Gilles,
This is the forum that I like most.
Average of the Europa builders have Rotax engines and the radiator (234 cm2)
and ugly cowling (underside) are part of the kit. Those who personalise
their build with other engines or modifications look forward to problems for
eligibility in the different countries in Europe. So as Remy Guerner once
said: I present my airplane for control without cowlings. But to the point
now: Your radiator is 410 cm2 and Glenn has 685 cm2. I am convinced that
your investigation and theoretical statement is correct. Why don't dare we
tell that the original radiator for EUPA is undermeasured and the cowling
design is a misfit for all those who are building following the manual?
Shall I tell you that in France the G.D.A.C. don't approve the build in of
the digitrak wingleveler because the kit is not that one who was eligible
for their administration! I was surprised to see Glenns photographs because
they show nearly what I realised and therefore encourage me to continue as
well as your technical support. But as I said already: I didn't invent the
wheel, unfortunately, and what I am doing at the moment is not finished and
tested enough, so when my cowl flap will be nearly perfect I will give you
more feadback of the results.
Karel Vranken, F-PKRL # 447 XS Monowheel Rotax 912ULS Airmaster CSU
----- Original Message -----
From: "Gilles Thesee" <Gilles.Thesee@ac-grenoble.fr>
Sent: Saturday, December 02, 2006 2:20 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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