StratoLogger CF Negative Velocity

[rlhatcher]

Hello all - My StratoLogger CF has recorded negative velocity from my last flight, which seems unusual to me. Is this normal?

 

[cbrarick]

yup. That negative velocity is when the rocket was descending.
think of velocity as directional speed between 2 fixed points, the ground and it's apogee. motor burn increases velocity then it goes down to zero at apogee. the way back down it has to be negative until it hits the ground and then it's zero. if you were dd you'd see a differential negative velocity on the drogue and the main (something less)

 

[rlhatcher]

That makes perfect sense - thanks!

 

[kevinkal]

Hello all - My StratoLogger CF has recorded negative velocity from my last flight, which seems unusual to me. Is this normal?

View attachment 321876

It looks like you touched down at -55 ft/sec. Did you have a problem with the main parachute opening or such?

 

[rlhatcher]

I did indeed. The shear pins didn't shear so came down pretty hard on the drogue and fond the only sliver of concrete in the whole area! Luckily a solid rocket and only a few chips and dings - all repaired now and ready to try again.

 

[Banzai88]

I did indeed. The shear pins didn't shear so came down pretty hard on the drogue and fond the only sliver of concrete in the whole area! Luckily a solid rocket and only a few chips and dings - all repaired now and ready to try again. View attachment 321885

Ouch. It's a law of physics, or at least rockets, that any landing that could hit the only piece of rock/concrete in a hundred square miles WILL be the spot that your rocket chooses to land in. Likewise with water and trees.

Do you know what your failure mode with the shear pins was?

 

[rlhatcher]

I under filled the ejection charge sadly. I kind of knew it at the time and should have double checked but lesson learned! At least it was only minor damage and gave me an opportunity to use the vinyl cutter to make some band aids to cover the repairs and not have to repaint anything.

 

[markkoelsch]

Ground test your charges/ shear pins with full up recovery gear packed. Get a good, energetic deployment. You do not want it where the chute just barely clears the tube- shoot it out there a bit into clear air.