Yet another GAUI CNC failure

[Phoinix]

After my colegue had a problem with GAUI CNC tail last month, i had one too. I had just transfered my system back to 35MHz waiting for FASST on MX-22, and i went out on a test flight.

It all went well when all of a sudden at a height of roughly 3 meters the tail blows. Spinning left like crazy i entered a hover AR and landed the bird without any further damage.

HS was only 1900 and the GAUI CNC tail had flown only 3 hours total. I had an inspection at about 2 hrs flight time with no obvious flaws in material.




http://i97.photobucket.com/albums/l236/BlenderPilot/Show%20and%20tell/Modeli/Hurricane%20550%20CF%20Build/DSC06416.jpg


http://i97.photobucket.com/albums/l236/BlenderPilot/Show%20and%20tell/Modeli/Hurricane%20550%20CF%20Build/DSC06415.jpg

[mjbrands]

Has the bolt holding the blade holder simply sheared off? My tired eyes can't really make it out for sure.

Anyway, this sucks!

[Phoinix]

Yes, the bolt sheared off, a very clean cut.

Guess who is coming back with an improved tail...

http://www.cnchelicopter.com/servlet/the-964/%28%28hot%29%29-HURRICANE-550-CNC/Detail

[mysticmead]

looks that way to me

[Phoinix]

My colegues tail bolt sheared a few weeks ago. Same pattern:

http://www.enduro-si.com/razno1/rep.jpg

http://www.enduro-si.com/razno1/rep1.jpg

[JaggedEdge]

Is that on the side that requires proper preload to be set and loctite or the side where preload is perfect with the bolt cranked down?

[skigolfmike]

Yep - looks familiar. Funny how it takes the blade off the other grip when the bolt shears.

Mine happened in forward flight about 50ft (15m) up. If I had hit throttle hold I might have had half a chance to get heli down without breaking anything else.

[Phoinix]

Fast reaction is cruital in this scenario. I had a chance of saving mine reacting uppon failure in 0,75 second according to eagle tree log. Very characteristic log since M/R RPM drops due to fuselage spinning. T/R servo went crazy of course .

[mjdee14]

Great job "Saving" the ship....."Shame on Gaui" and the older CNC parts.....what the F*** do they think we buy these things for....so we can destroy a $1000 worth of heli becuase of one Sh*ty part ???

I'm staying with the $16 plastic Trex 600 tail....made like a rock....went the cnc box and slider but the trex tail works just great...

look at the way they make their hub....the center comes up almost to the bolt head so side pressure is not put on the bolt. the center carries all the load of the bearings....

Doesn't take a Rocket scientist to figure these things out.....:thinking

[ukgroucho]

Well, I have to add this alternative option into the discussion... mentioned before but here we go.

I've been using the Quick UK Raptor 30/50 CNC tail grips since I commisioned my 10S Hurri 550 and I've had no issues. They are a direct fit replacement - no mods. Granted I only run around 2200 - 2250 headspeed but I've probably flown 150+ packs with them and performance has been flawless.
A little more expensive maybe but i know (from other helis) what a tail failure can cost in terms of collateral damage so it's a pretty good cost equation in my opinion.

edit: http://www.revolutionmodels.co.uk/acatalog/Raptor_30_50_upgrades_by_Quick_Uk.html

Near the bottom of the page.... select your own colour choice.

[Flinto]

I'm staying with the $16 plastic Trex 600 tail....

So, would this be a direct fit on the hurri?

http://flying-hobby.com/catalog/product_info.php?cPath=3_26_47&products_id=2661

[mjdee14]

yes...that would be a direct fit......looks good too......

If it could stand up to the trx 600 nitro...it should do fine on our little 550's. I just hate to pay all the shipping....

[Graeme67]

Guess who is coming back with an improved tail...

http://www.cnchelicopter.com/servlet/the-964/%28%28hot%29%29-HURRICANE-550-CNC/Detail

So what are we saying here? Is this a good tail, or something to beware of?

I like the idea of a CNC tail, but I am up to 300 flights with my original plastic tail with no problems. I'm sure as I start pushing it I might be chasing better response but for now it works fine.

Cheers
Graeme

[JaggedEdge]

Any possibility the bolt was over tightened a couple times?

[kahn10]

and did you put a shim between the radial and thrust bearings.if there was the bolts don't lock hard against the tailshaft and the grip seats right up on the hub.its not binding but you can't actually see a gap

[mjdee14]

So what are we saying here? Is this a good tail, or something to beware of?

I like the idea of a CNC tail, but I am up to 300 flights with my original plastic tail with no problems. I'm sure as I start pushing it I might be chasing better response but for now it works fine.

Cheers
Graeme

the picture from cnc show the improved tail hub.....it's much beefier and has a thicker area for the bolt and a bigger bearing.......We havenot heard any report from anyone that has the improved unit that has actually flown it yet.

[Phoinix]

The bolt wasn't overtihtened as i rely mostly on loctite than brutforce tightening. Didn't matter how careful i was.

