As loyal viewers may recall in my first flight two weeks ago my
oil temps were higher than desired. So, after using the fine
guys and gals here as a resource and some fact checking I
determined I was measuring the oil temps at the wrong location. Since
coolant was measured coming out of the engine, I assumed the oil
would be measured coming out too. Wrong.
So, over the last two weeks I moved one of my oil temp sensors location
after the
coolers just before it goes into the engine.
Ideally, I would have made it to the airport really early while still
somewhat cool
but my hostess and I lingered a bit this am. Then I had to drive
home to check on mom who is fighting cancer.
I finally made to the hangar about1:30pm<x-apple-data-
detectors://0. Yep. Hot ad hell. Called the tower on the phone
to let them know intent. Same as last time. Desire to climb to
about 1700 and fly around the field testing base flight and engine
characteristics.
I did a slow preflight. Cranked up the engine which cooperated nicely.
Taxied from my
hangar and called tower on the radio. Was cleared to Echo on 35L.
Proceeded to echo.
Ran-up. Temps were sweet at about 160 coolant and 140 oil. Tower
informed
me a C-130
was on final and asked how long I needed on the runway. I told
him I could roll and go. I was cleared for immediate take off
and to track the C-130. I applied power, lined up and added more
power. Leaned the mixture slightly and power came in. I had
coursed the prop a bit as to not again reach 3100 rpm. Airspeed was
slower to build but was developing. When I hit 70 kts I pulled
back and started flying. Wow. It was much more sluggish today
but I was climbing while maintaining around 90 kts. I flattened
the prop a bit and climbed a bit better. The prop was turning
about 2800 rpm now. Turned to crosswind and kept climbing. Turned
to downwind. I was around 1500 on downwind. Well, kinda. My
altitude was all over the place between 1400 and 1700. Really
bumpy today...not too surprising with ramp OAT showing 109. Hey, in
Houston, ya gotta test in the heat cuz ya gonna be flying in the heat.
I then started flying around in circles. Checking engine
parameters a lot while flying the airplane. Good news. Neither
the oil or water ever broke 203 that I saw. That was only on
climb. I seconded from 1700, this time on purpose and noted the
decreasing trend of both oil and coolant temps. Pressures were in
the middle of the green bands. EGT's were green too. The engine
sounded strong and steady.
I turned right, I turned left and low and behold, the dang thing turned
almost like
it was designed to do so brought back power and it actually kept flying.
Okay, the Dynon is telling me I have been FLYING working on 20 minutes.
Time to land.
Called tower and cleared to land but watch the jet wash of the
NASA T-38 taking off and the C-130 doing touch and goes with the
option. Damn, busy airport. I lined up MUCH better with the
runway this time. Nice shallow approach just like the folks at
the factory showed me in Florida back in April. A bit fast as I test
some throttle response. 120 on final slowed to 90 at the
numbers. Pulling power to a bit above 80 and settling nicely but
a little fast. Pulled nose up SLIGHTLY. Whoa, floated up. Engine
to idle and settled to the runway only a little hard, but pretty
smooth. No bounce. Rolled out. Exited Delta. Checked temps. Damn.
Oil at 165, coolant 175. Nice.
Taxied back. Temps played nicely. Shut down engine and no gushing
or hissing sounds. Big smile on pilots face
The engine even started back up a few minutes later ;-)
Not a bad flight, if I do say so myself. Now to finish my test
cards to help remember more stuff such as map relating to RPM etc.
Chris Barber
Velocity N17010
Turbo rotary
You make me jealous Chris. Good work. I have been so busy that I haven't
been able to work on my plane for almost 2 weeks now. I sit for my
Instrument at the end of this coming week, and I am hoping that in
the next 2 weeks I can work on mine for 1 or 2 days per week to try
to catch up.
Fly off your 40, and enjoy the plane!
What turbo did you use? Soon I will be mounting the ancillary
parts on mine, and I will be installing a turbo.
Kevin Alderman
These first flight experiences is really an inspiration to me when
I have still a long way to go. I've forwarded your first experience
to all my friends and relatives changing the Subject heading to "My
time will also come!" I got cheers all around!
Pierre
Future Vision Pilot In Command!
Pierre Swanepoel
Logistics Co-ordinator
GoReefers Logistics Cape Town
You did not say what you mean by high oil temp. I think oil should be
around 195- 210 min., enough to evaporate any moisture from the oil.
In your hot, dry climate, you would have less problem than I would
at the north in the winter. I would be comfortable with oil temp around
230-240F. Oil temp can exceed the coolant's temp boil limit,which is
256 F at 50/50 mix and 15 PSI, unless you are using Evans Radiator fluid
which is 375 F, it also depends on what oil you are using. My Chevron
book says the flash point of aviation oil is 450-478F, best you stay
well clear of that. As oil get near its operating limits, the useful
life expectancy of the oil decrease.
