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Thunder Tiger Raptors 30-90 - Imperio > Raptor Head explodes-please read!!!!
 
 
jbrundt
Veteran
Location: St. Charles, MO

I went out today to fly my R60. The weather was perfect. First flight was normal and uneventful. However, the second flight didn't even get off the ground. I had started the motor and brought it out to the runway and proceded to spool her up. At about 1/3 stick the head started to hesitate (slow down then sped back up) at first I thought it was the engine just a bit rich getting to hover throttle. I moved the stic to half, the skids got off the ground about 2" inches then the head just blew apart. It sounded just like a gunshot. One section of the head with the hub, grips and one blade flew off at a 45 deg angle about 100' from me. The other blade (broke near the root) flew in the opposite direction about 75'. The heli flipped up and landed on it's left side. The engine was still running. After about fifteen seconds I came out of my shock and shut the engine down.

I found one part of the jesus bolt with the nyloc nut on it and several yards away I found the other part with the head several yards away. It looks like the bolt failed. the funny thing was it didn't shear at the head where the most stress would be but about 1/8" down from it. When I was building the kit in the back of my mind I thought it unusual that this wasn't a shouldered bolt (like most other helis I've built). I'm just glad that i was the only one there and that I didn't get hit or that it wasn't 50 feet in the air and it could have come down like a brick.

Does Thunder Tiger warranty something like this? I've only been flying the heli since december. The worst thing is that I didn't directly cause the mishap. I could see if I was flying around and did a dumb thumbs manuever. I've never had this sort of thing happen before and I'm quite disturbed by it.

If one of the TT reps would like to contact me please email me at jbrundt@yahoo.com We can correspond via email or I can give you my phone number. I have pictures available for anyone that wants them. please email me. they are in a zip file format.

Jeff
02-23-2002 Over year old.
HOMEPAGE  
 
 
Michigan PI
Senior Heliman
Location: St Clair Shores, MI

I guess that would be me since I am the only one on the forums.
Sorry about your mishap Jeff. Definately contact Ace customer service, ask for Doug.
02-23-2002 Over year old.
HOMEPAGE  
 
 
FlyinBrian
Veteran
Location: USA

Hi,

What kind of blades where you running? I've only heard / seen a blade thrown once so far (luckily not my heli), it sounds like a shotgun going off, bent the main shaft to a 45 degree angle, flybar looked like an s, bent the main frames, etc but his head remained on which could account for a lot more damage.

Possibly the loud noise you heard was a blade being thrown and the tremendous force at that point either sheared the bolt or cracked the head block which opened up and broke the bolt (check the block out closely).

TT/Ace will probably replace your parts if it was something of there's that failed, just make sure you know what failed so you can avoid it in the future.

After the blade toss I saw and the lead weight I lost out of a set of tt 600mm wood blades the composite blades look cheaper than a visit to the emergency room. Have'nt flown woodies on anything I owned since, anything I test with woodies is well above body level and pretty far away.

Glad to hear nobody got hurt!

02-23-2002 Over year old.
 
 
Virtual1
Senior Heliman
Location: Waterloo, Iowa - USA

I was just trying to think that through to decide which broke first, the blade or the jesus bolt. First thought was the blade broke, and the momentum of the other blade still on the head caused it to fly off and sheer the bolt in the process.

Further retrospect has me thinking that if the bolt broke, that would allow the main shaft (and head) to rise, and with a leading-edge blade arm, probably pull the blades up to an insane pitch before the head could get clear of the main shaft. One blade couldn't take the pitch at that RPM and snapped, the other then was free to tilt up a bit more and hang on long enough for the head to rip itself off the heli and go flying away too.

