5 or more stages

I am a complete beginner in rocketry and this is my first post. One month ago I didn't know that Estes rockets came with igniters, so bought separate igniters, and didn't know that body tubes could be bought, so bought multiple motor retainers instead. I have just two launches, a kit rocket (Atomic Sky using C6-7) and a home-built 4-stage Estes C6 rocket.

In addition to the launches I've done tests on flammability and strength of glues and tapes, I did a 3-stage Estes C6 test in my garage by firing the rocket upside down with the body tube held by a retort stand and clamps, and I've been solving in a spreadsheet the differential equations for minimum fuel to given altitude.

I'm here on the forum looking for two things, the first is what someone else has tried (in the way of a diary or lab book) and how the trials went in the way of altitude etc. Traps for beginners to avoid. How to reliably attach fins. How to improve build quality. What works and what doesn't?

The second reason I'm on the forum is that I want to work up through a series of tests to massively multistaged (eventually to at least 12 stages and possibly as many as 30 stages). So far I've been attaching stages together with a single turn of sticky tape, and every stage has fired correctly in turn. I already have a solution to the flight stability problem - my home-built launch used a single set of fins to stabilize the first 3 stages of the 4-stage rocket (the fins fell off prematurely then) by attaching the fins to rods that were glued to the last stage. So I need advice from someone who has already successfully launched rockets with 5 or more stages. My 4-stage rocket only reached about 400 ft when calculations suggested that it should have made 1200 ft before the fins fell off. Have you ever launched a rocket with 5 or more stages?

I haven't, but it's on my to-do list. This guy has, it's rather impressive - nice design.
[video=youtube_share;rfnDEryI3Dk]https://youtu.be/rfnDEryI3Dk[/video]

Sorry to shoot you down but go to a library and pick up a copy of the Handbook of Model Rocketry and it will explain why you can not do what you are considering. I guess it really doesn't matter but I have to ask; why do you want to do this? School? Curiosity?

What you want to do can't be done using 18mm unguided model rocket motors, it's simply not possible to successfully go past 3 or 4 stages with any hope of staying vertical. There are too many variables for anything without active guidance to continuously stage and stay vertical. Cross winds, changes in the cp/cg relationship during staging of so many motors, many other reasons. I haven't done the math but I'm pretty sure a single C engine won't lift a stack of 30 with fins, etc. and even if it begins to push it all up the rod it would probably stage twice before clearing it. Since it would certainly be below even passive guidance speed off the rod, it would angle right away and crash close to the pad, as it continued to stage on the ground. Not a good thing.

I believe the book lists a maximum of 6 successful stages with number 7 staging on the way down and that was done by a very experienced flyer.

A radio controlled boost glider might get 5 stages, I've seen George Gassaway do 4 on one of his but again, it's RC and he is probably the best, most experienced glider flyer alive.

Verna
www.vernarockets.com

Keeping your CG in front of your CP is going to be a challenge as the initial weight will be high back end. Also, maintaining perfectly straight flight, and if you are sucessful with the staging finding the thing will be the hardest part.

As for attaching fins; for low/mid power with wood/paper - Titebond II is your friend, and fillets with Titebond molding and trim (You can use Titebond II also, but it shrinks so don't make the filets too big or you will have gaps). There are other glue combinations that work great, but with this one I can say from experience that the tube/fins will tear/break before the glue bond.

Eeverything I've said assumes you are planning to use bp motors, if you are planning on composites everything gets harder by orders of magnitude.

29mm Estes F15-0 or E16-0 in lower stage.

24mm Estes D12-0 in next stage. (E12-0 might work, but will be pretty heavy, and mass is your enemy if attempting stupidly large numbers of stages).

18mm Estes C6-0 or B6-0 in next stage.

13mm Estes A10-0T in next stage.

13mm Estes A10-3T in upper stage with a recovery system.

All booster stages need large fins. I would suggest looking at the fins on an old Estes Farside for an example. The center of gravity must remain as far forward as possible, and that will be extremely difficult with the heavy motors in the back end, but the big motors need to be in back to lift the absurd amount of mass that a 5 stage rocket will have. The Farside also had fins all at a tiny angle to induce roll to help keep the rocket from weathercocking severely, but you will need a 1/4" diameter by 6 foot long steel launch rod and launch only in NO WIND.

https://www.spacemodeling.org/jimz/estes/k-12.pdf

Rack rockets. I've gone as high as 5 stages. More than this, you will have to cluster (or use larger) motors in the lower stages as the rocket gets too heavy for 1 motor to lift straight.

Build of a 3 stage 29 mm rack rocket: https://www.rocketryforum.com/showthread.php?59577-Rack-Rocket-Build

3 stage 29 mm F15
[YOUTUBE]c1pqYgG-TOg[/YOUTUBE]

4 stage 24 mm E12
[YOUTUBE]4MpzXUhxCxY[/YOUTUBE]

5 stage 38 mm G160
[YOUTUBE]sIEKCBRKyZ4[/YOUTUBE]

Thanks for the quick response. My 4-stage design is extremely unimpressive, but keep in mind that it is my first home-made build.

