Reynolds Number

[dsn24]

The wing data given in the book "Theory of wing sections" by von doenhoff is at a reynolds number of 3,6,9 million but for my calculations im operating in a reynolds number of 0.7 million. SO cant i use the data given in the book or can i assume the values of 3 million for my calculations??

Thanks in advance!!

Im trying to design a front and rear wing

[CameronBeaton]

I am no expert but the wing in that book are probably intended for airplanes and not suitable for an FS car.

Look at what other have done and see if the wings look simular to the ones in your book. My guess is no.

CFD or wind tunnel tests are going to have to be done I´m affaid to say

[Lorenzo Pessa]

The airplane profiles are optimized for low drag.
In general it is correct to say you need to use a different wing shape.

Remember that front wing is working in ground effect. Maybe the profiles have to be different from the rear ones.

If your goal is to understand how FSAE aero works for a first guess design, I think it is not wrong to use an aircraft shape if you can't run a shape optimization (or if you don't have other data).
I made this kind of work in my thesis (I used eppler 420).
You can obtain useful data to develop in a next step a working aero package.

If you are going to run on the road your aero package, it would be better to make an optimization first.

Some months ago I posted my data here http://fsae.com/eve/forums/a/t...48/m/89320375941/p/2 (http://fsae.com/eve/forums/a/tpc/f/125607348/m/89320375941/p/2)
I hope you can find it useful.

[CameronBeaton]

Since you've done some work into this then maybe you can tell me why alot (mabye all) of the teams with wings have gurney flaps. I thought aerodynamically (L/D ratio) they were awful and it was much better to run a bigger wing (which is why they are used in other competitions because of wing size regulations).

Am I missing something or are they good for downforce compaired to the weight of the larger wing?

[Lorenzo Pessa]

Originally posted by CameronBeaton:
Since you've done some work into this then maybe you can tell me why alot (mabye all) of the teams with wings have gurney flaps. I thought aerodynamically (L/D ratio) they were awful and it was much better to run a bigger wing (which is why they are used in other competitions because of wing size regulations).

Am I missing something or are they good for downforce compaired to the weight of the larger wing?

Gurneys born when wing plan area was limited.
It works as a virtual rear extend of your wing.

Why gurney if you don't have a plan area problem?
I try to find some answers not in aerodynamics.

gurneys are set on a thin airfoil, the weaker of the entire wing. First of all adding a "L" beam on that element make it stronger.
Then a bigger virtual wing weight less the real one (but this statement may be not always true).

You can add gurneys also when you build a wing that don't reach the downforce you expect. Then you have a chance to gain downforce (or reach stall...)
If your wing stalls in some zones you can add gurneys in the bottom side to reduce local downforce. Not so good in the design event...

The final one!
I fear in several case that someone make a choice because everyone do in that way.

Asking yourself "why people do that?" is a very good way to approach Formula SAE.

[Z]

Originally posted by Lorenzo Pessa:
I fear in several case that someone make a choice because everyone do in that way.

Asking yourself "why people do that?" is a very good way to approach Formula SAE.
dsn24,

Lorenzo is giving you very good advice. If you copy aeroplanes, or any other formula aero, you will be going in the wrong direction.

FSAE is in the rather unique position of having relatively free aero rules. You can do much better aero on an FSAE car than on aeroplanes, or in other racing formula. Why?

1. FSAE (and other racing) is in "ground effect" so it works much better than up in the sky. Because of vortex drag aeroplane aerofoil sections are NOT optimised for good aero efficiency, ie. high 2-d L/D. They are primarily optimised for good STRUCTURAL properties. This is important to understand.

For the chief aeroplane designer it is the whole package that is important. An efficient aerofoil section is BAD if it means the wings keep breaking off. Or bending too much. Or fluttering. So aeroplane wings are FIRST designed so they make good (light, stiff, strong) cantilever beams (ie. they are fat boxes), THEN they are rounded off so the air flows smoothly over them.

A thin curved plate (arcuate) aerofoil can have better aero performance (L/D) than any of the deep section aerofoils in the textbooks.

2. Most of the aero on other racing formula (F1, Indycar, etc.) is the result of years of rulemakers banning the good stuff, and only letting the bad aero (high drag, low downforce) stay on the car. And they don't let the aero act directly on the axles (it has to go via the springs, making the suspension very stiff).

If you want good aero on your FSAE car, then do the things that have been banned over the last 40+ years. (Hint: undersurface aero acting direct to the axles.)

Z

PS. (Edit) Read all of Lorenzo's "Aero packages..." thread linked above, it has useful advice. But note that Lorenzo says his underbody was NOT optimised. There are big gains to be had there. http://fsae.com/groupee_common/emoticons/icon_wink.gif