(Frequently Asked Questions)
Part 1: General Information
Posted: November 17, 1998
Last modified: November 17, 1998
This portion of the r.m.r FAQ is maintained by Buzz McDermott, at
firstname.lastname@example.org. Comments, criticisms, suggestions and
corrections for this section should be sent to that email address.
1.1 What, exactly, is a 'model rocket' versus a 'high power' rocket? Where do
liquid fueled and homemade rocket motors fit in? What about amateur
'Model', 'high power', 'advanced', and 'amateur' are all terms which have
many definitions, depending to whom you are speaking. In r.m.r., and in the
FAQ documents, the definitions (if any) accepted by the NFPA, National
Association of Rocketry, and Tripoli High Power Rocketry Association are
used. If these definitions conflict the NAR definition is used.
'Model rockets' are rockets that conform to the guidelines and restrictions
defined in the NFPA 1122 document. These rockets weigh less than 1500
grams, contain less than 125 grams of total fuel, have no motor with
more than 62.5 grams of fuel or more than 160 NS of total impulse, use
only pre-manufactured, solid propellant motors, and do not use metal
body tubes, nose cones or fins. One inconsistancy with this is the
CPSC definition of a model rocket motor, which by their definition must
contain no more than 80NS total impulse. NFPA document 1127-94 contains
the most complete definition of a model rocket and the model rocket safety
code. This is the same safety code as adopted by the NAR.
'Large Model Rockets' is a term used in the FAA FAR 101 regulations. It
refers to NAR/NFPA model rockets that are between 454 and 1500 grams
(1 to 3.3 pounds) total liftoff weight and contain more than 113 grams
but less than 125 grams of total fuel.
'High power rockets' are rockets that exceed the total weight, total
propellant or single motor total impulse restrictions of model rockets,
but otherwise conform to the same guidelines for construction materials
and pre-manufactured, commericially made rocket motors. High power rockets
also allow the use of metal structural components where such a material
is necessary to insure structural integrity of the rocket. High power
rockets have no total weight limits, but do have a single motor limit of
no more than O power (40,960NS maximum total impulse) and have a total
power limitation of 81,920NS total impulse. NFPA document 1127-1985 contains
the most complete definition of a high power rocket and also the high power
rocketry safety code. This safety code has been adopted by both the NAR
and TRA. Metal bodied rockets are allowed by NFPA 1127 where metal is
required to insure structural integrity of the rocket over all of its
'Amateur' rockets covers all other non-professional rockets that do not
meet the criteria for model or high power rockets. This includes metal
bodied rockets, liquid or hybrid fueled rockets, and rockets with any
type of homemade rocket motor.
'Experimental' rockets is an ambiguous term. In the early 1980's it
was used (reportedly coined by the magazine 'California Rocketry') to
describe rockets that exceeded the model rocket limit at that time (1
pound total liftoff weight and no motor above F power). More recently,
it has been used by the Tripoli Rocketry Association to describe the
class of rockets that use pre-manufactured solid or hybrid rocket
motors but that do not qualify as high power rockets. This includes
metal bodied rockets and those with more than 80,000NS of total
'HPR-lite' is not any type of 'official' rocket designation but has been
used to refer to rockets that exceed the old NFPA model rocket limit of
1 pound but still qualify as NFPA model rocket under current guidelines.
These rockets typically use E through G power and are built with much
the same techniques as high power rockets. This term originated in the
internet rec.models.rockets newsgroup. It should be noted that this
term refers to legal model rockets, not any type of high power rocket,
and might therefore be misleading to many. The term 'Large Model Rocket'
should be used instead.
Another term that has no formal definition but is more and more being
used in the literature is 'hobby rocketry'. This term includes both
model and high power rockets, but excludes amateur rockets. The
term 'consumer rocketry' has also been used, and means the same thing.
The term 'non-professional rocketry' encompasses all forms of model,
high power and amateur rocketry.
