MOADS Frequently Asked Questions (FAQ)
What is MOADS?
The Molecular Optical Air Data System (MOADS) is a compact optical
instrument that can directly measure wind speed and direction, temperature,
and density of the atmosphere ahead of an aircraft. From these principal
measurements, all air data products can be determined. MOADS is a direct
detection system (i.e., it is based on incoherent rather than coherent
detection). MOADS can determine the air data products solely from molecular
backscatter and does not require the presence of aerosols to make these
measurements. It will, however, also utilize aerosols if they are present.
MOADS operates by sending out three laser beams and observing the scattered
energy. At the focal point of the telescope is a fiber optic cable that
transmits the light to a series of filters and a Fabry-Perot interferometer.
The resulting fringe pattern is then imaged onto a CCD camera and analyzed
to produce air data products. MOADS is unique in that it stimulates
and measures the return signal in three axes simultaneously, without
the use of any moving parts, is self-calibrating, and can be flush-mounted
to an aircraft.
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What is the current state
of Air Data System technologies?
Pitot Probe/Static Ports/Alpha Sensors are used on the F-16, F-18,
and the F-117. Flush Port Sensors are used on the X-15, Space Shuttle
(SEADS Experiment), B-2, and the A-12. A hybrid system (Pitot Probe/Alpha
Sensor/Flush Port) is used on the F-22. The B-2 has quad flush port
sensors for the quad flight control systems. Flush Port Pressure Sensors
are symmetrically placed on the airframe. The pressure measured at each
port varies as the airframe maneuvers. Pressure differences between
symmetrical ports correspond to changes in angle of attack and sideslip.
Pressure data is derived from wind tunnel and flight tests. The B-2
air data system is made up of two gust load alleviation static ports,
differential beta static ports, and left and right alpha/static ports.
Each port contains its own 1553 terminal, which is tied to the Flight
Control Computer (FCC) along with the total temperature (probe measured
at engine inlet) and nose gear position. The air data computation routines
in the FCC then determine angle of attack, angle of sideslip, static
pressure, pressure altitude, mach number, dynamic pressure, and true
air speed.
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What makes MOADS the
superior alternative?
MOADS has the following advantages over current air data system technologies:
-
flush mount design
-
less costly to calibrate or recalibrate
-
accurate for highly maneuverable aircraft as well as hoverable
aircraft
-
operates at high angles of attack (in the proper configuration,
MOADS can continue to measure air data products at angles of attack
of 90 degrees)
-
airframe independent
-
tri-service commonality
-
reduced Life Cycle Cost
-
provides a research tool for growth in detection of wind shear,
wake vortex, clear air turbulence, and engine unstart conditions
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