Born Slippy: 54mm Minimum Diameter for the 2550

[daveyfire]

A few years back, Carl Delzell of ROC (and Rocket Rage) noticed a gas station was being torn out near his house. He went over and asked if he could take the pipe off their hands... and of course they quickly obliged. He brought the pipe to the next launch, and it came in 2.25" and 3.25" sizes. I picked up a few pieces of each.

Well, the pipe sat around in the garage for a few years while I worked on other projects. Then earlier this year, I was presented with a 54/2550 motor loaded with PSAN propellant -- about a K200. Since this motor needs a minimum diameter rocket, and since I figured that anything I could fit a 2550 case in I would eventually fill up with a blue propellant load (Mach 2 anyone?), I decided to put two and two together and finally use that gas pipe sitting in the garage.

First task was cutting and slotting the tubes. I worked out a design in Rocksim and began the work.

 

[daveyfire]

We cut the tubes to length -- 40" for the booster, 18" for the payload -- and slotted the booster for the 0.062" G10 fins. The idea was to have the tubes go through and abut the liner used to bring down the ID of the tubing to fit the 54mm motor.

 

[daveyfire]

Since the ID of the tube was too large to fit 54mm motors, we had to build up the inside of the tube. The quickest and easiest way to do this was to peel off layers from the OD of a piece of LOC tubing and epoxy that in place. I had a 10" piece sitting around that was perfect for the task.

 

[daveyfire]

Next came the time to tack the fins into place. This is always my favorite part -- when it's done, you get to see what the rocket will look like in the first place. I scuffed up the gas pipe around the fin area (preparing for eventual 'glassing) and tacked the fins into the slots with 5-minute epoxy. We (myself and Eric -- rocwizard) stacked it up for the first time to see what it would look like. I stole the nose cone from my Phobos to complete the look. That's the 2550 motor case standing next to it.

 

[daveyfire]

After the fins were tacked in, we applied fin fillets. Nothing special here, just the typical Aeropoxy-silica-and-a-spoon routine. I used the curing oven to cure them in 1.5 hours, then do a post-cure routine to increase the heat tolerance of the epoxy.

 

[daveyfire]

After that, I put two layers of bias-cut (0-90 and 45-45 fiber directions) 6 oz glass tip-to-tip to reinforce and stiffen up the fins. They're still a little flexible but hopefully not enough to cause a problem. I finished it up with three coats of UV Smooth Prime and a little Krylon. Whew, just in time for Balls this weekend!

Here she is in all her painted glory next to the 2550 motor again. Should be a fun flight!

 

[DPatell]

Looks awesome man! That should get way up there. Looking forward to flight pics.

 

[LMazza]

Beautiful rocket Daveyfire. Just curious, what is the weight and expected altitude?

 

[Elapid]

FAST!!!!!!!

 

[Daedalus]

Originally posted by daveyfire
After the fins were tacked in, we applied fin fillets. Nothing special here, just the typical Aeropoxy-silica-and-a-spoon routine. I used the curing oven to cure them in 1.5 hours, then do a post-cure routine to increase the heat tolerance of the epoxy.

Looks good - I love minimum diameter, they are true miniature sounding rockets.

What temperature did you do the cure at and what is the post-cure routine?

I have only used marine epoxy and microbaloons for my fillets (The epoxy hardens a lot quicker than Aeropoxy). I'm gathering techniques for a couple of new minimum diameter rockets after the separation of my 54mm minimum diameter - the booster section came in unretarded in a flat spin from 5000 ft on a shakedown flight on an I240. It was built for the Hypertek K240 but is now a little too short for that tank.

 

[Missileman]

Looks great,
What kind of material is that gas pipe?
Can't wait to read a flight report.

 

[rstaff3]

IMHO that tube looked too cool to paint. Was it rough and did you do a lot of filling?

 

[daveyfire]

Thanks for the kudos guys. I'm not exactly sure about the weight, but it's pretty light without the motor in it. I'm hoping for 15K, but who knows what I'll end up getting.

I cure my rockets at 150 degrees in a styrofoam curing box with an infrared lamp to heat it up. I have a thermostat that controls the temperature, got it from Shadow Composites. Post-cure just involves letting the part cool from the inital cure routine, heating it up for another 90 minutes, and letting it cool down slowly in the box. It raises the glass transition temperature of the resin. Never had a problem with taking a fin off, even after slamming them into the lakebed at 500 mph with a really hot motor!

The gas pipe is actually FWFG. That's the reason that this rocket is so neat -- it's incredibly strong, and I built it from parts I had on hand or got for free. I love it when that happens It was actually pretty nasty looking, it just looks really awesome in the photos... it had numbers written all over it and was all scratched up and nasty. No big deal, some acetone and sanding and all that was taken care of. The only problem with it was that it was kind of wavy on the surface... I don't know how else to describe it, it had a weird ripple going down the outside of it. I just sanded it a little bit to take out most of the high spots and figured that nobody could see the wave while it was on the pad!


3 days till Balls!

 

[Daedalus]

Thanks for the curing info. I will have to look at getting a curing box setup and try it sometime.

Have a good flight.