A variable pitch or constant speed unit aircraft (CSU) is a superior type of its fixed pitch model and this is simply in terms of efficiency of the blade and variable power settings.
For the case of a Cessna 172, the variable pitch types (mostly reimsrocket) are preferred for the long cross countries, especially for the advanced student.
This day, we had a cross country to the Mara from Wilson airport and we were privileged to fly a variable pitch.
The variable pitch types use a special governor on the propeller to adjust the blade angle of the propeller depending on the pilot’s desired performance.
This is controlled by a lever in the cockpit, usually next to the throttle lever. By adjusting the propeller blade angle, a given engine rpm is selected and the governor continuously adjusts this blade to maintain the desired engine rpm despite increasing or decreasing speeds.
The movement of the blade is controlled by oil under pressure and as long as the blade has nor reached its max or mon angle, it will continuously adjust to the desired power settings.
The flight went well all the way to the mara. On the return leg, after doing our engine run-up, we were set for take-off at Olkiombo airstrip in the mara direct for Wilson.
It was a simple flight because Wilson was aligned to the direction of the runway such that after take-off, we would fly the runway heading home. A
After the take-off, we started registering rising engine temperatures on the climb, which is normal on the taking off phase due to the power settings.
The issue became alarming since the increase was really going up fast. around 12 minutes after takeoff, we could feel the heat in the cockpit as the windscreen was starting to turn foggy due to heat.
As protocol says, we leveled off so wee could troubleshoot. Suddenly there were oil drops on the cockpit which indicates damage to the propeller governor.
The immediate cause of action was to look for a field to force-land while we still had engine power as we scanned for possible airstrip we could divert to.
Before we could pick a filled, the governor spilled oil covering the entire windscreen. we could not see through the contaminated windscreen.
we immediately decided to land in the grass (thank God mara is a grassland) as the engine power was slowly falling due to loss of oil pressure.
Our biggest challenge was forward visibility. However, we managed to land the aircraft safely with minimal damage to the elevator which was struck by ground due to the hard landing. no damages to the two pilots, both student pilots at that time.
Story by Kennedy Munyao Flight Instructor
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