Quantcast

Recovery overkill and non-deploy

The Rocketry Forum

Help Support The Rocketry Forum:

RocketTree

Well-Known Member
Joined
Apr 10, 2020
Messages
87
Reaction score
57
Location
Canada
I built a fleet of 4 inch rockets, with Aerotech style exhaust baffle (steel mesh). All have 29mm motor mounts. Recovery is 48 inch nylon chute, 25 feet Aerotech style knit elastic shock cord, and NOMEX cloth. I should point out, this is the first time I have used a Nomex cloth.

Launched with a G38-4 last weekend on a first test flight to 500 feet. Nose cone separated as it should, but the Nomex+chute+cord stayed in the body tube..... and became a big lawn dart right above us.

The chute and cord were folded as normal inside the Nomex cloth "cup", and could be easily dumped out if the rocket was turned upside down - which makes me think it was not stuck.

During flight, the ejection charge lightly popped the nose cone off at apogee, but thats it. No laundry.

The Nomex had no sign of burn/residue and no exhaust scent to it after deployment. Pulled out the steel mesh, the bottom half was coated with black, while the top half of the mesh was as clean as new.

This brings me to my question - is NOMEX + Mesh Baffle TOO MUCH protection?
 

Attachments

BABAR

Builds Rockets for NASA
TRF Lifetime Supporter
TRF Supporter
Joined
Aug 27, 2011
Messages
6,512
Reaction score
1,720
The chute and cord were folded as normal inside the Nomex cloth "cup", and could be easily dumped out if the rocket was turned upside down - which makes me think it was not stuck.
Just a clarification.

You said the chute and cord could be easily dumped......was the NOMEX easily dumped as well?
 

RocketTree

Well-Known Member
Joined
Apr 10, 2020
Messages
87
Reaction score
57
Location
Canada
Just a clarification.

You said the chute and cord could be easily dumped......was the NOMEX easily dumped as well?
Correct, the entire lot was free to slide out easily.

I'm very surprised that it did not eject at all. Compared to some smaller rockets I launch, this was packed loose.
 
Last edited:

o1d_dude

'I battle gravity'
TRF Supporter
Joined
Jan 18, 2009
Messages
8,317
Reaction score
1,151
Location
Planet Urff
To quote Nina Simone, “It be’s that way sometime.”

In the online multi-player game of Diablo III, we blame the “RNG”...the PC’s random number generator.

In the military, we said “spit happens” and the general response was “There it is.”

How tightly did you cram the pot scrubber into the baffle? It’s there only to absorb the heat out of the delay grain/black powder explosion, not obstruct the air flow.
 

ntsgators

Active Member
Joined
Apr 2, 2020
Messages
31
Reaction score
8
Location
Florida
How tight was the nose cone on? If it’s to lose the problem could be that the pressure is escaping and isn’t building enough pressure up to pop the stuff out
 

RocketTree

Well-Known Member
Joined
Apr 10, 2020
Messages
87
Reaction score
57
Location
Canada
How tightly did you cram the pot scrubber into the baffle? It’s there only to absorb the heat out of the delay grain/black powder explosion, not obstruct the air flow.
I had that scrubber stretched out to 6+ inches as recommended for all these rockets, and it seemed to be that length when I removed it. Bottom 1/3 of the steel mesh was deep black charred, rest was shiny.

Will fly it again without the steel mesh and see what happens in a couple weeks.


How tight was the nose cone on? If it’s to lose the problem could be that the pressure is escaping and isn’t building enough pressure up to pop the stuff out
The nose cone fit was about as close to perfect as it gets. I could see that being a cause otherwise.

Almost 75 launches this year, and this one was completely unexpected.

I'll give it another go without the steel mesh baffle and see what happens.
 
Last edited:

o1d_dude

'I battle gravity'
TRF Supporter
Joined
Jan 18, 2009
Messages
8,317
Reaction score
1,151
Location
Planet Urff
I had that scrubber stretched out to 6+ inches as recommended for all these rockets, and it seemed to be that length when I removed it. Bottom 1/3 of the steel mesh was deep black charred, rest was shiny.

