More rocket data
29 November 2008
by
lolife
Filed under
Rockets
I got out and launched some more rockets. Although it doesn’t exactly compare apples to apples, you can see on the image to the right that things either went very wrong with my initial iPhone launch or the GPS data I’m getting is screwed up.
The black line is a flight with the red iPhone rocket but instead of an iPhone I flew a standard altimeter (a PerfectFlite MAWD). The red line is the prediction from RockSim for that flight. You can see it matches almost exactly.
The green line is the plot of the GPS data from the iPhone and the yellow line is the prediction for that flight. You can see it doesn’t match at all.
One would be tempted to think that the time stamps on the GPS data is just stretched out or something, because it would look a lot more normal if you compressed it so it had a faster climb at the beginning and a descent rate like the other flight. But I just checked again and on the video it is a 74 second flight. That is 20 seconds longer than it should have been.
Thus, the only theory that makes sense to me is that the motor burned slow and long. From the video I tried to determine the velocity and acceleration of the launch and it matches the GPS data within uncertainties. So I think the GPS data is good and the problem was with the motor.
As a rocketry dork aside, I was using the Copperhead igniters when I launched the iPhone and I used the FirstFire igniters the 2nd time. I think the Copperheads did not work correctly or I used them incorrectly, because one other flight seemed to have a weird start with them.
I tried to fly both the iPhone and the PerfectFlite altimeter at the same time but I couldn’t get them both to fit in the payload bay. That is the next test I need to to.
29 November 2008 @ 2:19 pm
I should add that the red iphone rocket and the yellow rocket are very similar, having the same diameters, nearly the same lengths and roughly the same centers of pressure and gravity. If anything the yellow rocket (an Aerotech Initiator) should perform slightly better because it has smaller fins and is more optimally stable. The red rocket is a LOC Graduator. I used the same 10″ payload bay on both of them.
I say this because I should have launched the yellow rocket with the altimeter and a G80 and it would have been exactly like the iPhone launch except for the weight difference (which is only 50g).