[PSAS] Tripoli/NAR certification process

Keith Packard keithp at keithp.com
Wed Aug 12 15:53:19 PDT 2009


Andrew asked me to post some information about Tripoli certification and
how PSAS members might go through this process.

(all of this information is available at the NAR or Tripoli web sites,
of course)

First off, I should explain what certification is and why it is useful.

Both Tripoli and NAR 'certify' amateur rocketry participants, this
certification is required to purchase high power rocket motors and fly
high power rockets at Tripoli and NAR sponsored flights. As a member of
one of these organizations, as long as you follow the rules, you are
covered by a liability policy carried by the organization. Part of these
rules limit the size of the motors you may fly -- higher certification
levels extends the maximum total motor size, and, hence, the maximum
rocket size and potential for damage or injury.

Rocket motors are classified by total impulse (in Newton Seconds), a
measure of the total energy produced by the motor when built as
specified by the vendor. These classifications are how the familiar
letter assignments are given:

	Class	Min(NS)	Max(NS)
	A	 1.25	  2.5
	B	  2.5	    5
	C	    5	   10
	D	   10	   20
	E	   20	   40
	F	   40	   80
	G	   80	  160
	H	  160	  320
	I	  320	  640
	J	  640	 1280
	K	 1280	 2560
	L	 2560	 5120
	M	 5120	10240
	N	10240	20480
	O	20480	40960
	P	40960	81920
	...

These classifications are applied to members as follows:

	Certification Level	Maximum Motor Class
	None			G
	1			I
	2			L
	3			unlimited

(Level 3 fliers are generally constrained by other things than motor
class, like the maximum altitude permitted for a given launch site)

Ok, so certification offers the ability to fly larger motors and remain
covered by the NAR or TRA insurance policy, an important, but perhaps
not absolute requirement for PSAS. There are additional benefits though,
the first is that with certification, you can fly high power rockets at
an NAR or TRA sponsored launch. Without certification, you can't even
fly *near* a sponsored launch or the organization sponsoring that launch
would be in violation of the rules and lose their coverage (and, most
likely, access to their launch site).

Finally, an NAR or TRA certification permits you to purchase commercial
rocket motors up to the specified class. This self-regulation by the
motor vendors in cooperation with NAR and TRA serves to keep rocket
motors unregulated by the government. 

An important statistic here is that while the NAR and TRA insurance
policies have been in effect for over 40 years, they've paid out only a
few thousand dollars in damage claims, and have never had a fatality or
serious injury. In other words, the system is demonstrably working.
Prior to this system, rocketry was quite dangerous with many people hurt
or killed while building their own motors (a family friend of mine had
his arms covered with black powder tattoos from an exploding motor, for
instance).

Ok, so now that you know what certification is and why it is useful,
let's see how you might go about getting certified.

For all three levels, the essential requirement is that you build and
fly a rocket using a motor from your target certification level and
recover it undamaged.

For Level 1, that's really the only requirement there is -- build a
rocket that can fly an H or I motor and then have the motor building,
loading, flight and recovery witnessed by a suitable certifying member
(the rules for NAR and TRA differ on who can act in this capacity).

Level 2 also requires that you pass a written test, along with flying on
a J, K or L motor.

Level 3 adds significant requirements to the rocket design, including
redundant electronic deployment systems, along with requirements to work
with a suitable mentor and document the whole design, build and flight
process. The Level 3 requirements are hard enough that there are far
more Level 2 members than Level 3 (I, myself, am a Level 2 certified NAR
and TRA member).

Because you can only fly certification attempts at one class above your
current certification level, you cannot simply jump to Level 3 without
first passing through Level 1 and 2.

Enough with the rules, let's examine the practical options for
certification.

Because Level 1 and 2 rockets can be simple motor-ejection rockets, it
is quite reasonable to consider building a single rocket for both
levels. While many people do build more complicated rockets for their
Level 2 certification, it's not necessary. With this in mind, we look to
rocket kits that can fly on both an H and J motor, and otherwise are as
simple as practical. A kit has the significant advantage of being stable
by design, and having all of the 'hard' machining done already, leaving
a fairly simple assembly process to complete the airframe.

Commercial rocket motors come in a wide range of lengths, but on a few
standard diameters -- (in mm) 18, 24, 29, 38, 54, 75, 98, 150. These
sizes come from old stock tubing sizes (usually measured in inches). As
such, most rockets are designed to accept one of these sizes, although
they generally accept a wide range of lengths. The PSAS rocket uses 98mm
motors, for instance.

Commercial H motors are available in either 29 or 38mm sizes. Commercial
J motors are generally either 38 or 54mm. So, building a 38mm rocket
means being able to fly both sizes in the same airframe.

The trick with flying a wide range of motor sizes is to build an
airframe which is light enough to fly stably under the smaller motor
while being strong enough to stay together with the larger motor.

Stability is a function of speed -- go fast enough and the fins generate
enough force to keep the rocket going straight. So, the goal is to be
going fast enough on leaving the launch rail. A typical rule of thumb is
to have a motor that generates 5 times more thrust than the weight of
the rocket. 

An H motor generates between 100 and 200 N of average thrust, so as long
as your rocket is less than 2-4kg, things should be fine. 

A rocket strong enough to withstand the J motor will generally need fins
made of plywood or some composite material (fiberglass or carbon fiber),
and be mounted 'through the wall' instead of just glued onto the
outside. The 38mm J motor will be about 14" long.

Beyond motor mount, there are only a few other variables of interest
here:

 1) total rocket length. Needs to be long enough to hold the J motor.
 2) fin design. It has to land undamaged, so avoid swept-back fins
 3) body diamter. Being able to get your hands inside is a huge feature,
    so 4" is a reasonable lower limit.

Let's look at some specific kit suppliers:

Madcow rocketry:
        They make a range of 4" models, with simple paper tubes, plastic
        nose cones and plywood fins. Make sure the model is long enough
        to hold the J motor; I think that rules out the Cowabunga. And,
        for less potential for fin damage, I'd suggest either the Little
        John or Super DX3.
        
Polecat Aerospace:
        They make a range of 4" and 5.5" models, but all of the models
        with a 38mm motor mount have fancy fins, prone to breaking on
        landing.
        
Binder Design:
        Lots of choices with 38mm mounts here, but Binder excels at
        weird fin designs. The Sentinel, Excel/Excel+ (yes, I know it
        says 'I' motors max, but they've flown fine with a baby J) both
        look like good choices.
        
Giant Leap Rocketry:
        The Liberty 4 looks like the best choice here, although I'd
        encourage anyone considering this to think about upgrading to
        the dynawind tubing and a kevlar shockcord protector.


Of these, the Liberty 4 stands out as something purpose-designed for
L1/L2 certification, although it's nearly $150 with the suggested
upgrades.

All of these can be built with simple hand tools; if there are several
people interested, we can hold a rocket building party some weekend as
it should only take a day or two to construct them.

In terms of upcoming launches, OROC is holding their only Willamette
valley launch down in Sheridan over the weekend of September 12/13, and
then the last 'big rocket' launch the weekend of October 17/18 out at
our usual launch site in Brothers. You'll need to let OROC know that you
want to fly a cert flight so you can make sure suitable people are
on-hand to witness and sign-off on the paperwork, as well as proctor any
written exams.

-- 
keith.packard at intel.com
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