F1 in Schools Help - Aerodynamics and Wheels

[Fulminex]

HI
Im participating in the UAE National Finals this year (2015 season).
I would like some help in the development of the intra-schools-car (pics attached).

http://s1164.photobucket.com/user/abdul ... 2.jpg.html
http://s1164.photobucket.com/user/abdul ... c.jpg.html
http://s1164.photobucket.com/user/abdul ... c.jpg.html
http://s1164.photobucket.com/user/abdul ... 8.jpg.html
http://s1164.photobucket.com/user/abdul ... 7.jpg.html

Thanks in Advance

[tok-tokkie]

It seems the rules must have changed quite a lot since the last time I looked at a F1 in Schools model. You are wanting to minimise the cross sectional area so as to minimise aero drag so that big channel down the length of the car looks great.
But what is it you want advice on? You will find that discussion about specific questions you pose may take place but you are unlikely to get any response to a request like the one you have posed.

[Fulminex]

The channel is the exact purpose you mentioned and the rules are very challenging.
1) Well, first there are rules that the wheels cannot be covered in the front up to 15 mm from the track surface and the rear of the front wheels cannot be covered at all (exclusion zones).
So i need help in this area mostly.....
2) Should the air be directed to the top or sides or top and side of the front wheel.
3) Also about the concept of golf balling. Golf balling reduces the wake of the car, so my idea is to add dimples to the rear of the car after curving the loft steeply at the extreme end to reduce the turbulence at the back.
4) The rear wing is compulsory and it causes a lot of drag on the car. So is there any place where I could 'hide" it somewhere behind the car.
5) The car usually jumps in the air at the start of the race, so there is a lot of friction between the tether guides and the line.
So reducing the height of the canister will help?
6) Are normal elliptical rear wings better or swept rear wings?
7) Since larger wheels have a larger circumference they travel short distances in less rotation..... my idea is to design a wheel with a smaller radius and wheel with a much larger radius. Both will have the same weight and the same width.
Will this idea work????

Thanks

[Fulminex]

Anyone [-o<

[variante]

2) complex argument...i would suggest both, if possible. However it depends on your design. Have a look at LMP cars.
3) just no. If not studied properly, that solution will give opposite results than the expected ones.
4) some guys attach the rear wing to the side of the reactor in order to reduce frontal area of the wing itself. Is that still allowed?
General rule: place it at a certain distance from any element of the bodywork so that the air can move more freely and cause less drag.
More complex solution (because you'd need some CFD work): use the wing to redirect air into the wake of the rear end. Or use it to increase the efficiency or the reactor (even more complex...)
5) might help. If placed nearer the centre of mass height, it should be better. However it's complex... You could study a slo-motion video to understand how it actually behaves...
6) General rule: elliptical wings are less likely to stall. But here we're talking about wings with 0 AoA, so this property is useless.
Still, elliptical wings may be less draggy than normal ones with the same cross section because their leading and trailing edges have an angle to the incoming wind.
7) greater radius wheels generate less fristion with the bearing (smaller frequency of rotation=less heat generated with the bearings) but they do create more drag. You should calculate the right tradeoff. Intuitively i'd go for the smaller wheels

[Fulminex]

Thanks variante
I had a look at LMP cars and they look great!! I'm interpreting that the airflow should be directed all around
This has been bothering me for a while......
The rules state that the front wheel can be obstructed only upto 15mm.
1) I have seen cars perform better with only 1 front wing with 0 AoA in front of the wheel.
Since a wing with 0 AoA has the least drag, most cars are designed with rear wings directing flow above the wheel with a high AoA.
Which one is better? Is high AoA a problem or Not covering the wheels???
2) Could I use a venturi effect in the channel without pressurizing the air but only to widen the channel at the back to reduce low pressure???
3) I have searched this everywhere but I didnt find satisfactory answers to this question....... What are the factors affecting rotation of a wheel?
4) Should air be directed towards the canister ( it is filled with pressurized gas and pierced at the end releasing the gas (Newtons third law)?

[variante]

I'm interpreting that the airflow should be directed all around

Yes, but especially upwards and outwards, where you have -let's say- more open space where to unleash the high pressure.

Which one is better?

