propeller balance

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voorheesh
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propeller balance

Post by voorheesh »

I have a 1950 170A with a O-300 approx 150 SMOH and a McCaulley 7653 prop. I havent noticed any unusual vibration or noise from the prop over the last few years but decided to send it out for overhaul since it was looking shabby and, I believed, worth $600 to bring it to same standard as the engine. The prop shop told me that one blade was pitched to 51 and the other 53. They told me that the prop was worth saving and re pitched it to 53 and sent it back with an overhaul/yellow tag. My mechanic installed it (I/A/W Cessna installation procedure) and it had a slight tremble in run up at 1500 rpm. At full power it was smooth. During approx 1 hour test flight, it had tremble at 2300 rpm and didnt feel the same as before overhaul (not a major vibration but a tremble you could see in instrument panel and feel by placing hand on top of panel). My mechanic did a Chadwick balance procedure which resulted in placing between 50 to 100 grams of weight between 2 of the bolts. The prop/engine is now smooth (per Chadwick and by feel). Prior to adding weight, we tried changing the position of the prop relative to crankshaft by 180 degrees with no change noted.
Have any of you had similar experience? Does this seem like excessive weight to balance? Now that it is smooth is the problem solved? I guess my concern is why did the prop with 2 blades 2 deg out of pitch seem smoother than the overhauled prop and is there a deeper problem that the weights are masking. Incidently, the engine has been running great, good jugs/temps and minimum oil consumption. I would appreciate any input.
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Bruce Fenstermacher
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Post by Bruce Fenstermacher »

These types of problems annoy the heck out of me.

The problem is who do you believe. Since you didn't do the work how are you sure the prop shop didn't screw up measuring the prop? Does your IA really know how to use a Chadwick? Perhaps all these years your prop blade was out of pitch masking an out of balance condition.

What to do.

As a helicopter pilot I get to assist the mechanics from time to time while they balance the main and tail rotors. This seems to be a black art that frustrates even the most experienced mechanics.

I don't know if 50 to 100 grams is a lot but I do know that sometimes it is not possible to put the least amount of weight in the best place and so more weight is placed in other locations to effect the same change.

If you are concerned I'd speak to the prop shop and tell them of your experience. Perhaps they can give you more insight into what they found. I'd also discuss it with your IA who did the balance. Chances are that if neither of them are concerned there is nothing to worry about.

Enjoy your smooth prop.
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voorheesh
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prop balance

Post by voorheesh »

Thanks Bruce. I test flew it again tonight and it is smooth as silk. Flew as fast as I could get it and as slow as I could get it. Tried every cruise power setting from 2000 to about 2500 (Max level flt full throttle 2000'), full power and no power stalls and I have no complaint. After talking with my IA, we believe if we had rotated the prop one bolt at a time and found the lowest Chadwick value, we might have balanced it from that index with less weight. The prop shop told us of another O-300 installation where their ovhauled prop would not balance at all. They exchanged for another prop and it worked fine without needing any weights. Apparently internal balance in the engine including wrist pins and crank counter weights can affect this. I plan to fly the heck out of this plane and hope it stays smooth. Have a good one.
Harlow Voorhees
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Bruce Fenstermacher
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Post by Bruce Fenstermacher »

Harlow

As for the proper prop position that should be with the number one blade at 11 o clock with the #1 cylinder at TDC. I would have put it one in this position and balanced from there. (this from memory I'd actually double check documents before I did it.)

At this point is yours in not in this position I probably wouldn't change it now but be sure to mark you prop and it position relative to the prop hub before removing it so that you can replace it exactly that way.
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Jr.CubBuilder
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Post by Jr.CubBuilder »

Bruce where did you learn that, and how would the position of the prop blades in relation to the crank affect vibration? The reason I ask is that I had my prop repitched and overhauled a year and a half ago. The mechanic that put it back on thinks it really makes no difference where the blades are since it is spinning not reciprocating. Anyway, I have had a bit more vibration at about 2000-2200rpm, and I always thought it started after we put the prop back on.
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cessna170bdriver
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Post by cessna170bdriver »

