Rocket Motor Jargon
This page contains a glossary of terms used on the site.
Most of these terms are standard for the hobby, but a few of them
merit additional explanation.
A further explanation of motor statistics can be found on the
Motor Statistics page
and more information on certification organizations can be found on the
Certification page.
- Average Thrust
-
The Total Impulse divided by the Burn Time (seconds)
yields the average thrust force.
See the Motor Statistics page for more info.
- Burn Time
-
The number of seconds for which the motor burns.
(Per NFPA 1125, the beginning and end of the curve,
where the thrust is below 5% of the maximum,
are excluded.)
See the Motor Statistics page for more info.
- Case Info
-
The hardware required by a reloadable motor.
- CD
-
The "coefficient of drag," accounting for the shape and smoothness of the rocket.
This term has no dimensions, it is simply a number used to describe how the shape of the body
and its angle to the wind influence drag. All shapes that move through the air posses drag
coefficients. There are theoretical models and experimental methods for calculating it, but for
hobby rocket simulation a simple approximation is generally used.
- Cert. Date
-
The start date for the certification of this motor.
- Cert. Desig.
-
The designation for this motor as assigned by the certification organization,
usually reflecting the tested values.
- Cert. Org.
-
The organization that certified this motor.
See the Certification page for more info.
- Common Name
-
The commonly-used name of the motor. This standard format includes
the Impulse Class and average thrust.
See the Motor Statistics page for more info.
- Data Format
-
The format of the simulator data.
Different flight simulators use data in different formats, although the "RASP"
format has become the standard for data interchange.
See the Simulators page for more info.
- Data Sheet
-
This is the web page provided by the certification organization or manufacturer on
a particular motor. Those pages often contain more detail on the motor,
including official thrust curves and other statistics.
- Data Source
-
Where the simulator data comes from:
"cert" is data provided by the certification organization,
"mfr" is data provided by the motor manufacturer,
and "user" is data authored by an unofficial source.
- Delays
-
The list of delays available for this motor (if any) in seconds from burn-out.
Note that for motors with adjustable delays, this includes all achievable delays
using the appropriate adjustment tool.
- Designation
-
The official name of the motor as specified by the manufacturer.
Some manufacturers (notable HyperTek) use a designation that is very
different from the Common Name and not very useful for searching.
- Diameter
-
The main diameter of the motor in millimeters.
- Dry Weight
-
The weight of the rocket ready to fly, but without any motor loaded.
- Impulse Class
-
The category of total impulse to which the motor belongs.
See the Motor Statistics page for more info.
- Initial Thrust
-
The average thrust during the first half second of the burn.
See the Motor Statistics page for more info.
- ISP
-
The "specific impulse" is the total impulse over the weight of the propellant,
which gives you a measure of the motors efficiency for lifting since the higher
this number is, the more impulse you get for the motor's weight.
See the Motor Statistics page for more info.
- Length
-
The overall length of the motor case.
- Max Q
-
The point in flight when the rocket encounters the maximum dynamic pressure.
For hobby rockets, which stay in the lower atmosphere, max Q occurs at maximum velocity.
See the Wikipedia article
for more info.
- Max Liftoff Weight
-
Estimate of the heaviest a rocket can be safely fly on a motor. This takes into account
not only stability but also appropriateness of the motor ejection delay.
Some model rocket engines are rated this way by the manufacturer, but because the value is
delay-specific, it is not recorded on this site.
- Max Thrust
- Peak Thrust
-
The largest instantaneous thrust force produced by the motor during its burn.
- Propellant Info
-
The name of the propellant formulation.
- Propellant Weight
-
The weight of the propellant used by this motor.
- Total Impulse
-
The total amount of energy produced by the motor (force × time).
See the Motor Statistics page for more info.
- Total Weight
- Loaded Weight
-
The total loaded weight of this motor (propellant and case).
- Type
-
The style of motor. Single-use motors (SU) are used just once and discarded.
Reloadable motors use solid propellant and a reusable aluminum motor case.
Hybrid motors use solid propellant and a gaseous oxidizer.
There is also a much more complete
glossary on RocketReviews.com
containing general hobby rocketry terminology.
