Staging rockets?

Discussions on high/extreme altitude and mach busting rockets.

Moderator: Moderators

ejection charge
Rocket Flyer
Rocket Flyer
Posts: 98
Joined: Sat May 23, 2009 1:54 pm
Location: Brisbane
Contact:

Staging rockets?

Postby ejection charge » Thu Jun 09, 2011 11:12 am

After recently attending a TRA Western Australia launch, and witnessing a few multi stage flights; has got me thinking.
How hard is it to stage successfully?
What are the best electronics to use?
Timer? Or accelerometer based altimeters?
What is the best igniter to use?
Is there any issues igniting a stage after mach 1?
Is it easier to stage small motors (24mm/29mm) or larger ones ( 75mm/98mm)?
I’m sure these questions have been asked before, so if anyone knows these answers or could point me to a good website that would be nice 
Thanks
Regards Alex
Motors usage since introduction to rocketry – 11,763.6 Ns (57% N)

Andrew Burns
Rocket Crew
Rocket Crew
Posts: 283
Joined: Fri Apr 25, 2008 1:14 pm
Contact:

Re: Staging rockets?

Postby Andrew Burns » Thu Jun 09, 2011 12:40 pm

In my limited experience staging isn't so hard as much as it is complicated and it requires you to be very anal about everything.

Basically any rocket with two stages has at least twice the complexity of a single stage, so there'll be lots of arming of timers and altimeters, lots of packing recovery harnesses and the ignitor prep between the two stages. Safety is also critical as you now have a rocket that's capable of igniting itself so you need to make sure that your electronics are up to scratch and you have interlocks to stop the second stage lighting before it should (like an external shunt across the ignitor).

As for keeping the ignitor inside the motor during burn it depends how many G the rocket will be pulling but something like taping the ignitor to a stick and poking that up inside the sustainer motor will help keep it in place. I've used a first-fire to ignite a second stage which worked, you obviously want a reliable ignitor (not a copperhead) and preferably one with lower current draw so that your electronics can handle it. I made my own timer for my 2-stage flight, it had an accelerometer on board that was sampled at around 250Hz (I think) and it required 100 consecutive readings above 3g before it would detect launch, this ensured that it was physically impossible for you to accidently start the timer somehow, my rocket was however pulling about 16g off the pad so it worked but if your rocket doesn't accelerate so hard it would be a good idea to drop the threshold acceleration or it might not trigger at all.

ejection charge
Rocket Flyer
Rocket Flyer
Posts: 98
Joined: Sat May 23, 2009 1:54 pm
Location: Brisbane
Contact:

Re: Staging rockets?

Postby ejection charge » Thu Jun 09, 2011 1:17 pm

Andrew Burns wrote: Safety is also critical as you now have a rocket that's capable of igniting itself so you need to make sure that your electronics are up to scratch and you have interlocks to stop the second stage lighting before it should (like an external shunt across the ignitor)..

Obviously I would work my way down the rocket, arming the altimeters before arming the timer and connecting the igniter to the first stage, and this would all be done on the pad vertically.

Andrew Burns wrote:As for keeping the ignitor inside the motor during burn it depends how many G the rocket will be pulling but something like taping the ignitor to a stick and poking that up inside the sustainer motor will help keep it in place. I've used a first-fire to ignite a second stage which worked, you obviously want a reliable ignitor (not a copperhead) and preferably one with lower current draw so that your electronics can handle it. I made my own timer for my 2-stage flight, it had an accelerometer on board that was sampled at around 250Hz (I think) and it required 100 consecutive readings above 3g before it would detect launch, this ensured that it was physically impossible for you to accidently start the timer somehow, my rocket was however pulling about 16g off the pad so it worked but if your rocket doesn't accelerate so hard it would be a good idea to drop the threshold acceleration or it might not trigger at all.


I assisted cryoscum with his 2 stage mach madness at Williams, and the ignite taped to a wooden dowel was precisely what he did and it seemed to work fine, my only concern is that on smaller motors (24mm or 29mm) having a wood dowel might cause the motor to CATO, as the nozzle diameter is quiet small, does anyone know if there is any glue that could be used to physically glue a igniter to the top grain?
Would that effect the motor performance at all?

Andrew Burns wrote:I made my own timer for my 2-stage flight, it had an accelerometer on board that was sampled at around 250Hz (I think) and it required 100 consecutive readings above 3g before it would detect launch, this ensured that it was physically impossible for you to accidently start the timer somehow, my rocket was however pulling about 16g off the pad so it worked but if your rocket doesn't accelerate so hard it would be a good idea to drop the threshold acceleration or it might not trigger at all.



So is that what a G switch is? A spencer that has to read X amount of gees before it will start recording?
Would something like this be a good first timer? http://www.perfectflite.com/cgi/PF_Stor ... =382873486
Motors usage since introduction to rocketry – 11,763.6 Ns (57% N)

Andrew Burns
Rocket Crew
Rocket Crew
Posts: 283
Joined: Fri Apr 25, 2008 1:14 pm
Contact:

Re: Staging rockets?

Postby Andrew Burns » Thu Jun 09, 2011 3:34 pm

I tried to superglue an ignitor to the top grain of a 29mm motor, it didn't work. I ended up hoping that the stiffness of the ignitor wire (cat5 solid core twisted pairs) was enough to keep the ignitor up there during acceleration and it worked fine, for small motors it's probably not such an issue.

That timer looks like it would work fine, mine used an accelerometer instead of a g-switch to give me more flexability but a g-switch based timer would also be fine assuming they put some sort of de-bounce routine in there (if you give a g-switch a sharp tap it could trigger for a fraction of a second and without some smarts the timer could arm at the wrong time).

User avatar
kopius
Elle3
Elle3
Posts: 2846
Joined: Mon Apr 23, 2007 4:30 pm
Location: Gold Coast, Queensland
Contact:

Re: Staging rockets?

Postby kopius » Thu Jun 09, 2011 8:28 pm

Have a look at the Clustard project for basics: viewtopic.php?f=32&t=1974&hilit=clustard

The just had the igniters installed as normal and due to the small core, there was no issue holding them up there. With something larger either a stick, or head end (possible modifications required which may considered Ex).

I would be careful with pure timers as it is critical to have them set correctly. I have seen a timer not set correctly and a very long walk was required.

accelerometer with motor burnout is good, however also depends on when you would like the motors started.

With the igniters, I was a little concerned about the amount of juice required for the 3 x FF Jr's, so initiating an original version of the clustermatic worked a treat as seen in the test on my clustard video.

Perhaps you can help me with Clustard v3 and v4 Alex? They are going to be something special, just need mega airspace for v4 (oh and to save for the next 10years... hehe)
QRS Secretary

AMRS #3 L3 ACO
Life member of QRS

NAR L2 #98260

MDRA Member #0241


Return to “Higher, Faster, Further”

Who is online

Users browsing this forum: No registered users and 1 guest