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HPR Background Information (view source)

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NASA's online [https://spaceflightsystems.grc.nasa.gov/education/rocket/shortr.html Beginner's Guide To Rockets] will get you started on many of the basic principles governing rocketry. If you manage to make your way through all of these, you will understand the vernacular often used in rocketry.
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High power rocketry (HPR) is an essential and hands-on part of learning the fundamentals of rocketry.
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NASA's online [https://spaceflightsystems.grc.nasa.gov/education/rocket/shortr.html Beginner's Guide To Rockets] will get you started on many of the basic principles governing rocketry. If you manage to make your way through all of these, you will understand the vernacular often used in rocketry. To learn more about rocketry, the theory behind it, and other useful things related to rockets, see [[So You Want To...]].
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In addition that resource, here are some concepts compiled so you can quickly grasp what you need to know. If you are attempting an L1 certification, check out [[L1 Certification]].
    
== Jargon ==
 
== Jargon ==
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There is one direction we care about when discussing motor retention, the y direction (axially). Simply put, the job of a motor retainer is to keep your motor from falling out of your rocket or allowing it to shoot through the nosecone upon ignition, resulting in a cato. Depending on the company, motor retainers have a couple different ways they work. For the slimline retainers used in the SSI Firestorm kit, the motor retainers use retaining rings. These rings are removable and are located on the lip of the the retainer. The purpose of the rings are to keep the motor from sliding out of the bottom while a lip on the body of the retainer prevents the motor from launching through the rocket's nosecone. For any 38mm motor being used in the 58mm Firestorm airframe, a motor adaptor is going to be used which has identical retaining rings, except smaller in diameter, to the motor retainer.
 
There is one direction we care about when discussing motor retention, the y direction (axially). Simply put, the job of a motor retainer is to keep your motor from falling out of your rocket or allowing it to shoot through the nosecone upon ignition, resulting in a cato. Depending on the company, motor retainers have a couple different ways they work. For the slimline retainers used in the SSI Firestorm kit, the motor retainers use retaining rings. These rings are removable and are located on the lip of the the retainer. The purpose of the rings are to keep the motor from sliding out of the bottom while a lip on the body of the retainer prevents the motor from launching through the rocket's nosecone. For any 38mm motor being used in the 58mm Firestorm airframe, a motor adaptor is going to be used which has identical retaining rings, except smaller in diameter, to the motor retainer.
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You can purchase/make motor adaptors which allow you to have a motor of a diameter that is smaller than the diameter of your rocket. For example: If one wanted to launch an L1 with a 54mm H motor but his or her rocket had an ID of 98mm, that person would purchase/make a motor adapter to keep the motor stable and restrained. Motor adapters consist of a tube that has the same ID as the motor's OD and uses centering rings to keep the motor centered between the airframe walls. If you are planning on using various diameter motors for the same airframe it might be a wise choice to invest in a motor retention system that allows the user to buy various components designed to work with different sized motors.
 
You can purchase/make motor adaptors which allow you to have a motor of a diameter that is smaller than the diameter of your rocket. For example: If one wanted to launch an L1 with a 54mm H motor but his or her rocket had an ID of 98mm, that person would purchase/make a motor adapter to keep the motor stable and restrained. Motor adapters consist of a tube that has the same ID as the motor's OD and uses centering rings to keep the motor centered between the airframe walls. If you are planning on using various diameter motors for the same airframe it might be a wise choice to invest in a motor retention system that allows the user to buy various components designed to work with different sized motors.
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Positive = not falling out the bottom.
 
Positive = not falling out the bottom.
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== Stability ==
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== Static Stability ==
    
[[File:L1_Guide_Stability.png|thumb|200px|right|CG and CP for stable flight]]
 
[[File:L1_Guide_Stability.png|thumb|200px|right|CG and CP for stable flight]]
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=== Brief History ===
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In 1958, G. Harry Stine published a simplified discussion of rocket stabilization geared towards model rockets using fixed fins on the rear of a rocket. The fins, if properly designed, provide a means of inducing a return to the desired flight path when a disturbance acts to rotate the rocket around its center of gravity (CG or c.g.). The air forces acting on a rocket can be thought of as all acting at a center of pressure (CP). He suggested a method of approximating the CP by constructing a cardboard cutout of the model and balancing the plan-form cutout.
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The next advance in design came in 1966, when James Barrowman, then of NASA’s Sounding
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Rocket Division, presented a closed form algebraic solution to equations based on potential flow theory. The approximations used to achieve the closed form solution rely on the assumptions that the rocket (a) is traveling at a speed below that at which shock waves are formed (somewhat below the speed of sound), and (b) has a small angle between its flight path and the relative wind (i.e. a small angle of attack, or AOA). The Barrowman Equations continue to be widely used, both in graphical form and as the basis for hobby rocket design analysis software. From the "Launching Safely in the 21st Century: Final Report of the Special Committee on Range Operation and Procedure to the National Association of Rocketry", 2005.
    
