The last surviving airmen who flew in Spitfires, Hurricanes and Lancaster bombers during the second world war, including Sqn Ldr George Leonard “Johnny” Johnson – the last of the Dambuster raiders of 1943 – have been tracked down and sketched by the artist Jeremy Houghton, to mark the centenary this week of the founding of the RAF.

His group portraits – The Last of the Few, depicting the surviving Battle of Britain pilots, and The Last of the Many, of the remaining bomber airmen – will be auctioned online after the centenary flypast over London on Tuesday, to raise funds for the RAF air cadets.

100 years of the RAF – in pictures Read more

Houghton used wax pencils, similar to those used by the navigators to track the routes for the missions on laminated maps that could be wiped clean and reused if the crew made it safely back to base. The men themselves, he said, did not want to be depicted in any heroic format such as oil paintings.

Play Video 0:51 RAF celebrates 100 years with 100-aircraft flypast - video

Houghton said he found it moving to visit the veterans at home, and find himself sitting opposite a man more than 90 years old. “Often he would rest quietly, calmly, he would submit to the process of sitting for a sketch. And yet before me would be someone who a lifetime ago engaged every sinew and sense, every faculty including his very last ounce of courage, to defend the skies above and land below.”

While sketching, he said he would often ask them to recall their war days. One man, John “Tim” Elkington, survived only because when he bailed out, another pilot managed to create a slipstream that carried him towards the land instead of an almost certain death by drowning in the sea below.

“Their almost matter-of-fact attitudes to what by any measure were extraordinary heroics reflect how they modestly underplay their own personal contribution to the defence of many privileges that we now take for granted,” said Houghton.

Facebook Twitter Pinterest The artist drew the portraits with wax pencils similar to those used by second world war navigators. Photograph: Jeremy Houghton

“My hope was simply to try and capture, in the uncomplicated and straightforward terms that they prefer, the sense of service, courage and bravery they showed.”

The largest flypast of military aircraft in years, up to 100 aircraft including the Dakota, Lancaster, Hurricane and Spitfire from the Battle of Britain Memorial Flight, training aircraft, along with the Red Arrows, helicopters and some of the RAF’s most modern planes, is due to pass over the capital and Buckingham Palace on Tuesday to celebrate the anniversary.

• This article was amended on 11 July 2018 because an earlier version implied all the airmen pictured were pilots. This has been corrected.