Read time: 8.7 minutes

"Steve… Steve! The flooring is on fire!

"What practise we practise?"

It's the summer of 2010 and, in the high-octane hustle and bustle of the Goodwood Festival of Speed, Principal Composites Engineer Steve Foster has just received a phone telephone call from colleagues carrying out straight-line aero testing with the MP4-25 in Spain – a call that would mark the get-go of i of McLaren's most extraordinary Formula i testing tales.

"I just recall being in utter disbelief when I got that call," reveals Steve.

"We had done and so much CFD analysis and wind tunnel testing. None of it had suggested that this was going to happen."

At this indicate, Principal Aerodynamicist James Ingles jumps in to elaborate on the science behind exhaust-blown diffusers and what led to this moment of sheer panic: "We were trying to feed more than energy into the diffuser.

"The edge of the flooring – adjacent to the rear tyre – is very of import aerodynamically, and if you tin direct the high-energy flow from the frazzle into that area, there is a lot of downforce to be gained.

"Merely when we starting time tried information technology on track, the frazzle flow didn't go anywhere near the tyre. Instead, it went inboard, over an area of the flooring that nosotros hadn't protected – it was just blank carbon – and it got scorched.

"It turns out, this was due to a phenomenon known every bit the Coandă effect, which our CFD analysis and wind tunnel testing wasn't picking upwardly.

"When you've got an frazzle flow, it pulses because of the cylinders in the engine and this pulsing sets up a vortex structure at the end of the tailpipe. When this vortex came into contact with nearby bodywork, it was pulling the whole exhaust plume inboard across the floor."

"From that moment onwards, we were on the ragged edge for the rest of the 2010 season – trying to keep floors in one slice and stop them from burning," admits Steve.

A parcel of crisps

Despite having our fingers – and floors – burnt, we persevered with a new frazzle-blowing concept in 2011 for the MP4-26, equally nosotros looked to push the boundaries and turn the tables on our rivals.

"We missed our opportunity in 2010 and felt we needed to get radical," says Steve. "So, we developed the fantail exhaust which was designed to deliver an fifty-fifty bigger aerodynamic do good past blowing the edge of the flooring ahead of the rear bicycle, through a flat nozzle at the end of the tailpipe.

"One time again, in CFD and air current tunnel testing it looked to be really powerful and a large step forward.

"Withal…"

And at this point, Steve goes all Marks and Spencer: "…these are not but any exhaust pipes. These are F1 frazzle pipes, which must endure pulsing that is very different to any ordinary road-car exhaust.

"When you await at an F1 exhaust pipe on the dyno with a high-speed camera, you tin can see that information technology vibrates and deforms like crazy.

"So when you've got a flat nozzle at the end of the tailpipe, unsurprisingly, it's not the best structure to react to that kind of ambitious loading.

"I can remember seeing the loftier-speed footage of the fantail, it was similar a foil crisp packet opening and endmost.

"We made so many of them and idea it would hold together once on track, but information technology simply kept on breaking during testing. It was a nifty thought, simply it was too aggressive.

"Then there we were: 3 weeks from the starting time race of the flavour, with an exhaust system that was completely unreliable. It was the stuff of nightmares."

"It had taken so many months of difficult work from everybody to develop it," adds James. "We were all so invested in it and desperately wanted information technology to work, equally it had the potential to exist a game changer.

"Because you're ever pushing the boundaries in F1, you frequently find that things never quite work exactly equally you want the first time. We were therefore convinced we merely needed to iterate a footling bit more and we would become in that location with the fantail. But, eventually, we realised that we were but non going to go it to work."

Cutting it fine

"We had to rapidly develop some other exhaust concept. This time with a flattened oval tailpipe, with an get out that was low down and immediately in forepart of the edge of the flooring, ahead of the rear wheel," says Steve.

"I can call back us hurriedly testing it on the dyno for durability and wondering if we would stop upwardly setting burn to everything considering the exhaust gases were over 900°C. It was crazy, but we had to try it.

Thermal epitome of revised MP4-26 exhaust undergoing durability testing

"We were and then tight on time that we couldn't make part of the rear flooring from composite materials for Australia, and so we had to 3D-machine information technology out of two huge billets of solid titanium."

"This meant the floor was heavier than we would have liked," admits James. "But even despite the extra weight, the performance information technology brought was massive. When it worked properly, it increased downforce by more than a tertiary in some atmospheric condition– improving lap time by as much as several seconds.

"To get to Australia with the new organisation, completely untested on track and for information technology to work straight abroad, was unbelievable. Nosotros qualified on the forepart row of the grid and were overcome with relief."

Finally

And then, 18 months after that fateful phone call to Steve, after everything the team had been through, we were finally able to use what we had learnt to put us ahead of the bend with the MP4-27.

"For 2012, to prevent teams from blowing the diffuser, the FIA banned low-leave exhausts and specified that the frazzle exits had to come out of the top body and point upwardly – a far more traditional position," explains Steve.

"Merely the FIA was unaware of what we had learnt through our travails with the MP4-25 in 2010.

"Having evolved our CFD and current of air tunnel tools to properly replicate the Coandă issue, we knew we could use the miracle to our advantage.

"We developed these slides – they looked like what yous might notice in a children's playground – that sucked the frazzle gases fired out of the tailpipe down towards the floor, mimicking the effect of what nosotros had been doing the year before with low-exit exhausts.

"Nosotros eagerly waited to run into if any of our rivals unveiled a car with a similar concept. And, to our surprise, none of them did.

"We had stolen a march on the opposition and went on to lock out the front row and have victory at the season opener.

"It was a far cry from fiery floors in 2010."

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