[SML] 5x safety rating?

[Dale Farmer]

On 7/20/2015 8:48 PM, Jerry Durand via Stagecraft wrote:
> So, the SpaceX failure seems to be from a steel strut rated for 10,000
> pounds that broke at 2,000.  Verified by testing struts in stock with
> more failures found.
>
> It's bad when you're not safe using a 5x margin on your designs.
> Anything like this happing with regular rigging gear?
>

Strut with a design breaking strength of that or safe working load of 
that?    Also this is an aerospace design, where every ounce counts, so 
components and designs are generally made to be just a little bit 
stronger than the largest expected load and not a jot or tittle more.

Each ounce taken up by structural load takes an ounce out of payload. 
Great temptation to make your things a little bit stronger to give you a 
larger safety margin, but that means the engines and airframe have to 
push more pounds off the ground, which means the engine needs to be that 
much larger and you need that much more fuel, so you have to increase 
the tankage, which increases the total weight, so you need more powerful 
engines, and eventually you get the Saturn V rocket.

   Dale