Staging Methods for LPR Rockets...

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bronicabill

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In my 50+ years of building and flying model rockets, I have only built one 2-stage rocket... an Estes Hercules back around 1980. It was right at 25 years later when I finally got around to flying it, and on the first 2-stage flight the booster section got stuck on the sustainer after burn-out (the spent motor dropped free) and got totally roasted by the upper stage motor. I did build a new booster section but have never flown that one again except single-stage only.

Seeing as how this rocket is around 40 years old, I suspect (hope) staging methods on LPR rockets have much improved over the years! I certainly hesitate to fly this one again with the booster in place, so I'm looking for websites that describe in detail the best modern methods for multi-staging LPR rockets.

Any help would be appreciated! Thanks in advance!
 

Rob Campbell

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The old-school method had the flyer tape the motors together using one layer of cellophane tape and friction fitting the motors in the motor mount tubes. Examples include the Farside and the Mini-Brute Midget.

The next evolution was "pop and go" staging that used couplers to create a closed path to the nozzle of the next stage. Examples include the Omega and Shrike.

My first two stage rocket was a Mini-Brute Midget. On the first flight, the booster motor was ejected and about all that was left of the first stage was the fins, held together by about 1/4 inch of unburned body tube.
 

David_Stack

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The articles on this Apogee page may be of interest: https://www.apogeerockets.com/Tech/How_2-Stage_Rockets_Work (plus there are additional links at the bottom of that page).

and there is also the dedicated "Staging, Airstarts & Clusters" sub-forum here in TRF.

I've built and flown both the Centuri/Estes "Long Tom" which is configured such that the booster and sustainer motors are taped together, and the ASP WAC Corporal / Tiny Tim configuration (air gap between the booster and sustainer motors) without issue in both instances.

As long as the fit between the booster and sustainer is 'just right', there is typically no problem. I've found that applying CA to the mating surfaces during the build, and sanding those surfaces smooth with 600 - 1000 grit paper (or finer) goes a long way to ensuring those sections separate without issue.

Not sure how much 'improvement' one could/should expect, as I think most LPR multi-stage rockets are using the same techniques established previously. In fact on the Apogee site there are links to the Centuri Technical Information Report (TIR) - 123 Multi-Staging Principles which dates back decades.
 

Joekeyo

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I flown many two stage rockets. I have had good luck with the kind that you tape the engines together with a single layer of clear cellophane tape. Often the booster has an engine block in the aft end. This makes putting the igniter in a bit more challenging, but pretty assures that the booster will depart upon the ignition of the sustainer. Make sure the coupler is neither overly tight or too loose. Perhaps in 40 years your skills to finesse this have improved.
 

BEC

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Well.... referring to this https://estesrockets.com/wp-content/uploads/Instructions/001377_HERCULES.pdf I see the Hercules uses direct staging (tape the motors together with ONE wrap of cellophane tape. It also requires friction fitting of both motors in their respective stages.
Screen Shot 2022-01-19 at 1.31.58 PM.png


From what you described, it sounds like the fit between the stages (specifically the fit of the stage coupler in the booster going into the base of the sustainer) is too tight. This is not uncommon with models that work like this. A little care with some 320 or so grit sandpaper wrapped around the coupler so that you can make that fit looser — it shouldn't be any tighter than a nose cone shoulder or even a bit looser — should let you fly it as intended. The tape holding the two motors together will keep things mated until the second stage lights without much help from the stage coupler.

I find that after two or three flights on models like this (in my case the Multi-Roc and the Apache-2 for 18mm motors and Checkmate for 13mm motors) I have to sand the coupler again since enough residue builds up from sustainer ignition both on the coupler on the top of the booster and inside the base of the sustainer that the fit gets too tight again.

I love flying two-stagers. There's nothing quite like a nice straight first stage boost and then the sustainer just leaps away at ignition.

(as an aside, these instructions show that the Hercules predates Mike Dorffler's creation of the plastic plugs for holding igniters in.)
 
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bronicabill

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I did find the referenced info on the Apogee and Estes websites after I posted my initial question. Obviously for LPR, things really haven't changed at all, and I'll just need to experiment with the fit of everything next time I fly this one. As old as it is, I may just keep it on the shelf and find something more easily replaceable for messing around with 2-stage flight... or better yet, design my own.

Cheers!
 
