Hollowed out body on F1 in schools car

[paulwils7]

Hi all, just wondering what the airflow effect would be if I hollowed out the body of my car to reduce the overall weight. Would this have a +ve or -ve effect to the aerodynamics? Would a particular cut out shape enable my car to ride on a cushion of air whilst it travels down the track? Any thoughts / diagrams/ sketches on this matter would be much appreciated.

Thanks in advance
Paul

[paulwils7]

I have also just been looking at the Lotus Ford 79 and the ground effect that that car generates. Seeing as the cars for the f1 in schools challenge do not really require downforce would it be possible to create upforce so as to create lift. This all needs to be done by hollowing out some sort of shape in the underside of the car. Any ideas?

Thanks
Paul

[manchild]

Event though this competition of yours if called "formula" for best result you should keep as much as possible from resemblance to any F1 car. You don't need downforce or upforce but pure aerodynamic efficiency and as much weight as possible. So, what you should be looking for is basically shape similar to FMJ rifle bullet - like V2 rocket for example only without stabilizers. F1 cars look like they do because they are designed to go fast in corners too. Your competition car isn't required to go trough any corners so it must be designed like land speed record braking cars or something similar to fulfill the regulations.

Make sure to check this topic viewtopic.php?t=1329

[paulwils7]

you say as much weight as possible? I would've thought that the lighter the car the faster it would travel. Remember these are powered by a co2 cartridge. I understand where you are coming from in regards to the land speed record types but we also need to try to be innovative in our designs. Thats why I was wondering what effect the hollowing out would have on the car body.

[manchild]

oops, sorry about weight it was a typo... less weight better results, naturally

If I knew what will get you better overall result - performance or creativity than I'd know what to say. You can make very interesting design but if that won't give you advantage over quicker but less imaginative designed car than it is not worth the trouble.

Hollow body would be positive thing when it matters weight but don't forget that you have to leave place for cartridge, than there is that longitudinal liner/channel at the bottom and all of that has to be designed using CAD and produced using CAM. In general, if you are designing good slim streamlined shape there won’t be much left to make hollow.

The racer must be made in one piece with cartridge at the back so I don’t think that you can actually make it hollow at all.

[DaveKillens]

Since the device is accelerated by the CO2 canister, it is desired that mass is kept as low as possible, to allow quicker acceleration. Only when the gas supply is spent and the vehicle is coasting, would added mass be beneficial.
The wish to use aerodynamics to provide lift is assumed to reduce the wheel rolling resistance. But the added drag of the aero may be equal, or more than the gains from reduced rolling resistance. Calculations and testing would be required to determine if this is feasable.

[Apex]

Is there any information availible on the thrust profile of the CO2 canister?

If there is, you might be able to achieve an optimal weight for the car. Thie main depencies are the duration of thrust, and drag coefficient of the car.

With out this information i'm afraid that I wont be able to help. It would be quite easy to get if you have a load cell and a data logger....

[DaveKillens]

That's a question I also ask myself, the duration of exhaust, whether the vehicle is still accelerating at the end of the run, or whether it is coasting, and for how long.
Because if there is still exhaust at the end of run, it may be feasable to incorporate some method of capturing the exhaust and converting it into mechanical energy. Maybe just a simple paddlewheel on the rear axle. So instead of the rear wheel just holding up the rear end and adding mass and drag, it may be possible to use them as tractive force.

[manchild]

http://www.f1inschools.us/misc/F1_Rules_2005.pdf
http://www.lelandltd.com/

[paulwils7]

Here are some examples of the types of cars from this years aussie comp. I would be interested to see which of the cars you all believe would perform the best...ie fastest.

Cheers
Paul

[manchild]

They all seam to have too wide wheels, which is good to resemblance to F1 car but very bad for performance. Sidepods also shouldn't resemble to F1 sidepods but be in size that is imposed by regulations - nothing else. So I'd pick those blue long slim at the bottom but I see the problems with regulations since they don't have sidpods as required by regulations.

I made this one just for hint previously this year...


They all seam to have too wide wheels, which is good to resemblance to F1 car but very bad for performance. Sidepods also shouldn't resemble to F1 sidepods but be in size that is imposed by regulations - nothing else. So I'd pick those blue long slim at the bottom but I see the problems with regulations since they don't have sidpods as required by regulations.

I made this one just for hint previously this year...
http://www.geocities.com/scriptforvideo/racer2.jpg

Finding a compromise between look that remembers F1 car and performance is a waste of time because as much as you get near to F1 car more distant you get from performance – sidepods, wide wheels and big wings are something to avoid in order to get quick car.

Also, I advise you add a link to that huge pic you posted because this way it makes people scroll in order to read the text. Just add this http://www.geocities.com/paulwils7/IMG_1190.JPG - delete

[paulwils7]

Thanks for all the replies, they are much appreciated!

The thin blue cars were the ones our team produced for the comp. It was running times consistently of 1.210 secs over 25m. The world record holder is in fact the yellow one on the far right, which ran a 1.131 secs over 25m! This car was infact hollowed out underneath. I would never have picked it to be the fastest!

I have been informed that this team used weights inside their wheels??? Any ideas on what this could've been?

Our blue car did actually have lift on the front wing...maybe it was this that slowed us down?

Thanks
Paul

[manchild]

I have been informed that this team used weights inside their wheels??? Any ideas on what this could've been?

Our blue car did actually have lift on the front wing...maybe it was this that slowed us down?

Weights in wheels make sense if car runs on inertia for large distance but that kills the acceleration. It is better to put weights in chassis/body than to put weight in wheels. They must rotate as freely as possible.

Making everything as lightweight as possible is the key including the wheels.

If your car was lifted by front wing than you've lost some performance for sure. Make wings neutral because they are there just for resemblance with F1 car and nothing else - just like sidepods.

[Apex]

My guess as to why the yellow cars performed better than the rest is because the wheels have been integrated into the design, with aero wedges infront and behind of the wheel.

A rather rough rule of thumb is that saving 1g on a rotating part is like saving 3g on a non rotating part. like i said its rough, but it illustrates that you should spend a lot of effort on minimising rotating mass. (which is partly why ceramic bearings are so good on a small scale)

[DaveKillens]

I agree with apex, only the yellow car had the wheels shrouded as much as possible by the bodywork, both in front of, and (maybe more important) behind. No one else had thought about airflow behind the rear wheels, which can be an omission, because there would be turbulence, energy that had to come from somewhere. As well, the wheels are tucked as close to the bodywork, and the inside of the wheels have minimal airlflow between the wheels and body.
Short wheelbase, narrow track, obviously in the interest of a small car, minimal mass.
As well, the "cockpit" fairing is very well integrated and appears to flow the air nice and clean.
On the yellow car, those horizontal fins on the sides where the gas cartridge reside is interesting. They may be much more than purely cosmetic, they probably capture some of the exhausting gas, and add forward propulsive force.
I hate to say this, but that yellow team is one good effort, and probably hard to beat.