It’s rare a technical development passes without anyone noticing and of all teams its surprising Red Bull pulled off that trick in the past few races. As they were seen to have a Mercedes-like Double DRS (DDRS) system in use in Japan. It transpires the system was track tested in practice at Monza and raced in Singapore. Part of the secret of the Red Bull DDRS is that the system is wholly contained within the rear wing. Only the plate over the end of the rear wing flap gave away the systems existence. With this system Red Bull are able to shed even more drag when DRS is open, thus giving them a top speed advantage in qualifying and when DRS can be used in the race.
Red Bulls adoption of DDRS is also surprising; as it’s the first time a team have exploited this technology since Mercedes introduced it for the start of 2012. This might be in part due to the system being banned for 2013 and teams are looking at the passive Drag Reduction Device (DRD) as tested by Lotus\Mercedes. As already mentioned the Red Bull DDRS stalls the rear wing and not the front wing, as with Mercedes solution. Thus the system is self-contained within relatively conventional rear wing elements. We can clearly see the oversized plate that seals the duct when the rear wing flap is in the closed position. When DRS is activated the flap swings open and the duct is revealed. The high pressure that builds up above the rear wing main plane, invites flow to pass through the duct and this flow can be used to stall other parts of the rear wing. From the shots of the system with the DRS open in Korea it’s clear to see the duct routes vertically down, passing inside the double skinned endplate.
What surfaces are being stalled?
Middle of the wing
Quite where this duct exits to stall the wing is not clear. Most reports suggest is stalls the centre of the beam wing or the centre of the diffuser. This is entirely possible, the Mercedes system routes through the endplate and then into the beam wing. If this is the case for Red Bull then the duct would either exit through a slot in the middle 15cm beam wing or ducting further down to the diffuser. Blowing a slot in the area will stall the airflow and this would lead to the reduction in downforce. The middle 15cm of beam wing is allowed to have a slot, as this area is exempt from the closed section and minimum radius rules, introduced to ban F-duct style stalling slots in 2010. However these central areas of the beam wing and diffuser are quite efficient, as they do not induce a lot of drag from tip vortices. Stalling the flow in the middle of the wing would have a knock on effect in stalling the general flow behind the car, but I don’t believe this would be an effective use of the stalling on the back of the car. It would be better to stall areas which do induce a lot of vortices and therefore drag. These areas tend to be at the wing tips, so the obvious areas to stall are top rear wing tips, the beam wing tips and the outer corners of the diffuser.
Both of these wing elements are allowed to have slots in the outer 5cm or in the endplate itself, while the diffuser is not allowed to have slots in this area. So the focus moves to stalling the wing tips. As the top rear wing is already rendered ineffective by DRS being open, the flap being open leaves the relatively flat main plane unloaded, so little drag will be induced at its tips. Looking at the Red bull wing at the past few races show only one sign of holes under the top rear wing, but these were only seen in one practice run in Japan and have not been seen again. Its possible Red Bull evaluated blowing this area and discounted it. It’s also possible that a system could blow both the upper rear wing and then beam wing simultaneously for the maximum effect. The Mercedes system manages to blow a wide slot some 3m forward of the rear wing to stall the front wing, so they should have enough energy in the stalling flow to stall two different areas of the rear wing. It will be important to keep an eye open for holes returning to this area.
This leaves the beam wing, its wing tip is heavily shielded by the endplate, although there will still be some drag induced by the flow off of the wing tip. Looking for evidence in this area under the beam is even harder to view, than the area under the top rear wing. some images appear to confirm that this is the area Red Bull have been focussing on. As two small slots have been visible in some shots of the car on the grid. Although on the grid a mechanic was positioned in the middle of the rear wing, this appears to be a decoy, as the outlets are at the side of the wing! Of these two slots one is positioned directly under the beam wing and the other about halfway between the first and wings trailing edge. The first slot would be most efficient at stalling the wing, is its positioned at the suction peak, the point where the airflow is moving fastest. The subsequent slot may be used to break up any residual airflow not stalled by the first slot.
From what I’ve seen and heard of the Red Bull DDRS I would suggest that when the DRS flap opens, the duct feeds vertically down to blow through a pair of slots underneath the endplate\beam wing junction. This would stall the outer tip of the beam wing and the resulting vortices would be broken up reducing drag for a small, but useful top speed increase. Red Bull have just a few races left to exploit this technology, as rules ban the use of DRS having an effect on ducts within the rear wing. But as we have seen so front this year, having pole position and managing the race and tyre wear from the front is a strong strategy. Having DDRS will only aid the team in qualifying with almost not performance penalties from having the system fitted.