What is the effect of crosswinds?

[Bicycle Bob]

In crosswinds, I think the odds are that a belly pan would show slightly more improvement relative to skirts. But aero on anything but pure shapes is full of surprises.

"Anyone who has ever ridden a racing bike (or even done hiking) knows this: if the wind is at your back, it's a gift. If you are headed into the wind or blown sideways by it, it's a drag... literally.

Now, maybe if our cars had adjustable sails... "

Most rigid-wing land sailers don't adjust for wind direction, they just work. Life is different in an airfol than a human body.

[aerohead]

In the late 1970s the EPA published a table showing the effect of an 18-mph wind as a tailwind,crosswind,and tailwind.
I've meant to post it.I do think the data is in the seminars though.
SAE criteria for coastdown tests limit crosswind testing to fairly low windspeed because of the difficulty of reducing the data.
If memory serves me,if any run has a standard deviation of 2 % or greater ( and crosswind will effect this ),that data must be discarded.They're very stringent.
Dead flat course and zero wind is almost absolutely necessary when you see the mathematics necessary to compensate for more than one variable.
If you've got no plans for the rest of your life,then I'd say go for it.

[stretch-hyper-commuter]

I am drawing up "boat tail" plans for my new project car 96 Geo Metro.
I am concerned about the side area increase by elongating the rear.
Can someone who drives a "boat tail" comment on the stability or instability feeling while driving in cross wind?
Thanks

[Frank Lee]

If it's properly boattailed, the side area doesn't necessarily increase. Depends on speed vs windspeed and angle, but plan for the most common condition in your area.

Here's how I visualize it (with sort of off-the-cuff numbers): Look at the vehicle from the front, offset at, oh, 10 degrees. That is what the x-wind sees (pic 1):







Looks like proper tapering in plan view added exactly ZERO to yawed "frontal" area and thus shouldn't adversely effect stability.

Perhaps this is 5 degrees yaw?



Perhaps this is why outside mirrors don't hurt drag much in the real world? (not adding much "frontal area" at all)

[basjoos]

My car is a little more sensitive to crosswinds than before the boattail was installed, but nowhere near as sensitive as my old VW bug used to be.

[aerohead]

Originally Posted by stretch-hyper-commuter

I am drawing up "boat tail" plans for my new project car 96 Geo Metro.
I am concerned about the side area increase by elongating the rear.
Can someone who drives a "boat tail" comment on the stability or instability feeling while driving in cross wind?
Thanks

My VW bus saw nothing funny.The CRX is rock solid.The T-100 is rock solid,and the full boat tail trailer pulled with no surprises in 15-mph crosswinds.

[aerohead]

Originally Posted by Frank Lee

If it's properly boattailed, the side area doesn't necessarily increase. Depends on speed vs windspeed and angle, but plan for the most common condition in your area.

Here's how I visualize it (with sort of off-the-cuff numbers): Look at the vehicle from the front, offset at, oh, 10 degrees. That is what the x-wind sees (pic 1):







Looks like proper tapering in plan view added exactly ZERO to yawed "frontal" area and thus shouldn't adversely effect stability.

Perhaps this is 5 degrees yaw?



Perhaps this is why outside mirrors don't hurt drag much in the real world? (not adding much "frontal area" at all)

Frank,I just wanted to thank you for the pics of the red 3-wheeler.That vehicle should be in a thread by itself.It's aft-body looks dead on! Thanks mucho!

[Frank Lee]

I heart that trike but unfortunately have zero info on it- just those three pics.

[puddleglum]

Crosswinds are almost always mor

I came across this link yesterday that illustrates crosswinds effect on mileage quite well. I'm guessing the hit would be even greater on a larger car with a worse Cd.

[Frank Lee]

Crabbing the whole car into the wind is an interesting concept, but I have to wonder if it would lead to more accidents- would crabbing down the road disorient drivers?