I still can't think of how you broke the bolt in the middle, unless you had it really torqued down hard and it simply gave out due to being over-torqued. It might have needed the heat of friction on the main shaft to expand the main shaft, just enough added pull on the bolt to snap it, leaving centrifical force to send the 1/2's of the bolt flying out. Or maybe a defective jesus bolt? I'd assume it broke at the boundary where it cleared the main shaft and entered the head?
02-23-2002 Over year old.
HOMEPAGE  
 
 
Axeman
Senior Heliman
Location: Auckland, New Zealand

Are you sure the Jesus bolt broke after the head exploded? Do you think the blade broke at the root first, then the rest of the head blew apart? ie. did you glue the blade roots!!??
Cheers from NZ!
02-23-2002 Over year old.
 
 
jbrundt
Veteran
Location: St. Charles, MO

I am quite sure it was the bolt that broke first. Here's why I think so:

1. the break at the bolt is right at the interface between the main shaft and the rotor hub. The exposed portion of the bolt just below the head is the same thickness as the plastic of the hub where the main shaft fits in.

2. the spasmodic jerk the motor did (which I initially attributed to the engine being rich from idle) indicated the bolt had failed then. The rotor slowed down and sped up ever so slightly like the hub was able to spin free on the main shaft. Then when I gave more collective/RPM it was enough to launch the rotor into space.

3. the jesus bolt was not a shouldered bolt. a bolt that has threads along it's whole length. A bolt of this construction is not strong enough to take shear loads such that you would see in a 60 size rotor head.

As for the blades I was using they were Airmaster 680mm blades from Gr8 Lakes Hobby. I have flown these for over 60 flights since mid December without any trouble. True they are wood but I did not experience a thrown blade from the grip. In fact the grip portion of the blade is still firmly attached. the blade failed about 1" from the grip. The blade grips are epoxied in with 30 minute epoxy. I am 100% certain the grips are not the cause of the problem.

If a blade were thrown I would expect to have more damage from the machine flailing around unbalanced for a second or two. As it was the heli popped in the air a few inches then landed on it's side. No flopping dance of death. The main shaft is not even bent. Most usually in a thrown blade the main shaft is bent in a noticeable fashion. The spindle shaft is also, for all appearances, straight. The collective servo is stripped though. When the rotor head pulled up that was the first thing to go.

For those of you that responded I have uploaded some pics to my gallery (or you can email me so i can send you the pics) and you can see for yourselves. I am going to wait and see what Ace has to say about warranty of this. Either way I am going to rebuild it BUT this time use a shouldered bolt. I would urge anyone with a R60 to do the same.

Jeff
02-23-2002 Over year old.
HOMEPAGE  
 
 
steve9534
Key Veteran
Location: yakima, wa.

Head failure

Jeff;
I've seen a blade come off on two occasions, and the helis really exploded. There was no dancing around for a second or two as you expect. I also have an R60 and the clutch engagement speed is rather high, and mine commonly jerks as the clutch engages/slips/re-engages as the head is spooling up, and I wouldn't consider that indisputable evidence that the bolt broke at that point in time. The bolt in the R60 is somewhat unique in that it's a 4mm bolt, and even a bolt with full length threads should be stronger than the more common 3mm bolts used in most helis. Finally, I've had a Jesus bolt break, and have talked to one other individual who had suffered a similiar experience. In both instances the head just came off the heli. The upward pull of the blades just slid the head off the main shaft, and the heli and head parted company. It's hard to explain the kind of assymetric forces that would cause a blade to break at the root, and the head to be destroyed by just having the Jesus bolt break. Don't mean to be argumentative, but you might reconsider that the blade may have failed. Steve.
02-24-2002 Over year old.
 
 
Michigan PI
Senior Heliman
Location: St Clair Shores, MI

I have to agree with Jeff. From the pics I saw, it looked to me like the bolt failed. With the R-60 having a "leading grip" as the head parts company, negitive pitch is induced. This is where I think the blade may have struck something on the way out and blew the whole dang thing apart. The marks on the mainshaft clearly indicate a bolt failure as the head gets twisted off the shaft also.
02-24-2002 Over year old.
HOMEPAGE  
 
 
FlyinBrian
Veteran
Location: USA

Hi,

Its hard to tell in the picture but on the broken blade is any of the wood slivers pointing up or down (like it folded) or are they still pointing perfectly straight out (like it flew straight out)?

Usually a bolt will take a while to break and you'll see a darkend area as the fracture spread across the bolt, yours is clean and looks like it failed instantaniously do to an extreme force that was put on it.

