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Pop balance has me stumped

Old 05-21-2013, 04:04 AM
  #1  
maxflyer
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Default Pop balance has me stumped

I recently ordered a couple of bags of these slowflyer props from HK:

#OR001-00309B/9845 SF E-Prop 9x4.7 / 229x119.5mm w/ Adapters Black (5pcs/bag) = 5.38

I figured, how could I go wrong, for a buck-a-piece, even if they broke easily, it's a pretty sweet deal. My opinion quickly changed when I tried to balance one of them. I've been attacking it in spurts over a couple days, and I can't get this sucker to balance no matter what I do. I've deducted and added weight to the blades. I've sanded off the logo, reduced the thickness of the blade roots, and filed down the seeming heavy side of the hub so that it's no longer round. It always ends up with that filed-hub-side on the bottom - blades at 9 and 3 o'clock. even if I flip the prop over 180 degrees, it still swings around as though there's a huge amount of weight on the well-worked side of the hub. Assuming there isn't some super-concentrated Chinese mystical weight still located somehow within that well-worked side of the hub, the weight must be located in the leading edge of one blade, and across the hub on the trailing edge of the other. It just defies logic! There isn't much meat on these flexible fans to begin with. No matter which area of this prop I work, that seeming heavy hub side always swings to the bottom. One would expect any removal operations to be rather minor to gain an effect on a prop with this little mass. This is the first prop I've not been able to balance. It's eerie. Anyone had this experience with this particular brand?
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Old 05-21-2013, 04:22 AM
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flydiver
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I don't know about those particular props but there are some items I simply will not get from HK at all, ever. Some of their cheap knock-off props among them. Horrible balance. If you value your time at $5/hour they end up costing $6 each.
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Old 05-21-2013, 06:26 AM
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Originally Posted by flydiver View Post
I don't know about those particular props but there are some items I simply will not get from HK at all, ever. Some of their cheap knock-off props among them. Horrible balance. If you value your time at $5/hour they end up costing $6 each.
I've been using the $$$$ APC-E props. Got a whole box of them accumulated over the past 6 years. These props vary from an 8-6 to a half dozen 19X12 Wide Blades. Never had to balance any of them.
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Old 05-21-2013, 07:36 AM
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First of all ... 9 - 3 o'clock always ? is this with ALL props of this bag ?

If all - then sounds like balancer is not centred. I use the helicopter blade balancer - two threaded cones on a threaded bar ... the cones automatically centre the prop hub.

Second - on a slow fly prop - I would not sand any blade and especially never the hub ... as you approach centre - you increase dramatically the amount of material / weight to remove. My way to balance slow fly is purely tape to the back of light blade. It is possible with very small piece of metal to insert into one side of hub ... drill small hole and glue it in ... but drilling / sanding / modifying a slow fly hub is not advised ...

Nigel

Originally Posted by maxflyer View Post
I recently ordered a couple of bags of these slowflyer props from HK:

#OR001-00309B/9845 SF E-Prop 9x4.7 / 229x119.5mm w/ Adapters Black (5pcs/bag) = 5.38

I figured, how could I go wrong, for a buck-a-piece, even if they broke easily, it's a pretty sweet deal. My opinion quickly changed when I tried to balance one of them. I've been attacking it in spurts over a couple days, and I can't get this sucker to balance no matter what I do. I've deducted and added weight to the blades. I've sanded off the logo, reduced the thickness of the blade roots, and filed down the seeming heavy side of the hub so that it's no longer round. It always ends up with that filed-hub-side on the bottom - blades at 9 and 3 o'clock. even if I flip the prop over 180 degrees, it still swings around as though there's a huge amount of weight on the well-worked side of the hub. Assuming there isn't some super-concentrated Chinese mystical weight still located somehow within that well-worked side of the hub, the weight must be located in the leading edge of one blade, and across the hub on the trailing edge of the other. It just defies logic! There isn't much meat on these flexible fans to begin with. No matter which area of this prop I work, that seeming heavy hub side always swings to the bottom. One would expect any removal operations to be rather minor to gain an effect on a prop with this little mass. This is the first prop I've not been able to balance. It's eerie. Anyone had this experience with this particular brand?
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Old 05-21-2013, 09:37 AM
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If the same blade always drops to the 6 o'clock position, even when you reverse the prop on the balancer, then it's not the balancer at fault. It must simply be that one blade is heavier than the other. The heavy blade is probably slightly thicker and/or the hub may be drilled off-centre.

Either way if your efforts at balancing fail and one blade remains significantly heavier then probably best to scrap the prop. Cheaper is not always better!
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Old 05-21-2013, 12:12 PM
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Originally Posted by JetPlaneFlyer View Post
If the same blade always drops to the 6 o'clock position, even when you reverse the prop on the balancer, then it's not the balancer at fault. It must simply be that one blade is heavier than the other. The heavy blade is probably slightly thicker and/or the hub may be drilled off-centre.

Either way if your efforts at balancing fail and one blade remains significantly heavier then probably best to scrap the prop. Cheaper is not always better!
Agreed .... but he is getting 9 - 3 o'clock not 6 ...

