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HK500GT Tail Victim
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gi1mo2 View Drop Down
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Posts: 29 		  Quote gi1mo2 Quote  Post ReplyReply Direct Link To This Post Posted: 28/Mar/2011 at 8:28pm
Not quite the same bolt from the pictures in the other thread. Here is a video of my two failures, and also shows soft start mode of Turnigy Plush 80A (fixed by rebuilding tail... Tail gear would shear very often by hard start).

http://www.youtube.com/watch?v=SGugehHZutU
Helis: HK500GT, 2 x HK450, HK450GT Trex 500 ESP, Trex 450 Sport, Blade MCX, MSR, CP Pro 2
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Demon View Drop Down
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Posts: 339 		  Quote Demon Quote  Post ReplyReply Direct Link To This Post Posted: 28/Mar/2011 at 8:33pm
hi G12mo2,

The problem you had is not the one i have pictures, it is the screws themselves that shear off which is what you are facing. The other problem highlighted is the binding in the pitch slider and case.

Although you have upgraded to the Align parts now i have still heard of them failing too. your best bet is to replace the screws with some high tensile Grade 12.9 screws (M2x6 or M2x8 i think). They are considerably stronger so should not fail as easily.

Good luck,
Demon
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Posts: 110 		  Quote kdawgdinner Quote  Post ReplyReply Direct Link To This Post Posted: 29/Mar/2011 at 6:31am
I special order 12-9 screws from fastenal in canada m2*6 specificaly for the tail blade grips.  However Yesterday i fell victim of a bolt failure.  The tail blade grip flew off in flight and lucky me the heli was only about 10 feet off the gorund in front of me and i could land it with out a total write off. 
12-9 strength bolts will not 100% fix this problem.  I was sooo shocked to see that the 12-9 grade screw had sheared off from the tail hub. 
Upon looking closely at the tail it appears that the cause of this can be related to 2 factors.
Tail blades are over tightened between grips--> they should be lose enough so they do not fall under there own weight but if you tap the tail of the heli with your hand they should fall. 
The tail blade grip trhust bearings appear to wear after a while and can lead to slop and should be replaced as well as the screw often. 
Tail blades should be ballanced --> unballanced tail blades can cause alot of vibration and side to side motion wich will end up putting to much stress on the tail blade grip screw.
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Posts: 455 		  Quote hairykarts Quote  Post ReplyReply Direct Link To This Post Posted: 29/Mar/2011 at 9:00am
Just a point, are the very high tensile screws/bolts more brittle, should 8.8 be enough ! 
I must remember .... when inverted .... down is up and up is down .
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Posts: 110 		  Quote kdawgdinner Quote  Post ReplyReply Direct Link To This Post Posted: 29/Mar/2011 at 9:39am
nergative, higher tensile screws bolt are stronger.  12.9 is the strongest you can get.  it just shows how much stress is put on the current setup of the tail.  even with the strongest screws they still will fail.  I think the design of the tail should have used a larger sized diameter screw of 2.5 to 3mm
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Posts: 29 		  Quote gi1mo2 Quote  Post ReplyReply Direct Link To This Post Posted: 29/Mar/2011 at 9:47am
So, some of the boys from HK posted an HK500GT review video on YouTube (FliteTest): http://www.youtube.com/watch?v=as4-sPtJn1M

@HobbyKingLive replied that they sent them an updated tail for review and they dared them to break it.

Send me an updated tail, and let a real customer evaluate it. I dare you! If I don't break it, I'll definitely promote it.
Helis: HK500GT, 2 x HK450, HK450GT Trex 500 ESP, Trex 450 Sport, Blade MCX, MSR, CP Pro 2
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Posts: 110 		  Quote kdawgdinner Quote  Post ReplyReply Direct Link To This Post Posted: 29/Mar/2011 at 9:55am
well usually the tail fails after 5-10 flights or something.  so sure it wont break on the first flight but...thats just marketing hokus pokus the problem with buying cheaper clones like the hk 500 is the fact that any minor crash and you have to replace the hole thing.  thats my experience align versions seem to be more durable
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Posts: 203 		  Quote 2Doggs Quote  Post ReplyReply Direct Link To This Post Posted: 02/Apr/2011 at 1:28am
Originally posted by kdawgdinner

I special order 12-9 screws from fastenal in canada m2*6 specificaly for the tail blade grips.  However Yesterday i fell victim of a bolt failure.  The tail blade grip flew off in flight and lucky me the heli was only about 10 feet off the gorund in front of me and i could land it with out a total write off. 
12-9 strength bolts will not 100% fix this problem.  I was sooo shocked to see that the 12-9 grade screw had sheared off from the tail hub. 
Upon looking closely at the tail it appears that the cause of this can be related to 2 factors.
Tail blades are over tightened between grips--> they should be lose enough so they do not fall under there own weight but if you tap the tail of the heli with your hand they should fall. 
The tail blade grip trhust bearings appear to wear after a while and can lead to slop and should be replaced as well as the screw often. 
Tail blades should be ballanced --> unballanced tail blades can cause alot of vibration and side to side motion wich will end up putting to much stress on the tail blade grip screw.

If a 12.9 bolt failed, you'd have to say that there was definitely something going on upstairs!

And 12.9 is more brittle than 8.8, though that should not be an issue with rolled threads.
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Demon View Drop Down
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Posts: 339 		  Quote Demon Quote  Post ReplyReply Direct Link To This Post Posted: 02/Apr/2011 at 2:57am
Im not sure if 12.9 is more brittle than the 8.8 but the number refers to the amount of tensile strength the bolt has...

http://www.roymech.co.uk/Useful_Tables/Screws/Strength.htm <- may be of some intrigue.

Im really surprised to hear a G12.9 screw has failed... that is actually very worrying... I may be tempted to start producing my own tail units which use M2.5 screws instead... might be an idea.

Cheers all,
Demon
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kdawgdinner View Drop Down
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Posts: 110 		  Quote kdawgdinner Quote  Post ReplyReply Direct Link To This Post Posted: 02/Apr/2011 at 3:49am
12-9 shouldnt be brittle?  it is the highest tensile i coudl get.
I was very surprised that it failed because i had just pulled the tail apart and reassembled it a week earlier and there was only 1-2 flights on it.  if you make the tail hub holes for 2.5mm you would have to redesign the entire tail because the tail blade grips internal bore are not big enough for that size of screw.  so you would need to redisgn the bearings and thrust bearings. 
One thing i thought about recently is that the tail has a tendancy to fail when the heli is being run at a higher head speed.  I have my heli goved at 2600 with a cc is 100. so i can fly pretty aggressive.  but it looks like the tail doesnt like being spun up that fast.  a thought?
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