Posts Tagged ‘deployment’

 

Air Flap Launch Detect & Deployment Timer Calibration

Air Flap Launch Detect

The Air Flap detects launch and releases the timer that in turn releases the parachute. I modified the Air Flap to make it longer and narrower. I expected that the original one which was shorter and wider would probably have been pushed down by the air resistance at launch, but I couldn’t make it release by blowing hard on it.

Its possible the original one would have worked but I cant be sure it would be at or just after (less than 0.5s) launch . The new one is able to be released by blowing hard on the end of it. The longer flap uses mechanical advantage by making the lever of the flap longer so it takes less force to push it back against the body of the rocket and in turn start the timer off.

Here is the flap in the ready to launch position . It is made from a section of corrugated plastic

Air Flap in launch position

Air Flap in launch position

The Air Flap is glued against the side of the nosecone and also has 3M strapping tape to help keep it against the side of the nosecone. I found when the timer is wound up a lot that the edge of the flap attached to the nosecone was starting to lift. This solution keeps it in position.

Close up of Air Flap attachment

Close up of Air Flap attachment

When the rocket launches the air flap is held back against the side of the rocket causing minimal aerodynamic disturbance, I think :) Here it is ready for launch.

Launch configuration

Launch configuration

Deployment Timer Calibration

In order to have the parachute deploy at the right time I needed to know how many turns of the timer would equate to how many seconds. This way as I increase the pressure in the rocket and the apogee height increases, I can tune in the right amount of delay in the timer so the parachute doesn’t open too soon or too late.

To do this I setup the rocket in launch configuration and timed how long it took from launch detect until the chute door opened and the chute was ejected from the nosecone. I can use this time and add another second or so to give me the time when the chute should open.  The results were

Timer Turns Seconds to Parachute Eject

4

3.5

5

4.2

6

4.6

7

5.4

The results were not linear possibly due to the non-linear spring mechanism or the varing tightness of the elastic band, however these are in the ballpark that I need.

I will use the water rocket simulators like Cliffords to approximate the apogee of the rocket prior to launch at a certain pressure and water fill, then dial in the number of turns on the timer to hopefully get the parachute ejection time correct. I will take this table with me on Launch day to use as I increase the pressure.

Posted by on August 28th, 2008 Comments Off