bones

Ok guys i know this was covered in a fair bit of detail on the ASRA site, though through the current going ons that is not possible to have access to it, though my thoughts on it are fairly simple and id like to hear opinions on it from any/every one.
The hub bars cracking/breaking that we thank god have had a repreve from at the moment, is still not resolved, so my thoughts are, the standard teeter block is 65 mm or 2 1/2", and the standard towers are about 3" apart to fit that, my question is why cant we/they the manufacturers of heads and hub bars start making a new width bar/tower combination, and gradually fase out the old style over maybe a 5 year period, as i know most people replace the heads and the likes sometimes, and if your only doing 50 hrs/yr you prob wont ever need to replace the gear at all, and lets face it a new head from most of the manufacturers is about $800-1000, that is peanuts, besides the price of your life, i'll guarantee all the people who have been involved with cracking/breaking bars would have paid many times that had they known..
Also then design the teeter blocks so they step over the side of the bar, to take some of the side loads of the prerotators, it might mean that we end up with a tower width of 4-41/2" and a bar width of 3",, but does it really matter,, it comes back to if some one could do the figures of it, and if it could be proved the by going wider with the bars, it will take even 25% of the stress out of the bar, and that in turn takes 25% of the risk of a bar cracking i would think it would be well worth the exercise.
thoughts on this please, it's been on my mind for a long time, wodering whether its worth kicking around..

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niquenaque

Mark,

Agree with what you say generally, but you should consider why the bars crack where they do.

From memory in all the cases of a bar cracking it occured at a point where the bar had been machined or drilled.

The RAF bars cracked where they had been milled down in thickness to meet the rotor blade thickness so the root straps could be attached to the bar.

The latest fatal failure, which Alan Wardill showed me some photos of and for which I did some drawings for the Coroner's illucidation, had a bar that cracked through one of the teeter block bolt holes and progressed through the rest of the bar. This was a bar which had 1000 hours up and which was used for mustering, not a hub bar friendly activity, especially when you watch the wizardry of the likes of birdy in the machine with maneuvering, most torturous.

What I think we really need to do is make the hub bars so they actually go *outside* the teeter towers and permit inspection, as when they are between the towers they are hard to see, certainly the last fatal due to hub bar failure could have been avoided in this fashion. The Magni arrangement in this respect is a good one, as are the Wallis blades and another one which I cannot name at this point, I think Dragon Wings but am not sure. The arrangement uses a centre post and a hole in the hub bar, which is quite wide with a teeter block outside the post, or as per the magni two vertical plates which pick up both the blades and the teeter tower height at the one time.

As to making the hub bar wider I don't concur, it would be better to make it deeper in its cross section as the 'extreme fibre' stress is then reduced and not so many rotor heads are affected by the change, that is if we are to keep them the same width, all it might mean in this instance is that the blade straps might need packers to keep the thickness right. I had Jack Allen make me a 1" thick hub bar - same width but for increased rotor diameter, it paid off till I flopped it over - silly me. I've no doubt the hub bar is good, not so sure about the blades, they're still in the shop.

Hope this helps,

Nick.

Gyrodes

Hi Mark & others, I made reference to what you have stated above with a general concenses from the people making the rotors that by just increasing the thickness of the hub bar to one inch was an over strength increase which will more than compensate for the increased stress applied. I have continued to fail to see the increase in thickness to be the only answer here. My personal opinion is that all dimentions should be increased equally, ie length by X% then width and thickness also by the same X%. The other point I wish to raise here is the distance the bolt holes in the hub bar from the outside edges on most hub bars where high stress is applied (teta block to hubbar) do not seem to be conforming to the recomended 3 bolt diameters from the edge as laid out in a chart in a aircraft design manual I was reading some time ago, which I can not recall which one at this time. Old timers setting in The information really caught my attention at the time. Of the pictures I have seen placed on the various forums of the hub bar failures, the cracks start at the holes on the thinest material area. Ok over to the engineering people now , I am only a simple driller of 30 years experiance what would I know Please note I am only raising discusion NOT RECOMENDATION here. There is logical explenations for it surely. All the best Des Garvin.

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Aussie_Paul

IMHO composite hub bars would be an extremelly good move.

Aussie Paul.

bones

Nic alot of the time its not the flying that will cause you problems, even the hard type of which you have seen on a few videos of late, i have personal seen two different bars, one an AK bar(about 1000 hrs) and the other a Patroney bar(with i think it was 1200 hrs on a twin seat machine) doin this type of flying, and they both looked fine no sign of cracks and they were being sent back for testing to Adrian(i think), its the ground handling that will start most cracks, rough ground and rotors not spinning quick enough to carry they own load is the thoughts of a lot of people.
The other styles you mention are worth looking into, and it maybe the way to go.



Des, Having read back through my post i meant to put in thinkness as well, it must have slipped me..
The holes thing is what i was trying to get at, if the bar and or the teeter block were wider and stepped over the side of the batr even just 20mm, and machined to a near size for size fit, then with the side load issue taken out of the equation(spelling?), then the holes that are put to the sides of the bar could then be moved back to the middle of the bar lessening the risk of a crack starting from that point..

Paul are they proven yet, to be able to stand up to this problem that we have facing us as a sport, ie. who has been making them and for how long??

I know you cant make every thing fool proof/crack proof , how ever as a group we must be seen to be trying to get on top of this problem, and in alot of way i believe that ASRA is doing the best they can at the moment, i'm just kicking a ball around and see who picks it up, as i feel if one more hub bar crack/break results in a crash, CASA will be all over us like a rash, and personally i like to stay out of the lime light, i was raised in the seen and not heard thought pattern and its worked pretty well, and it would be great if we never hear about another cracked hub bar again.

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Gyrodes

Hi All, Back in the mist of thought I seem to recall that Doc John Evans was working on the use of a spring steel set up, has anyone heard/seen anything of its operational behaviour yet. From the misty memory it was like a three leaf spring arangement upside down. Ah doc you visiting/ lurking here. Yeh I know I'm a dober. Could you make coment on your findings as we are interested. I recall that the drilling of the material was a bit of a challenge. Boron bits are the answer to that as i have had holes drilled in hardened bearing centres very successfully. All the best Des Garvin.

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russ

Couple of things..........that idea of machining a teeter block to drop "over" the hub bar a tad, works real good. Releases all the shock load off the 2 bolts.

Hub bars crackin................was a non event back yrs ago.............my theory

back then we flew like lame ducks coz we had bugger all power pushin us, now we got big horse powers available, which opens up all the doors.............we get really stuck into tossing em around, which to me , means we also exert huge forces to the blades etc etc now.

SO...........the weak link here is................hub bars, they are not up to it now.

That thrill of diving down......reefing the stick back and wacking your knee off as you also slam the machine into a tite turn..........then that bewtifull........boof boof boof as them blades howl under load, is now the prob here

buggered if i know..........but it seems to follow

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bones

I couldnt see why it could be a better idea either Russ, and not that hard to do.
Russ if it is done right, it shouldnt put any more stress into the blades than a heli comin in to land, mate i seen a pic of one comin into land at a property around here, it was a hughes 300 and fair dink the blade ends were about 3' above the hub, at all get back to rotor management, i believe they can take a fair amount of that type of flying AS LONG as it is smooth, and not as you put it What did you mean by this part mate??

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bones

Damn gettin good at thi quoting thingy

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BeefBear

Maybe you need to decrease the hours permitted on hubbars? Or make it a manditory remove and inspect procedure?

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