Joepilot - are you just an anti-christ, or do you just like antaganising real pilots?!!!
Think basic PofF =- when hovering next to any building, cliff, wall etc, where will all the downdraught go from the side of the disk nearest to the obstruction? - It must go up then fed back into the disc along with normal downdraughting air thereby increasing the induced flow on the side of the disc nearest the obstruction - basic P of F again increase in induced flow = decrease in lift = aircraft drifts into obstacle because the other side of the disc remains unafected thereby producing more lift than the other side hey presto A/C drifts into cliffs