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----- Original Message -----
From: <peon@pacific.net.au>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Sunday, February 08, 2004 6:15 PM
Subject: [FlyRotary] FD rads & Evap Cores Take 2
> Hi Ed, Rusty,
>
> Thanks fo the replies guys. However, now you have got my mate
> Wally (and me!) REALLY confused. (}:<)
>
> You are touting that 2 Evap cores as being able to cool better than
> an FD rad (plastic tanks aside), but having less drag. So should I
> throw away the FD core (with alloy tanks) in the race car and
> replace it with 2 evap cores?
>
> Will I then have less drag??? Will the race car then go faster, or
> have better fuel economy at the same speed (a very important
> factor in endurance racing)? Wow, ... talk about a "racer's edge"
> .... if it's true that is ... Does anybody REALLY know ... I mean
> from a practical rather than just a "running the numbers" point of
> view??
>
> Cheers,
>
> Leon
>
> P.S. BTW, why did Tracy need to spray his evap cores with water
> to keep the enigne from turning into kettle - in level flight and at
> high speed no less (in an air race or so I have read)???
> e wouldn't have any more than 200 BHP would he?? If they won't
> cool 200, how will they EVER cool 250?? The (lost) plot thickens,
> ... almost to the point of being thixatrophic (}:>).
>
> Thixatrophic? or not, Evaporator cores do cool a 200+ MPH aircraft with a
NA 13B. While Tracy did have a spray bar as do the war birds racing at
Reno, he did not need it to cool his engine in his 100 mile max speed race
at Sun & Fun. Actually, it was not his max speed as he was only running at
90 % power rather than 100% - still had throttle and power left as he raced
past his competitors. Tracy did turn on the spray bar for a few seconds
just to see its effect - and Paul Lamar picking up on this declared that
Tracy had "cheated" while at the same time handing him the award money for
winning the race. As best I recall, Tracy may have used the spray bar for 10
seconds of the 20 + minute race.
I would not throw away your FD with alloy tanks. As best I recall a race
car (depending on the type of racing) may have low speeds ( or lower speeds)
in turns/corners, spends considerable time accelerating (High power, low air
speed) from corners and such, may be shielded or have airflow to the
radiators disrupted by other vehicles, may be in draft situations, etc. I
understand the air temperature on a track can get right high down under as
well. Basically, the auto may be running full throttle and have less than
optimum cooling conditions. On the other hand, few of those adverse
environmental conditions exist for the aircraft racer. Drafting does not
occur (at least intentionally), no thermal effect from the black top, etc.
Also, do the auto racers pay as much attention to diffusers and ducting as
in aircraft? Whether or not a couple of evaporator cores is - or is not -
more effective than the FD radiator would depend on such consideration.
However, most stock automobile parts are not optimized for racing or full
power but rather for some nominal operating state such as 30-40% of max
power. Full power being only exercised for 0 - 60 MPH, in passing on the
highway or perhaps the quarter mile.
I don't know whether an FD radiator will cool 250 HP for more than a minute
or two, but they apparently will do so if they are successfully used in
racing. But, given the differences in the racing environment on the ground
track and that in the air, I think we are comparing apples and tangerines.
FWIW
Ed Anderson
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