Will fly it again without the steel mesh and see what happens in a couple weeks.
That sounds about right.

How close is the baffle to the BP charge well?
 

3stoogesrocketry

Well-Known Member
Joined
Feb 26, 2012
Messages
1,270
Reaction score
123
You had a weak ejection charge. You 1 need to slightly increase your charge , and 2 you need to add a small chute on your cone to destabilize the rocket . Even a 14 inch top flight will be more then enough. The air blowing into the rocket at 100 plus mph will keep the most freely packed chute inside your airframe.
 

GalantVR41062

Celebrate Recovery
TRF Supporter
Joined
Oct 25, 2017
Messages
281
Reaction score
201
Location
Plymouth MN
It sounds to me like the ejection charge on the su aerotech 29mm motor was not enough to push the recovery gear out.

The rocket is 4" diameter, about how long is it? If you were pack the rocket for flight and lift it by the nose cone what would happen? Do you have a vent hole in the airframe?

I would ground test the ejection charge in a spent motor pushing threw the baffle to make sure there is enough black powder and pressure to get the recovery gear out.

I also test my mid power and smaller high power rockets by packing them for flight, leaving the motor out, then take a deep breath and blow into the MMT. If I can separate the rocket and get the recovery gear out of the airframe I will call it safe to fly with the smaller amount of black powder that comes in single use motors, you can always add a little more to the ejection charge if needed.

I also use a 12" square nomex blanket in my 4" rockets, with up to a 45" thin nylon chute and 10' of tubular nylon I can pack this into a tight burrito that keeps things together and safe from a unbaffled ejection charge, but I plan to start adding a bit of dog barf to help dampen the flame.

~John
 

RocketTree

Well-Known Member
Joined
Apr 10, 2020
Messages
87
Reaction score
57
Location
Canada
You had a weak ejection charge. You 1 need to slightly increase your charge , and 2 you need to add a small chute on your cone to destabilize the rocket . Even a 14 inch top flight will be more then enough. The air blowing into the rocket at 100 plus mph will keep the most freely packed chute inside your airframe.

Well you are definitely onto something there. I was just saying that to my wife a few minutes ago... to use a small chute that will pull the rest out.
My concern would be that it would tangle with the main chute on descent. Should I have the main chute tied further down the shock cord or keep them together at the nose cone? Thanks!
 
Last edited:

cbrarick

Wildman CT
Joined
Jan 23, 2009
Messages
2,479
Reaction score
238
You had a weak ejection charge. You 1 need to slightly increase your charge , and 2 you need to add a small chute on your cone to destabilize the rocket . Even a 14 inch top flight will be more then enough. The air blowing into the rocket at 100 plus mph will keep the most freely packed chute inside your airframe.
He doesn't need more powder, he needs to loose the pot scrubber. If you have nomex and use it right, then you're ok....if you're not, get help and it will be OK.
He does not have dual deploy so number 2 is incorrect.... he doesn't need to stack chutes, just yank out the pot scrubber. Complicated answers just increase the possiblity of failure.
 

RocketTree

Well-Known Member
Joined
Apr 10, 2020
Messages
87
Reaction score
57
Location
Canada
It sounds to me like the ejection charge on the su aerotech 29mm motor was not enough to push the recovery gear out.

The rocket is 4" diameter, about how long is it? If you were pack the rocket for flight and lift it by the nose cone what would happen? Do you have a vent hole in the airframe?

I would ground test the ejection charge in a spent motor pushing threw the baffle to make sure there is enough black powder and pressure to get the recovery gear out.

I also test my mid power and smaller high power rockets by packing them for flight, leaving the motor out, then take a deep breath and blow into the MMT. If I can separate the rocket and get the recovery gear out of the airframe I will call it safe to fly with the smaller amount of black powder that comes in single use motors, you can always add a little more to the ejection charge if needed.

I also use a 12" square nomex blanket in my 4" rockets, with up to a 45" thin nylon chute and 10' of tubular nylon I can pack this into a tight burrito that keeps things together and safe from a unbaffled ejection charge, but I plan to start adding a bit of dog barf to help dampen the flame.

