Extreme Air Mail! Mailing Tube Rocket Project!

[Weldo]

Hey! I decided to start a separate thread to document the mailing tube rocket build. Thanks to @rwm for this cool idea!

So here's a quick recap, on what I've done so far...

First is a screen capture of the Open Rocket file I made. This configuration seemed to have the best compromise of stability, speed off the rod, and total apogee. It also conforms to the general rule of at least 5:1 thrust to weight ratio. The body tube is 22" long with a 6" conical balsa nose cone with 1.5" shoulder. Rings and bulkheads will be 1/8" ply. Motor is Estes D12-3. Fins will be 0.080" acrylic sheet because I have some laying around.



Here's the meterials I gathered. 2x4x12" balsa for the cone and 1/8" ply for the rings. Shout out to Bill and Walt's Hobby Shop in White Oak, PA! You can buy balsa online from them here.




I glued and clamped the 2x4s together to make a 4x4. I can whittle this down to a 3.25" diameter nose cone.




Next made a motor tube. It's just some heavy packing paper wrapped with wood glue. I used a motor as a mandrel. The motor ended up a tiny bit loose, it may need a wrap or two of masking tape on launch day.




The ends will be cut off and cleaned up later.




Next I began work on the rings and bulkhead. I used an old school fly cutter. I worked really well!




The fit is very good!




Next I cut the center holes with the fly cutter and a few holes in the bulkhead with a 1/2" forstner bit to pass the ejection charge. I also put a layer of foil tape on the motor side of the bulkhead, just in case it would want to scorch. The math is to set the fly cutter BTW.




Here's the balsa block really for shaping. I think I'll cut it down to about 3.5" square then shave off the bulk of the cone with a draw knife of spoke shave. Then I'll probably do the dowel trick that @brino suggested.




More to come!

 

[rwm]

This is very cool! Can't wait to see it. I like what you have done so far.
This will not be the "low and slow" vehicle I discussed so I hope you don't have difficulty recovering it. My particular vehicle probably had an "unsafe" thrust to weight ratio however it was very long, nose heavy, and more stable on that basis. At one point it experienced a Rapid Unplanned Disassembly due to nosecone failure. (It was a Leggs Egg container initially; apparently they are not flight certified )
I was thinking about those champagne glasses you showed before. I wonder if you could use something like that for a mold for a fiberglass nosecone?
Robert

 

[brino]

Watching your build.

Thanks for sharing!

 

[rwm]

 

[brino]

At one point it experienced a Rapid Unplanned Disassembly due to nosecone failure. (It was a Leggs Egg container initially; apparently they are not flight certified )
I was thinking about those champagne glasses you showed before. I wonder if you could use something like that for a mold for a fiberglass nosecone?

I once made a tapered body rocket, the body was a heavy cardboard spool from Mom's sewing machine.
(maybe 1 inch on the small end, three inches on the big end and 6 inches tall. I put a nose cone in the little end)
One of those would make a great nose-cone too.
-brino

 

[Weldo]

This will not be the "low and slow" vehicle I discussed so I hope you don't have difficulty recovering it.

Yea, it seems like it kinda turned into a regular rocket! I'm still unsure of what's safe and what's not so I'm erring on the side of caution with what was suggested in the general discussion thread. I really don't want some dangerous or catastrophic failure and I don't have the experience to recognize a potentially unsafe parameter in a build. But I want to learn so I'll give it a shot and see what happens.

Apogee is supposedly still only about 100 feet so as long as the wind is relatively calm it should come down fairly close to where it launches.

Not sure about recovery yet. This model might be a little heavy for streamers but I have my doubts about whether a chute will open quickly enough from only 100 feet. The simulation says the optimum delay would be around 1.75 seconds so at Estes' 3 seconds my rocket may already be descending before the ejection even happens.

This is getting exciting!

 

[rwm]

100 ft would be low and slow! My guess is more than that in spite of the simulation. It looks like you put the data in correctly. Go with the chute. Even with partial opening it will act like a streamer. I found the 3 sec delay too long for my vehicle but it may be perfect for you. I wish they made a D12-2.
You should go with a USPS Express Mail paint theme!
Robert

 

[Weldo]

Another update! I had the day off from work!

Got the engine block in. It's a tiny ring of 1/8" ply material. I drilled a 3/4" hole then sanded away until it fit in the tube.




Motor hangs out by 1/2" for taping. Or maybe I'll make a motor hook?




Started carving the nose cone! Glued in a dowel. My first lesson learned, use a bigger dowel...




Started out with a draw knife to get close.




Man does this stuff carve nicely! As Bob Ross would say, "Sometimes it gets working so well you just want to keep going." (Ominous foreshadowing... and second lesson learned...)




I moved onto the lathe to ensure an accurate fit in the tube. Looking good so far.




It fits the ID of the tube very nicely! Just a bit snug and it doesn't fall out upon inversion. You can see the first hint of a problem though...




Ugh! Third lesson learned, making a nose cone is harder than I thought it would be!




It fits OK on the other side though.




Do you guys think it's worth trying to fix this misalignment? I have a chunk of balsa left over. Maybe I can glue it on and take another crack at the lower extremity? The dowel can serve as a tenon to strengthen the joint.

 

[rwm]

Is the error in the nosecone or the tube? I think your plan of adding the block to the bottom would be fine if that would solve the problem.
Robert

 

[Weldo]

The error is in the cone. There’s a sector of the shoulder that has been sanded down to almost non existent. I think I will glue on that block and have a second go.