"Piss off, Trainee!"

[Centaurus]

Ken Andrews once told me the Wirraway can be very unforgiving in such circumstances

That applies to any aircraft if the barrel roll is started at too low an altitude and allowance not made for the height loss during the recovery segment. One tragic accident occurred at RAAF Laverton where a USAF pilot flying a high altitude derivative of the Canberra bomber attempted a barrel roll shortly after takeoff. The aircraft dished out and hit the ground. The pilot had seen RAAF test pilot Milton Cottee execute the same manoeuvre the day before in an RAAF Canberra except Cottee ensured the aircraft was climbing before starting the barrel roll and thus allowing plenty of room to complete the manoeuvre. See: https://aviation-safety.net/wikibase/158852

Then in September 1962 the RAAF Central Flying School Formation aerobatic team of four dual control Vampires known as The Red Sales crashed during a practice formation barrel roll near East Sale RAAF Base. That was a low altitude barrel roll misjudged. All six pilots were killed. http://www.adf-serials.com.au/research/redsales.pdf

I flew with Squadron Leader Ken Andrews in the Wirraway at CFS during my instructor course in 1955. He was a good aerobatic pilot. I believe he is still around at the age of 102 in Sydney? Lastly, I nearly made a twit of myself in 1953 when flying a Mustang at an air show at Townsville when I tried an unrehearsed attempt at a low altitude barrel roll in front of spectators. I recall flying along runway 19 at high speed and 300 feet and pulling up to commence the barrel roll. Passing through the inverted part of the roll l was startled to see through the windscreen a small 700 feet high hill called Mount Louisa. It looked awfully close when viewed from an inverted position. I quickly reversed the direction of roll and was relieved to see Mt Louisa pass a safe distance below me. The lesson I learnt from that was to never attempt such a low level manouvre without previous practice at a safe height.