User error?

[drfish]

Tried my first 29mm reload at the weekend after lots of mostly successful 24mm loads.

https://www.youtube.com/watch?v=qNqSlzBah5s

Not great, any suggestions what I did wrong? I've taken some photos of the remnanrs of the motor/rocket which I'll upload as soon as I have time.

Just wondering if it was me or the motor?

Cheers

Chris

 

[troj]

Seeing the motor bits would help, but it's altogether possible that the motor itself failed.

More details would help.

-Kevin

 

[sylvie369]

Just wondering if it was me or the motor?

I bet it was the guy doing the countdown. Did you hear that strange accent?

 

[sandman]

That launch area look awfully familiar!

Are you a member of EARS?

 

[kelltym88]

Could've been the delay was put in with the spacer towards the top. This causes the delay to burn almost as quick as the motor causing an ejection charge very early in the flight. I could be totally wrong, but that's what it looked like to me.

 

[Pantherjon]

Could've been the delay was put in with the spacer towards the top. This causes the delay to burn almost as quick as the motor causing an ejection charge very early in the flight. I could be totally wrong, but that's what it looked like to me.

That is what it looks like to me as well..I did that once..Placed the spacer towards the front and got an almost instantaneous ejection charger after propellant burn out..Tho this one looks as if it went off right at propellant ignition..Maybe the fiber seal disk wasn't installed?

 

[troj]

Keep in mind he said "remnants of motor/rocket". That to me implies the motor itself is damaged, as well, something I would not expect to see if it was simply an early ejection.

-Kevin

 

[shreadvector]

Keep in mind he said "remnants of motor/rocket". That to me implies the motor itself is damaged, as well, something I would not expect to see if it was simply an early ejection.

-Kevin

I would expect it. If the delay burned fast (bubble) or was bypassed (bad seal or a bad liner) and the ejection charge went off during the propellant burn (and the video shows this occurred right away), then the propellant would still be burning under pretty high pressure and exhausting through the nozzle as well as the larger and growing-larger-by-the-millisecond hole in the top closure. The top closure should be damaged.

 

[drfish]

I bet it was the guy doing the countdown. Did you hear that strange accent?

Have you ever been to England, that's nowhere near the funniest or un-understandable

That launch area look awfully familiar!

Are you a member of EARS?

No, but I am a member of Midland Rocketry, paid the Big Ears meeting a visit last weekend. Great day apart from killing my buzzie.

Could've been the delay was put in with the spacer towards the top

Don't think so, but worth rememberign why not to do it!

Photos of the aftermath as promised. Not sure if it will help.

Inside of rocket is completely black and charred, shock code was melted through hence the separation.

https://picasaweb.google.com/maddoctorfish



Only thing I've been wracking my brains trying to remember is if I put the forward O ring in the delay. But I'm sure I did, I just don't recall removing it again, mind you it was pretty black and grotty around the closure. The front of it looks like the enamel has been removed on the outside.

Thanks for all the messages, keep them coming.

Chris

 

[dave carver]

Another possibility is the delay it's self, did it fit loose in the liner tube? There for a while I was wrapping a layer of masking tape around the delay because it wasn't tight in the cardboard tube you insert the delay into.

Hard to have a seal when the delay is loose in the holder.


edit: looked at your photos, I've seen the like before and I'm pretty sure that was your problem. Now, if you confirm the delay was loose you have your answer. If not, then your guess is as good as mine

 

[troj]

Based on the pictures you posted, I'm gonna guess blow-by. In other words, the hot gasses from the motor went up and around the delay.

The first effect of this is that the ejection charge fires immediately. The second is that you end up with the motor spewing flames out both ends, along with the erosion of the hole at the bottom of the ejection charge well.

When that happens, the o-ring at the top of the delay burns away, which is why you don't remember removing it -- it's gone.

That also explains the black residue on the outside of the forward closure and the inside of the airframe being cooked.

Now, as to what caused it... It could be a defective part, it could be an assembly problem. At this point, it's tough to determine the exact cause.

-Kevin

 

[Graham Orr]

This happened to me a few years back with our Mudd II rocket. The motor was assembled perfectly (I've done hundreds of assemblies in the last few years) so we think that the delay element was "yellow". Happens to BT and other propellants when they sit for too long next to propellant and the chemicals eat the plastic away.

The event happened on our first test-flight of a $10k research rocket flying on a $30 H motor of all things. No harm done... the booster pressurized popping the motor out the bottom of the rocket and shooting across the lakebed. The rocket was ready to go again in 30 minutes.

Happened to get a snapshot:

 

[bobkrech]

... the booster pressurized popping the motor out the bottom of the rocket and shooting across the lakebed.
Happened to get a snapshot:

Motor Retention Required.

 

[Graham Orr]

lol. motor retention? the fact that we didn't have retention on that 38mm in the 54mm MMT is what really saved the rocket. friction fitting that motor was the best decision ever!

 

[bobkrech]

lol. motor retention? the fact that we didn't have retention on that 38mm in the 54mm MMT is what really saved the rocket. friction fitting that motor was the best decision ever!

To those of us who are concerned about range safety, motor retention is important. Saving the rocket is not.

