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marks73
Extreme 3D
Extreme 3D


Joined: 08 Apr 2015
Posts: 86
Location: Leland, NC. USA

PostPosted: Thu Aug 13, 2015 9:20 pm
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When I called it a day yesterday I had one blade at+1 and one at -5, 50% ID. This morning while connecting the battery I looked down and saw the problem. Can you see it?



Rotten rascal used two different blade grips. Why do I bother with Ebay?
Sad
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marks73
Extreme 3D
Extreme 3D


Joined: 08 Apr 2015
Posts: 86
Location: Leland, NC. USA

PostPosted: Thu Aug 13, 2015 10:31 pm
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Well, I have a new set of blade grips coming from a company I've been using called Amain. http://www.amain.com/rc-helicopters
I find from time to time that they have some pretty good deals. Such as their Eco Batteries. Anyway, I'm going to completely rebuild my rotating assembly just to be sure of what I have. Anyone know of a good way to verify if a bearing is good or starting to fail. I could use some pointers in that respect.
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admiral
Extreme 3D
Extreme 3D


Joined: 20 Mar 2009
Posts: 1100
Location: Brisbane, Australia

PostPosted: Fri Aug 14, 2015 2:44 am
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Hi Marks73, Apart from any obvious visible defects, the only way I can tell is to put a shaft through the bearing and holding the bearing in my fingers slowly rotate it and if it is on the way out it will feel notchy, if it is good it will rotate smoothly.
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Burgess
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Joined: 27 Mar 2012
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Location: Wales

PostPosted: Fri Aug 14, 2015 6:19 am
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Well that was hard luck with that main rotor assembly Mark.

I've just received a brand new T-rexSEV2 clone swashplate and the bearing was suspect so I've replaced it with a good quality bearing from Simply bearings.co.uk.

With regards to bearings, as Keith said to test...anything less than silky smooth, replace the bearing.

Also if the bearing has seen long service there will be signs of the grease leaking out and going black.

If so, gently ease off one or both metal dust covers, wash the bearing in acetone, dry and inspect again. The balls should still be bright. If the races are rough you'll hear and feel it. If OK, re-pack with height melting point grease Teflon or PTFE and snap back in the covers.
Have a look at this page:
http://www.align-trex.co.uk/catalogsearch/result/?q=grease


Burgess
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marks73
Extreme 3D
Extreme 3D


Joined: 08 Apr 2015
Posts: 86
Location: Leland, NC. USA

PostPosted: Sat Aug 15, 2015 7:02 am
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So which one of those greases should I use to repack a bearing?
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Burgess
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Joined: 27 Mar 2012
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Location: Wales

PostPosted: Sat Aug 15, 2015 7:57 am
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Try either of these

Super Lube Synthetic Grease with PTFE - 12g Tube,

Robbe Precision Grease and Teflon 1-5532,

and avoid mineral based oil/grease on bearings in plastic such as those in the tail gearbox.

Here's some bearings with three different stiles of dust covers removes, the covers are quite thin:

one 12x18x4mm and two 5x11x5mm




Burgess
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marks73
Extreme 3D
Extreme 3D


Joined: 08 Apr 2015
Posts: 86
Location: Leland, NC. USA

PostPosted: Tue Aug 18, 2015 9:13 pm
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Great info. Thanks gentlemen. I find now that one of my new blade grips is on the tight side. So tight that I'm wondering if I should send it back or attempt to spread it a bit. Without the nut installed the blade certainly needs to be looser as the blade won't move tapping on it from the side. Any thoughts?
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Burgess
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Joined: 27 Mar 2012
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Location: Wales

PostPosted: Wed Aug 19, 2015 8:45 am
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Check the root thickness of both blades -span-wise and chord-wise- and the width of the gap of both blade holders and check that the gaps are parallel.

I've found the root of some blades had slight defects, true-up with small sanding block and say 600 grit wet n dry -use wet.


Burgess
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marks73
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Joined: 08 Apr 2015
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Location: Leland, NC. USA

PostPosted: Wed Aug 19, 2015 8:06 pm
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I used a different set of blades and you are correct in that the blade had a defect not the holder. When I flew it yesterday after all of the rebuild work. It has now developed a main blade oscillation where the blades are moving up and down from side to side at about 70% collective and 3 feet off the ground. After landing and powering up to where the skids are light. It appears I have a blade tracking issue where one blade is about 4cm lower than the other. I didn't realize never having had a tracking issue that it would cause the heli to react in that manner. I'm going to to adjust it out and try again this morning.
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Burgess
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Joined: 27 Mar 2012
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Location: Wales

PostPosted: Wed Aug 19, 2015 11:51 pm
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Mark, 40mm is quite a large tracking error, indicating more than pitch linkage adjustment, check the thrust bearing assembly order, large internal diameter inboard, small internal diameter out board and ball-race cup facing inboard.

Do you have tracking tape on the blades, if not suggest using red and blue use exactly the same lengths and affix to identical locations on both blades. When tracking spot-on the colors merge to purple or show red or blue depending on which blade is highest.

Burgess
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marks73
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Joined: 08 Apr 2015
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Location: Leland, NC. USA

PostPosted: Thu Aug 20, 2015 8:10 pm
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I'm sorry. American error. It's 4mm (just over 1/4 inch). Anyway, What would cause the bird to oscillate the blades up and down at the tips looking from the rear as if you were moving the stick right and left. Feathering shaft appears strait to me but I'll recheck the thrust bearing assembly.
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Burgess
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Location: Wales

PostPosted: Fri Aug 21, 2015 6:31 am
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Mark,

A 4mm oscillation at the blade tips translates to very little movement at the blade holder.

If the blade holders don't move up/down, fore/aft on the feathering shaft, you'll need to check the blades.

#1 check the roots span-wise for parallel

#2 check each blade span-wise CG

#3 check the chord-wise CG...(if the CCG is rear-wards the blade will be unstable in operation)

Hang both blades vertically on a 3mm shaft, the blades need to be parallel to each other.
Hang a plumb line from that shaft in front of the blades. The leading edge of the blades ought hang parallel to the plumb line or closer to the line at the tip than the root.

If the LE slopes away forwards from the line at the tip, when the rotor spools up, this will cause the blades to deflect up wards and back when advancing once they reach a certain pitch angle and down-wards and forwards when retreating.




Burgess
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