Intro: Pot Pie in the Sky - Flying Pie Tins
On March 14th, 2015, The Vanguard School in Colorado Springs, CO (where I work as a teacher), celebrated “Pi Day” (3/14) with a carnival of pi-themed events for the students and plenty of awful pi puns. I wanted to include something with rocketry and eventually hit upon the idea of “Pi in the Sky.” A quick internet search for ideas turned up the Squirrel Works’ “Pie in the Sky” half spool rocket based on a pizza pan (http://www.squirrel-works.com/catalog/pie/pie.html). This set me to wondering if I could adapt the concept to an actual pie pan and “Pot Pi in the Sky” was born.
My requirements were: 1) keep it simple and easy to build, 2) make a low flier to keep it in a small field, and 3) keep it cheap. I found some small pot pie tins at the local supermarket and began experimenting. My initial thought was to fly the pan upside down in a more classic saucer configuration but I really wanted the look of an actual pie flying right side up. The more I thought about it, the more I realized that if I covered over the top of the pan I’d have a half-spool very similar to the Squirrel Works’ model. With confidence that such an unaerodynamic-appearing beast might fly I set to work.
My prototype model placed the motor tube roughly centered top to bottom in the pan with a cardboard disk to close off the top and help hold the motor tube steady. I cut a series of radial slits in the bottom of the pan, slid the motor tube through and taped the flanges to the tube to secure the bottom end of the motor tube. I taped a short bit of soda straw to the motor tube for a launch lug and cut a notch in the pie pan bottom and top space for the lug. Then it was off to the launch pad! I used a bit of tape to secure an Estes B6-0 black powder rocket motor into the rocket and with a quick check of the skies, gave the countdown. The flight was perfect. On ascent, the rocket was fairly stable albeit with a bit of wiggle. As soon as the motor burned out, the pan immediately went unstable and tumbled in for a recovery. Given how well the first flight went, I decided to try flying the pan upside down (saucer mode) and found it flew well that way, too. I also tried and settled on a C6-0 as the standard motor for the higher flight it gave vs. the B motor.
After my initial flights, I noticed that the bottom rim of the pan tended to dent easily upon landing. I therefore modified the design to include an inner cardboard spacer in the bottom of the pan to strengthen and support the lower rim. I also elected to move the motor tube rearward to preserve the appearance of a smooth pie top on the pan. Since our event was for Pi Day, I searched the Net and found a neat picture of a pie crust with the digits of pi running around the perimeter (courtesy of Philip Nel’s Blog at http://www.philnel.com/2014/03/14/9kindsofpie/). Perfect! I scaled the image to match my pie pan and “Pot Pi in the Sky” was born. The final rocket consisted of just six pieces: the pan, two cardboard spacers, a motor tube, a launch lug and the decorative skin on top. Assembly required only white/wood glue, a hobby knife, hot glue and some tape.
During Pi Day, we helped about two dozen kids build the rockets. For fun, I found a wide variety of pie and cookie pictures that I printed up and let the kids choose from. While the pi pie was popular, a picture of a large M&M candy/chocolate chip cookie was even more so! Sadly, due to legal issues, we were not permitted to launch that day on the school’s sports fields. However, our local club, the Colorado Springs Rocket Society (COSROCS), holds public launches on the 4th Saturday of each month. We therefore gave the students a voucher to bring with them to the launch where we’d provide the motor and let them fly their pies. We had several students show up to fly their creations at our next launch. One youngster had so much fun he begged his dad to buy him at least two, if not three, more motors. From leftover pie tins I created a small fleet of six pies of my own. Adding in a couple of more gave us an 8-pie fling at one point. All eight made it off the pad and the crowd loved the crazy swarm as it clawed skyward. The tinny “tink-tink” of the pans tumbling back to the ground added a fun touch. After Pi Day and in light of the various skins I’d used, I decided to let go of the pi pun and renamed the rocket “Pot Pie in the Sky.” If you’d like to try your hand at flying this pie, here are the list of materials, directions and templates for the spacers.
