Alright, huge life transitions are happening right now. Some for better, some for worse. I just have more time on my hands now. Hopefully more money starting December. C'est la vie.
1. The OD of the mcmaster tube is smaller than any commercial rocketry airframe tube.
2. Filament winding is not optimal for the forces an airframe experiences. Fibers are good in tension, resin is good in compression. Filament winding is great in pressure vessels like scuba tanks, paintball tanks, motor cases. Roll wrapped tubes are used in structural applications which require resistance to bending and crushing forces. This is much more optimized for rocketry.
The roll wrapped tube comes with 1 glaring issue though. To fit the loki case, a LOT of sanding needed to happen. This ended up being the most tedious task of the whole build.
Here is the beautiful tube from McMaster.
Here is the sanding setup. Some things to note:
I purchased a flap sander off mcmaster and had to make some modifications to speed up the process.
1. I added larger 80 grit pieces with hot glue (I bought a 150 grit or something similar)
2. I purchased a threaded rod so that it would be able to reach all the way down the tube.
3. I marked the threaded rod so that I could sand where it was needed based off how far the motor case could go in.
4. CRITICAL: During sanding I would feel less torque and see little to no carbon dust come out of the ends. This means little to no sanding was happening. To increase sanding, I would add pieces of shop towel in between the sanding flaps. This increases the diameter of the tool and applies more pressure during sanding. This must be done or you will spend days with little to no progress. I figured this out after Day 3 of sanding.
View attachment IMG_0747.MOV
Above is the general setup. However this was prior to really focusing on adding paper towels to increase pressure. As you can see, little to no carbon dust is coming out the end during sanding. There should be much more than this if you are sanding efficiently.
The next two photos are of the flap sander after the tube was finished.
After sanding, a significant amount of the wall thickness was removed. I didn't measure (my mistake) but the hard work actually benefited me well. It reduced the amount of my total weight (more altitude) while also slightly increasing stability. This definitely reduced strength by a lot. However, less than 0.25 inches of airframe was not supported by either the motor or the nosecone! Due to this along with it being roll wrapped, I was not worried about airframe failure!
Regarding cutting the tubes to length, I used a chop saw that I setup with a machinist square and a blade without teeth. I think there is a better way to do this but I have not figured that out yet. If anyone has a better way please suggest it!
With this finished it was time to prep the fin edges and bond them to the airframe!
Chapter 2: Construction
2.1 - Sanding the airframe tube
I chose a roll wrapped tube for two reasons.1. The OD of the mcmaster tube is smaller than any commercial rocketry airframe tube.
2. Filament winding is not optimal for the forces an airframe experiences. Fibers are good in tension, resin is good in compression. Filament winding is great in pressure vessels like scuba tanks, paintball tanks, motor cases. Roll wrapped tubes are used in structural applications which require resistance to bending and crushing forces. This is much more optimized for rocketry.
The roll wrapped tube comes with 1 glaring issue though. To fit the loki case, a LOT of sanding needed to happen. This ended up being the most tedious task of the whole build.
Here is the beautiful tube from McMaster.
Here is the sanding setup. Some things to note:
I purchased a flap sander off mcmaster and had to make some modifications to speed up the process.
1. I added larger 80 grit pieces with hot glue (I bought a 150 grit or something similar)
2. I purchased a threaded rod so that it would be able to reach all the way down the tube.
3. I marked the threaded rod so that I could sand where it was needed based off how far the motor case could go in.
4. CRITICAL: During sanding I would feel less torque and see little to no carbon dust come out of the ends. This means little to no sanding was happening. To increase sanding, I would add pieces of shop towel in between the sanding flaps. This increases the diameter of the tool and applies more pressure during sanding. This must be done or you will spend days with little to no progress. I figured this out after Day 3 of sanding.
View attachment IMG_0747.MOV
Above is the general setup. However this was prior to really focusing on adding paper towels to increase pressure. As you can see, little to no carbon dust is coming out the end during sanding. There should be much more than this if you are sanding efficiently.
The next two photos are of the flap sander after the tube was finished.
After sanding, a significant amount of the wall thickness was removed. I didn't measure (my mistake) but the hard work actually benefited me well. It reduced the amount of my total weight (more altitude) while also slightly increasing stability. This definitely reduced strength by a lot. However, less than 0.25 inches of airframe was not supported by either the motor or the nosecone! Due to this along with it being roll wrapped, I was not worried about airframe failure!
Regarding cutting the tubes to length, I used a chop saw that I setup with a machinist square and a blade without teeth. I think there is a better way to do this but I have not figured that out yet. If anyone has a better way please suggest it!
With this finished it was time to prep the fin edges and bond them to the airframe!