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I remember a certain chief model rocket designer commenting on a thread somewhere that the fit of the stage coupling should be quite loose.
I tried launching three two stage models about a month ago without the scotch tape holding the two engines together, just as an experiment. All three rockets staged perfectly, FWIW.
I've also flown rockets with engine hooks on both sustainer and booster stages with successful staging. There was a small gap between the motors.
And there is gap staging with vent holes, also perfectly viable.
IIRC the PS II booster unit has a screw on retainer and a stage cone to funnel the booster blowby gasses into the sustainer motor nozzle.
But scotch tape and friction fit remains the most widely used method for LPR, so not much has changed.
 

sjh1

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In my 50+ years of building and flying model rockets, I have only built one 2-stage rocket... an Estes Hercules back around 1980. It was right at 25 years later when I finally got around to flying it, and on the first 2-stage flight the booster section got stuck on the sustainer after burn-out (the spent motor dropped free) and got totally roasted by the upper stage motor. I did build a new booster section but have never flown that one again except single-stage only.

Seeing as how this rocket is around 40 years old, I suspect (hope) staging methods on LPR rockets have much improved over the years! I certainly hesitate to fly this one again with the booster in place, so I'm looking for websites that describe in detail the best modern methods for multi-staging LPR rockets.

Any help would be appreciated! Thanks in advance!
Not really. Other than gap staging thing are about the same.
 

GlenP

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Lots of good info here, just focusing on what you observed in your flight: The booster motor ejected but the booster itself remained attached to the sustainer. That is a pretty common mishap, and not too hard to fix.

As already mentioned, you need more friction between the booster motor in its own mount, and less friction between the booster coupler and the sustainer.

The cellophane tape wrap is used to couple the motors together so that there is less slop during boost and ignition, but it will safely melt during sustainer ignition and allow the booster and sustainer motors to separate when the sustainer starts producing thrust. It is not for friction, the single layer should not make the sustainer motor tight enough to get stuck to the booster coupler.

Give it a try again, you should be able to get it to work. I like to use a more powerful booster and then lower power in the sustainer, just so it stays on the field. I had a C booster with a C sustainer and got the booster back, but never saw the sustainer again.
 

Sooner Boomer

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There's also "CHAD" staging (CHeep And Dirty), where you just tape a booster engine onto the upper enging without any actual lower stage.
 

BABAR

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An idea, perhaps helpful.

as a static at home test, do NOT tape the motors together but go ahead and put the friction fit tape on the forward and the rear motors.

put a SINGLE wrap around the nozzle end of the sustainer motor, remember their will be a circumferential half wrap left at separation. This can unintentionally “friction fit” the booster to the sustainer motor.

put the forward motor in The sustainer.

hold the rear motor in position and slide the booster over it until it slides over the extruded tail end of the sustainer motor, including the tail end tape wrap.

set the rocket on the work table nose up.

the “coupling” should be firm enough to prevent any bending or lateral motion ,but loose enough so that if you abruptly lift the sustainer, the booster stays on the table.

if it is too tight, you can put TWO LAYERS of cello tape around the base of an EXPENDED motor casing and gently “force” it into the forward end of the booster to dilate it a bit so it will be loose enough, or you can play with thin CA and sand the internal diameter so it fits loosely over the sustainer motor with tape.

also, when you actually FLY only use one wrap of cello tape to hold the motors together, any more and the overlapping extra tape again may unfortunately friction fit the booster to the sustainer.


when I design non-gap staged boosters, I cut the booster tube length 1/8” longer than initially needed. I cut a 1/8” section of motor mount tubing (usually just the same BT-20 or BT-50 I am using for a minimum diameter Rocket.). I cut a snip out of it so it rolls up inside the booster, and I use white glue (paper to paper, slow to dry) and tuck it just inside the tail end of the booster. (I do the same thing to make engine blocks on regular rockets, for LPR it’s all you need, i haven’t had a LPR motor blow through one yet.). Anyhoo, this acts as a “backstop” to prevent the booster motor from ejection from the booster at staging. It is SHORT enough that it doesn’t cause Krushnic effect and usually doesn’t make igniter placement much harder.

Recommend use lowest viable thrust motor in sustainer for first flight, can even use adapter to step down a motor diameter, like substituting an A8-5 (or 3) for a 24 mm mount, or an A10-3T for an 18 mm mount.

for first flight boosters, use the lowest motor that thrustcurve.org or your sim of choice says will get the whole STACK off the rod or rail at a good speed. Can usually get away with subbing a B6-0 for a C, B should get you off the pad as well as the C.

