air density affects on aerodynamics

[bbb]

first post, new board. turned out well jon...

what kinds of affects will cooler or warmer dense air have on aero's vs thin air? say running in texas in the spring vs running at bonneville in august. at goliad I recorded some adjusted altitudes of -300' in march (180' actual) at the airfield vs some of the reported adjusted altitudes of 8,000' or more at speed weeks of the recent past. I understand engine performance factors, but not what air density variances will do in general to an aero package.

BTW, just recorded a 64mph gust here in charlottesville, va. its gonna be a good storm today I think.

[ddahlgren]

Run your hand through a bowl of molasses and then a bowl of water..
note the difference..
Dave

[bbb]

with dender conditions, will there be a larger vaccuous area behind a vehicle with fewer or smaller vortises and with thinner conditions will there be a smaller vaccuous area with larger and faster moving vortises? will denser conditions apply additional downforce via additional weight or because of the additional weight will it not move fluidly enough to apply additional downforce? I think I understand the theory with fluid, but not with air specifically taking into account frictional differences.

[ddahlgren]

It is a change that is more like viscosity than anything else. Thicker is more drag thinner less. Just as many issues but thinner they have less effect. Never make anything more complicated than it needs to be. If you change the viscosity 10% the drag will follow. You will change power with the high density air but drag is V cubed and the engine power is a percent change.
Dave

[PorkPie]

The different on the airflow is nothing - this is the reason why today more and more automotive companies use watertanks instead of wind tunnel to check the aerodynamic.

What's different is, is the resistance "force" on the front.

[bbb]

interesting.

[hotrod]

In general your aerodynamic forces will vary in direct proportion to the air density as it is one of the key variables in the drag equation.

Larry

[Rex Schimmer]

Let's don't mix viscosity up with density. As you go up in altitude the air becomes less dense, i.e. it weights less per cubic whatever, and, as Larry points out , density is a part of the basic aero drag formula; Drag=(Cd)(Area)(air density)(velocity)squared all divided by 2. So form drag is proportional to air "density". Now if you look a little farther into the total aero drag there can be an additional term, viscous friction, which is a function of the air viscosity. This component of aero drag is usually not included in land speed car calculations because: 1. It is pretty small compared to the Cd X Area component and 2. It is really only important it your car's shape has "attached" air flow. Viscosity is a measure of the shear within the fluid so where the air is attached to your body the boundry layer is "sheared" at the point that the air is against the body and this can be an additional force that has to be overcome. Again this component of drag is pretty small and certainly not very large especially on something like your motor cylce that probably has very little attached flow.

All explained in the first 10 pages of "The Leading Edge".

Rex

[bbb]

and I now have some new reading to do this winter...
thank you sir.

[PorkPie]

Rex,

I like your humor....motorcycle and airflow.......this are two different worlds.

A motorcycle has no airflow........only turbulences......

[bbb]

i'm 300lbs at current poundage. I will be down in the 270 range when I race in the spring. aerodynamics on my siton bike are severely impacted. however, I provide my own moveable balast.

[1212FBGS]

Air density or a lack of air density are of little consiquence to a high turbulant vehicle such as a bike. Injested air is of most importance for performance but your bike is turboed.... you bring your own air density.
no worries just race it!
kent

[PorkPie]

i'm 300lbs at current poundage. I will be down in the 270 range when I race in the spring. aerodynamics on my siton bike are severely impacted. however, I provide my own moveable balast.

How low can you go?

[bbb]

not much more. maybe 260 and thats about it unless I drop a lot of muscle mass.
this is me in much more muscular times, circa 1999. I was 370lbs in this picture. strongman event in toronto canada. first of 2 ruptured biceps. so you can clearly see aerodynamics are not my strong suit... no pun intended.

[Stan Back]

Now we know why Jon made you a Full Member!