Oil at a higher temp transfer heat better than at lower temp. The
key is the difference in temp with the cooling air. It will
stabilize at some point, and if you don't like that point, you will
have to get a bigger cooler, more oil capacity, or better ducting or
a combination of each.
You had it right the first time measuring oil at the hottest point.
All fluids have limits. Of course the temp would drop if you switch the
probe as you did. If you dunk it into the fuel tank, it would be
lower still ! The idea is to know the hottest temp the oil is
subjected to, not to make you feel good. For overheated oil have all
kind of nasty effects. Tony Lam
We don't need to use aviation oil. Synthetic oil like Mobil 1 can
function at a higher temp. Idmitsu makes a synthetic rotary engine
oil specifically for the Mazda rotary.
Paul Lamar
Petroleum oils are a witches brew of hydro carbons. Some are light ends
that
boil off at a fairly low temp. Some do not boil off until considerably
higher
temps. A 10W-30 oil subjected to 250F will boil off or evaporate the light
ends and it will tend to become a 15W-30 or 20W-30 oil. Also affecting
the oil
is the close tolerances and rotational speed differences of the internal
components. This tends to shear the viscosity improves that make the 10W
base
oil act like a 30 oil when hot. When this happens the oil looses its hot
qualities and becomes a 20 or 25 oil. This all leaves it as a 15W-25 oil
for
example. When doing oil analysis on used oil, this seems to be a common
result
that comes back. Synthetics or more expensive petroleum oils that have
better
additive packages are more resistant to this. Synthetics are blended of
single
hydro carbon base stocks. The blend gives a lot of the qualities required
of
the finished product combined with high quality additive packages that
stand
up better and longer. That is why synthetics are more expensive. Remember
the
Fram filter ad from years ago, "pay me now or pay me later". Av oils fit
the
same idea.
For conventional oils, I would feel much more comfortable with a max oil
temp
of about 210 - 220F. This leaves a better safety margin to the 250F start
of
oil break down. The temps measured are oil pan or out to the cooler. The
temp
at some point in the internal components like cylinder wall to ring
interface
will be higher. The bearing temps can also be higher. Many of the
industrial
engines now monitor bearing shell temps to catch imminent failure before
it
costs big happy cabbage. These use a thermocouple on the steel shell
backing,
so the wear surface can be hotter at the point of maximum bearing load.
This
is also where the shear happens.
Dale Davies
Just a simple question on oil sumps. As we have to manufacture our own in
any case to
carry more oil or in my case to incorporate the nosegear. Wouldn't
cooling fins,
added to the exterior of the sump, aid in cooling? It seems to work for
electronics.
Pierre Swanepoel
Its been tried over and over again without much effect. It all depends on
contact
surface area of the metal between the oil and the air. The surface area
in a heat
exchanger is 10 or more times the surface area of a finned pan. The stock
cooler has
at least five tubes about 3 inches wide and about 20 inches long. That is
120 square
inches for both sides. There are five tubes. 600 square inches. Soldered
to the tubes
are 100's of tiny fins each about 3 inches wide and .5 inch high each
with an area of
1.5 square inch for a total of at least 750 square inches.
The overall heat transfer coefficient for a wall or heat exchanger can be
calculated as:
1 / U A = 1 / h1 A1 + dxw / k A + 1 / h2 A2 (1)
where
U = the overall heat transfer coefficient (W/m2K)
A = the contact area for each fluid side (m2)
k = the thermal conductivity of the material (W/mK)
h = the individual convection heat transfer coefficient for each fluid
(W/m2K)
dxw = the wall thickness (m)
http://www.engineeringtoolbox.com/overall-heat-transfer-coefficient-d_434.html
Here is an oil pan with a heat exchanger built in.
Paul Lamar
Another factor is that, since it's gravity fed, the oil isn't being forced
through
the sump/pan very rapidly, so it's difficult to achieve the beneficial
turbulent flow
along the heat transfer interface. It obviously does some heat transfer,
but
compared to a pressurized cooler with manifolds (tanks) on each end, I
don't think
it's an efficient place to put metal from a weight and volume standpoint.
Regards,
Matt-
Good point Matt.
Paul Lamar
Chris,
It would be nice to see you and your Velocity at Rough
River for the Canard Fly-In September 28th through 30th this year. Each
year we have more Velocitys show up along with Cozys and Burt Rhutan
designs. It would be great to have you there too.
James Ealey
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