Goal statement
If we're going to make our own model rockets from scratch, we're going to need tubes for the body and the engine.
These will have to be:
- light
- strong (against both radial and linear compression and, in the case of the engines, significant internal pressure)
- easy to make consistently
- flame resistant or even flame proof
- reasonably smooth (for drag)
Methods
We considered several ways of making tube (drilling, lathing, molding, ...) but decided the most obvious way was what we should try first.
We rolled sheets of various materials around a piece of pvc tube that was the right size to use as a forming rod, applying white glue as we rolled to hold the layers together. There were two different rolling techniques tried: full sheet rolling (just like it sounds, the same way paper towels or toilet paper are rolled, but with glue) and spiral rolling (like the cardboard tube in the middle of the roll of paper towels or toilet paper is rolled). Having one person paint the glue while one rolls & controls the tension seems to work best.
Rounds 0 & 1
For the first few (round 0) we coated the pvc forming rod with non-stick cooking spray, but this didn't seem to be needed and we were worried that the residue might hurt us in the flame tests.
After each tube was rolled we carefully removed it from the forming rod, labeling most of them with a sequence number and recording the details of its construction, and set it in the drying room for a week.
We then removed them, reinserted the forming rod, and cut off one end and two ~10cm (it was supposed to be exact but this was impossible) segments. each of which was numbered with the same number as the tube it was cut from to use in tests.
Then we tested them and recorded the results.
.
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Note: the tube at the far left in this image, faintly labeled what looks like "0" is actually tube "8" and should be between the two ("7" & "9"). And the one that looks like an "h" is really "4" because ... symmetry.
Results
| Material | # of wraps | Type | Cutting | Surface | |
|---|---|---|---|---|---|
| 1 | Parchment | ~6 | Full | Frustrating and ultimately pointless; 0 out of 10 terrible cutting experience | Bumpy & squishy |
| 2 | PT tube | ??? | Spiral | Smooth to cut; 8 out of 10 great cutting experience | Smooth but ridged |
| 3 | cardboard | 1 roll | Spiral | 6 out of 10 ; not as good version of 2 | Same as 2 |
| 4 | paper bag | 8 | Full | More Difficult than Ideal; 6 out of 10 | Mostly smooth ; a little bumpy |
| 5 | paper towel | 5 | Full | Easy and quick to cut; 7 out of 10 ; A surprisingly fun experience | rough and bumpy |
| 6 | parchment | 6 | Full | Surprisingly easy based on prior experience ; 7 out of 10 | veiny and rough |
| 7 | comics | 7 | Full | Smooth to cut; 9 out of 10 cutting experience | Smooth (Tiny Bumps) ; entertaining |
| 8 | parchment | 6 | Full | unfortunate ; :( out of 10 | crinkle - crinkle |
| 9 | parchment | 6 hair spray | Full | not again... decapitation, execution, murder, had to be put down; 1 out of 10 only because it was fun | smooth... like paper |
There were more parchments than anything else since someone thought it would be a good material even if it obviously wasn't; it wrinkled badly when the glue was applied. It didn't wrinkle when hair spray was used instead of white glue but that seems a poor choice for something you want to be flame resistant.
| W1(g)/L1(cm)=D1(g/cm) | W2(g)/L2(cm)=D2(g/cm) | Radial compression | Linear compression | Burn | |
| 1 | 3.4g / 10.4cm = 0.32 | 2.8g / 9.9cm = 0.28 | 274.3 g 2.7N ; came pre-squashed | 3674g 36 N ; scrunch | Slightly flammable; it chars |
| 2 | 4.7g / 10cm = 0.47 | 5.3g / 9.9cm = 0.53 | 5896g 60 N ; still round | Off the charts (Tiny Tiny Bends) | slightly less flammable but still burns |
| 3 | 4.5g / 10cm = 0.45 | 3.9g / 9.9cm = 0.39 | 3855g 37.8 N ; Slightly more oval than before | Off the charts ; barely able to bend it (With hands!) | Hard to light but burns well once lit |
| 4 | 6.9g / 10.2cm = 0.68 | 6.6g / 10.1cm = 0.65 | Off the charts ; beyond our weights ability ; not a dent | Off the charts ; unable to damage | Same as 3 |
| 5 | 3.3g / 10cm = 0.33 | 3.8g / 9.9cm = 0.38 | 1360g and 450 g 17.8 N ; slightly flatter on one side | 4082g 40 N ; only little bends | lights quickly, burns steadily |
| 6 | 3.1g / 10cm = 0.31 | 3.2g / 10.1cm = 0.32 | 371g 3.6 N ; pops back into shape | 2267g 27.8 N ; Squish | Lights instantly, burns steadily ; 10 out of 10 good candle |
| 7 | 3.5g / 9.8cm = 0.36 | 3.7g / 10.2cm = 0.36 | 3628g 35.6 N : Slightly more oval than before | Off charts, but not by much | Same as 3 and 4 but less steady |
| 8 | 1.6g / 9.8cm = 1,6 | 1.4g / 10.3cm = 0.14 | 39.9g 0.4 N : pops back into shape | 1360g 35.8 N | 10 out of 10 Marshmallow ; you get that beautiful golden brown color ; If held over campfire to long it will light |
| 9 | 1.2g / 10.5cm = 0.11 | 1.4g / 10.9cm = 0.13 | 49.7g 0.5 N ; pops back into shape | 1133g 11.1 N ; Squash | 9/10 alternate fuel source |
Summary
| Material | Weight/cm | Weight/cm/wrap | Strong enough? | Flame safe? | |
|---|---|---|---|---|---|
| 1 | parchment | 0.3g | 0.05g | no | sort of |
| 2 | PT tube | 0.5g | ~0.12 | yes! | sort of |
| 3 | cardboard | 0.42g | 0.42g? | yes! | almost |
| 4 | paper bag | 0.66 | 0.08g | yes! | almost |
| 5 | paper towel | 0.36g | 0.07g | yes | no! |
| 6 | parchment | 0.31g | 0.05g | no | no! |
| 7 | comics | 0.36g | 0.05g | yes | almost |
| 8 | parchment | 1.5g | 0.02g | no | almost |
| 9 | parchment | 0.11 | 0.02g | no | no!!! |
Round 2
We followed basically the same procedure with a few small tweeks: if you lay the material on a working surface with the forming rod aligned with the closest edge you can keep up a more even pressure.