Graham;
I do have a few comments from my experience here in Florida. I do not have a
magic procedure to stop the overheating, as we have accumulated over 500 hours
and I still have not found the magic bullet to the problem.
My biggest problem here in Fl is ground running. On a long taxi to the active
runway, or if the controllers are slow in releasing me to the active, I see cyl
head temps reach 240 degrees F. In the summer this is about max 10 to 15 minutes
of ground running. This is the temp that I know I'm going to get coolant
venting on the takeoff run. I've learned that at this temp I only run the engine
to 5500 RPM to keep the turbo from going to full boost on take off which keeps
the heat down, and as soon as I get airborne I flatten out the climb profile as
much as possible to get the max amount of air through the tunnel to the
radiators.
One of the first things that I did was to take yarn strings and attach them all
over the front of the cowl. I also tufted the inside if the tunnel. At this
point I had a stock XS cowl. We then started the engine to observe the flow
pattern of the tufts. In the area just below the spinner and down to the top of
the tunnel, the tufts were pointed straight across in same direction the prop
was turning. In other areas the tufts were pointing straight up, but the
biggest surprise was the tufts just inside the tunnel. They were pointing OUT.
The air was so turbulent in this area that very little was actually going into
the tunnel.
Our fix was to remove the lower cowl, take some blue foam and glue it behind
the lips of the intake. we then sanded the foam so that there was a ramp from
the inlet to about 3 to 4 inches in the intake. This smoothed out the airflow
and air was flowing into the tunnel.
In the build process we had installed the oil cooler about two inches lower than
the water radiator. We then closed the small gap at the bottom of the oil
radiator, as well as sealing all gaps at the sides and tops of the radiators.
All air must go through the radiators.
We also took a look at the exit air from the engine compartment. One of the
restrictions we found, when looking up to the engine compartment from the
bottom of the aircraft was that the top of the tunnel just behind the radiators
was blocking some of the exit air. We cut the aluminum back to about two inches
---From the oil radiator. This allowed air to flow more freely from the engine
compartment.
It has been an on going experience, we have made improvements in some areas but
have a long way to go on the ground running side. We are able to climb at 100
kts to 17.500 and temps are stable at 230 degrees F during the climb. In normal
cruise at 5300 RPM 33 inches MP our cyl heads temps are 190-200 degrees F and
oil temp is 190 degrees F.
We are also using 80/20 mixture of glycol to water. The reason being that we get
a higher boiling temp with this mixture.
We still have a few things to do on the ground running side, but time
constraints have put that on hold. The building of our RV-7 is taking most of
our time for now.
One of the boys in Florida
Jim Brown
N398JB
Graham Singleton wrote:
>
> > wonder if any of you flying at high ambient temperatures 30 degrees
> > Celsius +
> >have any bright ideas about keeping the 914 turbo cool on climb out - 1'm
> >finding
> >temperatures creeping up past 120 degrees soon after take off which some
> >what limits my immediate climb - it returns to 106 - 112 on cruise.Any
> >hints tips
> >would be really appreciated!!
> >
> >Mike Toft
> >ZU CTG Trigear /914/Airmaster Prop - test flying!
>
> Mike
> The engine will run hotter when it is new and tight, after break in it will
> cool down a little.
> remember that if your coolant is 50% water it will boil at 115 deg
> C (129deg at 1
> bar)
> Check also That the coolant collector bottle has a good sized vent to
> overboard. You don't want glycol all over the windscreen.
> Check for good sealing around the radiators, you must force all the cooling
> air to go through them, not around the sides. The boys in Florida are
> probably the best people to talk to. Jim Brown, Jim Nelson? Bob Berube if
> he's not too busy
> Graham
>
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