How heavy is the flywheel?
Edit: oh I didn’t see that this wasn’t in a shitpost community.
To answer your question, there are a ton of variables at play here and it’s quite complicated, ranging from friction and heat, to material deformation and dynamics. Assuming a bunch of stuff and putting the answer simply, not super far. Likely, you’d drop the car onto the surface, and there wouldn’t be very much energy carried in the drivetrain and engine and stuff to start moving a VERY heavy vehicle (inertia). Depending on ratios and assumptions, somewhere between 0ft and maybe 15-20ft.
Assuming best case for forwards momentum though, you could have very heavy parts and a big turbo, and have the tires hit ground right as max rpm&mph reached, maximally creating friction the very second the throttle were lifted. That would give you peak all-kinds-of-stuff. If the vehicle were light enough, nothing went wrong, you had minimal realistic rolling friction, comically large flywheel, magically no engine compression slowdown what l whilst keeping engine inertia till stall, etc, I think you could get pretty far. Like maybe a half mile, maybe more, if keeping remotely in the bounds of reality but still having customized but feasible variables.
Now the real question is, what car are YOU imagining in your head? I think that can answer a lot of people’s questions here, and control for a lot of variables that will otherwise vary WILDLY.
Edit3: ahhh edit2 was too long and chaotic the car became a train. Friction is real. I think the trick is to use magnets.
Not very far at all. Very little power is needed to get wheels to spin in air at 100mph. When touching down, there would be a lot of wheel “spinout”. I’d expect well under 50 feet.
How high in the air? The tires spinning might not matter at all if it falls far enough to just flatten on impact. You could also test this in BeamNG.
Assuming nothing breaks (unlikely), you could potentially calculate it by calculating the energy stored in the engine/axle spinning. We know that energy must be conserved, so the energy after hitting the ground must be converted into heat and kinetic energy (of the car), with some energy left in the axle to keep it spinning.
I don’t know enough about car parts but it seems feasible to at least estimate an answer given enough information
Good approach. Start with the momentum of the rotational masses, assume no suspension (to make the math simpler).
My guess, a few feet. There’s surprisingly little momentum in all those components compared to the mass of the vehicle.
“surprisingly” is a strong word; cars are designed to have as small of a rolling mass as possible, because it’s much harder to stop than simple dead weight.
I agree. And initially it’s going to burn a little rubber, which won’t contribute to forward motion.
Just as a fun guess I would say it would move a feet assuming the engine was turned off as it hit the ground.
Otherwise if the engine was running it would just idle away at a few MPH.
Assuming it wasn’t a manual, burned rubber down to 0mph, and then just stalled out XD
MythBusters did a similar segment as part of “hit the ground running:” https://mythresults.com/end-with-a-bang
This is an annual event in Alaska
There are still some variables you haven’t mentioned. How high in the air are you talking, and will the car be dropped, or gently lowered? What kind of terrain is it? A flat, paved surface would be different than a field with rocks and bushes.
I seem to remember a toy car that kids could rev and set down, and it zoomed across the floor very well. A small plastic car isn’t the same as a real one, though.
It would almost certainly snap it’s driveshaft upon making contact with the ground, so maybe 15’. There are way too many variables here to come up with any kind of concrete answer, or even much of an educated guess. This would make for a fun mythbusters segment though.
Even if its tires were just 1 mm from the pavement?
The driveshaft wouldn’t be snapped from the downward force. It would be snapped because it’s happily spinning away at probably a couple of thousand rpm and then suddenly the rear tires make contact (assuming this is a RWD vehicle, otherwise it would be the CV joints breaking for the same reason) and try to get traction and move the car forward, but rubber is made to stick the surfaces and there would be an astounding amount of force applied along the drivetrain that was sped up to 100mph with no resistance suddenly trying to instantly accelerate from 0mph to 100mph with a very considerable amount of resistance.
I don’t think the driveshaft rotation would be in the thousands, as the rear diff is a 3:1 ratio, and the wheel diameter further effectively increases the ratio. Driveshafts are suprisingly slowly rotating parts.
But I still agree it would likely fail, as the weakest element in the drive train.
A pretty typical 5th gear transmission ratio is somewhere in the 0.75:1 (engine rpm: transmission output shaft rpm) range, meaning the driveshaft would be rotating at somewhere around (definitely plus or minus) engine rpm. My subaru cruises at 50 at somewhere around the 2k rpm range, so the driveshaft would be spinning at a similar rpm. The diff pinion to ring gear ratio in the differential slows things down quite a bit so your wheels aren’t spinning at engine rpm anymore.
Yes
Parts of the engine, drivetrain and tires would go up to 100 feet in all directions. Most of the car would stay where it dropped.
There’s a lot of variables, so let me make some assumptions and you tell me what I’m getting wrong.
- Let’s say it’s maybe 30ft in the air.
- It’s a car that will be able to withstand the impact as in not break apart and keep the motor running and tires spinning on first impact.
- It is dropped with 0 momentum, so there’s no initial velocity until gravity applies.
- Tires are spinning at 100mph, keep spinning through the first impact and stop spinning when it’s airborne again.
- The “how far” measures the distance between the first ground impact, and then the second ground impact after the bounce.
- Ground is your average road asphalt in dry weather.
- No slope, the ground is perfectly flat.
- The car is autonomous, so there’s no forces from the driver affecting the calculation.
Alright I’m not nerd enough to do some example calculations but if these assumptions fit your idea, someone else can run with it.
In order for the car to move forward, it needs to push against the ground. There needs to be a force of friction in between the tire and a surface to get that initial velocity. “Revving” it in mid air would not give you any initial forward motion, so you would expect a straight drop down - although depending on how the weight was distributed it might roll in the air.
Presumably they mean they’d rev the engine and spin the wheels to the same condition as 100mph on level ground, since you can’t rev to any mph, and starting at 0mph is part of the scenario.
So I guess the question would be if the KE stored in the spinning wheels would be enough to move the car forward in the absence of thrust?
I still don’t think this is working the way anyone is envisioning it.
I think it would be a nonzero amount, but not a lot.
Imagine spinning your wheels on ice at a high RPM, and then suddenly they catch traction. You’ll jump forwards, but since OP specified that you also cut power at that instant, you’ll just be rolling to a stop.
I don’t think it’s very far removed from dumping the clutch and stalling the engine, if that makes it a more familiar scenario.
There would be no forward momentum, but there would be angular momentum in the wheels, drive train, and engine. Friction with the pavement would convert some of the latter into the former.
It seemed clear to me that they meant how far it would go after it touched the ground.
Yes - I understood that. My point still stands.
It wouldn’t have built up any velocity. There would be no means for it to accelerate. After it touches the ground, it would have no forward momentum.
Tires are perhaps mostly air by volume, but the rubber and the rims would store some kinetic energy spinning in place, also some in the axles and perhaps even all the way to the engine if things don’t break instantly. That energy would go against the ground on landing and push the car some distance forward - I would expect the answer to be in the range of a few feet (meters) but it’s what I think OP is asking
