Hi Frans
Sounds like you are getting off to a good start.
A few points to make, and a few I disagree with
**Ask any Rotax distributor in the know, they want a 914 to run well below edge
of redline for longevity. Not too cold, but near the lower end is preferable.
I think we can agree on this. Lockwood loves the temps on his aircam in the air,
but hates them in water making a long taxi (twin 914 or 912S pusher)
**Now here is where I don't agree with you. True there is a big fan upfront, and
seems foolish to also add little fans to unconstipate the cowl. In a properly
designed cowl/cooling system I agree. I don't believe the europa has a properly
designed cooling system. I don't think it is too too draggy, but taxi on ground
and climb it is for certain less than ideal. Unless you increase drag more
than desired all the time, I rather dump some amps to do the deed on ground
and in climb than engineer an entirly new system. It also gives a side benefit
of being able to cool down cowl after shut down. Europa uses a smaller frontal
area radiator than many other Rotax installiations with same total area. This
means you need a faster flow. In cruise you have that faster flow, but let
me see you make that fast flow on ground and in climb? Lets see how Diamond
works
at 50 knots with Rotax radiator? I forget, perhaps Karl?? used a larger frontal
area radiator with good results i think with intake similar to yours. Anyway
I am installing a fan that can in-fact create a lot faster airspeed than
the prop in those configurations ever could by themselves. You make a pretty
weak
case that temps are fine in cowl because you don't see any plastic discolored.
My gut feeling is after a hundred hours you probably will. Plastic takes
a while before it becomes discolored and brittle in many instances. Measure
please
so there is no doubt. I bet you find stalled air not making its way out as
fast as you would like. The exit area of Europa is less than ideal, especial
when you dump intercooler air in there. I disagree that heating cowl air is a
good thing. Yes on fast glass, or a P-51 you can accelerate air faster and
easier
to airspeed on exiting and decrease drag a bit. That said you could close
all intakes or exits on cowl and reduce drag a little more, of course this does
not benefit cooling which is an issue. If cooling was not an issue, then drag
reduction is a good thing to chase. On Europa you will almost for certain heat
the da!
rn engin
e up exhaust. There is not a trivial amount of BTUs given off from the exhaust
and turbo, it can easily heat motor where through water, oil, air and gas
(enough
carbon monoxide per Rotax reccomondations) cooling, will not enough to lower
the temps to liking. There is enough intake air charging through Europa cowl,
yours included where if you are heating it, it means air is getting constipated.
I think it is very safe to say the discharge of a typical stock XS trigear
exit air or your plane is nowhere near as good a design as a P-51 or Gilles
exit design. Measuring temps and pressures is best way to make informed
decisions.
Be more concerned on ground and in climb than in cruise. With top cowl off
there is not much in way of constipation. The two gill fans are easy to try,
it semi replicates having the top cowl off. The motors are probably under 10
bucks for the two, and props and hubs about the same. If you find they lower
temps and pressures leave them in place. If they do nothing then take them off.
Same goes with rich switch. If you can climb between 85 and 100% power and lower
temps, then that is a good thing. Colors of spark plugs running mogas is
not too reliable of an indicator. running 100LL is better, but you would need
to shut down after a run at 100% and 115% to measure to get most reliable
reading.
Carbon monoxide the most accurate and reliable method. True burning a tad
more fuel with rich switch, but way way easier on motor until you can verify
with carbon monoxide detector. Also a good thing to fool with, if you see at
100%
power when you richen the EGTs first go up before they go down, or even stay
still for a bit, you are either lean of peak or at peak. A leak where you have
a slight high EGT can be adressed too. Alcohol in gas will lean mixture compared
to fuel with no alcohol. Type 64 carb on 914 does not compensate mixture
via a 02 or carbon monoxide sender, they are fixed. Run alcohol, will run
leaner.
On a car run more alcohol, will compensate if it uses a o2 sender system.
Anyway unconstipating air will most likely benefit your cooling. Now if you are
thinking you can use big fan upfront to cool in worst cases you will see and
have motor running cool enough, I am all ears. BTW against popular belief
according
to factory before shake up, gills do in fact evacuate air from cowl in
climb. Flying with doors prove that. also allow better cool down upon shutting
motor off.
In your case I think first is unclog the exit of the radiator by moving the oil
radiator.
As far as the water cooling goes, make something pretty temporary, this way
instead
of overheating that is pretty terrible on motor, you can cool with the water
till you figure out. Same goes with rich switch, same goes for gill fans.
On a 85F day at sea level, I want to be able to take off at 115% power and climb
at best angle of climb for 30 seconds and then best rate of climb in fine
Airmaster
pitch for another 3.5 minutes, then 100% power till I get to 18K near
gross and have temperatures happy. I also want to be able to taxi in 85F for
longer
than I care for and not be able to take off, but have temps at a reasonably
low level. Thats is my goal.
Have ability to cool worst case, then oil thermostat to keep oil temps warm
automatic,
and have reversible radiator intake duct to act as a cowl flap, constipate
amount of air flowing through.
Good luck, please keep us up to date.
Ron Parigoris
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