Allison sheds a light on Lotus' mistakes

The squad known these days as the Lotus F1 Team has four Drivers’ and three Constructors’ Championships to its credit, but slumped after its last crowns in 2005 and 2006. Lately it has been clawing its way back to the front under the technical leadership of James Allison. He first worked for the team in its Benetton days in the early 1990s. Having moved elsewhere, he came back to its Enstone base as head of aerodynamics in the mid-90s before moving to Ferrari in 2000. He returned again in 2005 and was Bob Bell’s deputy during the two title-winning years under Renault’s ownership. Appointed technical director in 2009, Allison knows all about the slump that followed the two successive title wins.

“We’d had a brilliant run in 2005-6 and had stolen a march on several teams,” he remarked. “We had a very good outfit doing a great job. But I think we existed for a large part of 2006 – actually quite a lot of it – behind the team we were competing with, Ferrari. We got by on good racecraft and a bit of good fortune, and we hadn’t actually recognised the fact that what had been the state of the art had become a bit second rate. And the whole way that we were modelling and approaching the tyres in the wind tunnel was not appropriate, or wasn’t at the level of our competitors. You know there comes a day when you pay the price for that, for slipping behind where everyone else is at. We paid a heavy price for that later on in some of the mistakes we subsequently made.”

Things have turned around since Genii got involved for 2010, Allison explained. “We’ve been upgrading our facilities in stages at Enstone. We did our first upgrade at the tail end of 2009 when we put in a new steel-belt rolling road. That was capable of taking a 60% model with the type of loads that we wish to put through the belt. Then, in the spring of 2011, we upgraded the working section of the tunnel to accommodate a larger model, and we have been using 60% rather than 50% models since then.

“They’re laughably called models – they’re not models at all really, they’re fiercely expensive and difficult pieces of kit to design and build. So we’d been investing in a 60% programme for a long time before we rolled it out in the tunnel.

“For CFD work we put a bit of investment into our computers a while back. It was an absolute fraction of what we paid last time around, and yet we now have more computing power. Mind you, the computers have to satisfy the Resource Restriction Agreement [RRA], which means we are limited in the number of floating-point calculations we can do in a given time period.

“Both those investments – the 60% model programme and the CFD stuff – are part of the new Genii era, along with a driver-in-the-loop simulator that we’ve also invested in. These quite substantial upgrades of the facilities at Enstone are all part of Genii’s commitment to try to ensure that we have a shot at being a championship team again. Not surprisingly then, with its in-house wind tunnel and CFD facilities, the Lotus F1 Team is operating these days at the limit of what is permitted in these respects under the RRA.

Allison said, “One thing the RRA in aero has been spectacularly good at – at least for us, and I would be surprised if it was not true elsewhere – is that it really focuses your mind on getting the most out of your equipment. At first it was a bit of a struggle to make sure we could carry on operating with the same level of intensity as before, when we had to fit it all into such a tight straitjacket. “It does focus the mind and over a period of 12 months or so we made massive improvements in our operational efficiency. That effort has continued because it’s a fixed limit, but if you can keep finding efficiencies then you can keep getting more out of the limit. “So that’s what we, and I’m sure every other right-minded team, is doing.

“From the sport’s point of view, it’s been a tremendous success as well because aero expenditure was really going up at an unsustainable rate, as it’s such a powerful thing for making the cars go quicker. What we found is that this RRA has allowed a gentle growth in the overall capability of the departments, while actually seeing a reduction in costs. And we still have a very satisfactory and rewarding environment in which to develop our aerodynamic ideas. It’s been a really good thing.” In terms of the level of downforce of contemporary Formula One cars, the new regulations introduced for 2009 were aimed at slashing it by 50%. But that didn’t take into account the double diffuser, development around which helped the 2010 cars actually exceed the level that had been attained in 2008. For 2011 the double diffuser was banned, but increasingly clever exploitation of exhaust gas discharge helped mitigate the effect of that. Indeed, midway through the 2011 season, Allison was able to remark, “I think it’s fair to say that downforce is at an all-time high in Formula One. I haven’t seen downforce as high as this in any period that I’ve been involved in Formula One.”

Forward exhaust

Allison’s 2011 car was characterised by a unique forward-facing exhaust system. Each four-into-one exhaust discharged on its respective side of the floor, at the front of the wide section spanning the two sidepods. Thus the exhaust discharged at the leading edge of the sidepod floor. This is an area of inherent low pressure as air squeezes under the floor, and in entraining that flow the exhaust discharge made the localised pressure drop even more pronounced. In other words, the car didn’t have so much a blown diffuser as a blown sidepod floor, the effect of the exhaust entrainment tailing off as air moved towards the diffuser section further back.