OK - I have question for original poster ... have you drilled the hub for larger shaft ?

Nigel
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Old 05-21-2013, 12:24 PM
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Originally Posted by solentlife View Post
Agreed .... but he is getting 9 - 3 o'clock not 6 ...

OK - I have question for original poster ... have you drilled the hub for larger shaft ?

Nigel
Ahh, yes, i see what you mean! It does sound like the hub is drilled off-centre.

Maxflyer.. DO NOT remove material from the hub, this is really asking for trouble. If the prop is drilled off centre then probably nothing can be done other than to scrap them and put it down to experience. Props is one area that I dont do cheap cloned parts, too dangerous for my liking, and good quality props arent very expensive.
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Old 05-21-2013, 02:39 PM
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Thanks for your input guys. I've balanced a lot of APC props, no problem. I know it's not my balancer. I have not drilled the hub, but am using one of the inserts. I ream them if necessary. Never drill them. Off-center hub - didn't think of that. It would make sense. At this point I wouldn't use this prop. I'm just determined to get it balanced, but it appears impossible. I considered these things throwaways. If they were no good, it,s just ten bucks for the risk. These things are flimsier than anything else I've purchased so far.
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Old 05-21-2013, 04:33 PM
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Ya see? Some HK is just junk. It would be good if you post the BRAND NAME so others can avoid them if they care to.
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Old 05-21-2013, 07:07 PM
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I have had some props that would balance in the 9-3 spot, but still seemed to run fine.
The props that had a definite heavy blade, I have balanced by putting clear shipping tape on the back surface of the prop, then they ran very nice.

I had an unbalanced prop on a geared Himax motor, get the ESC so confused, it stopped the motor, then restarted in flight, without touching throttle stick. It was a little scary at low altitude. Balanced the same prop, it ran fine, no problems.

The HK carbon fiber folding glider props appear to be very high quality. I have 3 sets, all of them, were perfectly balanced, track perfectly, and really bite the air, great performance. Great looking also, I am totally happy with them.
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Old 05-21-2013, 07:27 PM
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Originally Posted by maxflyer View Post
Thanks for your input guys. I've balanced a lot of APC props, no problem. I know it's not my balancer. I have not drilled the hub, but am using one of the inserts. I ream them if necessary. Never drill them. Off-center hub - didn't think of that. It would make sense. At this point I wouldn't use this prop. I'm just determined to get it balanced, but it appears impossible. I considered these things throwaways. If they were no good, it,s just ten bucks for the risk. These things are flimsier than anything else I've purchased so far.
I have a sport model .... foam copy of the Pilot QB10 I made up. It goes through props like nobody's biz !! So I bought a bag of cheapo props of HK ... (Flydiver .......... they are UNBRANDED ....) But they are so flimsy that I'm afraid to run them at speed. But balancing - yes they were of - but tape on back and fine.

Nigel
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Old 05-21-2013, 10:17 PM
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Sorry about the brand. I didn't think there was one. Just what looked like two "Y's" side-by-side, in script, with one flipped upside down. Now, in the light of day, I find "Haoye" on the back of one blade, so I guess the logo is actually supposed to be "HY." Haven't tried to balance a second one yet. Both my bags are 9 x 4.7's. I do commonly diamond-file a bit off any APC hubs or roots that are off-balance, but not enough to lose integrity. I also polish out the marks with a rotary fiberglass brush. I not satisfied to balance just the blades. An out-of-balance hub can still create significant vibration at high RPMs. I'm probably a bit too anal about it.
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Old 05-22-2013, 12:26 AM
  #13  
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Default Prop #2

OK, tried wildflyer's suggestion, using the packing tape on #2. This time I only balanced the blades. Didn't touch the hub. I did start on the heavy blade by filing off the logo, but it wasn't effective. With blades balanced and sitting at 9 and 3 this prop exhibits exactly the same behavior as the first one. If I flip the prop 180 degrees it's hub heaviness again flips it back 180 degrees to the former 9 and 3 position. If the hub is drilled off-center, I can't detect it, but somewhere in these props there is enough heavy material to exhibit, in effect, severe hub imbalance. Will report further as I run through them, but it looks like I won't be blowing anymore money on this line. BTW, that's two layers of tape.
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Old 05-22-2013, 07:07 PM
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OK guys, I've finished attempting to balance a full pack these things. They all exhibit the same flaw. Just to be consistent, I used the same method on each one. Packing tape was used to get a 9 o'clock 3 o'clock balance. The sprue stub was removed from the hub. The side of the hub that is always heavy was filed until the mold ridges were smoothed out, to remove a tad of weight without reducing integrity. From this point the reactions were the same for all props. The props would remain in a strict 9-3 balance in both positions, but when slightly offset, would flip around, like a hull-up boat in the water, to the heavy side, which is always the same relative side for every prop. The speed of the flip- flop is quite rapid, the effect of which seems to act as though that one side of the hub is extremely heavy. I suspect that the molding at the roots is involved as well. I tried mounting and running one of them. They are probably flyable, but some vibration is apparent. My personal feeling is that NO vibration should be introduced into the propulsion system, and because these things CANNOT be balanced, I would not purchase more of them. I may try to run them on my foamie 3D trainers, but will be very vigilant for possible damage from the vibration.
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Old 05-22-2013, 07:47 PM
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Make sure that the prop aligns along the tip-hub-tip axis when viewed from the front of the prop. That would be a line starting at a specific point on the first blade tip, running through the dead center of the hub hole, and ending at the exact same blade tip point on the opposite blade.

