

The Whirlwind GA prop is easy to clock, as their spacer has symmetrical holes and bushings where the prop hub attaches, so no crankshaft flange bushing rearrangement needed.
 
They have an instruction published that says to set #1 to TDC on the compression stroke and put #1 blade at 11 oclock.
Ed

Can't help you much with your vibration issue, but I'll add that Whirlwind has the same instruction for their props.

I just finished my 5th annual which required the WW200RV prop on my plane to go back for hub inspection, and while I was at it I had them strip and refinish the blades due to all the rock chips I had on mine (I taxi to a paved runway, on a caliche road). When I got it back (looks awesome BTW!) I removed all the balance weights on my flywheel, aligned it per their instructions at 11 o'clock, and it's smooth as silk.

Now I'm still gonna get it balanced with a real accelerometer - don't get me wrong - but a new prop in the correct clocking is pretty happy on it's own.
 
I received this from Van's last year when I had the same question.
 

Attachments

  • prop install, blade position.pdf
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Clocking at 2, 8 oclock?

I received this from Van's last year when I had the same question.

Strange that Lycoming says to clock it there and Sensenich says to clock it at 11 when #1 is at TDC. I am going to try it though!
Ed
 
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