London - Renault's radical approach to the design of this year's Formula 1 car has been a failure, according to technical director James Allison.Allison said: "I regard it as a bold, but ultimately failed experiment. We were the only team to adopt a forward exhaust layout, and we did so with high hopes, buoyed by very strong wind tunnel numbers."We came out of the blocks adequately well, although it was clear from the first test that the delivered downforce was not as high as we had expected. The season which followed has been difficult for everyone at Enstone," he said."The layout which had promised so much and which, had it delivered, would have been almost impossible to copy, proved very tricky to develop and had a fundamental weakness in slow corners that has been an albatross around our neck all year," said Allison.ROOM FOR IMPROVEMENTRenault started the campaign after impressive pre-season testing with Vitaly Petrov taking a third place in Australia and Nick Heidfeld doing likewise in the second race in Malaysia.The season then tailed off, with German veteran Heidfeld departing in August.Petrov has not scored in his last three races while Brazilian Bruno Senna, Heidfeld's replacement since Belgium, has managed just two points from seven starts.Renault are fifth overall with 72 points and well behind fourth placed Mercedes on 159.The aerodynamic rules are changing for 2012 and Allison hopes for an improvement."We look forward to moving on in 2012 with all-new exhaust rules and a chance to wipe the slate clean," he said.