Looks good. Use two back to back in a counter cross flow configuration
  on the right side of the engine.  I think a single 10 inch diameter inlet
  would work OK if you have a nice set of cowl flaps you can open
  to suck the air out the back side through the right side of the
  cowl.  Keep the oil cooler as is on the other side.

  Pointy noses are over rated as far as drag is concerned :)
  Paul Lamar


  Paul,

  I have a spare cowl which has dual 7" inlets (original cowl has 5.5"
  diameter inlets).  I would like to plumb both sides to the water radiator
  and then add a small chin scoop for the oil cooler.  I calculate the area
  for the two 7" inlets at 77 sq. in.  Assuming adequate exit area, do you
  think that 77 sq in would provide enough cfm to cool 350 hp?  I was told
  that I should have between 20% and 30% inlet area to radiator face area.
  If
  so, then 77 sq in. is not even close.

  Mark S.

  Kind of on the shy side. Also there will be some losses plumbing
  the right side over to the left.
  Here is a suggestion. Use the right intake and the lower center for the
  rad and the left intake for the oil.

  Paul Lamar


  Paul,

  Yes, that would probably work out better, especially for routing the
  plenum.  And it could be sized as necessary.

  Let me ask this.  I've seen some a/c with a cowl flap on top of the cowl,
  just aft of the spinner.  I understand this is a low pressure area,
  especially during climb mode.  I have considered trying that since my
  water
  radiator is directly below this area.  Once up to altitude and into cool
  air, it could be closed.  Any thoughts?

  Mark S.

  That works  for an updraft air cooled engine
  but hard to take advantage of with liquid cooling
  as a lot of stuff like the PSRU gets in the way of the exit
  flow. The internal geometry is just not favorable.
  However it would probably help your current
  configuration as it would lower the entire air pressure
  and temperature in the cowl.

  Here are some CFD's from Peter Garrison. The blue is dynamic
  pressure. At the aft end side of the cowl right in front
  of the wing is an ideal place for a cowl air outlet.
  A large flap there on the side of the cowl would work
  wonders for cooling.

  IMHO right now your rad is being affected by the
  high heat under the cowl as well as some radiation
  from the exhaust. Increaseing the air flow through
  the cowl will reduce the heat the rad is subjected to
  of course.

  It is always better however to duct cool air directly
  to the rad and shield it from internal cowl temperatures.
  A one degree F reduction in temperature the rad is subjected
  to is a one percent improvement in cooling. The reason for
  this is the temperature difference between the cooling air
  and the rad being only 100 F with 200F water temperature. The
  water temperature cannot get much higher than this as it would
  boil. In an air cooled engine with the heads running at 400 F
  the rule of thumb is more like one degree cooling air
  increase is worth  only .3 percent reduction in cooling.

  You need to get some actual static pressure numbers on
  various areas of the cowl using a water manometer. It is possible to
  state  a particular area is high or low static pressure but one needs
  to know how much relative to dynamic pressure.

  Send me the dimensions on the width and height
  of the fire wall and the length of the cowl from firewall to prop flange.
  I'll do some 3D's suggestions of the internal cooling ducting
  Also consider using a 16 inch diameter spinner as that results in more
  cowl volume for internal cooling ducting.

  BTW IMHO with all due respect Peter Garrison missed a point about
  air cooled aircraft engines in that most are designed for down draft
  cooling with the hot exhaust part on the bottom and the cool part
  on the top. Franklin discovered, back in the early
  1930's, that it is best to have cool air go over the
  cool part of the engine first and then the hot part.
  Most downdraft air cooled engines use this configuration.
  This is the same rational used on the counter cross flow
  heat exchanger. It maximizes the average temperature difference
  over the parts to be cooled. The rate of heat transfer is
  directly related to the temperature difference.

  Paul Lamar
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  Paul,

  Peter Garrison's a/c is the one I was thinking of when I sent my previous
  post.  If I understand the pressure graph correctly, the blue shading is
  the
  highest pressure, green is mid point, and red is the lowest pressure.
  This
  is where I got the idea that just aft of the spinner would be a good spot
  to
  put a cowl flap.  Airflow should be pretty good in that part of my engine
  compartment as the only thing in that area is the the psru, and the
  radiator
  core is directly below the psru.  Unfortunately, the oil pan is very
 close
  to the aft half of the radiator, but there's nothing I can do about that.

  I've seen other Lancairs with cowl flaps just aft of the spinner, but I
  suspect those were installed to enhance ground cooling, but that is just
 a
  guess, it could be they are using updraft cooling similar to Peter
  Garrison.

  I agree that exhaust heat is a big factor.  My current system is shielded
  to
  reduce IR, but the radiant heat is still a big factor.  It is a
  toss-up between finding a muffler that can live behind a rotary, and
  weight
  and drag.  Not sure what can be done about the radiant heat.  I really
  don't
  want a muffler hanging on the bottom of the airframe, so that restricts
 my
  options.  The current DNA muffler isn't the quietest muffler around, I
  would
  call it marginal, but it seems to be holding up to the challenge.  The
  problem with it is that it is blocking a good part of the exit air on the
  left tunnel, not good.  Cooling could benefit from enlarging the
  tunnel exit area.

