Williams moved the thinking forward in 2013, using a fixed tube inside a central hub - which negated the need for a moving component, and was therefore deemed legal. Red Bull adopted that design in their 2013 chassis, while Ferrari and McLaren used a version of it from the start of the 2015 campaign.
In Hungary, Red Bull reintroduced the concept on their RB11, together with a positive set of aerodynamic improvements based on their Silverstone package.
It is clear that Red Bull have significantly improved the chassis and closed the gap to Mercedes in the last two races, especially in terms of understanding how to manage the airflow at the front of the car. The blown axle plays a part in this, as well as helping to manage brake and tyre temperatures.