Why not use a fire hose like they used to use on the Bristol Sycamore? That had a problem if the droop stops did not engage as the blade, complete with 20mm. shaped mass balance, would punch holes in the boom.
The trick was to get the fire section to play a jet of water over the boom in the direction of the blade travel. On shutdown the blade would bounce (or surf) the jet and no harm would come to anything.
Apart from the blades; that were made of wood. They had to be taken off, dried out, and re-tracked in the tracking tower as a set.