|Posted by Christie on October 17, 2011 at 2:20 PM|
Pack Space Derby Rules:
All Rockets must pass the following inspection
to qualify for the race:
1. Only basic materials supplied in the Official BSA kit may be used. The hanging devise supplied in the kit must be used.
2. The nose cone (propeller assembly) must not be glued in place on the nose of the rocket. (It will need to be removed to load the rubber band motor)
3. A notch or groove should be formed in the tail of the rocket to seat the band holding dowel. The band holding dowel (white plastic piece that looks like a dumb bell) must not be glued in place. (we do not use these)
4. The RED staw provided in the kit must be on the wire hook before attaching it to the propeller. (this prevents the rubber band from breaking during winding)
5. The rocket body may be no longer than 7 inches, not including the propeller and fins. Width 2.75 inches -There are no restrictions on the weight or design of the rocket.
6. There are no restrictions on the weight or design of the rocket. Rockets may be detailed in any way as long as it does not exceed length restrictions, is flight worthy, structurally sound and does not interfere with another rocket during the race.
7. Rockets with wet paint will be disqualified
8. Scout may use graphite powder between the propeller and the bushing if desired. Other forms of lubrication are prohibited.
Tips for Construction of Rocket and Preparing for Flight
(These are tips used by the "Rocket Masters" use at your own risk)
SHAPING & CARVING THE ROCKET
-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.
-Rocket body is shaped as small as possible. FAST ROCKETS HAVE A MINIMUM PROFILE.
-Inside of body is hollowed out to reduce weight. If possible, select the lightest body you can obtain. LIGHTER ROCKETS GO FASTER.
-Use a sharp knife for cutting the grooves for the hanger fitting and fins. A dull knife will crush and splinter the balsa wood. But when you start to carve, remember that the end with the small hose is the rocket nose.
- A new potato peeler is good for carving the shape.
-To help increase the rocket's speed, reduce the wall thickness to a minimum of 1/8 inch. Do not weaken the area around the hanger (carrier) or carve away the nose button circle.
-Rocket is balanced fore and aft when a pin is inserted in rocket carrier hole.
-Plastic hanger is fastened securely to body.
-Groove for rear dowel is deep enough so dowel does not twist when rubber motor is wound tight.
MECHANICS OF THE ROCKET (PROPELLER ASSEMBLY)
-Do not glue the front nose/propeller assembly into the front of the space derby. It is pulled off to re-load new rubber bands!
-Do not glue the back dowel onto the rocket. It is pulled off to re-load new rubber bands!
-Propeller is balanced. Sand if necessary.
-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.
-The propeller should have the rounded shaft-end pointing into (touching) the space derby (this makes the bending of the wire easier and it reduces friction).
-Propeller wire is as short as possible. Notch on propeller engages propeller wire securely.
-The little plastic straw MUST go over the hook (not just the shaft as the drawing in the space derby kit illustrates) this is where the rubber bands will hook on - the wire hook will cut the rubber bands without the plastic straw liner!!!
- The plastic dowel at the rear of the space derby to hold the rubber bands MUST be kept from rotating (groove out the back so the dowel can sit in it!) - do not glue it!
-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. If 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.
-Propeller nose button is lubricated with graphite.
-Lubricate the rubber bands before the derby. This prolongs the bands' life and power and will help reduce the possibility of breaking during the competition. They can be soaked overnight in castor oil. Or mix two parts green soap, one part glycerin, and one part water and rub the mixture on the rubber band about an hour before racing.
-Have extra boxes of rubber bands on hand. Remember, it takes three rubber bands to fly each ship properly.
Experienced rocket racers "warm up" their space ships by gradually winding the rubber band motor numerous times before races (20 winds, then 40 winds, then 60, 80, 100) -- this helps relax the elastic properties of the band and makes it more pliable and durable (this is exactly why the clowns stretch the balloons before blowing them up!).
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 Klingon® vessel (from Star Trek©;). 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 assemblies were glued in place it would be 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.
Remember, it's only a game and this is for fun.
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 speed, reduce the wall thickness 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 paint 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 sand paper after each coat. Next spray on a topcoat. Don't use too much paint, you want a light 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.
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.