Quantcast

2 stage coupler assistance

The Rocketry Forum

Help Support The Rocketry Forum:

Killachrome

Well-Known Member
Joined
Aug 1, 2013
Messages
180
Reaction score
0
Hi Everyone,

I'm building my first HPR 2 stager and was looking for some help with the interstage coupler.

The Basics:

Booster:

Diameter: 3in
Motor: L1000 (54mm)

Sustainer:
Diameter: 2 in
Motor: J600 (38mm)

I was looking to make the coupler like Jim J did in this post: http://jcrocket.com/nike-tomahawk.shtml#interstage

My plan was to have the top coupler go about 1.5 inches into the sustainer. I was also planning on using a small bp charge to separate the stages. My problem is that I am not sure if Jim's method would be the best option.If you have any ideas, please share them.

(Also attached my okr file)View attachment 2016_2stager_KC.ork
 

MaxQ

Tripoli 2747
Joined
Jan 18, 2009
Messages
4,415
Reaction score
58
Location
Central Viginia - USA
Hi Everyone,I'm building my first HPR 2 stager and was looking for some help with the interstage coupler.
I was looking to make the coupler like Jim J did in this post: http://jcrocket.com/nike-tomahawk.shtml#interstage
My plan was to have the top coupler go about 1.5 inches into the sustainer. I was also planning on using a small bp charge to separate the stages. My problem is that I am not sure if Jim's method would be the best option.If you have any ideas, please share them.
Think that is John Coker's design with the transition/interstage in your web link...and he does great work.
Don't see why it wouldn't work.

Any reason you prefer not to rely on drag separation vs. the more complicated BP charge?
 

Killachrome

Well-Known Member
Joined
Aug 1, 2013
Messages
180
Reaction score
0
Hi Everyone,

I'm building my first HPR 2 stager and was looking for some help with the interstage coupler.

The Basics:

Booster:

Diameter: 3in
Motor: L1000 (54mm)

Sustainer:
Diameter: 2 in
Motor: J600 (38mm)

I was looking to make the coupler like Jim J did in this post: http://jcrocket.com/nike-tomahawk.shtml#interstage

My plan was to have the top coupler go about 1.5 inches into the sustainer. I was also planning on using a small bp charge to separate the stages. My problem is that I am not sure if Jim's method would be the best option.If you have any ideas, please share them.

(Also attached my okr file)View attachment 297960
Got the wrong person and it is John Coker's design. I was researching a lot and it seemed lots of people on the forum tend to go with BP seperation since it appears to be more reliable. Could I just use a tight friction it and be done with it? Sorry for the simple questions, I just want to make everything work and in a safe manner. Thanks!
 

GRIFFIN

Well-Known Member
Joined
Aug 25, 2009
Messages
3,207
Reaction score
88
I have about a dozen successful 2 stage flights using a charge for separation. With a Raven altimeter, you can program one of the outputs for that task. There is nothing "complicated" about this at all. It works, it looks great and it prevents the possibility of a failed drag separation and possibly cooking your booster with the ignition of the sustainer.
 

Titan II

Well-Known Member
Joined
Aug 24, 2013
Messages
912
Reaction score
116
This is a 3" to 3", but the principles apply. I use a RRC3 in the sustainer for the seperation charge. The wires for ignition and seperation charge are run down via a conduit. There is a RRC2 in the coupler for the booster recovery charge.

69.jpg


68.jpg


70.jpg


21.jpg
 

Eat, sleep, and Fly

Well-Known Member
Joined
Jan 5, 2012
Messages
735
Reaction score
2
I'm not a fan of drag separation, but i believe that there is also a downside to the black powder. I've flown a lot of 2 stage rockets, with about a 50% success rate. My last two stage flight experienced a number of new failure modes, all due to the black powder separation charge. First, torquing from the launch caused the coupler to get jammed into the sustainer. When the black powder separation charge fired, instead of separating the coupler from the sustainer, it blew the electronics bay out of the bottom of the ISC, and the coupler and transition stayed with the sustainer. This, along with causing the booster to lawn dart, caused a rapid deceleration of the sustainer, and something (I dont know what, I would assume that it was something related) caused the altimeter to sense incredibly low pressure, so it fired all if it's charges, and luckily did not light the sustainer (No, i didn't have it wired wrong). This destroyed the majority of the rocket. Had I relied on drag seperation, or the "fire in the hole" method, the rocket probably would have survived. Here is the video of this happening.
https://youtu.be/P4QbyOHm4PE?t=13m15s
 
