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prop-clawing for altitude = with the operation his screw propeller, he claws his way for altitude/higher place?

Context:
(a heroic World War II pilot whose various planes were always "prop-clawing for altitude"), then moved on to Jack London's bloodcurdling animal tales.
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Not a common phrase, except for Dave Dawson, but I presume that it means that the plane is going through a relatively difficult maneuver, so that the pilot feels that the propeller is making an effort to 'pull' the plane through the sky.
Comments  
I guessed so, more or less, in my heart, too.Emotion: smile