Using flywheels to increase FE

[Christ]

I've actually had a driveshaft come off my 1979 Plymouth Volare.... it was definitely a great ride, since the car almost endo'd before the rear joint broke and sent the drive shaft flying into an oncoming line of traffic.

Noone was hurt, nothing was damaged (other than my car.)

Changed the yokes on the axle and transmission, and installed a new shaft with new bearings, ran it once, and the damn car wouldn't start again after that.

[jamesqf]

I've had a wheel come off, and go rolling down the road. (Come to think of it, I've had it happen twice, once way back when I was in high school.) Again, no one was hurt, but that's just pure luck: it easily could have been otherwise. Then there's my ex's pickup, which caught fire as she was warming it up one winter morning.

The point is, there are all these real things that can and do go wrong with current automotive technology, but people seem to have become so familiar with them that they're accepted as just natural, and so discounted. Get some new technology, though, and they start imagining all the things that conceivably could go wrong, wildly exaggerate the risks, and so wind up making unreasonable decisions.

[Christ]

Speaking of wheels falling off...

Riding in my friend's 79 K20 Chevy... lifted 16" (12 suspension, 4 body) with 44" gumbo tires on it... We're doing about 60 down the road, and all of a sudden the front left corner dips down a bit... seems like we broke a shock, so we don't stop... keep going.

Less than 2 seconds later, the 44" monster Gumbo Super Swamper rolls in front of the truck, and bounces off into the field, at 60+MPH. We come to a complete stop, pulling off the road as best we could, and the hub is still 10" from the ground.

The tire is 200 yards out into the field, there is no way we can get it back up to the road by ourselves and get it on there, so we call a friend, who brings another friend, and they drive in front of and behind us with 4-ways on, while we cruise home at 15 MPH on 3 wheels.

Honestly, that experience was better than the mudding that day was.

Moral of the story: after mudding excessively, check your vehicle over before going home.

[IndyIan]

How about just putting heavier wheels on your car? I have a set of 15" alloy rims that weigh ~20lb each and I definetly notice a lack of acceleration with them on, compared to my normal 14" steel rims and tires. I should test it but given equal rolling resistance heavier wheels will help a bit with the gliding phase. Of course there are all sorts of downsides to heavy wheels but none of them stop the ricers from putting the biggest rims they can fit on many small cars.
Ian

[aerohead]

Originally Posted by jamesqf

I've had a wheel come off, and go rolling down the road. (Come to think of it, I've had it happen twice, once way back when I was in high school.) Again, no one was hurt, but that's just pure luck: it easily could have been otherwise. Then there's my ex's pickup, which caught fire as she was warming it up one winter morning.

The point is, there are all these real things that can and do go wrong with current automotive technology, but people seem to have become so familiar with them that they're accepted as just natural, and so discounted. Get some new technology, though, and they start imagining all the things that conceivably could go wrong, wildly exaggerate the risks, and so wind up making unreasonable decisions.

Have you ever had an entire car come at you,flipping end-over-end?

[i_am_socket]

A coworker of mine did a few years ago. Not pretty. He was ok, though.

I like the idea of the flywheel, if mounted horizontally. The only practical issue would be hills. Safety issues are safety issues, but let's assume that safety wasn't the issue. Who's a math major around here? What size and mass of disk rotating at what velocity would be required to move a city bus from a stop? What would the best methods of energy transference be for both energizing the disk and providing motive force to the vehicle? Would it be worth it?

I can see this being one of the many possible solutions for hybridization of buses and delivery trucks that stop and go frequently and don't do too much mountain climbing.

[Christ]

Originally Posted by i_am_socket

A coworker of mine did a few years ago. Not pretty. He was ok, though.

I like the idea of the flywheel, if mounted horizontally. The only practical issue would be hills. Safety issues are safety issues, but let's assume that safety wasn't the issue. Who's a math major around here? What size and mass of disk rotating at what velocity would be required to move a city bus from a stop? What would the best methods of energy transference be for both energizing the disk and providing motive force to the vehicle? Would it be worth it?

I can see this being one of the many possible solutions for hybridization of buses and delivery trucks that stop and go frequently and don't do too much mountain climbing.

I had a car come flying at me on a track.. that's about it. Not nearly as scary when you're semi-expecting it to happen.

Food for thought - Isn't the most wasteful event the initial takeoff time? So even if the flywheel's stored energy was enough to get the vehicle moving so the engine could take over, wouldn't that have a significant impact on efficiency? (For a bus, or a delivery vehicle, such as Postal Service trucks (which run on propane)).

Originally Posted by IndyIan

How about just putting heavier wheels on your car? I have a set of 15" alloy rims that weigh ~20lb each and I definetly notice a lack of acceleration with them on, compared to my normal 14" steel rims and tires. I should test it but given equal rolling resistance heavier wheels will help a bit with the gliding phase. Of course there are all sorts of downsides to heavy wheels but none of them stop the ricers from putting the biggest rims they can fit on many small cars.
Ian

I still use 13's or 14's, up to 16's, depending on what performance I want to see from my tires, and how much of the actual suspension duty I want my tires to see. My DD has had 16's on it, but never when they have stiff suspension.. I use my tires as more of a performance tuning setup than for style.

