Weak bolts

[BrendAn]

they still have the website up with the dandenong address . thats why i went there.

 

[turboplanner]

Unbrako is just a brand; for this safety-related item you need a specification from the manufacturer.

[BrendAn]

3 minutes ago, turboplanner said:

Unbrako is just a brand; for this safety-related item you need a specification from the manufacturer.

yes it is. 

[BrendAn]

5 minutes ago, turboplanner said:

Unbrako is just a brand; for this safety-related item you need a specification from the manufacturer.

i can not see a problem with good quality high tensile bolts . the original bolts off it are and have been holding the prop on for 20 years. they are too short to use with the hub extension.

[facthunter]

IF you can get them. That's the problem.. A poorly made thread is a good start for a crack forming. Nev

[APenNameAndThatA]

8 hours ago, turboplanner said:

Unbrako is just a brand; for this safety-related item you need a specification from the manufacturer.

That was the problem. The specification was written on top of the bolt but it wasn’t true. Sure, 8.8 and 8 bolts are different, but they’re not that different. And nobody is going to break a high tensile bolt by over torquing it attaching their propeller. 

[extralite]

We got bolts with an 8 on them for a Bolly prop hub after being supplied one without bolts with an aircraft and then being sent the wrong bolts by Bolly Aus (sent adjustment bolts.) I assumed the 8 was an AN reference.  They fit but after reading this might be time to get better ones. Would anyone know the specs of them so we can order them from Propbits?

 

 

 

 

Edited September 28, 2022 by extralite

[old man emu]

Before you go crazy, step back and consider what the bolt, or any fastener, is doing.

 

In the picture above, the bolts are clamping the propeller boss to the crankshaft end plate. 

 

Why 6 bolts? To balance the forces generated by the rotational forces created by the movement of the propeller. Leave just one bolt out  and the prop will shimmy like a jelly on a plate.

 

What is the most important type of force in this situation, tension or shear?

This is failure in shear   causing the bolt to split across its diameter, and this is failure in tension  where the bolt stretches.

 

 

You are trying to keep the surfaces of two objects together along the longitudinal axis of the bolt. You are employing tension forces which are trying to stretch the bolt longer. 

 

The rotational forces produced by the spinning prop will create some shear force to the bolts, but each bolt in this case only has to deal with 1/6th of the total shear force. For a particular prop, the rotational force  F = m v² / r    is limited by the weight of the prop, the location of the centre of mass in relation to the radius of the prop, and prop RPM. A decent M8 bolt should have a shear strength on its grip length of 39 kN and on the fine threaded section about 19 kN. You wouldn't be worrying about shear strength unless you don't use an even number of bolts

 

[BrendAn]

1 hour ago, extralite said:

We got bolts with an 8 on them for a Bolly prop hub after being supplied one without bolts with an aircraft and then being sent the wrong bolts by Bolly Aus (sent adjustment bolts.) I assumed the 8 was an AN reference.  They fit but after reading this might be time to get better ones. Would anyone know the specs of them so we can order them from Propbits?

 

 

 

 

Nothing wrong with grade 8 bolts. I just bought some cheap rubbish

[facthunter]

Tabs or lockwire would save the mass of 6 nuts and the extra bolt length. When you use a locknut in that way interesting things are going on with the thread loading. Nev

[Blueadventures]

4 hours ago, extralite said:

We got bolts with an 8 on them for a Bolly prop hub after being supplied one without bolts with an aircraft and then being sent the wrong bolts by Bolly Aus (sent adjustment bolts.) I assumed the 8 was an AN reference.  They fit but after reading this might be time to get better ones. Would anyone know the specs of them so we can order them from Propbits?

 

 

 

 

Hi you should not fly with those bolts as there is no thread pitch extending past the nylock; needs to be at least 1 and better still 1.5 pitches visible.  Just commenting to safe and helpful so need longer bolts.  Cheers

[facthunter]

Nyloc is marginal for prop hub as it gets pretty warm.  Nev

[BrendAn]

48 minutes ago, facthunter said:

Tabs or lockwire would save the mass of 6 nuts and the extra bolt length. When you use a locknut in that way interesting things are going on with the thread loading. Nev

Rotax use locknuts. Nothing wrong with that.

[facthunter]

My point is still valid. Just because Rotax do it doesn't mean it can't be done better. That type of locking is faulty and too heavy. Nev

[BrendAn]

8 minutes ago, facthunter said:

My point is still valid. Just because Rotax do it doesn't mean it can't be done better. That type of locking is faulty and too heavy. Nev

I am fairly confident bombardier know what they are doing nev. 

 

 

[facthunter]

Nice to know, but if we applied that to everything we wouldn't question anything. Rolls Royce make good things too,  BUT.  Nev..

[turboplanner]

46 minutes ago, BrendAn said:

I am fairly confident bombardier know what they are doing nev. 

 

 

Bombadier didn't do that prop installation+ that's a safety related assembly.

[Thruster88]

25 minutes ago, facthunter said:

Nice to know, but if we applied that to everything we wouldn't question anything. Rolls Royce make good things too,  BUT.  Nev..

Perhaps you should explain your concern with the back of flange lock nuts, something I think about when applying torque to the lock nuts on my rotax 582.

[BrendAn]

38 minutes ago, turboplanner said:

Bombadier didn't do that prop installation+ that's a safety related assembly.

The rotax kit includes nyloc nuts 

[pmccarthy]

I would be worried about Nylocs that aren’t actually locked.

[extralite]

All good, we know the bolts arent right, hence the question. Good discussion though. 

[turboplanner]

This being a safety related item, and two former members being dead after another assembly was found under the seat with a crucial nut missing, has it occurred to anyone that maybe, possibly this is an application for castellated nuts and cotter pins.

[BrendAn]

34 minutes ago, turboplanner said:

This being a safety related item, and two former members being dead after another assembly was found under the seat with a crucial nut missing, has it occurred to anyone that maybe, possibly this is an application for castellated nuts and cotter pins.

Can U explain please.

[BrendAn]

1 hour ago, turboplanner said:

This being a safety related item, and two former members being dead after another assembly was found under the seat with a crucial nut missing, has it occurred to anyone that maybe, possibly this is an application for castellated nuts and cotter pins.

do you have a link to this incident. i would like to read it if possible.

[BrendAn]

3 hours ago, facthunter said:

Nice to know, but if we applied that to everything we wouldn't question anything. Rolls Royce make good things too,  BUT.  Nev..

well said. i was not trying to be disrespectful.  everything should be questioned thats how we learn.