There may be a Cessna Service Bulletin for the "official" data for Proper Propeller Position :lol: , but I couldn't find it. There is an article in The 170 Book that illustrates the position for minimum vibration. I don't know what the mechanism is, but I do know from first-hand experience that if it isn't installed as Bruce says above, it WILL vibrate. The only balancing done on my recent overhaul was Nickson's replacing counterweight bushings and pins on the crankshaft, installing all the same weight pistons to within a gram, and having the prop overhauled, then installed per The 170 Book article. It ran smooth as an electric motor on the first try. 8)

Miles
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Jr.CubBuilder
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Post by Jr.CubBuilder »

Hmmmmm, I'm going to have to look into this, smoother is always better.
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bradbrady
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Post by bradbrady »

I just looked up the pisition of the prop in the 100 series service manual. It said that the prop on a 150, 172, and 175 should be set at 30 deg. trail of TDC. or at the 11 O-clock pisition like Bruce said. The instresting thing is, I was taught as a kid to set the props at this pisition, and have without question. 8O Yet I can't find any other (paper, or web based information), out side of hear say, to support this pisition for a 170! But for me it has alwayse worked!
brad
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Bruce Fenstermacher
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Post by Bruce Fenstermacher »

Actually (from memory now) the official spot with the early 170s was the number one blade at the 1 o clock position with the number one cyliner at TDC But then later Cessna found less vibration with the change to 11 o clock and that is approved for all 170s.

We have discussed this here before at the forum so a search should find more discussion and the documents that spell it all out.

Of course George will know and be able to tell us as soon as he reads this thread.

Let s see who can find the official stuff (again) before George. :D
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GAHorn
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Post by GAHorn »

N9149A wrote:Actually (from memory now) the official spot with the early 170s was the number one blade at the 1 o clock position with the number one cyliner at TDC But then later Cessna found less vibration with the change to 11 o clock and that is approved for all 170s.

We have discussed this here before at the forum so a search should find more discussion and the documents that spell it all out.

Of course George will know and be able to tell us as soon as he reads this thread.

Let s see who can find the official stuff (again) before George. :D
If you attended the Kelowna Convention you will have received the Service Information Manual I handed out free to all attendees, which specified the Official Cessna Service Letter that addressed this issue. :wink: (Hint: It came out in late '53/early '54.)
If you were unable to attend, you may buy this manual from headquarters.
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons. ;)
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Bruce Fenstermacher
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Post by Bruce Fenstermacher »

Darn it George I KNEW I saw it someplace recently.

I knew you'd remember where I did. Have any idea where I left my car keys?:lol:

Thanks :D
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GAHorn
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Post by GAHorn »

So.. THAT'S what those things are! I knew where they were...I just didn't know what they were! :lol:
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons. ;)
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lowNslow
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Post by lowNslow »

gahorn wrote: If you attended the Kelowna Convention you will have received the Service Information Manual I handed out free to all attendees, which specified the Official Cessna Service Letter that addressed this issue. :wink: (Hint: It came out in late '53/early '54.)
If you were unable to attend, you may buy this manual from headquarters.
George, I attended and never recieved mine. :cry:
Karl
'53 170B N3158B SN:25400
ASW-20BL
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Bruce Fenstermacher
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Post by Bruce Fenstermacher »

Karl

Unfortunitly you had to leave the convention before George could have them copied and hand them out.

Not sure we have a policy on these. I think George likes to have something value added for those that attend the MX meetings. I'm betting lots of it is paid for out of Georges pocket and as long as he can hand them out to you, you get it free. After the fact there is a cost involved.

Hopefully Karl, you saw this Cessna SIM at the meeting. It is not 170 exclusive but does have a far amount of 170 related information. In most cases it's not the only source of such information. If you have others you more than likely have it all.

This IS a Cessna Publichation though and is nice to have to include in anyones library of 170 information.
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lowNslow
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Post by lowNslow »

N9149A wrote:Not sure we have a policy on these. I think George likes to have something value added for those that attend the MX meetings. I'm betting lots of it is paid for out of Georges pocket and as long as he can hand them out to you, you get it free. After the fact there is a cost involved.
No worries. I'll order it from HQ once they get settled in the new location.
Karl
'53 170B N3158B SN:25400
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