Build Thread - Wildman Jr. Two-Stage

[Antares JS]

This will be my first two-stage HPR. I just finished washing the parts. I will be spending the next bit fixing the RockSim file I downloaded from the Wildman website - the file does not actually divide the rocket into two stages.

Tentative goal is to fly at LDRS on Saturday, June 8th.

 

[Antares JS]

https://www.rocketryforum.com/threa...r-kit-to-a-2-stage-build-vindicator-jr.55463/

I am placing this old build thread here for myself as a reference. I especially liked the idea of using a little metal tube as a conduit to wire the upper stage igniter.

 

[Antares JS]

For those who may want it, this RockSim file is exactly like the one available for download from Wildman, except it is actually divided into two stages.

 

[Lotronex]

Nice, I'm still waiting on the one I ordered during the Black Friday sale. Looking forward to see how this goes together.

 

[Antares JS]

Due to the very limited space to work with in a 2" rocket with a 38mm motor mount, I've decided that only the upper stage ignition will be controlled from the sustainer. The separation will be controlled from the booster. This means that I will need to wire a charge up from the interstage avionics bay into the interstage cavity itself, and I will need access to the top of the interstage avionics bay to wire a charge. The stock interstage coupler is not going to work for me.

To make this easier, I'm going to buy an extra length of airframe tube and build up the interstage as shown here. The extra length of airframe will have the interstage coupler epoxied into it, and will attach to the top of the interstage electronics bay with screws for flight.

I'm pretty sure this is standard practice for most people, but I'm planning for a blue thunder or super thunder motor in the booster, and a slower-burning black motor in the sustainer for visibility and ease of ignition.

 

[NTP2]

what are these?

 

[Antares JS]

what are these?
View attachment 632623View attachment 632626

If you're referring to the circles, they are "mass objects." They represent things like the harnesses, recovery attachment hardware, and electronics bay contents.

 

[NTP2]

If you're referring to the circles, they are "mass objects." They represent things like the harnesses, recovery attachment hardware, and electronics bay contents.

Ok, I have never used rocksim so that's why I am asking such obvious questions.

 

[David Schwantz]

why are you adding extra tube? Why can you not access the interstage coupler?

 

[Antares JS]

Ok, I have never used rocksim so that's why I am asking such obvious questions.

I figured it was something like that. I've been using RockSim since 2007, before OpenRocket existed, so I've stuck with it.

why are you adding extra tube? Why can you not access the interstage coupler?

The stock method of building the interstage coupler has you epoxy a 38mm electronics bay centered inside and sticking out the back of the interstage coupler, and it only opens in the back and there is no access to the front end. This would prevent me from being able to wire a stage separation charge in the front of the interstage electronics bay. I might have been able to work with just reaching my hand inside if it was a bigger rocket, but it's a 2" rocket so no way to get my hand in there to wire a charge.

My solution is to build a 54mm electronics bay with an interstage coupler that attaches to the front of it with screws for easy removal and access to the front end of the bay.

 

[David Schwantz]

Damn, don't think my hand would even go into a 54mm bay.

 

[jgarbus]

I'm on the same build and am currently working on the ISC. I too will be scratch building that section to allow for better electronics support. The sustainer is ready for a test flight in 2 weeks.

 

[NTP2]

I figured it was something like that. I've been using RockSim since 2007, before OpenRocket existed, so I've stuck with it.

That also explains spending 120$ on something that you can get for free.

 

[Antares JS]

I'm on the same build and am currently working on the ISC. I too will be scratch building that section to allow for better electronics support. The sustainer is ready for a test flight in 2 weeks.

Nice to know I'm not the only one who decided the stock interstage wasn't going to work for them.

 

[markg]

The stock method of building the interstage coupler has you epoxy a 38mm electronics bay centered inside and sticking out the back of the interstage coupler, and it only opens in the back and there is no access to the front end. This would prevent me from being able to wire a stage separation charge in the front of the interstage electronics bay. I might have been able to work with just reaching my hand inside if it was a bigger rocket, but it's a 2" rocket so no way to get my hand in there to wire a charge.

I have the stock setup on my 2.6" Competitor 2 stage. On the forward end of the ISC I have a small hole drilled. I feed the (long) separation charge wire through the hold, then connect to the electronics before I slide it in the bay and seal it up. I use modeling clay to seal the wire for the separation charge on the bulkhead, from the top. The ISC coupler is short enough that I can squeeze my fingers in there to push down the clay. On that rocket I'm using a Quantum for separation and single deploy on the booster.

cheers - mark

 

[cerving]

I've ended up buying extra bits of coupler and tubing with almost every two-stager I've ever built. You need enough room in the ISC for an altimeter, and the nozzle end of the motor plus some wiring.

