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HomeScaleAircraftScale HeliScale Helicopter Main Discussion › Blade balancing
03-19-2015 01:05 AM  3 years agoPost 1
ssmith512

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Indianapolis, IN USA

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OK. I cant figure this one out for the life of me.

For my Cobra I took a set of standard Align 800mm carbon fiber blades and painted them flat black. Longitudinal CG is within 0.5mm between each blade. Total blade weight is within 0.01oz of each other on my cheap little table top digital scale. Hanging each blade on a rod through the bolt hole and each blades hangs the same, so chord CG must be pretty close (I think). Putting the blades on a seesaw balancer and they level out nearly perfectly.

So I bolt them up to the mechanics test flying platform and it shakes pretty good during spool up and continues to shake once it is upto flying RPM (1200rpm). I do nothing but remove those blades and install a set of Rail 696mm carbon fiber blades from one of my 3D pod and boom machines that I have never even checked on the balancer and BINGO, it is now as smooth as I could hope for.

I dont get it. The metrics would indicate to me that the painted Align blades should be (relatively) vibration free, but my simple blade swap test clearly shows that the painted Align blades have "something goin on" that is causing a predominate shake.

What am I missing? I wonder if it was something I did during painting? Any help is greatly appreciated as I am sure that will be painting blades on future projects.

Thanks in advance.

Steve

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03-19-2015 01:35 AM  3 years agoPost 2
Keygrigger

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Mississauga, Ont. Canada

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Things you might look at: Blade washout, tension in the grips, tracking, and last, balance the blades in the head on a main shaft using a DuBro prop balancer. They might statically balance but dynamically, they might be off. Mojave had that happen to him at HSM last year and it really does make you go Whaaaaa....???? A tracking error can cause some shaking because of air disturbance and tension can do some nasty things during spool-up and spool-down. Washout might be a bit harder to detect but it will give you issues for certain. Trimming would be very hard to accomplish. Hope this helps.

Don

PS: I used that prop balancer to balance Short Course and Buggy tires and it did make a difference in vibrations. They drove very smooth.

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03-19-2015 07:03 PM  3 years agoPost 3
spy29

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USA

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Its the ROBAN AH-1w right?.. They are all like that..shakes.. blade pitch always changing. Slop eeverywhere..it will drive you crazy and end up doing damage while assembly and disassembly...or even worse crash.. ther was some threads on roban mechs poor quality, but.. maybe its best you read it. the "sponsored" people said all this is builder error..a big joke,because Robans "newer"upgraded parts mechs seems to address most of the old._"builder error" parts... nothing except the belt tension and ball links are adjustable. for the $2k we should not have to go through re-engineering, machining,re-fitting,and at the least the included parts should have some quality. .just my 2cents opinion..or should I say $2k opinion?.... Ill just stick to my old hirobos and varios.. more flying more fun.

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03-19-2015 07:21 PM  3 years agoPost 4
ssmith512

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Indianapolis, IN USA

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Thanks Don.

Sighting down the leading and trailing edge of the Align blades does not reveal any washout in the blades. Tracking was good. Blade tension was what I typically run and was similar to the Rail blades I tried that did not cause a vibration (swapping blades was literally a 3 minute operation - didnt even turn off the TX, just unplugged the main battery pack for safety, once the Rail blades were on, plugged the battery back in and hovered). What I didnt do was try different blade tension with the painted Align blades, just didnt think of it as once the Rail blades showed no vibration, I immediately figured the painted Align blades were the issue and not a blade tension issue. And dynamic balancing: I used a seesaw blade balancer, I figured that would be the same as the prop balancer (albeit without the head, but the heavy blade wold still fall). The blades balance out level on the seesaw balancer.

It is definitely a head scratcher for me.

Steve

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03-19-2015 07:49 PM  3 years agoPost 5
ssmith512

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Indianapolis, IN USA

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spy29,

It's a shame you had a bad experience, but my experience so far as been nothing but enjoyable. I've read all the threads. Read them many times and I still made the decision to buy one. My single issue I have is not at all related to the Roban mechanics. It is an Align blade issue, and might very well be an issue I created when I painted the blades. My mechanics are very smooth and run quite true with the Rail blades. The short flight I had with the Rail blades put a smile on my face. A few more flights of the test bed and I will have the comfort level with the mechanics I need to install them in the completed fuse.

Maybe the difference between my experience and your experience is that I "built" my mechanics and did not simply "assemble" them. There is a big difference between "building" something and "assembling" something (IMO). Anyone who simply "assembles" them, hoping they fall together without issue, is either naive at best or kidding themselves at worst.

Steve

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03-19-2015 08:23 PM  3 years agoPost 6
Keygrigger

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Mississauga, Ont. Canada

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I have painted a number of blade sets, two, three, and five blades. I ran the blades before painting them and I never had a single issue with any blade sets I tried. I am running Spin Blades 600mm SS Scales on my 500MD TD, Rotor Tech SS 600mm's on my AS350, and Rotor Tech 550mm symmetricals on my CH-139. I balanced my blades before and during painting so that they were never more than .02gr. off of each other. Picky, yes, results, you bet. I have talked to many that have had as much as .5gr. difference in blades and never had an issue. I like to keep mine really close to perfect as I can get them. I still feel that I need to spend an afternoon with a high power light, reflective tape, and some cool sodas to go over the tracking from scratch just to make sure. Hope you get the blades ironed out soon.

Don

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03-19-2015 09:30 PM  3 years agoPost 7
ssmith512

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Indianapolis, IN USA

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I'm like you Don, I like to get them as close as my measuring tools will allow me.

I did not check balance or CG prior to painting. A new set of blades will surely fix it (as has already been proven with my blade swap test).

Just bothers me. The measurements say those Align blades should work. But the real world says otherwise. At some point, I will spend the time and figure out why they dont work, even it requires me looking like a dork and determining I did something incorrectly (which is more than likely what I will find).

Thanks again for the help and suggestions.

Steve

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03-20-2015 02:22 AM  3 years agoPost 8
Calil

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Brazil

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Spin blades have asymmetrical in black and grey!

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03-20-2015 03:41 AM  3 years agoPost 9
Mojave

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Palos Verdes, Ca. USA

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I like Spin blades, but they are very poppy. They are very flexible and make a lot of lift at very low AOA. I ran them on my 700 AS350 with 1400 rpm HS and they hovered around 3.5 degrees of collective.
Barry

All helis and planes have an expiration date stamped on them...you only find it after you crash!!

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