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APC Prop Balance

Old 03-21-2007, 07:59 AM
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fancman
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Default APC Prop Balance

I've encountered a problem that I wonder if anyone else has come across. I use APC props in the 13, 16 and 17 inch size and have had problems when it comes to getting the prop hub to balance. I begin my balancing by getting the tips balanced which is no problem at all to do but when I go to get the hub to balance I have to always add weight to one side to get it right. I won't fly a prop if it won't stop in any position.

Has anyone experienced the same problem. I called APC and they assure me that their props are balanced really well. [] That hasn't been my experience lately. Here are a couple pictures of what I had to do to get the hub to balance. That's a strip of Velcro with thick ca built up on it in one pic. The other has Velcro, thick CA and a little strip of lead.

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Old 03-21-2007, 08:33 AM
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firstplaceaviator
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Default RE: APC Prop Balance

Fancman,
I have been flying APC's in many sizes for about 17 years. I have never had one that required more than minor dressing to get it perfectly balanced. I use an ancient Robart High Point balancer. What type of balancer are you using? I wouldn't glue anything to a propeller for balance. That seems like an accident just waiting to happen.
Doug
Old 03-21-2007, 08:43 AM
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Default RE: APC Prop Balance

http://www.dodvideos.com/don3.wmv

I balance according to this video from Down on the Deck. Never had anything fly off the prop and if it did it would be inside the spinner. I use the Dubro Prop balancer and I've experienced this with most of the larger APC props I've purchased.

I've been flying for more than 25 yrs so this isn't my first Rodeo. Just wondering if anyone else finds the APC props to be so far off. Gues I'll have to upgrade to a more expensive prop in the future if APC's don't get any better. I've got the old Robart balancer as well as a magnetic balancer. No difference.
Old 03-21-2007, 08:51 AM
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bhole74
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Default RE: APC Prop Balance

A very common problem with APC as well as other props. I have only ever had a few props balance out of the box even though many manufacturers claim they are pre-balanced. I just balanced 12 APC slow flyer props yesterday and only 3 had the hole drilled center, what a pain to balance but I got it done. On the larger ones, if the prop is too out of balance because of the hub, I toss it or take it back to the hobby shop. I used to have a Top Flight balancer but realized it was inaccurate. I now use a DuBro and it is a much better machine, besides, it will balance all my props reguardless of size. Good luck.
Old 03-21-2007, 08:51 AM
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Default RE: APC Prop Balance

That is a lot of weight.
I have use APC up to 20 inches and never had to do more than add a light coat of urethane to one side.
Is this just two propellers?
What happens after you fly.
Does the propellers still stay in balance?
Old 03-21-2007, 08:55 AM
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Default RE: APC Prop Balance

That's the story I got when I called APC. The guy swore the prop should have balanced on the hub with very little work. NOT!!!!! I think in the future I'll just start sending the junk back for replacement. If enough people do that perhaps they will upgrade their QA........probably not but it's a thoght.

ORIGINAL: bhole74

A very common problem with APC as well as other props. I have only ever had a few props balance out of the box even though many manufacturers claim they are pre-balanced. I just balanced 12 APC slow flyer props yesterday and only 3 had the hole drilled center, what a pain to balance but I got it done. On the larger ones, if the prop is too out of balance because of the hub, I toss it or take it back to the hobby shop. I used to have a Top Flight balancer but realized it was inaccurate. I now use a DuBro and it is a much better machine, besides, it will balance all my props reguardless of size. Good luck.
Old 03-21-2007, 08:57 AM
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Default RE: APC Prop Balance

More than just two. I've thrown 13 inch props in the trash because the hubs were so far out of balance. The pictures show what I had to do the get my latest 16 and 17 inch props to balance on the hub. Haven't experienced any failure of the add on weight in the air. Props stay in balance with no problem. I use the same method on wood props up to 27 inch as shown on the video.


http://www.dodvideos.com/don3.wmv

ORIGINAL: Geistware

That is a lot of weight.
I have use APC up to 20 inches and never had to do more than add a light coat of urethane to one side.
Is this just two propellers?
What happens after you fly.
Does the propellers still stay in balance?
Old 03-21-2007, 09:36 AM
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Default RE: APC Prop Balance

Just watched the video. I'll be darned! I have been flying R/C for just over 30 years. This is the first time I have ever seen that method of balancing. I haven't purchased any APC propellers for about 6 months. But, all of the APC's, except for the slowflyer props that I have used have been very easy to balance. I do think that for the price, you can't get a better prop. I'd agree that If we all start sending back out of balance props, APC would probably increase their QA.
Old 03-21-2007, 10:19 AM
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fancman
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Default RE: APC Prop Balance

I work as a millwright in a chemical plant and balance is very important to rotating equipment. Lot's of people are under the impression that if the tips are balanced then the prop is ok. NO WAY. I had a NX 26X10 prop from Airwild once that woldn't balance. When I called them on it they said as long as the tips balance then the prop is fine, as if hub balance didn't matter. Either they were just BSing me or they have much to learn also.


