Hello Greg,

This is off-topic, but I'm curious about the "wing surface radiators". I
have been mulling it over and am interested in anything that you've written
on the subject. I'm building a Lancair ES with a 20b.

Michael McMahon

Hello Michael:

I have written nothing on the subject.  But I do a lot of reading and
thinking "what if we did it this way" or "I wonder if that would
work".   To start us on the road of discussion re: wing surface
radiators try this link to airtalk.org.  The debate gets a little
raunchy over the 5 pages but brings a lot of ideas to the table.

http://www.airtalk.org/1-vt16732.html?postdays=0&postorder=asc&start=0


Then, try the following link about the history of wing surface
radiators, in particular, the Schneider Cup racers, and what they went
thru.  Some neat info.  The book is called  "Race with the Wind
<http://books.google.ca/books?id=JDg0qXuODnkC&pg=PA147&lpg=PA147&dq=wing+surface+radiator+Supermarine+Curtiss&source=bl&ots=delILLQK4W&sig=mWdEhuv462lINSGm0Vzdna1bHEU&hl=en&sa=X&oi=book_result&resnum=1&ct=result#PPP1,M1>"
and gives the technical side of the story.  Special thanks to Paul for
including photos of the Supermarine wing and fuselage in his last post.
Invaluable.

I'm constructing a prototype using 2 sheets of aluminum.  The outer skin
is .040 and the inner is .025.  The inner skin has a diamond pattern of
1/8" dimples all over it at 4" spacing.  When the 2 sheets come
together, with the top sheet resting on the dimples, there is a 1/8 gap
between the two.  I have joined them together at the dimples with Tox
Clinch Rivets <http://www.tox-us.com/index.php?id=16&L=4>, their webpage
gives you an idea of how that works.  The process leaves the outskin
smooth but the inner skin has the punched bump.  Not a problem since
this will be the inside of the wing.  The outside skin will be finished
smooth with primer filler before paint.  Try to maintain laminar flow.

The sheets will be joined at the two opposing sides with ultrasonic seam
welding leaving only the front and back open.  I am attaching small
tubes with "flute holes" at each of these edges to serve as headers.

Hot water goes in one tube, flows thru the gallery, and out the other
side to complete the path.  My test will explore:

   * How fast can a liquid flow thru this design.  Do I need to open up
     the gap, or can it be made more narrow?

   * How much recorded heat loss is due to radiation vs. convection.
     I'll be measuring the Delta T (change in temperature) between in
     and out under various conditions.  However, the most airspeed I
     can simulate is from the back of a pickup truck.  Not really a
     true test of in-cruise flight.

   * I intend to gradually pressurize the unit with shop air to watch
     the thing puff up like an air matress.  How much pressure before
     the flat skins start to distort.  Will the inner skin try to
     distort before the outer skin (which is why I'm using thinner
     metal on the inside).  Will this distortion be permanent or just
     during the pressurization?

   * Is there better heat transfer in flight with a laminar flow, or
     make the surface bumpy and get a turbulent flow?

   * Will the joints and seams hold during all of this?

   * Will the heat transfer be affected if I paint the outer skin?
     What kind of paint would transfer the heat best?

   * How much heat transfer to a liquid container placed against the
     inside skin (simulating a fuel tank).  If I insulate with foam,
     will that stop the fuel from heating up?  Is heating the fuel a
     bad thing?

   * What strength is there in this prototype?  If I build one with a
     curved skin, maybe even a complete airfoil from leading edge to
     spar, with both top and bottom skins with ribs and spar etc, how
     stiff will the surface be?  (I anticipate completely stiff, no
     oilcanning, composite-like finish and strength.

   * How hot will it get inside this "wing"?  Will I have to include a
     blower to circulate air around from the wing root in front of the
     spar, out to the tips, around the tip cap, and back along the rear
     of the spar to the wing root to complete the circuit?  How much
     air circulation is enough?  The entire wing will definitely be warm.

   * How heavy will all of this be?  I can calculate the weight of the
     metal, but what about the coolant.  As suggested earlier, a 1/8"
     chamber will equal about 50 lbs of coolant.  What if I make the
     dimples only 1/16"?  Might even be better *_if_* I can keep up the
     flow rates.  First prize goes to getting the most amount of
     surface area with the least amount of fluid.

   * Do the dimples within the chamber help mix the coolant around,
     like turbulators, or do they just restrict the flow increasing the
     work of the water pump?

   * How strong will this "wing" be?  Will it sustain a bird strike as
     asked earlier?  I suspect a goose would cause massive damage, but
     then you would have much bigger problems than just loss of
     coolant.  This wing will be strong, but flying is inherently
     dangerous no matter how strong we build.

  *  From an earlier question, what about field repairs?  This is
     definitely not a field repair item.  Any damage would need a major
     repair done to the wing.  I have to explore ways to make this
     radiator system a modular unit that can be changed out in sections
     instead of replacing the entire wing.

   * Why not just use a well designed Meredith Effect radiator and
     avoid all the trouble, expense and weight?  I agree that 99% of
     pilots are low-altitude, summer VFR flyers, short hops on
     weekends, etc.  A good radiator is all they will need.  On the
     other hand, my flying is long X-country (1,000+ nm) at altitude
     (FL250) all year round.  I'm trying to reduce cooling drag while
     heating the wings (de-ice).  My original thought was to place the
     coolant rads in the wings with intakes on the leading edge
     <http://contrails.free.fr/engine_aerodyn_radia_en.php>, then
     thought I could tap some of that heat to spread around the inside
     of the wing.  Wing surface radiators is the next logical step in
     the research.  The added weight gain of this cooling system is
     offset somewhat by removing the need for wing deicing equipment,
     whether it's pneumatic boots, or generator powered heating strips,
     or glycol based 'wet wing'.  How much weight at the end of the day
     will determine if it was a good idea.

As I proceed with my tests, I will pass on what I have learned to this
board.  I'm not very quick but I'm determined and thorough.  I hope this
helps, Michael.  My advise is to continue building your Lancair ES as
intended and save the radiant wing for your next project.  This is going
to take me years, not months.



Greg Fleming

London, Ontario, Canada