eh, x^2 isn't an exponential function since 2 is constant.... 2^x would be,
and e^x is the most common one.... ;-))))
-----Original Message-----
From: Randall Young <randallyoung@earthlink.net>
To: Trevor Jordan <tjordan@vic.bigpond.net.au>
Cc: triumphs@autox.team.net <triumphs@autox.team.net>
Date: Monday, March 15, 1999 10:31 AM
Subject: Re: Fans revisited
>
>I don't have my old calculus book handy, but I'm pretty sure Y=X^2 was
>the very first example of an exponential function.
>
>And, the losses between the flywheel and the road are probably mostly
>proportional to power. So, for your example of 105hp at the flywheel
>and 95 at the rear wheels, an added 5hp at the flywheel would add only
>4.5 at the rear wheels. IOW the percentage increase is the same,
>whether measured at the road or at the flywheel.
>
>I believe the drivetrain losses are a lot closer to 10% than 50%.
>Otherwise, the diff & tranny would get a lot hotter than they do, and
>need more cooling. I've seen the measurements somewhere, just can't
>remember where.
>
>OTOH, it's worth noting that most car manufacturers now use ATF instead
>of 90W, apparently to reduce friction to the oil. The racers seem fond
>of 5W synthetic gear oil, but again I have no hard numbers on how much
>difference it makes.
>
>Randall
>
>Trevor Jordan wrote:
>>
>> At 1:59 PM +1100 15/3/99, DANMAS@aol.com wrote:
>>
>> >Yes, but I hedged my bets! I didn't know if it was the square or the
cube, so
>> >I just said "exponentially," which covers them both. Slick, huh?
>>
>> Close, but not quite. Exponential is n^^x, not x^^n (where n is 2 or 3
in
>> this instance). Actually I believe that your original suspicions were
>> correct and the load will fall between the square and the cube of the
>> speed. The work done will be a cube function, but the losses (drag, etc)
>> will be a square of the speed. I have no idea of the relative
proportions.
>>
>> >Yep, using the cube changes my statement below to "will draw much more,"
>> >rather than "may draw more." I don't think there is any question but
that an
>> >electrical fan is the way to go for competition, but I wonder how many
of the
>> >folks on this list have EVER had their engine up to 5000RPM? Show of
hands,
>> >please! I wonder how many even routinely run the engines over 3500 RPM
(app
>> >75 mph in 4th)? 0.09 HP X (3500/1000)^^3 or 0.09 X 43 = 3.87 HP
>>
>> Well I will confess to this one. I do not use it for cruising but I do
for
>> acceleration. Up to about 4500 typically. My perception (no
measurements)
>> of electric fans is that they give improved acceleration at speed -
pulling
>> out to overtake. At low speeds it is hard to pick the difference, but
>> accelerating from 50 to 60 mph I notice it.
>>
>> >I agree, but there is another advantage to using a mechanical fan - if
the
>> >engine is running, the fan is running. With an electrical fan, there are
>> >several failure modes that can leave you with a functioning engine, but
not
>> >enough cooling to get you out of the traffic jam and back home. If you
can
>> >make to the open road, you'll be OK, but if you don't get moving soon,
you'll
>> >be in big trouble.
>>
>> Fit a manual bypass switch or know how to rearrange the wiring to have
the
>> fan on permanently in an emergency if the thermo sensor or relay fail.
>> Then there are only the fan motor and the wiring to worry about.
>>
>> Conversely, an electric fan running at 1800 rpm may save you in heavy
>> traffic on a hot day whereas a mechanical fan idling at 900 might not.
>>
>> An important apsect that has not been raised is how much power gets to
the
>> rear wheels in the first place. A carb TR6 develops about 105 hp at the
>> flywheel. If 95 get to the wheels then another 5 from an electric fan
>> represents a 5 per cent improvement. If only 50 get to the wheels then
an
>> electric fan represents a 10 per cent improvement. Any suggestions?
>>
>> Trevor Jordan
>> 74 TR6 CF29281U
>
>
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