Mayf
As for my .02 cents. Two years ago at Bonneville, I ran 228 MPH three times,
during the heat of the day in the afternoon. The next two mornings, for
return runs, could only manage 224 MPH in the cool air. Personally don't
believe it had anything to do with additional rolling resistance, but rather
air density. At these speeds pushing through the thick cool air takes more
HP than the increase of HP due to the reduced temperature.
Guess this doesn't fit anybody's ideas of what should happen, but we backed
up the results.
John Beckett
-----Original Message-----
From: Lawrence E. & Cathy R. Mayfield <lemay@hiwaay.net>
To: land-speed@autox.team.net <land-speed@autox.team.net>
Date: Sunday, November 14, 1999 3:33 PM
Subject: Early morning, Late Day runs at B'ville (LONG)
>One of the threads a few days ago captured my attention span for a few
>moments. It was thatthread that discussed the timing of runs during the day
>a B'ville. I did a small mind experiment (I have a small mind) and then
>chatted with my Excel Spreadsheet. The most significant factor in speed is
>aerodynamic drag on the body followed by losses derived from tires on soft
>surfaces, and rolling friction. Aero drag has density as a factor in the
>equation. Basic fluid mechanics gives aero drag as:
>
>D = (1/2)*(density)*(Vel)*(Vel)*(A)*(Cd) where * is multiplication
>
>density = rho = P(lbs/ft sq)/ (g)*(R)*(T)
>
>P = barometric pressure in lbs/square foot
>
>g = gravity constant = 32/174 ft/sec squared
>
>R = Universal gas constant = 53.3
>
>T = Temperature, degrees Rankine (460 + ambient)
>
>At an altitude of approximately 4000 ft, the standard pressure is 1827. 69
>lbs/ft^2. Assuming that the pressure remains the same during the day (this
>seems to be a good assumption, but is it? I am no weatherman), then the
>only variable needed to determine density is temperature. And once density
>is found then aero drag and horsepower are easily found.
>
>HP = D * Vel(ft/sec)/550
>
>For my little mind experiment, I used a vehicle frontal area, A, of 5.0 sq
>ft and a drag coefficient, Cd, of 0.3. For comparison purposes I used 200
>mph as the reference speed. When I run the numbers, I get the results in
>the following table.
>
>If a run is made in the early dawn when the temperature is at say 70
>degrees the the drag and hp are 130.02 lbs and 69.34 hp needed. If the
>backup run was made at at time of day when the temp was at 100 F, then drag
>and hp are 123.04 lbs and 65.62 hp. Or less hp is needed to move the
>vehicle when the temperature is highest! In this simple case 9.46 % less
>hp. Now the question is does the motor output reduce less that 9.46%
>between those temps? If it does, it would be bet to run when it is cool, if
>it does not, then run when the temp is up. Cars that are boosted and or use
>nitrous probably would be better off waiting until the temperature is is up
>to make their backup runs.
>
>My $0.02 worth and worth every bit of it! If some one has a engine design
>software code that lets you vary the inlet temp during performance calcs,
>then it might be interesting to see how normally aspirated engine looses
>power with temp, then a boosted motor with the same inlet conditions. This
>is relative so it wouldn't matter what the engine is, just the percentage
>changes. Have to be careful of the software tho, most reference back to
>standard conditions.
>
>What does it all mean? That I prolly have too much time on my hands! On
>Sundays I take off from working on my car and I get tied of watching the
>roundy round guys and football.
>
>L.E. Mayfield
>124 Maximillion Drive
>Madison, Al. 35758-8171
>1-256-837-1051
>
>old >>>>>>>> http://www.hsv.tis.net/~mayfield
>new >>>>>>>> http://home.hiwaay.net/~lemayf
>
>DrMayf@AOL.com
>lemay@hiwaay.net <<<<preferred
>
>Sunbeam Tiger, B9471136
>Sunbeam Alpine Bonneville Land Speed Racer,
>'66 Hydroplane Drag Boat (390 FE)
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