AeroMail - 2012/08

I appreciate the rocketry article by
John Boren in the June 2012 issue of
Model Aviation. Several points in the
article require elaboration.
First, the hobby is now generally
referred to as “sport rocketry” and is
comprised of model and high power
rocketry. Model rocketry, in general,
consists of rockets weighing under 3.3
pounds and containing less than 4.4
ounces of propellant (two “G” motors
would typically contain up to 4.4
ounces of propellant). The AMA only
permits rockets classifi ed as “model”
rockets.
High power rockets exceed the
limits noted above. The “K” powered
models featured in the article pictures
are high power rockets. Two important
elements associated with high power
rocketry are user certifi cation and FAA
authorization. There are three levels of
high power certifi cation; the certifi cation
level required depends on the motor
impulse class that the fl yer wishes to fl y.
There are two organizations that
sponsor high power certifi cations. They
are the National Association of Rocketry
(NAR) and Tripoli Rocketry Association
(TRA). Membership in either
organization is required for certifi cation.
Both organizations describe the
certifi cation process on their websites.
Part 101 of the Federal Aviation
Regulations covers sport rocketry.
In the case of high power rockets, a
launch authorization/waiver process
is required. Membership in a NAR
or TRA club is highly recommended
for those interested in launching high
power rockets as the clubs generally
coordinate the FAA authorization/
waiver requirements.
The “P” motor referred to in the article
is outside the limits of sport rocketry.
National Fire Protection Association
document 1127 (NFPA 1127) defi nes
high power rocketry. Total impulse is
limited to 40,960 Newton seconds (Ns)
or “O” motors by that document.
The reference to a P-150 motor
putting out over 40,000 Ns of thrust
is incorrect. The abbreviation Ns refers
to Newton seconds or total impulse
of a sport rocket motor. Thrust is a
measure of force, typically in Newtons
or pounds force. A “P” motor, if it
were permitted, would have between
40,960.01 and 81,920 Ns total impulse.
The conversion from Newton seconds
to pound seconds is to divide by 4.45.
The P-150 designation probably refers
to a reloadable motor casing produced
by Cesaroni Technology; P-150 is
nonsensical as a sport rocketry motor
designation