Analysis: McLarens Rear Wing Vapour Trails

Picture courtesy of F1Pulse

A feature of F1 for many years were the vapour trails spiralling off the rear wing tips. This phenomenon largely disappeared a few years ago, but was apparent once more on the rear wings of the McLarens at the recent damp race weekends. So what are these vapour trails and why do McLaren tend to create them more than other teams?

They are in fact more correctly termed ‘vortices’, they are created when the pressure differences are created at the wing tip. As you get high pressure above the wing, low pressure beneath and near ambient pressure to the side of the endplate. When these three flows meet, the higher pressure flow naturally moves towards the low pressure areas. This sets up a tumbling motion and a spiralling flow structure is created. As we know from the aerodynamicists use of vortices to shape and alter flow over other areas of the car, vortices are extremely high energy structures. But with them comes a lot of drag. These wing tip vortices rise upward and outward from the rear wing tips and eventually flatten out behind the car as their energy is dissipated in the free stream flow around the car.
The greater the pressure differential, the greater the vortex created, and this is generally seen better in damp conditions as the water in the air concentrates into the vortex to become visible as a vapour trail.

In years gone by, the site of vortices spiralling from wing tips was seen as a good thing, as the belief that the wing is working hard. To some extent this was correct, with a simple wing the fact that it can create visible vortices did prove the wing was highly loaded. However the drag that it created was less well understood. Since the early 2000’s teams have sought to reduce this pressure difference at the wing tip, in order to reduce drag. Several solutions have been tried to alleviate the pressure differences at the wingtip.

As F1 rear wing have such small aspect ratio’s, (width versus length), there’s little that can be done to reduce this high pressure created towards the endplate without sacrificing total downforce created by the wing. Teams have experimented with twisted wing profiles, reducing the angle of attack of the wing cross section nearer the endplate, to reduce the high pressure created above the flap. But this in turn reduces the downforce created by that section of wing. At tracks where lower downforce is required, teams will still ease the loading of the outer part of the wing, centering the pressure distribution in the middle of the wing.

The other option is to allow the whole span of the wing to be aggressively steep, but use other methods to reduce the pressure difference at the wing tip. Firstly teams such as BAR created a cut-out in the end plate ahead of the flap, this allowed some of the high pressure above the flap to bleed off outside the flap, negating the pressure difference and therefore the strength of the vortex. But this was a fairly blunt solution, so teams created the now-common louvers in the endplate.

This solution directs some of the high pressure air above the wing to the wing tip in a more elegant way. Renault, then latterly Honda and McLaren created a different approach by merging the flap into the endplate, this creates a small gap to direct the high pressure flow to the wing tip.

In the past two seasons reducing this effect has been negated somewhat by other means to reduce the rear wings drag. In 2010 the F-duct allowed the driver to reduce the rear wing downforce and therefore drag. In wet races in 2010 we saw the McLaren’s exit a turn, as speed built up the vortices would appear, then as the driver closed the cockpit control duct the rear wing stalled downforce\drag was instantly reduced. As the driver did this, the vortices also disappeared. This allowed us to see just how soon the F-duct was engaged out of turns.
With the F-duct banned and DRS allowed for 2011, teams are able to adjust the rear wing in qualifying and for overtaking in the race. Depending on the teams qualifying\race strategy, they have redesigned their rear wing to have a different flap size. A small flap, means that the DRS effect is larger, more downforce and drag are shed for more top speed. However the smaller flap means that the rear wing is limited in the downforce it can create, as the sot gap is further back on the wing and separation is likely with aggressive angles of attack. Most teams have followed a design path that errs on this level of DRS effect. As the wing tip is not loaded so highly, there are few vapour trails created.
McLaren however have been almost alone in creating a DRS wing with a large flap, this creates the opposite characteristics of a small flap wing. Less DRS effect is created, but the wing can create a larger amount of downforce when DRS is not activated. Thus their rear wing is steeper and more heavily loaded at the wing tips.

Its for this reason that McLaren tend to be the team in 2011 that create the vapour trails on damp days. McLaren do however have a small flap DRS wing in development. We can expect this to create less trails than their current if it gets to be run in the damp.


Book Review: Haynes Red Bull Racing F1 Car

When Red Bull Racing launched their new car for 2011, the event was marked by a very special press pack. The pack was formatted in the style of the well-known Haynes maintenance manuals (PDF). This in itself this was a great book, but almost unnoticed within its pages was the intended publishing of a complete Haynes style workshop manual on the RB6 car.
Now some six months later the Haynes Red Bull Racing F1 Car Owners Workshop Manual (RB6 2010) has been published. As its rare a Technical F1 book is published, not least one with insight into such a current car, I’ve decided to review the book in detail.

