Andrew Greenberg asked me to post some information about Tripoli certification and how PSAS members might go through this process.
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 Motor Classification
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:
These classifications are applied to members as follows:
|Certification Level||Maximum Motor Class|
(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.
Choosing a Certification Rocket
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:
- total rocket length. Needs to be long enough to hold the J motor.
- fin design. It has to land undamaged, so avoid swept-back fins
- body diameter. Being able to get your hands inside is a huge feature, so 4" is a reasonable lower limit.
Certification Rocket Suggestions
Let's look at some specific kit suppliers:
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.
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.
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.
The Liberty 4 looks like the best choice here, although you'd want to add a kevlar shock cord protector. Also, while the stock phenolic tubing is fine for cert flights, the dynawind upgrade would make the rocket more sturdy.
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.