The Holy Hand Grenade of Antioch

When I was looking for nozzles for the high-power Gemini Titan model, I discovered an oddly shaped water bottle that was almost ideal for a bell-shaped nozzle form. Stuck in the back of my mind from that day forward was this thought: the stylized rocket-shaped bottle would make a nifty flying model.

Here in the southeastern United States the bottles are sold under the name "Aquapod" and advertised to to be a blast of fun. With a pronounced Orbastic shape. (Avoid the attempt to repeat that three time real fast. Or to use it at all in reference to the movie Barbarella)

They feel pretty sturdy when thay are pressurized and full of water, but when empty they are about as stout as frogs hair. If you accept the challenge to make something you could call "the rocket formerly known as Aquapod (TRFKAA), you will need a light touch.

My first consideration was "how to put a motor in it?". After all, we know almost anything can fly if you put a big enough right motor in the right place. I keep giving this example to my wife with reference to M2500's and the refrigerator. (empty of course!); Since the bottle weighs almost nothing (about half an ounce without cap and neck), a regular 18mm Estes motor will be plenty.

The neck of the bottle posed the first real obstacle. It was very thick and the plastic was extremely tough. I sawed it off below the flange with a thin hand saw . It was a interesting task because I did not want to damage the paper thin sides of the bottle. To accomplish this, the bottle neck was held with a vise grip while sawing. After sawing off the neck I sanded the stub to conform to the shape of the bottle using a belt sander. The hole in the top of the bottle was already larger than a BT 20 tube so I enlarged it with a Dremel tool and a sanding drum so that a 24mm motor case just fit.

A spent D motor case makes great centering rings for 18 to 24mm tubes. Cutting spent motors on the band saw also makes many free motor blocks.

Next a hole was cut in the bottom of the "airframe". I used a rotary bit on the Dremmel and cut a hole about 1/2 diameter inch at first. By the try and fit method I enlarged the hole until the BT 20 just fit.

Before I glued in the BT20 with the slice of D motor on the top end I looked around for an appropriate nose cone. I was very close to compromising with an Estes 24mm conical nose for even a plain 18mm ogive -- but there in my box of flotsam used to build sundry rockets was a hemi-shaped dome.

I don't remember where the dome originally came from. It is a thin vacuum-formed part with about a 1/4-inch shoulder that has a slightly larger diamter than the dome. (If anyone recognizes what or where this thing came from they can mail in and win a PRIZE!) To make this nose work, I let it fit over a BT20 extending from the bottle. A slice of D motor with a slice of 24mm tube made a perfect transition ring. The finishing touch was a 1/8-inch thick balsa disk glued to the top of the motor case slice.

Above is the bottle with the motor tube bonded in with 5-minute epoxy. A light fillet was applied to the aft end to secure the slightly protruding motor mount. Also shown is the inside view of the nose cone. I later attached a piece of Kevlar thread to the nose with a small screw as an anchor point.

The recovery anchor was a piece of Kevlar thread tied around the motor block (visible above inside the motor tube).

Since the back of the bottle has bumps on it that look like the aft end of a delicious apple fin mounting was dictated by the spacing of the 5 lumps. The fins was cut from balsa in a whimsical shape that yielded a 5 inch span. The were glued on by tacking with CA in the valleys between the lumps. (Caution! I glued my hand to the fin on every other fin) After all the fins were tacked I went back and made small fillets of 5 minute epoxy over the full root area.

Here it is ready for putty and paint. To keep the found object theme the launch lug is the tube that Aerotech gives you with a Copperhead igniter.

It has a plastic trash bag parachute tied to the nose cord and a shot piece of elastic shock cord connecting to the main anchor thread.

Depending on how you see it, The Holy Hand grenade of Antioch, the Rocket Formerly Known As Bottle, or the bottle rocket, it is an unusual bird. It is only about an ounce without the chute, but it has a lot of air resistance to keep from going as fast or far as other one ounce rockets.

After applying the first coat and standing there watching the paint dry I was suddenly startled -- the great, cool-looking, finished-and-still-sticky rocket popped and one side collapsed. I stood there staring for a moment, holding the piece of conduit that I was using to maneuver the rocket for painting like I had a bird on a spear.

I thought, "what just happened"? Then it came to me, the solvent evaporating cooled the airtight "airframe". Cold air shrinks (just ask Boyle!) (The gas law Boyle if you can find him). Realizing the cause I ran and found a small drill and drilled a hole in one of the bumps on the aft end. (The bumps that make the aft end look like the aft end of a Red Delicious apple).

"POP" and it was instantly back to shape with no evidence of being collapsed, except for a small wrinkle over one fin.

It was in the Macedonia road Baptist church lawn (no, there is no artistic irony in flying from that field- Antioch was located in ancient Syria, not Macedonia), so big motors were not a good option. I flew it twice on A8-3's both flights were nominal. Good straight stable boost to about 250 or 300 feet.

Good recovery each time. The small motor helped make up for the lack of room for wadding. I packed the empty space in the motor with wadding. The airframe had room for less that one diameter of wadding over the motor. The chute had to be packed perfectly tight and small.

I will try a B motor next time. I don't expect motor size to be an issue as much as wadding space. A Nomex chute or Nomex streamer may be a good option to fly with no wadding.