mannyskid
Well-Known Member
- Joined
- Feb 2, 2011
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Last time you guys saw me, I had CATO'd my last big motor at Aeronaut:
Musket Chops Thread
In the mean time, I played a small role in helping my friend Steve Heller get his optimized 98mm rocket built and off the ground. After an awesome flight at BALLS to 62k', I was motivated to get back on the horse and do another large project. For the past couple weeks, the knowledge of a launch with a 75k' waiver in Las Cruces, NM in early January that some close friends will be attending has been in the back of my mind. Last weekend when I went back to my parents house, while building my mom a new chicken coop, the wreckage of the CATO'd 5" motor was staring me in the face the whole time. It was then that I decided that I had to try another 'O' motor for this New Mexico launch. After some discussion with friends and a little time in the computer lab (while procrastinating for writing my aircraft structures beam code), I decided that this project would be based around a 6' length of 4"sch 40 DOM pipe (4.5"x4.026) or a standard 114mm motor.
The 0.24" wall on this pipe will give me a larger safety margin then the 0.1875" wall used on the CATO'd 5" motor, and will allow me to run higher pressure and a "hotter" formula. Initial simulation on this motor puts it at around a 30k Ns O8000. The following is a list of major problems with the 5" motor that CATO'd that will be addressed in this motor.
-Liner Issue
~The 5" motor used a 4.5" fiberglass tube as a liner. This was a problem as there was roughly 0.0625" of clearance between the liner and case. It is possible that the liner cracked when the motor came up to pressure. This time, I will use a MAC performance 98mm XX phenolic airframe as the liner. This tube has an OD of 4.026, exactly what the ID of the aluminum tube is so I will have to sand the OD to get a dead nuts fit.
-No Set Screws
~The 5" motor used 1/4-20 set screws instead of bolts or pins. The problem with set screws (and bolts) is that the effective loading area is only on the minor diameter of the screw, which is less than 3/16" for a 1/4" bolt. Also, with set screws there is even less loading area due to the divot used for the allen head. This motor will use 3/16" pins in a yet to be determined pattern.
-Sealing Problem
~The 5" motor use 1/8" Orings instead of the normal 3/6" Orings, this was done so that I could get an over all shorter nozzle, however I discovered that with the amount of compression that I had there was not enough of a seal to make me comfortable, this motor will use 3/16" Orings with more compression.
-Airframe Transitions
~The rocket the 5" motor was more rushed than I had hoped it would be. For the transitions I had simply wiped RTV silicone around the lip where the airframe transitioned. For this rocket, the fin can tube will be hand wrapped over a 4.5" OD PVC pipe, then glued directly to the casing (it is designed to be single use) and the lip will transition to the case via a homemade ablative and sanded smooth. The upper airframe will be omitted on this vehicle and the nose cone will be coupled directly to the case via the same method used on Sunday Silent (see link for optimized 98mm rocket above).
RasAero puts this combination at roughly 40-45k', not record breaking but if I can manage to get an O motor to stay together and break my current altitude record (42k' commercial, 24k' EX) in the process I will be very pleased.
Also, the name E3M stands for "Eggs Three Meat", don't ask about the meaning I would prefer to keep it an inside joke.
Manny
Musket Chops Thread
In the mean time, I played a small role in helping my friend Steve Heller get his optimized 98mm rocket built and off the ground. After an awesome flight at BALLS to 62k', I was motivated to get back on the horse and do another large project. For the past couple weeks, the knowledge of a launch with a 75k' waiver in Las Cruces, NM in early January that some close friends will be attending has been in the back of my mind. Last weekend when I went back to my parents house, while building my mom a new chicken coop, the wreckage of the CATO'd 5" motor was staring me in the face the whole time. It was then that I decided that I had to try another 'O' motor for this New Mexico launch. After some discussion with friends and a little time in the computer lab (while procrastinating for writing my aircraft structures beam code), I decided that this project would be based around a 6' length of 4"sch 40 DOM pipe (4.5"x4.026) or a standard 114mm motor.
The 0.24" wall on this pipe will give me a larger safety margin then the 0.1875" wall used on the CATO'd 5" motor, and will allow me to run higher pressure and a "hotter" formula. Initial simulation on this motor puts it at around a 30k Ns O8000. The following is a list of major problems with the 5" motor that CATO'd that will be addressed in this motor.
-Liner Issue
~The 5" motor used a 4.5" fiberglass tube as a liner. This was a problem as there was roughly 0.0625" of clearance between the liner and case. It is possible that the liner cracked when the motor came up to pressure. This time, I will use a MAC performance 98mm XX phenolic airframe as the liner. This tube has an OD of 4.026, exactly what the ID of the aluminum tube is so I will have to sand the OD to get a dead nuts fit.
-No Set Screws
~The 5" motor used 1/4-20 set screws instead of bolts or pins. The problem with set screws (and bolts) is that the effective loading area is only on the minor diameter of the screw, which is less than 3/16" for a 1/4" bolt. Also, with set screws there is even less loading area due to the divot used for the allen head. This motor will use 3/16" pins in a yet to be determined pattern.
-Sealing Problem
~The 5" motor use 1/8" Orings instead of the normal 3/6" Orings, this was done so that I could get an over all shorter nozzle, however I discovered that with the amount of compression that I had there was not enough of a seal to make me comfortable, this motor will use 3/16" Orings with more compression.
-Airframe Transitions
~The rocket the 5" motor was more rushed than I had hoped it would be. For the transitions I had simply wiped RTV silicone around the lip where the airframe transitioned. For this rocket, the fin can tube will be hand wrapped over a 4.5" OD PVC pipe, then glued directly to the casing (it is designed to be single use) and the lip will transition to the case via a homemade ablative and sanded smooth. The upper airframe will be omitted on this vehicle and the nose cone will be coupled directly to the case via the same method used on Sunday Silent (see link for optimized 98mm rocket above).
RasAero puts this combination at roughly 40-45k', not record breaking but if I can manage to get an O motor to stay together and break my current altitude record (42k' commercial, 24k' EX) in the process I will be very pleased.
Also, the name E3M stands for "Eggs Three Meat", don't ask about the meaning I would prefer to keep it an inside joke.
Manny
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