Propeller powered car questions

[ARC123]

I'm trying to build a propeller powered car. Right now I'm trying to find ways to make if faster because I'm limited to a 6 volt battery pack. I was wondering if I used a nozzle shaped design like they do for rockets if it will make it faster or slow it down. The propeller is 6 inches and I was going to use a 3D printed material to build it.

 

[Vedward]

Nozzles on rockets are designed for supersonic flow - the area decreases then increases as it reaches supersonic. The force of your propeller will be best if it has no resistance behind it, just be able to move the maximum amount of air to propel the car.

 

[Merlin3189]

I think you are right about improving thrust with a "nozzle", though I'm not sure that rocket nozzles are the right idea. I'd look at ducted fans first. Then at augmenter tubes. The aerodynamics behind rocket nozzles might help, but I suspect not too much at such low speeds.

this link has a simple account of ducting.

 

[CWatters]

Perhaps experiment with changing/optimising the pitch of the propeller. Measure the speed of the car first then change the pitch and re-measure the speed. Make small changes do several runs with each prop. Keep careful notes so you can find the optimum pitch.

Increasing the pitch should increase the top speed but will reduce the initial acceleration. You might find that the best pitch for top speed means the car won't always start without an initial push (eg if the ground is rough).

 

[RonL]

Here's a book, if you can spend a few dollars, that explains electric motor power and also two charts that gives power absorbed by various props, based on diameter, pitch and speed. Also a wiki link to the Astroflight company.
I,m not sure how much information you can find doing an internet search, but this would go a long way to getting the answers you are looking for IMHO.

https://en.wikipedia.org/wiki/AstroFlight

https://www.amazon.com/dp/0964406500/?tag=pfamazon01-20

 

[szc]

https://www.google.com/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&ved=0ahUKEwiX8eKD2oXPAhWG7CYKHQYRChUQjRwIBw&url=%2Furl%3Fsa%3Di%26rct%3Dj%26q%3D%26esrc%3Ds%26source%3Dimages%26cd%3D%26cad%3Drja%26uact%3D8%26ved%3D0ahUKEwiX8eKD2oXPAhWG7CYKHQYRChUQjRwIBw%26url%3Dhttp%253A%252F%252Fslideplayer.com%252Fslide%252F4179827%252F%26bvm%3Dbv.132479545%2Cd.cWw%26psig%3DAFQjCNELO77unL8P6dpLu40rhLO8so2cIg%26ust%3D1473627918576314&bvm=bv.132479545,d.cWw&psig=AFQjCNELO77unL8P6dpLu40rhLO8so2cIg&ust=1473627918576314 The fluid flow through rocket nozzles are typically for supersonic flow conditions, but when reversed they enhance the flow of subsonic flow. Think of water flowing through the end of a hose and placing your thumb across the end the velocity will increase when you decrease the area. You need to be thinking about the air displaced by the propeller which will increase your thrust. Geometries of the propeller will be one of the largest factors.