Astar Main Rotor Balancing

[IFlySometime]

2 hours ago, DGP said:

I would say you are just noticing ground effect roughness as the air under the ship builds and spills...that is pretty normal in all landings...try hovering out of ground effect for a comparison.

Good point, maybe its just me. Hover and forward flight are great. I guess we’ll see once we pack it full of mouth breathers or with heavy sling loads. Thanks for the help.

 

 

 

[ray]

One thing to note. The AS350,  due to the inherent design of its swashplate, will produce a 3-per rev. On Bell/ Agusta aircraft, the swashplate is shimmed snug. On the AS350, it is not. A proper swashplate shim will allow you to rotate the center 'cup' around the mast, but have minimal up and down play. It's because of this that the aircraft has hammers installed to absorb the inherent 3-per. If it's smooth in flight, then it's good. If you're only noticing a little bit on descent,  it isn't necessarily abnormal, unless it's  really shaking the aircraft apart.

[CM119]

On 5/6/2021 at 9:20 PM, ray said:

One thing to note. The AS350,  due to the inherent design of its swashplate, will produce a 3-per rev. On Bell/ Agusta aircraft, the swashplate is shimmed snug. On the AS350, it is not. A proper swashplate shim will allow you to rotate the center 'cup' around the mast, but have minimal up and down play. It's because of this that the aircraft has hammers installed to absorb the inherent 3-per. If it's smooth in flight, then it's good. If you're only noticing a little bit on descent,  it isn't necessarily abnormal, unless it's  really shaking the aircraft apart.

There are limits when setting up the swashplate on the bench and the MRV and MET has a fairy tight axial limit on the low end, I think it’s around .003” if memory serves.  The last thing you want is it set up too loose that’s the number one reason they get pulled from service due to damage to the stationary star and / or the uniball being smoked out from the shims, spacer and cups spinning / scoring the surfaces of each.  That said I’ve never seen one set up “tight” with no axial play or the cups pinching the ball, it would have to be ridiculously tight to induce a 3 per but I guess it’s possible.  You do have to keep it clean and lubricated with approved PRF-23699STD, and NEVER add cut shims like some people do, always replace the cups if it’s too loose and it should come back to almost exactly where it was set on the bench. You also shouldn’t ever have to remove shims if it was set up properly on initial install either if cups are replaced.

[CM119]

On 4/21/2021 at 10:54 AM, IFlySometime said:

Looking for some tips to get a good main rotor balance on the Astar. My experience level on them is low but im rapidly fighting the wolves. 
We use the microvibe and using its instructions along with airbus you first setup ground track and take out ground lateral vibrations. Easy enough. Then hover track and hover lateral. Also easy however my issue is that hover balance is nice and smooth the ground track and balance  is no longer smooth. Normal or am I missing a step? 

When bending tabs, if you need 3 degrees tab on one blade do you bend both tabs 3 degrees or do you split it and either bend one 3 degrees or both 1.5 degrees? 
 

One more... on descent, it has a real nice three per rev vibe. Only noticeable in descent. I’ve checked everything recommended for three per revs. Had it on jacks and checked the gear etc. Hammers? Its a B3e with post mod hammers. With the washers. I tried removing some washers but was hard to say if it got worse or better. 

 

For the three per on descent the most common cause is ball joints / star flex bushes.  When they’re worn out the lead lag action during a power setting reduction can be bad enough you can get a three per so bad you can hear it from the ground.  Your ground readings are going to change as you fly and adjust, with microvibe 2 you have to follow the regime, if your hover and ground readings are good everything else should be just tabs if the head is rigged right and the elastomers and blades are healthy.   Hope this helps. 

[atari]

And how about balancing an Astar tail rotor assembly? What tricks d you guys have? 
I've had them done in just a handful of runs and some others up in the late tens…

Things that you guys look for in the ones that are giving a hard time balancing?

[ray]

Make sure the tail rotor is in track. Place a piece of masking tape on the horizontal stab and note where the T/R blade lines up. Then rotate the assembly until the other blade is at the stab and see where it lines up. Try and get this as close as you can before balancing a t/r.

[Superwrench]

I am curious what the general thought is on this method.  It is a super common practice, that is not in the manual.  I have done it many times, and still do occasionally.  I have on many occasions had hard tail rotors to balance after setting the track, so I loosen the tail rotor bolt, retorques with tool "Z" ( tail rotor block) and 2 runs later it is smooth as glass.  How much did that help in the end??  I think the torque on the tail rotor bolt and preload on the teetering bearing is more important than setting the track.  More times then not if you have troubles balancing, loosen the bolt or flip the bolt and retorque.  In my experience, this helps with balancing issues better then setting the track.  Also putting a little weight on stabs helps when readings seem to be hunting.  The book calls for 5kg on each side, I find just leaning on left stab works as well.  If after 5 or 6 runs with no progress or consistent move lines, undue and retorque the tail rotor bolt.  Then try again.

Also don't balance at idle, just balance it enough to be below 1-1.2ips then balance at 100% and remember the limit is 0.35ips at idle and 100%.  Below 0.2ips is ideal and preferred, but depends on tail rotor and time available may be a challenge.  

This is just my thoughts and experiences.  Go with what seems to work best for you. 

   

[Torque Split]

From Dave Dunstans notes.  He was a former tech rep for Airbus/Eurocopter

62.Vibration 3 per.doc 62.Vibration general.doc