Transmission + motor question

Black kNight

in theory yes the 370z can hit 195MPH but is it in practice do the same thing

but maybe if it have more power

and thanks crash for the information

TerribleONE

wow.. surprised... is the Z geared different than the G37?

Crash

Actually, I can tell you how much power is required to defeat the rolling resistance and drag (assuming that the wind-speed is 0MPH!):

NOTE: I couldn't find the frontal surface area on the 370z, so I'm GUESSING it's around 1.9m^2. It could be less.

First figure out how much drag force there is:
F_drag = (Drag Coefficient) * (Frontal Area-meters) * (Volocity-Km/s)^2
200MPH = 89.42Km/s
F_drag = 0.29 * 1.9 * 89.422 = 4405.76 N

Now we figure out the rolling resistance:
F_tire = (Vehicle Weight-Kg) * 9.8 * (drag_contribution)
F_tire = 1506 * 9.8 * 2.43% = 358.64 N

Now calculate how much power is needed to push against these forces:
P = F * V
P = 4764.4 * 89.42 = 426032.648 Watts = 571.32HP

So, approximately 571HP is needed to get the car to 200MPH

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TerribleONE

you sir... are brilliant. lol

Crash

Why thank you!

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grimm1

I'm curious as to where the (2.43% drag contribution) value came from. As I stated earlier rolling resistance is not a calculation I'm familiar with. I had no idea there were~745 Watts/Horsepower. I guess you learn something new everyday.

grimm1

Your physics is correct, however calculus is needed to give the exact ammount of power needed to go 200 mph

Crash

^^^ I based the drag contribution on math I did earlier for as similar car. I don't have the spreadsheet on this computer with the calculations, but drag contribution is recalculated based on the speed since speed is not constant, but rather squared. Originally 35MPH was calculated at approx 1.3%, at 200MPH my calculations gave me approx. 2.43%. When I get to my other computer, I'll post up the formula I used to get that contribution.

And, yeah, I've been doing the watts/hp conversion for a while because I've been researching electric cars for a long time, and most electric motors all have specs in metric units instead of imperial. So it's all in KW and NM instead of HP and TQ.

I don't see how calculus is needed for the exact number of HP need to achieve a certain speed.

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grimm1

How can you factor in the resistance produced as the drivetrain's speed increases. Similarly I'm wondering what is meant by drag coefficent? What is the unit for drag
coefficent. I do not believe calculating wind resistance is as
Simple as drag coefficent * surface area* velocity. As I stated earlier wind resistance is a
Fourth power function of velocity. It gets terribly complicated from there.

Crash

You've got the formula wrong (a little). It's drag_co * surface area * velocity^2

All cars have a drag coefficient. It's the ability for air to pass around the vehicle. The only way to find this number is to have the car tested in a wind tunnel. Here is a video of this being tested:


Then you derive the force of the drag (f_drag) from the amount of area pushing against the air, by the drag_co, and by the speed at which it is hitting the air.

If you've got a better formula for figuring this out, please let me know, because this is the way I was taught how to find the force of drag. As far as I understand, the only drag quadratic equation is for fluid. Am I wrong? Here is the formula I've broken down, maybe I missed a step, but this looks right to me:
Drag equation - Wikipedia, the free encyclopedia

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grimm1

Laminer flow on a Pagani Zonda... I guess now I've seen it all. I may be mistaken but I'll go fetch my fluid mechanics textbook, I could have sworn wind resistance was a fourth power of velocity function. However everything I've read off google agrees with Crash. It appears in the Zonda video that there are a few Eddies coming off the rear of the vehicle... There is an enormous amount of drag created as the air spins off the back of the car. Is Pagani hiring Aeronautical Engineers?

Crash

^^^ LOL. No idea. I have no clue about aerodynamics engineering. I just took the formulas off the internet and plugged them in accordingly. My engineering isn't in physics, it's in software! But I figure I have a freaking awesome learning curve. I took telecommunications management and screwed the bell curve for the rest of the class. Learned how to do the math for electronics engineering in a couple years of studying electric cars, and picked up some stuff for calculating power and time. I learn what I need to know at the time, but I retain pretty much everything. But I do have a firm grasp on mechanical engineering.

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grimm1

That's cool I remember my AP Physics class back in high school...The teacher would call out the test grades in front of the class. Needless to say I wasn't very popular with the kids who were asking for a curve on their grades. I even recall having a snickers bar thrown at me in the middle of a test. My father was a software engineer... Isn't most of that work being outsourced to the middle east. Just about every time I call Microsoft I get someone in India.

Crash

Yep... Sadly, that is the case. EVERYONE hated me in math classes and a professor at my college was fired because he was teaching the math wrong and I kept arguing with him about it in class.

And yeah, again, it's sad that all of the software is being outsourced to India and China. Although, from what I hear, it's getting out-sourced to the UK now as well. I'd imagine it's a lot more pricey, but who knows. I won't outsource to India. I did before and they screwed me.

When you call Microsoft, you're not getting their software development department. You're getting their customer-care department which was ALSO out-sourced to India. (as many companies have done) although, Canada also gets a lot of the out-sourcing for customer care too.

I do SPECIAL coding. Stuff people don't want outsourced or want it done fast and under the radar. I specialize in new technology programming. Not in building the same thing over and over for different people. That's where India does well. They have vast libraries of code they've created over MANY years of development and they just snap together code like legos to create something.

I'm the opposite. I write code that has never been written before for ideas that are right out of the wood work.

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