Gripenland
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| posted on 17/4/04 at 03:24 PM |
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Prop shaft?
It seems to me that most BEC:s use a two piece prop shaft? Why is that? I can understand it if you run a live rear axle. But if you run IRS or De
Dion, why not use a one peace prop?
kokos-racing.com
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Peteff
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| posted on 17/4/04 at 03:44 PM |
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There will be a lot of weight on the bike output and it will be hard to balance as it will tend to bend in the middle, like a bow.
yours, Pete
I went into the RSPCA office the other day. It was so small you could hardly swing a cat in there.
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Mk-Ninja
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| posted on 17/4/04 at 04:15 PM |
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Also you would have to alter the transmission tunnel to get a straight line from the output shaft to the diff.
I'm sure I've got one, just don't know where I've put it
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ChrisBradley04
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| posted on 17/4/04 at 04:50 PM |
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You can also make them a lot lighter if you support them in the middle, as each half can be made from smaller bore/thickness tubing.
Regards
Chris
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Gripenland
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| posted on 17/4/04 at 06:19 PM |
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Thanks for your input guys! 
Mayby I'm a bit slow but...
Peteff- Isn't the bike output shaft designed so take the load from the sprocket and chain of the motorbike? To me it seems that radial force is
much higher with a sprocket and chain than the weight of a propshaft? Or am I missing something?
ChrisBradley04- I thought tourque set the dimensions of the tube? Not vibration. Have I got that wrong?
kokos-racing.com
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undecided
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| posted on 17/4/04 at 06:27 PM |
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they break..believe me you want some kind of centre bearing to hold the bloody thing still because all sorts of nasty things can and do happen when
things spin at 10,000rpm!
Don't let some muppet say you can have a propshaft getting on for 4ft long without it being supported...i did and it snapped....enough said!
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Gripenland
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| posted on 17/4/04 at 06:35 PM |
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quote:
Originally posted by undecided
they break..believe me you want some kind of centre bearing to hold the bloody thing still because all sorts of nasty things can and do happen when
things spin at 10,000rpm!
Don't let some muppet say you can have a propshaft getting on for 4ft long without it being supported...i did and it snapped....enough said!
Damn, that must have been scary  I sure hope that it all ended well?
kokos-racing.com
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Gripenland
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| posted on 17/4/04 at 06:47 PM |
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undecided- You are right. RPM and length kills the prop. Angles are also important.
I found this on the web. This is for dragrcing props
 
Rescued attachment proptable.jpg
kokos-racing.com
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Bob C
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| posted on 17/4/04 at 06:53 PM |
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Critical speed is speed at which the natural fundamental resonant frequency of the tube (bending in the middle & twanging up & down) equals
its rotational speed. If anything is going to go wrong - this is when it will happen...
Good data, but I can't see material info, just diameter of tube - maybe it's just me not looking properly
Bob C
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Gripenland
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| posted on 17/4/04 at 06:59 PM |
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Here is a link to the data sheet.
kokos-racing.com
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woodster
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| posted on 17/4/04 at 07:06 PM |
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PROP SHAFT
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Gripenland
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| posted on 17/4/04 at 07:11 PM |
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quote:
Originally posted by woodster
PROP SHAFT
???
kokos-racing.com
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Peteff
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| posted on 17/4/04 at 07:35 PM |
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(bending in the middle & twanging up & down)
Like a bow in laymans terms.
To me it seems that radial force is much higher with a sprocket and chain than the weight of a propshaft?
I'm talking about the weight, not the force it exerts in rotation. The sprocket adaptor and propshaft all bear down on the bearing carrying the
output shaft.
yours, Pete
I went into the RSPCA office the other day. It was so small you could hardly swing a cat in there.
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woodster
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| posted on 17/4/04 at 07:35 PM |
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search ........... prop pic ........ and look in my photo achive ................ or search woodster
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Gripenland
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| posted on 17/4/04 at 07:47 PM |
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quote:
Originally posted by Peteff
The sprocket adaptor and propshaft all bear down on the bearing carrying the output shaft.
Yes, but when the engine turns the chain it will also load the the same bearing. So to me that inicates that the bearing is designed to handle some
serious loads. Ok the direction of the forces are not the same but still.
kokos-racing.com
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Gripenland
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| posted on 17/4/04 at 07:49 PM |
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quote:
Originally posted by woodster
search ........... prop pic ........ and look in my photo achive ................ or search woodster
Hmm, I see what you mean Did you use a one peace prop?
kokos-racing.com
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ChrisGamlin
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| posted on 17/4/04 at 08:13 PM |
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Someone in the know on the BEC list worked out that to make a single piece prop the length required for a BEC and able to rotate at the speeds
required, it would need to be something like 6" in diameter!
I only know of one person who had a single piece prop in a BEC about 3 years ago, and that too broke catastrophically. If you want to confirm it,
maybe give someone like Bailey Morris a call and ask them their opinion.
Woodsters wasnt a one piece prop, but it had the scariest bodge of a prop flange ever known to man (not done by him I must add!)
Chris
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JoelP
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| posted on 17/4/04 at 10:30 PM |
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someone said that there is an equation involving the square of the length, apparently this is why length makes things much worse.
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Gripenland
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| posted on 18/4/04 at 03:05 PM |
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It is obvius that a two peace prop is the way to go unless you go really high tec.
Us vans have very long one peace prop shafts. But they turn at a slow rpm and have a large diameter so they get away with it.
The Volvo XC90 have a 1.5m long single peace propshaft. Its only 60mm in diameter but I guess it turns slow to.
kokos-racing.com
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