[JaggedEdge]

I hear ya.. Even with a lot of side force from the blades and a bunch of play in the grip a bolt shouldn't shear off like that. I'd attribute it more to the bolt than the design of the grips and hub.

[mjdee14]

I hear ya.. Even with a lot of side force from the blades and a bunch of play in the grip a bolt shouldn't shear off like that. I'd attribute it more to the bolt than the design of the grips and hub.

Thats exaclty where it will break when you have all the side force concentrated on the bolt...instead off the shank...

look at the good ones like the trex...they have the boss extended all the way out, the bearings ride on the shank, (protusion/whatever) and all the bolt does is hold it and keep it from flinging off the end. it does not take any side load. The bolt sheared off from the side force. Any tail that has the bearings riding on the shaft of the bolt and not on the hub shank itself may have that type of failure. look at how long the trex shaft is....all the bearings ride on it...

http://www.helifreak.com/attachment.php?attachmentid=54552&stc=1&thumb=1&d=1215824600 (http://www.helifreak.com/attachment.php?attachmentid=54552&d=1215824600)

[kahn10]

is true mike.the gaui cnc grips i just got given have got a bronze?brass?gold:shock:? bish in the base that slips over the hub.as they are they stand off the hub slightly,maybe a mm,na under a mill and still have that nasty wobble.if you put the missing shim in it closes them right up you can't even see a gap between the grip and the hub,and no wobble at all while still gliding on their bearings.by bish i mean bush i guess.....

[JaggedEdge]

My gaui thrusted grips have no side to side play.. and I checked out dozers upgraded thrusted hdx/cnc heli grips and there was a lot of side to side play.

[Edit]To follow this up.. I just rebuilt mine again and I cant stand having to set up these like grips like this. Shortening bolts (or using washers under the head) and using loc-tite to keep it "safe" sucks. I've said it before but I forgot how much the gaui hub and grips sucks.

Also.. I failed to mention, I don't remember how they came, but I have the radial bearing at the base, thrust bearing on top.

( )=[]{}=

( ) - Hub
= - Bolt
[] - Radial bearing
{} - Thrust bearing.

[JaggedEdge]

After some screwing around I used a bearing from the stock grip and added it to the gaui metal grips. Had to cut a longer bolt to size but I'm thinking that will spread some of the load on the bolt.

I hate having to set preload and use loctite. Gaui is bad in this respect. :thumbdown:

Will probably switch to the rex600 grips.

http://helifreak.com/picture.php?pictureid=6646&albumid=830&dl=1215914096&thumb=1 (http://helifreak.com/picture.php?albumid=830&pictureid=6646)
Click image for larger view

[manos]

“Men are never so likely to settle a question rightly as when they discuss it freely”

[Wazzer]

Well, I have to add this alternative option into the discussion... mentioned before but here we go.

I've been using the Quick UK Raptor 30/50 CNC tail grips since I commisioned my 10S Hurri 550 and I've had no issues. They are a direct fit replacement - no mods. Granted I only run around 2200 - 2250 headspeed but I've probably flown 150+ packs with them and performance has been flawless.
A little more expensive maybe but i know (from other helis) what a tail failure can cost in terms of collateral damage so it's a pretty good cost equation in my opinion.

edit: http://www.revolutionmodels.co.uk/acatalog/Raptor_30_50_upgrades_by_Quick_Uk.html

Near the bottom of the page.... select your own colour choice.


Hey Groucho

Are you using the Tail Case as well as the Tail Blade Hub and Grips?

I really like the look of that one piece tail case

Its a real shame that Gaui hasn't addressed this issue as fast as some of the other issues they have fixed. As its the only real problem this Heli has left

Cheers

Ben

[Graeme67]

JE, You can't really "spread" the load in this situation. The sideways load that flex's the bolt will will always cause a stress fracture of the bolt at the edge of the hub it is screwed into. Lengthening the bolt will only serve to provide greater leverage at the stress point & may lead to failure quicker.

The only way the load can be removed from the bolt itself is when it can be locked down firmly against against the inner races & hub. This efectively increases the diameter of the bolt and increases ridgity. Since I've not had mine apart I have no idea if this is possible. Does the standard TR grips have 2 x radial bearings & no thrust bearing? If this is the case it should be possible to lock the bolt down firmly. If it's left loose it's going to snap.

I might have to look at my grips. After 300 flights some fatigue could be setting in. Thanks for the heads up.

Cheers
Graeme
After some screwing around I used a bearing from the stock grip and added it to the gaui metal grips. Had to cut a longer bolt to size but I'm thinking that will spread some of the load on the bolt.

I hate having to set preload and use loctite. Gaui is bad in this respect. :thumbdown:

Will probably switch to the rex600 grips.

http://helifreak.com/picture.php?pictureid=6646&albumid=830&dl=1215914096&thumb=1 (http://helifreak.com/picture.php?albumid=830&pictureid=6646)
Click image for larger view