~John
The rocket has a 36 inch body. The recovery device volume area is similar to all the other LOC and Aerotech models (G-Force, LOC IV, etc). Upper motor mount is high up in the body. No vent holes. The nose cone will gently lower itself into place while displacing the internal air, and can be removed with no friction.

Is there info on how to do the ejection charge test with a spent motor? I would be very interested in trying that. I used an Aerotech G38-4FJ. Can this be replicated? I am in Canada and looking at Cabelas. Any chance you can tell me which black powder to use for this?

Wish I could see your method of packing. Next launch (after a body repair) on the same rocket, I will try without the baffle. If all goes well, I might remove them from all the other rockets.

Thanks for the input!
 

bill_s

Well-Known Member
Joined
Jul 29, 2012
Messages
921
Reaction score
9
Some calculators:

It sounds like you just didn't get much ejection. G38 has .75 g while most CTI 29 mm has 1.5 g of BP. Even Estes 29 mm is more like 1.5. I've been more likely to reduce BP than increase it, but that's my rockets. I knew someone to add BP even with CTI and smaller rockets, but they were fiberglass.

This was your first flight so the mesh wasn't already clogged up, right?
 

RocketTree

Well-Known Member
Joined
Apr 10, 2020
Messages
87
Reaction score
57
Location
Canada
It sounds like you just didn't get much ejection. G38 has .75 g while most CTI 29 mm has 1.5 g of BP. Even Estes 29 mm is more like 1.5. I've been more likely to reduce BP than increase it, but that's my rockets. I knew someone to add BP even with CTI and smaller rockets, but they were fiberglass.

This was your first flight so the mesh wasn't already clogged up, right?

Interesting! I never realised they had different charges. Maybe I should try a different motor, and not the G38 again for next flight (after repairs).

This was brand new mesh, stretched out as far as it would go.

Is there a chart with the aerotech ejection charge amounts? Would like to know if the G40-4 has more BP charge before I make an order for motors.

Thanks!!
 
Last edited:

3stoogesrocketry

Well-Known Member
Joined
Feb 26, 2012
Messages
1,270
Reaction score
123
He doesn't need more powder, he needs to loose the pot scrubber. If you have nomex and use it right, then you're ok....if you're not, get help and it will be OK.
He does not have dual deploy so number 2 is incorrect.... he doesn't need to stack chutes, just yank out the pot scrubber. Complicated answers just increase the possiblity of failure.
 

3stoogesrocketry

Well-Known Member
Joined
Feb 26, 2012
Messages
1,270
Reaction score
123
He doesn't need more powder, he needs to loose the pot scrubber. If you have nomex and use it right, then you're ok....if you're not, get help and it will be OK.
He does not have dual deploy so number 2 is incorrect.... he doesn't need to stack chutes, just yank out the pot scrubber. Complicated answers just increase the possiblity of failure.

I did not mention DD either. Just a small chute to destabilize the airframe .

Now assume the Pot Scrubber is not removable. What would you do ?
 

KenC

Member
Joined
Dec 21, 2017
Messages
21
Reaction score
11
It's the momentum of the nose cone that pulls the recovery package out of the body tube via the shock cord or attachment to the nose cone. Take a slow motion video of a ground test and see the effect I'm talking about.

Tight recovery packages can cause a failure to deploy but that doesn't seem to be the case here.

If you have a light nose cone and/or a short effective shoulder length on the nose cone, then the pressure inside the tube will not generate enough kinetic energy in the nose cone deployment to pull the laundry out. Light weight Estes nose cones with a slanted base like the Big Daddy or Partizon are prone to leave the laundry inside the tube on deployment.

That being said you can either increase the deployment charge to increase nose cone's kinetic energy, or lengthen the nose cone shoulder with a coupler section, to give the lower pressure a longer stroke transferring more energy from the lower pressure to the nose cone.

