The first test created more questions than answers
and much work to do. Here is my development log entry for the
flight.
Tracy
(8-15-04)
Flight test report on Renesis engine installation,
N84TC
OAT 88 90 deg
Humidity 90+%
Pilot impressions:
Takeoff done with engine warm (~ 155 F) but water
Temp was 207 on first check after rotation. Reduced throttle and orbited SB for 64
minutes at ~ 1000 ft. MSL. Engine
very smooth with low cockpit noise level. Water temp slowly fell to 195 197 at
fuel burn of 5 5.5 GPH. Engine
RPM was 4300 4700 during flight.
Very brief (few seconds) full throttle test yielded only 5800
rpm and engine did not feel strong. MAP appeared to be limited to ~ 28 Hg.
Water temp immediately climbed to ~ 205 and power was reduced. Oil pressure continued to read 100 PSI
(full scale on instrument) as it has during ground tests. Engine builder used 3rd gen
rear pressure regulator and it has been my assumption that this was normal for
it. Reset oil pressure high limit on engine monitor to 102 PSI to get rid of
flashing alarm. Oil temps were
stable at 185F during entire flight.
Normal landing with engine temps falling rapidly during final
approach.
Post flight engine check (engine still
hot):
Gear drive had normal system
lash
Turning over engine w/ prop, engine felt tight,
higher friction than previous checks.
Rotor compression felt normal (very good) but feel
was hampered by engine friction.
Smell test through cooling inlets: Aroma was very different than earlier
engine installation although no sign of anything bad.
Significant data:
Air temp delta on right side rad was 80 85 deg
F
Water temp delta: 20 25 F
Oil temp delta: ~ 30 F
Oil cooler air temp delta was ~ 45 - 50 F which was
normal at the low power setting being tested.
MAP at WOT appeared to be 1.5 2.0 below
atmospheric.
Analysis:
High coolant temperature was very disappointing as I had expected much
better cooling with the improved diffusers. Reasons for the high temps can be
surmised by delta temps above. The
high air temp Delta would indicate one of two things:
1.
higher coolant temps indicating more heat rejection,
or
2. Lower
airflow through rad.
The coolant temp was higher but only marginally (10
deg after stabilized at 195) This
would not account for a 30+ deg increase in air delta. This leads me to believe that reduced
airflow is the cause. The
diffuser on this rad cannot possibly (?) be worse than before so my guess is
that the greatly extended duct divider that separates the oil cooler duct from
the rad duct is having an adverse effect.
Oil cooling was not a problem and delta was in normal range so it was not
hurt by the divider and may even have been improved.
The water temp delta would indicate that the water
flow rate is less than half of the previous value when deltas were in the range
of 10 12 F. Two possible
causes come to mind.
1. The
coolant manifolds I made are too restrictive.
2. The
water pump design is less effective than the 2nd gen
engine.
1 was a concern even while I was building them. I thought they would be adequate because
the coolant outlet arrangement does not appear to be any more restrictive than
the previous setup. OTOH, the inlet setup could be significantly
worse than before. It has 90 degree
fittings which could be a problem.
The water pump design is the same as the
3rd gen 13B which looks crude by comparison to the 2nd gen
but has evidently been adequate in the auto racing environment. It may require a much cleaner coolant
path in order to achieve adequate circulation. Or conversely, the 2nd gen
pump may be much more tolerant of restrictive coolant
paths.
Oil Pressure
The 100 (+?) psi oil pressure is a concern after
learning from the engine builder that the 3rd gen oil pressure
regulator (presumably equipped with a Renesis regulator spring) is supposed to give pressure in the range
of 70 85 psi. This would indicate
that the pressure is being regulated not by the rear regulator but the front
pressure relief regulator which does not become active until 150+ psi. As I write this, I decided to
check the Racing Beat Tech manual for info on oil pressure. According to their chart, the 93 -95
rear pressure regulator is set at 110 PSI !. This leaves me with no firm conclusion
about the oil pressure readings.
Engine builder later confirmed that he had pressure
spec wrong. 3rd gen is
specified as 110 psi. A
3rd gen car racer also said that his oil pressure runs 85 95 psi
hot. Off scale when cold. Have canceled tentative plans to pull
the engine for this problem. I
would still prefer to have a lower pressure regulator and will do this if I have
another opportunity.
Low MAP
This problem is probably due to the relatively long
and tortuous path between the NACA inlet and throttle body. There is over 4 feet of 2.75 Dia.
Aeroduct (SCEET?) between the two.
I was concerned from the start that this stuff would cause a pressure
drop. It will have to go. Many more hours of fiberglass work
required to fix.
Did prop pull-through test of engine feel and it
was same as earlier tests prior to flight test. Compression of engine when pulled
through in reverse is impressive.
Confirmed that the air temp sensor behind right rad
was accurate. In view of this I
have decided to cut the duct divider back to near its original position and
re-test.