pusher fan for small SUV

[trooper Tdiesel]

this is a idea ive been thinking about.

ive seen these small fans that have like a air plane fan on them for getting a brush fire burning, about 3' across, and was thinking.
would that make enuf force to lower gas use to the point that the little briggs and stratton or some other small engine would use less gas then the gas saved by the main engine

running non stop at full rated rpms are 5hp wood splitter 1/2 gal gas tank will run about 2.5 hours


and how far back would it need to be, i was thinking if its right at the back its in a low presser area and maybe it woudent have the force it would have 5' back???


i think it would be something like having a 5 to 15 mph tale wind, and increase main engine mpg accordingly.



any way its just a random odd idea, so i put it in this part of the board....


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[chumly]

Do you have any more of that stuff and are you willing to share?

[trooper Tdiesel]

LOL compared to HHO i thought this was 20/40% practical

[H-Man]

Not very useful. The SUV's engine uses less fuel to do the same amount of work compared to a single cylinder carburated engine that probably has a plastic camshaft.

[trooper Tdiesel]

ok base line for the auto, 360 miles 12 gal of gas = 30 mpg @ 60


at 60 thats 6 hours to go 360 miles, ok that would be an added 1.2 gal to run the little engine. for a total of 13.2 gal and 27.27 mpg

it would need to add 2.73 mpg to be brake even...i think that's in the realm of possible.

[H-Man]

It wouldn't. The engine still has to burn fuel, and the lawnmower engine would do about as much as peeing on a forest fire does.

[cRiPpLe_rOoStEr]

Seems like you were considering to do an auxiliary propulsion system similar to the one used in hovercrafts, which wouldn't be so effective in this case. But when I read "pusher fan" I was thinking about an electric radiator fan

[gone-ot]

Rolling tires have LOTs more friction than an airfoil being pushed through the air.

Trying to push a car on the ground has tire friction to contend with, which an airplane doesn't have as soon as takeoff occurs.

Hang the car in the air by a couple weather ballons filled with helium and THEN maybe the fan idea has possibilities (but economy ain't one of them).

[Ryland]

A fan like you are talking about might be able to push someone on a bicycle a few MPH, but lets say the fan makes a 10mph breeze, if it's behind a vehicle that is going faster then the breeze from the fan is still drag.

The fan also creates turbulence that slow both the fan and the vehicle down, so depending on placement, there is a chance that the fan just being turned on is going to slow the lead vehicle down more then it being turned off.

[ChazInMT]

Originally Posted by Old Tele man

Rolling tires have LOTs more friction than an airfoil being pushed through the air.

Trying to push a car on the ground has tire friction to contend with, which an airplane doesn't have as soon as takeoff occurs.

Hang the car in the air by a couple weather ballons filled with helium and THEN maybe the fan idea has possibilities (but economy ain't one of them).

What?

I think you over estimate the rolling friction, and/or you completely ignore lift drag. Keep in mind as well, a small airplane constantly produces 120-140 HP to stay aloft, unlike the 20-30HP or so required for an economy car steady state. Granted about 1/3rd of the energy sent to the wheels goes to overcoming rolling friction, I think this is still a smaller fraction than the lift drag created by the wing. Discussion on this really has nothing to do with the OPs original idea in the end however.



Anyway, where the OP runs afoul with real world physics is in the fact that it does not matter how the thrust is produced, the energy in vs. energy out equation remains unchanged. What we're all looking for here is a way to convert gasoline into thrust as efficiently as possible, and when the thrust is pushing our vehicles, we want them to go as fast as possible for the given amount of force applied.

His assumption is that somehow a fan is better at converting gasoline into thrust, if this were the case, we'd all have propeller cars. There's no magic in a propeller, a fan would simply not be more efficient at converting gasoline into usable thrust than turning the tires with a drive shaft.

Baseline physics then tells us, if the fan is less efficient, it will not yield an increase in overall fuel economy no matter what fudge factor numbers you want to throw at it, it is dead from the start. No need to get into any details other than that, it would be like having a discussion regarding the orbital dynamics of Pluto as justification for why it would or wouldn't work.