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A Lesson in Acceleration

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Rigil Kent
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« on: February 24, 2011, 12:40:13 PM »

Saw this posted on a local 4x4 forum - does this sound possible?

Quote
A Lesson in Acceleration:

* One Top Fuel dragster 500 cubic inch Hemi engine makes more horsepower
than the first 4 rows at the Indy. 500

* Under full throttle, a Top Fuel dragster engine consumes 1 gallon of
nitromethane per second; a fully loaded 747 consumes jet fuel at the same
rate with 25% less energy being produced.>>

* A stock Dodge 426 Hemi V8 engine cannot produce enough power to drive the
dragster's supercharger.>>

* With 3000 CFM of air being rammed in by the supercharger on overdrive, the
fuel mixture is compressed into a near-solid form before ignition. Cylinders
run on the verge of hydraulic lock at full throttle.>>

* At the stoichiometric 1.7:1 air/fuel mixture for nitromethane the flame
front temperature measures 7050 degrees F.>>

* Nitromethane burns yellow. The spectacular white flame seen above the
stacks at night is raw burning hydrogen, dissociated from atmospheric water
vapor by the searing exhaust gases.>>

* Dual magnetos supply 44 amps to each spark plug. This is the output of an
arc welder in each cylinder.>>

* Spark plug electrodes are totally consumed during a pass. After ½ way, the
engine is dieseling from compression plus the glow of exhaust valves at 1400
degrees F. The engine can only be shut down by cutting the fuel flow.>>

* If spark momentarily fails early in the run, unburned nitro builds up in
the affected cylinders and then explodes with sufficient force to blow the
cylinder heads off the block in pieces or split the block in half.>>

* In order to exceed 300 mph in 4.5 seconds dragsters must accelerate at an
average of over 4G's. In order to reach 200 mph well before half-track, the
launch acceleration approaches 8G's.>>

* Dragsters reach over 300 miles per hour before you have completed reading
this sentence.


* The red-line is actually quite high at 9500 rpm.>>

* The Bottom Line; Assuming all the equipment is paid off, the crew worked
for free, and for once NOTHING BLOWS UP, each run costs an estimated
$1,000.00 per second. The current Top Fuel dragster elapsed time record is
4.441 seconds for the quarter mile (10/05/03, Tony Schumacher). The top
speed record is 333.00 mph (533 km/h) as measured over the last 66' of the
run, (09/28/03 Doug Kalitta).>>

Putting all of this into perspective:

You are riding the average $250,000 Honda MotoGP bike. Over a mile up the
road, a Top Fuel dragster is staged and ready to launch down a quarter mile
strip as you pass. You have the advantage of a flying start. You run the
RC211V hard up through the gears and blast across the starting line and past
the dragster at an honest 200 mph (293
ft/sec). The 'tree' goes green for both of you at that moment. The dragster
launches and starts after you. You keep your wrist cranked hard, but you
hear an incredibly brutal whine that sears your eardrums and within 3
seconds the dragster catches and passes you. He beats you to the finish
line, a quarter mile away from where you just passed him.>>

Think about it, from a standing start, the dragster had spotted you 200 mph
and not only caught, but nearly blasted you off the road when he passed you
within a mere 1320 foot long race course.>>

That, folks, is acceleration!
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Mefiante
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« Reply #1 on: February 24, 2011, 13:29:33 PM »

The acceleration figures seem credible.  For a dragster starting from standstill to catch another vehicle that is moving at a constant 200 mph (= 322 km/h = 89.4 m/s) in a distance of 402 m (= ¼ mile) will take 4.5 s and require the dragster to accelerate at an average of 39.7 m/s², or near enough 4g.  After ¼ mile, the dragster’s speed will be about 400 mph (= 643 km/h).

Nitromethane is properly an explosive.  That is, it is its own oxidant and does not require air for its combustion.  At STP, it’s liquid and it has a very high calorific value (useable energy per unit mass).  I don’t know whether dragsters use pure nitromethane but if they do (pricey!), some of the other operational parameters (e.g. power output, supercharger specs) sound plausible.

'Luthon64
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Rigil Kent
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« Reply #2 on: February 24, 2011, 16:41:07 PM »

In that case .... Holy smoke! Shocked Shocked

Mintaka
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Mefiante
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« Reply #3 on: February 24, 2011, 17:31:16 PM »

Those figures and stats are corroborated by the Wikipedia entry.  From the article, it’s estimated that a dragster engine’s power output is around 4,500 to 6,000 kW with a torque peak of around 8,000 Nm.

In both departments, those’re the combined figures of roughly ten supercars.

'Luthon64
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« Reply #4 on: February 24, 2011, 21:35:42 PM »

From the little I know of top fuel dragsters, that sounds about right, and they do achieve those speeds and times, so it's a simple matter of working out the acceleration. They rebuild the engine after each run, it's one of the silliest and awesome types of racing, except maybe for tractor pulling.
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