If you have a lighter 24mm, especially with a smaller and lighter booster Motor, C11-0 can sub for a D. If thrustcurve puts the thrust as borderline, go with the bigger motor, as multistagers tend to weathercock and thrust is generally your friend here.


two reasons to go small on first flight.

first, Safety. Even with kits, and especially with scratchers, in an untested rocket sometime meconium happens and staging is significantly off vertical. In the unfortunate circumstance where the rocket decides to go cruise missile and depart the reservation, er… range, I’d rather have it on an A8-5 than a D12-7.


second, with the exception of staged saucers like Frick’n’Frack or Twin Factor, mulitstagers logically tend to go higher (ask @Ronz Rocketz about this:(.). You have two parts to track, and booster has no streamer or chute so much hard to track or find than regular chute or streamer rockets. And because they tend to weathercock, unless there is zero wind they tend to track into the wind, and often the degree of off vertical tracking greatly exceeds the winds ability to float it back to you. So the later the staging and the later the ejection, the further away you are gonna walk.


Wishing you two straight vertical trails and two short walks!
 
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second, with the exception of staged saucers like Frick’n’Frack or Twin Factor, mulitstagers logically tend to go higher (ask @Ronz Rocketz about this:(.). You have two parts to track, and booster has no streamer or chute so much hard to track or find than regular chute or streamer rockets. And because they tend to weathercock, unless there is zero wind they tend to track into the wind, and often the degree of off vertical tracking greatly exceeds the winds ability to float it back to you. So the later the staging and the later the ejection, the further away you are gonna walk.

I'm waiting with weighted breath for the C5-0.
 

boomtube-mk2

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1642796239609.png 1642796330622.png 1642796429629.png
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The Split Infinity is a canted motor two stage using gap staging, you can see the two ventholes on the sustainer.
You can also see the matching vent holes on the booster's coupler, the two must align.
The slot in the coupler is there to prevent the booster from twisting and to ensure it goes onto the sustainer in the proper orientation.
There are corresponding tabs within the sustainer's motor-shrouds which can be seen, barely, in the final pic.

All of this is to demonstrate that two stage rockets can be as complicated or simple as you desire.

I launched this rocket many a times and never had a flight where only one of the sustainer motors ignited.
 
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GlenP

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Or for a zero delay composite 18 mm. I am not a rocket motor scientist, so I am not sure if such is economically do-able.
Can a composite zero delay booster ignite a black powder sustainer?
 

afadeev

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Can a composite zero delay booster ignite a black powder sustainer?

Yes. The ejection charge is still BP, which will burn and ignite the 2nd stage BP sustainer motor just the same.
The other way around (1st stage BP, 2nd stage composite) would require electronically triggered ignition of the composite sustainer motor.

Or for a zero delay composite 18 mm. I am not a rocket motor scientist, so I am not sure if such is economically do-able.

Zero delay == delay timed to the length of the motor burn.
Challenge is that composite motors burn quicker and at higher pressures, so developing a quick burning but high pressure retaining delay grain is not simple. The longest 18mm burning composite I can find is AT D13 with 1.5 second burn. The shortest burning 18mm delay grain is measured to burn for 4 seconds (actual burn time +/- 1 second).
So a D13W-4T will almost do the trick, with some coasting before 2nd stage ignites.

a
 
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Paul Howard

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BronicaBill - Hi, I'm just guessing you (like me) are asking about the more commonplace "Low Power Rocketry" and Black Powder Motors such as Estes Mini-T through D size.
GAP STAGING - Everything mentioned above is relevant. But if you are wanting to start new, a good choice currently for GAP STAGING is the ESTES BOOSTED BERTHA or the SEMROC OMEGA (retro-re-do & better version of the old Estes Omega). If you look up the plans/directions for either one (erockets.biz sells both and erockets owns/makes Semroc kits and often has the plans to click on each rocket they sell on the rocket's display info). If you look closely at both kits, they're good examples of Gap Staging - Look at the Booster stage and how there is a significant gap between the booster motor and the 2nd/top stage motor, also look at the centering rings for the motor-mount-tube/body-tube interface - you should be looking for some holes in the centering rings of the booster of both models. This allows a wave of high pressure air and gasses to vent out (and not "pop" and separate the booster from the next stage) so that the hot flash and embers have a much better chance of getting fully into the nozzle and ignite the black powder propellant of the next stage. Both Booster and next-stage motors are held with either engine clips or retainer rings and avoid using friction fitting with tape. This has led to more successful boosting and ignition of the next stage. Also, it's always good to smear a thin coat of epoxy in the "blast zone" of both the booster and exposed motor-mount of the next stage for longevity of your rocket. Even coating with Yellow Alphatic Resin Wood Glue or Cyanoacrylate will be better than nothing. Hope that all helps.
 
