Polka Dot Roc --- Modifying the Estes Quark for helicopter recovery.

Thad Povey LUNAR #963

Description:

This hack uses an unusual recovery method on one of the smallest rockets available. Two fins of the rocket are modified with the addition of hinged flaps and a wire arm. An elastic runs from the end of the wire arm back to trailing edge of an adjacent fin to deploy the flap. A wire retainer is attached to the motor and is positioned to keep the flaps tight to the main fins until the engine is ejected. As can be seen from the rear view, the configuration of the elements is not radially symmetrical, but the drag is still balanced for stable flight. The design has been flown many times and can be a little squirrelly on the way up, but the rocket comes down like a sycamore seed with a beautiful, fast rotation.

I developed the idea when my wife was pregnant and the gender of our future daughter was still unknown. I made two rockets, one pink and one blue and covered them with polka dots. They were launched simultaneously as what I call Shot-and-Caught rockets (the one pushing the launch button has to be the one to catch the rocket). The pink one was caught more often than the blue to correctly predict the future. So the legend goes.

Construction:

The rocket is initially constructed per the plans, but I've found that, over time the body tube tends to collapse under the fins from the tension of the elastic (maybe this happens with a non-hacked Quark as well, but I've never made one that way). If I were to make one again, I'd reinforce the body tube in the fin area with some kind of reinforcing wrap on the outside.
The flap is cut from leftover balsa available in the kit. I used some fiberglass fabric and epoxy to make the hinge. This hinge gets highly stressed, so solid gluing is necessary.
For the wire arm, I used some stiff wire (flattened out paper clip wire works well) and used CA or epoxy to glue it to the leading edge of the flap. There's a tiny hook bent into the end of the wire as shown.
I made the elastic from very lightweight elastic sewing thread. It's a single piece of the thread tied into a loop about ¾ inch in diameter. Trial and error will give you the right size so that the flap will snap open, but not pull the joints apart or stress the fins too much. Most likely a standard rubber band could be found with the right size, but the tension is just right with the sewing thread.
The elastic attachment point is at the trailing edge of an adjacent fin (a fin without a flap). I took a standard office staple and pushed it through the fin, then bent one of the projecting ends around into a hook. A little CA keeps it from wiggling loose.
The retaining wire on the motor is also stiff wire and is wrapped around the motor a couple times. It extends out and back from the business end of the motor. I've bent little feet on the ends to press on the flap without touching anything else.
The trickiest part can be installing the motor and tweaking the retaining wire. You'll need to install the motor several times to get everything just right. It involves slightly rotating the motor and wire while inserting it, but the goal is to have the motor fully installed with the wire not touching the rocket anywhere except at the flaps. When you get it right, the flaps will be pressed tight to their fins and there will be no aerodynamic tendency to spin. Then use that first wire to make several copies, since they'll get lost.
Since the ejected engine will have the wire attached to it, I paint the assembly a bright color to facilitate finding it. This saves having to make another wire every time and also avoids foot injuries for the non-shoed.

Contact:
Thad Povey
830 Shotwell Street
San Francisco, CA 94110
barelyboy@aol.com

Return to Index

All content is the responsibility of LUNAR. If you have comments or suggestions regarding these web pages, please contact the