80,000 Pound Dragster 3

[dwbarlow]

One day I was thinking about muscle cars and tractor pulls. What would you need to take a semi-tractor and turn it into a dragster? Obviously you would need a heck of a powerful engine of some kind to start with. Massaging the problem a little bit, I asked myself, "What would happen if you take an extended wheel base semi-tractor, mount a 50,000 pound flywheel cylinder and spin it up to 10,000 RPM and then pop the clutch to the drive wheels. What would happen if all that stored up energy were suddenly released?

It seemed reasonable that with enough gears, a stock semi-engine could be used to gradually bring the cylinder up to almost any speed desired. That it might be able to put a 1,000,000 potential HP into the cylinder. 1,000,000 HP / 80,000 pounds of vehicle weight would give you 125 HP to drive 1 pound of weight. I don't deal with these sort of classical physics computations on a regular basis, nor do I know that much about materials and mechanics. Would the whole thing just explode with basketball sized shrapnel flying all over the place, or could the semi-dragster be designed to handle it and shoot down down the drag strip? I don't know about you, but I'd pay good money to see a semi go from 0-200+ MPH within a quarter mile.

While this is an interesting problem, there are some serious applications I can see that could benefit from a sudden burst of energy, harnessed to do a brute-force type of event. The thing is, if you couldn't build an 80,000 lb dragster as a starting point, then these other applications probably wouldn't be feasible, either.

What do you think?

 

[SnTMan]

dwbarlow, I don't know the first thing about these subjects really, but I do know that in the recent past Formula 1 racecars used a flywheel system to store and recover energy.

Can be done. Devil's in the details

Regards,

Mike

 

[1gibson]

1) What would happen is you'd break the weakest link in the drivetrain, fix it, then break something else. Rinse and repeat.
2) Hope you've got some good brakes.

 

[gasketguru]

There are already jet powered drag race trucks - wind them up, hold on the brakes then let 'em go - sub 6 second 1/4 mile... - search the internet and you'll find videos of such things - just don't stand behind them at the track...

(There was a project some years ago to power a tram using a high inertia flywheel that would charge up at each stop to power it down the track in-between the stops, though I don't remember if it ever got finally built.)

 

[Tmoose]

OP said - "What would happen if all that stored up energy were suddenly released? "

probably something similar to 3:54 here -

https://www.youtube.com/watch?v=-VF0JwxQqcA

The tires lose traction and go up in smoke.

Applying the excess power gingerly but precisely "off the line" is required. Nowadays in top fuel and funny cars that ccontrol is not so much a driver function, but done by tuning tools like retarded timing and highly adjustable slipper clutches.

 

[dwbarlow]

First off, this is not rocket propelled, and its not really engine powered.
Second, on a semi frame you could put at leas 4 tandom drive axels in place with 16 drive wheels, giving an awesome traction capability.
A triple clutch system could be deigned, one to get moving with lots of slip, once to start accelerating with some slip, and a final with no slip.
Each clutch could also be synced to the diesel engine (~600 HP) for the final 3 gears
Question, do they drag on concrete or asphalt?
Also, The original HP to Lb ratio is 12.5 HP/1 LB. Still pretty good I think.

 

[JStephen]

Drag racing (like tractor pulling) is either a hobby or a business. If you start using big expensive equipment that you're going to tear up, you either need to have a huge audience paying for it, or you need some rich people owning it. So yes, we could drag-race locomotives if only we could get somebody to pay for it all.

In the case of a semi, it seems the problem is, that given you're going to race a semi, the fastest option is to race the lightest possible semi. So you'll see the jet-powered semis or schoolbusses or whatever, but they do use the lighter options there, too.

With a flywheel, with high-performance engines, or whatever, the problem is getting power to the pavement, not in generating the power, so it doesn't much matter if it's a windup car or nuclear powered, so there's not a lot of reason to fool around inventing something that might be better.

If you tried something like this in regular dragracing, either it'd work well, or it wouldn't, and if it worked well, they'd regulate it out of existence.

Somewhat related: One idea I had for a tractor pull is a large reciprocating weight on the tractor so that you get double the normal contact pressure with the ground at peak points of vibration, enabling higher traction for a small part of each tire rotation. It might actually work, it's just getting somebody to finance a pointless venture.

 

[gruntguru]

Regarding traction - the best you can do is drive all the wheels. It doesn't matter if there are 4 or 18 of them, the maximum acceleration is going to be mu x g.

je suis charlie

 

[dwbarlow]

I got out some old texts and did some calculations for this idea. I think they are correct but take a look and see if you agree with them

 

[dvd]

It seems like the power curve for this is going the opposite direction, i.e. as you remove energy from the flywheel it slows down, and it would take some finesse to have a transmission that increased the rotational velocity of the wheels as the rotational velocity of the flywheel decreased.

