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Scott and all,
It seems a good idea to have a fixed aluminum tube going the last bit to the
bottom lip of the cowl.
That overboard dump, as you say, can be suceptable to icing depending on
many factors.
I have noticed over the years most aircraft with a similar setup have a
relief hole in the pipe nearer the top or, in any case, away from the icing
zone.  This hole is best made as a notch which is pressed in.  If designed
properly and facing downward there will be no outflow unless the tip is iced
over.
The location of the tip relative to the outside slipstream can be critical.
If there is to much negative pressure in the crankcase vent line (on some
installations) you can accelerate oil consumption by sucking too much oil
laden vapor overboard. A loose oil filler cap is bad.  Maintenance manuals
for some aircraft are very specific as to the location of the pipe tip
relative to the lower firewall.
I have run into this problem in years past, once even speaking to a Cessna
Tech Rep.  If memory serves, he said to closely follow the diagram in the
books.  Big help!
Lancairs are fast and have different engine installations so each type
design should find the best sweet spot for the vent line tip.  My feeling is
that some suction is good but too much may be a poor choice leading to
excessive oil consumption.  Next time you kick tires look at a few different
aircraft.
Walter Dodson,  IV-P 45%

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