From: Michael Coates List-Id: To: pipistrel@groups.io Date: Sat, 13 Jan 2024 10:27:38 +1000 Subject: Re: [pipistrel] -36°c flying dzubot@gmail.com wrote on 13/01/2024 10:16 am: > Hey all, I attempted to fly today in -36c. I’ve flown in -30 before > without issue but today after take off oil pressure dropped down to about > 13-20psi. Turned back and landed right away. After landing shut down > checked oil, no leaks, vent looked fine, restarted and had good oil > pressure. Did several stop starts with good pressure. But did not attempt > to fly again will wait until warmer weather. Any thoughts what could’ve > caused it? I have hydraulic prop, is it possible the oil there got so cold > that it restricted flow, or maybe at the radiator? Oil and coolant were > about 90c at take off. I block off air intake for oil rad and coolant rad > with tape and foam to help keep temps up in this cold. Also tape over half > of the cyl air intake. I had the cowl flap open during take off as my > temps were rising from taxing so perhaps somehow the oil vent line got > blocked as that’s where it exits. > It would have to be a few liters of super thick oil coming from the oil tank in one rush. If my memory serves me correctly, during the warmup the oil bypasses the oil tank because of the thermostat (if fitted) but then when you head out at full throttle and warm up the oil it will then close the thermostat and take the oil directly from the oil bottle. This brings in a couple of liters of super thick and cold oil straight into the engine I can't say too much about cold weather operations because of NDA's that are probably still enforceable but I do know that the military aircraft version of Pipistrel use special warmers made by Tanis  to warm the oil tank and the engine block completely before they use the aircraft. In the cold climates these were basically plugged into electricity whenever the aircraft was not being flown. They would have only done this to reduce the problem you have described and be able to get the aircraft airborne quicker with a much reduced warmup, most of these aircraft had the cowling completely closed to keep the temperatures warm enough.  -36°C  ??    Are you CRAZY !