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Author Topic: How to make pods separate in flight??  (Read 4215 times)

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emlang

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How to make pods separate in flight??
« on: July 08, 2016, 10:36:16 PM »

Hello everyone,


I have a question for all of you High-power builders.
I am starting to really design a 1:37 scale model of the Delta IV Heavy with Orion on top. My question is about pod separation in flight for a high power.
I will be using a I357 in each booster and one K185 in the core stage. When the boosters burn out they will separate and parachute back while the core burns for another 6.6 seconds. The engines used may change with the development but the concept is the same.
I have talked to the guys at eRockets and they suggested using a flight computer to trigger 2 charges which separate the boosters. I do like this idea but I am worried that it adds room for failure if one charge doesn't work.
I was thinking doing the same as some low power versions. They use air drag to separate the boosters. (i.e. boosters have a high peak and average thrust compared to the core booster and when they burn out the drag force causes them to slip down a rod and fall away.)
Which do you think is a better way? Maybe I should do both for redundancy?


The next issue is lighting the cluster. I can not have either booster get up to pressure before the other or have the core at pressure before the boosters. The guys at eRockets suggested to use an air start a fraction of a second after ignition of the boosters.


Thanks in advance for the help. Need more info, feel free to ask.


Best,


Evan Lang
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joe

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Re: How to make pods separate in flight??
« Reply #1 on: July 09, 2016, 08:05:13 AM »

Evan,

I read your post late last night and decided to sleep on it before responding.  My reply is only my opinion as I have never tried the strap on boosters mainly due to the same questions you have raised and I was never that committed to a particular rocket design that I pursued the answers.

I do know that in the mid 1990's there was a lot of discussion on this subject and it hinged on safety and keeping the boosters solidly attached rather than how to release them.  There seemed to be a few that, depending on how they were attached, would leave the rocket under thrust.  If I remember correctly TRA even banned the use of releasable side boosters for a while.  I do not believe that to be the case now.

As far as lighting the cluster I would talk to Bill Good. Not sure if you have met him but he and Gary have a motor starter that will light dirt on demand and Bill has lots of high power cluster experience.  A word of caution if you are going to try to light some motors in a cluster with a timer.  Make sure that, in your case, the side boosters are capable of getting the rocket safely off the pad by themselves and this goes also for the main motor.  With separate events happening on lift off if one of the ignition sequences fails the flight could be a failure, or worse, dangerous.

I do not have any advice on releasing the boosters without knowing how the would be attached in the first place but your initial goal is to assure that there is no possible way that they can come detached passively.  I would table the drag separation concept.  This sounds like an exciting project and I know it can be done as I have seen similar projects.  Some successful and some not so much but I think you can handle it.

I hope you get more responses on here.

Joe
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emlang

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Re: How to make pods separate in flight??
« Reply #2 on: July 09, 2016, 10:11:04 PM »

Thanks a bunch Joe for your reply!


I guess it will be a good engineering project to figure out a reliable method. I will probably look into what ULA does and scale it down. I am not opposed to making pyrotechnic mounts and blowing them off. Plus, I think that way one can design it with redundancy and make sure there is a symmetrical separation. I am planing on building it and doing several test flights with only the core motor to test the functionality.
If any combination of motors light it will lift off the pad. I will definitely talk to Bill and Gary about the ignitor as I get closer to launch. Although, In my balloon rocket endeavor, which was a partial failure due to computer malfunction, I was able to make one hell of an ignitor which lights every time in a near space vacuum.


This rocket will sure be a behemoth coming in at just over 7 feet tall and 17 inches from booster to booster with each core made out of 5.5 inch blu-tube. (Have not ordered the parts yet so it may change depending on the final design)


Evan
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emlang

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Re: How to make pods separate in flight??
« Reply #3 on: July 17, 2016, 06:27:09 PM »

Any other opinions on this topic out there?
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bob

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Re: How to make pods separate in flight??
« Reply #4 on: July 20, 2016, 08:25:48 PM »

1) Blue Tube is a nice choice for the airframe. Very durable and strong. That's what my 4" Ursa Major is made of.
2) I like the flight computer or timer option. Double up on the ematches (wired in parallel) to reduce the risk of one side not firing.
3) Lighting the main on a slight delay sounds interesting. Personally, until I had all the details worked out, I recommend using Cessaroni motors for clusters for now. They have a black powder puck at the top to make sure that the thing lights when you want it to. (DISCLAIMER: I've never done a composite cluster myself, but have contemplated it a bit.) Steve may have more info on Cessaroni motors if you can catch him.

Bob
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emlang

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Re: How to make pods separate in flight??
« Reply #5 on: August 03, 2016, 08:12:56 PM »

Thanks for the response and tips Bob. I will definitely look into 2 e-matches and maybe even 2 computers for redundancy. I have given it a lot of thought and think I will actually design a mounting bracket that will go on the foward and aft of the boosters and design in a weak section which would be loaded with 4F powder. I would make the brackets so that they can handle 3x the load seen in simulated flights so I know there won't be an early failure. But it has to rupture cleanly everytime the charge goes off.
I will let you know what happens when I get that far. Might even find a way to delay one charge by a fraction of a second so they hinge away like the real thing... we will see.
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greylond

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Re: How to make pods separate in flight??
« Reply #6 on: August 23, 2016, 11:08:28 PM »

That sounds like a great project!  I definitely want to see that one fly. I have no personal experience with parallel staging , but I am involved with a two stage tandem project with similar aspects. A couple of separation possibilities:

Pyrotechnic Fasteners, aka explosive bolts. There's an article in apogee newsletter #266.

Mechanical separation is another possibility. Eggtimer supports RC servos for instance.

In any case, you can program release by timer and tied to flight events for fail safe, such as after launch detection, but not before a set altitude or speed is reached. If the rocket doesn't reach the preset velocity or altitude within the time allowed, the boosters won't detach. That keeps it safe if something doesn't light, or worse, lights late.

I hope I was helpful, and best of luck with your project!

Doug

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Doug Peterson Tripoli 15622 hpr cert. Lvl. 2

emlang

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Re: How to make pods separate in flight??
« Reply #7 on: September 01, 2016, 10:56:04 PM »

Thanks for the input Doug!


I will definitely take a video of the launch and post it on here. I hope for it to be done in about 3 or 4 months.
I just got done with the scaling of the Delta IV heavy. My rocket will be six and a half feet tall and 18 inches across (Booster to booster) using 5.7 inch OD tube.


Anyway, I have experience with pyrotechnic fasteners. I have a design that I 3D print and used for a high altitude balloon terminator device. Only issue is redundancy and I must make sure that if one booster separates the other MUST go too. I think I am working on a few designs now but will probably use a fuse or some string to hold the boosters on then a charge will cut the string and both will be pushed away with a small spring.
I found some great parallel staging videos on Youtube and the guy was nice enough to reply with how he did it.


I plan on having 2 different flight computers for redundancy powered by 2 Li-Po batteries. I will definitely use your idea about timing. I am also building the rocket so in the event of a booster malfunction it will handle the results of failed separation.


Lucky for me, the place I launch at here in Albuquerque, NM is so open that I got approval from the club to build this monster and fly it in any configuration. We will use a pad 1000 feet out for safety. It will also require its own ground support for launch to hold the large size on the pad.


Will keep everyone updated with progress.
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