  With that said, I have gathered all of the materials for an inconel
  tangential muffler, but that puts more of the heat into the engine
  compartment.  I plan to build the tangential muffler and install it on
 the
  p-port engine.  It will have a heat shield, but I don't plan to ceramic
  coat
  it.  Until then, I will have to use what I have.

  Mark S.

  Putting some vents on the top of the cowl behind the spinner won't hurt
  and they will definitely help the heat soak situation as you will get
  air flow through the cowl you are not getting now when stationary.

  There are some small wall vents in Home Depot that will work great.

  I do want to point out the Peter's CFD does not take into consideration
  the rotation of the prop so pressures in the real world might be
  considerable
  different. There is no beating  a water manometer to find out what is
  going on under actual flight conditions. I would love to publish
  some of that data if you can find time to do it.

  Paul Lamar

  Paul,

  OK, before I start cutting up my cowl, I'll take some manometer readings
 at
  a few places on the upper cowl near the spinner.  If I understand it, one
  end of the tube goes to the point where you want to know the pressure,
 and
  the other end is open (referencing cabin pressure).  Or does the other
 end
  hook up to the static port?

  Mark S.

  You can do it either way. The static port is best as some times
  there can be large pressure differences in the cockpit.
  Don't forget to use porous foam on the static pressure taps.
  Unless of course you would like to measure local velocities
  and directions in the region behind the prop which Peter and I
  would be highly interested in :) You could also tape on some
  tufts just behind the prop as well to get the local flow
  directions. A digital cameras with video capabilities mounted
  on the dash  would be down right wonderful :)

  Here are some suggestions for the side mounted Lincoln rad.
  The cheek opening is 8 inches inside diameter with a 16 inch spinner.
  This is an RV10 motor mount and nose gear so there will be some
  adjustments for your airplane.

  Paul Lamar


 Paul,

 The drawings reflect exactly the configuration I have been considering,
 except that my inlets are 7" dia. instead of 8".  You know that I'm really
 looking forward to doing more fiberglass work (NOT!!!).

 I recently purchased a little Flip video camera, so I'll see what I can do
 about getting some video.  Be advised that the Lancair's windscreen is set
 to a very steep angle, so I'm not sure I can see much from a dash cam.
  I'll
 check and let you know.

 I think the spinner is a 16", but I will have to check again as it has
 been
 a while since I first ordered it.

 Mark S.

 Fiber glass work is bad news no doubt about it.

 Seven might work but I would tend to err on the large size.
 Here is a chart for a 170 HP engine based on somebodies
 best estimate of how much intake area is required to cool for different
 conditions. One would have to multiply these numbers by  350/160 or
 about 2.

 I think the old style elliptical intakes are a better match to the
 side mounted radiator than the round inlets. This is still a work
 in progress for the internal ducting. Slightly rotating the elliptical
 inlet
 counter clock wise on the right side and clock wise on the left
 side would give a better match yet. I know it is not as cosmetic
 as the round inlets but one cannot expect something designed
 for a down draft air cooled air craft engine to work well for
 a water cooled air craft engine and radiator.

 If you see any way of improving the cosmetics please let me know.

 Paul Lamar


 Paul,

 The chart appears to me to be mis-labeled.  I always thought the exit area
 needed to be larger than the inlet area, otherwise the air gets trapped
 inside the cowl.  Also, as the air is heated, it expands and needs more
 exit
 area.  Am I wrong on this?

 As for the cowl inlets, I actually like it.  I'll take a hard look and
 see how hard it would be to modify my cowl.  It looks like the oval inlet
 shape actually increases the area of the circle by about 50%.  That would
 really help the situation.

 Mark

 Well for cooling drag purposes people tend to reduce the exit air
 to squirt the air out at higher speeds providing a bit of thrust
 that mitigates the over all cooling drag. In the P51 some claim
 it actually added net thrust.

 This is a subtle change but it improves the transition from the
 air intake to the wedge diffuser. I think the cosmetics are
 also improved slightly. The left side could be partitioned off for
 oil and intake air. Two high flaps on both sides of the cowl
 just in front of the wings might work wonders.

 I know a guy with a large NC mill that we might talk into
 making a foam buck. It would be done in large pieces 20 by 40 by 20
 or so and then assembled at your place. The NC mill program takes
 30 seconds to enter using a Rhino file. What is the height and width
 of your firewall?

 Paul Lamar

Paul,

Width is approx. 48", height is more difficult as the firewall is tilted
back at about a 15* angle.  I will have to measure it this weekend.

Mark S.

That is a start. Have you thought about building an aluminum cowl?
I know you can tig.

Does this look about right?

Paul Lamar