Advanced Rocket Design
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The current User's Guide is very much a work in progress, any help would be greatly appreciated! |
Advanced Rocket Design
In this section, advanced design principles and concepts are discussed, with step-by-step instructions describing how to incorporate these techniques into designs created in OpenRocket. Implementing the techniques described in this section may require specialized materials and electronic devices intended for use only by experienced rocketeers.
Advanced rocket design encompasses configurations for high power rockets generally, including:
- recovery systems
- through-the-wall fin construction
- electronic and dual deployment
- complex multi-staging (such as motor racking) and motor clustering
- roll stabilization
Additionally, you may find that using mass and center of gravity (CG) overrides will improve OpenRocket flight and recovery simulation accuracy.
Recovery Systems
Recovery Techniques
Recovery systems are intended to return a rocket safely to the ground, without harm to people or damage to the rocket or other objects. Though recovery mechanisms vary greatly, recovery systems generally include elements of one or more of these techniques:
- featherweight
- break-apart
- streamer
- parachute
- helicopter
- gliding
Featherweight and Break-Apart Recovery
Featherweight and break-apart recovery work by creating enough drag to ensure that the terminal velocity of the rocket is so low that it won't be damaged or do damage when it hits the ground. Featherweight designs are often minimum diameter rockets that eject the burned-out motor casing altogether, or use the ejection charge to shift the casing position rearward after motor burnout (within an extended motor hook), to induce instability and cause the rocket to tumble. Break-apart recovery, aerodynamically, does the same thing, increasing drag and inducing instability by breaking the rocket into two or more sections connected together by a shock cord. Typically, a feather weight rocket, and each section of a break-apart rocket weighs less than one ounce.
Example Featherweight Design
In earlier years, Estes sold a few rockets that featured Featherweight Recovery, meaning that a very light model could spit out its used motor casing, and land directly on the ground with no damage, rather like a badminton shuttlecock.
Ejecting burned-out motor casings is not allowed in NAR contests unless a streamer or parachute is attached to the ejected casing.
Example Break-Apart Design
Another approach to bringing a lightweight rocket safely to earth is to break the airframe into several aerodynamically unstable pieces, and "flutter" them back to earth.
One such design: the Unicon (for "Unified/Consolidated" - a stretch, I know) appeared as a plan in the Estes Model Rocket News publication, probably about 1973-4. The body tube featured 3 pieces of launch lug, as did the nose cone. Into these lugs plugged one of 3 balsa sticks, each of which held a fin, and a piece of body tube attached to the fin root and the stick. to provide a stable anchor against the body. The entire assembly was connected with pieces of heavy-duty thread.
When the ejection charge fired, the nose cone popped off, releasing the sticks with fins, which, tied to the body tube and nose cone, fluttered in the air, and slowed descent of the main airframe as it landed.
This author built one, and it worked pretty well.
Streamer and Parachute Recovery
Streamers and parachutes add drag to slow the rocket descent rate. Generally, a larger streamer is always better. But, streamer size is an example of the principle of diminishing marginal returns, eventually making a streamer larger will only add slightly increase drag (a rocket weighing more than 10 oz is beyond the effective use of a streamer). On the other hand, because of their efficiency, parachutes create more drag with less cloth than any other method, and virtually all high power rockets use parachutes.
Example Streamer Design
A method of recovery favored on windier days is to attach a flame-retardant streamer to the shock cord, in place of a chute. Using OpenRocket you can simulate streamer recovery by equipping your rocket design with a streamer from the Mass objects section.
A streamer flaps in the wind as the rocket falls, losing altitude faster than an equivalent volume of packed parachute. Because it comes in faster, it won't drift as much in the wind. The rocket will also hit harder, potentially risking damage. OpenRocket can help you estimate how fast your model will land.
By using "snap swivels" - small brass clips usually found in the fishing tackle aisle - you can prepare both a parachute and a streamer for a rocket, choose your method of recovery at the field, and clip it onto the shock cord before you launch.
NAR requires 10 square cm of streamer area per gram of mass in contest models.
Example Parachute Design
Parachute recovery is probably the most familiar model rocket recovery mechanism. Most of the beginner kits start with parachutes, but even high-power, edge-of-space-kissing, multi-stage, electronic deployment rockets use parachutes to slow descent. They're basic to the hobby.
