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Cub Scout Pack 368

Space Derby Tips
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Make sure outside tips and help don't conflict with Pack specifics rules!!
 
 
Space Derby Tips from the net!

Cub Scout Pack 261, Nashua, NH

Hints - From a Father and Son experience!

Lighter is definitely better.

There is a limited amount of force and energy in two (2) rubber bands wound 100 times so minimizing the mass of the unit can only help. We've seen a number of winners and the shapes of those winners differ dramatically. One thing in common with both of them is their weight. Both were very light and well balanced. The key is making it light without removing so much material that the winding of the rubber bands actually splits the ship in two or causes serious cracking. That's happened to potential winners for both of the last two years and the kids are pretty upset when it does.

The shape is not the key.

We have seen a number of different shapes and the winners were very different. One was cigar-like while the other was more like a KlingonŽ vessel (from Star TrekŠ). A lot of shuttle look-a-likes have been used and various other configurations. As long as the vehicle is symmetrical and light then it seems to perform well.

No glue on the propeller assembly.

Never use glue on the propeller assembly. Other than the fact that you may slip a bit and get some glue on the prop itself or on the bushing underneath, if you break a rubber band you have to be able to remove the propeller. During the Space Derby this year we had a number of problems including the rubber bands breaking during the winding and the actual propeller breaking. If that happened to a space vehicle where the assembly were glued in place it would have much more difficult to replace.

Make sure the propeller is on correctly.

Several Space vehicles this year had the propellers on backwards. When looking at the hub (center) of the propeller closely, there will be rounded end and a rougher end that is not even. The rounded end goes towards the rocket ship and should be touching the small metal bushing. The rougher end has a little protrusion that is designed to catch the wire when it is bent over. Which leads to the next tip...

Don't cut the bent over wire too short.

We were guilty of this one. In the attempt to be neat I cut it too short and then during the winding, the propeller can slip and spin around. Leave a little more than you think is necessary and you should be fine. Just bend it over to form an inverted 'U', with plenty to grab the prop, and then there should be no trouble.

Make sure the red plastic liner covers the entire hook.

The red plastic sleeve that slips over the metal hook (on the inside of the propeller assembly) MUST be put in place. That is there to prevent the metal hook from cutting through the rubber bands during the winding. It sometimes takes a little effort to pull it all the way on but it can be done. You can always grab the end of the wire with some pliers and work it on slowly, but make sure it goes all the way to the end of the hook.

Don't glue in the tail unit that holds the rubber bands in place.

Basically for the same reason. The rubbers bands can't be altered in any way without disassembling the unit. This actually happened to one Scout's vehicles and repairs were difficult.

The tail unit needs notches to prevent spinning.

After you are all done with your space ship make sure there are two depressions, of 'V's cut into the tail to prevent the end unit from spinning during the winding or once the rubber bands start to unwind. It may wind up okay but when the pressure is released slightly it may start to spin. If you cut them to deep you will be essentially shortening the spaceship and decreasing the pull on the rubber bands. It's more of a trial and error type thing. Start shallow and increase as needed.

Various fin/wing sizes and configurations work.

We personally haven't had a lot of luck in this department - I guess I have to read up on my aerodynamics. What I've seen is winners with small fins all over the ship and winners with just two big wings and a tail like the space shuttle. The bigger wings seem to cause less spinning when the ship is released for a more level flight, while the smaller fins seem to allow the ship to carry its speed a bit better. The bottom line is they both seem to work if everything else is done right. My personal opinion is that the bigger wings seem a bit better but you'll have to figure that one out on your own. Why we keep using the small fins is a mystery to me.

Have fun.

Remember, it's only a game and this is for fun.

 

More Tips...

Tips for rocket builders:

  • Reduce air friction or "drag" by making all surfaces as smooth as possible. A blunt, rounded nose causes less drag than a sharp nose. A good design has all leading edges rounded and trailing edges tapered to reduce the drag.
  • Rubber bands should be lubricated before the race. They are the "motor" and must be strong and flexible.
  • Use a sharp knife for cutting the grooves for the hanger fitting and fins. A dull knife will crush and splinter the balsa wood.
  • When you start to carve, remember that the end with the small hose is the rocket nose.
  • A potato peeler is good for carving the shape.
  • To help increase the rocket's spped reduce the wall thikcness to a minimum of 1/8 inch. Do not weaken the area around the hanger (carrier) or carve away the nose button circle.
  • Do not apply too much apint to the outside unless you sand between each coat.
  • Be careful not to get glue on the plastic carrier, especially in the holes through which the monofilament line runs. Glue can interfere with smooth operation.
  • Make the propeller shaft as short as possible by bending it close to the prop. Cut off the excess wire with wire cutters.
  • Test the rocket's balance by hanging it from a string through the hole of the hanger fitting. If the rocket is nose-heavy, carve or sand a little wood off of the end. It it's tail-heavy, remove wood from the tail area.

