As already stated, on some aerobatic types, the prop goes fully coarse if engine oil pressure is lost. The Bulldog is one such type.
I recall a landing accident to an RAF Bulldog at Cosford, during my time as QFI on a University Air Squadron, probably in about 1990.
A student pilot bounced very hard on the nosewheel, after suffering PIO during his landing attempt. He damaged and displaced the nosewheel strut upwards into the engine bay. On a Bulldog, the top of the nose strut sits just below the oil pump for the CS prop. The pump was knocked and stopped, the oil pressure was lost and the prop went fully coarse as advertised.
Unfortunately, by now the student had given up trying to salvage the landing and opened the throttle to go around. The engine couldn't rev up due to the coarse prop setting and so the aircraft couldn't climb, drifted on down the full length of the runway, overshot the airfield. Eventually, the old Bulldog decided enough was enough and put itself down in a field, in a heap!