OpenRocket gives you a number of simulation options for parachutes, including material, construction, size, number of shroud lines. packed size and more. With OpenRocket, you can set your parachute's deployment to work just like your real rocket's.
One thing that you're not able to directly simulate here is the type of 'chute you have. Parachutes come in different types, from the semi-ellipsoid proper Parachute - an efficient shape (by drag to weight) which cannot be laid perfectly flat, to the "parasheet" - a 'chute that can be formed from a flat piece of material (the typical model rocket kit contains a parasheet), to X-shaped parachutes, to 'chutes with spill-holes, to parafoils and Rogallo wings. You'll have to experiment with these chutes, and perhaps try and adjust the Drag coefficient to compensate for difference from OpenRocket's ideal parachute.
NAR requires 5 square cm of parachute area per gram of mass in contest models.
Helicopter and Gliding Recovery
Helicopter Recovery
Helicopter recovery relies upon rigid lift-generating blades and auto-rotation to slow terminal velocity. This design technique is the most complicated of all, and requires that the entire rocket be designed around the recovery device. As important, the stresses generated by rapidly spinning blades hitting the ground effectively limits the use of this technique to low mass (model) rockets.
Gliding Recovery
A glider uses aerodynamic lift to control terminal velocity. However, because the aerodynamic requirements of vertical flight are vastly different than gliding flight, to make this transition there must be a shift in the center of gravity or the center of pressure. This transition can be made by reducing mass (ejecting the motor mount tube and weights) or changing aerodynamic signature (ejection activated fin-elevators or swing-wings). Radio and other control systems are currently being used to fly gliding recovery rockets, even high power.
Example Design
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Protecting Recovery Components
Recovery components are made from lightweight materials which, while often flame retardant, aren't necessarily heat-proof, or which may char and decay without bursting into flame.
To protect the recovery components and ensure they work properly for a safe landing, some method of shielding the "Laundry" (slang for the parachute and associated cords) from the heat of ejection, or of cooling the eject gasses must be used.
Heat Shields
Protecting the components starts during rocket design: you can choose something durable and flame-resistant like Kevlar cord for shock cord components that will be used in the eject area. A little later in this article, you'll see other built-in options you can use.
Fire Resistant Wadding and Blankets
The simplest way to protect the 'chute is to put something flameproof between the eject charge and the recovery hardware. In small rockets, this can take the form of "Flameproof ejection wadding", as packaged with Estes motors, or flame-retardant recycled cellulose insulation (nicknamed "Dog Barf" in the hobby community). Of the two, "Dog Barf" makes much less of a mess on the field, and is recommended by some clubs. If you do use "Estes Flameproof ejection wadding", please try and recover as much of the discarded paper as possible before leaving your launch site.
When using wadding, try and put in a minimum depth of 1.5 tube diameters of wadding. Wadding may be poked gently into a rocket with a pencil or stick, but don't pack it down.
You can also buy a reusable 'chute protector, called a "Nomex blanket" or a "'Chute bag" (also made of Nomex). Nomex blankets are typically square, often orange, and usually have a buttonhole sewn into the corner, to pass the shock cord through. One wraps up the parachute and as much of the shock cord as is practical with the Nomex facing the eject charge. This author was instructed to wrap the 'chute in Nomex "Like a burrito", but in reality there are several ways to pack a chute protector that will work well. Ensure that the Nomex faces the eject charge, so it takes the heat of ejection, and not your recovery device.
Nomex can be re-packed with the 'chute immediately after a flight. Nomex is machine-washable (and you'll probably want to wash it at some point).
A rule of thumb for sizing a Nomex blanket: The blanket should be a square, with a width that's 3 times the body diameter.
Piston Ejection
Another way of insulating the recovery material from the heat of ejection is with a Piston Ejection system.
In a typical piston ejection system, a piston is inserted into the body tube, and is free to slide up and down the tube's length. The eject charge is on one side of the piston, and the recovery material on the other. The body tube, the piston and the recovery material are all connected together, so as not to lose any parts.
At ejection charge firing, expanding gases push the piston (and the recovery material) up the tube and out of the rocket, without exposing the recovery material to the heat of the eject charge. The piston should leave the rocket body, in order to vent the ejection gases.
