HPR Level 2 Certification Rocket Design
HPR Level 2 Certification Rocket Design
Following the successful supersonic flight of a friend's Level 2 certification rocket, I began working on a design for my own Level 2 certification rocket capable of supersonic flight. The design shown below is the 3rd iteration, designed in May 2019.
Certifications are required to buy rocket motors above certain impulse ratings. Ratings A-G require no certification, H & I require a Level 1, J-L require a Level 2, M and above require a Level 3 certification.Following the successful supersonic flight of a friend's Level 2 certification rocket, I began working on a design for my own Level 2 certification rocket capable of supersonic flight. The design shown below is the 3rd iteration, designed in May 2019.
This 3rd iteration of the design was produced through a combination of Open Rocket and Solidworks. Open Rocket was used for aerodynamic and performance predictions, while Solidworks was used for the individual part designs and weight estimations. The rocket is designed around 2 motors, a J350 which would be used for an initial subsonic flight and to earn my level 2 certification, and a L1000 which would be used for a supersonic flight. One challenge presented by these two motors is the large difference in size and mass, meaning the rocket would need two different aerodynamic configurations. To allow the aerodynamic configuration to be changed between flights, the design includes a 3D printed removable forward ring. This ring allowed small fins to be added or removed, changing the center of pressure and allowing the rocket's stability to be tuned to the specific mass distribution of that flight.
This 3rd iteration of the design was produced through a combination of Open Rocket and Solidworks. Open Rocket was used for aerodynamic and performance predictions, while Solidworks was used for the individual part designs and weight estimations. The rocket is designed around 2 motors, a J350 which would be used for an initial subsonic flight and to earn my level 2 certification, and a L1000 which would be used for a supersonic flight. One challenge presented by these two motors is the large difference in size and mass, meaning the rocket would need two different aerodynamic configurations. To allow the aerodynamic configuration to be changed between flights, the design includes a 3D printed removable forward ring. This ring allowed small fins to be added or removed, changing the center of pressure and allowing the rocket's stability to be tuned to the specific mass distribution of that flight.
The rocket was to use a custom 3D printed nose cone, as no commercially available nose cone of the desired dimensions could be found. The nose cone would be printed from either PLA or PET. This presented a challenge, as the predicted stagnation temperature would be above the melting temperature for these materials, leading to potential deformation of the tip. This problem was solved by adding a removable aluminum tip. Aluminum would easily withstand the predicted stagnation temperature without deformation.
The rocket was to use a custom 3D printed nose cone, as no commercially available nose cone of the desired dimensions could be found. The nose cone would be printed from either PLA or PET. This presented a challenge, as the predicted stagnation temperature would be above the melting temperature for these materials, leading to potential deformation of the tip. This problem was solved by adding a removable aluminum tip. Aluminum would easily withstand the predicted stagnation temperature without deformation.
The design of the motor mount and fin attachment also presented a challenge. Conventional practice is to use a dedicated "motor tube" inside the outer "body tube", and to mount the fins via the "through-wall" method in which slots are cut in the body tube and fin "tabs" are inserted through the body tube and pressed flush with the outer surface of the motor tube. This allows the fins to be bonded via epoxy to both the motor tube and body tube. This design method is used on my Cert-1 rocket Leviathan. This method is widely used as it provides a very strong attachment of the fins. However, it requires the outer diameter of the rocket to be decently larger than the diameter of the motor. This is unfavorable for a rocket optimized for altitude or velocity, as it increases the rocket's cross sectional area and significantly increases drag.
The design of the motor mount and fin attachment also presented a challenge. Conventional practice is to use a dedicated "motor tube" inside the outer "body tube", and to mount the fins via the "through-wall" method in which slots are cut in the body tube and fin "tabs" are inserted through the body tube and pressed flush with the outer surface of the motor tube. This allows the fins to be bonded via epoxy to both the motor tube and body tube. This design method is used on my Cert-1 rocket Leviathan. This method is widely used as it provides a very strong attachment of the fins. However, it requires the outer diameter of the rocket to be decently larger than the diameter of the motor. This is unfavorable for a rocket optimized for altitude or velocity, as it increases the rocket's cross sectional area and significantly increases drag.
Instead, this rocket design uses a single tube as both the body and motor tubes, allowing the body diameter to be only slightly larger than the motor. This presents a challenge for fin attachment, as it prevents the through-wall method, and bonding the edge of the fin directly to the surface of the body tube is a very fragile attachment and is likely to fail. Instead this design mounts the fins to a series of external aluminum rings via machine screws. While these rings are a larger diameter than the body tube itself, this design still provides a smaller profile and reduced drag compared to the inner motor tube and through-wall attachment methods.
Instead, this rocket design uses a single tube as both the body and motor tubes, allowing the body diameter to be only slightly larger than the motor. This presents a challenge for fin attachment, as it prevents the through-wall method, and bonding the edge of the fin directly to the surface of the body tube is a very fragile attachment and is likely to fail. Instead this design mounts the fins to a series of external aluminum rings via machine screws. While these rings are a larger diameter than the body tube itself, this design still provides a smaller profile and reduced drag compared to the inner motor tube and through-wall attachment methods.
This design iteration has not been manufactured yet because the estimated cost exceeds my current budget. Additionally, I no longer have access to the manufacturing resources needed to build this design. As a result, I plan to develop a 4th iteration of the design that would be manufacturable with the resources I currently have access to.
This design iteration has not been manufactured yet because the estimated cost exceeds my current budget. Additionally, I no longer have access to the manufacturing resources needed to build this design. As a result, I plan to develop a 4th iteration of the design that would be manufacturable with the resources I currently have access to.