I have had props that deviated from the blade axis and which balanced at the 3-9 position but always with the same side of the hub up. If I turned the prop over 180 degrees it would again balance at the 3-9 position until rotated slightly off horizontal and would then roll over to the opposite 3-9 position.

If this is the case, they can't be fixed.

Rick
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Old 05-22-2013, 07:50 PM
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Try this; when the prop balances at the 9-3 spot, measure from the tips to the table. Then turn the shaft 180 degrees, hold the prop in this position, and measure from the tips to the table.

My guess is that, somehow, the prop blades are 179 degrees from each other on one side and 181 degrees apart on the other side.
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Old 05-22-2013, 08:36 PM
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Originally Posted by Wildflyer View Post
Try this; when the prop balances at the 9-3 spot, measure from the tips to the table. Then turn the shaft 180 degrees, hold the prop in this position, and measure from the tips to the table.

My guess is that, somehow, the prop blades are 179 degrees from each other on one side and 181 degrees apart on the other side.
Being the slow-fly with the 'bent shape' that's a distinct possibility

Nigel
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Old 05-22-2013, 10:07 PM
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Originally Posted by Wildflyer
Try this; when the prop balances at the 9-3 spot, measure from the tips to the table. Then turn the shaft 180 degrees, hold the prop in this position, and measure from the tips to the table.

My guess is that, somehow, the prop blades are 179 degrees from each other on one side and 181 degrees apart on the other side.
Originally Posted by solentlife View Post
Being the slow-fly with the 'bent shape' that's a distinct possibility

Nigel
This wouldn't necessarily prove the 181 deg vs 179 deg (or similar)...

Off-center hole in the hub could give the same result.
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Old 05-22-2013, 10:26 PM
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Default mystery solved

Well, you guys nailed it. These props are off-axis on one side. I constructed a simple jig that pins the prop to a center hole. Up on the left, a blade is aligned with the edge of the jig. Down on the right, a pencil mark was made, delineating the lowest reach of the opposing blade. The prop was then spun 180 degrees and the same measurement was taken again. There was approximately a 2 MM difference between the blade positions. You wouldn't think getting two opposing blades aligned along a common axis would be that difficult, would you? Oh well, as in everything else...you get what you paid for. glad I only dropped 10 bucks. An HK lesson learned the hard way, but perhaps worth it for future purchases.
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Old 05-22-2013, 10:42 PM
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possibly just pulled from the mold while the plastic was still too hot and the prop sagged.

Bad QC if not a bad mold.
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Old 05-22-2013, 11:48 PM
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Just opened the second bag and measured one. It had a 3 MM error! Does beg the question...are these priced the way they are because HK KNOWS they are defective, and a lot of unknowledgeable people will buy and use them anyway? I looked on HK to try to leave a review. The "write-a-review" button is grayed out and not available to me, even though I am logged in.
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Old 05-24-2013, 12:00 AM
  #22  
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Default Hub Hack

Just for grins, decided to see if it was possible to actually get one of these cheapies to balance. Look at the amount of hot glue it took to get a complete radial balance! This is the only one of four I've tried this with so far that has worked. Three others needed even more glue than this and I just aborted my attempts.I'm now wondering if that much glue would stay in place on the airplane.
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Old 05-24-2013, 12:25 AM
  #23  
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maxflyer
The position of that weight would suggest that the hub (or rather the hole) is indeed off centre. It no other weight has been added elsewhere it suggest that the blades themselves are reasonably well balanced.
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Old 05-24-2013, 12:41 AM
  #24  
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it will be dynamically out of balance... differential load on the prop shaft which might bend some of the weaker shafts. Then it starts wobbling...
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Old 05-24-2013, 02:28 AM
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These things are more or less all similar. The blade with the logo is very heavy, and the same side of each hub is really heavy. The light blades have required 2-3 layers of premium pkging tape to get a 9 - 3 balance. And as indicated earlier, they are all offset from the centerline. I'm not grasping why the one pictured would be dynamically out of balance. If the radial balance is neutral, it would seem that only bad tracking would introduce a dynamic imbalance. Of course, I have not checked any of them for tracking accuracy. These things are real dogs. I was finally able to review them on HK, but it has not shown up on the site. Interestingly, all reviews for these props, with a couple of 4-star exceptions, are rated 5 stars!!!!! Either, a lot of hobbyists are not the sharpest pencils in the box, or HK is manipulating the reviews.
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