Pistons are often made of tube couplers, which have been sanded down a bit to smoothly slide in the body tube. One end of the coupler is closed by a bulkhead. The closed end is called the "face" of the piston. The rounded wall of the coupler is called the piston's "skirt".
The attachment shock cord runs from the eject charge end of the rocket, attaches to the piston at the face (or is threaded through it and sealed) and more shock cord runs from the other side of the piston face and to the recovery material. The attachment cord needs to be long enough for the piston to escape the body tube so exhaust gases are vented. The piston must move smoothly and without sticking; if the piston sticks, the parachute may not be deployed.
Opinions differ on whether the "face" of the piston should face the 'chute or the ejection charge. According to one theory, if the piston face is on the nose cone side of the piston, exhaust gases could make the piston skirt swell and cause the piston to stick in the body tube, while if instead the piston faces the eject charge, eject gases that travel between the piston skirt and the inside of the body tube form a "gaseous lubricant" which should prevent the piston from getting stuck. Others beg to differ, and have had successful real world experience with the piston facing upward.
Ejection Gas Cooling
Another approach to protecting the recovery material is to cool the ejection gases before they contact the 'chute.
Cooling Mesh
Aerotech sells a metal cooling mesh for model rockets. The mesh looks like a tiny tangled slinky, or perhaps like twisted tinsel from a Christmas tree. Installing a metal cooling mesh in the rocket body allows cooling of the exhaust gases, which transfer much of their heat to the metal mesh as they pass. The configuration of the mesh also makes it something of a particle filter, so chunks of burning material from the ejection charge get filtered out, instead of passing their heat to your parachute.
Baffles
Still another approach is to install a baffle in the rocket, above the eject charge, and below the recovery system. A baffle is often made from a coupler with two bulkheads, one in each end. Designs differ, but basically there's a hole pattern in the top, and a hole pattern in the bottom, such that ejection gas will pass through, but because the holes don't align, it will need to make a detour through the baffle. Meanwhile, heavier burning solid material from the eject charge has much higher inertia, and won't be able to divert to the top set of holes. Much of it will be stopped by the top bulkhead.
Servicing
Both baffles and cooling mesh will have limited lifespans, and need to be cleaned, serviced, or replaced. Cooling mesh in particular can become clogged with particles from many flights, and may be placed in a difficult-to-reach position. Baffles may burn, break, or get filled with particles. When this happens, the best service option may be to "poke out" the cooling mesh or baffle, and go over to recovery wadding or a Nomex blanket.
One way to avert the "poke out" problem is to use screws to attach a baffle through the wall of the body tube. Nylon screws may be used to avoid placing "ductile metal" in the airframe. Screw attachment allows the baffle to be removed for servicing or replacement.
CO2 Ejection Devices
Another approach to eject is pioneered by Tinder Rocketry, who offer a CO2 ejection system. Because a minimal pyro device is used to trigger the CO2 ejection, there's not a lot of hot material flying around inside the airframe, and no need for wadding or a Nomex blanket. The CO2 is cold as it's released.
Tube Fins and Ring Tails
Tube Fins
A tube fin is just that, using a shorter section of body tube, adhered to the main body tube, as a fin, with or without other flat fins. Although this type of rocket is easy enough to build, creating an accurate simulation can be anything but.
The aerodynamic flight of a rocket is affected by both how far the tip of a fin is from the body of the rocket and the surface area and profile of the fin. Using a 1 inch diameter tube, 2" long as an example, the tube fin has a surface area equal to pi (22/7) times the tube diameter times its length, or about 6 square inches. But, looking at the tube fin from the side (in profile), its area is length times height (the tube diameter), or about 2 square inches. Dividing the former by the later, three "flat" fins are aerodynamically about the same as one tube fin.
So, to simulate tube fins, for each tube fin, three flat fins having the same profile as the tube fin are substituted. One tube fin equals three flat fins, two tube fins equals six flat fins, and so on. OpenRocket allows a maximum of eight fins per fin set, so six tube fins of the same kind can be represented by six fin sets (each containing three flat fins), or by three fin sets (two containing eight flat fins and one containing two flat fins). Just be aware that the Too many parallel fins warning in OpenRocket activates when more than eight total fins are created, and this warning appears in the results of every flight simulation.
