My first 2 stage

[snrkl]

Team: I am thinking about making my first two stage (I have ordered a JLCR and can't think of a better use for it yet!)

Question: How do people attach the booster stage typically?

My plan was to use a coupling tube glued at the top of the booster that essentially buts up against the FWD CR of the booster and friction fits the rear CR of the sustainer but I'm not sure if this will be enough... thoughts appreciated...

Modelled in OR (two screen shots, one with a pink dotted temp spacer tube to better show how the two parts would connect:



And the ORK file:
View attachment BT60_AirStart.ork

 

[BDB]

This looks good to me. Usually 1"-1.5" of exposed coupler is sufficient to join the stages.

For typical bp to bp staging, you should use cellophane tape to hold the two engines together, so plan to have your engines touching.

 

[snrkl]

This looks good to me. Usually 1"-1.5" of exposed coupler is sufficient to join the stages.

For typical bp to bp staging, you should use cellophane tape to hold the two engines together, so plan to have your engines touching.

I have a small engine block in the design forward of the booster motor in the plan - I'm guessing the tape wrap replaces this.

I'm also guessing the ejection charge / motor ignition is sufficient to kill the tape?

What do others use for booster motor retention? Tape wrap to the MMT tube at the aft end?

 

[Nytrunner]

For BP staging, you actually need some contact time for the sustainer to light.

A single thin wrap of tape will go when the sustainer gets going. For longer gap staging, you should drill a couple holes in the booster tubes so the gas will vent instead of pushing the stages apart prior to lighting.

You could put the booster motor block Behind it. That way its thrusting against the sustainer motor, and gets kicked back on to the block at ejection.

 

[BDB]

You could put the booster motor block Behind it. That way its thrusting against the sustainer motor, and gets kicked back on to the block at ejection.

I had never thought of this until my son built an Estes HyperBat. It's a pretty cool 2-stager with a rear motor block. Until this rocket, I never had motor blocks in the booster, just friction fit. For that matter, it isn't a big deal if the booster losses the motor casing after lighting the sustainer, that way it's lighter for tumble recovery.

 

[MALBAR 70]

A tape wrap at the bottom of the booster can be done. Most of the two stage rockets I fly either have a thrust ring at the bottom of the booster or the motor is friction fit with a wrap of masking tape. The sustainer is usually friction fit as well.
Alternatively, you can do a gap stage. A gap staged model typically has a space between the booster motor and the sustainer motor (the motors aren't taped together). For this type of staging a couple of pressure relief holes are drilled at the top of the booster tube to allow some of the gases to escape as the sustainer is ignited without blowing the booster off prematurely.

Your plan for using the coupler to hold the stages together is the right idea. Just make sure that the fit is just snug enough to keep the booster on during flight but loose enough to allow it to fall away at separation.

 

[lcorinth]

My first ever scratch build was a two-stager, and I taped the motors together and then friction fitted both motors into their respective mounts with tape wraps. Now, though, I prefer gap staging, which requires no tape.

You can have an engine block and hook in the booster, including the gap between motors that this entails, if you vent the booster.

You just need two to four small holes for ventilation. You can drill them directly into the side of the booster body tube, close to the front end (near the gap, in other words), or, if you have a large enough body tube and therefore enough room on the centering rings, you can drill or punch holes in both centering rings, so that any pressure can vent out the back.

This is necessary due to the "Barber delay," a 0.001 second delay between booster burn through and upper stage ignition.

The vent holes should be evenly spaced around the tube. If drilling them directly into the tube itself, I usually line them up directly with the fin lines. You want them evenly spaced so that you don't get any accidental sideways thrust in one direction or another, knocking the rocket off to one side.

As for the coupler, and inch or inch and a half should do it. It should be just tight enough so the booster doesn't fall off while on the pad, but loose enough that it's quite easily removable. When I build them now, I coat the exposed bit of coupler - the part that will go into the upper stage - in medium CA glue. Once that's cured, you can sand it very smooth. I like to have it about as tight as a nose cone, but no tighter. In other words, I can pick up the rocket and the booster will stay put, but if I wiggle the rocket back and forth, it will slowly start to wiggle loose.

