2026 active aero discussions

[henry]

I was responding to @Stu’s estimation of how to size the battery. The “leak” is not compensated for by the K and H. The leak happens in the battery but the SOC is measured outside the battery and so can be compensated for by energy stored before the race begins.

While the SOC variation is fixed at 4MJ the maximum battery capacity change is SOC + leakage, 6MJ in my example. So to operate between 20 and 80% the battery capacity would need to be 6/.6, 10MJ.

Since we’re way off topic I’ll mention also that even though the 2026 regs have the same SOC requirement the battery capacity will likely be higher because the typical C rate will be much higher leading to higher losses during the race. The 2026 regs expect the ES to be heavier even though SOC is the same which supports this rationale.

5.4.8 The difference between the maximum and the minimum state of charge of the ES may not exceed 4MJ at any time the car is on the track.

To me that means the minimum o r maximum state of charge at any time of a race or practice session.

So you can't have min to max of 2MJ and 6MJ one lap and 1.5MJ and 5.5MJ on another lap.

Your example is not allowed at the measurement point, but is within the ES. They never measure the actual, physical, absolute SOC of the battery. They only measure the change.

There is a difference between the Physical State of charge (PSOC) , the energy actually in the Battery, and the SOC as measured and monitored for the regulations. The regulations measure the integral of energy into and out of the Energy Store. It’s at this measurement point that the SOC is established. Within the ES there are some losses but the regulations are such that the losses can be replaced by energy that is preloaded into the energy store.

As an example, suppose at the beginning of a lap the Battery has 8MJ PSOC. During the lap 2MJ goes in and 2MJ is extracted. The measured SOC change is Zero. But the PSOC will have reduced, let’s say by 2%, 40KJ. If you do this for 50 laps, the PSOC will have decreased by 2MJ, but you will still be able to vary the measured SOC by 4MJ on lap 51, if you wish, and the Physical battery capacity allows it.

To be honest the physical mass allowed in the regs would allow larger batteries than being discussed here and since it is a minimum mass you would think they would spec large batteries with attendant lower losses and hence cooling requirements.

[AR3-GP]

I was responding to @Stu’s estimation of how to size the battery. The “leak” is not compensated for by the K and H. The leak happens in the battery but the SOC is measured outside the battery and so can be compensated for by energy stored before the race begins.

I can assure you, you have misunderstood something fundamental here.

The amount of energy inside the battery before the race starts doesn't matter (although it's best to top up the battery before the race starts for tactical reasons). The only consideration for the size of the batter comes from accounting for capacity fade. Any inefficiency in the battery operation (self discharge, internal resistance, active material deactivation) simply comes as an energy penalty per lap. You have the opportunity to mask this if the MGU-K and MGU-H are able to compensate within the maximum allotted fuel and braking energy available.

[henry]

I was responding to @Stu’s estimation of how to size the battery. The “leak” is not compensated for by the K and H. The leak happens in the battery but the SOC is measured outside the battery and so can be compensated for by energy stored before the race begins.

I can assure you, you have misunderstood something fundamental here.

The amount of energy inside the battery before the race starts doesn't matter (although it's best to top up the battery before the race starts for tactical reasons). The only consideration for the size of the batter comes from accounting for capacity fade. Any inefficiency in the battery operation (self discharge, internal resistance, active material deactivation) simply comes as an energy penalty per lap. You have the opportunity to mask this if the MGU-K and MGU-H are able to compensate within the maximum allotted fuel and braking energy available.

I disagree. Why would you use fuel and braking energy to heat the battery and its cooling system when you could use it to drive the car? And when you’re scrabbling to find weight savings why oversize the cooling system? (The Battery mass is specified so other than COG there’s no real benefit to specifying a low capacity, and choice of C rate might influence cooling as well)

There is no means to measure the SOC other than the sensor(s) that measure flow into and out of the ES. So the teams rely on the integral of these measurements to ensure they meet the regs. So to use the technique you’re suggesting they’d need to have additional measurements to know what the losses are in order to compensate for them. Maybe they do.

The regulators don’t know, and don’t care, what the actual capacity and charge level is in the ES. So from their point of view you can extract energy from the ES up to the regulated limits no matter where that energy originated.

But it matters not since neither you nor I are charged with sizing the ES and its cooling system. It’s purely a matter of conjectural discussion about how the cars work given the regulations and technical constraints. And we disagree, fair enough.

