Re: Wings and back plates

[rockport@xxxxxxxxxxxxx (John Grogan)]

On Jan 07, 1998 10:24:42, 'Chris Pitts <cpitts@xxxxxxxxx>' wrote: 
 
 
>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. 
 
Oh go on Chris - you know yo want to ;-) 
 
>Let's think about this carefully.  The wing lifts the cylinders.  True. 
But 
>it can only lift them at the points of fixing.   
 
True, but because it is wrapped around the cylinders, it supports them
directly as well. 
 
>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. 
 
Probably.  But then he also used steel stages (one on each side) and had
his twinset lower down. 
 
> 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.
  
 
My cylinders are positioned higher so I can easily get to the valves.  The
top of the wing is where the cylinder neck starts.  Also I do not use a
weight belt.  Any extra weight needed is sandwiched between the twinset and
backplate.  Therefore all my weight is on my back.  The type of wing does
not directly cause the problem but it is a contributory factor.  There are
a number of factors involved, but every little bit helps. 
 
John.