Here, you see a small scratch build with vent holes drilled in the sides (before fin attachment):



And here are some pics from my Estes Photon Probe I built as a two-stager. In this case, I vented the centering rings, so I do not need holes in the side of the rocket. Note that I didn't have to be as careful with the spacing of the vent holes, because all ventilation will be out the aft end of the rocket.







And here is my first two-stage - and scratch build. I was so thrilled when it worked!

[video=youtube;Qu8BZL-zLsI]https://www.youtube.com/watch?v=Qu8BZL-zLsI[/video]

Now I build optional boosters for most of my kits.

 

[snrkl]

For BP staging, you actually need some contact time for the sustainer to light.

You could put the booster motor block Behind it. That way its thrusting against the sustainer motor, and gets kicked back on to the block at ejection.

I like this idea...

I have modified the fin design some what and I was trying to figure out what the motor load process would be for the tape wrapped staging:

I really dislike the idea of kicking out a spent motor and dropping it in a dry grass field here in Australia

The only sequence I could figure out to ensure retention of all motors was to:

1) load the sustainer motor and tape wrap the end to the MMT
2) add the booster motor and tape it to the Sustainer motor
3) Then slide the booster on and tape the booster motor to the back of the booster MMT

I do like the idea of a rear engine block.. this is actually pretty neat..

I will look at gap staging and venting options. For this model, I will investigate CR vents but the tube vents will be useful on designs where there is less space between the MMT and CR (this is planned to be a BT60 with a 24mm MMT, so there should be room for vent holes to be drilled...

Question for @lcorinth: were you worried about the vent holes weakening the CR?

 

[CORZERO]

...You can have an engine block and hook in the booster, including the gap between motors that this entails, if you vent the booster.

You just need two to four small holes for ventilation. You can drill them directly into the side of the booster body tube, close to the front end (near the gap, in other words), or, if you have a large enough body tube and therefore enough room on the centering rings, you can drill or punch holes in both centering rings, so that any pressure can vent out the back.

This is necessary due to the "Barber delay," a 0.001 second delay between booster burn through and upper stage ignition.

I still don't understand why venting is necessary? What are you venting? What are you preventing by venting?

 

[JStarStar]

I still don't understand why venting is necessary? What are you venting? What are you preventing by venting?

It actually takes a couple milliseconds for the upper stage motor to ignite (the "Barber delay" referenced above).

The venting is necessary to keep the stages together for the 0.001 seconds (or thereabouts) it takes for the upper stage motor to light.

When the booster stage motor burns through, the hot combustion gases from the booster surge forward toward the upper stage motor.

Without vent holes to allow pressure to escape, this combustion gas may pop off the upper stage and separate the stages before the upper stage lights. If that happens your upper stage is SOL.

With the vent holes, the high pressure gas escapes out the side, while burning combustion gas will still surge forward and enter the upper stage nozzle. Once upper stage ignition occurs the stages separate and you are set.

 

[OverTheTop]

I still don't understand why venting is necessary? What are you venting? What are you preventing by venting?

In BP staging it is little chunks of burning BP that need to fly forward to ignite the next motor. Providing vents allows some gas to move forward during burnout, carrying the burning fragments for the ignition forward. The gas tends to go around the corner and out the vents, but the chunks have more inertia so continue more straight forward. Adding vents increases the probabilities of igniting the following stage.

 

[MALBAR 70]

There is always open air gap staging too, like the ASP WAC Corporal with Tiny Tim Booster. Although ASP provides a small tube with vent holes that can be slid into the space between the sustainer and booster (approx.2-3cm.) it really isn't needed.
To preserve the scale look, I've flown mine several times without the tube and have never had a problem with upper stage ignition.

Open air gap staging is where the booster and sustainer are separated by a few centimeters (usually thin dowels) and the gasses are allowed to vent into the open air via the separation between the stages. I was skeptical at first, but does work and looks really cool too.

https://www.asp-rocketry.com/ecomme...m-Version-.cfm?item_id=632&parent=8&navPanel=

 

[neil_w]

I'm really going to need to try a gap-staged model one of these days. Sounds like fun, and really opens up design possibilities for the booster.

