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ends one line and returns to the start of the next line. Retracing is also called flyback.
retract. To draw back or draw up. The landing gear of most modern airplanes can be retracted, or drawn up
into the wing or fuselage.
retractable landing gear (aircraft landing gear). The type of landing gear that can be folded up into the
structure when the aircraft is off the ground. A fixed (nonretractable) landing gear produces a large amount
of drag when the aircraft is flying at a high speed. To reduce this drag, the landing gear is retracted, or
folded up into the structure.
retraction test (aircraft landing gear). A part of a 100-hour or annual inspection of an aircraft. The
aircraft is raised off the floor with jacks, and the retractable landing gear is operated through its retraction
and extension cycle. It is checked for its operating time and for any indication of improper operation.
retread (tires). To apply new tread to a tire. The tread wears off most airplane tires long before the tire
carcass is damaged or worn out, so for economical operation, the tire can be retreaded. The remaining tread
is ground off and the carcass inspected. If it is in good condition, a new tread can be put on and vulcanized.
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
Page 489
A properly retreaded tire is as serviceable as a new tire, and it costs much less.
retreating blade (helicopter rotor blade). The blade of a helicopter rotor moving in the direction opposite
to that in which the helicopter is flying. The blade on the opposite side of the helicopter is called the
advancing blade.
retreating blade stall. The stall of a helicopter rotor disc that occurs near the tip of the retreating blade. A
retreating blade stall occurs when the helicopter airspeed is high and the retreating blade airspeed is low.
This results in a high angle of attack, which causes the stall.
retrofit. A part made by a manufacturer, to be installed on a device that is no longer in production. If a new
engine is developed that improves the performance of an older aircraft, a retrofit can be made to install the
new engine on the older aircraft. When a retrofit part is produced, it is often sold as a kit which includes the
new part and all of the necessary hardware and instructions.
return manifold (fluid power system). The portion of a fluid power system through which the fluid is
returned to the reservoir.
return to service (aircraft maintenance operation). An aircraft is returned to service when it completes a
test flight by an appropriately certified pilot. A certificated mechanic or authorized inspector must approve
an aircraft for return to service after it has been inspected, repaired, or altered.
revalidate. To make something valid again. Certain licenses and certificates are valid for a definite length
of time. After this time has lapsed, the holder of the license or certificate must take some specified action or
pass some type of test to revalidate the license.
reverse-biased junction (semiconductor device). A voltage placed across the PN junction in a
semiconductor device, with the positive voltage connected to the N-material and the negative voltage to the
P-material. When the PN junction in a diode or a transistor is reverse-biased, the depletion area is enlarged
so electrons cannot cross the junction to flow in the external circuit.
reverse current (semiconductor device). Current in a semiconductor device that flows across a PN
junction when the junction is reverse-biased. Reverse current is the movement of minority carriers in the
semiconductor material. Also called leakage current, it increases with the temperature of the device.
reverse-current relay (generator control device). A normally open, magnetically closed switch in the
output circuit of a DC generator, between the generator and the battery. When the generator voltage is
lower than that of the battery, a spring holds the reverse-current relay contacts open, and the generator is
not connected to the battery.
As soon as the generator voltage rises above that of the battery, an electromagnet in the relay
closes the contacts and connects the generator to the battery. The more current flowing from the generator
to the battery, the tighter the contacts are pulled together.
When the generator voltage drops below that of the battery, reverse current flows from the battery
to the generator. When reverse current flows, the magnetic field holding the contacts closed is cancelled,
and a spring pulls the relay contacts open. This disconnects the generator from the battery. If a DC
generator control circuit did not incorporate a reverse-current relay, the battery would discharge through the
generator when the generator voltage was lower than that of the battery.
　
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