Boys Ranch Rocket Club – March Launch

Waylin
Waylin and Mr. Wheatley getting ready to launch

Rocket club member, Waylin,  successfully launched his first mid power rocket.

 

It was a North Coast Rocketry Lance Beta using an Aerotech G40 motor.  It was a great flight! The wind did carry the rocket into the trees where it made a safe landing 30ft up. I’m sure the wind will blow it down and it will fly again. This was Waylin’s first rocket and he did a great job building it.

 

D.E.R.K.2  Rocket

Landing_Site_nosecone_main_ebayD.E.R.K2 is named after the team that built the rocket.

This carbon fiber rocket did not fair so well.  The rocket endured an anomaly 3.86 seconds into the flight at around 4,600ft while traveling at Mach 2 (1533mph or 2249ft/second) . The rocket came apart unexpectedly. The motor continued to burn for .8 seconds. Under normal conditions the motor burnout would have occurred around 7,100ft with the rocket coasting to a little over 22,000ft. We were able to locate the nosecone/main parachute airframe and electronics bay Saturday  using our tracker. The parts were recovered 1.2 miles north of the launch site( see attachment for google earth pic) . Ethan, Waylin and I hiked the distance using our radio tracker as a guide. I thought it was good exercise and fun they didn’t share my opinion. This week we will start working on Derk3.

D.E.R.K.2 – Successes – the motor performed perfectly, the airframe\fins survived the transition to Mach 2, electronics allowed us to track the parts and analyze the data, cause of failure determined Failure – ejection charge fired early due to pressure air anomaly caused by blocked air vents

Thanks Mike Pacino for the video. In the video you will hear 2 pops. The first pop is the ejection charge firing and the second is an echo.

D.E.R.K. 2 – Explanation of failure

Derk2_AfterThe electronics  bay has a flight computer and data logging altimeter. The flight computer is also a data logging altimeter but it also collects more info than altitude and speed making it a flight computer. Altimeters sense air pressure to determine altitude and both recorded the same air pressure error. The electronics bay has 3 vent holes which allow the altimeters to read air pressure. Apparently 1 or more of the vent holes were blocked or partially blocked by wiring. Around 3.86 seconds into the flight the blockage cleared which caused the altimeter to sense and increase in pressure even though the rocket was still travelling up.  The invalid reading caused the rocket to fire a separation charge prematurely which caused the failure. The separation charge normally fires once the altimeters sense the air pressure is increasing which means the rocket has reached it’s highest point (apogee) and is moving back towards earth. (air pressure decreases as altitude increases)

Suspected cause of problem To arm the electronics two wires which hang outside the electronics bay are taped together to turn on the altimeter. Each altimeter has 2 wires so 4 wires total. The wires are then pushed inside the electronics bay so they do not hang outside of the rocket during flight.  Somehow these wires moved and blocked 1 or 2 vents prior to launch and then under acceleration they moved again causing another invalid pressure readings.

Problem Identified with Data Verification  the blue line in the attached graph represents the altitude. Under normal conditions the line will ascend in a slight slope rapidly until the maximum altitude is achieved. (in our case 22,300ft) . The line in the graph is relatively flat (100-300ft of altitude) until around 3.19 seconds into the flight where it takes a slight dip and then starts to ascend rapidly. The rocket at this point in the flight is actually around 4,000ft. You will also notice the red “crazy lines” which are the G forces the rocket experience when it came apart +88 G’s and – 40 G’s. The backup altimeter showed very similar pressure issues although it does not log as much data as the flight computer.

It was just one of those odd failures. I could probably launch 10,000 rockets and never have this happen again.

Chalk one up to the rocket gods.