W-Duct: FIA move to ban wastegate based Drag Reduction Devices

It’s been discovered the FIA have issued a Technical Directive in response to a team’s request for clarification on potential exhaust aero interaction with the 2016 exhaust tailpipe rules.
In September last year, the FIA confirmed the change in the exhaust tailpipe regulations that separates the pipework for the wastegate\s from the turbo. This move was made in order to add to the sound, previously muted by having both devices blowing through the same tailpipe. To prevent any obvious aero trickery with blown effects from the extra tailpipe\s, the rules fix the pipe’s exit in the same area as the current tailpipe. However, opening up the exhaust outlets could still bring some potential exhaust interaction with the aero, along the lines of the F-Duct or Drag Reduction Duct. This new FIA TD bans any interaction between the exhausts and fluidic switches.

Stalling effects
Its long been the aim of the team’s designers to have downforce for the corners and cut drag on the straights. With the Downforce\Drag relationship being fixed, there needs to be some adaptation of the aero to allow this to happen. Over the years; bending wings, F-Ducts and the unraced Lotus DRD have sought to ‘legally’ achieve this. Regulations were put into place to ban overly flexible bodywork and driver physical interaction which prevents the first two of the solutions. However, the Lotus prototype DRD system sought to create a passive switch to alter the wing airflow above a set speed, but Lotus along with several other teams failed to make a race worthy system. With the change to trigger the fluid switch being too sensitive, for a consistent effect. Since then there’s been no legal or reliable way to trigger a stalling system, until now.
With the Wastegate system being an on\off system and under ECU control, Logic in its software could be applied to open the wastegate at an opportune time to blow for an aerodynamic effect.


Copyright AMuS

Firstly, we need to understand why and when an F1 wastegate opens, typically on a conventional (i.e. not a 2014-2016 F1 PU) the wastegate acts a pressure relief valve. When at wide open throttle and high RPM, there is more than enough exhaust pressure to spin turbo to produce the required boost. So the wastegate opens to vent some of the pressure, to preserve the engine from over boosting. Wastegates can be a simple sprung mechanical valve responding to pressure within the system. Latterly these have become ECU controlled, with a Hydraulic or pneumatic system opening the valve according to the map in the ECU.
Now, in a current F1 PU, the wastegate effect is inefficient, instead teams use the MGU-H to slow the turbo to prevent over boosting recovering energy in the process. With the sizing of the turbo and the effectiveness of recovering energy, most cars can recover energy at full throttle, indeed they actually run otherwise inefficient turbo sizes in order to recover more energy. With this system the wastegate will rarely be used to prevent high boost levels. Only in the rare situation when the engine is fully boosted, where the battery is fully charged and the MGU-K cannot use the recovered energy, will the wastegate open. Even then the MGU-H may dump its electricity through a shunt and heat sink arrangement to further prevent the wasteful loss of exhaust pressure through the wastegate. So if a wastegate does open it will be briefly and not always along a straight.
With that in mind teams would be reticent to blow large amounts of excess exhaust gas through a wastegate to gain a blown effect. The loss in energy recovery not being offset by the gain in top speed from drag reduction.

Potential blown effects
So ignoring the obvious inefficiency, what could be blown with the exhaust tailpipes? Firstly, the main turbo exhaust could, and often is used to blow up under the rear wing, via the monkey seat. The benefit of this is limited, nowhere near the level of diffuser exhaust blowing. It would add downforce, but it’s not influential enough to stall the wing off throttle. So simply switching all the exhaust flow through the wastegates at speed, to stop the main tailpipe blowing the rear wing, will not be an effective drag reduction strategy.
So what about the wastegate blowing something when they open? Again an ineffective strategy from an energy recovery point of view, but the blowing could try to stall an aerodynamic surface. Either the top rear wing or monkey seat. Again the limited pressure, direction and timing of the wastegate blowing the top rear wing are unlikely to be a useful means of stalling the Top Rear Wing (TRW).
More likely is blowing the monkey seat to stall it, thereby cascading a stalling effect to the TRW. In this mode, the pressure, timing and position of the wastegate pipes could theoretically be used to create a stalling effect. However even if the monkey seat could be stalled, the cascading effect to the TRW would be slow and inconsistent, especially when the airflow tries to reattach to the surfaces when the blowing effect stops, making for a tricky braking event at the end of the straight.
So the lack of exhaust pressure, tail pipe positioning and timing do not make for a good directly blown solution.

But the lessons of the Lotus DRD project could be applied here. Knowing the wastegate blown effect is not strong enough alone, but the timing of a wastegate opening could be contrived to be at an opportune time, what’s needed is a mechanism to amplify its effect directly at the TRW.

With the TD unbeknown to me, I proposed a system on Twitter where the wastegate could be used to activate a fluidic switch to allow a wing stalling system to be operated. Others such as Matt Somers SomersF1.co.uk had similar ideas around the same time. Using the common parlance, we’ll call this a W-Duct, W for Wastegate.
I’ll not explain the F-Duct\Fluidic switch (LINK) or Lotus DRD (LINK) here, as these have previously been explained on my blog.

Taking the basic ducting of the Lotus DRD, with a high pressure feed to a fluidic switch, that fed either a stalling duct or neutral duct, pressure at a wastegate tailpipe could be the signal to trigger the duct. So the system would work like this; firstly, the car would have two separate wastegate tailpipes, one for true wastegate use for over boost protection, this tail pipe exit would be in a neutral position, such that it blowing has no effect on the W-Duct set up. Then the other (up to two wastegate tail pipes are allowed) would be the trigger, with its SECU software mapped to open at high speeds to bleed pressure from the exhaust system out through its tail pipe exit. This control strategy would be entirely legal, as it’s the typical mapping for a wastegate. There would be a duct formed around the wastegate tailpipe’s exit, in this position it would contravene the exhaust\bodywork rules. Thus exhaust duct would be routed up to the fluidic switch as the signal duct. Now when the wastegate opens, the blown effect entrains airflow from within the duct, causing low pressure inside the fluidic switch, this would change the airflow through the switch sending airflow to the stalling duct at the TRW and not through the neutral duct. In this blown mode, the TRW will stall increasing top speed, with ECU controlling when the wastegate is open this would be at the strategic control of the team, thus entirely predictable.
This is an entirely feasible system with relatively simple requirements for construction and mapping.

Tech Directive
However, as the TD proved, other teams and ex-Lotus staff had this idea as soon as the tail pipe rules were announced, albeit they probably had advance notice of the impending change. With this potential system in mind, one team questioned its legality with Charlie Whiting at the FIA. The clarification asked if using the entrained wastegate flow could be used to trigger a fluidic switch to either reduce drag or add downforce counts as an aerodynamic influence (Tech Reg 3.15). Whether this was a genuine request to test legality to simply to have the system banned ahead of time (as the TD is distributed to all teams), isn’t clear. But unsurprisingly the response was the system was illegal under the moveable aerodynamic regulation 3.15 as parts within the wastegates move and will have a direct aero effect.
Therefore, this clever system is already banned and the teams must go away and try to find another means to create a non-linear relationship between aero efficiency and speed.