Remicooling on the ground is best addressed by using exhaust extraction, th
is is how
the old steam locomotives drew the air through the firebox. It's usually do
ne on Long EZs this way, the exhaust stacks are cut off inside the cowling
and draw cooling air through the fins on the cylinder head very effectively
. I could run the
160 HP Lycoming on my Long full throttle for ten minutes on a warm day befo
re reaching CHT limits.Graham
On Wednesday, 24 August 2016, 8:41, "nigel_graham@m-tecque.co.uk" <nige
l_graham@m-tecque.co.uk> wrote:
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 pe
rforms 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 t
he unintended consequence of forcing them to use a smaller diameter spinner
, which exposed the propeller cuffs and roots. These cuffs thrash around du
ring 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 larg
ely 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 aircra
ft reaches flying speed that the apparent wind comes more from the front th
at air begins to enter the vents/ducts and the cooling improves. This is on
e 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 g
ive better ground-running temperatures because they produce a much better a
irflow 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 origina
l Classic position - but maintained the XS forward position. This allowed m
e 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 fa
r back as I can practically get to collect useful propwash and feed the rad
iator 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 cyli
nders 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 mountin
g 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 fligh
t. 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 indefi
nitely at idle on the ground in the summer heat ?
Remi
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=459805#459805
|