Hub-bars

[Ken Watson]

The bar is the same on the top as the bottom. Ken

[Greg Mitchell]

Ordinarily I enjoy happy coincidences.

[maulonir]

With rerards to the contact area of the piller block to the hub bar. I"ve seen lots of blades with the plllar block shimmed on one side to correct out of track blades on blades that have no adjustable pitch blocks like patroney"s and ak"s

[Ken Watson]

I thought i would post how I corrected my problem. This is only advice and it suited my circumstance. I clamped the naked bar on a good bench and also clamped a guide along the length of the bar to keep my lappinp movements of the block in line with the bar. I placed wet and dry on the bar upwards facing using the assumption that the paper will follow the deformation. I then used minor(1") movement to lap the block in. It took no time at all to get to zero clearance. I used WD as a lubricant, and also worked from opposite ends to balance out any favouritism. I"m happy with the outcome, but also plan to bond the block to the hub bar. Ken

[Mark Horan]

I was discussing hub bars with a mate this evening, and the possibility of one of the epoxy"s with a metal filler in it to take up any play between the block and the hub bar.I guess that the particle size of the filler would have to be quite minute (nothing to do with Time) and obviously not one that could give rise to electrolysis being a dissimilar metal to the alloy.

[Greg Mitchell]

I got a 0.06mm into one opposing corner fron the bolt holes on the block and 0.04mm into the other corner. Distance feeler gauge went in was approx 5 mm and 3 mm respectively.The block is slightly softer material than the bar material which is 6061 T6. The bar is 1" and the bends put into it is approx 3" out from the centre point. The blades a heavy stiff composite.The two bolts are fixed firmly in the bar and the block it self slides on and off a little to easily, indicating the holes are slightly oversized. The manufacturer says that they should not be elongated even if high torque pre-rotator has been in use.Markings to face of block around teeter hole (on both sides) is consistent with markings on 6061-T6 cotton reels and would be indicative of high torque pre-rotator use. Not to discount any possible effects that a double slider head may impart or negate.Bar is flat in the middle where the pillar block sits, check out the pics you can see mated and non-mated surfaces. You can see the corner sections where the feeler gauge, went in.The pillar block was slightly twisted (as was my Bensen Bar/Block armstrong rotor) and I am told this is pretty normal, though again pre-rotators add to this.There are witness marks on the top of the block at the two holes, indicating broader washers such as the like at the strap ends of the bar. However, in this case one AN thick washer has been used. It appears that the thick washer was not thick enough to prevent the nut from bottoming out on the shank. This may have contributed to some of what is seen in the pics.Recommendation was to install the broader washers plus one extra washer.Further suggested to consider doing as Ken has done, lap the block in, if there are further concerns.Where a space exists as Mark has commented, previously members have used such compounds to address these concerns. The down side I am told is should the part need to be separated, often heat need be applied to effect same.Rob M makes a valid point though, here and O/S gyro pilots have been shimming hub bar/pillar blocks as "par for the course". I intend to lap the block in, add broad washers plus one AN5 thick washer to each bolt.The markings on the reels and block face can be worked and 25 thou alum sheet material used to make up some washers (sub them down to required thickness) to interface between the two.I thoroughly checked out the double slider head and need to add a thin AN washer to geometrically locate the head dead centre. Mitch

[Greg Mitchell]

Pic would help.

[Ken Watson]

This is pretty much the same as mine. The thing that concerned me was with the blades on at rest. Try pushing the feeler in at diagonals then and you will see what i mean. It goes in substantially further. This is not too unlike the larkin hub bar AD. Movement at the block point was a contributing factor. On mine the contact only went half way into the bolt holes. Ken

[Greg Mitchell]

That makes sense Ken. The weight would be opening up those points rather than the corners which are bolted.Another thing which Rob mentioned again about the chordwise bow in the bar...from the centre of the hub bar to just short of where the bends are placed, there is no apparent bow when checked with a straight edge and looking for day light (high tech). However, the bar does have a noticable bows at the bend sites.Ken did you get any pics, it would be good to compare.I am hoping that the right amount of washer material atop the block and some lapping will stop most of the twist.What type of bonding agent are you considering.Mitch.

[maulonir]

Ken/GregWouldn"t it be better to set the hub bar up on a bench with the blades attached with the weight of the blades acting on the hub bar as it would be when sitting on top of the gyro. I reckon you will still get the gap happening when the blades are re-attached if you don"t. Rob

[Greg Mitchell]

That"s a point Rob. I would be more inclined to have fully mated surfaces when the blades are conned and in flight. That"s when all the real work is being done and for the longer period of time.Like Ken, I always strap my blades when not in use.Mitch.

[Brian]

Does anyone know just how much a hub bar is going to flex? I mean in flight from a high G pull around to mayby a slight pushover.

[Ken Watson]

Loctite 680. I dont disagree with anything said, but it doesn"t seem right to have a matchbox sitting on the side of an aerosol can. At the moment the weight is shared by the bolts and the block contact seems to do nothing much.Everything is working against itself. If your car has 5 nuts holding the front wheel on, you would not only bother using 2 would you. If there is consensus on one thing with the people I have talked to it is that none of them seem to know. If a front wheel was mounted to a race bike with a tolerance like this, I wouldn"t ride it. And I wouldn"t let others either. Ken

[Greg Mitchell]

Thanks. Mitch.