Finally, the editor of this document wishes to get on his soapbox for
just one moment and add the term 'stupid rocketry' to cover all those
who attempt to casually produce their own rocket fuel and/or motors
without the benefit of very serious study, and implementation, of the
processes involved and safety measures required. Especially note
that this comment is NOT aimed at serious amateur rocketry
organizations, college level research, etc. End of soapbox.
1.2 NFPA, FAA, DOT, ... Who are all these organizations and how do they
affect the rocketry hobby?
DOT (Dept. of Transportation) regulates shipping of rocket motors and
CPSC (Consumer Products Safety Commission) regulates what may and not
be sold as a 'consumer' items at the retail level.
FAA (Federal Aviation Administration) is responsible for airspace
control and regulates flights of rockets that exceed 1 pound and
enter FAA regulated airspace.
NFPA (National Fire Protection Association) makes recommendations for
use of non-professional rocket motors. Although the NFPA only
makes recommendations, most state and local laws concerning the
use of model rockets are based, at least in part, on NFPA
recommendations; especially NFPA 1122. The NFPA also has a draft
definition and safety code for High Power rockets, NFPA 1127.
BATF (Bureau of Alcohol, Tobacco and Firearms) has responsibility for
regulations concerning storage and use of explosives. This agency
has taken a recent interest in looking into how high power rocket
motors are stored and used.
ATC (Air Traffic Control) You must notify the nearest FAA ATC center
prior to flying Large Model Rockets or High Power Rockets.
1.3 What is the current legal status of model and high power rocketry in the
A. FAA Regulations:
* Rockets containing less than 113 grams of total fuel and weigh
less and one (1) pound do not require any type of FAA notification
and are not restricted by the FAA except where they pose a threat
* FAA "large model rockets" (see the definition in #1, above)
require that the nearest Air Traffic Control center (ATC) be
notified of the launch between 24 and 48 hours prior to the
launch. This is notification and not permission. In the U.S., try
calling 1-800-WX-BRIEF to get the number of the ATC center nearest
* FAA High power rockets (weighing more than 3.3 pounds, containing
HPR motors, or containing a total of more than 125 grams of
fuel) require a formal waiver be approved by the FAA and activated
prior to the launch. Refer to the full r.m.r FAQ (dated 1 Oct 94
or later) for more complete details.
* NOTE THAT THE FAA DOES NOT PLACE ANY RESTRICTIONS ON FUEL-PER-
MOTOR OTHER THAN THE TOTAL LIMIT OF FUEL. HOWEVER, MOTORS WITH
MORE THAN 62.5 GRAMS OF FUEL ARE HIGH POWER ROCKET MOTORS AND
REQUIRE HIGH POWER CERTIFI- CATION TO FLY. This does allow HPR
certified flyers to conduct low-end HPR launches (with up to about
240NS composite motors) without having to obtain a waiver.
* Remember that HPR waivers, ATC notification and high power
certification are all separate issues and must all be properly
B. CPSC Regulations/Restrictions:
* G class model rocket motors (80.01-160.00NS total impulse) have been
classified as high power by the CPSC. They are considered model
rocket motors by the NFPA. These motors are now restricted for sale
to buyers 18 years of age or older. This includes the sale of G
C. DOT Shipping Restrictions:
* Most single use rockets motors with less than 62.5 grams of
propellant are now classified as UN 1.4s and can be shipped via
UPS (with a HAZMAT fee) or regular parcel post.
* Most reloadable rocket motor fuel grains weighing less than 62.5
grams each are now classified as 'flammable solids' and may be
shipped via UPS (with HAZMAT fee) or regular parcel post.
* The UPS HAZMAT fee is now $10
* Any single use rocket motor containing more than 62.5 grams of fuel,
and any reloable motor fuel grain weighing more than 62.5 grams
are classified as UN 1.3c, or Class B, explosives. These motors and
reload grains may be shipped ONLY via Federal Express to certain
designated shipping points.
* Aerotech has announced it has received an exemption for single use
motors up to K class and reload grains for at least L, and possibly
M class motors, which allow these motors and reload grains to be
shipped UPS ground in the same manner as motors containing less
than 62.5 grams of propellant. Aerotech says these are now shippable
as class 4.1 flammable solids.
