One for the brits - why do we say 'gone pear shaped', as opposed to 'gone lightbulb shaped'?

it came from flying where someone tried to do a perfect circle and it went wrong going "pear shaped" and not circular, hence its all gone pear shaped..hope this helps
One for the brits - why do we say 'gone pear shaped', as opposed to 'gone lightbulb shaped'?
"It went pear-shaped" is used, in common English jargon, to refer to a project that resulted in failure. It suggests that the fiasco was beyond the control of any specific individual. The expression it is not in any way regarded as offensive or vulgar.

Now for the etymology: There are several versions and it's a case of choosing the one which seems to you the most likely.

Some sources insist that its origins lie in ballooning, and that a pear suggests the shape of a collapsed balloon. Others believe that 'pear-shaped' is rooted in aircraft terminology. The story goes that certain types of aircraft engine casings might go 'pear-shaped' in the event of failure. There is a sidebar theory that the expression relates to pilot efforts to attempt perfectly circular loops in the air. Often, their circles would become pear-shaped; hence the connection to failure.

Math experts have yet another opinion. Quoting from an English website : Pear-shaped refers to a so-called "normal" distribution where the extremities of the distribution have become enlarged. In such a situation, improbable events would becomer much more probable. This at the moment (according to the site) is the preferred origin for "It's all gone pear-shaped".
Reply:I'm from the states but lived in Britain awhile back and this is one of my favorite brit-icisms. You guys have some great phrases. :)
Reply:Because a pear is big at the bottom and a light bulb big at the top.
Reply:don't know, maybe the saying has been around longer than lightbulbs.