At 180 pages long the book has enough space to cover quite a wide range of topics and it does so. Starting with a background to the team, moving on to the cars technology, to overviews of its design and operation. With its familiar graphical style and hardback format it certainly gives the feel of a proper workshop manual. However this is somewhat skin deep and the pages within, soon revert to a more typical book on F1, although some flashes of the Haynes style do remain.

Steve Rendle is credited as the writer of the book and Red Bull Racing themselves have allowed close up photography of the car and its parts, as well as providing a lot of CAD images.
But clearly a lot of editing has been carried out by Red Bull Racing and the book falls short of its presentation as a manual for the RB6. Despite its confusing title, the book is probably better described as a summary of contemporary F1 technology from the past 3 years.
As the last in depth technical F1 book was the heavy weight title from Peter Wright showcasing Ferraris F1 technology from 2000, this remains a useful source of recent F1 technology.
This places the books target audience, somewhere between the complete novice and those already of a more technical mindset.


With forewords by Christian Horner and Adrian Newey, the opening 21 pages are a background to the team and detail of the 2010 season that brought RBR the championships. Then starts the core 100 page chapter on the cars anatomy, which opens with a pseudo cutaway of the car showing a CAD rendering of its internals.

Firstly the monocoques design and manufacture is covered, with images of the tubs moulds being laid up and CAD images of the RB4 (2008) chassis and its fuel tank location. Although little is made of the fuel tank design.
Moving on to aerodynamics, the text takes a simplistic approach to explaining aero, but there is an interesting illustration of the cars downforce distribution front to rear. This does highlight the downforce created by the wings and diffuser, but also the kick in downforce at the leading edge of the floor, but this is not adequately explained in the text. Mention is made of the front wing and the flexing that RBR deny, this is explained with a simple illustration showing the deflection test. The driver adjustable front flap, which was legal during 2009-2010 seasons, is explained, in particular that the wing was hydraulically actuated. When I understood that in 2009, only Toyota used a hydraulic mechanism over the electric motor system used by all other teams. In trying to explain the nose cone, the text and an illustration show a high nose and low nose configuration, but does not remark why one is beneficial over the other.

This section also covers very brief summaries of bargeboards, sidepods and the floor. Some nice close up photos of these parts included, but again with little explanation. An illustration at this point highlights the other FIA deflection test altered in 2010, which was aimed at Red Bulls alleged flexing T-Tray splitter. In this section the text cites Ferraris sprung floor of 2007, but not the allegation that RBR’s was flexing in 2010. A further simple graphic illustrates the venturi effect of the floor and diffuser, and then the text goes into simple explanations of both the double diffuser and the exhaust blown diffuser.
Having been one of the technical innovations of 2010 and since banned, the book is able to cover the F-Duct is some detail. A complete CAD render of the ducting is provided on page 53; this shows an additional inlet to the drivers control duct that was never visible on the car. This extra duct served the same function as the nose mounted scoop on the McLaren that introduced the F-Duct to F1.
Thus with aerodynamics covered in some 23 pages, the text moves onto suspension and the expectation of detail on the RB5-6’s trademark pullrod rear suspension. After a summary of the purpose of an F1 cars suspension, Pages 58-59 have some fantastic CAD renderings of front suspension, uprights and hub layouts. However the rear suspension rendering stops short at the pull rod and no rocker, spring, damper layouts are detailed. Hardly a secret item, so lacking this detail is let down for a book announced as an RB6 workshop manual. A lesser point, but also highlighting the censorship of some fairly key technical designs, was the lack of any reference to Inerters (Inertia or J-Dampers), The suspension rendering simply pointing to the inerter and calls it the ‘heave spring’, while naming the actual heave spring damper as simply another ‘damper’. Inerters have been in F1 since 2006, predating Renault’s mass damper. Their design and purpose is well documented and shouldn’t be considered something that needs censoring. It’s also this section that fails to showcase the RB5-6 gearbox case. Instead using a pushrod suspended RB4 (2008) gearbox, albeit one made in carbon fibre.
The steering column, rack and track rods are similarly illustrated with CAD images. This usefully shows the articulation in the column, but little of the hydraulic power assistance mechanism. Page 67 starts the section on brakes, again fantastic CAD images supply the visual reference for the upright, brake caliper and brake duct design. As well as a schematic of the brake pedal, master cylinder and brake line layout of the entire car. A nod to more typical Haynes manuals shows the removal of the brake caliper and measure of the Carbon disc\pad. A further CAD image shows the brake bias arrangement with both the pivot at the pedal and the ratchet control in the cockpit for the driver to alter bias.
Although not a RBR component the Renault engine is covered in the next Chapter. An overview of the complex engine rules regarding the design and the specification freeze kicks off this section and cites the tolerances and compression ratio for a typical F1 engine. Pneumatic valves, for along time an F1-only technology are explained, but even I failed to understand the schematic illustrating these on page 77. Also covered in the engine section is some more detail on the fuel, oil and cooling systems. With useful specifics, like capacity of the oil system at 4 litres and water coolant at 8 litres. Again some nice CAD images illustrate the radiators within the sidepod. Many sections have a yellow highlighted feature column; this sections feature is on the engine start up procedure, one of the mundane, but rarely talked about processes around an F1 car (other features are on the shark fin and brake wear). As KERS wasn’t used up until 2011, this topic is skipped through with a just a short explanation of the system.

