Rotor Balancing

PW_Plack

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Does this method offer a benefit over Sport Copter's simpler system using reflective tabs? I can see how it might be easier if you wanted to test in flight.
 

Mike G

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Paul
For simplicity it's hard to beat the Sportcopter method but it requires some sunshine and there ain't a lot of that around here in winter.
There is some concern about potential unbalance especially if one broke off and also Peter seems to be having some concerns about air flow around the tip which is the first time I've heard this but he is using them on a helicopter perhaps that's relevant.
I use these tip LEDs quite often and there's never been a problem but I use them mainly on gyros, I've used them on a Dynali and an Angel helicopter once.
They need to be fixed with a screw/bolt to the blade tip and not all gyro blades (eg AutoGyro) have a threaded hole at the tip for this.

As you realised the big advantage is that you can check tracking in flight without having to operate anything like a mirror or strobe gun while your flying. For helicopter pilots who have both hands full all the time this is an advantage.

Don't forget that all these methods (flag, strobe, mirror, LEDs) only get you to the point where the blades are tracked visually to follow the same tip path and as any helicopter guy will tell you you often have to detrack a rotor to get the smoothest ride. To do that you need a dynamic balancer.

I had an interesting experience in Senegal (Africa) last month, I tracked the rotor of an MTO in flight using a PB3 balancer down to below 0.1IPS and the owner wanted to compare my setup with his using the flag method. It turned out that my setup with virtually zero measurable 1/rev vibration in flight gave a 1cm difference in tip path using the flag method at 180 rpm pre rotation speed.
That started a debate about which was correct and the owner asked me to fly both setups to see which was most comfortable. Honestly I couldn't feel a big difference. I now have enough experience balancing gyros to be able to seperate by feel the 1/rev from the 2/rev vibration and while I could feel a slight reduction in 1/rev with my setup the 2/rev was so dominant that it masked any gain due to my dynamic tracking method.

So I would say that tip lights are generally easier to operate than any other method, it's a one man hands off operation and can be done in flight. The results are perhaps not perfect compared to dynamic tracking but while we have such dominant 2/rev vibration on our Eurogyros (I can't comment for US gyros I've never balanced one) they get you cheaply into the ball park.
Mike G
 

JAL

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Do you mean you tracked the blades using the balancer than put the tip lights on and saw there was a 1cm difference in the blade tip paths
 

Rick E

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If ever you decide to come to Australia Mike G I reckon we could keep you pretty busy!
 

500e

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Mike would really like to see a set up balanced like I suggest on a autogyro.
The time spent faffing with T&B can be huge we are convinced the idea works
Have a read I appreciate we are talking huge difference but basics are the same, you have to log in to read some of the info.
http://www.rwas.com.au/blade-balancing.html
 

Mike G

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Jordan
No, we tracked the rotor using the PB3 in flight with different shims to change the blade pitch.

you can see the PB3 cables running down from the top of the mast, and my tablet strapped to my left leg, that's me holding my wig on.

Then we checked the tracking using the owners method (that scared me sh...less). He tapes a Stanley cutter type blade to each blade and coats each one with a different coloured nail varnish.


We couldn't use the tip LEDs because the AutoGyro blades don't have any threaded holes at the tip.
He then pre rotates and a second guy approaches the blade tip path with a cardboard "flag".

You can hear when the two meet. Then you look at the flag and see two razor slashes of different colours giving you the distance between the two blade tip paths.
We did this the first time with my tracking set up and that showed a 1 cm difference and then returned the rotor to his optically correct setup (ie the two razor cuts were on top of each other). I flew the balance runs with the PB3 and again with the original optically correct setup and as I say in the previous post I felt the difference was there but it really wasn't that obvious because of the dominating 2/rev vibration.

Rick E
Don't tempt me I love your country, was there many years ago and regret leaving.

Peter
I've seen that link before it's really impressive what they do. I think there's a big difference between balancing our typical gyro rotors and the problems those guys and you face with commercial helicopters.
Your rotors are much heavier, there are more adjustment possibilities and you're looking for a degree of interchangeability that we don't really expect with a gyro and you have different rotor responses for hover and flight. Also helicopter hours are so expensive that it probably pays to spend time statically tracking and balancing rotors on the ground. With a bit of practice you can do a balance run in a gyro within a short low level circuit, 5 minutes tops.

