go pear-shaped

Reader's Digest ３月号の記事 'Scamming The Scammers' から引用します。
John's having the op today. Just in case things go pear-shaped, he's willed 9.2M to me to spend "as frivolously as possible." Let me know how I can best receive the money? I've run up a sizable water bill that I neet to pay off ASAP.
慣用句らしい "go pear-shaped" の意味を調べます。
・Collins Dictionary: If a situation goes pear-shaped, bad things start happening.: He feared his career had gone a bit pear-shaped.
・Cambridge English Dictionary: If a plan goes pear-shaped, it fails: We'd planned to go away for the weekend, but it all went pear-shaped.
意味は分かりましたがこの言葉の由来が気になります。
多くの語源と同様に次のWikipediaの説明もすっきりしませんが、他に明快な説はないようなのでこれで良しとします。
The OED cites its origin as within the Royal Air Force; as of 2003 the earliest citation there is a quote in the 1983 book Air War South Atlantic. Others date it to the RAF in the 1940s, from pilots attempting to perform aerial manoeuvres such as loops. These are difficult to form perfectly, and are usually noticeably distorted?i.e., pear-shaped.