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machine-sewn seams (aircraft fabric covering). Seams in aircraft fabric made with a sewing machine.
French fell, folded fell, and plain overlap are the seams most generally used.
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machining. The process of removing material by turning, planing, shaping, milling, or otherwise cutting
with machine-operated tools. Lathes, milling machines, shapers, and planers are the most commonly used
machine tools.
machinist. A person skilled in the use of such metalworking machine tools as lathes, shapers, planers, and
milling machines.
Machmeter. A flight instrument that indicates the flight Mach number of an aircraft. The mechanism
inside a Machmeter includes a bellows that measures the difference between pitot pressure and static
pressure. It also contains an aneroid that modifies the output of the differential pressure bellows to correct
for the changes in altitude.
Mach number. A measurement of speed based on the ratio of the speed of the aircraft to the speed of
sound under the same atmospheric conditions. An airplane flying at Mach 1 is flying at the speed of sound.
14 CFR Part 1: “The ratio of true airspeed to the speed of sound.”
Mach technique (ICAO). A control technique used by air traffic control whereby turbojet aircraft
operating successively along suitable routes are cleared to maintain appropriate Mach numbers for a
relevant portion of the enroute phase of flight. The principal objective is to achieve improved utilization of
the airspace and to ensure that separation between successive aircraft does not decrease below the
established minimums.
Mach tuck (aerodynamics). A flight condition that can occur when operating a swept wing airplane in the
transonic speed range. Under certain conditions a shock wave forms in the root portion of the wing and
causes the air behind it to separate. This shock-induced separation causes the center of lift to move aft. At
the same time, the disturbed air causes the horizontal stabilizer to lose some of its effectiveness. The
airplane develops a nose-down pitch, or tucks under. See shock stall.
mackerel sky (meteorology). A condition of cloud coverage of the sky consisting of rows of altocumulus
or cirrocumulus clouds. These clouds look like the pattern of scales on a mackerel fish.
magamp. See magnetic amplifier.
magnesium. A light, silvery-white, malleable, ductile, metallic chemical element. Magnesium’s symbol is
Mg, its atomic number is 12, and its atomic weight is 24.312. Magnesium burns with an intense white light,
and because of this, it is used for making flares.
Magnesium’s light weight makes it useful as a structural material, but it has disadvantages. It
corrodes easily, and vibration causes it to crack.
Magnesyn. The registered trade name for a remote indicating system, used in certain aircraft instruments.
A Magnesyn transmitter consists of a permanent-magnet rotor, free to rotate inside a toroidal coil. The
magnet is rotated by the physical movement being measured. The indicator contains a small permanent
magnet on a shaft, free to rotate inside a toroidal coil. A pointer is also mounted on the shaft.
The toroidal coils in the transmitter and indicator are tapped in such a way that they form delta
windings. The cores of these coils are rings of soft iron, and the two coils are connected in parallel and
excited, or powered, with 26-volt, 400-hertz alternating current.
The AC alternately saturates and demagnetizes the soft iron cores, so the magnetic flux from the
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permanent-magnet rotors is alternately accepted and rejected by the cores. This changing flux cuts across
the windings of the coils and induces a voltage in them. The relationship between the voltage induced in
each section of the windings is determined by the position of the rotor inside the transmitter coil. Since the
two coils are in parallel, the voltage induced by the flux from the magnet is the same in both coils, and the
small permanent magnet rotor in the indicator follows the movement of the larger magnet in the transmitter.
magnet. A piece of material or a device that has the ability to attract pieces of iron or steel and to generate
an electrical voltage in a wire passing near it. A piece of ferrous metal (metal containing iron) contains
billions of tiny magnetic fields, called magnetic domains. When the metal is not magnetized, these domains
lie in a random fashion, and their fields cancel each other, so the metal has no overall magnetic field.
But when the metal is magnetized, the domains are aligned so all the north poles point in one
direction, and all the south poles point in the opposite direction. The metal now has a magnetic field.
　
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