Defintely looks like it was sheared as if some tremendous force pulled on the head block and it sheared off where the main shaft ended. But why is the other side intact? If the head block had cracked on the other side (quite a few square corners in the nut hole) then that would leave all the force on the the side that sheared. I'd be tempted to put the head back on the main shaft and put some force on it in different directions to see if a crack opens up in the head block where the main shaft sits.

There really is'nt much load on that bolt, keep in mind the blades are balanced so the only forces put on it are whats needed to turn the blades and to pull the lower body in the direction the head is going. My minair's all have a 3mm dowel pin holding the head on, a 4mm bolt is considerbly stronger even if it is threaded.

I can understand what you guys are saying about the blade going to an extreme collective angle but would'nt the blade lag behind before the point of breaking the blade?

Did the motor pick up a ton of rpm as the head slowed down during the takeoff? I just can't picture a friction fit between the head and mainshaft being enough to turn the blades, especially with 5 degrees of pitch needed to get the heli off the ground.

Out of curiosity what head speed do you run?

The thrown blade I saw on a 60 took less than a second and pretty much completely destroyed the heli but his head stayed on so that could account for all the damage.

Just some thoughts.
02-24-2002 Over year old.
 
 
jbrundt
Veteran
Location: St. Charles, MO

Auger,

The splinters on the blade are straight out. I can fit the two parts together pretty easy. There's a small chunk of wood missing but the ends of the break aren't all mangled so they won't re-join. When the head departed the blades went their separate ways at the same time. The whole incident took less than 2 seconds and it was over. It was that fast.

I'm running about 1650rpm on the head in hover in normal mode. (idle up is around 1750-1800). The headblock was a pretty tight fit when I originall installed it. It still is now. So I could see the head still trying to turn with the shaft even after the bolt sheared. The longer part of the bolt was still engaged to the main shaft/head block so even as the engine was spooling up it would be enough to keep the head/rotors moving. Then when the RPM was critical centripetal force took over and the head bolt peices flew out and the whole assy blew apart.

It's that motor/head/rotors catching and letting go catching/letting go during throttle up. It's hard to describe in words here. But I really think it's at that point when the blade broke. And don't for get you have all the linkage rods to the mixing leveres and flybar still attached even after the bolt sheared to help keep things moving together. Remeber the R60 has an overslung flybar. Most other helis out there have an underslung flybar.

From what I have seen and experienced I can't see this happening from a thrown blade. The wood that maked up the blade is of different types and expecting a break to occur at the same point along their lengths is highly unlikely due to the different wood's tensile strengths. If the wood failed I'd expect a failure breaks at different points along the blade's length depending on the wood type. That and the sheer fact that everthing broke at the exact same time to prevent a self flaggelation of the machine.

I will do like you suggested and put the hub back on and check for cracks. I may need to replace this part as well.

Thanks,

Jeff
02-24-2002 Over year old.
HOMEPAGE  
 
 
jbrundt
Veteran
Location: St. Charles, MO

Topdogg,

Yes. I did glue the blade roots on. If you read the other replies you'll see I mentioned that. What happened had nothing to do with blade roots. Look at the pics in my gallery and you'll see.
02-25-2002 Over year old.
HOMEPAGE  
 
 
bburton56
Heliman
Location: Clinton Township, Michigan

how do i get to your gallery to seel crash pictures

please post link
02-25-2002 Over year old.
HOMEPAGE  
 
 
engineer
Heliman
Location: Southern California, USA

Hi, bburton56

If you look at jbrundt's (Jeff's) post, there is a link to GALLERY on the bottom section along with PROFILE, MESSAGE, and etc. You can click on it, or you can click on THIS to go to his gallery.

Best regards,

Alex
02-25-2002 Over year old.
 
 
raptor30
Key Veteran
Location: Tilburg,The Netherlands

Raptor Head explodes-please read!!!!

Hi Jbrundt,

Sorry to hear about the crash dude!

I almost finished my Rappy V2 and i wonder where did you get the right Jesusbolt?

