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HomeAircraftHelicopterBergen R/C Helicopters › Intrepid - Almost a $5000 disaster........
11-04-2004 10:45 AM  13 years agoPost 1
JamesC

rrNovice

Melbourne, Australia

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A close call:

Just built a beautiful new Intrepid Gasser..........today the following occurred.....

I was hovering about 3 feet off the deck, had been doing so for about 20 minutes just doing final trimming and gyro gain (Futaba 501) setup. This at about ½ throttle or just above. Light breeze.

All was going very well (very stable, great cyclic responses). Had been doing slow piro’s (e.g. 20 seconds to rotate 360 deg) and faster ones (3-5 sec) but nothing wild.

Suddenly, the tail rotor just flew off. Throttle cut and max collective bought me a few nanoseconds before the machine sort-of corkscrewed in, thankfully landing undamaged on the skids (PHEW!). Talk about lucky. Found the rotor nearby, but my nice new MAH carbon tail blades were a mess.

Inspection revealed the tail shaft had BROKEN just outside the bearing. The threaded sleeve that forms the innermost structure of the pitch slider also seems to have parted. My tail blades were also wrecked. (SEE PICS)

On looking closely, the shaft seems bent. Don’t know how that happened. The tail rotor did not hit anything causing the failure.

I have talked with the Aussie Bergen Distributor (who is always helpful) and am hoping Bergen will warranty cover the replacement parts.

It's a stunning heli and I can't wait to really fly it.

Has anyone had similar experiences? I followed the instructions to the letter, and static tested every function may times before actually taking to the air.

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11-04-2004 01:56 PM  13 years agoPost 2
dariof

rrVeteran

Henderson, NV / Laguna Niguel, CA

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If the tail shaft were bent prior to flying, you probably have your answer. You may not have even noticed if it was bent.....even a slight non-discernable bend would probably cause the shaft to crack at the bend and shear off. Was there any shaking of the T/R or T/R fins prior to this incident?

Are you sure you did not strike the tail output shaft on anything..perhaps when loading or unloading the heli into a vehicle, at home, etc?

I ran a RR search for you petaining to this, and nothing really fits what happened.

I'm sure Malorie will have some answers for you...she's pretty good at diagnosing these things.

Best Regards, Dario

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11-04-2004 10:39 PM  13 years agoPost 3
G.Man

rrProfessor

Bristol

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The tail shaf comes pre built as well, so unlikely you could have messed that up...

Tail blades out of track may be my conclusion...

Cutting the 2 ball links down and you should track the tail blades... if they are out of track the tail shaft will be stressed and break...

Thats just my guess..

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11-04-2004 11:38 PM  13 years agoPost 4
gyan

rrKey Veteran

Surrey, BC Canada or Blaine Wa.

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I work with alot of aeronautical engineers I copied the picture & I'll send it to one of them. But to me that shaft end looks porous like maybe the steel had some impurities in it. I'll let you know what he says tomorrow.

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11-05-2004 02:37 AM  13 years agoPost 5
llamatrails

rrApprentice

Gainesville GA - USA

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Question:
What happened to the screw that is supposed to hold the output shaft bearing in place ? It is missing in picture #2 and #3.

Rick

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11-05-2004 02:46 AM  13 years agoPost 6
uh1b1

rrApprentice

usa

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how many set screws did you put in the tail rotor hub when you mounted it on the shaft 1 or 2,there are two holes in the hub but you are only suppose to use one.

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11-05-2004 03:22 AM  13 years agoPost 7
JamesC

rrNovice

Melbourne, Australia

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Thanks for all the helpful replies so far..............

Addressing each in turn

1) Dariof/Galifrey (is that a Dr Who reference?): Blades were a
balanced pair MAH carbon, tracking perfectly. Had not banged the
tail either - built it in my shed then walked it 50 metres to my field (8
Acres of backyard). No strange vibes that I notived prior to the
break. Galifrey, what do you mean when you say 'cutting the 2 ball
links down'?

2) gyan - thanks, I'd appreciate the opinion. I was surprised at the
grainy/porous nature of it too.

