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HelicopterMain Discussion › Blade balancing
AirWolfRC

rrProfessor

42½ N, 83½ W

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never heard of the tennis racket effect apart from when hitting ground after poor serve.and the effect is a knackered racket or dent in the grass
"tennis racket effect" is what makes constant speed propellers want to go to flat pitch if the pitch actuator breaks free. In pre-WWII aviation, you will see "hockey pucks" at the prop hub to offset that tendency. The solution after that was to just make stronger actuators and gear systems and forget the weights.

Tail rotors on many full size helis have such weights built into the system. Often the weights are positioned so the "neutral position" is for a tail blade pitch required for normal flight so the pilot doesn't have to fly with his foot on the rudder all the time.

04-19-2017 06:15 PM
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EEngineer

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TX

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"In pre-WWII aviation, you will see "hockey pucks" at the prop hub to offset that tendency."

I saw a video of that on TV.....

They were re-building an old Lysander...and they touched on that subject....was very cool.

Logo 600SXs, 700XX, 800XX

04-19-2017 06:17 PM
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Heli_Splatter

Key Veteran

Silver Spring, MD by way of Sidney, Ne - USA

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Just a thought;

There is a right way and a wrong way, there is no almost right way.

04-19-2017 06:18 PM
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MattJen

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UK

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it would be interesting to see if any updates have been done from that report Airwolf, as it was written in 2003.

cos it is interesting they acknowledge that dynamic balancing is still better but Static is quicker..

Dynamic balancing is always the final solution Static balancing procedures do not replace dynamic tuning procedures, but augment the dynamic tuning process. Dynamic balancing accommodates any cause for imbalance in the entire rotating system.

not quite sure how you'd do it on our models spinning at 2500rpm

All The Best

04-19-2017 06:32 PM
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EEngineer

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TX

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"I still stand by my findings that by adding weight to the tip you change the c of g and alter the blade performance on a large heavy scale model...and at different rpm you will induce vibes, even if it is momentry, over time it will affect bearings and stress out parts of the machine.. "

I never doubted that....

I was just in disagreement with your description of the physics terms you used to describe what's causing it.....

For me, carefully balancing the blades(both mains and tail) on a "seesaw" balance(AC and house fans off) seems to be sufficient.

With the tail blades, I carefully "sand" the heavy blade tip(even the hub, if the blade weight differs a lot)....with the mains, I add "stripes".

With regards to blade tracking, I ensure during setup that the blades will rotate orthogonally to its main-shaft....easy with Logo rotor heads(they have a "flat top" on the rotor)...and I use turnbuckle swash and grip links....and use the "blade tip foldback" method to achieve 0-pitch @ mid-stick.

Works great and is repeatable from heli to heli.

Have you experimented with main blade damping?

Sometimes during spool-up, there can be an RPM point where there's more vibration....other point where it's smooth.

Damping?

Logo 600SXs, 700XX, 800XX

04-19-2017 06:40 PM
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EEngineer

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TX

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"2500rpm"

Mains?

Did you get a TDR-II?

Cool.....

Logo 600SXs, 700XX, 800XX

04-19-2017 06:42 PM
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MattJen

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UK

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EE
I have never flown at 2500,my machines are far to big and heavy to reach that, although 2.5 meter blades moving at that speed would make an interesting expensive experiment, I have seen many display pilots at rotor live in Germany go well above that, in the early days a fellow flyer was testing blades and rotor heads to the point of failure as he wanted to develop a turbine camera platform, his findings were very insightful as he uncovered on the first edition of the Trex 700 a design flaw in the cap screws, they were big chunky bolts but they only went into the grip by a small amount of turns, result was at certain headspeeds the blades let go, looking back through the forums you can probably see posts of people reporting this..

He spent thousands testing parts to failure in a controlled environment with controlled results, I learnt a tonne about how and why things work on a helicopter, when I was flying comp F3c I was looking for perfection in the hover and aero's, for those who flew F3c they will understand where I am coming from, it was constant experimentation to get the right constant head speed, the correct roll rate, the correct tracking in FFF, ( adjusting boom fin, different paddles etc) I learnt a hell of a lot. ( this is before high tec FBL units of today)

When it came to my large turbine longranger one of the things I found with Vario is people in youtube videos were spending thousands on these machines and had vibe problems, tails letting go,frames cracking,premature bearing wear etc,I spent days, weeks, months, getting my Zealous longranger right, limiting any vibration I could..

this is where I learnt about the balance on the c of g, especially in the event of the first FBL units where any vibrations would take you out of the sky.

with 9 scale trophies won over the time I flew comps I must have got something right LOL.. shame I lost all my models in a lypo fire in 2014.

As said before, really enjoyable thread

All The Best

04-19-2017 07:03 PM
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AirWolfRC

rrProfessor

42½ N, 83½ W

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cos it is interesting they acknowledge that dynamic balancing is still better but Static is quicker..
What they mean by "dynamic balancing" is to mount some accelerometers and go fly - - - not this Moment of Inertia stuff.

04-19-2017 07:20 PM
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EEngineer

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TX

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"I was flying comp F3c I was looking for perfection in the hover"

Used to fly F3A....I can appreciate that.

What about wind turbulence?

"with 9 scale trophies won over the time I flew comps I must have got something right LOL.. shame I lost all my models in a lypo fire in 2014."

Outstanding....I mean the scale contest wins....Nats?

Best your models in the fire than you/family....

A friend of mine's apartment complex caught fire, a fireman wouldn't let him enter his place to get some of his "stuff"...

He yelled "My baby's in there!"......so the fireman let him in.

He emerged carrying his pattern plane(with Tx)....the fireman tried to have him arrested.....

We still laugh about that to this day...."My Baby".....LMAO

Logo 600SXs, 700XX, 800XX

04-19-2017 07:20 PM
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MattJen

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UK

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He yelled "My baby's in there!"......so the fireman let him in.
He emerged carrying his pattern plane(with Tx)....the fireman tried to have him arrested.....
We still laugh about that to this day...."My Baby".....LMAO

now that is funny, sad but funny.

All The Best

04-19-2017 09:32 PM
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