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

z
Greg,

This sounds like an interesting experiment.A couple more thoughts
from the peanut gallery:

- Any shop air applied will cause the shape to distort.Even with
thick skins.Every structure has springiness/flexibility.How much
so is the critical question.

- Flat skins will be flexible and easy to distort.Curved skin -
like a wing leading edge will be much stiffer and take much more
pressure - as you alluded to.How much pressure the flat section
takes won't really matter as you won't ever use that in a real
structure.

- One obvious thing I missed in my previous comments is that the
pressurized cooling system will apply a force equal to the pressure
times the area.15 lbs/sq-in x 144 sq-in/sq-ft = 2160 lbs/sq-ft (!!).
My guess is that 4" spacing on the rivets isn't close enough.I may
be thinking about it wrong, but I think each rivet is responsible for
16 sq-in of the container.15 lbs/sq-in x 16 sq-in = 240 lbs.Is an
1/8 in rivet good for that much working load?15 lbs is actually kind
of low pressure for the system.Probably want to build it for double
that much.I think this illustrates the value in using tubing to
contain the pressure.Doing so means the skin doesn't carry the
considerable load due to system pressure.

- I had thought that it might work nicely to roll chordwise beads in
the inner skin for the coolant to travel through, and then rivet along
the edges of the beads.These beads would in-essence form ribs for
this section of the wing - adding significant stiffness to the
section..Like the Thorpedo, but on the inside instead of the
outside.Although from a cooling performance standpoint, putting the
rolled beads on the outside skin would probably improve things quite a
bit.

- How about adding an external diffusion scoop to the wing root -
inside the propeller arc, and variable sized outlet somewhere outboard
on the wing - further aft.In hot weather and low airspeed, leave the
flap open, causing outward spanwise flow through the inside of the
wing - increasing cooling, and in the winter, close the outlet cause
the air to flow around the inlet instead of through it.


Regards,

Matt-

Hey, Matt, thanks for the comments.I'm looking at my drawings
and think, at 4" spacings for the rivets, they will be responsible
for holding 8 sq in (2" in all 4 directions).If my prototype is
going to hold any pressure, I should double up on the spacing, maybe to
every 2".

I've been trying to avoid using tubes attached to the inside of
the skins.Yes, the tubes will be great for holding the pressure
but will provide for little surface contact to the outside world.
That's why I thought my double-skin idea would give the most surface
area for the least amount of fluid.Aren't there products on the
market that allow the coolant to operate at much higher temperature
 without boiling? How about Evans NPG??

What kind of distortion happens in a regular tube/fin radiator
 with equal pressure loads.The cap is normally set to vent at 15 psi,
 so the tubes can handle at least that??The tubes are not round but
elongated, flattened out.Do they try to "puff out" at high pressure
or are the fins holding them from distorting?

I like the idea of small inboard air intakes controlled by variable
size outlet.However, my aircraft design is a pusher.I won't be getting
a lot of propeller wash on the ground, but still a good idea for controlling
 the temp inside the wing cavity in flight.

Good questions to discuss prior to any testing.

GregFlemming

Why rivets?

Spot welding seems like an ideal process for joining the skins.

-Chris