3) llamatrails, I took the panhead screw out for the photos. It was in at
the time of the failure

4) uh1b1 - yes, only used the 1 grub screw to mount rotor to tailshaft. I
am aware of the problem of using opposing grub screws. Note also
that the hub was still connected to the remains of the shaft. It was
the 'gearbox' end of the shaft that broke.


I appreciate all the ideas offered so far. It may well be just a freak failure - but keep the ideas coming 'cause if I can avoid it in future (during actual flight for instance ), that would be GOOD...

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11-05-2004 05:48 AM  13 years agoPost 8
Lawso

rrNovice

Sydney Australia

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Tail problem
James C,
I suspect that you have had a tail linkage problem.
Did you build the helicopter or did you buy it complete?
I have had a similar problem. This was due to a small amount of loctite finding it's way into the tail grip joint whilst installing the shoulder bolt.
This will make the joint tight and can cause the blades to go out of track rapidly.
I have a couple of hundred hours on these machines and one thing that I have learned is that everything on the tail MUST be silky smooth for everything to work right.
Oh, and there is no Australian distributor. There are 2 dealers and I am one of them....
If you need any assistance with this heli, please do not hesitate to ask. I am in Sydney but do get to Melbourne from time to time.

Lawso

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11-05-2004 08:09 AM  13 years agoPost 9
JamesC

rrNovice

Melbourne, Australia

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Lawso,
Thanks mate.........Yep, built it myself. Got it from Noel Blake at Radiocontrol Australia. My apologies, I assumed that he was the only Oz dealer

Anyway, your advice is appreciated very much - could you elaborate on what are the 'tail grip joint' and 'Shoulder bolt'?.

Everything seemed silky smooth in preflights and early hovers. Was lubed with Triflow.

The gearbox came pre-built, so assume you mean the actual blade grip?

Be great to clear this up so I can fly with confidence.

Cheers

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11-05-2004 08:25 AM  13 years agoPost 10
G.Man

rrProfessor

Bristol

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what do you mean when you say 'cutting the 2 ball
links down?
Part number 1961 has to be trimmed down to a smaller length and the "flanges" on the side of the ball link trimmed off.

Strangely this step appears to be missing from the manual I now have on my PC...

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11-05-2004 02:37 PM  13 years agoPost 11
dariof

rrVeteran

Henderson, NV / Laguna Niguel, CA

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No news from the manufacturer yet? I think they will nail it down as to what happened. Why don't you shoot them an e-mail. They may not be on RR the last day or so...they are usually really good about jumping into these issues.

Best Regards, Dario

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11-05-2004 07:26 PM  13 years agoPost 12
Chris Bergen

rrElite Veteran

cassopolis, MI USA

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As it happens, I have been keeping an eye on this.

I suspect that dario may have been the one to hit on the cause.

Two things catch my eye. The shaft is possibly bent, and the pitch slider tube is broken.

These shafts are half hardened. We don't want them so brittle that they snap, but we don't want them soft enough to bend under normal use.

In effect, what normally happens is that the shaft will bend to a point due to an imbalance or vibration somewhere, until it finally does break.

The clue is the pitch slider tube being broken. This would more than likely be caused by the shaft bending inside the tube.

I'm not a big fan of the hollow tail blades. I've had NHP's split, and when spinning at appx 8,000 rpm, puts one hell of a load on the hub.

Check your tail hub for being bent. Easiest way is to spin the tail hub while holding the blade grip. Look for wobbling at the blade grip.

I have had this happen to my own bird, when one of the plastic tail blades broke in flight. The whole assy then parted ways, and I pirouetted to the ground. It was a freak occurence, but sh** happens.

It is difficult to know the exact cause in your case James. I am just glad that the damage was not worse.

Chris D. Bergen

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11-05-2004 11:05 PM  13 years agoPost 13
JamesC

rrNovice

Melbourne, Australia

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Thanks Chris,

This is just the sort of personal response that helped convince me to go with a Bergen in the first place.

I'll certainly check the hub alignment now. I think the blades did not split, as the damage to them seems from impact only, though of course I cannot be sure of this.

I am sure that the tail was running true just prior to the event as I was really watching it during my gyro gain adjustments.

