Jesus Bolts

[Fixxxer]

And for those noobs this ain't any religous crap

Was sitting here wondering what the strength of these little bolts are, considering they are the sole thing between a flying heli and a pile of bits they must be pretty tough cookies and the same must apply to the blade bolts. I'm Sure I read that blades can put upto 100kg on a bolt.

So does anybody have any idea of breaking points. just curious.

[Jamez]

Hold on we have a 30 ton bearing press here and some M3 hi tensile bolts, give me 10 mins and I might have something for you

[Stuart]

Haven't a clue but I would suspect a few factors come into play.

1. The grade of the material used
2. The shear loadings
3. Ensuring the shank covers the whole area and not just one side...

example below: std one is the top on where the shank doesn't go right through.....changed for bottom one where it does - obviously trimmed it down to fit.



4. Size of bolt M3 or M4 the Synergy uses 4 x M4 bolts that bolt into the main mast at the base, but uses a M3 Pin in headblock locked in with a grub screw.

[Jamez]

The answer to this is next to f.. all, it didn't even move the gauge needle before it cut it in half. So a static shearing load of less than 100kg per cm (much much less as this is the first increment on the gauge). on an M3 high tensile steel bolt through a piece of 6mm mild steel bar.

[Jamez]

M4 blade bolt hit about 50 kg per cm before it snapped.

[Toolman]

Jamez,

I am not sure those figures sound correct to me, though I am no Stress man.

On another post on RR, it was calculated that the pull on a 550mm blade at about 1600rpm could be as much as 300kg & we used to run those on 3mm bolts. 600mm blades on 2100rpm could be as much as 600kg on 4mm bolts! I sure someone posted bolt strengths as well, I'll try to find the post.

Tim.

[xygax]

JAmez could you repeat the tests with stainless bolts these should be better in sheer than high tensile

Steve..

[Fixxxer]

Interesting stuff guys, I was aware of the shank needing to be thru both sides like stuart pointed out. 300 to 600 kg's seems a little too much, that's a hell of a lot of stress to be putting on one small bolt and that's not taking into account the force on the threads of the feathering shaft bolts.

[Toolman]

Those figures are rough orders of magnitude & I am not sure from memory exactly what rpm's they were calculated at.

I do know though that Hirobo Sceadu Blade grips are tested to a loading of 1400kg.

Tim.

[ross]

You can always swop the bolts for "high tensile" types or Titanium (they are about and a bit pricey). Probably far east bolts are plain mild steel types. If you do swop for high tensile get them from a reputable stockists like a model engineering outfit (see Model Engineering mag or Engineering in Miniature at the usual High street store ).

Interesting theory though. .Makes you think.

[Jamez]

Can do, but not todays as I am at home now.

[warboysastro]

Bolts in shear can be incredibly strong. Most 1 tonne electromechanical hoists I've used rely on a single M6 bolt between the hook and whatever you're lifting.

Also, in the course of my work, I've relied on eight M10 bolts to hold down a rig whilst a rocket motor fires, producing around 12 tonnes of instantaneous thrust.

I would have thought the M4 (whatever) bolts used on heli's would be pretty strong. Failure probably only comes about through some other cause such as movement of the rotor head causing nicking at the sides of the bolt to create a failure point, or dare I say it poor quality bolts from the far east.

Cheers - Rob

[gazza]

The answer to this is next to f.. all, it didn't even move the gauge needle before it cut it in half. So a static shearing load of less than 100kg per cm (much much less as this is the first increment on the gauge). on an M3 high tensile steel bolt through a piece of 6mm mild steel bar.

Probably perform better tightened down & under tension as it is when the blades are fitted & 'Nipped up'?

[Jamez]

I don't have an inexhaustable amount of bolts to try this with, but just to let you know how we done it, we drilled a 3mm hole through a piece of 6mm thick mild steel bar. we then placed the bolt half way through (onto the shank) standing the bar up on the plates of the press so as the head end ( head was removed so it would sit flat ) was on one side of a gap and the bottom was the other side of the gap we then pushed down on the 6mm bar which cut its way through the bolt with 2 areas in shear.

I was surpised at how easy they gave up.

[Toolman]

So a static shearing load of less than 100kg per cm (much much less as this is the first increment on the gauge)

I am wondering about what the units mean, abvoiusly the bolt sectional area is less than a square cm. Does this mean 100kg per sq cm?

Also were the bolts high tensile steel type?

Tim.