It’s been a source of many a joke, that High Tech F1 cars run with a piece of wood bolted underneath them. The plank as it’s known by the regulations, is in fact a bit cleverer than a mere piece of wood. Its aim to prevent excessively low ground clearance in the wake of Senna’s 1994 crash has been challenged by the designers and now teams regularly run the tip of the plank along the ground.
Post 1982 aero regulations enforced a flat floor between the front and rear wheels, this lead the team to run even lower ground clearances to make the most of the accelerated flow and ground effect beneath the vehicle. These rewards are only available until the ground clearance reduces to zero and the airflow stops and downforce is lost. Post active suspension it was clear that teams no longer had the means to adequately control ride height and in the wake of Imola the rules were changes to enforce a stepped underfloor and a plank with skid blocks to ensure ride heights kept the car clear of the ground.
3.13 Plank and skids : Beneath the surface formed by all parts lying on the reference plane, a rectangular plank, with a 50mm radius (+/-2mm) on each front corner, must be fitted. This plank may comprise no more than three pieces, the forward one of which may not be any less than 1000mm in length
Over the subsequent years the plank regulations have been relatively simple, a 300mm wide plank, 10mm deep and of a specific gravity (1.3 and 1.45). The plank sits over the flat reference plane and has to meet the FIA specification for its openings and fittings.
The plank must have seven holes in FIA specified positions, wear will be measured in the four 50mm diameter holes and the two forward 80mm diameter holes. The other 10mm diameter holes are for access to the bolts which secure the Accident Data Recorder inside the cockpit.
The plank can be chamfered along its edges, while the trailing edge can be chamfered over a length of 200mm, the sample plank in the images below is a rear piece and shows the taper allowed for this section.
In fact, up to three separate sections are allowed to make up the complete plank. But the front section must be at least 1000mm long, as teams where running a shorter front plank section to allow greater flexibility of the T-Tray splitter. Despite this the plank is highly flexible and any movement of the floor\splitter would still be accommodated by the plank flexing.
Initially the plank was made from a beech wood product called Jabroc, but has long since moved over to a phenolic resin material called Permaglass made by BTR Permali. This is a glass reinforced laminated product, so it’s no longer a wood plank at all! The material has good fire resistance, produces little smoke and toxic fumes, making it ideal for its application in F1.
From the close up images you can see where the panel has been machined, with the machining marks and underlying glass matt being visible.
The regulations make allowances for fitting the plank to the car, with specific locations mounting and some free allocation for subsequent fasteners, subject to a maximum cross sectional area. This has given the teams a vague definition to be exploited, so with the current nose-down raked set ups the front of the plank is filled with titanium fasteners both mount the plank and resist wear as the plank rubs along the track. In addition, teams bond the plank to the floor with a semi-permanent glue, although the regulations do state the plank can only be fastened with the aforementioned fittings, not adhesive. Both the forward biased fittings and the glue layer appear to be allowed by the FIA. Although the skid block material is now specified as Titanium rather the previous used tungsten, the latter of which is denser, more wear resistant and produces few sparks.
Preventing wear to the plank is critical as the measurement taken in scrutineering can lead to disqualification if the plank is over worn. Running the plank along the track means a lower front ride height can be achieved for better front wing performance. Infrared images taken of the Red Bull a few years showed the front of the splitter\plank glowing hot, this was due to the almost wholly metallic front edge of the plank being run hard against the track. This practice is still in use throughout the grid and the increased splitter deflection tests and change in material appears to have made little difference to the practice.
3.13.2 The lower surface of the plank may be fitted with flush mounted metal skids which :
- a) May only be fitted in place of plank material.
- b) Have a total area no greater than 20000mm² when viewed from directly beneath the car.
- c) Are no greater than 4000mm² in area individually when viewed from directly beneath the car.
- d) Are fitted in order that their entire lower surfaces are visible from directly beneath the car.
- e) Must have a minimum cross sectional thickness of 15mm across its external boundaries in plan view. The minimum wall thickness between an internal fixing hole and the external boundaries of the skid must be no less than 7.5mm.
- f) Must have an upper surface no more than 3mm below the reference plane.
- g) Must be designed such that they are secured to the car using the fasteners described in 3.13.3 and that, when viewed from directly beneath the car, no part of the skid is more than 50mm from the centreline of a fastener which passes through that skid.
- h) Must be made from Titanium alloy.
3.13.3 The plank and skids must be fixed to the car using fasteners which :
- a) Are no smaller than M6 and are made from grade 12.9 steel.
- b) If used to attach a skid to the car, must employ at least 1 fastener per 1000mm2 of skid area.
- c) If used to attach a skid to the car, the team must be able to show by calculation that the shanks of the fasteners (which may be no less than 6mm diameter) are the weakest point in the attachment of the skids to the car.
- d) May use a load spreading washer if required.
The total area of the fasteners and any load spreading washers employed with them when viewed from directly beneath the car must be less than 5000mm2. The area of any single fastener plus its load spreading washer may not exceed 500mm2.
No part of any fastener or load spreading washer may be more than 8mm below the reference plane. For the avoidance of doubt, the skids referred to in 3.13.2 will not be treated as load spreading washers.