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HomeAircraftHelicopterHIROBOOther › Pls help..problem with the spooling up of freya SST eagle
03-07-2008 05:15 PM  10 years agoPost 1
viperviper

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Australia

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After the freak incident of having my 2 main blade grips gave way during the starting up... till date, i am still puzzled what is the cause of it.. beside fatigue on the main grips which i thought. but thinking it thru, how can 2 main grips gave way at the same time.. However, there is one important observation that i have noticed, that is, while in the process of spooling up the heli from low to mid stick, there is this weird feeling of 'resistance' of the blade rpm when i move the TX stick from low to the mid position, kind of a feeling of tightness and no room for the rpm to spool up further at that instant position of mid stick. and the next moment 'BANG!'...sending the 2 blades flying off like bullets... in different directions.

Now that i have just rebuilt the heli... i just wanted to seek some expert opinion what could be the problem and what are the things i need to check or precaution to take note before i test it the next flight... just dun want the same freaking incident to happen again.. it may kill....

Pls advise.

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03-07-2008 05:32 PM  10 years agoPost 2
racingstripe

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Sacramento, CA

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The spindle bolt(s) were not sufficiently tightened.

Make sure to use the appropriate thread locking compound on these bolts during assembly.

andy-

Proofread carefully to see if you any words out.

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03-07-2008 05:50 PM  10 years agoPost 3
viperviper

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Australia

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spindle bolts? r u refering to the main shaft bolts or feathering shaft.?

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03-07-2008 05:54 PM  10 years agoPost 4
racingstripe

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Sacramento, CA

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Feathering shaft.

When you went to pick up your blades, was the spindle in the head or one of the grips?

I had this exact same thing happen to me when I was helping out a guy... he forgot to tighten the bolts.

andy-

Proofread carefully to see if you any words out.

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03-07-2008 06:01 PM  10 years agoPost 5
viperviper

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Australia

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my feathering shaft was tight and still in the head hub. the blades flew off with the blade screw and nut still in the blades when i picked them up, the grips just burst off..

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03-07-2008 06:27 PM  10 years agoPost 6
Leif

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USA

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This discussion is useless without pictures of the damaged parts or a better description of the failure.

Are you saying that the main blade GRIPS failed? If so, exactly where did they fail? Did they crack or did the outer bearing come apart causing them to rip off of the heli.

The geometry of most blade grips would make it almost impossible for the grips to depart the heli while the feathering shaft bolts were still in place. I suppose it is possible that a failure of the outer bearing could have this result, but it seems pretty unlikely that this would happen with both grips.

Without more data we can only speculate.

Leif

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03-07-2008 07:29 PM  10 years agoPost 7
tadawson

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Lewisville, TX

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Did you use too thin of a set of main blades, and thus have to flex the grips to come together to hold them? If so, there is the failure reason . . . . . the blades should fit the grips snugly before the screws go in. If not, then never mind . . . . but this **would** cause a failure pretty much exactly as you have described.

- Tim

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03-07-2008 10:14 PM  10 years agoPost 8
Ivan

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Wichita

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Over tightening the grips can cause this. On many helis there is a hollowed out place where the bearing slides into the grip, and the bolt tightens directly on this part. Since there is no direct support below the bolt its self, it can cause the grip to flex and create a fracture in the grip from the bolt hole outward. Most of the time you won't see this fracture unless you really look close. When this fracture occurs, it is only a matter of time until you get a catastrophic failure. I am not sure why the go at the same time either. Shuttles will do this. This is also the reason the Pantera manual tells you not to tighten the tail grips too tight and then puts it all on you by saying "You've been warned". This is a bad design, but it doesn't seem to cause many problems on the Freyas. I have had it happen on two shuttles, the pantera tail, and a few others. In my opinion the Eagle tail grip, that splits in two with bolts is the best and a design like the Vigor/Vibe is best for main grips, even though shims can be a pain. I have never seen this happen to either of these types.

I made a pic to help clear it up a bit.

Back to it!

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03-08-2008 01:04 AM  10 years agoPost 9
viperviper

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Australia

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kind of regretted for not taking the failed grips pics. Btw, like what Ivan has posted, the 1/4 portion of the grips ripped at the bolt hole outward.

Ivan,
As extracted: "On many helis there is a hollowed out place where the bearing slides into the grip, and the bolt tightens directly on this part. Since there is no direct support below the bolt its self, it can cause the grip to flex and create a fracture in the grip from the bolt hole outward."

1. but how do i know if the bearing that slides into the grip is not too tight? I have even check for the tighteness of the blade gripping when the blade bolt is being tighten. I'm pretty sure that the blade bolts are not overly tighten. Pls advise.

2. I noticed that the grips are different from the new one i have currently changed out. The old grips are smooth in both upper and lower outer surface, there is no 2 parallel notch lines that runs on the upperor top surface of the grips, where the word HIROBO imprinted there. Will this different in part cause a fatigue problem? I have not replace these grips before.

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03-08-2008 02:08 AM  10 years agoPost 10
Ivan

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Wichita

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Not the bearings, the blade bolts themselves. If you tighten them too tight it makes the hollowed out part compress and ends up cracking the grip. They really only need to be snug enough to keep the blades from folding back on spool up.

The missing chunk on the grip tells the story. I have seen similar results on every failure.

Back to it!

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03-08-2008 03:54 AM  10 years agoPost 11
viperviper

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Australia

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ok. then, i will watch the blade bolts tightness. Will spool it up tmr when the blades arrive today.

Thanks ALL for the replies above. cheers and happy flying.

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03-08-2008 10:52 AM  10 years agoPost 12
viperviper

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Australia

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Spooled up the heli today and hovered. It's serviceable now... seems like its the main grips fatigue that cause the problem. now thinking of changing out the grips to the cnc metal parts which i have just bought.. what holding me back is just short of one more hex driver to remove the 2 bolts on the feathering shaft that hold the main grips. Is removing them easy.. i tried one with hex driver and one with L-shape allan hex tool... i wore out the allan hex tool.. any opinion in removing the bolts in order to change out the grips to the cnc type., pls advise.

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03-08-2008 07:25 PM  10 years agoPost 13
F3CWNB

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Napier, New Zealand

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Ivan

Thanks for your input... We should all take note on saftey issues.

'Life' is Looking Up!!!

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03-09-2008 01:54 AM  10 years agoPost 14
viperviper

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Australia

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Can anyone advise on the max headspeed that the heli can hit before the grips give way? i have a tachometer, thinking of taching the headspeed to prevent any overspeeding.
Pls advise.

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03-09-2008 06:19 AM  10 years agoPost 15
Ivan

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Wichita

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Max headspeed on a 90 shouldn't be much more than 1950 or there abouts. I think 2000 would be pushing it a bit hard.

To get a worn out screw loose there are several tricks. If the driver is worn out, try one of the machined hex drivers, instead of the stamped ones. Also you can buy valve lapping compound from a parts store and coat the driver with it and it gives the driver "bite". Valve grinding compound is basically a paste with garnet sand in it.

Back to it!

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03-09-2008 01:38 PM  10 years agoPost 16
viperviper

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Australia

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thanks Ivan,

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HomeAircraftHelicopterHIROBOOther › Pls help..problem with the spooling up of freya SST eagle
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