Slingshot launching: FTLongEZ and a Foam Gyroc

by NYCBobby | June 17, 2019 | (4) Posted in Projects

Inspired by Alex's and Jeremy's article on launching a plane using a bow and arrow we made a slingshot launcher out of aluminum extrusions and surgical tubing then we launched a foam version of the Estes rocket, the Gyroc, and an FTLongEZ.

The slingshot consisted of a main tube, 8 feet long pitched at 67 degrees. This tube has a roller on the end and the surgical tubing is tied to the back end, then looped around the roller and stretched to the end.  Two other aluminum tubes mounted in front form the tripod support.

The Gyroc's design is covered in the video but here is a picture of the mechanism. The FTLongEZ has two servos for control but no motor.

A small lead weight is tied to the plastic tube.  This tube is slid into place so as to lock the Gyroc's fins in place during launch. When the rocket flips nose down the lead weight will pull the tube inside the fuselage and release the fins putting it in helicopter mode. A small rubber band is used to make the mechanism more sensitive.

Off to Morningside Park, located on 116th Street and Morningside Drive, NYC.

Here we are ready to launch.

Some Calculations
Surgical Tubing Stretch
3.37 meters
Force Required to Stretch Tubing
3.34 Kg= 32.73 Newtons
Spring Constant, K9.71 N/m
P.E. In Tubing
½ *K*x^2 = 55.13 Nm
Mass of Gyroc
46.6 gms
Mass of FTLongEZ
138.7 gms
Slingshot Angle
67 degrees
Ideal Exit Velocity, Assuming A Projectile With No Drag And 100% Efficiency At Converting The P.E. Of The Tubing To K.E. Of The Projectile
48.6 m/s
28.2 m/s
Theoretical Max Height, Assuming No Drag
102 meters
34 meters
Theoretical Maximum Distance, Assuming No Drag
57 meters
FTLongEZ25 meters

Of course these numbers are not anywhere close to what actually happens though it is worth noting how much energy is stored in the stretched surgical tubing.


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Slingshot launching: FTLongEZ and a Foam Gyroc