Last edited:

Eat, sleep, and Fly

Well-Known Member
Joined
Jan 5, 2012
Messages
735
Reaction score
2
I'm not a fan of drag separation, but i believe that there is also a downside to the black powder. I've flown a lot of 2 stage rockets, with about a 50% success` rate. My last two stage flight experienced a number of new failure modes, all due to the black powder separation charge. First, torquing from the launch caused the coupler to get jammed into the sustainer. When the black powder separation charge fired, instead of separating the coupler from the sustainer, it blew the electronics bay out of the bottom of the ISC, and the coupler and transition stayed with the sustainer. This, along with causing the booster to lawn dart, caused a rapid deceleration of the sustainer, and something (I dont know what, I would assume that it was something related) caused the altimeter to sense incredibly low pressure, so it fired all if it's charges, and luckily did not light the sustainer (No, i didn't have it wired wrong). This destroyed the majority of the rocket. Had I relied on drag seperation, or the "fire in the hole" method, the rocket probably would have survived. Here is the video of this happening.
https://youtu.be/P4QbyOHm4PE?t=13m15s
I should add that this was entirely preventable and was only a result of a less than great design. The av bay was held into the inter stage coupler with nothing more than a bulkhead of 1/2 inch plywood secured with epoxy fillets. I had assumed that this would be adequate, but evidently not (this was the rockets third flight, it worked flawlessly on the first two). In addition to this I used about 15% more BP than when I ground tested it. With adequate testing and a very well built ISC, Black powder separation can be a very good method. I just wanted to point out that there are things to be weary about.
 

Killachrome

Well-Known Member
Joined
Aug 1, 2013
Messages
180
Reaction score
0
One more quick question before I head out to Balls this weekend. Do you put rail buttons on the sustainer as well as the booster stage or can I get away with only the booster stage? I have read conflicting information.

Booster Diameter and Length:
Diameter: 3in
Length:36in.
Motor: L1000 (54mm)

Sustainer Diameter and Length:
Diameter: 2 in
Length:57in
Motor: J600 (38mm)

Thanks again for everyones help!
 

OverTheTop

Well-Known Member
TRF Supporter
Joined
Jul 10, 2007
Messages
4,362
Reaction score
1,583
Location
Melbourne Australia
I am building a 1/2 Scale Nike Apache. My current plan is to have the 75mm motor hang a little out the back, and have a non-locking taper on the back of the sustainer. The motor hanging out the back will provide sufficient leverage to resist the bending moments in the stack. It sits in another annulus which has minimal clearance to keep everything straight.
MotorPosition.JPG

Build thread here: http://www.ausrocketry.com/forum/viewtopic.php?f=6&t=5019&start=48

As it stands there is almost no movement at the top of the stack.

I have yet to do the flight ISC for the stack, and when I do it will have some positive retention for the sustainer. I don't particularly like relying on drag separation only either.

The ISC I have done is only for display purposes. The final one will be significantly stronger, with an aluminium central core (rather than PVC pipe) and a different skeleton.
 

Titan II

Well-Known Member
Joined
Aug 24, 2013
Messages
912
Reaction score
116
I have done both without any issues. Though adding a single button to the second stage booster my not be necessary, it also cannot hurt. I use shear pins at the stage 1 to interstage coupler, and at the interstage coupler to stage 2 booster. This assures everything is aligned and cannot rotate.

Have fun at Balls and I wish you success.
 

Killachrome

Well-Known Member
Joined
Aug 1, 2013
Messages
180
Reaction score
0
Thanks for everyone's replies and I hope to get some great images and videos to share :)
 
Top