Scratch - TerrapinOriginal Design / Scratch Built Contributed by Clive Davis (Contributed - by Clive Davis - 06/23/06)
Brief: Construction:
After printing up the plans on a sheet of cardstock, I carefully cut out all the parts. This basically consists of 8 fins, two body tubes, a nose cone, a shoulder, a launch lug, and two tri-fold shock cord attachments. Next, I used a dowel to help roll the body tubes and used yellow glue to glue them into cylindrical tubes. Then I rolled the nose cone. Once the nose cone has dried, there are tabs on the top of the upper body tube that are used to attach the nose cone to the black upper body tube. I rolled the shoulder and test fit it into both the bottom of the black body tube and top of the yellow body tube. Once I was sure that the shoulder fits both lower and upper body tube, I glued it into the top of the yellow body tube. I set this aside to dry. I folded and rolled the engine block and then used an empty 13mm motor mount to glue the engine mount into the bottom of the yellow body tube. I just made sure the motor stuck out the back of the rocket by about 1/4". I used an empty ball point pen and a ruler to run a crease along the fins so that they can fold easily. Once this was complete, I put glue in the fins and folded them over so that they were now double sided. I placed them on a flat surface, covered them with wax paper, and then placed a few heavy books on top. After they dried, I removed them. I then glued the small swept back fins on the upper body tube using the gray lines as a guide. Since the fins are so thin, it is a good idea to use white or yellow glue to add some fillets on either side of the fins. I also glued on the lower clipped delta fins on the lower yellow body tube.
The recovery system is simple. I just placed a shock cord with the tri-fold shock cord attachment (one on either end of cord) in the rocket, one inside the top of the yellow body tube and the other inside the bottom of the black body tube. I then filled the nose cone with clay and then covered the clay with a good portion of yellow glue. After everything was dry, I added a streamer to the shock cord. Finishing: Since the paper rocket is already finished with colors, all I did was use a clear coat to seal the ink from the ink jet printer. Currently, I am using watered down Mod Podge to get a nice finish on my paper models. Not only does this cover the ink, but it also strengthens the paper. Flight:
The only CONs I see in this design is the fact that the fins are very thin and they must be glued well onto the body tubes. They do have a tendency to bend, which doesn't necessarily make the flights unsafe, but it does contribute to some squirreliness in the flight, particularly in the coast phase. Just make sure the fins are on straight. Recovery: Since there is weight in the nose cone, this tends to come down first. I would probably seal the nose cone with CA glue internally first before adding any clay so that it is more robust on landings. Other than that, the Terrapin held up well to flight and recovery. Summary:
CONs: Fin attachment needs to be done well. Ejection charges may discolor and eventually burn through paper model.
What You Can Do
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I rolled the
launch lug around a launch rod and then glued it in shape. After this was dry,
I glued it half way up the yellow body tube between two fins on the model.
On the third flight,
I used nose weight again and selected an A3-4T. It zipped off the pad, had
great altitude, and I was able to watch the recovery all the way down.
Beautiful flight with nice recovery. Next up, I need to try a 1/2A3-4T.