This project was inspired by my desire to build a one stage single-finned model rocket that would boost to apogee, then return to ground spinning like a maple seed. I failed. However, I was able to modify the design to build a model rocket that used the principles of the maple seed to recover a part of the rocket using "whirling recovery". The first step of the design was to build a rocket that would accelerate upwards in a straight stable path, then become unstable when it reached apogee, and spin on the downward return. Two pieces of data from previous folded paper models were used:
- a thin and long "tail" will cause the model to fly straight (the "bottle rocket" theory, as almost demonstrated in the second model in Experiments with Maple Seeds with Taped Wings)
and
- a change in weight distribution will create imbalance to make the model spin (see both Origami Folding Variations and Weight Distribution of Origami Maple Seed).
The first model was relatively stable, but did not spin reliably.
Based on the results of Experiments with Maple Seeds with Taped Wings and Experimenting with Cut Wings I added a vane to the fin. Hand-launching the rocket indicated that it was stable to apogee, and would then spin on the return. String testing it by rapidly swinging the model around me on a string indicated that it would be stable under powered flight. I was wrong.
The rocket ascended approximately ten feet in the air, then began to rotate under power. When the engine burned out the rocket continued to whirl, then descended by rotating. The rocket is assumed to act like a maple seed thrown hard. In this case the throw exaggerates instabilities and causes the seed to rotate. The same thing probably happened to this design which rotates a little too reliably to launch safely.Unstable powered flight is dangerous to observers and bystanders, so this design should not be used.
I gave up on the single-finned design and compromised by adding a finned stabilizer that would separate from the maple seed unit at apogee. The finned unit would tumble to earth because it would be unstable, while the maple seed unit would rotate. Hand launching and string testing indicated that this design would be stable during powered flight.
It was not. The large fin area forward of the rocket's center of gravity made it sensitive to small gusts of wind. The tendency to rotate caused the rocket to fly in a "loopy" path during its ascent. The design was still too "delicate" to be safe.
I then began to reduce the fin area forward of the center of gravity to stabilize the rocket. At the same time I was constrained by the need to preserve the ability of the maple seed unit to rotate. I did not want the unit to plunge back to earth like an arrow. First I cut away as much of the leading edge of the fin as I could.
The rocket still was not stable. I trimmed the end of the maple seed unit's fin based on Experiments with Maple Seeds with Taped Wings.
The stability improved, but I trimmed the triangular part of the vane to increase stability even more, and move the center of gravity forward. This design was stable under difficult tests (such as starting the string test with the rocket facing backward). The maple seed unit did spin faster, as predicted by the experiments with Wing Size Variations.
This rocket launched safely and stably, reached apogee at approximately 150 feet, separated into the maple seed unit and the stabilizer unit, and both returned to the ground as expected, with the maple seed unit falling more slowly than the tumbling stabilizer unit.
Frankly, it was a beautiful and delightful experience! You can see some Big Pictures of the Maple Seed Rocket, and the Plans for the Maple Seed Rocket that contain a parts list and assembly instructions to build one of your own. Here are some suggestions for designs and experiments that you can do to improve on the maple seed rocket. Try them! But always be sure to be careful!
