May 30 2011

Temporary Eductors

I have been having MAJOR issues with engine cooling.  I can get up to a max of 2400 rpm before the CHT’s get up to 425f.   Yesterday I decided to go flying before I cut off the front of the inlets and installed larger cowl inlets to let more air in the cylinder plentum boxes.  Sure glad I did as I found out it wasnt the inlet size, but major cooling issue is back pressure in the cowl area.    I thought I would just cut some reverse scoops in the cowl per Jerry Schneider’s SOOMA analysis (Jerry’s famous “Straight Out Of My Ass” method of problem solving).

When I woke up this morning, I realized the only difference between my plane’s cowl (excellent cooling) and the new plane’s cowl is just eductors.  I do not have holes cut in the cowls to let the air out so openings might not be necessary in the new plane, just a set of eductors..  cool!

When I went out to the club today and took a close look at the cowls and sure enough,  I notice a LOT of carbon on the cowl just aft of the exhaust pipes.  AaaaHAAAA…  the hot exhaust is basically clogging the outlet of the cowl not letting the cylinder cooling  air out

You can see on the cowl how the exhaust was backing up in the cowl and most likely causing a pressure wave not letting the  cooling air out.

I have two choices, extend the exhaust pipes or build eductors like in my plane, so I fabricated a set quick and dirty set of eductors for testing.


These are the pictures of the cowl and my temporary eductors made out of house flashing, and went flying.

Overall the minimal effort was a very good success as my temps were much better (almost normal) until one of the eductors ripped itself from the plane at 203 kts TAS and was apparently eaten by the prop at which time the temp of #3 (my hottest) cylinder again quickly started climbing up.

I think I am now on the right track and will be building a formal set of eductors tomorrow.

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