Allison explained that the forward exhaust creates additional low pressure slightly ahead of the car’s overall, non-exhaust influenced, centre of pressure, whereas a Red Bull-type rearward exhaust discharge creates additional low pressure well behind that centre of pressure. This means that when the driver gets on the throttle, maximising the exhaust gas fl ow, with the Red Bull approach there is a far more pronounced rearward shift in overall centre-of-pressure location.

As it happened, that rearward balance shift was less of an issue given the characteristics of the 2011 Pirelli tyres than it would have been in the case of the previous year’s Bridgestones. With the Bridgestones, it would have created excessive understeer, whereas with the Pirellis it created additional rear grip that was more beneficial. Arguably then, the position in the Lotus was less effective after the change in tyre characteristics. Another drawback of it was the inevitable if very subtle deterioration in the form of the leading edge of the sidepod floor over time, as hot exhaust gas kept blowing over it. That form needs to be as clean as possible for maximum aero effect. Midway through 2011, Allison remarked of the forward exhaust, “It’s been less successful than we had hoped but it’s still been a very powerful concept. In the wind tunnel and in CFD, where we developed the concept, our model had suggested that the low-pressure area that would result from the exhaust would extend further down the car than it appears to do in reality. However, there are always differences between what you model and what you get.

“In the tunnel you try to get the air simulating the exhaust gas flow moving at the correct relative velocity so that the ratio of energy in the exhaust to the energy in the free stream air matches what you see on the track. However, if you match the energies, you won’t get the velocity right because in reality it’s a hot flow.

“Having to use a cold flow in the tunnel, you can’t get the velocity and the energy to match. There’s also the fact that when you do it in the wind tunnel it’s a continuous airflow, like a jet, whereas when you’re doing it on the track it’s a pulse from the engine. But you know, for all intents and purposes, it’s a decent simulation.” The forward exhaust was a brave experiment that didn’t live up to initial expectations, partly because it was tricky to set up the car around it – particularly on circuits with a lot of acceleration from low-speed corners – and partly because it proved difficult to develop through the season.

We asked Allison: to what extent is exhaust activation influenced by driver technique? “Well, it is clearly important that the driver can find lines that will allow him to get on the throttle as soon as he can,” he said. “The more you can get the thing pumping, the better. Even though the throttles are held open, if they’re held open but the engine is at low torque because the driver isn’t getting the power down, if it’s just pumping but it’s not actually combusting, then the energy of the flow is lower. The quicker the driver can actually get on with the power-generating part of it, the higher the energy flow.”

How much does the forward exhaust compromise the engine performance? “Actually a lot, but only a similar amount to the rearward blowing. If you look at a rearward-blowing exhaust you’ll see that the first thing it does is head quite a long way forward, and then turns around and comes back. And if you unfolded both pipes, they’re about the same length. Everyone’s paying a fairly heavy horsepower price, but it gives you an idea of how powerful aero is.”

Indeed, the implementation of the forward exhaust required extensive cooperation from Renault’s Formula One engine department in Viry Chatillon, Paris. “Renault are a great engine supplier and very straightforward to deal with,” Allison said. “They were incredibly helpful and constructive about exploring what you can do to make the most out of blown floors, and really very enthusiastic; just what you want from an engine supplier – taking a car-level view of something. No engine guy wants to bolt some socking great exhaust pipe on their car and throw their horsepower that they so lovingly found down the toilet. But [Viry] know that the car is the thing, and they are wonderful to deal with like that. “They put a lot of effort in trying to show on the dyno that their engines can operate at higher temperatures than they were previously comfortable with. That requires them to spend their cash building engines and using them on the dynos to prove that they can indeed push the temperature limits up. They don’t do that for their benefit, they do it for their teams, and they are a very good bunch to deal with.

“If you look at the cars over the last few years, the rule that you can’t open the car up between qualifying and race means that we have to qualify what we’re going to run in the race. If you also look at the trends over the last few years, Formula One cars are getting tighter and tighter in their cooling packaging. Some of that’s because we are better at managing airflow through radiators, but some of it, from Renault, has been that they have been great about extending the operating range of the engine, so that we can still operate reliably at higher allowed temperatures.”