Step 1: Materials Required
To build your own flying pie pan, you'll need:
1 – Piece of corrugated cardboard approx. 5” x 5”
1 – Piece of corrugated cardboard approx. 3 1/2” x 3 1/2”
1 – Soda straw, 1 1/2"
1 – Motor tube, 18mm x 2 1/2" Note: commonly called BT-20, available from vendors such as Apogee Components (https://www.apogeerockets.com/#)
1 – 5 5/8” pot pie tin (measured across outer rim)
1 – Decorative skin of your choice
1 – Top template
1 – Bottom template
Scissors; hot glue and white or wood glue; and masking or duct tape; hobby knife
Step 2: Mark and Cut Top and Bottom Spacers and Pie Pan Bottom
1. Cut out the two template pieces (4 5/8” and 3 1/4”) including the 3/4” center hole and 1/4" notch.
2. Using the templates, trace and cut out two cardboard disks including the center hole and notch for launch lug.
3. Place the small template into the bottom of the pie tin and trace the hole and notch in the bottom center of the pan.
4. Using a hobby knife, cut out the square notch in the bottom of the pan. Then make radial cuts around the center hole, making sure to leave the pizza slice-shaped flanges attached to the bottom of the pan. One flange will be lost in the process. IMPORTANT: DO NOT CUT OFF THE FLANGES!!
Step 3: Glue Bottom Spacer Into Pan, Add Motor Tube and Launch Lug
5. Glue the smaller cardboard disk inside the bottom of the pan with hot glue, making sure to line up the notches in the pan and disk.
6. Tape the straw launch lug to the motor tube, flush with one end of the tube (the lug is shorter than the motor tube).
7. Push the end of the motor tube that extends past the launch lug through the pie tin bottom from the inside of the pan until the launch lug is flush with the outside bottom of the tin. You should have about 1" of motor tube exposed at this point. The flanges should now lie parallel to the motor tube and point away from the tin.
8. Wrap a strip of masking or duct tape around the motor tube to secure the metal flanges to the side of the tube.
Step 4: Add Top Spacer and Decorate
9. Place the larger disk onto the motor tube, across the top of the pie pan. The motor tube may stick up past the top of the disk a fraction of an inch. Run a bead of hot glue around the perimeter of the disk to secure it to the pie pan. Run a bead of wood or white glue around the motor tube where it meets the disk.
10. Using the larger template, trace then cut a hole and notch in the center of the decorative skin and glue it to the top disk. Note that the skin is larger than the template in order to cover the entire top of the pie pan.
Step 5: Prep for Flight
11. This rocket flies on Estes black powder motors (available at hobby and craft stores or online). IMPORTANT: Only use B6-0 or C6-0 motors. "B" and "C" indicate the motor class (C is more powerful and is what I typically fly on). "6" indicates the thrust of the motor in Newtons. The most important part is the "-0". This indicates there is no ejection charge in the motor. In a normal rocket, the ejection charge pops the parachute out after a few seconds of delay. These rockets do not fly very high and tumble back to Earth as soon as the motor burns out. If they had an ejection charge it might go off when the rocket is close to the ground which could cause damage or injury to a spectator. DO NOT fly this rocket with a motor other than a "-0."
12. Insert a motor with the nozzle pointing downward (to the bottom of the pie pan). The top end of the motor should be nearly even with the top of the pie pan and the nozzle end should stick out about 1/4".
13. Use a wrap of masking tape to secure the motor into the motor tube.
14. Insert an igniter (sold with the motor pack) into the nozzle until it stops and insert the colored plug that comes with the motor to secure it. Your rocket is now ready for flight.
Step 6: Flying Your Rocket
15. Before you launch, check your local laws and fire codes to be legal. Some cities don't allow launches in public parks or in excessively dry conditions. Note that most schools may require specific permission to use their fields as well. The Colorado Springs Rocket Society (COSROCS) has permission from the Challenger Middle School to use their fields for our club launches.
16. You need to fly this rocket from a launch pad. A 3' length of 1/8" steel rod works great as a launch guide. Attach alligator clips to the igniter leads and run wire at least 15' back from your launch pad. The igniter will glow incandescent and fire your motor on 9-12V. A "jump start" battery works great.
17. After a suitable countdown, complete your firing circuit and watch your pie claw its way skyward.