Drag effects at low speeds?

[examorph]

Me and a group of people are making a small car which is powered by an electric motor for a race, I am having a hard time deciding on a design for the bodywork, after researching I thought the best design would be a tear drop since many say it has the lowest drag coefficient of any natural shape, what are your thoughts on this?

Some extra information: The cars maximum speed will probably not go over 30mph, the front and rear wheels have to be in-line.

An additional question, we are using bike tyres for the wheels on the vehicle, is it worth covering these up or at such low speeds will the drag not be noticeable?

[NeilBlanchard]

Think of riding a bicycle at 20mph; let alone at 30mph. Drag is significant, and the churning wheels also add drag. Look at the performance of a velomobile vs a bicycle. The only time when the weight of the body is a greater penalty than the lower drag is up long steep hills.

[MetroMPG]

You can also run the numbers yourself: aero & rolling drag calculator

[California98Civic]

Originally Posted by examorph

Me and a group of people are making a small car which is powered by an electric motor for a race, I am having a hard time deciding on a design for the bodywork, after researching I thought the best design would be a tear drop since many say it has the lowest drag coefficient of any natural shape, what are your thoughts on this?

Look up "the template" thread here on EM. I would imagine a really good and not too difficult design would be a version of the 1930s Schlorwagen's shape, which resembles a "tear-drop" a little, adapted with a trailing edge that is a bit more like the template, which also resembles the tear drop a little. Get a copy of Hucho's book on the "Aerodynamics of Road Vehicles" through your library's inter library loan program, or buy it ($$$). For fun and design ideas, spend some time on the thread called "interesting aerodynamic vehicles." It features pics of classic and little known vehicles almost entirely. The Schorwagen is on it too. Good luck!

[Sven7]

Instead of the Schlorwagen I would imagine something like this:


But following the template where possible. Full boat tail. Full under body covering. Enclosed wheels (unless you'll be making tight turns)

[euromodder]

Originally Posted by examorph

An additional question, we are using bike tyres for the wheels on the vehicle, is it worth covering these up

Definitely.
The spokes add a lot of drag.
On many Velomobiles, the spokes get covered with a circular cloth so the shape is smooth.

Keep weight low, and use narrow bike race wheels and tyres pumped up to their advertised limit for low rolling resistance.

[Frank Lee]

I would look to the HPV crowd for the best examples of things to copy.

[euromodder]

Originally Posted by Frank Lee

I would look to the HPV crowd for the best examples of things to copy.

Yeah, having to power something yourself tends to make people more inventive at reducing their workload

[Varn]

I have two running HPV's
This one takes about 100 watts of power at 30 mph


This one is a tricycle.


There are lots of photos of my liners at: veloliner.com

[Grant-53]

Even a simlpe touring fairing on my city bike improved my cruise speed from 11 mph to 14 mph. Every bit helps.