Gilles,
Did you measure air temperature increase across the radiator (i.e. inlet air
temperature and outlet temperature)? Which, in accordance with Boyles Law
would dictate the inlet/outlet ratio; we are not in to compressibility at
our speeds!
I agree that the actual area of these is dictated by the size/type of
radiator core and the amount or air that it is able to pass. PE Irving in
his 1960's book ('Tuning of the Automobile Engine'(?)) stated that the inlet
area only needed to be 1/6th (17%) of the face area of the radiator (with
proper ducting) and cited the early E-Type Jaguar sportcar as an example.
The XS inlet area is about 60%. Mine is 30% (77cm2)and works well. I did not
have the nerve to make this smaller; preferring evolution, not revolution!
But with the experience, it could have been a bit smaller, although I made
no allowance for leakage around the sides of the radiator. My non-adjustable
outlet area is 115% the size of the inlet; which was a guess but the
measured air temperature rises suggest it could have been less.
Rgds.,
Duncan McF.
----- Original Message -----
From: "Gilles Thesee" <Gilles.Thesee@ac-grenoble.fr>
Sent: Saturday, December 02, 2006 1:20 PM
Subject: Re: Europa-List: Perfect cooling diffuser
> <Gilles.Thesee@ac-grenoble.fr>
>
> Duncan,
>
>>
>> What is your ratio(s) of inlet area to outlet area?
>
> What really matters is the ration of outlet area to RADIATOR area. As
> already stated on Contrails, too large an opening won't flow more air than
> a correctly proportioned one, since it is the radiator that governs the
> flow in the duct.
> It may help to figure the radiator duct system as a duct with 3 valves in
> series. The middle valve is the radiator. As it is partly closed, opening
> the other valves more than necessary won't change the overall throughput.
> There is no use opening the outlet more than about 1 time the radiator
> frontal area, you would only add drag without increasing air flow through
> the radiator. Drag decreases as you reduce outlet area by means of the
> cowl flap. In cruise, outlet area should be smaller than the inlet area to
> achieve minimum drag. It is advisable to construct the adjustable cowl
> flap with a range of openings from 1 time the radiator area to near zero
> (power descent on a cold day).
>
> In our setup, inlet area is 25% of the radiator frontal area, whereas exit
> cowl flaps can be adjusted from 70% to 0% of the radiator area (410 cm).
> We currently cruise with flaps adjusted to 18% of the radiator area, or
> less on cold days. On summer hot days, best cruise (75% power) is with the
> exit adjusted at about 28% radiator area. Of course we open more in a
> prolonged climb.
>
> During flight tests I installed a data logging system to check adequacy of
> the pressures and temperatures.
>
> Adjusting CHT and oil temps to within 5C of desired temperatures is a
> breeze, and we found no special limitations concerning ground run time. A
> thorough cooling study is really worth the time and hassle.
>
> Hope this helps,
> Regards,
> Gilles
> http://contrails.free.fr
>
>
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