Model Rocketry and Siege Engine Glossary Letter M

Model Rocketry and Siege Engine Glossary Letter M

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Mach Number
An expression of velocity calculated by dividing the actual velocity by the speed of sound.
The ratio of the velocity of a body to that of sound in the medium being considered. At sea level in air at the Standard U. S. Atmosphere, a body moving at a Mach number of one (M-l) would have a velocity of approximately 1116.2 feet per second, the speed of sound in air under those conditions
An ATF or other government body approved storage device for large rocket motors and other low-explosive devices
Mass (m)
A measure of the quantity of matter in an object

m = weight/gravitational constant

= w (lbs.)/ g (ft./sec2)

The unit of mass is sometimes called a "slug."
Mass Flow Rate (m)
Propellant consumption rate in slugs per second
Mass Ratio (Lamda)
Total weight of rocket divided by weight without propellant
Mass Ratio
Final mass (after propellant burn) divided by initial mass
Max Q
The point during the powered flight phase of a rocket’s ascent at which acceleration stresses on the airframe are the greatest. This is the point at which a shred is most likely to occur
Maximum Thrust
The peak thrust a motor generates
Mean Chord
A wing’s root chord plus its tip chord, divided by two
Mercury Switch
An electrical switching device consisting of an oval glass bulb which contains two electrical contacts (penetrating the bulb, and at one end of the oval) and a drop of mercury.
In hobby rocketry, mercury switches are used to detect the absence of acceleration in a moving rocket. When the rocket launches, acceleration forces hold the mercury drop at the bottom of the bulb, away from the electrical contacts. When the rocket’s acceleration ceases, the mercury - which is a heavy metal and stores considerable momentum - moves forward in the bulb, bridges the gap between the contacts, and closes the electrical circuit.
The electrical circuits controlled by mercury switches are most commonly used to activate recovery system deployment charges or sustainer motor igniters
  • In the nomenclature of Chapman, a stratum of atmosphere sometimes called the chemosphere
  • In the nomenclature of Wares, a stratum that extends approximately from 250 to 600 miles, lying between the ionosphere and the exosphere
Micro Bubbles
Tiny glass globules which are sometimes added to epoxy adhesive in applications like fin fillets, to reduce weight
Small, toothless electrical clips commonly used to connect the launch system to the igniter on model rockets
Mid-body Ejection
The practice of placing a rocket’s separation point midway up the body tube, helping to prevent tube zippering
Mid Power
Typically rockets flying on motors in the E to G range
Minimum Diameter
A model whose diameter is just large enough to accommodate its motor
Misfire Alley
A rangehead in which all the launchers are arrayed in a long line. Launchers may be controlled by a master controller or by individual launch controllers
A self-propelled unmanned vehicle which travels above the earth's surface
millimetre - 1 / 1000 of a meter
Model Rocket
An aircraft that ascends into the air using some form of reaction motor, without the use of aerodynamic lifting surfaces. Model rockets have the following characteristics: Gross launch weight, including the motor(s), does not exceed 1500 grams. Motor power does not exceed 160 newton seconds of impulse and/or contain more than 62.5 grams of propellant each, and no more than 125 grams of propellant in multiple motor configurations. All components of model rockets must be of wood, paper, rubber, breakable plastic or similar material and without substantial metal content
Slang for Model Rocket
A combination of parts or components arranged and mounted or packaged as a single unit. The parts work together to perform a specific function or functions
Molecular Weight (Mw)
The atomic weight time s the number of atoms per molecule, expressed in pounds. For example, the molecular weight of water (H20) = (l x2 ) + (l6xl) = 18 lbs
Momentum (M)
A quantity of motion measured by the product of the mass of an object times its velocity. M=mV
Model aviation covering consisting of colored heat shrinkable vinyl, applied with a tacking iron. Often used as trim tape
A rocket propellant , especially a liquid propellant , in which the fuel and oxidizer make up a single substance before injection into the combustion chamber
A device that imparts motion through reaction
Motor Clip
See Motor Hook
Motor Code
The accepted method of expressing the characteristics of a particular motor.
Motor power ranges (total impulse) are expressed with letters A through N. Each letter expresses a power range twice as powerful as the preceding range. The power ranges are as follows:

Motor Class
Minimum-Maximum Newtons
¼ A
0.0- 0.625
80.01 - 160
½ A
0.626 - 1.25
160.01 - 320
1.26 - 2.5
320.01 - 640
2.51 - 5
640.01 - 1280
5.01 - 10
1280.01 - 2560
10.01 - 20
2560.01 - 5120
20.01 - 40
5120.01 - 10,240
40.01 - 80
10,240.01 - 20,480

The motor code is expressed as a letter followed by a series of numbers. For example, C6-3, in which C is the power range (5.01-10 Newtons), 6 is the average thrust in Newtons, and 3 is the delay time in seconds(counting from propellant burn-out).
Motor Diameter
The diameter of a hobby rocketry motor casing. Most commercially-manufactured motors are made in standard sizes. Motor diameters are most commonly expressed in millimeters. The most commonly seen motor diameters are 10.5mm, 13mm, 18mm, 24mm, 29mm, 38mm, 54mm, 75mm, 98mm, and 150mm
Motor Hook
A device for retaining the motor on a model rocket
See Mid Power
Multistage Rocket
A rocket having two or more thrust producing units, each used for a different stage of the rocket's flight
Murphy’s Law
The guiding principle of Rocketry preparation: "If anything can go wrong, it will."
Music Wire
A high grade, stiff wire made to low tolerances that comes in a wide variety of diameters. Commonly used to make springs, it is also known as piano wire. Most often used in model rocketry as launch rods.

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