Turkey marked the start of the mid-season rush of classic European tracks. It's fitting too that the Istanbul circuit marks this point in the season, as it is such a challenge to the cars, with both the super-challenging Turn 8, as well as fast, straight and slower, more technical sections.
Cars that suit this track will do well over the summer months, and the teams know it. As a result, almost every team brought major updates to its cars for this track, in order to prepare themselves for the second half of the season.
With the testing ban still in place, teams are using Friday's practice sessions and the entire weekend as an extended test. This gives little chance to predict the on-track benefits of any developments, so we are seeing a see-saw effect on teams' relative performances. A team that might be up on one weekend is struggling at the next race.
Ferrari brought an evolution to its double diffuser (outlined yellow) for Turkey © AUTOSPORT
The rear wing was also revised without the extra slot and with the addition of notch cut out on the endplate behind the wing. This notch reduces drag created by the wing for more straight-line speed.
Although Ferrari had moved up the grid to challenge for wins in Spain and Monaco, the changes did not keep the cars up with their rivals whose revisions seemed to have gained them more pace.
Yet more diffuser changes for McLaren this is their fifth version © XPB
Still lacking downforce, the car struggled around Istanbul, particularly through the fast Turn 8 sequence. The language coming from the team is now about considering the 2009 season as a lost cause and the impacts of new tyre and refuelling rules for 2010 as a better investment in resources.
The diffuser now gains an inverted "U" section in the middle: this creates a venturi-like channel and although this limits the volume inside the diffuser, the airflow could well attach better to the new shaping, reducing drag or stalling. Meanwhile, the beam wing is no longer hooked up and over the crash structure, instead it splits conventionally either side of it.
Having updated the car in Spain, BMW Sauber ha waited until Turkey to introduce their double diffuser © AUTOSPORT
Even though the car was updated considerably for Spain, BMW Sauber brought yet more changes the F1.09 for Turkey.
The long expected double diffuser arrived as well as numerous changes to parts of the bodywork. Having run KERS for Nick Heidfeld in the first races, the revised car continues to run without it, partly due to the repackaged sidepods not creating space for the KERS hardware, but also the weight of the system is big a penalty to lap times.
As mentioned, the major change to the BMW was the new diffuser: this follows the outlines of the old diffuser, but gains both a Brawn-like dipped centre section and a Toyota-like third diffuser sitting behind it.
Part of the Spanish upgrade was a new rear crash structure and this now sits clear of the diffuser, no longer encroaching into it, which has been a BMW Sauber characteristic for several years. Other developments to the car, included new front wheel fairings, which extend forward to pick up the flow from the revised front wing.
Renault announced some front wing changes for Turkey: these were not visible differences but merely smaller geometry changes. More importantly and all but unnoticed in Monaco, was that Renault introduced a new sidepod inlet and front wheel fairings.
No longer running KERS, Renault appears to have optimised the sidepod package around the lack of KERS hardware and its associated cooling demands, resulting in the inlet now being narrower and reaching almost down to floor level, rather the air dam set-up with the KERS cooling inlet of the launch-spec car.
This new design probably improves airflow to the rear of the car and reduces drag with it. Having run conventional wheel fairings for most of the season the team introduced a vane arrangement inside the exit of the disc.
Formed of three fences holding a curved vane, these would seem to direct the exit airflow more accurately down the flanks of the car. Married with the revised sidepod inlets this should see the flow over the top of the diffuser and lower rear wing improved.
A new diffuser and this extended rear wing endplate for Toyota © AUTOSPORT
Meanwhile, the car's aerodynamic development was clearly progressing with a major revision. The diffuser and rear wing endplate were all new: Toyota were the first team to exploit the double-deck and centre extension to the diffuser. This has gone largely unchanged while the other teams caught up.
Its new diffuser shows inspiration from its rivals in a simpler overall design. Gone is the centre channel and a Brawn-like dipped centre section has replaced it, this is now topped by a very large exit for the upper deck, creating the largest volume possible for added downforce.
Then the rear wing endplate has been extended downwards like Red Bull's to form three vanes to act like extensions to the diffuser, effectively lengthening the diffuser, again for more downforce.
Other areas of the car have not gone unchanged, the inner front brakes ducts now extend forward to reach to the front perimeter of the wheel.
Only minor changes were made to the Red Bull cars for Turkey, as the major update introduced at Monaco was sufficient to keep the cars in touch with Brawn. While Monaco was a struggle for Red Bull, the Turkish track was far better suited to the cars' aerodynamics, the step the new double-deck diffuser brought was not evident at the low speeds of Monaco.
Taking clues from Brawn's solution, Williams had this new front wing endplate set-up © AUTOSPORT
For the first event in a long time, Williams was on the pace with the frontrunners, not just in the practice but also in the race.
Aiding the team's performance was a new front wing, influenced as so many teams have been by the Brawn BGP001. Thus the new front wing now sports cut down endplates, a large vane fitted to the footplate performs the function of steering the airflow around the front wheel.
These vanes also supports the cascade element above the wing. Williams uses a split cascade forming two elements, not as wide as McLaren's nor Red Bull's, and requiring a narrow strut to support its inner end. Allied to the new endplate arrangement, the wing itself sports a two-element flap and a shorter snowplough-vane fitted under the nosecone.
Force India was able to make some small changes in Turkey before the bigger Silverstone upgrade. These formed a revised front wing flap and new wheel fairings. The team used a larger, more rounded inner flap next the tall fence on the front wings: this two-element flap now bows upwards to create a larger area for more downforce. The front wheel fairing gained a fin running horizontally along its upper edge.
A new front wing flap and wheel fairings have kept Brawn's pace ahead of its rivals © XPB
This mechanism sits inside the front wing, just ahead of the tall fence, which itself houses the linkage to move the flap. Therefore this adjuster mechanism now moves the entire flap rather than just the small triangular flap. This revised wing was amated to new front wheel fairings with a different-shaped exit.
Elsewhere on the car, the rear suspension was modified with some new elements. These and the changes brought to Spain and Monaco have kept Brawn ahead of the field on race pace, although the team struggled in the opening practice day and lost out on pole.
This suggests, aside form its innate speed, the Brawn is kinder to its tyres in the race. The pace over long stints and the ability to keep the softer tyres from degrading is a trait the other teams will be seeking to emulate now they have nearly caught up on one-lap pace.