Anyway, I'll let you know here about the hub. BTW, the blade grips do have a little 'slack' or movement at the attachment to the hub. THe thrust bearings are assembed correctly and the bolts are tight so I assume this in normal.

One other question - what exactly should I be doing with part #1961 (see Galifrey's last post)?? How much shorter?

As you say, I too am glad the damage was not worse. Just can't wait now to replace the parts and get back in the air.

Thanks again
Regards
James

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11-06-2004 12:03 AM  13 years agoPost 14
Ozzy Pilot

rrApprentice

Victoria, Australia

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Hello James

Further to our phone conversations over the last few days I have spoken to Larry this morning and in his usual good mannered and friendly way he has explained the situation to me almost identical to the post by Chris above.. Whilst we can not be absolutely sure of the cause I am sure that it was not through any neglect or abuse on your behalf and talking to you I know how precise and exacting you like to be when putting this heli together.

Larry has shipped a complete tail assembly this morning and your parts will be replaced on my behalf free of charge. Unfortunately I have just sold my last kit in stock otherwise I would have the parts.

Lastly thanks for being such a great customer and taking this in such a great manner it makes it a pleasure to deal with you.

Be in touch soon
Noel

PS Hey Lawso stop tring to poach my best customers

Member of Good Guy list (seller) Pg. 23. Turbines - Audile pleasuring

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11-06-2004 01:39 AM  13 years agoPost 15
gyan

rrKey Veteran

Surrey, BC Canada or Blaine Wa.

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I spoke to the engineer at length on this. I was concerned about the porous nature of the break but he assures me that It's normal for a shaft under tension load to do that. He explained that an out of balance would put it under tension but as well as a seized bearing or anything that would stop the shaft when it was suppose to be turning. An inclusion (air pocket or even an impurity that wouldn't allow metal flow during extrusion of the rod) could be the cause but unlikely he said as it would have to be at the fracture point & since that fracture was just outboard of the support it's more likely from tension. A torsional load on the shaft would happen if there was a blade strike & the shear would look different than what the picture shows. So my guess would be an abrupt out of balance from something.

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11-06-2004 03:10 AM  13 years agoPost 16
rtrickyjr

rrVeteran

Drumore, PA (SW of Quarryville)

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Noel ...
You proudly carry on the Bergen tradition! Glad you're a dealer, word travels fast, I wish for you a profitable venture

Rick

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11-06-2004 04:49 AM  13 years agoPost 17
Ozzy Pilot

rrApprentice

Victoria, Australia

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Hello Rick

Nice to hear from you it's been a long time since we last communicated. That gorgeous gasser of yours still takes pride of place on our business cards.

All the best.

Member of Good Guy list (seller) Pg. 23. Turbines - Audile pleasuring

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11-06-2004 10:29 AM  13 years agoPost 18
G.Man

rrProfessor

Bristol

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JamesC

http://hi-techhousing.com/manualgas_R1.pdf

Download this manual, top of page 80, for some reason its not mentioned in the manual that came with my bergen, but had already printed of malories instructions and used those to build my gasser..

You will know if you need to do this as the ball links will bind on the blade grips when the pitch change slider gets closer to the hub..

Disconnect your tail pushrod and move the slider by hand, feel for the binding...

Don't Email me as I wont reply - PM Only (spam countermeasures)

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11-06-2004 08:26 PM  13 years agoPost 19
shykmaster

rrApprentice

New York

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regarding using only 1 grub screw
I noticed that one of you mentioned that you are supposed to use only one grub screw to hold the tail on the shaft. Why is that if you can use 2 shy not use them.
I just got a metal tail case and in my Rappy, and doing low hovering, the tail suddenly beang piroetting and I too got lucky and was able to land with no damage. Upon inspection I noticed that the rotor assembly was loose on the shaft. There was only one grub screw holding it on and it was loose. Well, I tightened it up and added another grubb screw to the opposite side. Is this not O.K.???

Thank,
Josh

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11-06-2004 09:48 PM  13 years agoPost 20
rtrickyjr

rrVeteran

Drumore, PA (SW of Quarryville)

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Ozzy ...
And I'm still proud as a peacock

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HomeAircraftHelicopterBergen R/C Helicopters › Intrepid - Almost a $5000 disaster........
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