 

[Jmhepworth]

https://www.rocketryforum.com/threa...r-kit-to-a-2-stage-build-vindicator-jr.55463/

I am placing this old build thread here for myself as a reference. I especially liked the idea of using a little metal tube as a conduit to wire the upper stage igniter.

I use brake line as the conduit for the lighter to light the sustainer. Make sure you put it on the inside of the centering rings so that you have adequate clearance for the interstage coupler. The centering rings are not large, so if you put the conduit in the middle of them, the interstage coupler won’t fit. It’s not a bad idea to put the conduit right up against the centering rings. And there is no reason to extend the conduit any further than the forward-most centering ring. The conduit is tight to begin with, so pushing the wire through the conduit can be challenging. So don’t make it any longer than necessary. Once you get the wire though the forward end of the conduit, you can fish it out with some long forceps.

 

[Titan II]

I frequently use K&S aluminum tubing for the wire channel. It is lighter, and has a larger ID than brake line with the same OD. I use the tubing with .014 wall thickness.

 

[Banzai88]

I frequently use K&S aluminum tubing for the wire channel. It is lighter, and has a larger ID than brake line with the same OD. I use the tubing with .014 wall thickness.

Oooooooooo........trade secrets! That calls for a hobby shop trip!

 

[Kane]

I am also building my first two stage, although it's a 65mm airframe and scratch built.
https://www.rocketryforum.com/threads/design-and-build-thread-aro-b-two-stage.182419/

I am routing both sustainer air-start and sep charge from the sustainer avionics bay. I am curious how one times these two events when they are controlled by separate altimeters as you are proposing.

 

[Jmhepworth]

I am also building my first two stage, although it's a 65mm airframe and scratch built.
https://www.rocketryforum.com/threads/design-and-build-thread-aro-b-two-stage.182419/

I am routing both sustainer air-start and sep charge from the sustainer avionics bay. I am curious how one times these two events when they are controlled by separate altimeters as you are proposing.

It really doesn’t matter much which side you fire the separation charge. Whether you do it from below or above, you typically want to dump the booster soon after motor cutoff. Lighting the sustainer motor is a fun art. When I did my first one, I wanted it to light right after separation so it was close enough to the ground so I could see it. So with a Wildman Junior, I used an I to an H, separating about a half second after motor cutoff and lighting the sustainer a second later.

I have never fired the separation charge from the sustainer, but if I did, I would use an altimeter with four channels, like the Raven or the Proton, to fire separation, light the sustainer, deploy the drogue, and deploy the main. And then use a simple altimeter like the Quantum or RRC2+ as backup on the chutes.

 

[Jmhepworth]

I thought I’d give you the benefit of some things I learned with my first two-stage rocket (coincidentally, also a Wildman Junior).

1. Make and use a checklist. There is way too much going on to think you’ll remember it all.

2. I launched mine as a single stage with the sustainer-lighting e-match connected to the altimeter. I wanted to make sure it would fire. Although you can’t see it fire, when you recover it, you can see whether it did or not. For me, it was part of working up to launching it as a two stage.

3. Getting the sustainer to light is a challenge. After I started putting a Pyrodex pellet in the top of the sustainer motor, I’ve had 100% success as long as the altimeter told it to fire (thanks, CJ). The .50 cal. fits nice and snug in the grain of most 38mm Aerotech motors. Or use Cessaroni, which already has a black powder pellet.

4. The interstage coupler has no weight, so it’s not going to pull the chute out of the booster. Ground testing demonstrated that I couldn’t get the chute to come out unless I ran the ejection charge to sit on top of the motor. Then it worked fine. I’ve also become a fan of thin mil chutes so the chute isn’t too tight. If the chute doesn’t come out, it will come in hot.

All of this is unsolicited, so feel free to ignore it. One of the reasons I was successful is that I had some really good mentors guiding me. Dave Spencer taught me how to use a Raven, and the day I first launched it as a two stage, Kip Digaurdis was the RSO. He’s helped me more than he’ll ever know. I’ll add more when I remember it.

