Jun 02 2011

Eductor craziness

The overheating of the engine is driving me crazy.  The plane flies wonderfully well, it is super fast but I cant push it yet because of the cylinder temps being too high.

As you saw in my last post, I installed some eductors in my quest to solve the problem.

Nice shape and well built, but when I flew the plane, I only got about 15 f drop in cylinder temps at 2400 rpm but that is not near enough to allow full power operations and the cowl pressure did not significantly change (95 mph at 150 kts same as before installing eductors).     After thinking about it I wondered why my plane which also has eductors cools wonderfully well…. 

After looking at my plane


one can see my eductors are much bigger (both inlet and outlet) and the back of the cowl is compeletelyblocked off.    At 130 kts TAS my cowl has a pressure of 55 mph differental from the cowl to the static port.


As a last resort, I decided I would try and modify the new plane to mimic my plane.

The first thing I did is enlarge the eductors.

The next thing is to block off the entire outlet to ensure the air only had one way to escape…. through the eductors.



After the mods, I went out flying.  The first thing I noted is while taxiing, I had a NEGITIVE pressure in the cowl on the ground, -10 mph and when I increased RPM, the cowl pressure actually decreased!   The eductors really worked and the more exhaust (higher the RPM) the greater the negative pressure.  

After take off the cowl pressure was 45 mph (it was around 80 mph).  The strange thing is, the cylinder temps when up VERY quickly????  what’s up with this?   Maybe it is because the engine was heat soaked waiting to take off, or the fact fact the OAT was at 95 F.  I quickly decided to land to check thing out and on downwind,  the temps had started to decrease.  Tomorrow I’ll fly again when it is a bit cooler and I can do a more extensive testing….  I got to figure out what’s going on!!