This is the simplest form of a nose cone for a rocket that uses a parachute, it is not made to survive any kind of impact on its own. There are no extra moving parts, timers to set, or expensive electronics. It is simply intended to remain in place at the top of the rocket until the rocket loses momentum or tumbles, then it separates and allows parachutes to drop out of it and open.
It is lightweight, weighing less than 35 grams for the nose cone and mounting ring but not including the parachutes. I think the cup blends well with the parabolic shape of the egg. The cup’s taper makes it easier for parachutes to drop out than with a cylindrical container.
This nose cone was created thanks to several coincidences discovered while playing around with my collection of junk, a.k.a. rocket engineering raw materials, rescued from the recycling bin.
I first discovered that a plastic Easter egg, the type larger than a chicken egg and usually sold in packages of 6, matched the diameter of the bottom of an 8 oz. plastic yogurt cup sold at the Aldi grocery stores.
Earlier I had found that a plastic lid from a Pringles snack can by chance was a tight fit on those same yogurt cups, even though they came sealed by a foil top and had no lid of their own.
And lately I found that Pringles cardboard tubes are a snug fit around the bottom of 24 oz. Pepsi bottles. That is a piece from a Pringles tube covered by brown plastic tape in the photo above. The lids fit tight on the rolled top edge of the can but they fit loosely on just the cardboard tube. Just the right fit that’s needed here.
In the photo above that is the inside of half an egg directly facing the camera but it looks like a shiny plastic ball. Optical illusion?
Glued to the bottom of the yogurt cup is a heavier plastic disk cut to the exact diameter to allow the egg half to snap onto it just like it would the ridge on the other mating half of the egg. Two small holes are drilled through both the disk and cup so that a loop of string can be tied there and a parachute can be attached to the loop inside of the cup. A small amount of weight could be added to the top of the disk under the egg if necessary.
Barely visible is the Pringles transparent lid on the mouth of the cup. Actually it is not the entire lid. The center flat disk of the lid was carefully cut out leaving only the rim. The lid rim was reversed and pushed over the bottom of the cup and snapped onto the cup’s edge to extend and widen it. This enables the nose cone to ride loosely on the section of Pringles tube.
A section of Pringles tube about 1 3/4 inch high, seen here covered by brown plastic tape, is forced over the bottom of the bottle and aligned as much as possible. A 3/4 inch strip of thin cardboard cut from a cereal box is made into a ring and glued inside the tube about a quarter-inch down from the top to form an inner ridge.
Resting on this inner ridge is a 1 inch section cut from another yogurt cup. Its purpose is to help hold and align the nose cone on the rocket. Cut only the rim off the spare yogurt cup, leaving only the flat side. Use 1 inch of this widest part and it should just fit inside the tube.
Building Tip: If you carefully cut out just the bottom of the spare yogurt cup, you can slip the remaining tapered tube snugly over your nose cone to help align the egg part while gluing.
A loop of green cord is glued to the bottom of the bottle for attaching a parachute. Heavier rockets should have a backup line for the parachute in case the glue doesn’t hold under stress.
A piece of orange foam has been placed on the bottom of the bottle to keep the folded parachutes from settling down too deep to fall out when the nose cone separates.
The nose cone was tested using just a bottle with no fins to launch it to tree top height. An 18 inch plastic parachute was attached to the nose cone and another to the bottle, both packed easily inside the yogurt cup. During several test flights it repeatedly flew straight up and easily separated, continuing on for some distance above the bottle before both parachutes opened and everything floated gracefully to the ground.
Adapting this nose cone to a slightly larger 1 liter bottle
Updated June 13, 2011
This nose cone can also be used with bottles slightly larger in diameter by making an adapter from the bottom of a 24 ounce bottle.
Cut the bottom off a Pepsi products bottle where the straight side meets the rounded, larger part that fits tightly inside a Pringles tube. This will be attached bottom to bottom to a 1 liter bottle.
Making the parachute attachment point on the bottle
Tie two pieces of cord into similar sized loops, leaving tails below the knots about equal in length to the bottle radius. Tie another piece of cord around the two loops just above the knots and leave a tail the same length. This leaves you with a little five legged “squid” made of cord.
On the 1 liter bottle’s bottom, locate the heavy center area about the size of a small coin. It’s one of the thickest parts of the bottle. Lightly scuff just this small circular area with sandpaper. Apply a spot of hot melt glue at the center point. With the tails of the cord held up around the loops, carefully press just the knot into the hot glue. When the glue cools, apply a little plastic cement from the hot melt glue lump down toward the valleys between the five bumps on the bottom. With a small stick, press the five tails down into the cement and let the cement harden.
You will need to drill a hole in the bottom cut from the smaller bottle so that the loops and lump of hot melt glue can pass through. Make it as small as possible. When the hole has been made big enough to let the bottoms fully mesh, apply ten small spots of plastic cement where the bumps contact each other. After the cement has hardened, cover the loops with a piece of drinking straw for protection and fill in the hole around the loops with hot melt glue. Remove the straw when the glue cools and slip a fishing swivel with snap over the loops for attaching a parachute.
Push an appropriate length piece of Pringles tube over the finished adapter and you have a place for mounting the same nose cone as before.