staging

Is anyone here familiar with high power staging? If so what method of connecting the stages together? Did you have your staging electronics in the sustainer stage or in the lower stage like PMLs interstage coupler?I am helping my dad design a 4" diameter two stager but before things are set in stone I wanted to get more info on getting that upper stage lit!

Thanks in advance!

This sounds like a question for Mav - where are ya, buddy?

Roc...

Some people have used couplers, to include PML, for some models. Others use some form of drag seperation, like carbon fiber rods that protrude out of the booster and into hollow tubes of the sustainer. When the booster motor finishes burning, the drag of the booster slows before the sustainer and seperates the rocket.

I can tell you that from what I have seen on electronics, most keep the timer in the sustainer/upper stage. That way, when the unit seperates either through ejection or drag seperation, the Sustainer can light it's own motor.

Carl

Thanks Carl! but one question. Where do you get carbon fiber rods?

If you're doing something 4" or smaller, you can go to an archery shop, and pick up Carbon Fiber Arrow Shafts... this works VERY well, and has been done many times... you'll want to find aluminum or steel tubes that they'll slide into... I've used Steel Brake lines from AutoZone before...

Ron

rocwizard:
carbon fiber rods:

https://www.acp-composites.com/acp-cr.htm

https://www.cstsales.com/carbon-rods.htm

https://www.homefly.com/

https://www.intothewind.com/cgi-bin/detail.cgi?ctgy=ks&keywords=Micro-Carbon+Rods&criteria=ALL
(they also have fiberglass rods..)

https://citystar.com/hang-em-high/

carbon fiber and fiberglass rods.......

HTH

shockie B)

Hmm, I guess I should jump in here somewhere and do some of flying ****...

BTW- I haven't been real active the forum lately becasue of my studies...5 honors classes...including a double Science class to help my college aplication to PSU for Aerospace engineering... anyway...

Now, about staging, there are two definite ways to go with this. I, personally, have used PML's intersatge system because it eliminates having to change the design of my Thunder N Lightning kit. It works well in most cases and you don't have very many complexities with it. Unfortunately, because the pieces don't seperate, drag is increased and optimal flight performance is reduced. Also, in the event of a lawndarted booster (this happened to T&L a month ago) the electronics WILL vaporize!

The second route would be my perferred method in a scratch built kit. This involves an electronics bay in the fincan of the sustainer that lights the sustainer. Theoretically, with a few modifications, the interstage unit from PML could be inverted and placed into the fincan coupler with relative ease. Or, the bay could be built into the side of the fincan or something similar. In this case the way to go, in my opinion, is to put the staging electronics in the sustainer's fin can coupler, the deploy electronics in the typical bay in the sustainer and another set of deploy electronics in a bay in the booster (where the interstage would normally be) that deploys its chute, instead of motor based ejection. I say this because, with high altitude flights, the booster can reach 5000 and it would be good to have dual deplyment on the booster. Some say this is impossible, but it isn't using today's technology...the tether. Use a tether as your deployment method for the booster so that the length of the tube required for the recovery section is minimal. Also, in the event of a motor malfunction in the booster, you can still recover it intacted.

Dave

PS: If you go with electronics for staging in the sustainer, then the carbon fiber rod idea is a good one.

Resurrecting an old one.....when you say a tether setup? What exactly are you speaking of. I think I've seen something like this in a publication or two, but can't accurately recall.

Thanks,

Shane

Shane,
The tether is a device from Defy Gravity (their website appears to currently be down). Basically, with a small charge set off by your altimeter, the tether releases whatever chord it is attached to. This allows the chord to be pulled out of the rocket. This is usually used as means of keeping a single shockcord inside a rocket during descent in a dual deployment type recovery. After the apogee charge seperates the pieces of the rocket and deploys a drogue, the tether keeps the main from being pulled out. Then, at your selected altitude for main deployment, the tether pops open and releases the main.

Does this help?

David

Yeah that helps. I was aware of this one, but thought maybe you knew of another setup.

Thanks,

Shane

There is another similar product. Blacksky sells a pyrotechic device called Advanced Release and Retention Device (ARRD). I've never seen one but, have heard that it works similarly to the Tethyr.

Hey Mark,

I think this is the one pictured in the back of Extreme Rocketry, et. al. that is a very simple looking rectangle contraption - right? You're correct - it probably works fine, but I think it would be a bit heavy for a bashed 4" V2 or something and maybe even too big. Well...let's say heavier with respect to the tethye. And at somepoint even building a "brick crap house" type rocket has to deal with saving weight where possilble.

Shane

Shane,
You know, I've always wondered if it would be wise to put one of these devices in a rocket of 4" diameter or less. When that charge goes off, those pieces are going to separate fast and they are certainly going to impact the walls of the airframe. I wonder how much damage they would inflict over time? I've just kinda assumed that they would be more suited to 5.5" and up diameter airframes. I may be wrong (and I hope I am) but, until somebody tells me that they work fine in small airframes, I'd be hesitant to try them on my own rocket.

Mark,

I guess I should tell you that I push the envelop in smaller diameter stuff and SAFELY attempt what appears to be possible. Somewhat of a risk taker I suppose (i.e. my personal icon of me climbing an 85' ice fall).

But on that note, I don't see where the Public Missle setup would work. However, the defy gravity job shouldn't present a problem in my mind or at least I would be comfortable making an attempt. My delima lies in trying to do DD in a stubby beast such as a V2 or something.

I've toyed with putting stuff in the nosecone to accomplish this, but here one often encounters air disturbances that upset the altimeters here. I've used Tim VanMilligan's program very successfully to overcome a transition concern in the past and will certainly implement the same study where it pertains to putting electronics in the nosecone.

I've been engrossed in a 7 motor, 6" x 10' rocket with airstarts as of late, but will embark on the stubby issue very soon. I'll certainly post pics etc. Carl is going to assist me in getting a site set up for this purpose.

Shane

Ín the Caveman Nessus we used drag separation with good succes.

just use a normal coupler that slide into the sustainer and use a timer to to airstart the booster motor. During test flights we found out that drag separation will occur but only 4-5 seconds after burn out. Since we airstart the second engine 1 second after burn out there is no problem.

For the booster we use motor ejection (works fine with 38 mm engines), for the airstar we make use of a
TRAX timer

https://www.cavemanrocketry.com/electronics/trax-art.html

In the sustainer we use an RDAS with motor backup.

The first rocket we build this way flew only 12 times before it retired and now we have build an improved second rocket.

see picture https://www.cavemanrocketry.com/rocket kits/caveman kits/nessus.htm