There was only one way to find out: Martin-Baker built a number of rigs to test the effect of the upward compressive thrust on the body of a seated man shot up a near-vertical path. They would then measure the accelerations and rates of rise of g involved and quiz the subject about how they felt. The first rig comprised a 4.8m-high (16 foot) metal tripod with a pair of seat guide rails fitted to one of the legs. The seat was driven by telescopic tubes "energised by an explosive cartridge".

Tests with a 91kg (200lb) dummy load worked well but what was really needed was a man – and a brave Martin-Baker aircraft fitter called Bernard Lynch stepped up. Lynch would later act as the guinea pig in 30 aircraft ejections, mainly in Gloster Meteors.

"Bernard Lynch undertook the first live ride, being shot up the rig to a height of 4ft 8in. In three further tests, the power of the cartridge was progressively increased until a height of 10ft (3m) feet was reached, at which stage he reported the onset of considerable physical discomfort," the company says.

‘Massive explosion’

The handlebar-mustachioed Lynch was feeling back pain when pulling a mere 4g - so Martin began studying the human spine, including observing surgical operations on them, in a bid to understand its limitations. Indeed, Sharman’s biography reveals that Martin's secretary was shocked to receive human spine parts from a surgeon friend of Martin's, dubbing them "ghastly bits of body".

The first ejector seats, which fired the pilot using only an explosive cartridge (or a pair of them), were hard on the spine. Modern seats - whether they are the British, American or Russian types - further reduce the vertical g pulled on the ejectee by having the ejection gun only just powerful enough to get the pilot clear of the tailfin. At that point, a pack of rocket motors take over, taking the seat a further 60 metres (200ft) higher.

It wasn’t always like this. Former RAF flight lieutenant Craig Penrice, a member of the Royal Aeronautical Society who comments on ejection issues, knows that all too well. In 2003 he was flying a 1950-era Hawker Hunter back from an airshow in Portrush, Northern Ireland when both its electrical system and its engine failed over the Welsh coast. For the second time in his flying career, he had to eject. "There was a huge, massive explosion and I felt the most enormous force on my behind. The pain in my back felt like I had been hit by a plank of wood."