Already the risks associated with cobalt, one of the propellers of the clean tech revolution, have come under the spotlight, through links to child labour in the Democratic Republic of Congo (DRC). Source: Internet
A motorboat generates thrust (or reverse thrust) when the propellers are turned to accelerate water backwards (or forwards). Source: Internet
Air Ministry 1945, p. 13. (NF 38 notes) The most-produced variant, designated the FB Mk VI (Fighter-bomber Mark 6), was powered by two Merlin Mk 23 or Mk 25 engines driving three-bladed de Havilland hydromatic propellers. Source: Internet
Among drone types, the rotary drone operates like a helicopter, with multiple propellers to take off and land. Source: Internet
A notable example were the Silverplate project built for the Manhattan Project with Curtiss Electric reversible pitch propellers. Source: Internet
Another issue with the P-38 arose from its unique design feature of outwardly rotating (at the "tops" of the propeller arcs) counter-rotating propellers. Source: Internet