How does that work in OpenRocket? First, load the Simple model rocket example:
- At the OpenRocket main window, left-click the File menu, then left-click Open example design in the drop-down menu.
- In the pop-up Open example design box, left-click the "A simple model rocket" selection, then left-click the Open button.
Tubes as Fins
Keeping in mind how tube fin simulation is done as described above, the Simple model rocket example design is converted to six tube fins, each with a 45 degree slant on the leading edge, following these steps:
- Double left-click the Body tube component in the Rocket design view, and write down the Wall thickness of the tube.
- Double left-click the Trapezoidal fin set component in the Rocket design view.
- Change the Number of fins to 6 (six tube fins).
- Change the Root chord to 2 cm.
- Change the Tip chord to 1 cm.
- Change the Height to 1 cm.
- Change the Sweep angle to 45 degrees (the Sweep length will automatically calculate).
- Change the Thickness to match the fin tube Wall thickness from Step 3 (.039).
- Now, to create flat fin sets for each tube fin, left-click the Split fins button. At this point, six individual fin sets have been created, each fin set containing one fin.
- Next, double left-click Trapezoidal fin set #1, and change the Number of fins to 3. Make sure the Fin rotation is 0 degrees, then left-click the Close button.
- Left-click the Back view button so that you can see the fin angles for the remaining steps.
- Double left-click Trapezoidal fin set #2, and change the Number of fins to 3. Change the Fin rotation to 20 degrees (360 degrees divided by 18 fins), then left-click the Close button.
- Double left-click Trapezoidal fin set #3, and change the Number of fins to 3. Change the Fin rotation to the previous rotation plus 20 degrees (20 degrees + 20 degrees = 40 degrees), then left-click the Close button.
- Repeat the previous step for each of the remaining fin sets, increasing the Fin rotation by an additional 20 degrees for each set (0, then 20, then 40 then 60, and so on). At this point, each fin set contains 3 fins, 18 fins in all.
- Now, rotate the launch lug so that it is between fins. Double left-click the Launch lug component and change the Radial position to 10 degrees, then left-click the Close button.
The conversion is complete. Left-click the Side view button to see the completed rocket in profile.
By adjusting the Tip chord length and Sweep angle, tube fin angles from 90 degrees to virtually any other angle can be created.
Tube Around Each Fin
This section describes how to convert a simple model rocket design to flat fins with tube fins surrounding each at the trailing edge. The tube fins are the same diameter as the main body tube.
Beginning with the Simple model rocket example started above, modify the main flat fins as follows:
- Double left-click the Body tube component in the Rocket design view window, and write down the Outer Diameter, Inner Diameter, and Wall thickness, (2.5, 2.3, and .1 cm). Then, left-click the Close button.
- Double left-click the Trapezoidal fin set component in the Rocket design view window.
- Change the Root chord to 8 cm.
- Change the Tip chord to 2 cm.
- Change the Height to the outside diameter of the tube fin, 2.5 cm.
- Change the Sweep length to 6 cm (the Sweep angle will automatically calculate).
Now, the main flat fins need to be converted from trapezoid to freeform, and then notched to accept the tube fins.
- Left-click the Convert to freeform button.
- Left-click the Shape tab.
- On the graph of the fin, left-click on a fin line to create a new coordinate, and repeat doing so in different places until there are seven coordinate boxes.
- In the x/y table, change the coordinates to the following points:
- 0 | 0
- 6 | 2.5
- 6 | 2.4
- 8 | 2.4
- 8 | 0.1
- 6 | 0.1
- 6 | 0.1
- Then reposition the fin, left-clicking the General tab, and changing the Relative position to - plus to "-2" cm. Then, left-click the Close button.
Now that the main flat fins are done, its time to add the surrounding tube fins.
- Left-click the Body tube component in the Rocket design view window, then, in the Add a new component window, left-click Trapezoidal fin set.
- Change the Number of fins to 3 (three tube fins).
- Change the Root chord to 2 cm.
- Change the Tip chord to 2 cm.
- Change the Height to 2.5 cm, the inside diameter of the tube.
