[WRC] FORUM8 Rally Japan 2023

[linni]

Listen to br21, he knows.

Please follow this small example.

It's cold outside and it's raining.

You have a road car with internalvolume 2 m3. There is 22°C inside. You come inside completely wet and the water starts to evaporate. The maximum amount of water the 2 m3 of air at 22°C can take is 38 gramms. The rest stays in the form of liquid in the clothes or on the floor.

Now you have a second car with the same internal volume but the inner temperature is 50°C. Again you bring some water inside on your clothes and shoes. The maximum amount of water which can evaporate in 2 m3 of air is now 164 gramms. So your air in the car now contains 4,3x more water.

Where the air hits the cold glass it cools itself and the water condenses because the colder the air is, the lesser amount of water it can take. If you have the same heated windsreen which is capable to heat the screen to let's say 30°C average you have no misting in the road car but you still have big misting problem in the other one (the air at 30°C can take only 37% of water compared to the air at 50°C) and due to the fact that the inner humidity is already 100% the blowers don't work.

So the resume is that you have to either heat the windscreen to higher temperature than what the ambient temperature inside the car is. Or you need to bring less water inside (may not be possible), or you need to lower the humidity (not possible without A/C). Or you need to somehow cool down the temperature inside the car. If you have very high temperature drop between the inside and the outside, heating the screen enough might not be possible, so you need to let as much air from the outside to get in because the air from the outside even if it's wet, will still help because it's much colder but the amount of air you can let in is very limited by the vents. You can't drive on stage with opened windows because it's forbidden. After all you might end in a situation where nothing helps.

Yes, it all makes sense.

Everything but why the teams do not take it in consideration.
Just read an interview with Loeb, where he said, that having a mist problems in a 1 million eur car is nonsense.

[Mirek]

Yes, it all makes sense.

Everything but why the teams do not take it in consideration.
Just read an interview with Loeb, where he said, that having a mist problems in a 1 million eur car is nonsense.

We woud need to do some pretty complex math but heating the windscreen to 50+ °C at cold weather and high speeds definitely requires a lot of power because the windscreen is actively cooled from the outside with very high efficiency. I can't compute that myself but it's definitely several kilowatts. That doesn't mean only that you need a source to deliver such power but you also need to have thick enough wires in the glass. My very rough estimation is around 5 kW in situations like here in Japan. That is 10x more than what standard road car heated screens are capable of. You also need 3-4x thicker (and much better visible) wires.

I'm also not sure whether there wouldn't be a risk of cracking the glass from temperature shocks combined with mechanical shocks and vibrations.

For sure if it had a simple solution no team would have problems.

[linni]

We woud need to do some pretty complex math but heating the windscreen to 50+ °C at cold weather and high speeds definitely requires a lot of power because the windscreen is actively cooled from the outside with very high efficiency. I can't compute that myself but it's definitely several kilowatts. That doesn't mean only that you need a source to deliver such power but you also need to have thick enough wires in the glass. My very rough estimation is around 5 kW in situations like here in Japan. That is 10x more than what standard road car heated screens are capable of. You also need 3-4x thicker (and much better visible) wires.

I'm also not sure whether there wouldn't be a risk of cracking the glass from temperature shocks combined with mechanical shocks and vibrations.

For sure if it had a simple solution no team would have problems.

If you cannot heat the things up, you have to think, how to ventilate the moisture out. Sunroof will do, or full cabrio (smile). Or something between.
Anything, but I have to give credits to Ogier - how the hell the windscreen is misty in my 1 mil eur car?

[Mirek]

If you cannot heat the things up, you have to think, how to ventilate the moisture out. Sunroof will do, or full cabrio (smile). Or something between.
Anything, but I have to give credits to Ogier - how the hell the windscreen is misty in my 1 mil eur car?

IMHO the only reliable solution is A/C unit. The problem is that it has about 20 kg and takes a lot of space.

[linni]

IMHO the only reliable solution is A/C unit. The problem is that it has about 20 kg and takes a lot of space.

There has to be another solution. Let`s see, what`s coming on in Monte. The moisture is there a problem as well.
I wonder if no team has taken any measures due to it.

[COD]

There has to be another solution. Let`s see, what`s coming on in Monte. The moisture is there a problem as well.
I wonder if no team has taken any measures due to it.

I think Ogier said that problem is the cars are tube framed with plastic panels, a lot of water getting in from cracs. He said these problems are not happening with real car based rally2 cars of previous WRC machines