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On 07/29/2016 11:41 AM, Roland wrote:
> The oil/water exchanger is generally a brilliant idea, but only
> with ample cooling reserves, which I don't have unfortunately.
Just a few notes:
After a lot testing it became obvious that the whole single problem of
the Europa cooling is that the radiator is way too thick, so air won't
flow easily through it. (It is NOT a cylinder wall cooling problem
like some people seem to think. Although you could get a little bit
more margin by blowing more air over the engine, it is not an
efficient solution. It is like driving your car with a clogged
radiator, and then discovering if you leave off the hood that it will
improve the situation a bit. It works, but it is not the correct way
to do it).
This became quite obvious when I observed the Dimona's towing gliders
at my homefield, they have exactly the same engine but tow gliders
during a hot day with full power climbs at low airspeeds, without any
problems.
After going through the whole process of lowering the oil radiator,
widening the dog house exit, making more holes in the cowling, I had
still not a very good cooling.
All problems were immediately solved when I kicked out the old coolant
radiator and replaced it with a thin radiator just like they use in
Dimona's and other commercial Rotax driven aircraft.
So, what I did was:
1) Close the two "eyes" in front of the cowling. They don't serve any
purpose. Also close the "gills".
2) Put a thin radiator in the "belly" of the cowling. The air exiting
the radiator is dumped "as is" into the cowling, and aimed at the
bottom of the engine (and exhaust tubes and damper). It helps cooling
the bottom of the engine where the oil collects and of course it also
helps if the heat from the exhaust is blown away before it can heat up
the engine bay.
3) Cooling the oil is done with a heat exchanger where the oil heat is
transferred to the coolant. This has several benefits:
a) The oil temperature will be slightly warmer than the coolant,
exactly what you want.
b) The oil will be warmed up more quickly when you start the engine.
c) If you get the coolant temp right, the oil temp will be right as well.
d) It doesn't need any airflow, the whole setup is straigtforward.
4) I took away the doghouse and cowling exit and replaced it by an
almost level flap. Typically during flight the underside of the flap
is only 1cm(!) lower than the rest of the airplane. That's right, the
cooling is now so efficient that you don't need the doghouse at all
but just a sleek 1cm "doghouse" is sufficient.
5) I rerouted the exhaust through a "tunnel" ending short of the end
of the tunnel. This will create a ventury which will suck air through
the tunnel. I never tested this but it is assumed that this will help
the airflow through the cowling and it also lowers the drag of the
exhaust.
The result:
1) Enough cooling for any circumstances. Cooling is no longer an
issue. I can idle the engine unlimited time while on a mediterran hot
tarmac with temperatures around 40C. I can climb at full power with 60
knots airspeed as long as I want. There are no cooling problems at all
anymore.
2) Way less drag. The doghouse is gone, with its associated vacuum
hole and turbulent air dragging behind it. Less air is spilled for
cooling, so less air is disturbed. I estimate that I gained around 8
knots of speed by this conversion.
> As for the efforts with the Dutch CAA - there isn't a Europa
> Trigear flying with the Woodcomp SR 3000 W AFAIK (Frans Feldmann
> has the 2-bladed). For the "glijkstelling" this is required IIRC.
So you can have the 2-bladed prop because I (Dutch) have it already. A
2-blade prop is more efficient than a 3-blade prop, just like a single
plane aircraft is faster than a bi-plane. Leading edge is costly. The
less "leading edge" you have racing around bumping air molecules away,
the less drag. I did not find any disadvantages of having a two blade
prop, although it is said that carb balancing is more important. I
keep my carbs balanced anyway so for me it is no issue. Oh and it
saves some 4 Kg of gyroscoping weight at the nose.
Because the two bladed prop is a little bit longer, I extended the
nose gear 5cm to restore the ground clearance, but probably it is not
really necessary.
I would have invited you for a look at the PH-DIY, but I'm sailing
around the world (I'm currently in Tahiti).
Frans
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