Recovery overkill and non-deploy

[RocketTree]

What he said ^^^. I would be adding a small chute to the NC to help pull the laundry out and stop it pointing front down, till the main is out anyway.

I would like to try that! Is a 9" nylon chute enough?

 

[3stoogesrocketry]

[QUOTE="RocketTree. Was moving less than 10 mph during deployment.


I'd love to see those numbers

 

[OverTheTop]

I would like to try that! Is a 9" nylon chute enough?

I have a rocket of similar diameter but a bit heavier and I use a 12" X-form chute typically. Yours is a little lighter so a 9" may work. You need enough drag to keep the top up and then pull out the main. Probably better off slightly larger or you just end up with the same situation. It is your call as you are the flyer!

 

[RocketTree]

[QUOTE="RocketTree. Was moving less than 10 mph during deployment.


I'd love to see those numbers

Do you prefer openrocket or rocksim file? Onboard video as an added bonus I was just going by the sim numbers. Was almost dead-on 4 seconds suggested delay. Maybe its not good to be stalled out during deployment!?

 

[cbrarick]

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.

https://www.aerotech-rocketry.com/u...c485_AeroTech Master Motor Matrix 8-12-20.pdf

my best guess off the picture you supplied. With your numbers, VCT calculates 30.3 psi. Even more crazy.

powder? https://www.rocketmotorparts.com/Ejection_Charge_12-Pack/p1577809_16501630.aspx if you must. That's what was in the LMS kit.

And, no, you don't need a pilot chute for a tiny chute like that. Just get the damn thing out. I don't pilot CERT 3 XXL, 129 SQUARE FOOT CHUTE. much bigger, and most L3 flights don't have pilot chutes. Stop by my trailer and look at my rockets next cato.
In your case, it would just be making up for too much stuff in the motor tube. Solve the root problem(s) and you won't have to come up with a more complex answer.

 

[RocketTree]

Are you dumping and weighing the Aerotech motor BP charges, or is there an actual resource for this information?

 

[GalantVR41062]

If the BP comes in a plastic mini/micro 2 ml centrifugal medical vial like this:


I have been setting up my ejection charge for ground testing, motor eject or dual deploy measuring by volume. 1ml is about 1 gram of bp.

I thought about getting a scale, I can prep the rocket for flight using the same method as ground testing and should see similar results.

I have talked with friends that shoot muzzle loaders and load there own ammunition. BP is a linear pressure rise as I add more BP. I can add a little more BP and get a little more pressure.

I can post some pictures of how I prep my daughter's largest park flier, a 4" MC Torrent payload single deploy. I also have a electronic pressure sensor with the capability to log pressure and have been planning to get some more accurate data on deployment charges for some of my rockets.

I flew Her rocket last week on a 38mm Aerotech I 161w 12sec delay and about 1-1.1ml BP, the flight sketch mini recorded 27g peak on deployment that was .8sec early. The event looked good on the ground and the JLCR did its job holding the chute until 300'.



Good luck on the next flight with the baffle out of the equation, do you have a open rocket file for this project?

Also please put in a vent hole, this might not a issue with the low and slow G motor flight but a RSO at a high power launch will/should ask if the airframe is vented.

~John

 

[KilroySmith]

A lot of people with a lot more knowledge than me have responded, but for some reason I feel a need to throw my $0.02 in. Frankly, from your descriptions, I would be expecting good ejections, and it's a bit of a puzzler as to why you're not getting one.

The mesh you're using does several things of interest:
1. It filters out the hot particles that BP generates when burning. This is a good thing, and protects your chute.
2. As the hot gasses pass through, the mesh cools the gasses. As a result, the pressure at the nose cone will be less than if there were no mesh.
3. As the gasses cool and work their way through the mesh, the pressure spike from the burning BP will spread out, and have a smaller peak value. Maybe the slow pressure rise pushes off the nosecone before full pressure is available, making for a weak nosecone ejection and lots of ejection gasses working their way past the chute bundle.

So, if you're gonna use the mesh, you're probably gonna have to increase the ejection charge size over what would work without a mesh. A cheap, tiny scale like this:
https://www.amazon.com/Accuweight-Jewelry-Digital-Kitchen-Calibration/dp/B07D3PWMSYis useful in this kind of experimentation. You'll also need a supply of BP. Lot of tips on here about acquiring some - I'd recommend asking someone at a launch if you can borrow a cup, or at least a couple of tablespoons worth. Seal the hole at the bottom of the ejection cup of your used motor (put it a drop of Silicone or somesuch), pour in a measured amount of BP, put an igniter on top, and use the red cap (hopefully you recovered it) or a piece of tape with some wadding to hold the igniter/BP in place, and you can experiment in your back yard. I prefer enough BP to fully stretch out the recovery harness, but not much more - but there's lots of opinions on that subject on here also, ranging from "Just enough to get the job done" to "Blow it out or blow it up".

Based on the answers you and others have given here, I'd first ask if the Nosecone is separating from the rocket before the ejection charge fires? Your onboard video may be able to answer that question. If it is, that needs to be fixed - lots of possibilites ranging from a strip of tape to a ring of CA inside the body tube.
If it isn't, then your problem is confusing. cbrarick's 30psi calculation, and your indication that ejection occurred at slow speed, would indicate plenty of pressure to fling the nosecone out to the end of the recovery harness. Test in your backyard, or at the next club launch (you'll get lots of help) to see what happens. You could also rip out the mesh as others have indicated, and run a few tests to see how it affects the ejection.

 

[Mightyrocketman]

Did the motor use a plastic cap above the ejection charge? If so the plug and steel mesh don’t work together. The plug will plug the steel screen enough that not all ejection gasses will get by. Sometimes just enough to push off nosecone but not enough to push out parachute also.

 

[Dane Ronnow]

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.

I found this thread while searching for info on baffles and blankets. I'm building a 2.6 inch rocket that has a coupler 14" above the MMT. The plan was to use the coupler as a baffle, but I'd prefer not to if I could figure out how to keep the parachute from sliding down under acceleration if it's not sitting on a baffle. The parachute would be wrapped in a 9x9 Nomex blanket.

 

[GalantVR41062]

A laundry shelf could be glued into place on top of the coupler. A centering ring with a 29mm or 38mm hole should do.

 

[Dane Ronnow]

That's what I was thinking, but using the top plate that came with the baffle, and drilling a few extra holes to open it up a little more. Thanks. I appreciate the tip.

 

[DaHabes]

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

I would tend to agree. I have never had an ejection charge not get the laundry out on a 4" bird, BUT, depending on how long your airframe is it could be marginal and wouldn't take much to have the result you did. I have a LOC Minie Magg (5.5") with a 38mm MMT and the standard ejection charges on AT DMS motors is too small, I have to augment to be on the safe side. I highly recommend calculating the BP charge needed for 15 PSI on a 4" or larger airframe if you're using manufacturer provided ejection charges (DMS or reloads).

FWIW, when my 4" Patriot lawn darted last year, I rebuilt it with an airflow redirected baffle system. No wadding, no nomex, no dog barf, no stainless steel scrubbers. I'll likely never build a 3" bird or larger without a baffle again unless it's too short or I'm weight limited on the design. I started using dog barf but it's so damn messy I got tired of it real quick (anybody need a bale?). A lot of it tends to stay in the airframe, then it falls out everywhere, in the car, in the house. Bleh. Baffles are the bomb.