Chapter 12. The Level 3 Certification Process
Getting your Level 3 certification takes more planning and time than the first two certifications. It involves creating a detailed engineering package for your flight, getting it approved, and documenting the construction of your rocket. A senior member of NAR or TRA will review and approve your engineering document, and a second member must sign off on the flight. The process is slightly different for NAR and TRA, although there are a lot more similarities than differences.
This chapter covers the certification for both NAR and TRA. A few of the steps are required for one but not the other; however, none are a bad idea no matter which agency you intend to use. Once you’ve read the chapter to get an overall idea of how to get your certification you can fine-tune the process by visiting the NAR or TRA website.
Project Requirements
Every engineering project should start by establishing the requirements. This seems simple and obvious, yet it turns out to be an often-neglected step. For example, twice this year I have seen people struggling with their Level 3 certifications, trying to figure out how to keep a rocket they have already built from exceeding the local altitude waiver! It’s fair to say the important step of establishing requirements was skipped. So let’s start by looking at the base requirements for your Level 3 project:
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You must build a rocket that uses a single M or larger motor. Clustered or staged rockets are not allowed for the Level 3 certification flight.
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The rocket must be a relatively standard, normal-looking rocket. That means a basic body tube, nose cone, and fin set.
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The rocket must use electronic deployment with redundant systems. There must be redundant power sources for flight computers, arming switches, the computer itself, and igniters used for the deployment charges. You may use a motor ejection charge as a backup, but two computers, as you saw in Chapter 7, is the more common choice.
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The rocket must stay within the FAA waiver for the flying site. You probably know the altitude limit for your flying site by now, but do you know the horizontal distance? If your rocket goes above the altitude ceiling, or drifts outside of the distance limit, your flight will be disqualified. The simulated altitude should generally not exceed 90% of the actual altitude limit.
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The rocket must be returned by parachute. It is acceptable to return the rocket in multiple pieces, as long as each piece has its own parachute. The maximum descent rate at landing should be 20 ft/s or slower.
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The rocket body tube must be at least four times longer than the body tube diameter. This requirement is not quite as odd as it might seem at first. The calculations used by most rocket simulators are not valid for very fat rockets.
You might add your own requirements to this list. For example, the Level 3 flight can be expensive, although there are many ways to cut costs. What is your budget? Your flying site might be relatively small, and winds might be relatively high, especially at altitude. You might add dual deployment to the list of requirements to help keep the rocket inside the waiver area.
No matter what, though, start your project by creating a well-thought-out set of requirements.
Your Certification Team
The composition of the certification team varies slightly depending on whether you are being certified by NAR or TRA. Either way, your primary mentor will be a senior member who is approved by the national organization. In both cases, a second person must sign off on the paperwork.
For NAR, this first member of your certification team must be a member of the NAR Level 3 Certification Committee, or L3CC. You can find a list of current members at the NAR website. This person will be involved throughout the design and construction process, so picking someone who is geographically close is important. The second certification team member can be any NAR member with a Level 2 or 3 certification. This person does not need to be involved right away, although it doesn’t hurt if they are.
TRA flights must be approved by a member of the Technical Advisory Panel, almost always abbreviated as TAP. A second TAP member must sign some of the paperwork. I worked with two TAP members from the very beginning of my own certification flight, which turned out to be very useful, since I decided to fly my rocket at BALLS rather than our local flying site. The TAP member who approved my Level 1 and 2 flights did not go to BALLS that year, so my flight was approved by the second TAP member. You can find a list of TAP members at the TRA web site.
Whichever organization you select, get in touch with the selected L3CC or TAP member right away. Let the person know you are starting to plan a Level 3 certification flight. Show them your engineering requirements to see if they have any corrections or additions. You probably have a general idea what sort of rocket you want to build. Perhaps you would like to build a 4-inch fiberglass rocket, like Ganymede, coming up in Chapter 13. Your mentor might steer you away from that rocket because local flight restrictions make it very hard to keep under the altitude waiver, or might have a prepared outline for the engineering package. In any case, it is a good idea to discuss your plans with the L3CC or TAP member even before you start the engineering package.
The Engineering Package
The major document for your Level 3 certification is an engineering plan describing your rocket, how it was built, and how it is expected to fly. This section provides an outline and discussion of what should go in that document. It follows the excellent outline NAR provides on its website, but also fulfills the requirements for TRA. NAR also has a sample engineering package on its website.