The other thing I've noticed is that rotors supplied by the major European manufacturers (Magni, ELA, AutoGyro, Averso, Trendal etc) are surprisingly well matched out of the box. Of all the rotors from these manufacturers that I've balanced none were really bad and most were below 0.5 IPS before I started. The worse was my ELA when I bought it second hand because we repaired the leading edges and repainted the blades so they were badly mismatched and I balanced them without even a static balance.

There is an interesting comment in the link about water in the blades, one of the owners I worked with suggested that with his aluminium extruded blades he thought that on humid days in the morning water condensed inside the blades and was centrifuged out slowly during the first flight because he noted that vibration on the first flight of the day was often bad and got better on the second flight. I could never establish if it was true but it's worth considering if you ever have a similar problem.

There is an Aviomania in France with one of Ernie's rotors (I think) that I want to balance when the weather improves. I really want to see the difference with the typical Eurogyro.

Mike G
 

500e

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Not had that as far as I know, heard that rumour a blade had water in that froze & blew a skin but we think there was another reason for damage.
Had condensation in fuel tank on a 300 that had about 5 galls in checked drains no water, flew it off 300 Ft silence :suspicious: when we removed cushions we looked in tank the empty portion of tank still had water adhering to sides, drained about 1\2 a cup full from sump, Always look in tank if there is any chance of condensation now.
Love the BLADES though :whoo:
I hear what you say regarding balance but would still like to try it just out of interest
 

JAL

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Yikes! Not sure about "flagging", I would be tempted to do it old school and use stick on reflector tabs and a bright torch.

How heavy are those LEDs. Could you attach them to a length of say 1 inch flat aluminium that is angled at one end (to attach the led) and tape the aluminum to the blade just like they did with the stanley knife blade. You may have to wrap the tape entirely around the rotor blade.
 

Mike G

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JAL
25 grammes. I wouldn't recommend trying to tape them on.
Here are some photos of the prototype LEDs on a Calidus,

we replaced one of the rivets with a threaded rivet


and made a 90° bracket out of Al.




Smart Avionics now offer 3D printed straight and 90° brackets.
See the Smart Avionics "notes" paged on this link.
http://www.smartavionics.com/rotor_tip_led_notes.pdf

Mike G
 

Uncle Willie

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Please! Do not take rotor balancing Lightly! (Pun!)

At 200 rpm, a 28ft. Rotor generates 190 g's at the tip.
A 1 ounce light assembly will generate 12 pounds of force on the mounting bracket.
If it comes loose, it will fly off at 200 mph and the remaining light will cause a serious imbalance.

At a 350 rpm flight speed, you will be looking at 585 g's and 37 pounds of force.
This may exceed the strength of 3D printed brackets and Tye Wraps.

Be sure to do your homework before concluding that a couple of wraps of duct tape should be good enough to hold it!
 

Mike G

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Uncle Willie
If you are addressing your message to Smart Avionics or myself, please read the Smart Avionics link I gave.

http://www.smartavionics.com/rotor_tip_led_notes.pdf

It explains the level of forces involved and that the brackets are limited to 1500G. There is even a graph giving G loads for different rotor diameters and speeds.
I think we have done our homework.

If you are addressing it to the forum in general I agree with you, I didn't like the "flag" technique with the duct tape and razor blade either. The tie wraps in my photo that you are apparently referring to were (as I explained) a prototype and did not see the centrifugal force, they only had to withstand the aerodynamic drag force.

Mike G
 

Uncle Willie

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My advisory post was directed to the forum at large. Sorry for any misunderstanding.
There are plenty of ways to redneck the mounting by underestimating the forces generated by a spinning rotor.
As long as the user understands and takes the physics under consideration, they should be fine.
Your decision to advise the user to avoid using the lights as permanent tip lights is commendable.
 

Mike G

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Uncle Willie
No problem, as I said, I agree with your warning to others to beware.
Mike G
 

timdrnec

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I've recently rigged and have been using the Smartavionics LED's on my Helicycle and they are working a treat. Because I use a flathead bolt as a retainer (as well as the final tip weight adjustment...) I had to make my own brackets out of Delrin, but the lights themselves are very bright and easy to see even in the day with lots of snow on the ground. I've had the ship flying at 80kts with them and don't sense any ill effects from the aerodynamics of the housing. They made getting the blades in track a snap, very happy with them

Tim Drnec
Helicycle N202AP
 

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Mike G

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Tim
Your brackets look really slick, are they 3D printed or machined from solid?

Brent
Excellent idea and cheap, I'm all for it. I suppose you have different colors?
Mike G
 
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