Start your engines: A radial engine only limited by the imagination

Mebberson himself is trained as a mechanical engineer who has also developed a passion for aerospace and aviation engineering. 

He has enjoyed a 20-year career in a successful family business that specialised in the design and manufacture of food grade thermoforming packaging machines. 

He credits his time designing, building, and installing these machines as the key to his broad-based real-world engineering skill set. 

“They were five-tonne, quarter-of-a-million-dollar high-speed packaging machines and we got a reputation for supplying the best of these machines all around the world,” says Mebberson.

“In hindsight, the skills that I learnt there, made [Radial Motion] all possible. It wasn’t just engineering skills, it was cash flow, people skills, all of the things you need to be able to do in a family business.” 

Ready to fly

After moving back to his hometown of Adelaide, Mebberson secured a million-dollar order from a former customer to design and make a new thermoforming packaging machine, which provided the funding to establish Bespoke Engineering in 2013. 

“At that point I was cobbling together second-hand machines and getting together a bit of machine capability. But during this whole time, I was designing a small aircraft and it needed a particular engine that wasn’t available, so I started to look at, and learn about engines,” he says.

“I’m a recreational pilot and love aircraft, but also love aircraft design, so for the last 20 years my bedtime reading has been aircraft design books — I’ve got like a pallet of them,” he laughs.  

Despite being self-taught when it comes to the topic, he explains that the concept for his aircraft engine started as a two-cylinder but quickly evolved into the three-cylinder radial.

It was four years ago, Mebberson met successful Adelaide engineer Loui Burke through Burke’s ownership of Harrop Casting Technology, a well-regarded Adelaide-based non-ferrous foundry, which he’d visited when searching for someone to cast his engine.

“Loui immediately recognised the [engine’s] potential and early on we both recognised the opportunity to stick these things in vehicles like Porsches or VW Kombis. Since then, we’ve invested the best part of three million dollars in developing the radial engine,” Mebberson says. 

“It’s quite an unusual engine configuration, but the concept we had worked, and we first went from air cooled to water cooled, then continuously developed it and started to make patterns and casts, all the time being serious about low-volume production.”

Working out the bugs

Having built numerous prototypes, the company now has a batch of five pre-production engines and is halfway through a batch of 10 production engines.

“We’ve put them in and raced in a ‘72 Volkswagen Super Bug — which is a little scary as it’s got far too much power, but it’s good fun — as well as a Kombi and a 356 Porsche,” he says.

While most engines are vee or inline, Mebberson explains that his radial is what the Germans call a “stern” or star motor, with the cylinders arranged around the crankshaft, which makes for a short and torquey engine. 

“What we’ve done that’s a little bit different to original radials is the originals didn’t have a conventional crankshaft and conrod, they had a master crank that was thrown off and then little slave rods that connected to it,” he says.

“We’ve got three conrods on a common journal, so it’s like a V-Twin with a single throw crank and two conrods. Having three conrods on a single throw crank is quite an unusual way of doing a radial engine and makes the diameter quite small.” 

To ensure customers have ready easy access to parts, all the internal consumables, such as the pistons, conrods, valves, and valve springs are from a General Motors LS1 V8 engine.

“For that consumable stuff we’ve deliberately chosen one of the world’s most common engines, so that our customers can just go and get parts. We don’t have to machine or develop all that stuff either. We’re doing the unique, bespoke parts but the consumables are from the LS1,” Mebberson says.