DRS Mechanism Analysed

DRS_exposed

The Drag Reduction System, DRS, was introduced to F1 in 2011. It’s a system to open the rear wing flap for reduced drag to boost top speed. Over the subsequent years DRS operating mechanisms have evolved and converged on the same set up, with a wing mounted pod containing a high pressure hydraulic actuator to pull the wing open. This is an opportunity to see the mechanism in detail and explain how the set up works.

DRS_covered

DRS was a response to two factors; The failure of the adjustable front wing flap in 2009 as an overtaking aid when following another car, plus the advent of McLaren’s F-Duct. Both these systems were banned in order to introduce DRS. So DRS was a specific idea to aid overtaking, to allow a following car a cut in drag to boost top speed to allow a pass on the straight. Drag was reduced by the DRS mechanism pivoting the rear wing flap up at speed, the reduced angle of attack of the flap both reduced drag directly and the main plane also stalled in the process further reducing induced drag.
When introduced there were several systems in use to open the rear wing flap. The electric stepper motor set up commonly used to the post-2009 adjustable front wing flap was deemed ineffective, as it was too slow and teams wanted a quick change from full rear wing to DRS being open to get the immediate speed boost, then have it quickly close for a return to full downforce for the braking zone.

DRS_SideElev
The first and immediately most logical solution was a hydraulic actuator inside the rear wing pillar that operated vertically to push open the rear wing. Secondly Mercedes had two separate actuators inside each wing endplate that opened the flap. Thirdly there was the wing mounted pod set up, initially used by Red Bull, the pod housed the actuator and that in turn pushed a rocker to open the flap. This set up had marginally better aero and the trend away from wing mounting pillars, made it a convenient route for most teams.

DRS_Exploded

However, one further evolution of the design lead to the current set up, this is where the actuator pulls the wing open via a link, rather than pushes it via a rocker. This was in response to a number of DRS failures where the flap remained open when something in the hydraulics failed. It is this pod mounted pull type that we are able to examine here.

DRS_Assy
The DRS pod I have in my parts collection is a Caterham set up from 2012, conceptually it remains the same “pull type” as used by all teams today. Weighing in at less than 400g the compact set up features a mounting post, actuator, spring, rocker and cover. With the thin carbon fibre covers removed the mechanical operation is quite clear and simple. The mounting post fits atop the rear wing, the foot of the mounting is machined to match the curvature of the wing, and the lower section of post has a teardrop cross section, it’s also shaped to match the slot gap separator that wraps around the wing. Then the inner section of the post is machined to pass the hydraulic fluid up from within the wing to the actuator.

DRS_foot

.

DRS_Actuator

Doing the physical work is the actuator, bolted to the post, the fluids enters the chamber and moves the piston, this action pulls the piston rod backwards against the spring’s pressure to move the rocker. We have to also consider the effort the actuator already has to cope with as DRS commonly opens at near top speed, so that the rear wing flap is already highly loaded with air pressure. Team’s will have a DRS set up that opens the rear wing in a few milliseconds, such is the power of the hydraulics, one team told me they tested their early DRS set up with a tennis ball rested against the wing flap. When deployed the DRS mechanism flicked the ball high up into the factory ceiling!

DRS_rocker
Caterham use a rocker that connects to the piston rod, then pivots on the mounting post and lastly connects to the wing’s flap. The piston pulling the rocker lifts the wing flap open. Other teams make do with a simple drag link, featuring no pivoting point and simply pulls the flap open directly. Without the mechanical advantage of the rocker, it’s likely the drag link set up needs a more powerful hydraulic set up.

DRS_Spring
Should the hydraulics fail, such as a loose dry-break fitting or hydraulic pressure failure, the spring and a bleed valve set up allow the wing to return to its safer closed position. I haven’t calculated the spring’s pressure, but it is nearly impossible to push the spring closed with hand pressure. The spring employed is 12 coils of 2mm steel wire around a 27mm diameter.