LSR Math

[Stainless1]

Back to the subject, which was LSR math.

   Start with this formula:  F=MA

And simply go from there!     

IB, in your formula
F, I take it is for fast, M is money and A is adrenaline ?
 

[willieworld]

mcrat  and anyone else do me a favor and go to    http://www.rbracing-rsr.com/aerohpcalc.html        and  plug your information and see how accurate it is for you and post the results   thanks  willie buchta

i will go first
 cd----------------------.8
 frontal area-------------6.3 sq. ft.
 weight------------------675 lbs.
 speed-------------------135 mph

 horsepower needed----85.1     

[McRat]

Well, my truck is not a good reference, since I've yet to use all the power. 

Cd - .45 (from a GM document, not testing)
Area - 35sqft
weight - 6400
Speed (peak GPS) - 181mph

HP - 676hp (actual sea level power was 798rwhp uncorrected, about 1000hp at the crank)

Using calculator such as the one you listed, tell me I'll need ~915HP sustained to hit 200, which is probably right. 

[rebelce]

These folks have a lot of good formulas.

http://www.bgsoflex.com/auto.html

[octane]

Ahh, this is fun !

My bike: SALT CRACKER INDIAN




I have no idea about my 'cd' so I've set it to 0.9
based on it being more than Willieworlds bike ( 0,8 ) judging from his avatar picture.
It's probably even more , with all this not-so-stream-lined blower crap hanging out there:





Willie; what did you base your cd on ?
...and do you have a full-size pic of your bike so I can compare ?
Thanks !


For calculating the frontal area I took a pic from the front
with markings for each 10 cm.
( The right leg will eventually come in further. Kick starter  will be modified)



...then made a 10 x 10 cm grit
( Arms tucked in more, on this pic )


...and calculated the area.
That came to 0.3355 sq. meter ----> 3.605 sq. feet.
As the parts further back from the grit-line appears smaller than they are,
so I adjusted it up to 3.9 sq. feet

Still wondering why the figure is so much lower than Willie's ( 6.3 )
( Something must be wrong with my calculations ?)


cd----------------------.9
frontal area-------------3.9 sq. ft.
weight------------------539 lbs.
speed-------------------100 mph

 Horsepower needed....: 24.9

...............

cd----------------------.9
frontal area-------------3.9 sq. ft.
weight------------------539 lbs.
speed-------------------120 mph

 Horsepower needed....: 42.3

Wow; those extra 20mph takes a LOT of extra power.
I knew that , but didn't realize it took SO much

[Rex Schimmer]

Lars,
Like your approach to aero and you are probably pretty close. Other than going to a wind tunnel your method is as good as any other.  Speed really does cost and it is paid in horse power. As it is a cube function going twice as fast takes 8 times as much hps, so going from 100 mph to 120 requires 1.2 to the third power and I get the same approx 43 hps that you got.

Rex

[interested bystander]

If you can find it, there is a book from the late '70s by a gentleman named Landa published by Automotive Aerodynamic Research Company of America and printed in pretty casual form (copies of typed sheets with a thicker yellow top and bottom, the whole thing stapled together) and produced by The Film Instruction Company of America, Milwaukee, Wi .

It's a read that contains the simple equations of time, distance to speed, etc. and should be understandable to anyone with the slightest HS Freshman Algebra ability. (Includes general descriptions of Aerodynamics also found elsewhere).

Not putting down the simple CdA, weight , power = speed  required stuff, but this extends into the realm of accelerating to speed in a given distance, which is a bit more real world and less Dream Wheel.

Newton? I think he was a grade or two older than I, Willie.

[Rex Schimmer]

When Lars is tucked in tight and is nearing the last timing light the power required for acceleration will be very small compared to the power to over come the aero loads. He is frontal area x CDa x mph(cubed)/aero constant limited plus some power going to over come rolling resistance. If you are talking about a 4000 hp, 400 mph+ car then there may be some power required for acceleration at that speed. I was always impressed with rate of acceleration of Don Vesco's turbine car, it was picking up 40-50 mph thru the last timing traps, still in the over all equation for the speed it went, that is a pretty small amount of hps required for this rate of acceleration.

Rex

Rex