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neil_w

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Yes. The ejection charge is still BP, which will burn and ignite the 2nd stage BP sustainer motor just the same.
The other way around (1st stage BP, 2nd stage composite) would require electronically triggered ignition of the composite sustainer model.



Zero delay == delay timed to the length of the motor burn.
Challenge is that composite motors burn quicker and at higher pressures, so developing a quick burning but high pressure retaining delay grain is not simple. The longest 18mm burning composite I can find is AT D13 with 1.5 second burn. The shortest burning 18mm delay grain is measured to burn for 4 seconds (actual burn time +/- 1 second).
So a D13W-4T will almost do the trick, with some coasting before 2nd stage ignites.

a
I haven't heard much about folks using non-zero delay motors to ignite an upper stage. An ejection charge is much more energetic than the burn-through you get from a -0 BP motor, is it really safe and effective? Here, by "safe", I mean "safe for the rocket".

Also, 4 seconds is a pretty long coast between stages of a low-powered rocket. Would need to be very to sim and confirm that the upper stage would light with sufficient velocity, otherwise good chance of cruise-missiling.
 

UhClem

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Can a composite zero delay booster ignite a black powder sustainer?
No such animal.

A black powder booster motor has no ejection charge at all. It has an end burning fuel grain and at some point the remaining propellant fails due to pressure. At that point burning bits of that propellant blow forward and they are what ignites the upper stage. An ejection charge is loose powder and thus much faster burning so upper stage ignition from it would be less likely.

A composite motor is not end burning (with some exceptions but they are all plugged) and there has to be enough delay grain remaining when the propellant is exhausted to hold the pressure. Minimum delays are not close to zero and drilling down to zero will result in failure before the propellant is exhausted. (It does not fail in the same way as BP so can't ignite an upper stage that way.) Plus of course such an alteration is in violation of NFPA 1122.
 

Paul Howard

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I agree with the last 2 posts concerning Composites and Delays : Apogee Rockets says basically the same thing on their website. Engine-to-engine staging is pretty much a "Black Powder Thing" and not something Composites are even designed to do since they ignite and burn differently. As far as time-delay motors in the booster, I "think" there even might be a NAR rule against that (at least in Low Power - which is all I do and pretty much all I know about) for safety reasons since any delay invites tilting-before-igniting the 2nd or later stages at least, and possibly reaching apogee first and heading downward before igniting the next stage at worst.
 
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Here's an idea.
Hybrid BP/APCP booster motor.
Delay grain is replaced with a thin solid delay grain with a BP grain in front of it.
Forward APCP grain ignites, delay grain burns and ignites the BP grain.
No ejection charge, forward closure has a widened opening to allow blowby gas from the BP grain to ignite the sustainer(BP) motor.
Reason for the thin delay grain is so that both BP and APCP propellant grains do not ignite at the same time. Allows time for the composite propellant to come up to pressure and mitigates problems in timing due to chuffing.
Cost? Probably prohibitive.
Market? Probably limited.
But I would definitely get one if such a thing were possible.
 

dpower

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In 1964, Centuri introduced "Dual-Lock" coupling for 2-stage models.

In 1971, Centuri renamed it "Pass-Port" staging.

I'm not sure when Estes started using venting, though they never adopted the dual-coupler design.

I've built a few clones of multi-stage Centuri kits (using Semroc parts), flown them many times, and staging has been very reliable. I prefer this method to the taping method used in many Estes designs, though I use both. Taping motors in a 3-stage design, like the mini-comanche-3 is tedious, but still works ok. Did I mention I like multi-stagers? Almost as much as clusters.

A number of altimeters are now available for electronic staging of model rockets, that will fit in 18/24mm tubes, there's even one that fits in a 13mm tube.
 
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