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1 Sep 2012

Lotus & Mercedes DRD (Drag Reduction Device)

In response to the original Mercedes DDRS, Lotus have gone on to develop a system they simply call 'the device'. I start here because most of the mainstream media are calling the Lotus version DDRS which simply isn't the case. DDRS or Double DRS is when DRS is used as a fluid switch to create a secondary function, in the case of the Mercedes DDRS this reduces drag on the Front Wing for a enhanced straight line speed. Most importantly DDRS (Secondary usage of DRS) is now banned within the 2013 regulations so calling it DDRS will only make things more confusing for the casual / less Tech driven F1 fan

The beauty of Lotus' device of which I'm coining DRD (Drag Reduction Device) is it doesn't need DRS in order to work and reduces drag at a certain threshold. This means unlike the Mercedes DDRS system it will reduce drag even when DRS isn't available during the race. 

How I believe the system works

(1)In terms of additional parts the system appears uncomplicated with the addition of the Airbox 'Ear's, (2) internal ducting (3) the engine cover cooling exhaust, (4) the periscope that leads to the rear wing with the small ejector holes and the appropriately shaped beam wing Monkey Seat (5).

1. Airbox 'Ears' Starting at the Front these little ducts serve a few purposes:

During normal conditions air is presented to the 'Ears' and air moves down the internal tubing (2) toward the periscope.

When 'Off Throttle' the main airbox receives more air than it can extract and so blocks off the entry point. This normally creates a backwash effect whereby the air stagnates in front of the airbox before counter rotating off the sides and over the engine cover at an undesirable speed. This is 'Air Spillage' and creates a turbulent airflow pattern over the engine cover but more importantly then goes on toward the rear wing.
So when the Lotus is off throttle this airflow is collected by the 'Ears' and utilized further down the device but just as importantly it doesn't impede the more ideal laminar flow heading to the Rear Wing.

2. Internal Ducting during the build up phase on Thursday Sutton Images managed to get the following image of the Lotus E20 which shows that there are clearly 2 outlets from the airbox into the engine cover.  Previously we had assumed the air was being moved en mass from both the Airbox and Airbox Ears down the engine cover to the outlet at the rear. This now shows that the airbox and ears have seperate outlets with the top one most likely the pipe from the Airbox Ear's that feeds to the periscope.

3. Engine Cover Exhaust: Usually the engine cover stops much more abruptly at the rear of the car that when the 'device' is fitted.  The additional exhaust section serves a few purposes: It allows the addition of the periscope that extends upto the rear wing but also acts as an exhaust for the airflow which exits into the beam wing Monkey Seat / Mini Diffuser.  As we can see from the great picture Sutton got during the rain hit Free Practice Session it would appear that even at the rear outlet two pipes remain in play, allowing the airflow a route to exit once the periscope is at full capacity (blockage)

4. Periscope: This is most important aspect of the whole system as it's how the air is transported to the underside of the Rear Wing in order to create the additional downforce at low speed and 'Stall' the rear wing over the speed threshold.  In the picture below Lotus had the ejector holes taped over in order to stop the device operating (due to bad weather conditions)

5. Monkey Seat / Mini Diffuser is placed / being used in order to take advantage of the situation presented by the device in general.  By adding this Diffuser shaped Monkey Seat the airflow will be pulled through the exhaust as Downforce is generated on top as seen by the stagnation of the Flow Viz paint at the trailing edges of the outer section of the Monkey Seat.

 Airflow Pattern

In the images above we can see that air consumed by the Airbox 'Ears' is transmitted along the top pipework and branches off to the Periscope.  In the enlarged image of the Periscope we can see the ejector holes that blow air tangentially across the width of the Rear Wing main plane (The image below shows the effect of this when the team used flow viz at the Hockenheim weekend), blowing the underside of the wing reduces boundary layer build up which allows for a steeper Wing AoA to be run giving a net downforce gain. The amount of rear downforce available to teams has been reduced since the regulations stopped blown diffusers. Making the amount of downforce generated at the rear wing once again imperative.

At a certain velocity the amount of air being blown isn't enough to prevent the boundary layer build up and the wing stalls. (CL Max) This reduces the amount of downforce and drag on the rear wing.
Simultaneously the air in the periscope now creates a blockage which allows the airflow to feed out toward the Monkey Seat / Mini Diffuser which will increase it's effectiveness creating downforce in this region.
The switch from downforce creation to drag reduction is aided by the use of the Monkey Seat / Mini Diffuser as it helps transition the forces involved.

So in essence with DRD the rear wing is passed more air than usual underneath the main plane allowing it to generate more downforce until such a point it stalls, allowing the car to attain a higher top speed (I'd predict anywhere from 5-10KMH)

So far all I have shown you is the Lotus variant but during Free Practice on Friday Mercedes also placed a similar device on Nico Rosberg's car.  The weather forced the team into blanking off the ejector holes and so DRD was never actually used.  However it did afford us the opportunity to see their version....

As we can see from the image above the Mercedes variant has their Airbox ducts slightly further back which allows them to be fitted with the engine cover. (Rather than be part of the Airbox structure and un-removable if the system isn't used, as we saw Kimi with the taped up over the Hockenheim and German GP weekends when not in use)
The arrangement at the rear of the car is very similar to that shown on the Lotus however one thing is yet unknown due to the weather not allowing the 'Device' to be tested.  We can see in the picture above and below that the Periscope doesn't extend to the underside of the Rear Wing Mainplane.  It may be the case that Mercedes simply ran their usual Rear Wing configuration and didn't bolt on the Deeper/Higher AoA Wing they could use in conjunction with the DRD.  The other plausible reason is that it is infact designed this way and Mercedes plan to attempt blowing a larger section of the Rear Wing to gain downforce / reduce drag.

I see absolutely no reason as to why Mercedes can't continue to use DDRS in conjunction with DRD as one will not impact the other even in terms of packaging.  As we can see below the twin pipes leaving the beam wing going through the chassis don't intefere with the placement of the Exhaust / Monkey Seat arrangement.

If you wish to understand my interpretation of the DDRS system that Mercedes use it is included in my recent Mercedes article:

In terms of others copying the Lotus design, as we have already seen Mercedes a team that is known for taking a long time to implement upgrades take up DRD I see no reason why others won't do the same.  One crucial factor however is that both Lotus and Mercedes run fairly aero neutral exhaust designs.  Whether this will factor in the design of everyone elses DRD is something I very much look forward to.  As I have previously alluded to Mercedes and Lotus (nee Renault) have good experience with Passive devices but I see no reason for the likes of McLaren and Ferrari to adopt the designs too.

EDIT: Additional Images of Mercedes DRD from the Young Drivers Test 10-12th September

Above: Day One, Sam Bird Tests the same configuration as Nico had fitted in Spa

Above: Day 3, Brendon Hartley Tests the configuration without the Monkey Seat straddling the engine cover exhaust (However as it was wet the system was removed)

Images used in this Article are copyright their respective owners: Mario Keszeli / Sutton Images / Xpb Images

1 comment:

  1. Somewhere down the line I would like to see a variation of the DRD that uses the monkey seat diffuser together with ducts blowing the floor as the periscope will be redundant next season. Won't be DRD then will it !


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