 

[Gary Byrum]

Back in the day, taping motors together was a standard procedure until "pop-n-go" staging was introduced. I never liked taping motors together because there were always separation issues. Usually a bit of unnecessary pressure would build up and cause the sustainer to veer. When I started "pop n go" (no tape required) my staging issues disappeared. I never looked back at taping motors together again. Unless you were going to CHAD stage. I have a dozen 2 stage rockets and all of them are friction fitted using a staging coupler.

So ask yourself this question. If it's perfectly fine to gap stage without the ability to tape your motors together, why bother using it at all? The only thing to look for is making sure your coupler is fitting correctly. Snug but not tight. Easy to pull stages apart but not so loose as to fall off. Taping is totally unnecessary.

 

[BDB]

@ Gary. What is pop-n-go staging? I love multi-stage rockets and this is the first time I've heard that term.

 

[shreadvector]

"little chunks" are not really involved (contrary to years of reading the nice drawings in the Estes tech reports).

[video=youtube;1Nhe5Y78PRQ]https://www.youtube.com/watch?v=1Nhe5Y78PRQ[/video]

https://www2.estesrockets.com/pdf/2845_Classic_Collection_TR-TN.pdf
See page 3 (which is page 5 of the PDF)

In BP staging it is little chunks of burning BP that need to fly forward to ignite the next motor. Providing vents allows some gas to move forward during burnout, carrying the burning fragments for the ignition forward. The gas tends to go around the corner and out the vents, but the chunks have more inertia so continue more straight forward. Adding vents increases the probabilities of igniting the following stage.

 

[Gary Byrum]

@ Gary. What is pop-n-go staging? I love multi-stage rockets and this is the first time I've heard that term.

It's an old school method that was an alternative to taping in that, it was quicker and more convenient. The only difference is the lack of tape. This method was considered adequate when using motors with wider nozzles. The old report can be seen HERE. Scroll to page 12. This is old news like the introduction to pop-n-go is, but motors have changed a lot since then. Different nozzle shapes and ejection charges and such. They even stated it wasn't ideal for mini motors, but truth be known, I've never seen a motor it didn't work on. It's basically a friction fit stage that allows motors to butt up to each other. Gas can and will vent between the motors and by the time enough pressure develops in there for separation, the upper stage motor is lit. My biggest problem with using tape was tape not burning away completely and tugging at separation. This always caused a sharp veer. This year I built my first mini engine 2 stage rocket and the circle is complete. I have staged every LPR designation there is. Except for the 29mm F motor. I have done the E's and they work just fine also. I will point out that, there's probably nothing wrong with taping your motors together. It just didn't work well for me.

 

[samb]

To continue this slight digression...
It occurs to me that the current Booster-55 and Booster-60 mated to one of their E2X models is the modern version of pop-and-go staging. I also note that the stock configuration of one of those is not vented. Naturally, Centuri had their own patented Pass-Port system with vented couplers.

snrkl, I think the sequence you have outlined in post #8 sounds right. I share your concern about spitting hot motor cases. Nice design !

 

[BABAR]

"little chunks" are not really involved (contrary to years of reading the nice drawings in the Estes tech reports).

[video=youtube;1Nhe5Y78PRQ]https://www.youtube.com/watch?v=1Nhe5Y78PRQ[/video]

https://www2.estesrockets.com/pdf/2845_Classic_Collection_TR-TN.pdf
See page 3 (which is page 5 of the PDF)

I KNEW you would be clarifying this issue!

 

[snrkl]

Ok, so a design update...





Decisions; I have decided to go for:
1) Direct contact staging with a cellotape tape wrap. Reason being: I want the booster to be as short as possible (aesthetics), so this makes this decision for me.
2) Tape wrap for booster motor retention over an AFT engine block - again, it comes to booster length for aesthetics. This means I can overhang the motor and make the booster shorter.
3) Transitions: I decided to use a 24mm BT all the way through to the payload section and add fore and aft transitions. Planning on using CRs fore and aft as the method of attaching the 24mm into the BT60 fin can and payload. Again, I just decided the rocket looks much cooler this way...

Things left to think about:
Transitions: to fabricate from paper and soak with thin CA or to use cut off nose cones (I am not fussed if the transitions are longer on the mid section of the airframe...)
Flame Pattern: given this is my first 2 stage, and my first fabricated transitions, is frisket film too ambitious?

