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JulianEdgar · 04-20-2021, 05:28 PM

There seems to be a lot of confusion - and some excellent points - in this thread.

1. Cooling drag, as defined in all aero textbooks, relates to the drag caused only by the cooling of the engine, ie through water or air cooling. I take the point, though, that in the case of ICE cars, cooling of the exhaust system should be included. As far as I am aware, it is not currently included in any reference or tech paper.

2. Cooling drag, as a proportion of total aerodynamic drag, varies for ICE cars from basically zero (very well designed ICE cars - and very rare) to 6-14 per cent. Jaguar's head of aero told me that, at least for ICE cars, cooling drag percentage was likely to increase as cars got slipperier.

3. It would be logical to expect cooling drag percentage to increase with engine power (more power needing more cooling flow) but this relationship doesn't exist in real production cars. That's because the quality of the cooling system design (quality in terms of aero drag penalty) is a greater variable than engine power.

4. BEV cooling drag, again as a percentage of total aero drag, appears at this stage to be far higher than has been often suggested here (where it was assumed to be zero or very low). That could be because:

- the reduced delta T (ie the reduced temperature difference between the cooling circuits and atmosphere, so requiring larger radiators)

- the fact that BEVs still require an air conditioning condenser - in area at least, these are often as large as the engine cooling radiator in ICE cars

- the currently available data on BEV percentage cooling drag is only for two high power BEVs (but see point #3 above)

5. To suggest that BEVs have zero cooling drag, or ICE cars will always have higher cooling drag than BEVs, is simply wrong.

6. The use of radiator shutters is a red herring: they can be used equally in any car (ICE, BEV, hybrid) to give reduced cooling system drag at lower loads.

7. My prediction is that far more attention will be paid in future car design to cooling system drag reduction, as:

- the proportional drag penalty gets higher as the rest of the car gets slipperier

- without the need for a big ICE engine up front, BEVs have the potential to much better package cooling systems around the car, in turn siting them for lower drag increases.

04-20-2021, 05:28 PM	#162 (permalink)
JulianEdgar Banned Join Date: Nov 2017 Location: Australia Posts: 2,060 Thanks: 107 Thanked 1,605 Times in 1,136 Posts	There seems to be a lot of confusion - and some excellent points - in this thread. 1. Cooling drag, as defined in all aero textbooks, relates to the drag caused only by the cooling of the engine, ie through water or air cooling. I take the point, though, that in the case of ICE cars, cooling of the exhaust system should be included. As far as I am aware, it is not currently included in any reference or tech paper. 2. Cooling drag, as a proportion of total aerodynamic drag, varies for ICE cars from basically zero (very well designed ICE cars - and very rare) to 6-14 per cent. Jaguar's head of aero told me that, at least for ICE cars, cooling drag percentage was likely to increase as cars got slipperier. 3. It would be logical to expect cooling drag percentage to increase with engine power (more power needing more cooling flow) but this relationship doesn't exist in real production cars. That's because the quality of the cooling system design (quality in terms of aero drag penalty) is a greater variable than engine power. 4. BEV cooling drag, again as a percentage of total aero drag, appears at this stage to be far higher than has been often suggested here (where it was assumed to be zero or very low). That could be because: - the reduced delta T (ie the reduced temperature difference between the cooling circuits and atmosphere, so requiring larger radiators) - the fact that BEVs still require an air conditioning condenser - in area at least, these are often as large as the engine cooling radiator in ICE cars - the currently available data on BEV percentage cooling drag is only for two high power BEVs (but see point #3 above) 5. To suggest that BEVs have zero cooling drag, or ICE cars will always have higher cooling drag than BEVs, is simply wrong. 6. The use of radiator shutters is a red herring: they can be used equally in any car (ICE, BEV, hybrid) to give reduced cooling system drag at lower loads. 7. My prediction is that far more attention will be paid in future car design to cooling system drag reduction, as: - the proportional drag penalty gets higher as the rest of the car gets slipperier - without the need for a big ICE engine up front, BEVs have the potential to much better package cooling systems around the car, in turn siting them for lower drag increases.