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Keeping a Sukoi 31 cool in the desert:

My friend Bill Parker and the other Marana Sukoi boys are very keen to make the most of their training days. Flights last about fifteen minutes each with about 10 minutes in the aerobatics box pulling +10G -7G with the M-14P engine running on full throttle throughout. After landing on a hot day the engine needs as much as an hour before oil temperatures return to normal and another training flight can take place.

Bill invited me to come up with a solution to this problem. I suggested adding a second oil cooler mounted in series with the existing oil cooler. I turned up with one mounted in a specially made duct with the intention of hanging it underneath the fuselage.

After looking at the plumbing and also considering the pressure loses across the second cooler we abandoned the second oil cooler option. (The fact that the primary cooler has a by-pass valve that might open if the second cooler was more restrictive could lead to disastrously high temps possibly while the pilot was too involved in pulling G's to notice). There was also the desire not to add significant weight or to make large scale changes to the structure of the airplane.

After some careful thought, Bill and I implemented a very simple but effective oil cooling solution using just a few dollars worth of parts.

We plumbed the smoke system oil tank to a water spray bar mounted across the front of the standard oil cooler. The smoke system oil tank is pressurizes by the engine driven pneumatic pump. This forces the oil out via a solenoid valve to the exhaust pipes. The solenoid valve was capped off on Bills plane as the smoke system was not in use...

Our mod involved drilling and tapping one of the caps for a small pipe fitting. The fitting was obtained from a model aircraft shop, along with a length of 1/4 inch fuel line. The line runs to the 1/8 inch copper primer line which is mounted across the oil cooler air intake duct. The copper line has three holes equally spaced across the intake duct. The flow rate of water under pressure is such that there is sufficient capacity for at least two aerobatics sorties before the tank is refilled with water.

In operation, the pilot simply turns the "smoke" on just before entering the aerobatics box, and hopefully remembers to turn it off again before landing. This solution has been very successfully used to increase the number of sorties that can be flown in a day. Bill reports that the oil temperatures are towards the bottom of the green arc after landing whereas before they where towards the top of the green arc.

© Copyright Andreas P Christou 2002