# Electric drag racing

Antiphon
There is actually a national association for this.
http://www.nedra.com/

The specific energy (Watt-Hrs/kg) of gasoline and hydrogen are
quite high (which is why we drive with gasoline) compared to batteries
or flywheels which have ~100 times lower specific energy.
The specific (theoretical anyway) energy of Metal Oxide Capacitors in
development is 10 times lower still.

But the specific specific power (Watts/kg) of the capacitors
is 10-100 times higher than that of gasoline or hydrogen.

This means a capacitor-powered electric dragster could someday
produce 10-1000 times the thrust of a hydrocarbon-based combustion
engine.

Anybody know what the tires would have to look like to grip the pavement
for such a beast?

## Answers and Replies

Staff Emeritus
Science Advisor
I doubt that one can increase the coefficient of friction much more than has been done. To increase adhesion, other than by increasing the coeff. of friction, one must increase the normal (downward) force.

IF 10-100 times the tractive effort is the goal, it makes no sense to transfer mechanical energy by wheels.

Consider a rocket or jet power car - the thrust of the rocket/jet is (obviously) in the opposite direction of travel.

For capacitive powered cars - linear motor would be the solution - which is basically means maglev or railgun technology.

So putting in 10 times the energy means roughly the velocity increases by sart of energy, from E = 1/2 mv2, or roughly 3x the velocity of a conventional dragster.

These days dragsters are pushing over 200 mph (perhaps as much as 220-230 mph). So one may be looking at 600-700 mph - like the rocket/jet powered cars.

One could use metal wheels magnetically/electrically attached to the track.

And at 600-700 mph, a guided track may be necessary to avoid high rate of wipeouts. Controlling a vehicle at ground level at these speeds is very difficult. Note that the FAA has speed restrictions on commercial airliners below 10,000 ft (about 250 kts, or in some cases 285 kts).

hitssquad
Astronuc said:
These days dragsters are pushing over 200 mph (perhaps as much as 220-230 mph).
Over 300.
http://www.nhra.com/stats/natrecord.html [Broken]

--
336.15 05/25/05 Tony Schumacher
--

The Pro Stock class (third from the top) is just over 200 MPH right now.

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Science Advisor
With a modern top fuel dragster going 330 MPH in less than 4.5 seconds in a 1/4 mile track, the limitations are not the chemical engine technology per se but more the regulations preventing the teams from going too much faster for safety reasons. Although how much faster they could go if unregulated is not a dramatic amount, the forces involved already are incredible and pushing the boundries of safety for entertainment.

The tires are purpose built slicks but are only one part of the equation - the track is equally important with an adhesive substance called VHT (very high traction) applied to the track. The VHT is applied the entire length of the track because the 8,000HP motors can spin the tires at any point on the track, even with 10,000lbs of downforce from the wings. If you visit a local dragstrip they'll likely apply a little VHT to the track for the Friday night opens where people can take their street cars to the track for fun, and if you walk on the parts prepared with VHT application you'll feel your shoes stick to the surface.

The upper classes in drag racing use a slipper clutch that progressively engages the motor to the wheels to prevent the incredible power generated from breaking the tires' traction. Since they have enough extra power available they can afford to throw it away to cook some sacrificial clutch each time they use the car, power doesn't seem to be a limiting factor.

So I don't think you'd be able to increase the acceleration much beyond the current chemical fueled cars by a dramatic amount simply because they have been limited by traction issues for decades now.

But if the vehicles were mechanically accelerated via a rack and pinion like some of the new amusement park rides...

hitssquad
Cliff_J said:
power doesn't seem to be a limiting factor.
Power is a limiting factor. Otherwise, they wouldn't bother using multiple transmission speeds. One purpose of slipping the clutch is to prevent the tires from breaking lose when the gears are shifted. That doesn't equate to having all of the power you can use.

Staff Emeritus
Science Advisor
hitssquad said:
Over 300.
http://www.nhra.com/stats/natrecord.html [Broken]
--
336.15 05/25/05 Tony Schumacher
--
The Pro Stock class (third from the top) is just over 200 MPH right now.
Yeah - I was think pro-Stock class.

So 3 x 336 is just over 1000 mph - that's supersonic. Wheels are pretty meaningless at those velocities. A guideway is pretty much the only way to go.

Specially design wheels are needed for vehicles going land speed record, e.g. http://www.landspeed.com/VehicleInformation.asp [Broken]

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The Ippster
hitssquad said:
Power is a limiting factor. Otherwise, they wouldn't bother using multiple transmission speeds. One purpose of slipping the clutch is to prevent the tires from breaking lose when the gears are shifted. That doesn't equate to having all of the power you can use.

right, when you shift a gear, you get a new surge of power to the wheels, and the tires can slip, if the tires could not slip then the car would have a higher top speed. Friction is the limiting factor. like stated before, increasing the normal is really the only way to increase traction now, the Mu is pretty much at its terminal

Science Advisor
Gold Member
hitssquad said:
Power is a limiting factor. Otherwise, they wouldn't bother using multiple transmission speeds. One purpose of slipping the clutch is to prevent the tires from breaking lose when the gears are shifted. That doesn't equate to having all of the power you can use.

No, I'd say that the horsepower isn't the limiting factor, but at what RPM range that horsepower comes from is the reason for the transmission.

Science Advisor
Homework Helper
The army dragster has a mass of about 1000kg, and about 6000000 watts of power. Let's assume, for a moment, that it can actually put all that on the ground at all times.

Then, in 4.4 seconds the total work would be 26000000 joules - that figures to about 350 mph.

So, it looks like power is an issue, especially at the end of the run.

http://www.goarmy.com/racing/nhra_top_fuel_dragster.jsp
Claims that the starting line accelertion is a *massive* 6G's.

The Ippster
you just said that is all power was going to the ground, then they should go 350, the top speed was 336 something, tire slippage can account for some of the loss of power/speed, often times also drag racers find themselves "throttling" the car, so they can get taction again once they loose it, which is very very often.