D. BATF Restrictions:
* Any rocket motor or reloadable fuel grain containing more than 62.5
grams of propellant is now classified by the ATF as a Class B Low
Explosive. This includes Aerotech reloads from J power and up.
* You must have a federal Low Explosives Uers Permit (LEUP) to
legally purchase Class B rocket motors and reloads, except under
certain restricted circumstances.
* You must have a federal LEUP to legally store rocket motors or reload
grains which contain more than 62.5 grams of propellant.
* You must comply with federal low explosives regulations when
transporting and storing Class B rocket motors.
* You must be 21 years of age to obtain an LEUP.
E. Other High Power Restrictions:
* You must be 'high power certified' to fly high power rockets.
* The NAR and Tripoli both have programs for obtaining high power
certification. You need to join one or both of these organizations if
you want to fly high power rockets.
* You must be at least 18 years of age to become high power certified.
1.4 I would like to get into Large Model Rockets. What are my options?
Who has NAR certified E, F and G motors today?
The following manufacturers currently have NAR certified E, F and G motors,
Motor Class Manufacturer Propellant Type
E Flight Systems, Inc. Black Powder
E Aerotech Composite (ammonium perchlorate)
F Flight Systems, Inc. Black Powder
F Aerotech Composite (ammonium perchlorate)
G Aerotech Composite (ammonium perchlorate)
There are 18, 21, 24, 27 and 29 mm diameter motors available. One
manufacturer (Aerotech) has reloadable motor casings for 18, 24, and
29 mm motors.
Several manufactuers sell rockets designed for E through G powered
flight. Refer to the previous list of addresses and get a few catalogs.
R.m.r readers have recommended kits from NCR, THOY, LOC, Aerotech,
Vaughn Brothers, Microbrick/MRED, and others. Look for the following
minimum features in E through G powered kits:
- plywood or fiber centering rings rather than paper or cardstock
- plywood, thick plastic, or G10 fins rather than balsa
- thicker motor tubes
- cloth rather than plastic parachutes
- thicker-walled body tubes
Remember to build these models stronger than smaller model rockets. Use
CA and epoxy rather than white or yellow glue. These rockets will
have to survive much higher stresses than smaller model rockets.
1.5 Is the proper term rocket 'engine' or rocket 'motor'?
I don't know. I don't really care. And neither should you! In this
document 'motor' and 'engine' are taken to mean the same thing and both
refer to "the thing in the rocket which makes it go 'whoosh!!' (or 'roar',
if flying high power :-)". If you want a sure way to start a fight with
a fellow rocketeer, just argue that whatever term he/she uses is the wrong
1.6 What do the letters and numbers on a model rocket motor mean?
The NAR has developed a motors classification scheme which has been
mandated by NFPA 1122 and most state regulations. This system
specifies the motors total impulse class, average thrust, and ejection
charge delay. This is printed on any motors certified by the NAR.
the pieces are as follows, given the example:
The first letter indicates the power range, as specified in the table
below. The number to the left of the dash is the average thrust of
the motor, in newtons. The number to the right of the dash is the
approximate ejection delay in seconds starting at the time of motor
burnout. The final letter is an optional manufacturer designation
for motor or fuel type. Note that letter designating total impulse of
the motor specifies an impulse *range*, not an exact total impulse. For
example, there are G motors that have anywhere from 90 to 160 NS of total
impulse....an Aerotech G42 is rated at 90NS and a G40 is rated at 120NS.
Motors with more than either 62.5 grams of total propellant or have more
than 160NS of total impulse are considered High Power motors. You must
be certified to purchase and fly these motors. Soon, it may also become
necessary to have a license to store high power motors.