Thanks,
Raptor30
02-25-2002 Over year old.
HOMEPAGE  
 
 
jbrundt
Veteran
Location: St. Charles, MO

Raptor30,

I used the bolt that was supplied with the kit. After I rebuild it I'm going to go with a 4mm blade bolt from an R30/Nexus or similar. The local hardware store also sells metric shoulder bolts in that size as well. Rest assured in all future heli builds this bolt will be a shouldered bolt.


as an aside.....I did talk to Ace today but they told ne that Greg Saywer is out until later this week. He is supposedly the man to talk to about this issue. I'm still waiting to see what their word on all this is....

Jeff
02-25-2002 Over year old.
HOMEPAGE  
 
 
EdVp
Heliman
Location: Bedford, Ohio

Dear Jbrundt,

Sorry to hear about your bolt failure. This is very interesting to me because I'm currently building a R60 and was very concerned about this very problem after reading Steve DiFranco's R60 review in MHT. He really slammed TT for not providing a shouldered bolt.
Well, the weird part is that in my V2 kit, TT seems to have changed the bolt because it is shouldered for at least 3 or 4 mm I think...

If I don't know what I am talking about please let me know!
02-25-2002 Over year old.
 
 
Unbalanced
Veteran
Location: Melbourne, Australia

My 2 bits:

It would be more likely for the bolt to break in shear rather than tension. The threads do magnify the shear forces on the bolt and you would expect this to be greatest just where the bolt exits the mainshaft hole. I don't think we come close to applying enough tension the the bolt to set it up for failure, given that the mating surfaces on the head are plastic after all. Still a threaded bolt under shear forces, as with the stock R60 would be far more likely to fracture than a shouldered bolt which distributes the shear forces across a greater and thicker amount of metal.

Against this is that the shear forces are be distributed across both ends of the bolt and like others I would find it hard to imagine that this force would be enough to induce a sudden failure, unless the bolt had already been weakend through fatigue or prior damage. From the photo it looks like the bolt broke at once and the surfaces are clean, which would indicate that it sheared due to a single drastic event, which would tend to support the theory of a blade breaking rather than the bolt first.

If you can see discoloration or corrosion of the bolt across the face then this would be a clear indication that it was on its way to failing and was the more likely culprit.

Jeff
02-25-2002 Over year old.
 
 
Virtual1
Senior Heliman
Location: Waterloo, Iowa - USA

Setting aside the "which broke first" question for a moment, I was looking at the bolt and wondering how it only sheered in ONE place. If the bolt was indeed sheered, it should be in three pieces, since the central shaft meets the outer in two places. How could it cleanly sheer off one without damaging the other?

Also from the looks of the bolt, it appears to have been snapped by pulling force, looking a lot like what you'd get if you over-torqued a nut and broke the bolt. (been there, done that, looks just that way) If we follow an assumption that the bolt was torqued down too far, but not far enough to cause immediate failure, then forces applied by the engine/head during spool-up may have actually caused the bolt to fracture. The break happening to be where the main shaft and collar meet because that's where there was a small sheering force that took the bolt beyond its limit. (random chance causing the specific one of the two meeting points to break) Then centrifical force drove out the longer end as the head came up to speed, leaving the remaining short end to spin around and scratch up the main shaft as the head took off for an independent flight.

It's possible that the jesus bolt may have even been broke prior to that day.
02-25-2002 Over year old.
HOMEPAGE  
 
 
SemiArticulate
Veteran
Location: On Location

Can I get a closeup picture of both damaged faces of the broken bolt?

02-26-2002 Over year old.
 
 
Vance
Veteran
Location: York ,PA

Steve DiFranco said that all manufacturers do not supply the correct bolt, or at least the vast majority of them don't supply a bolt with the correct shoulder length. Mainshaft, mainblade grips and tail blade grips are the areas where they should be. Bottom line is that the manufacturers cut costs wherever they can and supplying the correct bolt is more expensive.
VD
02-26-2002 Over year old.
HOMEPAGE  
 
 
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Thunder Tiger Raptors 30-90 - Imperio > Raptor Head explodes-please read!!!!
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