Misery to joy in less than a second - what causes this?

[billdz]

Rocket lifts an inch off the pad and then drops back down, an apparent fail. But then suddenly it lifts off nicely for a perfect flight. How did this happen?
https://youtu.be/pW_ANeHAe38

 

[dhbarr]

Classic chuff pogo. What motor?

 

[blackjack2564]

One possible cause, igniter not inserted to top of motor.

 

[billdz]

"Classic chuff pogo. What motor?"

AT I-180. What's chuff pogo? I believe the igniter was all the way up but anything's possible.

 

[Nytrunner]

Only time it's happened to me is with a D10. Given the tiny slot size, could have been partial igniter insertion, but it certainly made a nice 8" hop!

 

[dhbarr]

"Classic chuff pogo. What motor?"

AT I-180. What's chuff pogo? I believe the igniter was all the way up but anything's possible.

The motor briefly started to come up to pressure, causing the rocket to hop. The motor then lost pressure and fell backwards. Finally the motor repressurized and took off.

If it was a CTI load w/ a starter pellet I would have guessed that as the cause. Stock igniter? If so, my guess would be it briefly hung in the throat on the way out, and the rapid drop in pressure almost extinguished your burn.

 

[Keisling]

It looks like the rocket just fell a few inches. Were you using a standoff that could have been pushed out of the way while the motor was coming up to pressure?

 

[dhbarr]

It looks like the rocket just fell a few inches. Were you using a standoff that could have been pushed out of the way while the motor was coming up to pressure?

Good eye!

 

[billdz]

There was a standoff, I'll bet that was it, thanks.

 

[jd2cylman]

Be really worried when it chuffs hard enough to come completely off the rod... If it lights then, all bets are off as to where it will go. Ask me how I know...
Luckily, heavier models don't come off the rod easily.

 

[Keisling]

There was a standoff, I'll bet that was it, thanks.

It happened to me once and the rocket fell to where the motor's nozzle was resting against the deflector when it came up to full pressure. Toasted the entire bottom of the rocket and bubbled paint on my fins, soot everywhere.
I now try to place the standoff in such a way that it won't easily fall over.

 

[Onebadhawk]

Be really worried when it chuffs hard enough to come completely off the rod... If it lights then, all bets are off as to where it will go. Ask me how I know...
Luckily, heavier models don't come off the rod easily.

We have an acronym for this Adrian...

PDAMHIKT...

Teddy

 

[Keisling]

PDAMHIK what PDAMHIK means.

 

[rharshberger]

Be really worried when it chuffs hard enough to come completely off the rod... If it lights then, all bets are off as to where it will go. Ask me how I know...
Luckily, heavier models don't come off the rod easily.

Oh yeah, JD how did that "scratch" heal? Everything okay?

We had several chuff pogos at our recent 3 day launch, one jumped off the 8' rail, thank goodness it A) didn't relight and B) didn't land facing the crowd.

 

[Nytrunner]

I will likely regret this, but what does PDAMHIK mean?
(And will the answer require a pM)

 

[dhbarr]

Please Do Any Mean Horrible Idea ( Kidding )

 

[jd2cylman]

Oh yeah, JD how did that "scratch" heal? Everything okay?

We had several chuff pogos at our recent 3 day launch, one jumped off the 8' rail, thank goodness it A) didn't relight and B) didn't land facing the crowd.

I've got a nice < mark to remind me which direction the inside of my leg is... :wink: But that's all, luckily. Sounds like you guys got lucky.

 

[jd2cylman]

We have an acronym for this Adrian...

PDAMHIKT...

Teddy

OK, Teddy, I give, what does it stand for???

 

[jimn]

Google is your friend.

 

[Exactimator]

Please Don't Ask Me How I Know This.

At one of our launches someone tried an old motor (I think a white lightning formula. That thing sputtered and bounced on the pad for what felt like the length of Ben Hur then it flew fine, optimum delay and all.

 

[cavecentral]

Most of my chuffers are vintage single use motors with some corrosion / grain swelling. They don't always light very easily.

For a new motor, I'd agree that not having the igniter in to the top will cause this.

I did have a rail humper that did actually come off the rail. It lit just before landing - making a spectacular / very lucky flight. Couldn't plan that if I tried.