Looking for Dual Deploy Advise

[leegscott]

All

Well a rainy day here and doing a little rocket building and working on new designs.

We are building a 2 1/2" diameter rocket with a 38mm motor for my son. He is wanting to get a little more altitude with this rocket. He has been building his own rockets, motors and prepping them himself for about two years now. However, he is not ready for a dual depoly yet. We are considering using one of those motor top devices by either aerotech or giant leap for deployment of the main. It looks like the rocket will go to about 6,000ft (depending on which motor he uses). Do you guys think we can let it free fall to about 1500ft (without breaking the rocket apart via dual deploy) and then deploy the main without a zipper?? The airframe will be fiberglassed.

Thanks

 

[sylvie369]

No.

If it falls from 6000 ft to 1500 ft without opening up something to increase drag, it'll be going pretty quickly when you do open it up. You might be able to build something bulletproof enough to survive, but frankly, that's no way to fly a rocket. If I were RSOing, I'd tell you "no go".

Just my opinion - I'll be surprised if someone doesn't pipe in with a contrary one. It'll be interesting to read.

 

[leegscott]

Yep pretty much what I thought too.

Just don't want him to get in the dual deploy yet. It is nice now, he can build and fly rockets with a little oversite from me now. There is more room for error with the dual deploy and he will have to depend on me more!!

Thanks for the sanity check!!

 

[WillMarchant]

A lot people recommend shooting to descend from apogee at about 40 to 50 feet per second. Once the mains open you should shoot for about 20 fps or so.

You definitely want to do something at apogee! At least split the rocket in two for a drogue-less recovery.

 

[bobkrech]

All

Well a rainy day here and doing a little rocket building and working on new designs.

We are building a 2 1/2" diameter rocket with a 38mm motor for my son. He is wanting to get a little more altitude with this rocket. He has been building his own rockets, motors and prepping them himself for about two years now. However, he is not ready for a dual deploy yet. We are considering using one of those motor top devices by either aerotech or giant leap for deployment of the main. It looks like the rocket will go to about 6,000ft (depending on which motor he uses). Do you guys think we can let it free fall to about 1500ft (without breaking the rocket apart via dual deploy) and then deploy the main without a zipper?? The airframe will be fiberglassed.

Thanks

A rocket coming in ballistic descending from 6,000' to 1,500' would be moving at 350 MPH when you want to deploy your main parachute. Your chute will immediately strip and your rocket would impact the ground at high velocity. It's an unsafe design and shouldn't be launched.

Bob

 

[Handeman]

Just wondering, why isn't your son ready for dual deployment? If he's building, flying, and assembling 38mm (G-J) motors and rockets, he should be able to handle dual deployment.

I get the impression that Dad oversees the work and maybe Dad isn't ready for dual deployment yet.

Give it a shot, it's not that difficult. Personally, I would rather fly DD then motor ejection. You get much better and consistent deployment.

Just my :2:, even if it isn't worth that much.

 

[leegscott]

Nope, Dad is good with building and flying dual deploy been doing it for years but I must admit I am still learning and I do not know if I will ever learn it all. We have posted quite a few builds on the forum.

No, this is more a case of my son wants to do it himself as well as I want him to do it himself as well. He is able to build motors with an ejection charge just fine. I am just not ready for him to take the next step to dual deploy. There are a lot of safety concerns when working with dual deploy and electric matches not only during the prep but making sure it has been done right to insure a successfull deployment.

Thanks

 

[n5wd]

No, this is more a case of my son wants to do it himself as well as I want him to do it himself as well. He is able to build motors with an ejection charge just fine. I am just not ready for him to take the next step to dual deploy. There are a lot of safety concerns when working with dual deploy and electric matches not only during the prep but making sure it has been done right to insure a successfull deployment.

Lemme tell you a little story about some high school kids... only two of the seven had ever flown model rockets, before... the Estes kits you find on shelves in Hobby Lobby. With a bit (maybe just a bit more more than a bit) of tutoring, they designed, built and flew a 2.5" 40-some odd inch tall rocket with dual deployment a couple of times two weeks ago as part of their NASA-Student Launch Initiative team requirements. While our team mentor (a NAR L2) and I (also a NAR L2) built/designed the ejection charges and selected the mains deployment altitudes, they did everything else, including putting the rocket together at the range both times, wiring up the pre-built ejection charges to the electronics, buttoning everything up and mounting it on the rail. You can see the pictures and videos here: https://www.texanengineering.org/halfscale.html

We got 509 feet and 300' mains on a Roadrunner G-80, and 998 feet with 500' mains on a Cesaroni V-185... and the neatest thing about the flights was that we could see all of the events!

So, while Dad probably would want to double-check things a bit for the first couple of times, my suggestion would be to let the offspring get a little bit of experience with relatively low altitude (1000' or so) dual-deployments so he can see what's supposed to be happening... then, when he's got some experience under the belt, go for the mile + flights, being assured that everything should go as planned.

Wayne

PS: If you merely hand him the ejection charges pre-built, wires shunted together, there shouldn't be much more safety concern than him handling a reloadable motor. Walk him through the process of deciding how much black powder or Pyrodex to use, how it's going to be contained, how it's going to be mounted, etc. We stressed safety quite a bit with our guys/girl, and they seemed to get it.