I don't think you'd frag an engine by digging a prop in but the damage would likely be reduced by shutting 'em down before landing. At the very least you'd only bend up two prop blades versus all of 'em by shutting down. After all, at least one of 'em is gonna be sticking straight up and free of the runway.
I heard a story about a Blenheim in North Africa when evading an Me109 flew so low against the desert floor that at one point the props dug six inches into the sand. As they were still turning at maximum revs the tips of the prop blades bent themselves forwards. The resulting lack of resistance then caused the engines to rev higher and caused the Blenheim to fly faster. After this the other pilots in the squadron had to be physically restrained from sawing six inches off the prop blades on all their aircraft.
I heard a story about a Blenheim in North Africa when evading an Me109 flew so low against the desert floor that at one point the props dug six inches into the sand. As they were still turning at maximum revs the tips of the prop blades bent themselves forwards. The resulting lack of resistance then caused the engines to rev higher and caused the Blenheim to fly faster. After this the other pilots in the squadron had to be physically restrained from sawing six inches off the prop blades on all their aircraft.
I would want to read about that one. Can't see it myself, but that is not to say it did not happen. If an object is moving forwards and at speed and then touches the ground, how will said object bend in the direction of travel? Sound like a military urban myth.
Matt
I heard a story about a Blenheim in North Africa when evading an Me109 flew so low against the desert floor that at one point the props dug six inches into the sand. As they were still turning at maximum revs the tips of the prop blades bent themselves forwards. The resulting lack of resistance then caused the engines to rev higher and caused the Blenheim to fly faster. After this the other pilots in the squadron had to be physically restrained from sawing six inches off the prop blades on all their aircraft.
I would want to read about that one. Can't see it myself, but that is not to say it did not happen. If an object is moving forwards and at speed and then touches the ground, how will said object bend in the direction of travel? Sound like a military urban myth.
Matt
Prop blades under power always bend forwards in a strike. It's the A of A of the blade that does it. It really twists more than bends, at least intitally. The back side of the blade makes contact, and the force of the crankshaft torque very suddenly meeting the resistance of the dirt or whatever causes the tip of the blade to "want" to go in the opposite direction... so, overall the distortion is forward.
This is how crash investigators can determine immediately if a crashed plane was developing thrust or not on impact, in most cases. If they're not under power, the blades will always bend back.
Interesting... I was looking for a pictue that shows this, and found a sort of in-between example... the engine was near idle (taxiing) when the brakes locked and this Corsair nosed over... with the wide blades set at coarse pitch, they bent sideways...
I suppose it depends on how fast the prop is turning. This Blenheim had the throttle to the wall when it's props touched, and as the sand was so much thicker than the air they pulled themselves forward and bent.
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