- Change the Sweep length to 0 cm (the Sweep angle will automatically calculate).
- Change the Thickness to .1 cm.
- Now, create substitute flat fin sets for each tube fin, left-click the Split fins button.
At this point, three individual trapezoidal fin sets have been created, each fin set containing one fin.
- Left-click the Back view button so that you can see the fin angles for the remaining steps.
- Double left-click Trapezoidal fin set #1, and change the Number of fins to 3. Change the Fin rotation to 30 degrees (360 degrees divided by 12 fins [9 tube fins plus 3 flat fins]), then left-click the Close button.
- Double left-click Trapezoidal fin set #2, and change the Number of fins to 3. Change the Fin rotation to the previous rotation plus 30 degrees (30 degrees + 30 degrees = 60 degrees), then left-click the Close button.
- Double left-click Trapezoidal fin set #2, and change the Number of fins to 3. Change the Fin rotation to the previous rotation plus 30 degrees (60 degrees + 30 degrees = 90 degrees), then left-click the Close button. At this point, the rocket has three trapezoidal fin sets containing 3 fins each, plus the 3 flat fins, 12 fins in all.
- To finish, rotate the launch lug so that it is between fins. Double left-click the Launch lug component and change the Radial position to 15 degrees, then left-click the Close button.
The conversion is complete. Left-click the Side view button to see the completed rocket in profile. Although the tube notches can be seen, separate from the substitute tube fins, this design is the aerodynamic equivalent for simulation purposes.
Ring Tails
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Through-the-Wall Fin Mounting
Model rocket fins are usually glued to the surface of an airframe. However, when higher thrust motors are used (E and above) the increased thrust can literally rip fins off or shoot a motor up through the airframe. Instead, "through-the-wall" (TTW) mounting refers to fins that protrude through a slot in the airframe and are glued to the motor mount tube, one or more centering rings, and the airframe surrounding the slot. This construction technique significantly strengthens fin joints and motor mounts.
There are three measurements necessary to create a fin tab: tab length, tab height, and tab position.
Relative to:
- the chord root leading edge – the tab position is the distance from the fin chord root leading edge to the fin tab leading edge.
- >the chord root midpoint – the tab position is the distance from the fin chord root midpoint to the fin tab midpoint.
- the chord root trailing edge – the tab position is the distance from the fin chord root trailing edge to the fin tab trailing edge.
OpenRocket will automatically calculate fin tab dimensions, within the following constraints:
- If there are no centering rings beneath a fin, the trailing edge of the fin tab is the fin chord trailing edge and the leading edge of the fin tab is the fin chord leading edge.
- If only one centering ring is beneath a fin, the trailing edge of the fin tab is the fin chord trailing edge and the leading edge of the fin tab is the trailing edge of the centering ring.
- If two centering rings are beneath a fin, the trailing edge of the fin tab is the leading edge of the trailing centering ring and the leading edge of the fin tab is the trailing edge of the leading centering ring.
- If more than two centering rings are beneath a fin, referring to the centering rings in order from the trailing edge to the leading edge of the fin chord, the trailing edge of the fin tab is the leading edge of the first centering ring and the fin tab leading edge is the trailing edge of the second centering ring. OpenRocket supports only one fin tab on each fin.
Converting a simple rocket to through-the-wall design:
- At the OpenRocket main window, left-click the File menu, then left-click Open example design in the drop-down menu.
- In the pop-up Open example design box, left-click the "A simple model rocket" selection, then left-click the Open button.
- In the Rocket design view, double left-click the Trapezoidal fin set component.
- Left-click the Fin tabs tab.
- Left-click the Calculate automatically button.
And, a through-the-wall fin tab is automatically created between the two motor mount centering rings.
Electronic and Dual Deployment
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Clustering and Multi-staging
Complex rockets fall into two basic categories, a rocket that is propelled by a cluster of motors intended to be simultaneously ignited or multi-staged (massively-staged), propelled by a series of motors that successively ignite the next in line when the prior motor burns out.
Motor Clustering
Clustering refers to launching a rocket with more than one simultaneously-ignited rocket motor. Clustering is common in "real" aerospace programs. Familiar American examples include: the Gemini Titan - a two-motor cluster, the Saturn V - a cluster of five Rocketdyne F-1 motors driving the first stage, and the Falcon 9 - a cluster of 9 Merlin motors driving the main stage.