ORIGINAL: firstplaceaviator

Just watched the video. I'll be darned! I have been flying R/C for just over 30 years. This is the first time I have ever seen that method of balancing. I haven't purchased any APC propellers for about 6 months. But, all of the APC's, except for the slowflyer props that I have used have been very easy to balance. I do think that for the price, you can't get a better prop. I'd agree that If we all start sending back out of balance props, APC would probably increase their QA.
Old 03-21-2007, 10:31 AM
  #10  
Ed Smith
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Default RE: APC Prop Balance

First of all it is pretty dificult to produce balanced, injected molded props. There are too many variables such as the mix consistancy of the plastic, the maybe unequal pressure pushing it into the mold and probably many others.

I have used APC props at high rpm for many years of Pylon Racing. We must have them balanced. I have had to balance every one. I have not used the larger props but I think the general construction is the same. The centre hole that slips onto the crankshaft is a drilled hole it is not molded. The counterbore at the back of the hub is molded. This hole is the only hole that is true to the blades and square with the back of the hub. Now I am sure that when the shaft hole is drilled the prop must be in some sort of fixturing for accuracy. However it is still a drilled hole. It could be that the drilled hole is not dead centre in the body of the prop. If it was then the prop would probably balance. Maybe this is why APC claims its' props are balanced.

This is what I do. I drill the centre hole so that it is clear of the crankshaft. Usually the next standard size up from the shaft size. I then make up some sleeves from say K&S tubing that are a slide fit on the shaft and a tight fit in the c/bore.

I have noticed that on some of the electric props APC supplies plastic bushings for this purpose.

Ed S

Old 03-21-2007, 10:39 AM
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fancman
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Default RE: APC Prop Balance

Good thoughts but the bottom line is that I don't have the capacity to determine hole centers at home. The manufacturer should QA some props and get it right instead of sticking to thier story that their props are balanced. I've never had this problem with the smaller APC props and balance doesn't really concern me as much on my .46 engine but when swinging the heavy 16 and 17 in props on a gas engine you want your prop balanced and not just close. Should be simple thing to do but again I'm not a prop MFG so I don't really know how difficult it would be for then to get it right I have used the little pylon props also. It's a whole different world and those props balance easily.


ORIGINAL: Ed Smith

First of all it is pretty dificult to produce balanced, injected molded props. There are too many variables such as the mix consistancy of the plastic, the maybe unequal pressure pushing it into the mold and probably many others.

I have used APC props at high rpm for many years of Pylon Racing. We must have them balanced. I have had to balance every one. I have not used the larger props but I think the general construction is the same. The centre hole that slips onto the crankshaft is a drilled hole it is not molded. The counterbore at the back of the hub is molded. This hole is the only hole that is true to the blades and square with the back of the hub. Now I am sure that when the shaft hole is drilled the prop must be in some sort of fixturing for accuracy. However it is still a drilled hole. It could be that the drilled hole is not dead centre in the body of the prop. If it was then the prop would probably balance. Maybe this is why APC claims its' props are balanced.

This is what I do. I drill the centre hole so that it is clear of the crankshaft. Usually the next standard size up from the shaft size. I then make up some sleeves from say K&S tubing that are a slide fit on the shaft and a tight fit in the c/bore.

I have noticed that on some of the electric props APC supplies plastic bushings for this purpose.

Ed S

Old 03-21-2007, 12:58 PM
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Default RE: APC Prop Balance

By my calculation, at 9000 RPM your 1 1/4" hub is turning 33.5 MPH at the outside circumferance. Your 16" prop tips are travelling 428 MPH. This shows little chance of your weights flying off, but does it not show how much more important tip balancing is? Any correction of my calculations are welcome.
Old 03-21-2007, 02:25 PM
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Default RE: APC Prop Balance

For sure, tip balancing is most important but to eliminate all vibration from any prop the hub must be balanced also. The bigger and heavier the prop the more you need to have it totally balanced IMHO.

