Frans,
I have the 912 set up so I might not know what I'l talking about but...
I had the very same issues for the first 150 hours. Every time it got
hot I was in trouble with temps at their limit. I made the shroud for
over the cylinders. I lowered the oil radiator 2 inches behind the
water, I sealed everything, I made new inlets in the upper cowl, and
still didn't get it solved completely. I then finally lowered the
metal duct down an inch or so, so the bottom radiator reached the
lower cowl without the sealant and bam. My temps dropped 30 to 40
degrees. I believe two things helped in this. The radiators we're
getting more air but the big thing was by lowering the duct it opened
the bottom for escaping air. Not sure if this all applies to you but
if you have the duct up to high close to the muff all you need to do
is lower it. You'l be needing to ad a flap in colder days to get
things in the proper temp range.
By the way the shroud did even the cylinder temps out but it didn't do
much to cool the water or oil.
Jeff R. N128LJ Gold Rush
On Jun 5, 2010, at 5:28 AM, Frans Veldman wrote:
> >
>
> 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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