Your pad needs a standoff.
By - Feisty_Papaya24
Your pad needs a standoff.
Small 3D printed rocket running a 18mm C first flight thought the small hop was interesting. Suspect it's from escaping gasses against the tile before motor kick in? Anyway think it's about time a 3D printing section related to Rocketry only is available made if interested
Yes please. It would be great to connect amateur rocketeers with printmakers.
Honestly it’s pretty normal, that’s just a motor chuff. The motor quickly pressurized but wasn’t quite burning enough fuel to sustain the chamber pressure, the pressure dropped down a bit, then enough of the motor lit to fully start the burn. You’d see it a lot more often in higher level APCP motors, I don’t remember seeing it often in Estes.
I have not seen it before untill this slowmo does larger motors do the same ? Any risk around this ?
I suspect that rather than being a chuff (which rarely happens with black powder motors) this happened because the rocket was in direct contact with the blast deflector. Estes motors have a ramp up at the beginning of [the thrust curve](https://www.thrustcurve.org/motors/Estes/B6/thrustcurve.svg) (yes, I know that's a slightly different motor, but that picture shows the ramp up much better). That first initial bit of gas wouldn't have been enough to lift the rocket on its own, but because the back end was in direct contact with the blast deflector, that high pressure gas was acting over a wider area, and thus kicked the rocket off the pad. The thrust alone still wasn't enough to keep the rocket going up though, so it started to fall back down again, until the thrust ramped up enough to get the rocket going.
[Here's a slow mo video of another estes rocket lifting off pressed right up against the blast deflector.](https://www.youtube.com/watch?v=BS4AP8f0DBg) [Here's another.](https://www.reddit.com/r/rocketry/comments/13hytg3/up_close_slowmo_of_a_small_rocket_launch/) Neither one hops quite as dramatically, but there's still a little bit of a bounce at ignition. Contrast this with videos like [this](https://www.youtube.com/watch?v=BbO-PSlgvfk) or [this](https://www.youtube.com/watch?v=6QjCXpfiOtw) which do not have the motors pressed up against the blast deflector and you can see a clear difference. I think yours is the most dramatic because the blast deflector has no give to it. With the other examples, the blast deflector can tilt and flex somewhat to get out of the way. Yours cannot.
I've seen similar liftoffs at public launches as well, and they've all occurred when the back end of the rocket motor was making contact with the blast deflector.