Two test flights were performed at the AARG club launch on August 18, 2007. The wind speed was about 10 mph. The first flight turned downwind and went up about 10 feet. The second flight turned upwind and went up about 14 feet. These flights showed the method used for passive stablization does not work well.
Simulations showed that the rocket should have gone about 6 feet high if it went straight up. I also simulated weights that were 10% higher and 10% lower, which should be similar to the results if the motor was 10% weaker or 10% stronger. In the case of 10% stronger, the rocket would go up about 20 feet, so the experimental results are more consistent with this case. I will weight the rocket by 10% more to 2.42 pounds (1.1 Kg) to compensate for this on future flights.
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The following diagram shows the force vectors that were being applied to the rocket.
The left diagram shows the force of the rocket thrust in red and the force of gravity in cyan.
The magenta vectors show the components of the rocket thrust.
There are horizontal and vertical components that will cause translational motion on the center of mass.
However, there is no rotational component which would tend to move the rocket to vertical.
The diagram on the right shows what happens when a vertical force is applied. In this case there is a rotational force, which will tend to move the rocket to vertical. The conclusion from these experiments and the vector analysis is that the rocket motor must be maintained in a vertical postion. The next version of the Quad Pod rocket will contain a gyro and servos to keep the motor vertical. |
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1. Estes E9-4, 1010 grams. The rocket turned downwind, as shown in this picture and this video.
2. Estes E9-4, 1010 grams. The rocket turned upwind, as shown in this picture and this video.