In model and high-power rocketry, typical clusters seen are 2-motor, always side-by-side, due to the geometry, 3-motor, in a triangle or straight line, 4-motor, in a square, and 5-motor, typically arranged with one central motor surrounded by 4 in a square - though other arrangements are possible. There's nothing preventing much larger ones, but 2, 3, 4 and 5 are most-often seen.
In three- and five-motor clusters, it's not uncommon to see a larger or higher-power central motor, surrounded by smaller or weaker motors. This may be done for effect, or due to modeling constraints, or to more closely resemble its full-scale inspiration, or possibly for reasons of cost. Clustered motors may be "canted" - that is, pointed to the outside of the rocket fuselage's circumference, for effect, stability, or spin.
Designing a Rocket with Clustered Motors
OpenRocket makes it easy to design motor clusters. To begin with, add an Inner Tube to your aft-most Body Tube. On the Motor tab, check the "This component is a motor mount" box. Set its inner diameter to one of the standard motor sizes, unless you have a unique need: 13, 18, 24, 29, 38, 54, 75 or 98mm. Next, click on the Cluster tab.
The Cluster tab lets you choose a common cluster configuration, and adjust it in your model.
First, pick a cluster configuration from the image tiles on the left side of the tab. Realize that depending upon the sizes of your motor tube and body tube, not every cluster that you can make will fit.
Next, adjust the Tube separation. This value controls how close the clustered motors are to each other. A value of 1 places the tubes in contact with each other. You can enter decimals like "1.25" in the separation field. In addition to potentially affecting your rocket's stability, the Tube separation you choose may influence the difficulty of wiring your clustered motors for ignition, and your ability to place adhesive and parts around tightly-packed tubes during construction.
The Rotation setting rotates your cluster around the major axis of your rocket (the Up <--> Down one). It's used to line up the motors with other decorative and structural components of your rocket. This alignment may be critical if you're creating a design that ducts eject gasses from one part of the rocket to another.
The Split cluster button changes this component from a clustered motor component that can be handled as a unit, to individual motor tubes, which may be positioned and edited independently of each other. You may want this option if you have motor mount tubes of different lengths or diameters in the cluster. Once split, a cluster cannot be recombined. You must re-create the cluster as a unit if you'd like to revert to that approach.
Igniting a Cluster
Important to the stability of the rocket's flight is that all the motors ignite more or less simultaneously. The initial concerns here are that all the motors' igniters are wired to take a single application of voltage from the launch controller, and that the controller be able to provide adequate voltage and current to ignite all the motors.
Estes Rockets used to advise that igniter wires be twisted together in either series or parallel configurations. Each has its advantages: with a series connection, any burnt igniter will show an open circuit upon arming, while with a parallel connection, the launch controller can use the same voltage as always, but supply more current to ignite multiple motors at once. Today, most clusters are wired in parallel, and the rocketeer must ensure that ample current is available for launch.
Some cluster igniter wiring schemes use a buss bar - a short length of regular conductive wire, typically non-insulated, for ease of connecting to it as needed - as a way of bridging what can be complex connections in a tight space, into an easier connection plan. For example, you can twist one end of each igniter together in a bundle, and the other end of each to the buss bar. The launch micro-clips then connect one to the bundle, and the other to the buss bar, for a parallel connection.
A convenient tool for igniting a cluster is a cluster whip - a set of wires and micro-clips that allows the single pair of clips at the launch pad to be easily broken into multiple sets of clips, to attach to multiple igniters, and providing a parallel connection. The cluster whip connects to the igniters, and the launch controller's micro-clips connect to conductors on the cluster whip.
Igniting Clustered APCP motors
APCP (Ammonium Perchlorate Composite Propellant) motors typical of Aerotech, Cesaroni, and Loki, are slower to ignite than Black Powder motors (typical Estes motors). They may unpredictably "chuff", sit quiet for a moment and then ignite, or even "spit" the igniter out. Because of this difference, and the unpredictability of APCP motor ignition, it's more than a little likely that clustered APCP motors won't ignite simultaneously, if at all. When designing for an APCP cluster (if you decide to roll these dice...), take into account what will happen to the rocket if not all motors ignite before it pulls away from the pad. The safety of observers, and of your airframe hang in the balance.