=== Center of Gravity ===
 
=== Center of Gravity ===
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As a rule of thumb, having your CP 1.5-2 calibers in front of your CG is considered good, while numbers outside of that range tend to be either under-or-over-stable.
 
As a rule of thumb, having your CP 1.5-2 calibers in front of your CG is considered good, while numbers outside of that range tend to be either under-or-over-stable.
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== Failure ==
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[[File:MASA_flight_failure.PNG|400px|thumb|frame|right|Failure mode pie chart]]
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There is a fantastic NAR case study, "Launching Safely in the 21st Century", written by the Special Committee on Range Operation and Procedure which goes into rigorous statistical analysis of rocket failures. The following categories are common failure modes recorded from the fight log database of the Minnesota Amateur Spacemodeler Association (MASA, NAR 576):
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'''Unstable.''' The rocket flies with at least part of the boost phase in a nose-down attitude. For
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the purposes of this study, based on the goal to characterize unsafe events, comments such
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as "kind of unstable" were not counted, nor were "horizontal", "cruise missile", or "coning"
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flights (unless they resulted in a crash; see below).
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'''Lawn dart.''' The rocket descends in ballistic flight with the nose cone still on. This category
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includes "No ejection" and a few "power prangs". Some rockets are designed to do this and
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these flights were not counted. Boosters on two stage rockets also did this.
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'''Separation.''' The rocket descends in multiple parts with at least one part not slowed by a
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recovery device. For the purposes of this study, the few flights with a comment of "stripped
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chute" were included here. The unplanned ejection of motor casings should also have been
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collected here, but MASA LCOs almost never recorded them as outcomes.
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'''Motor CATO.''' The motor failures catastrophically at ignition or during boost. The nature of
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the CATO (spit nozzle, forward closure failure, blow by, etc.) was sometimes recorded, but
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not consistently.
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'''Core sample.''' The rocket descends in ballistic flight, but with the nose cone off the rocket
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and acting as a (not very effective) streamer. These events typically have lower impact
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speeds, and higher surface areas at impact, than do lawn darts.
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'''Motor unrestrained.''' The motor exits the rocket at ignition or during boost (thankfully, this
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was rare).
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'''Shred.''' The rocket comes apart during ascent, other than by design.
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'''No chute.''' The rocket descends without a recovery device deployed, but is not ballistic. This
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category does not include chutes that were described as merely tangled, although it is likely
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that some LCOs write "no chute" in those circumstances. The rationale here is that if the
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LCO described the result as "No chute", it was potentially unsafe.
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These would be called "recordable incidents" in the jargon of safety professionals. When more than one failure occurred during a flight (e.g., unstable flight leading to lawn dart), the most severe event was recorded.
    
== Motor Specs ==
 
== Motor Specs ==
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== Simulations ==
 
== Simulations ==
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[[File:exampleOpenRocket.jpg|thumb|right|300px|Example of the OpenRocket infterface]]
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[[File:exampleOpenRocket.jpg|thumb|right|300px|Example of the OpenRocket interface]]
    
It is always important to know what your rocket will do (assuming that things go according to plan), and we use a program called OpenRocket to find the flight profile of our rockets. The program is free, and can be found here[http://openrocket.sourceforge.net/]
 
It is always important to know what your rocket will do (assuming that things go according to plan), and we use a program called OpenRocket to find the flight profile of our rockets. The program is free, and can be found here[http://openrocket.sourceforge.net/]
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One other program of note is called FinSim, which can model possible vibrations within fins. If unchecked, these vibrations can grow and shear the fins off, likely dooming the rocket. The program is required for transonic and supersonic flights, and can be found here[http://www.aerorocket.com/finsim.html]
 
One other program of note is called FinSim, which can model possible vibrations within fins. If unchecked, these vibrations can grow and shear the fins off, likely dooming the rocket. The program is required for transonic and supersonic flights, and can be found here[http://www.aerorocket.com/finsim.html]
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{{reflist}}
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[[Category: Rockets]] [[Category: Rockets Guides]]
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