Re: 200 MPH (long, ignore if math bores you)

["John Stricker" <jstricke@domain.elided>]

Howard (and everyone else interested in this thread)

The first recorded timed event of breaking the 200mph record was by Henry
Seagrave in 1927.  This was at Daytona Beach, FL before they moved the Land
Speed Record attempts to the Bonneville Salt Flats.  He ran 203.7mph in
1927.  I couldn't find the exact date in my references. Or what he was
driving, but I have some references of him driving Bentleys competitively.

Now for a little math.  The equation that aerodynamicists use (and this IS
abbreviated and chopped up a bit so don't jump all over me for being not
accurate to 11 decimal places) is roughly (146625*HP*(Propeller
efficiency)/Flat Plate Drag Area)^(1/3) (that's raised to the 1/3 power for
you spreadsheet challenged out there).  The 146625 is a constant I computed
that isn't a constant for somebody working on a/c as it comes from things
like temp, altitude at which you're working, etc.  If I remember right, this
is for a standard day at sea level, but it's been a while since I messed
with it.

For our purposes, we can call Propeller efficiency 1 (although if you like
you could figure that as your geartrain loss).  Then all you need is to
figure out your true horsepower at a given speed and you can solve for the
Flat Plate Drag Area which in this case will include rolling friction drag.

OK, let's crunch some numbers.  A very good, clean, composite airframe,
4-place, retractable gear, near laminar flow wings, will have a FPDArea of
about 2.5-2.8 sq ft.  Your production Cherokee or Cessna will have roughly
twice that at around 4.5 to 5 square feet.  The frontal are of almost every
domestic car I know of is at least 25% greater than these a/c, not as well
streamlined, and also adds into the equation rolling drag from the tires and
aerodynamic problems from ground effect issues.  I don't recall exactly, but
I used to have some literature around here somewhere that showed the early
nineties Corvette with a Drag Area of about 5 WITHOUT considering rolling
friction and ground effects.  Let's call it 9 (and I think that's being
generous.)  As a quick explanation of what the "9" is, that is the
equivalent area of flat plate, in square feet, that would give the same
amount of drag if held up in the relative wind (i.e., a 2X4 sheet of plywood
is 8 sq ft.)

Plug in the numbers, and let's see what we come up with.

At 70 mph, our car would require 22 hp to maintain on a level road, etc.
So, how much power do we need to run 200?
Plug the numbers in again and I come up with 492 hp.

Now, if you build it for 492 hp, you will never see 200mph because you must
accelerate to that speed.  In my case, I have a 1973 Pontiac Grand Am with a
(factory) SD-455 and an NOS nitrous system.  It runs very strong, but it's a
very large bodied car.  If I go out on interstate and let her fly, she will
run 136 mph.  (BTW plug that into the formula with a drag area of 13 and you
come up with about 235 hp.  Not unrealistic when you figure that's net hp.)
Now, If I hit the nitrous, I have accelerated it up to 153 (on the
aftermarket mileage/speed computer I have in it), let off the nitrous, and
had it settle back down and maintain 142-143mph.  That puts my true peak at
about 255 hp net.  This is a stock SD-455 except for the nitrous and I think
these numbers work out just darn close.

Also, going by the above experiences, to get a 'Vette to run 200, IMHO it
had better have 650+hp or it will never get there.  And we haven't even
begun to touch on the gearing required to make those tires turn at speeds of
200+.  That requires even MORE excess HP to get it there. (BTW-If memory
serves, my Scouts, while truly handsome beasts, do not appear to my critical
eye as being very aerodynamic.  You could probably measure width X height
and add another 25% and come pretty close. After all, it IS basically a flat
plate!  Could it be that that's why our mileage suffers "a bit"? )

So, as Howard said, the next time somebody's bragging about running 200+,
unless you can see some kind of forced induction and some pretty heavy duty
engine equipment, just smile, nod politely, and go home knowing better.

John Stricker

PS:  In case you're curious about the how's an why's of the Grand Am, we use
to have a little thing here called the Hays-Denver run back in 1976-1977 or
so.  Go for pink slips.  330 miles on I70.  My stock fuel tank held 26 gal
usable, I had a fuel cell with another 30 in the trunk.  At those speeds, I
could average 6mpg if I could stay off the nitrous and could non-stop it.  A
good run was anything under 3 hours (traffic you know).  I don't claim to
hold the record, but I still own my car and ended up with a Camaro, a Trans
Am, and a GTO.  I sold all but the GTO back to the owners for $1,000. I
thought I was being fair at that price, considering I spent over $100 in gas
and the risk. The GTO tossed a rod at Limon and I had to go get it and the
owner didn't want it back.

jstricke@domain.elided

"I didn't spend all these years getting to the top of the food chain
just to become a vegetarian"

Date: Fri, 06 Mar 1998 21:37:21 EST
From: n9ads@domain.elided (Howard R Pletcher)
Subject: Re: 200 MPH

>On Thu, 5 Mar 1998 09:09:01 -0600  Doug Wooten <DWooten@domain.elided>
>writes:
>>Harvestors,
>>
>>A quick note on the 200 MPH thread:  If memory serves right, the first
>>car to hit 200 MPH on a closed track was the Dodge Superbird (426 cid
>>hemi) driven by Richard Petty.  (During speed trails, not during an
>>actual NASCAR event).  The stock 426 Hemi had 425 HP.  I doubt that the
>>highly modified Richard Petty car had anything close to 700.  I would
>>guess max a little over 600 HP.  It would seem that the limiting factor
>>is air resistance and gearing, and that HP has very little part in the
>>equation...
>>
>>
>Just read in Sports Illustrated that Buddy Baker was the first to hit 200
>driving a Dodge Daytona in 1970--perhaps this is the first official 200
>and Petty's was in practice.

>AIr resistance is the limiting factor, but the thing it takes to overcome
>it is HP.  Gearing just translates the 6000 engine rpm (or whatever)
>needed to produce its maximum HP to the 2000 (or whatever) wheel rpm is
>needed to go 200 mph.  If the gearing is wrong, the engine may be turning
>5800 or 6200 rpm as the speed approaches 200 and not producing the HP
>needed to overcome the air resistance.

>Howard Pletcher
>Howteron Products Scout Parts