Be 100% sure that no air are bleeding out through gaps around your air
baffles! Just a little gab is enough to spoil your day.
Regards Gert
OY-GDS / mono / 914 / 500 hours
Den 05/06/2010 kl. 12.28 skrev Frans Veldman:
<frans@privatepilots.nl>
>
> Gentlemen,
>
> Although my initial cooling issues have been improved upon, I'm not
> satisfied at all with the cooling of my 914.
>
> Now, with increasing ambient temperatures, I have to severely limit my
> climb outs. Cruising is ok. During climb, both the water temperature
and
> oil temperature approach the red line, more or less at the same time.
> Water temperature recovers faster than the oil temperature after I
power
> down. At this time I can barely make it to circuit height and then
have
> to level off, build more speed, and then limit my climb with 200
ft/min
> until I'm in cooler air. The engine has now 32 hours on it, so it
might
> still improve somewhat further, but I don't expect miracles from that.
>
> I had to do something.
> First I made an additional exit in the cowling, under the turbo,
hoping
> to provide more airflow. Whether the airflow in the cowling improved I
> don't know, but it had zero effect on the water and oil temperatures.
>
> Temperatures inside the cowling seem to be ok anyway, no discoloured
> spark plug indicator labels (still bright yellow), no melted
tie-wraps, etc.
>
> My conclusion was that the problem is not in cooling of the cowling,
but
> somewhere in the efficiency of the radiators.
>
> So then I built a new radiator inlet, somewhat larger than previous
one,
> with a lip to avoid digesting the boundary layer and making sure the
> inlet receives ram air, angled straight into the airflow, and with a
> diffuser for which I copied a profile out of a famous book.
>
> It was no improvement over my "free style" sleeker inlet and diffuser.
> None. Very frustrating, as I ruined my nicely shaped and painted
> original inlet for this.
>
> I need to do something, but to avoid ruining again something in order
to
> solve this problem, I need to hear some experiences:
>
> 1) A shroud over the cylinders. I don't have it, but instead I have
two
> naca ducts in the upper cowling, curved down to release air aimed at
the
> cylinders.
> Has anyone ever tried whether the Rotax shroud (or home made shroud)
> makes any difference? Sure, it will cool the cylinders, but does it
have
> any effect over the water temperature and/or oil temperature? Or is
this
> again going to be a loss in time and effort?
>
> 2) In my setup the oil cooler receives exit air from the water cooler.
I
> know there is a "trick" mentioned in the build manual for hot climates
> to lower the oil radiator 2 inches to receive cold air instead of warm
> air, but I didn't opt for this as I don't consider our climate as
> extremely warm, and in winter the oild could actually get too cold.
> Has anyone tried both options, and did it make much difference? Also,
> did it have any influence over the water temperature? Relocating the
oil
> radiator will be a large project, and I fear that after that I will
> still have to limit my climb outs to avoid the water from boiling.
>
> Yesterday on the airfield I took a closer look at the Rotax 914
equipped
> Dimona, which is used by the glider club to tow all day long gliders,
> with full power at 50 knots, in all ambient temperatures. They never
> have cooling problems.
>
> What I saw was shocking. The water radiator is fully exposed to the
> airstream, no diffuser whatsoever, it is just part of the cowling, as
if
> someone took out some skin of the cowling and fitted the radiator in
the
> resulting hole. The oil radiator is mounted in an angle behind a naca
> duct (I was taught that a naca duct does not provide ram air and
> shouldn't be used for cooling a radiator?). Both radiators just dump
the
> warm air inside the cowling! It can't be easier than that.
> Then, at the bottom, the Dimona has a cowl flap which just opens the
> cowling to dump *all* air overboard. If it is closed, all radiators,
as
> well as all cowling ventilation, is blocked.
> How can this system, which looks less sophisticated than our system,
> while violating all rules and knowledge, work so well?
>
> Anyway. At the moment I'm grounded, can't fly like this, and after
> spending a week trying to improve things with zero effect, I'm out of
> options and I'm inclined to leave the airplane in the hangar and find
> another hobby. :-(
>
> Seriously, what should I do?
>
> Frans
>
>
>
>
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