Recovery

Intro

A variety of methods have been devised to bring a rocket safely down to the ground. While using a parachute seems to be the most popular, it isn't the only method. Even among those that use parachutes, there are many ways of deploying the chute.

[edit] Passive Methods

The main passive method is known as Back Sliding or Back Gliding. It involves designing the rocket so that it's center of mass is behind it's center of gravity. Once the rocket reaches apogee, it stalls and begins to fall horizontally. A horizontal fall is slow enough to prevent damage to the rocket. It is a neat, no moving parts system.

Another method involves using an energy absorbing nose cone and allowing the rocket to nose dive or "lawn dart" into the ground. Tennis balls and pieces from foam toys are popular. Having a long nose cone area to act as a crumple zone can also help.

[edit] Active Methods

These require something to occur before deployment of the recovery device. An Air Speed Flap is a thin sheet of plastic held against the rocket by the wind as it goes up. As the rocket nears apogee and slows down, the flap (under a light tension from above) is now able to hinge up. This movement releases a rubber band or string holding the nose cone or parachute.

Chemical Deployment is nothing more than a chemical reaction in a medical syringe. At apogee when the rocket turns over, chemicals are mixed together causing gas to be produces. This gas pressure causes the syringe to open up and can be used to push a parachute out of the top of a rocket.

A Tomy Timer is any plastic timer found in a variety of wind-up toys. At each launch, a guess is made as to how many seconds it will take the rocket to reach apogee. The timer is wound up that much and the rocket is launched. As it winds down it can be rigged to pull a string or release a mechanism that sends the parachute on its way.

[edit] Air Speed Flap Parachute Recovery

[edit] Chemical Deployment of a Parachute

[edit] The Basics

This method often uses a medical syringe. Inside the syringe can be a variety of chemicals, but usually there is a liquid and dry chemical that are separate. After apogee, as the rocket begins to go horizontal or nosedive, the chemicals are mixed together. This mixing causes gas to be produced and makes the syringe go from almost closed to open. This pushing can either literally push the parachute and nosecone out of the top of the rocket, or the opening syringe can move the nosecone up, causing a gap that allows the parachute out. The action of the syringe opening up can be used to trip a multitude of things.

[edit] Chemicals

Usually an acid and a base are mixed together to create a gas. This can be as simple as baking soda and vinegar. Some heat up the vinegar before adding it to the syringe, presumably to speed up the reaction. Another chemical combination is baking soda and citric acid. Both are in a powdered form and can be mixed together without a reaction. Once you have the mix, only water is required to cause it to gas off. The benefits of this combination are that you can mix it ahead of time and keep it in a bottle. When you go to launch, you only need water to complete the reaction, no stinky vinegar. And you should already have water with you. Citric acid can be found anywhere that sells winemaking supplies.

[edit] The Syringe

Syringes come in a variety of sizes. A 60cc syringe just about fills up the space in an FTC rocket and has a lot of travel. Syringes come in two tip styles: luer and luer lok. The luer tip has a smooth taper and items placed on the end are friction fit. The luer lok allows things to be locked onto the end of the syringe with a twisting motion. This is one you want. If you can get luer lok syringes with an end cap, all the better. Syringes can be purchased locally at most large animal feed stores or at medical supply stores. They can also be mail ordered.

After loading up the syringe, you need to be able to close off the end. Having a locking, twisting cap makes it easy and secure. If your syringe doesn't come with a cap, you'll have to make one by getting a large gauge needle made for the syringe and cutting the needle part off right at the base. Try to open the hole in the needle back up as best you can with some needle nose pliars. Put your now blunt needle on the syringe and suck up some PL Premium with it. When you see it just inside the tip, stop and take it off to set up. You now have your end cap.

Some syringes also have a few plastic tabs on the end of the plunger behind the rubber that make removing the plunger part difficult. They're like stops. Some syringes don't have these. Most of the time, the gas generated has enough pressure to pop the two part apart even with the stops.

You will also need a syringe with a needle to add the liquid to the other syringe. To make it easier to get the liquid where it needs to go, gently bend the needle to one side. File the sharp tip off of the needle for safety, it isn't needed. Even with the bend, you should be able to get the safety cap back on the needle for storage.

[edit] Separation

There has to be some type of separation between the chemicals in the syringe, but they have to be able to react when the rocket is turned on its side or in a nosedive. You also have to have a way of getting the chemicals in there and sealing it all up. One method for a 60cc syringe is to make a little 'cup' for the dry chemicals with a piece of 1/2 inch PVC pipe. Cut off a piece a little more than 1/2 inch long. Put a piece of tape on one end and put some PL Premium in from the other side, covering the tape. Give it a day to dry and remove the tape. Give it another day to dry. You should now have a small cup for your dry mix. If you use a smaller syringe, you'll have to find something smaller to use.

To prevent the cup from sealing onto the syringe when it is turned over, preventing the liquid from quickly contacting the powder, you can put a few small nails on the open end of the cup.

[edit] Push Plate

If you are using your syringe to push the parachute out of the top, you should make a push plate. This prevents the parachute from getting wedged between the syringe and the rocket wall. Use any thick plastic (peanut butter jar lid) and cut it into a circle so that it easily fits inside your rocket body. Don't make this a tight fit. Also cut a smaller hole so that it can be mounted onto the area around the luer loc of the syringe.

[edit] Leashes

After all of this work, you don't want your syringe to separate from your rocket at 500 feet, never to be seen again, so you'll want to tether it to the rocket. Tie a string to the end of the plunger and tie the other end to the bulkhead end of the rocket. Of course, make the string long enough to allow the plunger to come completely out of the top of the rocket for reloading. Because the syringe is a separate from the plunger, you have a couple of options. You can tie a string to this and the rocket as well, however, because this part moves, you want to make sure the line won't get snagged anywhere. Another simpler method is to pull the plunger almost out of the syringe, to the stops if it has them, and then drill a small hole just above the plunger. Now, as the plunger gets close to popping out of the syringe, the extra gas is vented out.

[edit] Loading the Syringe

Getting things all together is fairly straight forward:

• Separate the syringe and plunger pieces.
• Put your powder into the cup. 50-75% full.
• While balancing the cup on the top of the plunger. Place the plunger into the syringe.
• Slowly push the plunger until the nails from the cup are pushing on the top of the syringe.
• Using your syringe with the bent needle, add your liquid of choice into the top of the syringe, shooting it to the side of the cup and filling it about half of the way up the side of the cup. You may have to move the plunger down a little temporarily while you do this.
• Place your locking end cap on and the syringe is armed and ready.
• Carefully place it in your rocket.

You may want to put your rocket on the launcher before adding the syringe if you think there is a possibility of shaking things too much. As your rockets get longer and this movement is magnified, you'll have to do it this way.