teeter blocks

[asra]

i spoke to a bloke the other day that a long time ogo had put a large starter on as a prerotator. being an engineer he saw the 'sheer' forces that aplied to his larkins that werent originaly designed for this load and made a much longer teeter block. this block utilised the original bolts as well as haveng an extra bolt on each end diagonaly accross from the originals.there are now 4 not 2 bolts sharing the stress of pre rotation as well as later two are further from the centre of the hub bar and therfore have less leverage acting on them from the sprocket on the hub.is this correct??? and is this a simple option for ading strength while we ad mare stressful forces[pre rotator]???why are there 6 bigger bolts ataching the sprocket to the hub when the two on the teeter block share the same load yet have more leverage working against them??? ie. are closer to the centre of the hub. [the sprockts bolts are about where the teeter stops have left a dark mark.]Image Insert: 16.92 KBImage Insert: 11.52 KBthere seems to be more enginering holding the sprocket to the hub then the hub to the rotor!!!why dont all hub bars that are used in conjunction with a starter motor have more enginering put into the attachment of the teeter block to the hub bar?

[NiqueNaque]

Grant,I'm sure the ASRA board would love to get hold of the hub bar you speak of. Please contact Adrian Stoffells in relation to same.Regards,Nick.

[Brian]

You have a lot of flaking material happening Hoody, do you live next to the beach?You never know how far you can go, till you get there !

[asra]

no but this gyro did.i am sorting out another hub bar for easter and in the future i hope to have a 3ft 1 inch thick one making them 27ft.if i can get hold of the hub bar mentioned in time ill try to send it with some one to cooma.do the extra bolts and longer teeter block sound like a good idea???id like to incorporate one in my next hub bar if so and to do that ill need to know before the coning angle is pressed in the road,ie...close to the teeter block

[asra]

It's good to see this vital topic continue to attract attention. I must admit that the 'tear along the dotted line' holes in the middle of the hub bar don't seem like a good idea at the best of times! I doubt if adding further holes is prudent.Of even greater concern is the current trend to place the coning angle bends away from the centre of the hub bar, or by adding wedges at the ends. I recently learned that back about 1972 the then CAA did an engineering analysis and recommended that these bends be in the middle under the teeter block, but later accepted that in the middle 7 inches of the hub bar was OK, i.e. within 31/2" of the middle, to minimise flexing at this critical point.I realise that beefing things up is often regarded as the answer in this situation, but without a proper engineering analysis could actually make things worse.Let me point out that I am in no way qualified to make this judgement, but critics should ensure they are well qualified to defend these practices and produce calculations to back their assertions. A history of safe operation is OK up to a point, but if say 10% fail at a certain life that's 10% too many.I would suggest that we need to be a little more critical when we purchase components.John EvansThink logically and do things well, think laterally and do things better.

[asra]

excluding misstreatment or use with pre-rotators/accidents/or retirement due to age and hours, what is the failure rate of larkin or other hub bars with the coning angle out to the ends ??????has any one bothered to ask bert if he had a reason for putting the coning angle there???if the holes are diagonly opposite and far enough apart,would they be any more likely to tear than with one hole each side???what about the hub bars that have 4 bolts already???

[NiqueNaque]

This is what John means about the flexing:Image Insert: 4.36

[NiqueNaque]

Bending it in the bar also removes some of the bending stress suffered by the bolts, this scenario exists where wedges are used to provide coning angle. It means that the bottom bolt in the knuckle suffer less tension if the coning angle is set in the bar as opposed to the blocks.

[Tim]

Correct Nick. Also in the top diagram the normal flight forces are trying to bend the hub bar upwards, and the stresses raised would greatly reduce the fatigue life of the hub bar. Some manufacturers do this for manufacturing convenience, others for an alternative method of raising the teeter height for longer blades, without having to change the teeter block. Tim McClure

[asra]

Thanks for the diagrams Nick. One day I'll have to learn how to do that stuff!Hoody, how dare you ask such inconvenient questions![:0] You're getting to be a bit like the ignorant child who couldn't see the king's new clothes, cease and desist immediatly! Seriously though, all very good questions, keep it up[]I think the answer lies in the evolutionaty process, by which our machines have been 'improved by 'eye-ball engineering' to the point where the anomalies you have seen occur. Unfortunately this appears to be a result of the use of the 'history of safe operation' argument, which appears to be OK for some things, but may be quite invalid for others such as hub bars.As I pointed out in the previous post, good engineering information has been available since 1972, and was published in Gyro News at that time. While it is not the role of ASRA to be a design bureau, we do have safe information in the Standards which are available on this site.John EvansThink logically and do things well, think laterally and do things better.

[asra]

[Greg Mitchell]

Pete,Are you looking to move into the market place? What size blades and how much do they weigh?Regards,Mitch.www.thebutterflyllc.com

[asra]

Good stuff Pete, that sort of authorative material should be permanently available in a 'Techo' section on this site.John EvansThink logically and do things well, think laterally and do things better.

[NiqueNaque]

Pete,Why not just have a hinge in the guts like they did with the Cierva gyros?

[asra]