Almost Misfire?

[SkiesAreClear]

Hello all,

New here, and eager to join the conversations.

At my launch last night, I had what I was sure to be a misfire or some sort of CATO. I put a LMS G78-7G in my Apogee Aspire and at the end of the count, I was left with a short puff that actually bumped the rocket a bit. Then the longest 2 seconds of my life of nothing, I was sure it was going to pop. The motor then fired and the rocket screeched up. Deployment seemingly on time.

See the linked video here:

Excuse my audible moment of fright.

I was using a Go-Box and 2 brand new 6V lantern batteries (they lit another motor minutes after this with no issue).

Has anyone seen something like this before? Sorry I didn't get the full flight in the video, I was so startled I forgot to look up with my phone.

 

[Tech 68]

Has anyone seen something like this before?

That was a "chuff".
Not all that uncommon with AP composite motors

 

[OverTheTop]

Seen that sort of thing from time to time. That's why there is a wait one minute rule before going to the pad.

I remember seeing video of an O motor that coughed and spluttered for quite a while, and somebody commented they could get campfires going quicker than that.

 

[SkiesAreClear]

What is it about the motor that causes a chuff?
Great to know why the misfire procedure has that wait period.

 

[ksaves2]

That was a "chuff".
Not all that uncommon with AP composite motors

Yup,

Like tech 68 said, a chuff. Sometimes a motor “chuffs” and it doesn’t fire necessitating a change in the igniter.

In fact, I gotta get a video out as it’s stashed on an old laptop hard drive in the basement. I posted it here many years ago.

I had a rocket at an old Midwest Power chuff four, yes 4 freaking times before it went off the rail for a nominal flight.

It went, “Chuff”, then “CHuff”, then “CHUff”, then “CHUFf” and then “WHAM” off the rail on an AT 29mm I-200.

Each time it chuffed it bounced up and down the rail. Higher and HIgher and HIGher, until the motor caught and propelled the rocket off the rail.

I had a close up video of it and it was hilarious. Tim Lehr didn’t know what to think of it. It was an absolutely highlight of my launching experience. Funny as all get out. Especially since the DD system of the rocket worked nominally and I got it back. Still in my basement today and could be made flyable easily.

I gotta go and see if I can salvage that video!

Kurt

 

[Tech 68]

Here's a link to a research paper "synopsis" about it.
https://www.sciencedirect.com/science/article/abs/pii/S1540748902803558The middle part gives a pretty good "in a nutshell" idea of what happens.
What hurts is when the delay grain lights and the motor fools around coming up to pressure and you end up with an early deployment.

 

[SecondRow]

Not mine. Posted on the NAR page a couple years ago.

 

[MOF410]

Not mine. Posted on the NAR page a couple years ago.

That was AMAZING, I'm so happy this was caught on video. looked like a good flight after all!

Thanks for sharing!

 

[OKTurbo]

That video is something else!

Composite propellant burns faster as the pressure builds up in the casing. If ignition doesn’t happen to get enough burning it causes it to chuff. once enough gets going to maintain pressure in the case it’s good. You’ll also find certain propellant types are easier or harder to light reliably. The blue propellants usually light right up....reds seem to be the toughest. Haven’t had issues with white, but the white grains tend to oxidize and swell quicker as they age.

After I put the igniter in, I try to either use the red nozzle cap that comes with lots of the reloads or at least put tape over the nozzle in an attempt to give it a better chance of coming up to pressure quicker. The danger with a bad chuff is if it comes off the rail and heads in an undesired direction.

Here’s my big Praetor going up on a Loki red motor. Even with a good igniter and my precautions, it still gave a little chuff before it really got going.

 

[neil_w]

Not mine. Posted on the NAR page a couple years ago.

That is absolutely amazing.

Kind of like watching Sergio Garcia putt, or Mackey Sasser try to throw the ball back to the pitcher (Mets deep cut there).

 

[mbeels]

Not mine. Posted on the NAR page a couple years ago.

That is the mother of all chuffs! Maybe that's what happens when you count "...five, four, three, maybe, two, chuff one ..." Chuffed itself right off the launch rail! Spectacular!

 

[SecondRow]

That is the mother of all chuffs! Maybe that's what happens when you count "...five, four, three, maybe, two, chuff one ..." Chuffed itself right off the launch rail! Spectacular!

IIRC, it was an old white lightning motor. They were expecting some chuff, but not like that. This is one of those videos that looks great because everything worked out, but man, if that rocket’s nose tilted toward the flight line...everyone would need a change of shorts. That’s why I’m glad the safety guidelines we have are in place.

 

[OverTheTop]

Looks like a good reason to use longer launch rails.

 

[BABAR]

Not mine. Posted on the NAR page a couple years ago.

Boy, glad that one finally got a steady plume while still vertical, a 1/2 second the other way and that would have been unpleasantly exciting!

We had a saying at the Academy, "If the minimum wasn't good enough, it wouldn't be the minimum." For some reason it was more popular among the cadets then the AOCs (Air Officers Commanding)

 

[Neutronium95]

Here's the most extreme chuffing I've ever seen on video.

 

[tomsteve]

wonder how the blast deflector fared on that one

 

[BABAR]

Here's the most extreme chuffing I've ever seen on video.

Is 3 minutes and 20 seconds a record burn time for a model rocket motor?
Clever song.