 

[Kane]

It really doesn’t matter much which side you fire the separation charge. Whether you do it from below or above, you typically want to dump the booster soon after motor cutoff. Lighting the sustainer motor is a fun art. When I did my first one, I wanted it to light right after separation so it was close enough to the ground so I could see it. So with a Wildman Junior, I used an I to an H, separating about a half second after motor cutoff and lighting the sustainer a second later.

I have never fired the separation charge from the sustainer, but if I did, I would use an altimeter with four channels, like the Raven or the Proton, to fire separation, light the sustainer, deploy the drogue, and deploy the main. And then use a simple altimeter like the Quantum or RRC2+ as backup on the chutes.

That's exactly what I am doing. I'm using a Proton to initiate all events from the sustainer.
I guess my question was directed at timing between two devices that may be measuring slightly differently. If the separation and air start are purely timer initiated and start their respective clocks at some established event (such as some pre-established safe altitude), different calibrations of the devices would result in the two timers not being in sync.
Granted this is probably negligible in most cases.
Until it's not and a separation charge fires way too early leaving a coasting sustainer.
I guess that's where altitude/accel lockout comes in handy to prevent an off-nominal air start.
Regardless, two separate devices controlling two events that are so sensitive to timing just seems like an error-prone strategy to me.

 

[Jmhepworth]

That's exactly what I am doing. I'm using a Proton to initiate all events from the sustainer.
I guess my question was directed at timing between two devices that may be measuring slightly differently. If the separation and air start are purely timer initiated and start their respective clocks at some established event (such as some pre-established safe altitude), different calibrations of the devices would result in the two timers not being in sync.
Granted this is probably negligible in most cases.
Until it's not and a separation charge fires way too early leaving a coasting sustainer.
I guess that's where altitude/accel lockout comes in handy to prevent an off-nominal air start.
Regardless, two separate devices controlling two events that are so sensitive to timing just seems like an error-prone strategy to me.

I’m not sure I understand. If you use the Proton for all four events, how is that two separate devices?

 

[Kane]

I’m not sure I understand. If you use the Proton for all four events, how is that two separate devices?

It's not. I was referring to the OP's setup and that type of two-device setup in general.

 

[cerving]

I’m not sure I understand. If you use the Proton for all four events, how is that two separate devices?

Second one for recovery redundancy I hope...

BTW, if you haven't thought of this already, you need something to hold the sustainer igniter in place. You can't just stick it in there, or even use a plastic cap to hold it in... it won't stay. What I do is to tape the igniter to a stick to hold it in place, then use masking tape to tape the stick to the nozzle of the sustainer motor so it can't slide out during launch or staging. Poke a small hole in it too. Obviously this needs to be done at the pad. I recommend using a pull-pin switch on the sustainer igniter for added safety, pull it out then you can arm your Proton.

 

[Jmhepworth]

It's not. I was referring to the OP's setup and that type of two-device setup in general.

I have always used two separate devices to manage separation and sustainer ignition. Not a problem.

And I second Cris’ suggestion to use a thin dowel to keep the ematch at the top of the motor.

 

[Antares JS]

All the advice and comments are very much appreciated.

My plan is to use these for the upper stage igniter conduit after finding out the width of the ematches is 2.5 mm

https://www.amazon.com/CynKen-10pcs-Stainless-Capillary-Length/dp/B071YDJ8FQ/

I plan to use a Quickburst e-match dipped in ProCast to ignite the upper stage. I was going to get 7-foot MJG's, but they are out of stock. At least two of the matches I bought will be used for tests: one to connect to my Raven3 to make sure it can set off these ematches (I haven't used the quickburst ones before), and one to test-ignite the upper stage by augmenting the match with procast as intended for flight and using it to launch the sustainer at an MDRA launch.

I plan to use an Altus Metrum EasyTimer to ignite the separation charge, and motor eject to deploy the booster parachute. I will be using my Raven3 to ignite the upper stage and dual-deploy the sustainer.

I was thinking to just set the ejection delay on the booster motor as short as possible, as RockSim doesn't give me the ability to investigate the ideal delay for the booster, but if anyone has advice in support of this idea or to the contrary, I'd be happy to hear it.

 

[Jmhepworth]

My plan is to use these for the upper stage igniter conduit after finding out the width of the ematches is 2.5 mm

You don’t need to put the ematch head through the conduit. You push the wire through from the aft end.

 

[Antares JS]

You don’t need to put the ematch head through the conduit. You push the wire through from the aft end.

Yes, that's what I was planning to do. The wire is 2.5mm across, not the head.