Conventional Staging
A "closed-hull" design with a separating airframe in which finned-stages holding motors are stacked up, and lower stages holding burned-out casings separate under pressure as upper stages ignite. Conventional staging is inherently limited to three stages because of the "Pisa Effect" which results in an increasing arcing trajectory with each stage.
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Rack Staging
An "open-hull" design with a non separating airframe in which motors are staked up, end-to-end, in a frame, and only the burned-out casings are ejected under pressure as higher stages ignite, stage-after-stage. So long as high average impulse lower stage motors are used to ensure adequate initial velocities, rack staging is not inherently limited because this design overcomes the "Pisa Effect."
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Roll Stabilization
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Regulatory Concerns
Rocketry is subject to regulation by federal, state, and local governments, and most of the regulations that rocketeers must follow are promulgated by the National Fire Protection Association (NFPA) and the Federal Aviation Administration (FAA). The NFPA divides rockets into two major classifications, model rockets (NFPA § 1122) and high power rockets (NFPA § 1127), the difference primarily being weight and power, as follows:
- Model Rocket. A rocket vehicle that weighs no more than 1500 g (53 oz) with motors installed, is propelled by one or more model rocket motors having an installed total impulse of no more than 320 N-sec (71.9 lb-sec), and contains no more than a total of 125 g (4.4 oz) of propellant weight. (NFPA § 1122, subd. 3.3.7.2.)
- High Power Rocket. A rocket vehicle that weighs more than 1500 g (53 oz) with motors installed and is either propelled by one or more high power rocket motors or by a combination of model rocket motors having an installed total impulse of more than 320 N-sec (71.9 lb-sec). (NFPA §1127, subd. 3.3.13.1.)
Within the high power rocket classification, a subclassification for “complex” rockets is defined as a high power rocket that is multi-staged or propelled by a cluster of two or more rocket motors. (NFPA §1127, subd. 3.3.13.1.1.) And, a high power rocket launched with an installed total impulse greater than 2,560 N-sec (576 lb-sec) must have an electronically actuated recovery system. (NFPA §1127, subd. 4.10.2.)
National Association of Rocketry
National Association of Rocketry pursuits the goal of safe, fun and educative sport rocketry. It is the oldest and largest sport rocketry organization in the world. Visit dedicated Wiki page or NAR official website for more information.
The major work of the NAR includes, but not limited to:
- Certification of Rocketry-Related products and establishment of safety codes The NAR is a recognized authority for safety certification of consumer rocket motors and user certification of high- power rocket fliers in the U.S. It plays a major role in establishment of safety codes for the hobby used and accepted by manufacturers and public safety officials nationwide.
- Certification of experienced rocketeers NAR issues three levels of High Power Rocketry (HPR) certificates, Level 1 (L1) through Level 3 (L3). Certificates are necessary to purchase powerful rocket motor components.
- Communication with public officials The NAR helps in communication with local public safety officials, and government regulatory agencies such as the Department of Transportation, Federal Aviation Administration, Bureau of Alcohol Tobacco Firearms and Explosives, and Consumer Product Safety Commission.
- Other work The NAR publishes the bimonthly color magazine Sport Rocketry (sent to each member and selected libraries and newsstands around the nation). The NAR provides a wide range of other services to its members, including: education programs; national and local competitions; grants to teachers and scholarships for student members; flight performance record recognition; liability insurance; and publication of technical literature.
Tripoli Rocketry Association
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User Guide Contributions
Use the clustered, staged and dual-deploy example designs to cover the more advanced motor and recovery configuration options. Talk about using mass and CG overrides to improve accuracy.
Special designs that might have their own sub-chapters:
- clusters + staged (including rack rocket (https://sites.google.com/site/theskydartteam/projects/model-rocketry/rack-rocket-design))
- dual-deploy and other more advanced recovery options (if we can think of any)
- roll stabilization
It would be good to include a description on how the different components affect the simulations and what the limits are (e.g. an inner tube won’t affect the aerodynamics even if you move it outside of the body tube).