Also, there have been cases where a larger wheel/tire combination were actually less weight than the OEM config, and made sense for a particular application. It doesn't happen often.

[jamesqf]

Originally Posted by aerohead

Have you ever had an entire car come at you,flipping end-over-end?

Not flipping end over end, no. But spinning in circles 'cause the idiot driving didn't realize that 4WD doesn't improve your steering control, yes, several times. And what else is new?

Anyway, you're missing the point. You've made up some superficially plausible thing that could go wrong, sort of like the theory that hybrids were going to electrocute rescuers after accidents, or that magnetic fields from electric cars would cause cancer, and try to use that as a justification for not developing what might be a useful technology. The point is that if you bother to actually think about what's involved, instead of running in circles claiming that the sky is falling, you soon see that your superficially plausible threat is nothing of the sort.

Start with your basic thesis: that the bearings of a flywheel might somehow seize up, and suddenly transfer the momentum of the flywheel to the whole car, causing it to tumble end-over-end down the highway. The first problem is that a sensible energy-storage flywheel design uses magnetic bearings, spinning in a vacuum. There's no physical contact, and thus nothing to seize. Second, the flywheels are built of things like carbon fiber, so when subject to a sudden severe stress of that sort, they would harmlessly disintegrate into tiny pieces.

You know, you can actually look up these things on the web. People have built these sorts of flywheels, and destroyed some of them in testing. It's something called engineering, you know.

[Christ]

Even if the bearings were physical bearings, rather than magnetic, would the flywheel really contain enough force to actually flip the car? Probably not.

Considering the amount of horsepower it takes to lift the front tires of a 3000 lb car off the ground, that flywheel would REALLY have to be moving to create anything more than a "goose" to the car.

Also, placing the flywheel somewhere in the center of the car will create an offset " axis" effect, would it not?

IOW - If the flywheel is spinning in one direction, in the center of the car, on mechanical bearings, and contains it's full power capacity, then suddenly the bearings seize, and it just STOPS. Lets say it was spinning clock-wise, as you face the driver's side... so spinning toward the rear of the car.

Obviously, even with 100 HP of force applied instantly, the axis is the center of the flywheel, the contact point is the rear wheels, and the force is attempting to lift the front wheels/front half of the car, creating a bi-axial motion. (The car is trying to spin around the flywheel's axis, but the rear axle is stopping it, creating an axis between those two points.) Now, move the spinning flywheel to the rear of the car, just behind the rear axle, where it will be the least dangerous to passengers in the vehicle:

Still spinning backwards, stops immediately. This places the first axis ahead of the force axis, so that now that same 100 HP is trying to lift the WHOLE car, except the 100 lbs in the trunk area, and whatever weight the flywheel's assembly contained. It's not likely that 100 HP is going to be able to lift 1300 LBS 13 or more feet on an axis, allowing it to flip over, even once, let alone more than once.

Add to that: bearings don't just "seize", at least not to my knowledge. They create friction first, as they heat up, before failing, which would lessen the power storage capacity of the flywheel, and might also aid the theory that it wouldn't just STOP spinning all at once. It would begin slowing (as it would take more power to keep the flywheel spinning than it used to) until the bearings could cool enough to solidify and seize, which would create a less than impressive "jolt", rather than the full rating of the flywheel exploding into an axial force, sending the vehicle endo'ing down the highway.

Since HP can be seen as a property of force and speed, (HP = TQxRPM/5252) the slower it's rotating, the less power it will have, making even the strongest setup not able to do what some contend may happen. (Be reasonable here - Yes, maybe 1000 HP could do it, but that kind of power storage would be far too expensive and large to use for our purposes.)

Good reference to this - Mythbusters did an experiment where "Buster" was riding a motorcycle, and they jabbed a stick/pipe through the front wheel, stopping it instantly. The motorcycle became quite unstable, but did not flip. At speeds where the force was supposedly able to make the bike flip, all it did was drag the wheel. (That part doesn't apply here.)


It doesn't seem likely, as even the lighest street driven cars weigh at least 1300LBS, AFAIK.

[Bicycle Bob]

Flywheels have to be used in pairs to avoid major gyroscopic effects, and the bearings have to deal with major forces between them. However, bearing failure is not a major problem - there can be two or three backup modes during failure. The usual concern is over disintegration - the NHRA used to mandate armour plate around the flywheels on dragsters. Modern, high-speed flywheels are made of composite fibers, and turn into fluff when they fail. Unfortunately, it is a lot of high-speed rotating fluff that wants to expand as much as any other explosion, and it contains all the energy of the "fuel," without waiting to be mixed with air. The armour is cheaper than when dealing with chunks, but it still comes to about as much material as an air tank to contain the same energy.