Moving rearward to the transmission system, the old RB4 gearbox makes a reappearance. Again this disappoints, as some quite common F1 technology does not get covered. Page88 shows some close up photos of a gear cluster, but this is not a seamless shift gearbox. In fact seamless shift isn’t mentioned, even though it made its RBR debut in 2008, the year of the gearbox showcased in the book. I know many will highlight that this might be a secret technology. But most teams sport a dual gear selector barrel, each selector looking after alternate gears to provide the rapid shift required to be competitive in F1. So I think this is another technology that could be explained but hasn’t been.
Tyres, Wheel and Wheel nuts get a short section, before the text moves onto electronics. A large part of the electronic system on a current F1 car is now standardised by the Single ECU (SECU) and the peripherals that are designed to support it. So this section is unusually detailed in pointing out the hardware and where it’s fitted to the car. From the tiny battery to the critical SECU itself. Other electronic systems are briefly described from the Radio, drivers drink system to the rain light.
Of critical importance to the modern F1 car are hydraulics, which are detailed on p105. As with the other sections, CAD images and some photos of the items themselves explain the hydraulic system, although there isn’t a complete overview of how it all fits together.
Rounding off the anatomy chapter is the section of safety items and the cockpit. The steering wheel and pedals are well illustrated with CAD drawings and keys to the buttons on the wheel itself and on the switch panel inside the cockpit.

While I have pointed that the hardware shown in the anatomy chapter isn’t necessarily of the RB6, what is on show is obviously genuine and recent RBR. So for those not so familiar with the cars constituent parts, there isn’t a better source of this available in print today. Even web resources will fail to have such a comprehensive breakdown of an F1 car.

The Designers view

Moving away from the Haynes format of a workshop manual, the book then moves into a chapter on the cars design, with comments from Adrian Newey. It details the Design Team structure and some of the key individuals are listed. The text then covers the key design parameters; centre of the gravity and the centre of pressure (downforce). Plus the design solutions used to understand them; CFD, Wind Tunnels and other simulation techniques. Each being briefly covered, before similar short sections on testing and development close this chapter.
Although the text makes reference to creating ‘the package’, something Newey excels at. This section doesn’t provide the insight into the overall design philosophy, which one might have hoped for.

The Race Engineers view
Where as the Designers view chapter was limited, the race Engineers section was a little more insightful into the rarely talked about discipline of getting the car to perform on track. The process of setting up the car is covered; from the understanding of the data, to the set up variables that the race engineer can tune; suspension, aero, ballast, gearing brakes and even engine. Usefully the grand prix weekend is broken down onto the key events from scrutineering, to running the car and the post race debrief. Feature columns in this chapter include; Vettels pre race preparation and the countdown to the race start.

The Drivers view
Ending the book is an interview style chapter on the driver’s time in the car, mainly the driver’s perspective from within the cockpit when driving the car on the limit and the mindset for a qualifying lap. A simplistic telemetry trace of a lap around Silverstone is illustrated, although there is little written to explain the traces (brakes, speed and gear), this is accompanied by Mark Webbers breakdown of a lap around the new Silverstone circuit.

