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Re: REFLECTOR: Oil Cooler Question
On the question; "Do we need two oil coolers using an IO540", the simple
answer is no, -- however ......
Both Jean Prudhomme and (I think) also Don White are flying their XLs (IO540,
300 hp) with one somewhat larger oil cooler than what the factory sells and
uses (two of) in its XL (260hp). They also have a pilot operable flap at the
naca inlet to increase the surface area and provide a ram effect to the scoop.
I also want to avoid using two oil coolers but have committed (space, purchase
and building status) to use the smaller oil cooler with modifications as
a. I have (somewhat radically from what the builder's manual proposes) changed
the geometry of the exhaust from my oil cooler and expect a much larger
pressure drop (thus a larger volume of air through it per time unit). This is
all empirical, but with a background in the design of steam ejectors some 35
(Don't know about induced drag, but it looks pretty streamlined).
b. Encouraged by the findings from Scott and Martin's testing of heat transfer
between the oil lines in the pilot duct, I have:
- Installed the two lines in the pilot duct without the use of shrink tubing
(aside from about six inches at each end of the duct).
- Separated the two lines with 4 pairs of Adel clamps to avoid heat transfer
- Opened the forward end of the duct to the outside (about 6 inches aft of the
canard bulkhead), and the aft end of the duct (about 2 inches forward of the
gear bulkhead). The forward opening is "scoop"-shaped with an area of ca. 4
The exhaust opening is somewhat larger, ca. 5 - 6 sq. in.
Both openings have insertable/removable "plugs".
I will install thermocouples at each end of both lines to measure the effect
of the duct cooling. My rough calculatins of an ideal situation indicates that
the duct cooling should give me a temperature drop of 30 - 35 degrees (not
counting the oil cooler).
I am about 2 months away from first flight. Will keep you posted.
N190J (XL/RG - IO540, 260hp)