[mzso]

This 98% roundtrip efficiency is only compensated by working the MGU-K and MGU-H harder within the upperlimit of the braking and fuel energy available. It's not compensated by using a larger battery.

I think you're missing the point of his. Because of inefficiency and the maximum energy-input, the effective usable capacity would be always less after the first lap. But if the physical capacity of the battery is larger the extra charge can be used up. (Edit: but the rule wuzak pointed out cancels this possibility.)

But I guess this is only relevant, if the driver needs to push constantly, otherwise there's no need to use all the energy, and the battery can fully be filled.

[henry]

This 98% roundtrip efficiency is only compensated by working the MGU-K and MGU-H harder within the upperlimit of the braking and fuel energy available. It's not compensated by using a larger battery.

I think you're missing the point of his. Because of inefficiency and the maximum energy-input, the effective usable capacity would be always less after the first lap. But if the physical capacity of the battery is larger the extra charge can be used up. (Edit: but the rule wuzak pointed out cancels this possibility.)

But I guess this is only relevant, if the driver needs to push constantly, otherwise there's no need to use all the energy, and the battery can fully be filled.

I think you are right in your first thoughts. The rule you refer to in your edit depends on how you interpret the use of SOC. I believe the rule refers to a Virtual, 100% efficient, Energy store. SOC is short and for the “instantaneous sum of energy flowing into and out of the ES”. There is a whole section (5.3.2) in the rules, which describes how this will be monitored. The measurements are outside the ES, so if you put 2MJ into the ES you can take 2MJ out, and the difference in “SOC” will be zero even though the physical realisation of the ES will lose some of the 2MJ that went in.

This is similar to the power measurement of the MGU-K. the “Virtual” K has a power output of 120kW. But the energy flow into the Control for the K is controlled at 126kW, 95% efficient. Whenever there are discussions involving the K power people almost always use 120kW because it gets us to answers close to reality. But the, small number, of people in the teams responsible for the detailed design and operation of those features will use the real rather than virtual number. So it is with the ES, which has to be sized to cope with the losses due to efficiency. (And those due to degradation over its life)

It’s a few years since I first thought about this in detail so I’ve had to re-educate myself. The reality is that it is the Virtual SOC that is measured and any attempt to top up the losses in the Physical ES would exceed the regulation limits.

Here’s a relevant bit of 5.3.2,

In order to verify that the energy and power requirements are being respected, all cars must be fitted with electrical DC sensors which have been manufactured and calibrated by the FIA designated suppliers to specifications determined by the FIA. These sensors may only be installed outside the sealed perimeter of any PU-CE and used as specified below:
a. One sensor must be connected to the ES negative DC pole to measure all electrical energy into and out of the energy store.
The voltage sense wire must be connected to the dedicated measurement point on the ES positive DC pole sensor.
The sensor data will be made available to the Competitor.

b. One sensor must be connected to the ES positive DC pole.
The voltage sense wire must be connected to the dedicated measurement point on the ES negative DC pole sensor.
The sensor data will be available to the FIA only.

[wuzak]

The other day I read somewhere that the movable aero was to allow following cars to increase downforce so they would be able to follow through corners more closely.

They had adjustable (2 position, IIRC) front flaps years ago, and it didn't help.

I still think they will have to shed drag on straights to compensate for the weaker power unit package.

[BassVirolla]

The other day I read somewhere that the movable aero was to allow following cars to increase downforce so they would be able to follow through corners more closely.

They had adjustable (2 position, IIRC) front flaps years ago, and it didn't help.

I still think they will have to shed drag on straights to compensate for the weaker power unit package.

What drove me to open this thread was that I read somewhere the posibility of increasing rear downforce under braking for increasing the maximum available regenerating power in the rear axle.

Your thought and mine are not that far apart. Increasing under braking / turning or reducing in the straights is a matter of where you stablish your zero.

[wuzak]

My feeling is that they will be generating some way from the corner, well before starting to brake.

Reading the rules it would seem that they will be able to reduce power at full throttle up to 450kW. That means that they can generate up to 100kW whilst the driver has the throttle fully down.

On a straight they could go from 750kW down to 300kW! They'll want less drag.

But the comment about using adjustable aero to compensate when following another car would suggest that the difference between max drag/downforce and min drag/downforce won't be that much.

[Stu]

An interesting take on active aero, using pneumatic cylinders (so either on or off)

https://youtube.com/watch?v=dhrpi-LVWiI&feature=share

Sounds pretty cool too!!