Before getting into the details, though, let’s step back and set some expectations. Your L3CC or TAP mentor may have some specific requirements or recommendations, but in general, keep in mind that there is no requirement to write a production-quality document for your engineering package. It can be a relatively short, concise document consisting of hand-drawn plans, or it can be a polished digital document with embedded photographs or videos. This is your project. You need to meet the minimum requirements outlined here, but beyond that, the only people you have to satisfy are your mentor and yourself. If the content and format of the document work for the two of you, it is acceptable.
Also, this document should be written in two stages. The first is a planning stage. Write all of the document you can without actually buying any parts for the rocket. Create the plans, write your checklists, pick a motor, and run the simulations. This planning step will help you think through all aspects of the design before you shell out money for parts that you might end up exchanging for an alternative. At this point you have a great plan for your Level 3 attempt, and it’s time for a review by your mentors. Their suggestions may save you a great deal of time and money, as their experience with rocketry and local flying conditions will allow them to make suggested changes well before you start buying parts. Once that review is complete, buy your parts and build your rocket. With the rocket complete, go back and fill in the portions of the document that remain.
Introduction
The first section starts with a general overview of the rocket and flight. This is a good place to list or describe your project requirements. Give a brief description of the rocket, motor, and flight. Be sure to mention any novel design features, risks associated with those features, and how the risks are mitigated.
This section could be fairly short and still meet all of these requirements. For example, here’s an introduction using Ganymede (discussed in Chapter 13) as an example:
Ganymede is a 4-inch-diameter, 90-inch-long, all-fiberglass rocket. It will fly on an AeroTech M1279M motor. Using RockSim, the simulated altitude is 13,831 feet, close to but still well under our local altitude limit of 15,000 feet.
The rocket uses dual deploy to bring it down close to the launch pad, keeping it inside the waiver area. A single 36” hexagonal parachute is deployed at apogee, and a 60” Sky Angle parachute is deployed at an altitude of 1,000 feet.
The projected altitude is a bit over 90% of the waiver altitude. As will be seen, previous simulations show that the actual altitude is generally a bit below the simulated altitude, so the risk of flying too high is minimal.
Scale drawing
Throughout this book, you’ve been using RockSim or OpenRocket to design and simulate rockets. You will need to do the same for this rocket. The drawing produced by either of these programs is perfectly adequate for this section. It shows the major dimensions, center of pressure, caliber, and center of gravity.
NAR also asks for the aft limit for the center of gravity. This is the position one caliber in front of the center of pressure. It’s handy to know, since you can balance the final rocket to find the approximate center of gravity. Knowing the aft limit gives a quick final check on the stability of the rocket.
Construction
This section describes the materials and techniques used to build the rocket. Look at the construction chapters in this book. Each has a table showing the materials used, photographs showing the steps and techniques used for construction, and a description of the process. That’s what you need here, although not necessarily to that level of detail. Remember, you need to get the point across. You don’t have to write perfect, publication-quality prose.
You must provide a complete list of all parts that will be used. This includes major parts, like the body tube. Will it be fiberglass? If not, and if the rocket will exceed Mach 1, expect your mentor to take a very close look at the possibility your rocket will collapse from aerodynamic forces. What sort of launch lugs are you using? Are they sufficient for the weight of the rocket? Your list should even include types of glue, fasteners, fillets, and other reinforcements. Be very complete in this section. If it will fly with the rocket, list it.
Cover construction techniques. Be sure to include drawings that show where the fillets will be, what type of glue will be used where, and how the glue will be cured. Epoxy dries better at warmer temperatures. If you are building your rocket in a colder climate in the winter, will you bring the rocket indoors for the glue to cure properly? Will your fillets be large, and if so, will you be using any sort of filler? If you decide to fiberglass any components, how many layers will be used, and in what direction will the grain of the fabric lie? Are you using screws or bolts? Will you use Loctite to make sure they don’t rattle loose? These are all important questions for any rocket, but especially one this size. Be sure the answers are in your construction section.
Your introduction contained a scale drawing of the rocket. This section needs to expand on any details the overall drawing does not show. In particular, you need to show where the motor mount centering rings are placed, how fins are attached, where the launch lugs are located, and how the instrument bay is constructed.
