[Milsurplus] Milsurplus Digest, Vol 171, Issue 44

[Michael Hanz]

On 8/2/2018 7:55 AM, Mark K3MSB wrote:

> I think Gladwell mentioned in his video that the bombsights had a 
> small explosive charge (thermite if I recall) in them so they’d get 
> destroyed if the bomber crashed.     My immediate thought was what 
> triggered those charges?  G-Forces?    That could have some nasty 
> consequences for the Bombardier and Navigator in the nose section that 
> survived a rough crash landing.

I can't specifically connect the bombsight with it, but that standard 
method of doing what you describe for the IFF sets was the SA-3/BC-706 
inertial impact switch.  The early ones had a bad habit of occasionally 
triggering on hard landings or heavy turbulence, even though the setting 
was 9g.  Turns out there was a spring inside that was weakening over 
time and testing showed they were triggering at 6 to 8g.  The solution 
was to raise the set point to 10g and ask the field to report any 
further accidental firings.  The couple of examples of unfortunate IFF 
sets I've seen that have endured this experience show the aluminum case 
blown up like a balloon from the pressure.

Image result for BC-706 inertial switch

There was a separate switchbox (BC-765 /et al/) with two pushbuttons 
wired in series mounted at the pilot's/copilots station.  In the event 
of an impending crash, the pilot could press those two buttons 
simultaneously to set off the charges....hopefully before he bailed out...

Image result for BC-765 switchbox

  - Mike  KC4TOS
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