dynamic braking (electrical braking). Braking of an electric motor done by switching the power leads of the motor from the source of power to an electrical load. The electrical load consumes power which is changed to a mechanical force that opposes the rotation of the motor armature.
dynamic damper (reciprocating engine component). Heavy weights mounted on some of the cheeks of a reciprocating engine crankshaft to absorb torsional vibrations.
The weights are attached to the cheek by small pins that ride in larger holes in the weights. This arrangement allows the weights to rock back and forth as the crankshaft rotates. It is this rocking motion that absorbs the torsional vibrations of the engine.
dynamic load (aircraft structural load). The apparent weight of an entire loaded aircraft. The apparent weight is the actual weight of the aircraft multiplied by the load factor, which is the increase in weight caused by acceleration.
For example, an aircraft in a properly coordinated 60° banked turn has a load factor of two. This means that if the loaded aircraft weighs 3,000 pounds, its dynamic load in a coordinated 60° banked turn is two times 3,000 pounds, or 6,000 pounds.
dynamic microphone. A type of microphone in which sound pressure vibrates a cone on which is mounted a coil of wire. The coil vibrates in a magnetic field, and a voltage is produced in the coil. The frequency and waveform of the voltage is similar to that of the sound waves that vibrated the cone.
dynamic pressure, q (aerodynamic parameter). The pressure a moving fluid would have if it were stopped. Dynamic pressure is measured in pounds per square foot.
dynamic restrictions (air traffic control). Those restrictions imposed by the local facility on an “as needed” basis to manage unpredictable fluctuations in traffic demands.
dynamic stability (aerodynamics). The stability that causes an aircraft to return to a condition of straight and level flight after it has been disturbed from this condition.
When an aircraft is disturbed from straight and level flight, its static stability starts it back in the correct direction; but it overshoots, and the corrective forces are applied in the opposite direction. The aircraft oscillates back and forth on both sides of the correct condition, with each oscillation smaller than the one before it. Dynamic stability is the decreasing of these restorative oscillations.
dynamite. An explosive made by mixing nitroglycerine with a material such as sawdust, flour, or starch, and some type of oxygen-supplying salt.
dynamometer (electrical measuring instrument). An electrical measuring instrument that measures current and voltage at the same time and displays the results as electrical power. The instrument pointer moves over the dial an amount proportional to the product of the current and the voltage.
The current being measured flows through two series current coils and produces a fixed electromagnetic field whose strength is proportional to the amount of current. The voltage being measured forces current to flow through a movable voltage coil and produces a magnetic field proportional to the amount of voltage.
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