 

[tbuelna]

As gruntguru noted, the max amount of power that can be effectively used at launch is limited by the traction capability of the drive tires. And it doesn't matter much how many are used. If we assume the static load radius (SLR) of the drive tires is around 21", the tires have a traction coefficient of 1.0, and the vehicle weighs 80,000 lbs, then the max torque that can be applied to all the drive tires before loss of traction is 140,000 ft-lbs. And this would not include the impulse torque spikes experienced by the drivetrain when you "...spin it up to 10,000 RPM and then pop the clutch to the drive wheels...". Designing a drivetrain capable of that amount of torque would be quite a challenge. Here's a white paper on a similar situation.

 

[SomptingGuy]

Putting all other discussions to one side, why the "traction coefficient of 1.0" limit? People often assume this.

Steve

 

[IRstuff]

Your last equation doesn't seem to have its units balanced

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[Tmoose]

"Putting all other discussions to one side, why the "traction coefficient of 1.0" limit?"

I blame my high school physics teacher Mr Prescott.

 

[geesamand]

Put whatever traction coefficient is appropriate for the tires you intend to employ. However, remember that while the friction coefficient of a tire may be nonlinear, it tends upwards at lower specific loads. For a load this heavy, using conventional race tire materials, you may find that dragster references are not useful.

My first inclination about this question conjured images of the Saturn V rocket engines.

 

[dwbarlow]

I broke down and did some calculations. I have attached the spread sheet (*.xls). You can check the math.

I found out if you take a single steel disk with a radius of 2 feet and a width of 1 foot, spin it up to 5,000 RPM you get a potential of about 35,450 HP

I also found out you need in excess of 32,000 HP to move 80,000 lbs a quarter mile in less then 6 seconds.

So, theoretically it is possible to create an 80,000 lb dragster that will do a quarter mile in under 6 seconds.

But with these kind of forces you have to be concerned about what kind of materials could take this kind of stress. So now it is a design problem. I was thinking if the flywheel was mounted on a tempered steel shaft 6 inches square, if that might take the stress.

I was also wondering if instead of U-Joints, each drive wheel is directly connected to the flywheel axel. There are no joints. Could it now take the stress? The drive wheels are off the ground as the flywheel is spun up. Popping the clutch in this case consists of slamming the drive wheels to the pavement simultaneously, or in some sort sequence. Instead of one big flywheel, and one set of drive wheels, 2, 3, or 4 drive shafts with integrated flywheels were utilized. Spinning up the flywheels would use conventional gears and joints powered by the truck engine. Some of drive shafts are identically geared for initial clutch pop. After the first one or two drive shafts are dropped, then the last one or two are geared higher (bigger tires).

As I said, this problem is a simple proof of concept for something more awesome (maybe).

 

[dvd]

Your spinning disk has potential energy, how fast you remove the energy results in power. You could develop nearly infinite power if you removed the energy fast enough.

Are you considering all of the potential energy of the spinning disk, or just some percentage. It is going to very hard to get much useful energy out of the disk when it slows to nearly zero rpm.

 

[IRstuff]

I think your required horsepower is less than 1/2 of what's actually required; I get something more like 87000 hp.

Your example disk weighs nearly 6000 lb, all by itself. When you add in the the structure required to hold and constrain that large a mass, you're probably adding 20000 lb to the vehicle. I think you'll find that the engine required to crank the flywheel up to speed in any sort of useful time will be gigantic. Getting 87000 hp is a nontrivial. As an FYI, the nuclear power plant for a Ohio-class ballistic missile submarine with 170-m length is rated for 60000 SHP.

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[dwbarlow]

I think a potential of twice the HP is needed. Peak HP is only used for 6 sec or so. After that event, any left over power would be allowed to dissipate, unless of course in a drag competition there were more heats.

Again, it is a mental experiment. It wouldn't take much more than $75,000 to make it real, but as others have said, unless there is an actual profit somewhere, either in dollars or recognition for a sponsor, I wouldn't invest in it just for the heck of it.

I am getting my payback by extending my knowledge about something I hadn't thought of before. My background is in aerospace and defense software. While this problem is interesting, I'm kind of thinking about a compact laser or magma canon. I'm also thinking about a first stage lift system for sending payloads into space using simple mechanics instead of expensive and unstable rocket fuel.

In the case of the canon, I look at what a lighting bolt is made out of, could a flywheel based generator, generate a controllable bolt of energy of the same magnitude. I think it could and it could be mounted on a heavy truck and be mobile. I know in the case of the canon that work has been done. I also am aware of some of the limitations currently being encountered with some of the existing systems being studied.

A first stage lift system that accelerates a payload to the upper atmosphere where rockets could take over would simplify current launch systems and reduce costs. If it were possible. You know of those twirlly thingies we played with as kids. You spin a shaft with a propeller on it and let it sail up. Could it be possible to borrow from that concept and make something useful out of it?

I still don't know much about lighting bolts, or lift capacity of propellers, but I know a little bit now about flywheels. I sincerely thank you all for your help.

 

[tbuelna]

I ran your 80,000lb, 32,000hp, AWD drag truck concept in HP Wizard and got the result below. I used a tire traction coefficient of 1.0. It gave a 9.9sec 1/4 mile time at 179mph. This includes the effects of aero drag which I don't think your spreadsheet calculation did.