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Kasama Helicopters and Upgrades Kasama Srimok 90 Helicopters and Upgrades Discussion


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Old 11-06-2011, 05:42 AM   #1
Mercuriell
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Default Lucky escaqpe - sheared tail bolt

Fired up the ECO for a bit of 2.5D practice and was just congratulating myself how smooth and straight things seem to be when the tail blew out - lucky I was pretty level and only 20ft off the ground so auto'd down, old fashioned weathervane style, and landed upright with no apparent damage - except for the tail push rod dangling free!!

The pivot M3 bolt on the tail arm had sheared just where it leaves the thrust bearing - not had this one before. Attempts to extract the sheared stud proved unsuccessful - qv video - so I drilled it out to 3mm, put a collared bolt down and milled the top square to take an M3 nyloc nut - Lucky escape

Really don't know why the bolt sheared - been a very smooth heli with no discernible vibes at all!
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Old 11-06-2011, 08:19 AM   #2
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Dang! that makes me feel like taking mine out & replacing it with a titanium one, would'nt want to experience that on my maiden.
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Old 11-06-2011, 09:00 AM   #3
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Wow .

There is no such a shearing force there. Faulty M3 bolt ?

Thanks for sharing.
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Old 11-06-2011, 11:28 AM   #4
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Yeah, when are those Ti bolts gonna be in stock.....?

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Dang! that makes me feel like taking mine out & replacing it with a titanium one, would'nt want to experience that on my maiden.
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Old 11-07-2011, 03:04 AM   #5
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Wow John that was a lucky one. My 550 didn't survive the weekend quite as well!

Any idea as to cause? Overtightened, undertightened, wear & tear?
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Old 11-07-2011, 04:30 AM   #6
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Quote:
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Any idea as to cause? Overtightened, undertightened, wear & tear?
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Yeah, when are those Ti bolts gonna be in stock.....?

I personally think that sometimes some of these bolts just go weak probably due to the manufacturing process.

Brett, the titanium bolts I'm speaking about are just some I picked up from my local hobby shop that fit the bill, with my local you can go in and find several types, sizes & shape titanium bolts (mix & match).
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Old 11-07-2011, 05:23 AM   #7
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I think it was a one off bad bolt. Titanium is not suitable as it is plastic and tends to bend, although light and hard it lacks tensile strength.
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Old 11-07-2011, 05:42 AM   #8
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It's another maintenance candidate then. I'm keen to put the Ti bolts in the certain areas like the frame bolts and maybe motor mounts, but for the most part I'd prefer the steel as it's not as brittle.
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Old 11-07-2011, 05:57 AM   #9
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One of my buddies did actually notice excessive play in the lever earlier that day but I thought it was slop in the flange bearings
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Old 11-07-2011, 06:04 AM   #10
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Quote:
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One of my buddies did actually notice excessive play in the lever earlier that day but I thought it was slop in the flange bearings
John, what kind of play was noted? I also noticed play in the tail and tightened that bolt a little - probably 3 or 4 flights ago.
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Old 11-08-2011, 04:13 AM   #11
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Hey Mercuriell thanks for bringing this issue up at this moment that made me check my tail too. I crashed 2 weeks ago - minor damage and the tail was intact - i thought but today i noticed some tail vibes and investigated. it tourned out that the bolt was bent and a bit loose and may be ready for snapping!

Changed it and try again later if the tail vibes are gone!

It pays of to read in the forums every now and then! :-)

Greets from Germany
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Old 11-16-2011, 09:37 AM   #12
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I'm not that lucky. The 4th tank in my engine breaking in...the tail just started to swing and I did an auto as well and just landed in an uneven patch of the grass and the main blade touched the ground and the heli lost balance...costs : broken boom, tail drive shaft, tail boom supports and a pair of main blades.

Just found out the same pivot screw was bent when I was checking and re-loctite all screws at the tail. Need to get another 20mm bolt at the hardware shop this week.

Can anyone get an answer on the reason why it happened. Seems like this is one design issue as there are 3 occasions in this thread already.
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Old 11-19-2011, 03:43 PM   #13
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i do not think that it is really a design issue just vibrations which loosens the bolt over time mine was installt since 6 - 8 month on my FIFA. I had two time the bolts of the arm on the main blade grip coming loose. Luckily found it during preflight inspection so loctited it and all good. Helis vibrate all the time and how sure can you bee that your bolt or whole is correctly degreased. and on some you put a little bit more loctide than on others. i think every bolt or screw on a heli needs to be checked from time to time especially on nitro's due to more violent vibes! We tend to forget that those thing are complex machines and need maintenance like the real once!
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Old 11-20-2011, 01:45 AM   #14
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Quite right. Def. not a specific Kasama problem. My Vibe 50 sheared the tail unit clean of the boom by itself during ther first 30 flights. High freq. vibes- didn't notice anything wrong at all until it came right off in flight.

/Henrik
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