Engine out !!
This is a story about one of those flights you can be glad you can walk away from ! First, let me introduce the main role players in this story, first, we have the plane:
X-Air ZU-XAF
And here is the second main character, the engine, a Rotax 618
Now picture this, an early morning flight, taking off from Petit airfield using runway 21. During taxi and run-up everything seemed fine, the engine had recently (20 hours) been rebuild, the temperatures were a bit slow in coming up but it was quite a cool morning. So, after a normal take-off the plane was turned down wind with the intention of doing a few circuits, after take-off the RPM was reduced from about 6300 to 6000, still climbing on the left hand downwind.
The first indication that all was not well was a slight, about 200, drop in RPM, at first thought to be caused by a bump on the throttle (The throttle on the X-Air sits right next to your knee, easy to bump). The throttle was reopened to about 6000 RPM, only to be followed by a second of bad vibration and then SILENCE !!!
The plane was still quite low, about 350' and going downwind at about 65 mph indicated. By this time the plane was beyond the end of the runway and it was decided that it was to low too attempt a 180deg turn back to the runway. The only option was a 90deg turn to the right, crossing a set of high tension wires, 2 notches of flap were quickly added and a cross wind landing was performed on a soft ploughed field.
Clearing the wires, then a ditch and then stopping before the fence all happened in seconds. The plane stopped and all was quiet, NO DAMAGE !
A few planes that were in the circuit who noticed the problem were circling, a quick radio call to assure them all was well and that a 4 wheel drive vehicle was needed for recovery send them racing back to the airfield.
I decided to start walking back to the airfield, it was about 3km away, halfway there I was met by one of the guys from the field, since he was in a normal vehicle he took me back to the field to fetch my 4 X 4 . Here is a photo of the Pajero towing the X-Air out of the soft ploughed field !
The wires in the background were the ones cleared on landing!
Ok, so all is well that ends well? But why did the engine quite ?
Easy, it was a "cold seizure", caused by the aluminum pistons expanding more than the cold steel barrels, causing the pistons to touch the barrel and seize. I believe in this case it was caused by the engine heating up to almost normal temperatures but the thermostat was still closed, during the take-off and climb out the the engine temperatures increased to the point where the thermostat opened, causing very cold coolant to enter the engine block and causing the barrels to cool down very fast, result? A "cold seizure" !
So, how can it be prevented? Making sure the engine temps are really high enough before take-off and making sure the engine does not run to cold. This particular 618 had a tendency to run quite cold, about 65C water temp and below 500C EGT.
Lesson learnt, Watch those temps !