Be sure to discuss anything that is even remotely unusual. For example, breakaway launch lugs are popular on some rockets. If you plan to use them, that’s certainly something you should discuss. Some people use weight to reduce altitude. A popular method is to use water or sand that gets dumped at apogee. If you intend to drop water, sand, or anything else from the rocket in flight, discuss the reasons and mechanism in detail.
NAR recommends a completely separate section for the recovery system, so you can skip details about how the recovery system works and how the components are attached for now.
The initial package you show your mentors consists of drawings and descriptions, but the final package should also include photographs. In particular, it should have photographs showing the internals. For example, you should include a photograph of the motor mount with the centering rings attached before it is mounted in the rocket, as well as ones that show how the fins are attached, including the interior fillets. Include a ruler or a quarter (which is very close to 1 inch in diameter) as a scale reference in photographs where the size may not be obvious. You can also use the same technique you see in this book, where most photographs are taken with a cutting board for a background. The major divisions on the cutting board are also 1 inch apart.
It is also a great idea to invite your certification team over to inspect the rocket at key points of construction. An M motor is a powerful device. They’ll want to make sure the rocket will stand up to that power.
Recovery
According to NAR statistics, a staggering 72% of model rocket flight failures are recovery system failures. This includes flights where pieces fell off, the parachute did not open, and the rocket returned ballistically. Many of the flights monitored by NAR are low-power rockets, where the danger is relatively small, but a Level 3 rocket is very different from a few ounces of light paper tube, balsa wood, and plastic. That’s why the recovery system gets its own section. You don’t want a failure with a large Level 3 rocket.
Start by describing, in general terms, how your recovery system will work. For virtually every Level 3 rocket, this will mean flight computers controlling dual deployment, with a small parachute or streamer deployed at apogee and a larger parachute deployed about 800–1,000 feet from the ground. Be prepared to defend your choices if this is not what you are planning.
The detailed description consists of six parts: recovery speed, venting and shear pins, flight computers, the recovery chain, recovery charges, and testing. Many of these sections need some sort of calculation. In all cases, tables or manufacturer’s recommendations can be used instead of an actual calculation, but be sure to include the source for the table or recommendation.
Recovery speed
Chapter 9 described parachute selection in detail. Use that chapter to decide on the type and size of parachutes you will use at altitude and for the final descent. NAR recommends a maximum descent rate of 20 ft/s for landing. This might seem a bit slow, but this is a large, heavy rocket. As you recall, the landing energy is proportional to the weight of the rocket times the square of the speed. Reducing the speed of the rocket dramatically reduces the energy it will impart when it lands.
Show the complete calculation for recovery speed, including the coefficient of drag for the parachutes, the weight of the rocket, and the calculated terminal velocity. If the parachute uses parachute bags, cable cutters, or any other unusual mechanism, describe it fully.
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Be sure to recheck the recovery speed calculation once the rocket is built and you have an actual weight.
Venting and shear pins
Your flight computer needs vent holes to work properly, and the parachute bays need vent holes so a rapid ascent does not overpressurize the compartment, forcing the rocket apart early. Refer to “Finding Altimeter Vent Hole Sizes” for help calculating vent hole sizes. Be sure to include the calculations here.
Level 3 rockets that fly high and fast almost always use shear pins to prevent drag separation of the rocket and to reduce the chance that the rocket will separate because of rising pressure in the parachute compartment. Include the size and location of the shear pins, or the reason you don’t think you need them.
Flight computers
Describe where the computers will be mounted, how they will be powered, and how they will be turned on and off. Notice I said computers, not computer. Some sort of backup deployment system is required by NAR. While that can be an ejection charge on a motor, most M motors don’t use ejection charges. Plan for two computers from the start.
Include the make and model of the flight computers, along with a brief description of their sensors. Most flight computers use barometric sensors, but most also use accelerometers for launch detection. Many Level 3 rockets will break the sound barrier. For these, it is important to use a flight computer that uses some sort of algorithm and sensor combination to guard against spurious altitude readings as the rocket passes through the sound barrier. If your rocket will break the sound barrier, be sure to get computers that can handle it, and say so in this section.
Each computer must have its own power chain. That includes separate batteries and arming switches. It also includes separate igniters for both the apogee and dual-deploy ejection charges. While there is no requirement to use separate ejection charges, it is still the most common choice. Why skimp on a little black powder? A completely redundant ejection charge could easily be the difference between a safe recovery or a lawn dart.
