Re: Wings and back plates

[Chris Pitts <cpitts@xxxxxxxxx>]

John Grogan wrote:
> > Eh?  So you're really suggesting that 1 kg of lift from a bungeed wing is
> > not  equal to 1 kg of lift from an unbungeed?  Now _that's_ a good reason
> > for  taking those bungees off!!   ;-) 
>  
> No, my point is that the DR (or similar) wing will wrap around the tank
> when inflated thus directly supporting the main source of weight (your
> twinset).  The bungeed wing cannot do this as well thus transferring some
> of the weight to your back to support.  A friend of mine used to use OMS
> double-bungeed wings and complained of back ache after long decos.  He
> tried my set-up for 1 dive - no backache. 

Interesting theory, but I'm not sure that I believe it yet.

Let's think about this carefully.  The wing lifts the cylinders.  True.  But
it can only lift them at the points of fixing.  Normally these are the bolts
holding the harness onto the cylinder bands, and the fabric of the wing
sandwiched between the cylinders and the harness (which is what distributes
the load).

There is no definite fixing to the sides of the cylinders, so there can't be
much, if any, lift there.  So, AFAICS there is no difference from this point
of view between bungeed and unbungeed wings.


It sounds far more likely that your setup is more evenly balanced in other
aspects than your friend's, hence the difference in stresses on his back.  A
favourite could be the height of the cylinders relative to the top of the
wing (turning effects)?  Or harness adjustment?  Badly adjusted or
overweighted weight belts are another common cause of backache.  I really
don't think that it is the type of wing directly causing the problem here.  


Chris
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Chris Pitts, Principal Software Engineer
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