Diverging duct.  A duct, or passage, whose cross-sectional  area increases in the direction of fluid flow. DME.  Distance measuring equipment. Dope proofing.  The treatment of a structure to be covered  with fabric to keep the solvents in the dope from softening  the protective coating on the structure. Dope roping.  A condition of aircraft dope brushed onto a  surface in such a way that it forms a stringy, uneven surface  rather than flowing out smoothly. Double-acting actuator (hydraulic system component). A linear actuator moved in both directions by fluid power. Double-acting hand pump (hydraulic system component).  A hand-operated fluid pump that moves fluid during both  strokes of the pump handle. Doubler.  A piece of sheet metal used to strengthen and stiffen  a repair in a sheet metal structure. Downtime.  Any time during which an aircraft is out of  commission and unable to be operated. Downwash.  Air forced down by aerodynamic action below  and behind the wing of an airplane or the rotor of a helicopter.  Aerodynamic lift is produced when the air is deflected  downward. The upward force on the aircraft is the same as  the downward force on the air. Drag (helicopter rotor blade movement).  Fore-and-aft  movement of the tip of a helicopter rotor blade in its plane  of rotation. Dragging brakes.  Brakes that do not fully release when the  brake pedal is released. The brakes are partially applied all  the time, which causes excessive lining wear and heat. Drag wire.  A structural wire inside a Pratt truss airplane  wing between the spars. Drag wires run from the front spar  inboard, to the rear spar at the next bay outboard. Drag wires  oppose the forces that try to drag the wing backward. Drill motor.  An electric or pneumatic motor that drives a  chuck that holds a twist drill. The best drill motors produce  high torque, and their speed can be controlled. Dynamic pressure (q).  The pressure a moving fluid would  have if it were stopped. Dynamic pressure is measured in  pounds per square foot. Dutchman shears.  A common name for compound-action  sheet metal shears. Dutch roll.  An undesirable, low-amplitude coupled  oscillation about both the yaw and roll axes that affects many  swept wing airplanes. Dutch roll is minimized by the use of  a yaw damper. Duralumin.  The name for the original alloy of aluminum,  magnesium, manganese, and copper. Duralumin is the same  as the modern 2017 aluminum alloy. Dummy load (electrical load).  A noninductive, high-power,  50-ohm resistor that can be connected to a transmission line  in place of the antenna. The transmitter can be operated into  the dummy load without transmitting any signal. Ductility.  The property of a material that allows it to be  drawn into a thin section without breaking. Dry rot.  Decomposition of wood fibers caused by fungi. Dry  rot destroys all strength in the wood. Dry ice.  Solidified carbon dioxide. Dry ice sublimates, or  changes from a solid directly into a gas, at a temperature of  –110 °F (–78.5 °C). Dry air pump.  An engine-driven air pump which used carbon  vanes. Dry pumps do not use any lubrication, and the vanes  are extremely susceptible to damage from the solid airborne  particles. These pumps must be operated with filters in their  inlet so they will take in only filtered air. Drip stick.  A fuel quantity indicator used to measure the  fuel level in the tank when the aircraft is on the ground. The  drip stick is pulled down from the bottom of the tank until  fuel drips from its opened end. This indicates that the top of  the gauge inside the tank is at the level of the fuel. Note the  number of inches read on the outside of the gauge at the point  it contacts the bottom of the tank, and use a drip stick table  to convert this measurement into gallons of fuel in the tank. G-13