You must be able to arm and disarm the computers on the launch pad. This does not have to be super fancy, like the mechanism shown in “Modifying Deimos or Phobos for Dual Deploy”. It can be as simple as twisting two wires together, as long as you have some sort of access panel that allows them to be untwisted while the rocket is on the pad. You also need some way to disarm the computers after the rocket lands. This covers disarming unfired ejection charges so the rocket can be safely handled.
Include a circuit diagram showing how the computers, batteries, arming switches, and igniters for ejection charges will be wired. Don’t include the complete circuit diagram for the computers; it’s fine to show them as a block with their various input and output connections. Circuit design software like Eagle, used in this book, is great for creating your circuit diagram, but a neat hand drawing will do just fine.
Recovery chain
Methodically work through the entire recovery chain, starting with the eye bolt that connects the recovery system to the rocket and working your way to the parachute. Include how the eye bolt is mounted in the rocket; the kind and rated strength for the bolt; the length, rated strength, and attachment method for the shock cord; the rated strength for the quick links or any other attachment mechanisms; and the method for connecting the parachute to the shroud lines.
The parachute must be protected from the hot gases of the recovery charge. While some kind of recovery blanket is common, there are other mechanisms. Describe the mechanism you’re using and how it is attached to the rocket.
Recovery charges
Show your calculations or cite sources for the choice of recovery charge size. This is covered in detail in “Predicting the Recovery Charge Size”. Describe how the ejection charges will be contained until deployment. Be sure and describe the type of igniters used to fire the ejection charge and how they will be secured.
Testing
Calculations and theory are fine, but an actual test is the only way to verify your choices, especially the choice of ejection charge size. Do a complete test like the one described in “Testing Recovery Charges”. Include photos and videos if possible. This is also a great time to invite your mentor over to watch, both to show that your recovery system will work and to get comments and advice on improvements.
I’ve seen several people bring their rocket to a launch specifically to do a recovery system test. These tests are treated just like a launch, running through a full checklist and performing a countdown, but the rocket never leaves the launch pad. This is a great way to make sure you mentor or others in the club get a chance to help with suggestions or to correct any issues.
Stability Evaluation
While we tend to concentrate on the center of gravity and center of pressure, if you think back to the material you have already read, there is a lot more to stability than just the rocket’s caliber. Stability literally starts on the launch pad, and that’s where this section should begin.
Describe the launch buttons or whatever mechanism you will use to guide the rocket for the first few feet of flight. Be sure to include information about how the launch buttons are attached. Describe the launch pad, and in particular the length of the launch rod. Level 3 rockets tend to be fairly large. Unlike smaller rockets, the weight of the launch pad may not be sufficient to keep the launch pad itself on the ground. Describe any stakes or tie-downs used to secure the launch pad.
Your rocket must be going fast enough for the fins to work before it leaves the launch pad. The generally accepted minimum launch speed is 45 ft/sec, but that really is a minimum. It is easy enough to get twice that with most Level 3 rockets. Include a calculation or the number calculated by your simulation showing how fast the rocket will be traveling as it clears the launch rail. If it is a bit on the slow side, consider adopting more stringent requirements for wind speed than the generally accepted 20 mph maximum.
You also need the traditional center of pressure and center of gravity calculations. Your simulation gives the location of the center of pressure. The center of gravity needs to be at least one body tube width in front of the center of pressure. Mark the calculated center of pressure and the actual, measured center of gravity. A Sharpie works great for this.
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Don’t mark the calculated center of gravity on the rocket. Wait until the rocket is complete and mark the actual center of gravity. Depending on the particular motor you use, you may need to wait until launch day for a final check, but you can get a pretty good idea with a partially assembled motor.
Flight Profile
Describe the flight itself. This is essentially a summary of the flight simulation. A printout of the simulation is probably acceptable, although you can summarize the key points, too.
You may want to include more than one simulation. Your club may have multiple launch locations. The rocket’s performance can vary quite a lot depending on the altitude of the launch site. You might want to include simulations for high and low temperatures, which can also have a big affect on the flight parameters. Flight simulators can simulate the effect of wind; be sure to check the simulated recovery distance against the expected flight waiver.
This section should include the specific motor to be used for the certification flight. It must be an M, N, or O motor that is currently certified by NAR or TRA. Check their websites for a list of certified motors.
