Mat Coch writes:

Lotus will not debut its controversial rear-wing stalling device at this weekend's Belgian Grand Prix after rain interrupted practice on Friday.

"With discretion being the better part of valour we will conduct P3 tomorrow with a conventional aero package rather than attempting to squeeze Friday's intended evaluation into the precious final practice session," admitted Technical Director, James Allison.

The device, dubbed a 'Double-DRS' by many, despite the fact that it is an independent system, is understood to operate via an air pressure switch on the car's engine cover. Once the car reaches a pre-determined speed the air pressure operates the switch, directing air on to the car's rear wing via a vent, which increases the cars top line speed and reduces drag.

It's a similar concept to that employed by Mercedes, which uses its DRS system to expose a hole in the rear wing, with the airflow channelled to the front wing. However unlike Mercedes system, which relies on DRS being activated, the Lotus solution is passive and available at all times - once a car reaches a particular speed.

Already banned for 2012, on Thursday Martin Whitmarsh all but scoffed at suggestions that a similar system would appear on a McLaren before the end of the year.

"We have, at any one moment, a whole variety of development projects ongoing," he explained. "We've got a finite amount of resource and we try and extend it where we get the biggest bang for the buck and our judgement so far is that we've been able to find other projects that deserve that resource and we've had a great performance resource from."

Lotus' device first appeared on Kimi Raikkonen's car at the German Grand Prix, though mixed conditions prevented the team from completing the testing programme it had planned. Similarly changeable conditions in Hungary, along with the circuit's tighter layout, hindered any meaningful running.

It was hoped dry conditions on Friday in Belgium would allow the team to properly evaluate it for potential use during Sunday's race, though its now looks set for the Italian Grand Prix next weekend.