Described herein are apparatuses that provided various features related to unmanned aerial vehicles. An example apparatus may include, (i) a support structure, (ii) at least one shaft coupled to the support structure via at least one swing arm, wherein the swing arm allows upward movement, and restricts downward movement of, the at least one shaft from a resting position, (iii) a spool, wherein in the spool is shaped so as to rest on the at least one shaft when the at least one shaft is in the resting position, and wherein the spool is operable to unwind a tether coupled to a payload, and (iv) at least one fan coupled to the at least one shaft, wherein rotation of the spool when unwinding the tether also causes rotation of the at least one fan coupled to the at least one shaft, thereby controlling a descent rate of the payload.

An apparatus directed to unmanned aerial vehicles including (i) a support structure, (ii) at least one shaft coupled to the support structure via at least one swing arm that allows upward movement, and restricts downward movement, of the at least one shaft from a resting position, (iii) a spool shaped so as to rest on the at least one shaft when the at least one shaft is in the resting position, and wherein the spool is operable to unwind a tether coupled to a payload, and (iv) at least one fan coupled to the at least one shaft, wherein rotation of the spool when unwinding the tether also causes rotation of the at least one fan coupled to the at least one shaft, thereby controlling a descent rate of the payload.

Described herein are apparatuses that provided various features related to unmanned aerial vehicles. An example apparatus may include, (i) a support structure, (ii) at least one shaft coupled to the support structure via at least one swing arm, wherein the swing arm allows upward movement, and restricts downward movement of, the at least one shaft from a resting position, (iii) a spool, wherein in the spool is shaped so as to rest on the at least one shaft when the at least one shaft is in the resting position, and wherein the spool is operable to unwind a tether coupled to a payload, and (iv) at least one fan coupled to the at least one shaft, wherein rotation of the spool when unwinding the tether also causes rotation of the at least one fan coupled to the at least one shaft, thereby controlling a descent rate of the payload.

An apparatus may include (i) a support structure, (ii) at least one shaft coupled to the support structure via at least one swing arm, wherein the swing arm allows upward movement, and restricts downward movement, of the at least one shaft from a resting position, (iii) a spool, wherein in the spool is shaped so as to rest on the at least one shaft when the at least one shaft is in the resting position, and wherein the spool is operable to unwind a tether coupled to a payload, and (iv) at least one fan coupled to the at least one shaft, wherein rotation of the spool when unwinding the tether also causes rotation of the at least one fan coupled to the at least one shaft, thereby controlling a descent rate of the payload.

A back-up load retention system includes a retention line which is connected to a load, a counterweight unit which is connected to the retention line, and a double-acting hydraulic cylinder which is connected to the counterweight unit. The counterweight unit maintains a tension force in the retention line. The double-acting hydraulic cylinder brakes and/or stops the load in a case of a failure in a main lifting system.