In conclusion
When I first got this book, I was constantly asked if it was worth the purchase or if I’d recommend it. If my review is critical at points, it’s mainly because some technology that could have been covered wasn’t. Or, that the content falls short of the books title suggesting it was a manual for the RB6.
Those points aside, I have learnt things from this book. Like details of the F-duct system, the Front Flap Adjuster and a wealth of smaller facts. There isn’t a better book on the contemporary F1 car. In particular the CAD drawings and close-up photos, just simply aren’t in the public domain. From the pictures we got over the race weekends, we never get to see half the hardware and design work that’s pictured in this book. So I’ll keep this book on hand for reference for several seasons to come.

Overall I’d recommend this book to anyone with a technical interest in F1.

Many thanks to Haynes Publishing who have allowed me to use their Images and PDFs to illustrate this article

This book is available from Haynes

McLaren New DRS Rear Wing

McLaren have followed their own strategy on the DRS rear wing this season. In contrast to other teams McLaren have designed their wing for the best Non-DRS Performance, thus when deployed the DRs provides a more modest boost in speed. This Strategy appears to have been reviewed as their new rear wing tested at Silverstone shows.

Already being one of the fastest cars in a straight-line, McLaren perhaps haven’t needed to exploit DRs as much as other teams. Their current wing sports a large flap which due to its geometry flattens less when DTS is deployed. See DRS Geometry. But we have seen that McLaren can deploy their DRS less on Q-laps and despite their KERS and speed, sometimes struggle to pass other cars. SO their new wing exploits more conventional geometry with a shorter chord flap that flattens out more completed to maximise the drag reduction system.

Along with the shorter flap other aspects of the wings design have changed, the slots on the endplate have been made even more shapely and the endplate merged into the flap. These slots have been a feature on F1 rear wings for nearly ten years. They aim to take some of the high pressure air above the wing and direct it out through the endplate at the wing tip. This reduces the pressure differences that create the vortices at the wing tip, these vortices often seen in damps condition create a large amount of drag, reducing them further aids top speed.

Although the slots are so curved it’s hard to detect, but the sections between these slots on upper part of the endplate are directly joined to the flap, thus the flap is remotely mounted, the loads pass through these three narrow section of endplate. This must be quite a structural feat. This design harks back to McLaren’s 2008-209 wings (see below) which mimicked the Renault practice of merging the endplate into the flap. Again the aim of this design was to manage the pressure differences at the wing tip for reduced drag.

Ferrari: Silverstone Upgrade

Silverstone brought Ferrari’s major mid-season upgrade to the F150, which was effectively a complete new rear end package. Their upgrade comprised of new exhausts, rear suspension, engine cover, diffuser and rear wing. While the changing rules and weather conditions made it hard to judge if their win was a result of these changes, it was clear that the car had found new pace in fast turns. This in its self is a sign of improved downforce, one of the aims of the upgrade.
Ferrari have been open throughout the year in stating they lack downforce and struggle to get heat into the tyres. The former issue hurts pace on faster turns, while the latter has the combined effect of lost pace on harder tyres and poor single lap qualifying pace.
Again Ferrari s honesty in saying the car was not aggressive or innovative, was clear from its launch. Red Bull, McLaren and other teams tried new ideas. Not all these created the package to beat Ferrari, but Red Bull and McLaren were well ahead of Ferrari in the aero race early in the season.
It seems Ferrari chose to make the car as soft on its rear tyres as possible; as the original expectation was that the Pirelli rear tyres would degrade more rapidly. Certainly Ferrari have been easy on their tyres, but the flipside of this characteristic is that the car can struggle to get heat into the tyres. This is why their pace at Barcelona on the hard tyre was so poor and why they struggle to get the pace on a single flying lap qualifying run.

So with this Silverstone package these areas were addressed and the initial signs are the car has improved.

Firstly the rear wing was all new, aerodynamically, structurally and with its DRS operation. Their new rear wing no longer used a central pylon to support the upper wing and house the DRS actuator. This clears up the underside of the wing from obstructions; this was probably not to reduce the minimal amount of drag created by the support, but more to removes its turbulence from the underside of the wing. Perhaps this will aid the reattachment of the air flow when the DRS closes the flap. Instead the DRS actuator is inside a small pod above the wing, where it will less affect the airflow. Cabling and hydraulic lines to the actuator route inside the wing and endplates. As the pylon has been removed there remains a small section of it on the crash structure ahead of the beam wing (highlighted).

Ferrari have been playing with their rear suspension layout for several races. Visibly the main change appears to be where the upper wishbone meets the upright. This has been moved away from the wheel, by making extending the position of the pickup point on the on the upright. This creates a shorter upper wishbone. The effect of this would be more camber change and lateral scrub as the suspension is compressed. In simple terms as the cargoes down on its suspension the wheel will tilt inwards more and slide across the track surface towards the centre of the car. Both these actions move the tyre about a lot more and help create heat in the tyre. This is how Ferrari have been able to get their tyres into their operating temperature window.