A small pilot chute attached directly to the nose cone would probably work. I use this method to extract and extend the deployment bag on my L3 rocket

Also in free fall the entire airframe and contents are in zero gravity, and there is no acceleration on the content of the airframe to make it fall out no matter how loose it is.
 

cbrarick

Wildman CT
Joined
Jan 23, 2009
Messages
2,479
Reaction score
238
he said he took it out and inspected it. I'd just grab a crochet needle and yank it back out. no need to cross the "he can't get it out" bridge.

If he couldn't get it out, a 1/4" x24 drill bit will allow you to get it out.
more bp isn't the answer, eventually you'll just blow up the motor tube.
 

Handeman

Well-Known Member
TRF Supporter
Joined
Jan 18, 2009
Messages
7,730
Reaction score
324
Location
Stafford, VA
The pot scrubber shouldn't affect the ejection that much. The problem is the small ejection charge. I've seen this many, many times on G-Force type rockets. 4" diameter and Hobbyline or SU F or G motors. They land hard with just nose pop recovery and when picked up, the chute fall right out of the BT.

The ejection charge does not push the laundry out. It only pressurizes the BT so the nose cone pops off. If you don't pressurize it enough, the nose cone doesn't have enough energy to pull the laundry out. The 0.75g ejection charge just isn't enough to pressurize a 4" rocket enough to force the nose cone off with enough energy to pull the laundry out too.
 

rklapp

NAR# 109557
TRF Supporter
Joined
May 8, 2020
Messages
778
Reaction score
507
Location
Oahu, Hawaii
To quote Nina Simone, “It be’s that way sometime.”

In the online multi-player game of Diablo III, we blame the “RNG”...the PC’s random number generator.

In the military, we said “spit happens” and the general response was “There it is.”

How tightly did you cram the pot scrubber into the baffle? It’s there only to absorb the heat out of the delay grain/black powder explosion, not obstruct the air flow.
Sometimes we pray to the RNG god who is not a benevolent deity and demands constant sacrifices, especially when it comes to the KTD ratio.

It is said at the beginning of each game, we should sacrifice ourselves once or suffer the disastrous divide by zero error and cause the universe to become nonexistent.
 

ShoelessJoe

Member
Joined
Jul 30, 2020
Messages
5
Reaction score
3
This may be a stupid question, but could this be a result of too short a delay? Does your sim suggest that your ejecting at apogee?

If you have not reached apogee and your rocket is still traveling at a high rate of speed, it seems like a "weak" ejection relative to the characteristics of your rocket could have some difficulty getting laundry out, whereas the same charge might work effectively at apogee.
 

TheTank

Well-Known Member
Joined
Feb 2, 2020
Messages
124
Reaction score
101
Why are you running both a nomex chute protector and a pot scrubber? I'd ditch the pot scrubber and make sure I had a good seal at the nose cone All the way to the base of the shoulder) to ensure it wasn't venting the charge before the cone came completely off.
 

cbrarick

Wildman CT
Joined
Jan 23, 2009
Messages
2,479
Reaction score
238
no, just too much stuff preventing proper pressurization of the tube.

the picture suggests that the body tube is a little less then 2 times the size of the nose cone.
It's a cardboard rocket, so most likely the nose cone is a PNC 3.90 or one of it's clones.
the total length is 16.5 with 3.75 being the shoulder, so it's visible height is 12.75.

that would make our body tube less then 24 inches.
then give him at least 6 for the motor mount and the 3.75 for the shoulder, he has to pressurize 14.25 inches (unless I'm short or long on the motor mount length)

VCT would give us 14.8 psi for the standard 1.3 gram ejection charge. I usually shoot for 8.

Too short a delay would have just zippered the rocket
 

58pan

Well-Known Member
TRF Supporter
Joined
Dec 10, 2017
Messages
136
Reaction score
62
Location
Michigan
The nose cone will gently lower itself into place while displacing the internal air, and can be removed with no friction.
Nobody caught this? It probably drag separated, IE the drag on the fins and body slow the rocket down and nose cone is so loose it just fell out. The ejection charge never built pressure because there was nothing to push against. The nose cone needs to fit tight enough that you can lift the rocket by it.
 