ORIGINAL: scratchonly

By my calculation, at 9000 RPM your 1 1/4" hub is turning 33.5 MPH at the outside circumferance. Your 16" prop tips are travelling 428 MPH. This shows little chance of your weights flying off, but does it not show how much more important tip balancing is? Any correction of my calculations are welcome.
Old 03-21-2007, 03:29 PM
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Default RE: APC Prop Balance

Hi!
Never ever add anything to a prop hup !!! Very dangerous when it comes flying off...!
What you do is to carefully file and sand the hub on the heavy side! This sounds perhaps to be dangerours too but most of the time you only have to remove so very little material that it will not weaken the prop.


Old 03-21-2007, 04:18 PM
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Default RE: APC Prop Balance

G'day Mate,
I have had the same problem with APC props in the 16", 17", 18", sizes, but I found it was MY fault not the APC props, when I enlarged the prop hole to fit the motor shaft, I was using a drill, as it turned out, VERY bad idea, can't get it drilled on centre.
Now I use a prop reamer, have not had to add or remove anything on the prop hubs, since I started using the reamer.

How do you enlarge the centre hole in your props?
Old 03-21-2007, 04:39 PM
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Default RE: APC Prop Balance

I always use a prop reamer in my drill press and I balance the prop before I drill the crank hole. It's the prop!!

ORIGINAL: alan0899

G'day Mate,
I have had the same problem with APC props in the 16", 17", 18", sizes, but I found it was MY fault not the APC props, when I enlarged the prop hole to fit the motor shaft, I was using a drill, as it turned out, VERY bad idea, can't get it drilled on centre.
Now I use a prop reamer, have not had to add or remove anything on the prop hubs, since I started using the reamer.

How do you enlarge the centre hole in your props?
Old 03-21-2007, 04:42 PM
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Default RE: APC Prop Balance

I don't thnk it's dangerous at all. We're talking way, way less than on ounce and if it did somehow come off (never has so far) the little piece of Velcro will just be lodged inide the spinner and my prop will all of a sudden be out of balance. I've tried filing the heavy side off and believe me it ain't pretty with half a hub gone. I'll stick to the Velcro.

http://www.dodvideos.com/don3.wmv


ORIGINAL: jaka

Hi!
Never ever add anything to a prop hup !!! Very dangerous when it comes flying off...!
What you do is to carefully file and sand the hub on the heavy side! This sounds perhaps to be dangerours too but most of the time you only have to remove so very little material that it will not weaken the prop.


Old 03-22-2007, 08:54 AM
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Default RE: APC Prop Balance

Fancman, I came across that video a couple months ago and think it’s a great idea. Have to agree if that the Velcro should happen to come off, no big deal.

And yes I’ve had the same issues with APC props and the hub being out of balance. Haven’t tried the Velcro method yet, always removed material from the heavy side of the hub.
Old 03-22-2007, 09:45 AM
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Default RE: APC Prop Balance

That video demonstration was very interesting. Seems to work well on very large props. What about 10" props?

Fancman: I find it hard to visualize how the hub being out of balance could make much difference, on an object that is 16" in diameter. Have you ever run an 'unbalanced' hub prop and measured the vibration, then run the same prop after balancing and again measured vibration?
Old 03-22-2007, 11:56 AM
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Default RE: APC Prop Balance

I have a vibration probe at work that I can check it out with. My feeling is if I can eliminate all the vibration then I should do so. I'm not saying that I expect perfect balance in every prop, only that it should be a lot closer than what I've encountered. Next time I get one way out of balance I will be sure to pass the problem back to my LHS or APC.


ORIGINAL: Kmot

That video demonstration was very interesting. Seems to work well on very large props. What about 10" props?

Fancman: I find it hard to visualize how the hub being out of balance could make much difference, on an object that is 16" in diameter. Have you ever run an 'unbalanced' hub prop and measured the vibration, then run the same prop after balancing and again measured vibration?
Old 03-25-2007, 04:55 PM
  #21  
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Default RE: APC Prop Balance

The Oily Hand, by Brian Winch in R/C Report had a very good article on prop balancing in
I believe the march issue. I have had problems, like you of late, with the prop hole off center, causing a out of balance hub. I have been using his method of balancing the hub for a long time, and it works for me. I rarely use a prop larger than a 14 inch. I use shot out of a
shotgun shell to do my balancing.

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