The team ran a new engine cover, with the tail of the sidepods formed in a tighter shape, with some of the cooling accommodated by louvers in the tail of the coke bottle shape.

Lastly the floor and exhaust were subtly changed, with the exhaust pipe shape being altered and the cut away sections of floor being a different profile. Unlike Red Bull, Ferrari have not gone very far in aiming exhaust flow under the car. However they have still gone further than the other teams running the outer blown diffuser. The floor in between the tyre and the diffuser is no longer carbon fibre. But instead a plate of titanium, pictures show this flat metal floor is fully exposed and carefully curved to invite some flow to pass under it. Changes in this area no doubt were made with the 10% engine mapping rule in mind, but also as the diffuser itself used a new geometry.
The next series of races with fast turns and harder compound tyres will prove if Ferrari have reversed their cars characteristics and can take the fight to Red Bull for the remaining ten races

Renault & Wiliams: Complex low drag wings for Canada

Both Williams and Renault had complex wings for the low drag demands of the Canadian GP. In Williams case the wing is shaped to create most downforce in its centre, leaving a much shallower span near the endplates. This design reduces the pressure difference where the wing meets the endplate. This reduces the vortices produced at the wing tip and hence drag. Although the Williams wing is fitted with DRS, low drag is still critical as DRS can only be used in the race in the situation where the car is less than 1s behind another at the DRS detection zone.

Renault meanwhile have twisted their rear profile to match the oncoming airflow. This is in fact an old wing already seen in 2010.

DRS: Optical Illusion why some wings appear to open wider

Having failed since 2009 to make the driver adjustable front wing a tool for overtaking, the driver adjustable rear wing flap has replaced the adjustable front flap for 2011. Known within the sport as DRS, for Drag Reduction System, this is now a proven way to allow overtaking. Within a set of complex sporting rules, the rear wing flap can be pivoted to reduce its angle of attack (AoA). This reduces downforce and drag, allowing the car to go some +10kph faster. This effect is similar to the F-duct stalling rear wings raced last year. Although the DRS effect on top speed is even greater than the F-duct. In theory the larger the flap the more drag can be shed when its activated, however the rules set out certain geometry the flap needs to operate within. Firstly the flap has to pivot within 20mm of its trailing edge, thus the flap must move upwards, lifting its leading edge clear of the main plane of the rear wing. Secondly the slot created between the two rear wing elements must be between 10 and 50mm.

Currently F1 rear wing flaps are only 10-20 degrees off vertical, to bring the angle of attack down to nearer horizontal will require a large change in AoA. With only a 50mm opening, simple trigonometry will prove that to find the maximum reduction the angle of attack of the flap, will require a shorter flap. Although in its normal position, a smaller flap will not be as heavily loaded with downforce as a larger flap, the reduction in downforce\drag will be greater, due to the change in AoA.

To demonstrate the effect I have drawn two wings, one with a large flap and one with a short flap. With the large flap in its closed position you can see a large area of wing exposed in the left of the illustration (shown yellow). When DRS is activated and the wing opens to the maximum 50mm slot gap, the reduction in exposed wing area is noticeable.

Large flap – Closed

DRS: Large flap- wing closed, large amount of wing exposed (yellow)

Large flap – Open

DRS: Large flap- wing open, less wing exposed (yellow)

Now when we look at the short flap wing, the difference between open and closed is far more noticeable, as pretty much only the thickness of the wing profile is presented to the airflow. The challenge for the teams is produce a short flap wing, which still produces the level of downforce of the large flap wing. Also in creating this downforce, the wing must not stall or separate. As the reason for the slot in wings to reduce the airflow separating off the underside of the wing. Moving this slot rearward, by using a shorter flap, is likely to induce this sort of separation.
Small flap – Closed

DRS: Small flap- wing closed, large amount of wing exposed (yellow)

Small flap – Open

DRS: Small flap- wing open, hardly any wing exposed (yellow)

Optical Illusion.
Looking at DRS rear wing in use between different cars creates an optical illusion. Some wings appear to open far more than others. Red Bull and Mercedes are teams who have raced short flap DRS since the start of the season. When their DRS is activated, the slot gap appears much larger compared to McLaren who continue to race with a larger flap. Their flap appears to be only half as much as the other two teams. Although if we could measure it, all three wings are creating the same 50mm slot gap.