Andrew Mossberg (email@example.com) recently posted this chart to
rmr, which includes approximate propellant weights for maximum impulse
motors for each class:
W Low High Low High 200 ISP Propellant
E Limit Limit Limit Limit Weight
R (NtSec) (NtSec) (lbsSec) (lbsSec) (grams) (lbs)
= ======= ======== ========= ========= ======== =======
A 1.26 2.5 0.28 0.56 1.3 0.0028
B 2.51 5.0 0.56 1.12 2.5 0.0056
C 5.01 10.0 1.13 2.25 5 0.0112
D 10.01 20.0 2.25 4.5 10 0.02
E 20.01 40.0 4.5 9 20 0.04
F 40.01 80.0 9 18 41 0.09
G 80.01 160.0 18 36 82 0.18
H 160.01 320.0 36 72 163 0.36
I 320.01 640.0 72 144 326 0.72
J 640.01 1,280.0 144 288 652 1.44
K 1280.01 2,560.0 288 575 1,305 2.88
L 2560.01 5,120.0 575 1,151 2,609 5.75
M 5120.01 10,240.0 1,151 2,301 5,219 11.5
N 10240.01 20,480.0 2,301 4,602 10,438 23.0
O 20480.01 40,960.0 4,602 9,204 20,875 46.0
P 40960.01 81,920.0 9,204 18,409 41,751 92.0
Currently, consumer rocketry stops at rockets with a total of no more
than 81,920NS of total impulse. Anything larger than that is by
definition an amateur rocket.
1.7 What is a CATO? Is it CATO pronounced KAY-TO or CAT-O?
The following definition has been posted to r.m.r. by Jack Hagerty,
(firstname.lastname@example.org) editor of the excellent r.m.r Glossary. For even more
complete information on the term CATO, refer to the glossary.
A motor failure, generally explosive, where all the propellant
is burned in a much shorter time than planned. This can be
a nozzle blow-out (loud, but basically harmless), an end-cap
blow-out (where all of the pyrotechnic force blows FORWARD
which usually does a pretty good job of removing any internal
structure including the recovery system) or a casing rupture
which has unpredictable, but usually devastating, effects.
Another form of CATO is an ejection failure caused by either
the delay train failing to burn or the ejection charge not
firing, but the result is the same: the model prangs.
Opinions on the meaning of the acronym range widely. Some
say it's not an acronym at all, but simply a contraction of
'catastrophic' and should be pronounced 'Cat-o' (which sounds
better than 'cata' over PA systems :-). Others maintain that
it is an acronym but disagree on the meaning, offering a
broad spectrum of 'CAtastrophic Take Off,' 'Catastrophically
Aborted Take Off,' 'Catastrophe At Take Off' and the self
referential 'CATO At Take Off.' The acronym crowd pronounces
it 'Kay-Tow', like the Green Hornet's side kick. It has been
pointed out, though, that all of the above are 'post-hoc'
definitions since LCO's were using the term over range PA
systems long before any formal acronym was established.
1.8 When a consumer rocket motor fails (i.e., CATOs) does it explode or
To be precise, consumer rocket motors do NOT 'detonate'. Black powder
rocket motors 'deflagrate'. Detonation involves the creation of super-
sonic shock waves. Use the term 'explode' when discussing CATOs involving
split motor casings, holes blown out the sides of models, etc.
1.9 Why don't I just make my own model rocket motors? Shouldn't I be able
to custom-make better, more powerful motors at a cheaper price?
This subject has been hotly debated on r.m.r. It is one of those
'emotional' subjects that find people either firmly for or against.
The bottom line is that rec.models.rockets is primarily a newsgroup for
discussing *consumer* rocketry (which covers model rocketry and high
power rocketry). Some amateur issues are discussed, but these are not
the primary focus of the group. Manufacturing your own rocket motors can
be a very dangerous thing to do, unless done properly, and with extreme
care. The odds are you will not make motors that are of any higher quality,
total impulse, reliability, or cost less than pre-manufactured consumer
It is the opinion of the editor(s) of this FAQ that you should NOT try
to manufacture your own motors. If, however, you insist on partaking
in amateur rocketry, then the editor(s) of this FAQ urge you to get in
contact with an established amateur rocketry group for guidance and
Copyright (c) 1996 Wolfram von Kiparski, editor.
Refer to Part 00 for the full copyright notice.