Tracy,

 

Wow!  That is less than 40 sq in of inlet area!  Total!!  How much exit area do you have?

 

You mentioned a pressure sensor.  What pressures are you seeing at wherever you measure it?

 

Bill B

Yep, not too bad for a 300 HP engine. 

 The total outlet area is 53 sq  in. ,not including some louvers I put in the bottom of the cowl.   The louvers didn't help at all so I plan to remove them.  Outlets as large as 120 sq in were tried without seeing much change.  I am more convinced than ever that the key to efficient & low drag cooling lies more in the inlet side rather than the outlet in under-cowl cooling system installations.

53 Sq in may sound like a small outlet for 300 HP but if you research the planes that are really going fast and cooling well at the same time you will find that they have a SMALLER outlet area than the inlets.   I haven't been able to get there but it IS possible.   It usually requires that the heat exchangers have ducts on the outlet side which is hard to do unless you use a P51 style cooling arrangement.

My air pressure instrument is a modified EM2 and is not calibrated in " of H2O  or anything else.  It just reads out the converted digital value of a sensor (same as the TAS sensor) so it's just a relative value.   When the reading doubles it means twice the pressure.   Someday I'll get around to converting the reading to something we are used to.

Tracy

On Thu, Apr 28, 2011 at 9:42 AM, Bill Bradburry <bbradburry@bellsouth.net> wrote:

Tracy,

 

Wow!  That is less than 40 sq in of inlet area!  Total!!  How much exit area do you have?

 

You mentioned a pressure sensor.  What pressures are you seeing at wherever you measure it?

 

Bill B

 

---

From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Tracy
Sent: Thursday, April 28, 2011 9:08 AM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: Cooling Inlets

 

Finally got around to finishing my cooling inlets. (pictures attached)  Up until now they were simply round pipes sticking out of the cowl.   The pipes are still there but they have properly shaped bellmouths on them.   The shape and contours were derived from a NASA contractor report (NASA_CR3485) that you can find via Google.  Lots of math & formulas in it but I just copied the best performing inlet picture of the contour.   Apparently there is an optimum radius for the inner and outer lip of the inlet.   There was no change to the inlet diameters of 5.25" on water cooler and 4.75" on oil cooler.

The simple pipes performed adequately in level flight at moderate cruise settings even on hot days but oil temps would quickly hit redline at high power level flight and in climb. 

The significant change with the new inlet shape is that they appear to capture off-axis air flow  (like in climb and swirling flow  induced by prop at high power)  MUCH better than the simple pipes.    First flight test was on a 94 deg. F day and I could not get the oil temp above 200 degrees in a max power climb.    They may have gone higher if the air temperature remained constant but at 3500 fpm the rapidly decreasing OAT kept the temps well under redline (210 deg F).

I have an air pressure instrument reading the pressure in front of the oil cooler and was amazed at the pressure recovered from the prop wash.  At 130 MPH the pressure would almost double when the throttle was advanced to WOT.   That did not happen nearly as much with the simple pipes.  

These inlets ROCK!

Tracy Crook