HP needed to go 60mph IN A STREAMLINER?

[trautotuning]

Hey guys,

I know you need around 10hp in a car to go 60mph.

But how about a streamlined motorcycle? It only has two wheels (lower friction) and WAAAY better aerodynamics?



(dont think about how much hp it takes to get it to go 60mph, just how much to sustain it once your there (with perfect gearing for 60mph lets say)).

[GasSavers_RoadWarrior]

Actually you could pedal something like that up to 60mph, it's been done, a cyclist is presumed capable of putting out 1/6 HP sustained.

[VetteOwner]

would work, till someone merged on top of you...

[samandw]

It's just a simple matter of calculating three numbers:

Rolling Resistance:
This is generally considered to have a linear relationship to weight. To find the resisting force, you simply multiply the Rolling Resistance Coefficient (RRC) by the vehicles weight. Here's a link to a list of LRR tires to give you an idea: RRC

Aerodynamic Drag:
The aerodynamic drag is simply a function of CdA and the speed according to the following formula:
Drag = 1/2*rho*V^2*Cd*A
Where:
rho = .002378 (at sea level)
V = velocity (in feet/second)
Cd = (coeffient of drag)
A = frontal area (square feet)

Powertrain Losses:
Typically this would be 15% for a manual transmission.

For this particular case, I'd throw out a guess of 550 lbs operational weight, Cd of .10 and frontal area of 4 square feet. That works out to the following:

Drag = 1/2*rho*88^2*.10*4 = 3.7 lbs
RR = 550 * .005 = 2.8 lbs

hp = force*speed/550 = (2.8+3.7)*88/550 = 1.04 hp.
Factor in a drivetrain efficiency of 85% and you get 1.22 crank hp required.

Since all the above is really a bunch of guesses, I'd say it's easily less than 2.5 hp to maintain 60 mph on level ground.

[ChrstphrR]

I saw that more as asking around for... a formula. I did find something that was similar to what I dug out of books years ago, from a book about aerodynamics:

"The formula"
http://www.engr.colostate.edu/~allan...e8/page8f.html

This formula takes both rolling resistance (which is linear-proportional to velocity), and the air drag (which rises with the cube(?) with velocity).

They actually stop short of combining the two formulae, to express the left side only in terms of Power, not just Force.

The 10 hp number tossed about wouldn't fly with my own car; working off the formula plugged into their applet, I need around 22hp for my Jetta.


Java applet applying formula stated on the prior link.
http://www.engr.colostate.edu/~allan...wer/power.html

The applet lets you calculate power needed on velocity range... so you could see the power curve for say, 0 to 26.82m/s (60mph), or past.
Nota Bene: All quantities are metric. But the output graph does graph and both in kilowatts and horsepower.

But for imperial to metric, and vice-versa, you have conversion formulae... or a nice site like this:

http://www.tdiclub.com/misc/conversions.html

There!

Now, use it like I did back in my teens, scheming and planning to make a nifty little low-drag sports car.

[ChrstphrR]

Originally Posted by samandw

rho = .002378 (at sea level)

Whoo, I remember that from the book I reminisced about! Goodness, and it was over half a lifetime ago now

Great explanation, and I love the link for specific tires' rolling resistance coefficients.

[samandw]

If your interested, here's a post I made a while back in another thread regarding a veihicle design I have similar to the picture you attached:
http://www.gassavers.org/showpost.ph...0&postcount=39

[GasSavers_RoadWarrior]

Hmmm, guess a cyclist would need a lightweight machine... though I ran numbers on metrompg's resistance calculator and it came out around 3/4 HP for a 250lb combo... where it seems that 35-40mph in a .4 Cd tuck on a racing bike needs about the same. I dunno where I got 1/6HP from for human output, probably from human powered flight data.

[Drag Limited]

I just wanted to note that a Motorcycle has HORRIBLE aerodynamics, case in point....

On a highway my friends TT Viper raced a Turbo Hyabusa(spelling). The Busa had a better power to weight ratio, but after about 130mph the viper just walked away from the bike like it were nothing... the reason? Aerodynamics of the viper made a huge difference when approaching 200 mph.

Garyjavo.com was the guy with the viper's website.

[Big Dave]

I don?t think there is any question that a properly faired motorcycle can do better than any four-wheeler. The lower CdA and rolling resistance of two tires should do it, but the key is properly faired. I own an unfaired Honda Valkyrie and that thing is much draggier than my pickup. I can coast the pickup a half-mile easy but the Valk practically runs into a wall when you roll off the throttle.

I agree with Vette owner about somebody merging into you. Motorcyclists survive on a mixture of 75% situational awareness and 25% raw acceleration. Thus bikes cannot be operated quite like cars or trucks. That's also why bikers say: "Loud pipes save lives."

I also worry about cross winds when I see this streamliner.

All that said, I think a Honda Gold Wing could be made into a streetable streamliner. The Gold Wing is very reliable and easy to get parts for (not true of many metric bikes). With greatly reduced aero drag, the Gold wing would have plenty of acceleration. The fact it is water cooled would allow you to relocate the radiator and still get adequate cooling and it would allow you to have a heater which would allow operation nine months a year out here on the frozen steppes. Drawbacks: Gold Wings are heavy ? about 900 pounds as is. Secondly, their drivetrain is designed for a heavy, draggy machine and is way over-geared for this application.

Believe it or not you can find ?landing gear? (retractable training wheels) to make them easy to handle at low speeds and that could be built into the streamlined fairing setup.