REFLECTOR: Plenum drain?

Jerry Teitsma jerryteits at comcast.net
Fri Nov 13 12:31:01 CST 2009


Don Johnston asked an interesting question.  I have experienced engine 
compartment pressure that forced hot air back up through the ducts.  I also 
have a plenum drain that extends through the firewall into the engine 
compartment.  I do not have it plumbed to the outside, just into the engine 
compartment, just under the plenum.

One time I reached altitude and leveled off at 3,000 ft AGL and suddenly had 
a mist in the cabin.  The mist was thick enough to obscure vision.  After I 
shut down power and put the plane to best glide speed, the mist gradually 
went away.  Upon landing, I found that an oil fitting in the engine 
compartment had failed, spraying a fine mist of oil over everything.  I had 
less than a quart of oil remaining in the engine.  In a way, I was lucky to 
have the mist carried back into the cabin or I would have left the vicinity 
of the airport and would have run out of oil while flying over the 
mountains.

Re-thinking this situation, I think I will duct that drain line to the 
outside and reduce the possibility of taking in carbon monoxide.  As an 
additional measure, I have constructed a reverse scoop in the bottom of the 
cowling to try to create a negative pressure zone in the engine compartment, 
assisting in more cylinder cooling.  Will fly this configuration within the 
next 2 weeks.

Jerry Teitsma, Inc
PO Box 796, Granby CO 80446 970-887-3910 (Phone/Fax)
jerryteits at comcast.net
Jerry Teitsma, RRC, RRO, CCCA
RCI, Inc
PO Box 796, Granby CO 80446 (USPS mail/shipping)
36 Lodgepole Ct, Granby CO 80446 (UPS/FedEx shipping)
970-887-3910 (Phone/Fax)
jerryteits at comcast.net
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