Electric Pusher prop?
 

theshreves.com - Project: Prop Car

http://www.theshreves.com/rc_stuff/i...fancar2.3b.jpg

Electric pusher props can generate a pretty fast air flow. Some of the little RC model airplanes I've seen can fly over 80 MPH with a tiny prop driven by a bushless motor. Those little fans can blow your hat off from 50 feet away!
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Anyways, my question of the day has to do with toaster shaped cars like vans or square back SUVs (like my CRV).

What if, I had a 3' pusher prop mounted in the center of the rear hatch?
And once I got out on the highway, I turned on about 10 HP of thrust?

How would blasting the area of turbulence & drag with prop air effect the over-all cd of a van or CRV?




I already have an idea what would happen to my MPG...:thumbup:

Edit:
http://blog.modernmechanix.com/mags/...4/prop_car.jpg

I guess you could start by looking at these.
http://www.sippingfuel.com/pics/airboat.jpg

Those are pretty low profile in the front, except for the people..

My question is what effect would a pusher prop (or even a rack of ducted fans) have on the cd of an SUV or van.

If the air-mover was mounted in the center of the back of a square shaped van, would it help the cd ??

That is a very ... yes it is a question. You may want to look into the legality of having whirling blades of death on the back of your vehicle first.

Being able to tell whether or not it helps Cd would be difficult to tell without a windtunnel as the extra propulsion would first need to be calculated out from the drag forces. Then to see if its worth it is to compare fuel consumption of standard vs possibly lower drag but with extra energy consumption.

I'd love to see the test.

Dem old blades-o-death!
 

Yeah, after thinking about it for an extra 8 seconds, I decided that a bank of four ducted fans (16" OD) might work just as well.

Here's what they are using for fake jet engines in RC models these days.

http://www.hooked-on-rc-airplanes.co...ducted-fan.jpg

If the impeller housing was made out of heavy gauge stuff, they would be safe enough.

Maybe use 4 of these motors..?.
Battery Powered Systems

Beer usualy adds a lot of weight to those boats...yet they are still pretty fast...lack of teeth must be a pretty efficent weight reduction.:)

It could be run on a secondary battery that was charged at home. Can we say plug in hybrid?

That's where my mind has been lately. How to convert my CR-V into a plug-in mild-hybrid.?.

Even with all the hardware (old 4WD setup) I've got to work with, it's still gonna be a biaash to get a pre-charged battery pack to deliver me some better MPG out of the old V..

But, could a motor like the Mars ME-0708 PM Pancake 12-48 VDC Brushed

Battery Powered Systems

deliver a thrust equal to 4 or 5 HP?
Assuming one could be installed in a 20" or 30" OD ducted fan? Modeled after the little RC Ducted Fans?

Humm, I might have get a MUCH bigger lathe.. ;)

Edit:
Looking at the plots in this RC EDF manual,
http://manuals.hobbico.com/gpm/gpmg3...anual-v1_1.pdf
it sure looks like the thrust goes up nicely with RPMs..
Maybe I should buy one of these and see if it's possible to scale it up..?.
(And, I could stick in on top on my little glider and make it say ZOOM!).

Dang!! Check out this mod..
Jet Beetle

http://www.ronpatrickstuff.com/image..._15_05copy.jpg

your also adding an abundance of weight that also needs to be pushed.
interesting idea though.

You could try a slot around the back corners of the car (top and possibly sides) where the air is squeezed out at high speed, with the intake wherever, at the front grille, perhaps. Rather than a few big round ones.
They've tried that sort of thing on aircraft wings to keep the air energised and laminar at low speeds/high AoGs, but it wasn't really worth it as far as lift went.

Of course it may not be worth the extra energy and weight.

prop
 

A few thoughts: the prop on the RC car is in relatively "clean" air,whereas behind the van/suv,it would be in the lee of the vehicle,with only the turbulent wake as a source of air.That means the prop would have to induce air from behind itself,forward around the outside of the disc area.Then the air would be blasted rearward through the prop,setting up a circulation of sorts(like a helicopter in ground-effect,only sideways)making it difficult to induce the air forward again,to re-circulate through the prop.Unlike a suction slot,the prop would have no boundary layer effect,and a dubious amount of thrust if any,only stalled,in a region of recirculating air within the wake.--------------------------------- Also,to get 10-hp of thrust would require about 12.5-Bhp at the shaft (very inefficient).-------------------------------- Finally,as others have touched on,the safety ramifications,should some unfortunate motorist or cyclist rearend the prop,is too grim to even contemplate.

If I were to drive the wheels with a hybrid conversion kit, I would still
be adding weight.

Add weight to gain the short term advantage of gaining some MPG
by using power that came off the grid the night before..

When you build a full EV, you gain all kinds of weight and shorten your
range for the advantage of not making trips to the gas station.
It's a trade off.

If you converted your car into a Weak plug-in hybrid, you gain FE
for the short haul only. Once you start heading across the state,
you run down your pack and end up using extra fuel to carry it..

If you could afford very light batteries, your over-all FE could
be a lot better.

Yeah, forget the prop. I've seen too many RC airplane accidents to think
a large prop is anywhere near safe.

BUT, a ducted fan might be usable. A good one might develop some pretty good thrust. EDFs have the advantage of shorter blades (impellers), thus lower RPM & tip speeds. Big props & big HP get tips speeds up near mach1.. Not good.


Now that I have the coro spoiler and wake boards installed, I did some yarn testing back there.
There is almost zero turbulence on top of the spare tire and across the rear glass..
http://i46.photobucket.com/albums/f1.../BBlftside.jpg

Where did it go?? :o

http://images.lowes.com/product/026715/026715153336.jpg


I've wondered about something like that for years.
Daydreaming of something like this,I wanted to buy one of these and run it from my cigarette lighter. I planned to relocate my plate and attach the blower in its place.

Then I thought .... WHY ?

I don't have the link right in front of me, but something like this has been used to great effect in semis using a compressed air system that channels air into a tighter wake.

( If you are really interested, I can try and find it )

I had always thought of building two of these to sit inside the vehicle, where the back seat use to be and ducted from the rear doors to draw the air in. I had always wanted air to help push the car at hwy speeds in order to reduce engine LOD. Nice to see it is not impossible ..

IMO this wouldn't be a good idea at all. No offense intended. It is a neat and fun idea. My reasoning is, the prop is not going to give you an equal amount of thrust per amount of energy spent that an electric motor is going to give coupled to your tranny. Thus you have one more loss of efficiency and a less efficient system overall.

Have you seen the cars/trucks with the little propeller stuck in the hitch receiver? You would have that but bigger.

Propellers are sensitive to incoming air direction. You would find such an arrangement would produce little or no thrust. But it would consume power thrashing in the air. Biggest advantage would be a deterrent to tailgaters.

The answer is....no. Just....no.

Okay guys! Let's forget I ever mentioned the word "Propeller" and assume that
B. F. Ponder was an early scammer..
http://blog.modernmechanix.com/mags/...4/prop_car.jpg
And this car never really got over 25 MPH..

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What about using a Ducted Fan ? (As shown above, but bigger).

If you could make one that delivered 300 pounds of thrust, using 200 pounds
of hardware and batteries..?.

The idea here is to somehow get power off the grid to help propel your car,
without performing major surgery on it.. ;)