Hi Remi,
The honest answer is of course "no". Until I can test fly it I won't
know for sure.
There are some historical reasons why the standard XS cowl arrangement
performs badly on the ground. When the XS was developed from the
Classic, the factory moved the engine up to give them better prop
clearance. This had the unintended consequence of forcing them to use a
smaller diameter spinner, which exposed the propeller cuffs and roots.
These cuffs thrash around during ground running producing no thrust and
a large amount of turbulent air.
The designers threw every known orifice at the new cowl; two Lo-Presti's
(popular at the time), two NACA vents (because all _real_ aeroplanes
have to have NACA vents), two louvres to complete the set and a shoe-box
underneath to keep the radiator out of the cold (I think someone added
that for a bet).
The problem when ground running is that all this swirling airmass is
largely passing across the mouths of these vents - not into them. The
Lo-Presti's are positioned adjacent to the blade roots and the radiator,
positioned way back in its duct, is sitting in stagnant air. It's not
until the aircraft reaches flying speed that the apparent wind comes
more from the front that air begins to enter the vents/ducts and the
cooling improves. This is one reason why Frans Veldman's front mounted
radiator arrangement is so much more effective. High twist blades such
as the Woodcomp have been shown to give better ground-running
temperatures because they produce a much better airflow at the blade
roots than many of the flatter blade options.
I started with the prop/spinner and worked back. I lowered the engine to
the original Classic position - but maintained the XS forward position.
This allowed me to design a much larger spinner to completely shroud the
blade cuffs and most of the blade root. This fairs seamlessly into a new
cowl that has only one duct opening. This F16 style scoop is positioned
as far down and as far back as I can practically get to collect useful
propwash and feed the radiator and engine bay duct. For the air cooled
cylinders, I have chosen not to use conventional "high drag" vent and
baffles but have shrouded the cylinders and ducted the cooling air (like
a VW Beetle). I have managed to save so much weight by eliminating the
original landing gear and engine mounting frames that I have enough
weight budget to allow for a cooling fan within this ducting - should
one prove necessary. Only time and testing will tell - but I've had a
great time doing it!
Nigel
On 23/08/2016 20:16, Remi Guerner wrote:
>
> The dimensions will be defined by
> the aircraft speed at which the cooling should be most efficient
> (climbing, full power - probably around 80kts (41 m/s)
>
>
> Hi Nigel,
> One common issue with the Europa is overheating on the ground, not in flight.
It is very tempting to optimize a cowling design for low drag as you did but
are you sure that such a design will allow the engine to be run indefinitely at
idle on the ground in the summer heat ?
> Remi
>
>
> Read this topic online here:
>
> http://forums.matronics.com/viewtopic.php?p=459805#459805
>
>
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