RocketTree

Well-Known Member
Joined
Apr 10, 2020
Messages
87
Reaction score
57
Location
Canada
This may be a stupid question, but could this be a result of too short a delay? Does your sim suggest that your ejecting at apogee?

If you have not reached apogee and your rocket is still traveling at a high rate of speed, it seems like a "weak" ejection relative to the characteristics of your rocket could have some difficulty getting laundry out, whereas the same charge might work effectively at apogee.

In this case, deployment was under 10 mph with G38-4, so no problem there. If I used a G79-4, it would have been travelling much faster during deployment and that could certainly be an alternate cause for this condition.


Why are you running both a nomex chute protector and a pot scrubber? I'd ditch the pot scrubber and make sure I had a good seal at the nose cone All the way to the base of the shoulder) to ensure it wasn't venting the charge before the cone came completely off.
Already had steel mesh scrubber installed and decided to add Nomex cloth to prevent burning brand new 48" chute. I believe the combination is too much protection. In my opinion, the nose cone fit was excellent, but that could be subjective. I removed the scrubber and will fly it again with Nomex.

Fingers crossed...
 

TheTank

Well-Known Member
Joined
Feb 2, 2020
Messages
124
Reaction score
101
In this case, deployment was under 10 mph with G38-4, so no problem there. If I used a G79-4, it would have been travelling much faster during deployment and that could certainly be an alternate cause for this condition.




Already had steel mesh scrubber installed and decided to add Nomex cloth to prevent burning brand new 48" chute. I believe the combination is too much protection. In my opinion, the nose cone fit was excellent, but that could be subjective. I removed the scrubber and will fly it again with Nomex.

Fingers crossed...
Good luck. Everyone seems to have different opinions about cone fit. I prefer mine a little tight ensuring a good seal. Pressure builds and pushes evening against the base of the cone as long as there are no pressure leaks anywhere. That said, that is just the way I prefer to set them up.
 

RocketTree

Well-Known Member
Joined
Apr 10, 2020
Messages
87
Reaction score
57
Location
Canada
no, just too much stuff preventing proper pressurization of the tube.

the picture suggests that the body tube is a little less then 2 times the size of the nose cone.
It's a cardboard rocket, so most likely the nose cone is a PNC 3.90 or one of it's clones.
the total length is 16.5 with 3.75 being the shoulder, so it's visible height is 12.75.

that would make our body tube less then 24 inches.
then give him at least 6 for the motor mount and the 3.75 for the shoulder, he has to pressurize 14.25 inches (unless I'm short or long on the motor mount length)

VCT would give us 14.8 psi for the standard 1.3 gram ejection charge. I usually shoot for 8.

Too short a delay would have just zippered the rocket

🤣 Where are you getting those numbers? The rocket is 52" tall.

Body tube is 36", nose cone 16" exposed. Inside shoulder on these cones are an additional 4".

Inside height for recovery gear is 7.5" with nose cone installed. Was moving less than 10 mph during deployment.

Can you provide a resource for Aerotech ejection charge BP weights of each motor? That would be very helpful in this case.

 
Last edited:

RocketTree

Well-Known Member
Joined
Apr 10, 2020
Messages
87
Reaction score
57
Location
Canada
Good luck. Everyone seems to have different opinions about cone fit. I prefer mine a little tight ensuring a good seal. Pressure builds and pushes evening against the base of the cone as long as there are no pressure leaks anywhere. That said, that is just the way I prefer to set them up.
Thanks, I appreciate the advice. I have removed 2" of upper body tube for the repair, so fitment is now a little different than before. I may have to go with this advice and add some light friction (tape) to seal the nose.



Nobody caught this? It probably drag separated, IE the drag on the fins and body slow the rocket down and nose cone is so loose it just fell out. The ejection charge never built pressure because there was nothing to push against. The nose cone needs to fit tight enough that you can lift the rocket by it.
It was more of a vacuum fit, definitely not tight enough to lift the rocket by the nose, but also did not fall into the body tube easily.

Does this concept hold truth in both light and heavy rockets? If so, then I will certainly consider this for future launches.

All the best.
 
Last edited:

Latest posts

Top