Air Car Assignment

[billythekiddrummer]

Pretty much, my science teacher needs us to build an air car. I have some basic ideas, but nothing major yet. ideas would be appreciated. also, im trying to find some kind of 3d modeling program so i can show ideas online. anything would be appreciated. the only limitations are that it can only be 11 inches wide and as tall and long as you want it. it has to be able to go 20 feet. it can be made of anything and you can only use air (ex. rubber bands connected to propellers, balloons ect.) no co2 or batteries or moter. :Waldo: :cup: :hihi:

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-dante b.

[ronthepon]

I'm deleting the one you've posted in the physics forum, and editing the title of this thread.

[InfiniteNow]

To get your thoughts rolling, I would like to ask you to search through the Science Projects and Homework forum. You'll notice that many individuals have come to Hypography looking for help with a car type project.

 

Then, once you've shown some effort, you will also likely have more specific questions. That's when it gets juicy and we can really jump in with suggestions... :)

 

 

Cheers. :hihi:

[Jay-qu]

This is unlike most of the others we have had.. So you can use anything you want right? I say get yourself an aerosol can of compressed inert gas, strap her on, stand back and let her rip! that baby will fly!

 

(not actually recomended, probably dangerous!)

[billythekiddrummer]

well, we cant actualy use anything, i posted some requirements. :naughty: :hihi: :hihi:

 

ps- i checked on some of the other projects, i will post some more later.

[billythekiddrummer]

To get your thoughts rolling, I would like to ask you to search through the Science Projects and Homework forum. You'll notice that many individuals have come to Hypography looking for help with a car type project.

 

Then, once you've shown some effort, you will also likely have more specific questions. That's when it gets juicy and we can really jump in with suggestions... :)

 

 

Cheers. :hihi:

 

 

I looked there but couldent find anything:hihi: :naughty: :hihi:

[billythekiddrummer]

I had a brainstorm, and decided on making it out of balsa wood, have four propellers powered by and have balloons to blow air out the back. (*=propellers, O=balloons, o=weels)

 

 

I was also wondering if it is posable to make it so the propellers dont start spinning untill 2 seconds after the balloons start letting out air. my idea will make it so the balloons will get it up to speed, and then when they are through, the propellers will take over. is this more efficient, or would it be better if the balloons and the propellers all started at the same time.

 

 

this is a rear view of my proposed air car. please offer any suggestions...

 

(*)============(*)

| OOOOOO |

(*)============(*)

 

KEY:

((*)=propellers, O=balloons, (=)=the wood frame, |= the vertical balsa wood)

:shrug: :hihi: :hihi:

[moo]

Unless you get extra credit for complexity, I'd stay with balloon power.

 

- Add paddles to the rear axle (4 or more) to make a simple turbine.

- Clamp the balloon to a piece of tiny tubing for a "nozzle" to direct the air flow on the turbine paddles.

- Place the tubing lower than the axle, and have it blow on the bottom side of the turbine, pointed toward the rear (perhaps slightly upward). Axle rotation is forward, and the rear facing exhaust will provide a tiny bit of jet propulsion.

- You can use a small valve to control on/off and air volume, but I'd use a short piece of tubing for the nozzle or the valve may diffuse the flow somewhat. This would depend on the valve design of course.

- Also, larger wheels roll easier than small ones on the same size axle (more leverage on the axle's friction).

 

Just a few thoughts, hope this helps. :)

 

moo

[Jay-qu]

I dont see what the propellers are meant to do.. I think they would just add extra drag

[Turtle]

I dont see what the propellers are meant to do.. I think they would just add extra drag

I think he has in mind that the balloons will 'run-out' before the 20 feet is reached, but you are right that the propellers add drag when not under power. I observe that the drag presented by the balloon(s) is steadily reduced as it/they deflate.

I would improve the efficiency of the balloons by using laminar flow nozzles as well as use laminar flow grooving on the body to reduce drag.

Here is a drawing of a laminar flow nozzle for water, but the priciple is the same for any fluid. (click image to enlarge)

 

[Jay-qu]

So long as he wasnt planning on powering the propellers with the ballons ;)

 

What does laminar flow do in this case, I dont get it :P

[Turtle]

So long as he wasnt planning on powering the propellers with the ballons :hihi:

 

What does laminar flow do in this case, I dont get it :beer:

 

I think he meant to have the balloons go first as it were and then have the rubber-band powered propellers kick in. In this case, the shrinking balloons can be used to trigger a release of the propellers by some clever mechanical means.

Laminar flow in all cases involving velocities below the speed of sound breaks up turbulence and therefore reduces drag which increases the efficiency of the system.

Try this demonstration:

Light a candle, and by experiment determine the farthest you can be from it and still blow it out. Record the measure.

Now repeat the experiment, but blow through a cardboard tube of the kind found in wraps of foil or film plastic. Record the measure.

Now repeat the experiment again, but this time pack the cardboard tube with drinking straws. Record the measure.

Now compare the measures. Which setup allows you to blow out the candle from the greatest distance?

[Jay-qu]

I see what you mean, by cutting off the air in the tube from the surrounding air it is able to travel further without turbulance having as much of an effect, the smaller you make the cross sectional area of the flow, the less turbulence it will experience :beer: so how does one implement this for a ballon powered car?

[Turtle]

I see what you mean, by cutting off the air in the tube from the surrounding air it is able to travel further without turbulance having as much of an effect, the smaller you make the cross sectional area of the flow, the less turbulence it will experience :beer: so how does one implement this for a ballon powered car?

 

Mmmmm...I think it's a bit more than restricting the cross section, which as you describe it sounds more like the venturi effect. The laminar flow is more about a wave guide type effect wherin parallel structures (the straws in my experiment) align the fluid's turbulence boundarys.