ORK file: View attachment BT60_AirStart_transition.ork

 

[Gary Byrum]

Transitions! A man after my own heart...:grin: FWIW, you could stand to loose that 1st stage launch lug. 2 is a gracious plenty.

 

[Cabernut]

I love that color scheme! Very cool design as well.

 

[neil_w]

Transitions: to fabricate from paper and soak with thin CA or to use cut off nose cones (I am not fussed if the transitions are longer on the mid section of the airframe...)

Do them with paper. You can practice as much as you want with very little cost. After you make a few you'll think they're easy. I use 65 lb card stock. Make several of each and pick the best ones to use.

On my last build I recessed the centering ring from the large end of each transition, and put a short piece of smallified BT in to create a small ledge for the transition to glue to. That worked well, although there are lots of other methods as well.

There are occasions where cut nose cones make more sense, but this is probably not one of them. It is worth developing the skill of doing paper transitions.

 

[Gary Byrum]

Do them with paper. You can practice as much as you want with very little cost. After you make a few you'll think they're easy. I use 65 lb card stock. Make several of each and pick the best ones to use.

On my last build I recessed the centering ring from the large end of each transition, and put a short piece of smallified BT in to create a small ledge for the transition to glue to. That worked well, although there are lots of other methods as well.

There are occasions where cut nose cones make more sense, but this is probably not one of them. It is worth developing the skill of doing paper transitions.

+1 for Cap'n Ring Bling. 65# paper is a better percentage of what I use also. But for those lengthy jobs and especially for printing fin templates I go with 110#. You can use either because there's not a great lot of difference. Also, when you want to CA those, you can opt for a Q-tip to spread your CA on or make your own with scrap balsa and some "pill bottle" cotton. I like my swabs a little bigger than Q-tips so I make my own.

 

[Mugs914]

Wow, great design! I really like the look of that.

Agree completely about paper transitions, BTW. Paper transitions are fun to make, easier than most people think and a good skill to have in your pocket!

op:

Mike

 

[snrkl]

OK: for the metric folks out there, apparently 65lb card stock is 172GSM for the rest of us...

I also had a thought whilst falling asleep - I will need to make sure I remember to put the transitions on the 24mm tube BEFORE I put the CRs on each end...
(** 😀👈🏻 up here for thinking!! **)

 

[snrkl]

Do them with paper. You can practice as much as you want with very little cost. After you make a few you'll think they're easy. I use 65 lb card stock. Make several of each and pick the best ones to use.

I think the real reason for using paper is that BT60 nose cones are HARD TO COME BY and it would be a waste to use them for transitions!!

On my last build I recessed the centering ring from the large end of each transition, and put a short piece of smallified BT in to create a small ledge for the transition to glue to. That worked well, although there are lots of other methods as well.

I can't really picture what you are saying here: I will go back though your build thread and see if I can find some pics...

 

[snrkl]

Thinking about grain direction on the fins.

Because of the square end on booster fins, I can't just cut the whole fin out of a single piece of balsa. (The hashed part of the pic is the bit I'm worried about - the fwd corner is BOUND to get knocked off)

I'm thinking of two options:

Option 1: I make the whole fin less the hashed section in the pic out of a single piece using the sustainer fin LE for the grain direction, then adding a tip cap with the grain parallel to the rocket on the end. This means cutting and gluing pieces which is prone to cutting inaccuracies.

Option 2: I use a horizontal grain for the booster fin as pictured

Thoughts?

 

[snrkl]

Brainfart...

Option 3: use a single piece with the grain following the sustainer fin LE and just paper the fins.

#sigh: I think it's time to go do something else for a while.

Incidentally, @Neil_W I didn't find a pic but I finally figured out what you meant with the smallified BT rim.

I'm thinking of making the coupling and transitions all using tube couplers a little like what TVM suggests in the design and construction book:



Just means I sand the CRs to fit the coupler vs to fit the BT...

 

[neil_w]

I can't really picture what you are saying here: I will go back though your build thread and see if I can find some pics...

Pictures always work better:


For the gray piece I just take a shortie piece of BT, cut out a small strip, and then just compress it into place. Doesn't matter if it fits perfectly or if there's a gap.


For your fin, *I* would cut a single piece, grain parallel to leading edge, and paper it.