Such thing doesn't exist. It only exist the most suitable solution to your car's layout. That must be studied through CFD work; if you don't have any CFD software, just use your intuition and hope you don't come too far from reality.

2) Could I use a venturi effect in the channel without pressurizing the air but only to widen the channel at the back to reduce low pressure???

I'm not sure what you mean, but "without pressurizing" and "widen the channel" sound like good points.

What are the factors affecting rotation of a wheel?

hehe that could be anwered in a couple of words or with an entire book...depending on what you want to know exactly.

4) Should air be directed towards the canister ( it is filled with pressurized gas and pierced at the end releasing the gas (Newtons third law)?

There should be the lowest pressure around the nozzle, in order to let pressurized gases expand more freely. But that's tricky and probably useless in such context. However i remember a team using a curious Venturi channel around the canister...

Anyway, you may want to focus on stabilizing your car so that the longitudinal component of the thrust is always parallel to the track.

[Harybald]

The car usually jumps in the air at the start of the race, so there is a lot of friction between the tether guides and the line.
So reducing the height of the canister will help?
6) Are normal elliptical rear wings better or swept rear wings?
7) Since larger wheels have a larger circumference they travel short distances in less rotation..... my idea is to design a wheel with a smaller radius and wheel with a much larger radius. Both will have the same weight and the same width.
Will this idea work????

[Lightspeedrt]

The car usually jumps in the air at the start of the race, so there is a lot of friction between the tether guides and the line

Your idea should be to ask why this happens, and then try to tackle it. Going in with your eyes closed and hoping that you fluke a solution wont help. You should get some high speed footage done of the launch of your car and analyse it. Take it to an industry partner, or even post it here so we can help you understand what is happening.

All of the questions you are asking require testing to back them up, as a previous competitor and now judge, i can tell you that analyzing the problem before trying random stuff will provide much better results and your ability to understand and apply is much more important in Engineering Judging than your actual solution.

You have good ideas, test them, then post the results if you need help interpreting them.

Dylan

[Fulminex]

Thanks for the replies
I have CFD (Symscape) and testing the cars along with the rotation of the wheels, moving ground and thrust from the canister.# really helps.
After track testing, we found out that the rear wing is responsible for a considerable amount of drag (because it is a protrusion).
A dummy car with the rear wing had a fastest time of 1.135 seconds while the car without had a fastest time of 1.095 seconds.
The main problem is to reduce the effect of the rear wing (drag).
After CFD testing, we found out that swept wings in the shape of an aerofoil is the best with the lowest drag.
So is there any way i could make it less like a protrusion?

And to the previous competitors....
What is the exact preference
1) Aerodynamics
2) Wheel System
3) Weight
4) Surface Finish and Friction

For me it is Weight, Wheel System, Aerodynamics, Surface Finish & Friction. I am confused whether Aerodynamics or surface friction is more important.

and btw
Dylan- you are from A1 Racing right? Could I get some overall tips while designing?

Also many teams use teflon just because it has a low coefficient of friction.
Based on my research, this is a wrong practice. The coefficient of friction always changes with different solids.
So the coefficient of friction of PTFE with the track material may be larger than the ideal one.
So, to find the ideal material, knowing the material of the track (the official one) is very important. So if anyone could tell me the material of the track, it would be very helpful.

My guess is Laminated MDF. But since i do not have any proof I don't know for sure.

And I started developing the Previous National Finals Car (Fastest with a time of 1.067 sec).
I have analysed the problems on that car and I am developing it.

Previous Car- Drag- 0.366 N
Developed Car - Drag- 0.21 N

I will be testing the cars in Wind Tunnel and on Track.
Results will be shown soon

I tested the car in symscape and found a low pressure are just behind the rear wheel. (the half diffuser looks like a reverse arrow from the top). And I do not have a clear idea to reduce that.

Harybald wrote:
The car usually jumps in the air at the start of the race, so there is a lot of friction between the tether guides and the line

Your idea should be to ask why this happens, and then try to tackle it.

This happens due to the difference between the thrust plane and COG.
The only thing to solve this is to refine the COG.
I have asked Many ppl about this but i have different answers. Should the COG coincide with the Thrust Plane?