Be sure and include the speed as the rocket leaves the pad, the maximum speed, and the landing speed. Include the maximum acceleration, which gives some idea of the forces on the internals of the rocket, and the coefficient of drag, which gives some idea of the forces on the external components.
List the expected altitude. This should generally be at least 10% lower than the FAA waiver on flight day.
Give the launch weight and recovery weight for the rocket.
Checklists
You’ve seen checklists throughout this book. They are a required part of your engineering package, and you will be expected to use them for the flight.
You can use the checklists in this book as a guide. NAR also includes a very detailed outline of its checklists. Honestly, this is one area where I think they go overboard. According to Atul Gawande’s The Checklist Manifesto: How to Get Things Right, an ideal checklist should have five to nine items. If it gets much longer, it becomes tedious to use and is often ignored. It should be short, specific, and to the point. It should not include instructions on how to do routine tasks like pack a parachute and wrap it in the recovery blanket, but it should include something like “pack the parachute in the recovery blanket.”
With that in mind, be sure you have checklists for both normal and abnormal situations. Here’s a good checklist of checklists. It includes the checklists from NAR’s outline, plus an additional one of my own.
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Things to take to the launch
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Prelaunch checklist
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Launch checklist
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Post-flight checklist
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All recovery charges did not fire
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Misfire checklist
If you find a checklist is growing too long, break it up into several smaller checklists. For example, instead of a prelaunch checklist, you might write a rocket assembly checklist and a launch pad checklist.
Keep these on a clipboard or in a notebook on launch day.
If your mentor wants more detail than you are inclined to put in the checklist, it’s likely because they want to know you have thought through all of the contingencies. In that case, one good strategy is to put your checklists in the engineering package with comments under each checklist item. This shows that you have thought through the details—and forces you to do so!—while keeping the checklists themselves short and to the point. On launch day, use the checklists without the comments.
Building Your Rocket
Once your L3CC or TAP mentor approves your engineering package, and only once they approve it, buy the parts and start building your rocket. For must of us, this is the fun part. Take your time and enjoy it.
Remember to take photographs for the final version of your engineering package. Plan plenty of extra time for ejection charge tests and coordinating visits with your mentor.
Flight Day
Your L3CC or TAP member will probably want to watch you build your motor and assemble the recovery system. I like doing most of this work the night before the launch. If you do, too, invite your mentor over for the final preparations.
Each organization has paperwork that needs to be filled out and signed. Go to the NAR or TRA website and download the latest paperwork. Fill out everything you can, and then take the paperwork with you to the launch on a clipboard with a pen. Make things as easy on your TAP or L3CC member as you can. It is up to you to make sure the paperwork gets filled out and turned in.
By now, you are quite ready for the flight, and you are probably anxious to get your rocket in the air! In addition to all of the other preparation, following all of the checklists, and coordinating with your evaluation team, there is one final step to take: you need to check the weather.
This is more than a check of the ground weather conditions. That’s important, but you also need to check conditions aloft. Level 3 rockets are either very large or they will go very high. A typical Level 3 rocket like Ganymede, which we’ll build in the next chapter, can easily hit 13,500 feet. If your launch site is at a high altitude, that’s enough to reach the jet stream. Even if you don’t hit the jet stream, winds aloft are often very different from surface winds. Unless you want to risk drifting outside of the waiver area, you need to check the winds aloft for any high-altitude flight.
Fortunately, pilots have great resources for keeping track of the winds aloft, since that’s where they work. You can get the same weather reports pilots use. One source is the Aviation Weather Center. Spend some time getting used to this site well before launch day, and then check the site on launch day to make sure your rocket will not drift too far.
Once everything is ready, take one more moment. It took a lot of preparation to get to this day. Were you rushed? Did you follow your checklists? Does everything feel right? I have literally walked out to the pad and taken a rocket off when there was nothing left to do but push the launch button because things just did not feel right. Perhaps the winds picked up, or some clouds were getting a bit close. It is far better to pull a rocket off of the pad because you are not sure it is ready than it is to fling 30 pounds of aluminum-tipped fiberglass into the air at Mach 1.5 and find out later the parachute popped off because a quick link wasn’t closed.
OK, so you’re ready? Point that tracking antenna at the rocket, give the LCO the final OK to launch, and enjoy the moment.