HPR Staging

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cyrus lloyd

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Newbie reaching out here on the subject of two stagers. I'm thinking of projects for Bama Blastoff this year and, having recently achieved my L1, though I'd try a more ambitious multistage rocket. I was thinking of using a LOC Goblin as the booster and a LOC Hi Tech H45 as the sustainer (they're what I have on hand), running a H550ST and H45W, respectively. (preliminary brainstorm design below)
upload_2018-9-25_19-15-18.png
I've got most of the design sorted, but the one question I have is coupling for staging. Does anyone know of a good thread on this, or what's the common method for staging in HPR? I'm guessing something to do with drag separation but if there's another way I'm all ears.
 
If you plan for the timer (or other firing device)to be in the booster, you don't want drag separation.
The BumperWAC in the pic uses a timer in the lower to fire the upper.
I have found Blue Thunder lights more consistently than anything else I used.
But if you have a hot enough lighter, the white should be ok.
You plan well to kick it hard off the pad so the vehicle doesn't "lay over" before the upper stage lights.
Carefully select a short delay for the 2nd stage to fire because you have to account for the time for the upper motor to come up to pressure.
 

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I've always wondered but never researched the second stage lighting. Is it generally done from the booster or sustainer? I'm sure the standard answer is both but which is more practical? Can it be as simple as an altimeter in the sustainer lighting the second stage from a drag separated electronic free booster with motor deploy?
 
I've always wondered but never researched the second stage lighting. Is it generally done from the booster or sustainer? I'm sure the standard answer is both but which is more practical? Can it be as simple as an altimeter in the sustainer lighting the second stage from a drag separated electronic free booster with motor deploy?

Electronic free boosters are not uncommon, the trick with drag separation is getting reliable drag separation, the design and implementation of the interstage coupler has much to do with how easily it occures. I have seen a number of methods work from guide rods between the two stages (three rods inserted into the rear of the sustainer into sleeves), boosted dart style tailcone devices (think Nike Ajax and Hercules interstages) which use a tailcone and socket, and simple couplers similar to LPR staging except hardened with CA and sanded to a pretty loose fit.

Other methods can use the above only with a separation charge in the ISC (interstage coupler) to increase reliability of the separation. Sometimes the separation charge electronics are in the booster some in the sustainer. Ignition is can be accomplished from either booster or sustainer, however if the motor is lit while still attached to ISC then the ISC gets a bit toasted.

Other will hopefully be along with some photos and better/more experienced techniques as my electronic staging experience is somewhat limited (but I have several projects in the works).
 
I’ve used an interstage coupler for the only two stage rocket (PML BBX with Terrier booster) I’ve done individually. Staging electronics were in it. When the sustainer lit the interstage coupler and booster was pushed off. Motor deployment for the booster and sustainer recovery.
 
Thanks for all the suggestions so far. Here's something I whipped up last night. I modeled it off of the geometry of the bottom of the hi tech so it registers on the top of the mount well, and then I was thinking of drilling four holes for those pins to register in. The bottom just fits in the goblin like any other nosecone, and the inside is hollowed out if I chose to put the electronics in there. Obviously this system would rely on drag separation. Thoughts?
upload_2018-9-26_8-39-16.png
 
Looks like it'll work. Just make sure fit and alignment is absolutely perfect. Might want to make those pins a bit longer. Carbon arrow shafts work well for that, Wal Mart usually has discontinued ones for a buck or two. K&S metals sells "nest able" tubing but the strength might not be there.
 
Obviously you've been simming flights, I see motors in there;). What kind of results are you seeing?
 
Most HPR staging is done by electronics in the sustainer. That way you can get some coast time before the second stage ignites.

Note- doing a HPR second stage with only a timer and no other "lockout" is starting to be banned at most clubs, given the danger of it. The idea is to have an altimeter that triggers the ignition with an altitude, speed, and/or g force lockout. The one I'm doing with an RRC3 has a "fire the ignition 2 seconds after the liftoff of the rocket, assuming it's altitude is at least 1000 feet". Not perfect, but you figure if the rocket is already 1000 feet up, then it's highly likely that the rocket is performing nominally.

@Wallace- if you're at the Bong launch for WOOSH this saturday, I'll be making another attempt at my 2 stager.

The previous launch- the ignitor lit on the motor, but didn't actually start the motor on the upper stage. Everything else performed ok:

 
Thanks for all the suggestions so far. Here's something I whipped up last night. I modeled it off of the geometry of the bottom of the hi tech so it registers on the top of the mount well, and then I was thinking of drilling four holes for those pins to register in. The bottom just fits in the goblin like any other nosecone, and the inside is hollowed out if I chose to put the electronics in there. Obviously this system would rely on drag separation. Thoughts?

If the Goblin is already built, this looks okay. Maybe make those rods a little longer - at least equal to the diameter of the Goblin, and make sure they are made of something strong. If the Goblin isn't built, then you want to use a tube coupler instead.

If you are going to light the sustainer from the booster, then you'll want to shear pin the booster/sustainer together to make sure they don't drag separate before the sustainer lights.

My preference for electronics (1xHPR 2-stage built so far) is to have the have the sustainer ignition controlled from electronics in the sustainer. For my HPR 2 stage, I have an Eggtimer Quantum in the av bay of the sustainer than runs a break-away wire down through a conduit in the MMT rings, to the ignitor for the sustainer. I have another Quantum in the booster that fires a separation charge as well as an apogee charge for the booster.

cheers - mark
 
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