Reverse thrust propeller for extra braking on wet or icy roads (probably completely impractical)

[NiHaoMike]

So I was chatting with a new friend of mine and she and I together came up with the idea of a propeller on a car that would provide reverse thrust and downforce for extra braking on wet or icy roads, kind of like thrust reversers on an airplane. I assume it's impractical or it would have already been done. But how impractical is it? Is it just a matter of being way too expensive to implement or would making one that can actually make a significant advantage be beyond our current limits of technology?

[arber333]

So I was chatting with a new friend of mine and she and I together came up with the idea of a propeller on a car that would provide reverse thrust and downforce for extra braking on wet or icy roads, kind of like thrust reversers on an airplane. I assume it's impractical or it would have already been done. But how impractical is it? Is it just a matter of being way too expensive to implement or would making one that can actually make a significant advantage be beyond our current limits of technology?

Where would you take the air in then? You must think of propeller as a pump. It has low pressure area and high pressure area. Air flow must come from somewhere...

What you are thinking about is downforce that is the opposite to normal result of air being forced to go the long way around the car = lift.
Lift will inevitably cause some component of drag, but the shape of the car is inappropriate.
To create drag racing cars use simple drag spoiler or some more sophisticated vortex generation to provide more downforce to the rear wheels that are also driven wheels in most racing cars.
Vortex generators are point attached spoilers that will swirl the air and air flow will become more stable.
In your case you could mount some spoilers with integral fans but those really become effective at higher speeds.

I think you want active system to act at low speeds... You could achieve downforce by scooping the air under the car and injecting it just before the spoiler on the top side. But fitting integral ducts and fans required will be a major redesign for the car. I expect you would make a 2 seater out of 5 seater...

[NiHaoMike]

It would be on top of the car, angled forward so that the thrust would act downwards and backwards. (Ignore the drag it would impose during normal driving, let's say the actual implementation would normally be retracted and pop out when needed.)

[Zieg]

Just as a point of reference, a Cessna 172 has a 180hp engine and produces all of 211 kg of thrust from a 75" propeller.

[muehlpower]

Look 'McMurtry Spéirling' race car.

[jrbe]

Look 'McMurtry Spéirling' race car.

T50 and McLaren F1 as well.

Basically an air boat or a hovercraft.

Gets sketchy with people around.

[arber333]

It would be on top of the car, angled forward so that the thrust would act downwards and backwards. (Ignore the drag it would impose during normal driving, let's say the actual implementation would normally be retracted and pop out when needed.)

That would make it a real hazard for birds and people nearby... See my post where i proposed ducted fans.

What kind of limits would you impose on your system? There has to be some for physics to work in real world at all.
Like which mode of operation in which speed range etc...

Check this mod and his experience with lift/drag...
https://www.aerocivic.com/

Again I would propose aerodynamic principle instead of rotordynamic...
You could put a low aspect ratio inverted wing over/under the car to provide your downforce. For larger effect at low speeds you could use fowler principle to make more force at lower speeds...
https://ntrs.nasa.gov/api/citations/197 ... 019130.pdf
Remember wing has to be inverted to provide downtrust!!

Or study vortex generators...
https://www.carthrottle.com/features/wh ... -they-work
https://tomitryglass.wordpress.com/2020 ... enerators/
https://www.akademiabaru.com/doc/CFDLV11_N6_P1_17.pdf
You could add active vortex generation from the car by air pump...

Offtopic i found some info of cooling cells with vortex generators...
https://www.mdpi.com/2227-9717/11/2/500
https://www.mdpi.com/2313-0105/9/4/208