Ducted fan or exposed prop for scale fan-powered car?

[Rudukai13]

So I've been thinking it would be neat to build an rc fan-powered car. I'd like to go for something relatively scale. I got the idea after seeing this;



I thought it'd be pretty neat and relatively easy to build something like this. Not an exact replica, but something fairly close. I'm considering basing it on a rerelease Tamiya Sand Scorcher kit, to stick with a VW Bug body and overall appearance. I wouldn't mind giving it a similar junkyard-build appearance when all said and done. My question however is on what kind of fan to use for thrust - an electric ducted fan, or a true exposed propellor? Which would give me more power? Would either be strong enough to drive a Sand Scorcher that was lightened by removing all unnecessary drive components? If not, what would be suggestions for other scale kits to use as a base vehicle? I don't want to build something entirely from scratch, so having something to start with and slightly modify would be best. If anyone has any ideas or suggestions, I'd greatly appreciate it. Thanks in advance!

[Rudukai13]

Actually, Tamiya's Fast Attack Vehicle looks like it would be a better option for a starting point. Fewer metal parts = lighter, and the stock gearbox is easy not to install so there's a good place to mount the fan motor. And although it doesn't look like a Beetle it still has a good scale buggy appearance to it.

[Gula]

I think I took that pic! Yeah I've been wanting to make a behicle with duct fan power, something like the HPI honda odyssey sp. braking would be the only issue

[Rudukai13]

That's the other thing that's got me leaning towards an exposed prop. You can just reverse thrust to slow the car down. With a ducted fan sticking out of the back of an enclosed body, if you reverse thrust you're just blowing air back into the body and not moving air to slow the car down. But the HPI Odyssey body would also work great to cover up the propellor motor.

I also had the thought of sticking with wheel-driven power for main forward momentum and modifying a chassis with a couple of jet boat impeller drives to create something like the Brabhum BT46 F1 fan car;



Putting the jet drives on a separate controller or slaved to the main throttle and using them to create a low-pressure area under the car and create much more additional down-force. It'd just be something a little different and unique to play around with.

This kind of project will have to take a back-burner on my ideas list though - I created this thread before finding out about the new Axial Yeti IFS truck and that will now definitely be my next purchase for a project. It's just too good to pass up.

[Gula]

I'll probably still do it using a ducted fan unit. For the front I will use a fwd or 4wd end ,expose the diff and create a band brake over the diff cup. that will slow down the vehicle.

[Rudukai13]

That's actually a pretty good idea. It'd be faster to brake than if you just use reverse thrust. The Odyssey body would give you plenty of room to hide all of the electronics too. The beetle body would leave quite a bit of the motor exposed.

Tell you what, you build yours as a ducted fan and I'll build mine with an exposed prop and we'll get together and race them

[jason]

After having already had to get stitches from a prop once, I'd be using a ducted fan.

[Wade]

Hope it wasn't your tongue

[ped453]

Originally Posted by jason

After having already had to get stitches from a prop once, I'd be using a ducted fan.

lost the tip of my finger on a 7" prop.

[DTB1]

Originally Posted by ped453

lost the tip of my finger on a 7" prop.

Ouch, I once saw a guy get a nasty gash in his knee trying to setup a plane motor.


KCCO

[canadianbacon]

Since you'd be using the prop for, well, propulsion, could you just setup a solid axle for the wheels and run mechanical brakes like nitro's use?

[STANG KILLA SS]

prop no question. the thrust numbers will be much higher, and lower amps.

ducted fans are ineffeciant amp hogs compared to a prop.

performance wise there not even close.

<---- spent a lot of years thrust and amp testing.