What kinds of things make a difference for the long-term survival of a rocket?
I'm realizing that although I built a lot of rockets when I was younger, I didn't fly all that often so I probably never had a single rocket that flew more than a dozen or so times. Now that I'm Born Again, I'm building more rockets but I haven't flown any of them many times yet either.
So I'm asking for people's experiences with how rockets age as they fly many times.
What kinds of things do you see wear out or go wrong over time?
What kinds of design and build techniques make a difference in how well a rocket survives into its old age?
I'm mostly interested in low power, classic cardboard, balsa and black powder; I imagine the high power world has some differences...
Building for durability comes down to materials used an building technique.
- Use quality adhesives. Titebond I, II and Thick and Quick, Elmers All Purpose (not school). Various thickness's of CA and Epoxy. Never use model cement on an Estes model. It doesn't stick to their plastics. These things work and they are in every hardware store. Why reinvent wheel?
- Sand all the mating surfaces of all items. Especially plastic to plastic or plastic to cardboard/wood.
- Clean plastic parts before assembling as most have some type of release agent or oil on the surface.
- Remove the outer layer of the body tube where the fins attach. Score and peel off the shiny outer coating as glue won't penetrate it.
- Don't use the stock hooks on plastic nose cones. they will break and you will lose the nose cone. Instead, drill a couple of holes and pass the shock cord through them and tie a knot.
- Attach your parachute / streamer to the shock cord, not the nose cone.
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Examples: Lets start with something simple like the plastic fin Alpha 3. If build to the instructions there are a couple of places for improvement. When inserting the motor tube into the plastic fins, sand the insides of the fin can as well as the outside of the cardboard ring then assemble with a good amount of thick CA. When gluing the upper ring to the mount, sand the inside of the ring so the glue can soak in.
If yours didn't come with on, add a thrust ring above the motor hook. Use Kevlar as an attachment point for the shock cord. This can be wrapped around just below the upper ring of the motor mount. A small slit is cut in the upper ring to allow the Kevlar to pass up. Use a small section of heat shrink tubing to protect the Kevlar at it's base.
When attaching the Fin unit, Sand the outside of the ring as well as the top of the fins where they insert into the body. Glue in with a fair amount of medium CA.
Replace the stock rubber shock cord with elastic that is 2 to 3 times the length of the rocket. This gets attached to the Kevlar. Use thin CA around the inside top of the body tube to add strength to prevent dents and zippers.
Another Example: I recently built / rebuilt a Big Bertha. I knew I wanted something more robust as this one was headed out to AZ with us. Out there I have the room to fly pretty much any motor I can get my hands on so E and F composites are the norm. For this rocket I began by adding a full length coupler that stopped about 3/4 inch from the top of the tube so the nose cone would still fit.
I then built a 24mm motor mount using plywood centering rings and heavy wall BT50 tubing. A thrust ring was added above that allowed fitment of the Estes E motors. A second ring was added to the outside of the motor tube at the very botom even with the end of the tube so that the ring on composite motors had something to push against.
Used 300# Kevlar as a leader for the shock cord and covered most of it with heat shrink for protection. This is attached to a screw eye that is attached to the upper centering ring. Added about 10ft of elastic for a shock cords. Cut the base of the nose cone off and inserted a bulk head with screw eye as an attachment point for the shock cord.
The bottom of the body tube was sanded for good adhesion before the fins were attached.
Finally, Everything was assembled with 30 min epoxy.
This rocket has seen a dozen flights on D and E black power motors and 6 flights using composite E's and one flight on an F44-8. It's still alive to tell the tale and fly again.
Here is a quick snippet. I'll post a full video as soon as I have time to edit all the flights together.
With all that said there are still additional things you can do like through the wall fins that mount to the motor tube, papering fins, Fiber glassing the body tube and fins, coating the inside of the tubes with heat tape or sealer. Etc etc.