Dens may wish to secure a 100-foot length of 50-pound monofilament fishing line for test runs in the backyard before the derby. Tie the line to a tree or post and string the rocket carrier on it. Tie the other end to a tree about 100 feet away. Make the line as tight as possible.

Even More Tips...

Space Derby Rocket Assembly Tips

  1. Glue the two halves of the rocket body together, shape with a potato peeler, then sand. Carefully align and glue the two halves of the rocket body with Elmer's glue, or something similar. After the glue dries for 15 minutes, shape the body with a potato-peeler until it looks roughly like a rocket. Then sand it into its final shape with medium grit sandpaper. Wrap sandpaper around the body, holding it with one hand while you twist the fuselage with your other hand. Design tips: Fast rockets are smooth, aerodynamically shaped, and lightweight. Make the shell of the rocket thin, but thick enough to hold the hanger that will be attached in step 4 and thick enough to support the pressure of a tightly wound rubber band.
  2. Cut notches for the plastic dowel. The rubber bands will slip without these notches. Do NOT glue the dowel onto the body! The dowel will be held in the notches by the rubber bands - and must be removable so that broken rubber bands can be replaced.
  3. Hold the body upright on a nail when you paint. Tap a long nail a few millimeters into a block of wood. Set the block on a newspaper-covered floor or table with the nail pointing straight up. Slide the rocket onto the nail, inserting the nail into the rocket’s hollow center. Paint with a couple coats of primer, sanding lightly with fine sandpaper after each coat. Next spray on a topcoat. Don't use too much paint, you want a light rocket.

    Assembled Rocket

  4. (TAKE SPECIAL CARE WITH THIS STEP!) Attach the hanger, making sure that the rounded end points forward and that the hanger doesn't protrude into the rocket’s hollow center chamber. Glue it on with generous amounts of glue. Cut a grove for the hanger in the top-center of the rocket body. This 1" grove should be centered, 3" from the front and 3" from the rear of the body. Press the hanger into this groove, rounded end forward. The hanger must not protrude into the hollow chamber in the center of the body or it will interfere with the rubber band. The hanger must be firmly glued in place or it may detach during launch with disastrous consequence. Use a generous amount of glue to affix the hanger to the rocket body and allow the glue to dry overnight; a couple hours dry time may not be enough for Elmer's glue. Warning: the rocket pictured on the front of the space derby kit box has an incorrectly attached hanger. Don’t use it as a guide.

      Don't forget.

    1. The hanger’s rounded end must point forward.
    2. The hanger must not protrude into the rubber-band chamber.
    3. The hanger must be very firmly glued on.
  5. Cut and attach the fins. Shape the fins with scissors, then cut slits in the rocket and press the fins into the slits. Glue in place. Design tip: some claim that the fins should be angled upward very slightly. In theory this lifts the rocket slightly off the line during flight, reducing friction.
  6. Trim and balance the propeller. Sand loose pieces of plastic from the propeller. If the propeller is unbalanced, one side will swing to the floor when it is placed in a horizontal position. Sand the edges of the propeller to balance it.
  7. Don't tighten the cable tie. The rubber bands have already been attached to the dowel and a loop made from a cable tie has been added. Well use this loop to wind rockets at the races. Don't tighten it.  (Don't panic.  This pre-assembly and the cable-tie are NOT part of the standard kit.  Some packs/troops add this before kits are handed out.)
  8. Pull rubber bands through with a wire hook. You can make a hook from coat hanger wire.
  9. Fine tune. Test the rocket's balance. Hold it lightly by the hanger with your fingers. If the rocket is nose-heavy, carve or sand a little wood off that end. If it's tail-heavy, remove wood from the tail area or from the fins. You may be able to unobtrusively take wood from the rocket's hollow center chamber. Some advocate lubricating the propeller with a touch of graphite at the point where it touches the bushing. Other lubricants may melt the plastic.

 


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