Having a fully functioning motor traveling horizontally at high speed is not safe. You probably wouldn't think too much of it until you see someone hit in the face by a free flying motor 100' away from a launch pad. Fortunately for the individual involved, the motor made a glancing blow off his glasses and he was not hurt, but it could have been real bad. I'd much rather see a $10,000 rocket burn up or crash safely than someone loose an eye or worse. You can always build another $10,000 rocket, but you can't replace an eye.

Bob

 

[troj]

Having a fully functioning motor traveling horizontally at high speed is not safe. You probably wouldn't think too much of it until you see someone hit in the face by a free flying motor 100' away from a launch pad. Fortunately for the individual involved, the motor made a glancing blow off his glasses and he was not hurt, but it could have been real bad. I'd much rather see a $10,000 rocket burn up or crash safely than someone loose an eye or worse. You can always build another $10,000 rocket, but you can't replace an eye.

Amen to that!

We had a motor shoot up through an adapter and rocket, leaving the rocket on the pad. It then arced over and embedded itself in the ground less than a foot from the heel of one of our members.

If the motor had him in the ankle instead of embedding itself in the ground, he would've been in a world of hurt, as it was a J350 that did this.

Scared the bejeezus out of all of us.

We still cannot figure out why it happened -- the guy who built the rocket builds 'em solid. The critical glue joint failed for some reason, and examining it afterwards showed there was plenty of bonding surface coated with epoxy, and the epoxy was a type that's shown itself to work fine for high power rocketry.

-Kevin

 

[kelltym88]

To those of us who are concerned about range safety, motor retention is important. Saving the rocket is not.

Having a fully functioning motor traveling horizontally at high speed is not safe. You probably wouldn't think too much of it until you see someone hit in the face by a free flying motor 100' away from a launch pad. Fortunately for the individual involved, the motor made a glancing blow off his glasses and he was not hurt, but it could have been real bad. I'd much rather see a $10,000 rocket burn up or crash safely than someone loose an eye or worse. You can always build another $10,000 rocket, but you can't replace an eye.

Bob

This why I think the delay elemant was put in backwards. Same thing happened to me with a G64. I had no motor retention, only friction fitted. Upon ignition, the ejection charge almost immediately fired, sending the rocket into a twirling frenzy. The motor shot out the back, danced on the ground, then took off, ricocheting off an umbrella and into the back of someones car. Talk about scary. No one was hurt. Moral of the story:

MOTOR RETENTION A MUST!!!!
MAKE SURE DELAY WITH SPACER FACING DOWN IS INSTALLED PROPERLY!!!

 

[shreadvector]

This why I think the delay elemant was put in backwards. Same thing happened to me with a G64. I had no motor retention, only friction fitted. Upon ignition, the ejection charge almost immediately fired, sending the rocket into a twirling frenzy. The motor shot out the back, danced on the ground, then took off, ricocheting off an umbrella and into the back of someones car. Talk about scary. No one was hurt. Moral of the story:

MOTOR RETENTION A MUST!!!!
MAKE SURE DELAY WITH SPACER FACING DOWN IS INSTALLED PROPERLY!!!

"Someone's car" will not be at the next Lucerne launch. He has to attend a wedding of a close family member. I will bring a few of the large tripod pads and a few heavy duty controllers and an assortment of rod sizes.

 

[Mikus]

At least *MY* motor stayed in the rocket. :clap: :confused2: :clap:

 

[Graham Orr]

Bob-
No matter the type of motor retention, a full blow-by in a sealed booster chamber would make the motor kick.

Suppose the chamber pressurized to half pressure:

300 psi.

Considering the diameter, that is over 1000 pounds force of required retention force. Even the PML threaded aluminum system would fail at the bond joint to the MMT.

I'm afraid even the 304 stainless anchored with 7075 retention ring (the actual 54mm retention device) would have failed as well.

So, while I understand your desire to keep the range safe, a motor ejection from blow-by on a sealed CF rocket is inevitable. This is why we switched to plugged forward closures as well...

So no, I'm not willing to so easily put aside a 1600 man-hour fabrication because of inherent dangers of rocketry. Rocketry is an inherently challenging activity that requires some caution, yes, but eliminating all the risks is impossible and getting on my case about this is really starting to grind my gears.

Furthermore, the ROC RSO approved the rocket for flight after several in-depth inspections. We were placed on a pad fairly far away.

By nature of this activity, things will unfortunately happen. Anyone who says any differently either has figured out a way of cheating probability or is not realistic.

 

[Graham Orr]

This forum is way too frustrating. It is like kiddies corner here.

Smothering anything on the edge is a good way to make something stagnate. You'll see less utility of rocketry in the future with this attitude.

 

[Peartree]

This is an impressively civil discussion but both sides have had their say. I know there are strong feelings on both sides. I suggest that the range safety part of this discussion be allowed to drop while it's still friendly.

 

[drfish]

Thanks for the posts.

Having read and digested the info, it must be a blow-by. Only question remaining for me, is am I am a numpty and built the motor wrong, or did something fail, don't suppose theres any way of knowing. Just hope my only other 29mm bird does not befall the same fate when she gets her turn to fly.

Cheers

Chris