Hi, all....just wanted to share the results of my recent experiment.
Dan
Cruger recently suggesting adding VG's in front of the NACA duct, as
did
several other canard builders on another list. I decided to try it, and
here are the results.
First, let me provide the latest numbers from today's flight
immediately prior to the addition of the VG's.
With an OAT of 85 degrees, highest water temp durning climb was
210. Level flight provided a water temp of 205 WOT. (Oil temps never
exceeded 190 at any configuration)
I landed and installed the thin aluminum VG's with 3 rivets each,
and took off again. Water temp during the climb maxed out at 190, and
took much longer to reach those numbers. I raised the nose to climb at
90 IAS and the temps slowly climbed to 195. I dropped the nose to climb
at 100 IAS and temps came back down to 190. After leveling off, water
temp was 180 at WOT. At approximately 3/4 throttle (cruise), water
temp
was stable at 172 at 3000 AGL. After throttling back for descent, water
temps stabilized at 160 where they remained until landing rollout.
During taxi back to the hangar, temps rose back up to 182. Highest oil
temp during the flight (at any configuration) was 182.
It was a very humid, oppressive day. We were sweating just
standing
around. It would seem that the VG's had a positive influence on the
cooling efficiency. Here is a link (with pictures) showing the mod
that
I shamelessly copied.
http://users.telenet.be/westlandfamily/cozy/vg/index.htm It also shows
an oil flow analysis test. I don't profess to having knowlege regarding
how the VG's trip the airflow into the NACA duct... All I know is that
it turned my marginal cooling into a success story, and that's all I
can comment on. I should note that I did not retract the nosewheel, so
the plane had more drag and did not attain higher cruise speeds, but I
was trying to test it in the worst possible conditions, ie slow climb
speeds and nosewheel still deployed. I suspect that temps should drop
a
few more degrees once the nosewheel is retracted and I hit higher
airspeeds at the same power settings, but this is assumption, not
backed
up by actual test results. (I will raise the gear on the next flight).
I finally consider my cooling system experiments to be completed
(happy with the results), so I can now move on to other small details
necessary to finish the airplane (such as wheel pants, paint, etc). I
still need to replace my 7 psi radiator cap with a 22-24 psi cap, but
otherwise, I think I'll just go fly and enjoy the fruits of my labor.
Many thanks to all who contributed ideas and advice regarding my
cooling
system. I can finally fly without staring at the temp gages. A very
happy Paul Conner in Mobile, AL
I certainly would not draw any conclusions from that test.
Too many variables. Why don't you build a water manometer
and measure the air pressure in front of the rad directly?
Paul Lamar
Very interesting, thank you for the detailed report Paul.
After thinking about it I realized that humidity should help cooling as
the air with more water vapor means more cooling mass for a given
volume, right?
Hans
Probably correct but I am not sure about that. Humidity does not
help a person cool off as sweat is less likely to evaporate.
When water evaporates it absorbs a lot of heat. That is the
reason that dribbling water over your heat exchanger works so well.
In this case the outside of the heat exchanger is.. or should be.. dry.
This is one of the many variables I was talking about. I am sure
many things changed between the time Paul took off, landed, added
the vortex generators and took off again. Little things like
angle of attack can make a large difference to a NACA duct located so
far back on the aft fuselage. One can be easily fooled into thinking
one made some improvements when further experience will show nothing has
changed.
CUT
Hi, Paul....I failed to explain the test method we used to evaluate the
VG's. First, we cut the VG's to length (aluminum stringer angle material)
and marked the bottom of the fuselage with Magic Marker where they would be
attached. We pre-drilled 3 holes in each VG and into the bottom of the
fuselage for the 1/8" rivets. I then took off and flew the first flight
without the VG's and recorded the above temps. I landed, and while one guy
held the VG's in place, my brother (on a mechanic's creeper) quickly riveted
them in place. I stayed in the aircraft on the taxiway. I was airborne
again less than 10 minutes after landing. I then recorded the second set of
numbers. I made an honest effort to keep the aircraft climbing at the same
airspeeds and rate of climb on both tests. The only variable I could not
control was that the engine/cowling was heat soaked right after the first
flight (without VG's), so temps at takeoff were a little higher on the
second flight (with VG's) due to heat soak and taxi time. However, the temps
on the second flight were much lower than the first flight.
Yesterday, the radio said the Mobile temps were 91 degrees, so I
decided to play hookey and see how it worked on a hot day, and rushed out to
the airport. When I took the active runway, the OAT was 90 degrees. Here
are the numbers I observed...
OAT 90 degrees F
Water temp on Climbout.......190F
Water temp level, WOT........181F (3000' AGL)
Water temp level, cruise........173F (3000'AGL)
Highest oil temp...................182F
I flew it again today and observed the following numbers...
OAT 85 degrees F
Water temp on climb out.........190F
Water temp level, WOT.........180F (3000'AGL)
Water temp cruise..................172F (3000'AGL)
Highest oil temp....................180F
Not sure why, but very little difference in temps for the two days. I have
not had temps like this since flying it in the winter, so something is
working. I cannot explain why it works....I can only provide the data
observed following the VG installation. (Just my conclusion, based on temps
only). Take care. Paul, love my rotary, Conner
Totally amazing repeatability for widely different ambient temps.
Are you sure some instruments are not stuck someplace? :)
The last pieces of the puzzle are a few numbers.
Climb rate?
Test gross weight?
Top speed.
Size of the radiator core?
Stock Mazda oil cooler. Yes or no?
EGT's?
Mixture monitor readings if you have one?
BTW keep flying those hours off. Hope to see your airplane
at OSH.
Paul Lamar
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