" Aerodynamics doesn't begin to have an effect until 60 MPH "

[aerohead]

Originally Posted by Cd

I keep seeing this comment over and over.
I remember a comment that Darin made about how important that aero is even at 45 MPH.

Can someone suggest a direct link to some info on this ?
It gets frustrating.

* There may have been a specific case in which the comment had merit. Perhaps a Bonneville streamliner class vehicle, or the 1993 EV1 land speed record car at Ft. Stockton, Texas. Without the context, we'd be at a loss.
* We know that aerodynamic drag varies as the square of the velocity.
* And we know that the power to overcome aerodynamic drag varies as the cube of the velocity.
* Here's an aero power profile for the 2019 Chevy BOLT ( using Cd 0.31 )
35- mph = 2.3316-hp
45- mph = 4.9557-hp
55- mph = 9.048- hp
60- mph = 11.7468-hp
65- mph = 14.9351-hp
75- mph = 22.943- hp
85- mph = 33.3983- hp
95- mph = 46.6271- hp ( 1-mph over rated top speed )
* One thought, which could explain the comment, might have had to do with the 'cross-over point' velocity, at which aerodynamic drag just began to exceed that of the rolling resistance on a road load power curve for this particular vehicle. For this to be true for the BOLT would require Cd 0.142.
Honk if you have a small one!

[freebeard]

Most of us in this community know that mechanical drag is a linear function, whereas aero drag is exponential.

Vman455 posted Permalink#5 in vain.

[aerohead]

Originally Posted by freebeard

Vman455 posted Permalink#5 in vain.

* Road Load Horsepower leaves 'mechanical' drag outside, dealing solely with rolling resistance and aerodynamic drag, by definition.
* To go from the Road Load Horsepower to Brake Horsepower, you would introduce all the transmitted power inefficiencies between the tire/road interface, and engine's flywheel, including any engine-driven accessories ( differential, wheel bearings, CV-Joint shafts, propeller shaft, transmission/ transaxle, power steering pump, water pump, alternator, AC compressor, etc. ).
* EV power electronics, motor losses, transmission losses, heat pump load, cooling system pump, etc. would have to be factored in to compute an EV's 'brake' kilowatts and BSFC-e, on top of its Road Load Horsepower/ Kilowatts.

[Blacktree]

Originally Posted by freebeard

Vman455 posted Permalink#5 in vain.

So we're nitpicking terminology?

Common speak and math jargon are two different things. And I'm not a mathematician. So you'll have to excuse me for using the common definition of the word "exponential."

[freebeard]

I stand with the common man.

But I repeat myself.

[Blacktree]

My mistake. Totally misunderstood your post.

[Gasoline Fumes]

I assume the speed that aero matters depends on whether you're talking about drag or lift/downforce, right?

[Cd]

@ everyone : thanks for the replies !

[freebeard]

My mistake. Totally misunderstood your post.

I get that a lot.

I was empathising with Vmann455 without necessarily agreeing. Or covering for my error.

It's hard to shepherd the hive mind. There was a major kerfluffle over the Template recently, people got banned.

My effort was to get people to say first approximation instead of rule of thumb. You can imagine how that went.

[Blacktree]

Originally Posted by freebeard

It's hard to shepherd the hive mind. There was a major kerfluffle over the Template recently, people got banned.

My effort was to get people to say first approximation instead of rule of thumb. You can imagine how that went.

Sounds exciting.

I'm sure that template has its uses. But let's be realistic; it's almost a century old. Our knowledge of aerodynamics has come a long way since then.