The fins are attached to pieces of wire cut from wire coathangers and the pieces of wire are attached to the 4th stage.


> This guy has, it's rather impressive - nice design.
I like it. It's particularly useful to me to see the angle that he's used for fin attachment.

> go to a library and pick up a copy of the Handbook of Model Rocketry
It's not in either of the two libraries I normally go to. Looks like I may be buying it. Do you have more info on what is inside, eg. chapter headings?

> I have to ask; why do you want to do this?
I'm recently retired. I've had a long-standing interest in space telescopes, and met someone who invited me along to the Tripoli (Australia) rocket launch last month. That got me thinking about the mathematics of minimum fuel usage to space. I figured out that fuel usage is a minimum if and only if the downward force due to gravity is exactly the same as the downward force due to air drag, I call that the "optimum velocity" phase of flight. (This doesn't apply to first stage of course, where the rocket needs to accelerate to optimum velocity as fast as as possible). To test that out I'm starting to build models.

> I haven't done the math but I'm pretty sure a single C engine won't lift a stack of 30 with fins, etc.
Absolutely. The first stage has to be a cluster or a much more powerful booster. I've calculated that 12 stages ought to be possible if the first stage is a 3 C6 cluster (i.e. each of the C6 in the initial cluster lifts the equivalent of 4 stages). 30 stages requires something like a first stage strap-on booster consisting of ten Estes E12 rockets, or equivalent single H or I motor. I really don't want to go up to 30 stages.

> Even if it begins to push it all up the rod it would probably stage twice before clearing it.
LOL. There's some truth in that. With a 3 C6 cluster as first stage it stages at a calculated 150 feet.

> Keeping your CG in front of your CP is going to be a challenge as the initial weight will be high back end.
I don't understand this because the staging extends the effective length of the motor towards the top of the rocket. With multi-staging the CG moves forward towards the half-height of the rocket which should help stability rather than hinder it.

> Also, maintaining perfectly straight flight
Yes. The home-made launch spiralled very noticeably.

> and if you are successful with the staging finding the thing will be the hardest part.
Yes. Lost my first launch, despite spending an hour and a half systematically searching the forest downwind of the launch site.

> As for attaching fins; for low/mid power with wood/paper - Titebond II is your friend, and fillets with Titebond molding and trim
Thanks. Will look for this, I'd never heard of it. It seems to be only available from a single specialty distributor (Carbatec) in my city.

> Everything I've said assumes you are planning to use bp motors, if you are planning on composites everything gets harder by orders of magnitude.
Why?

Am planning to use both. Will not start on composite until I have a thorough understanding of bp. I calculate that a 12-stage composite motor rocket will be able to get past 100 km altitude, for a total motor cost of about $500, but there are a number of assumptions and subtleties in that calculation that may not be valid.

> 29mm Estes F15-0 or E16-0 in lower stage. 24mm Estes D12-0 or E12-0 in next stage. 18mm Estes C6-0 or B6-0 in next stage. 13mm Estes A10-0T in next stage. 13mm Estes A10-3T in upper stage with a recovery system.

Have saved that. Will analyse.

> I would suggest looking at the fins on an old Estes Farside ... The Farside had fins all at a tiny angle to induce roll to help keep the rocket from weathercocking severely, but you will need a 1/4" diameter by 6 foot long steel launch rod and launch only in NO WIND.
Thanks for the tips.

> Build of a 3 stage 29 mm rack rocket: https://www.rocketryforum.com/showthr...k-Rocket-Build
Exactly what I need to know, have bookmarked page.

> 5 stage 38 mm G160
That's getting into serious rocketry. I like it.

One thing to keep in mind is the total amount of propellant. You might get it to fly, but you can go over the 62.5 gram limit. Of course, if you're flying alone, or at an unsanctioned event, or are a "certified "Level" flier" then this might not apply.
From Thrustcurve.org

Estes BP motors
18mm C6=11gr

24mm D12=21gr
24mm E12=36gr

29mm E16=40gr

FAA waiver propellant limits apply to everyone in the USA.

Sorry to be a buzzkill but this is yet another classic example of the cart going before the horse.

The opening comment of the thread is "I'm a complete beginner".

This is not the hobby to just jump in and start experimenting. You really need experience before you start tackling crazy experimental projects. When complete beginners go off and start doing crazy experiments is when bad things happen and this hobby gets unwanted bad press for dropping a ballistic rocket into a car park or causing a fire to ignite that burns down someone's barn.

I've seen a 5 stage Comanche - D12-0, D12-0, C6-0, C6-0, C6-7. The most I've personally done is four stages in a scale model of the German WW2 Rheinbote, which you can see in my avatar; its first stage was a six C6 cluster, as much for scale accuracy as for an initial kick to get the rocket going.

Beyond that, as has been pointed out, more stages means the CG moves further back - the motor is the heaviest part of the rocket and you're adding more of them. And each extra stage must lift the combined dead weight of all the ones above it.

There's usually a very short delay between one stage burning out and the next one igniting. During this time the rocket begins to decelerate and tip over. By the time 12 stages have done their work, the rocket is quite likely to be pointing either horizontally or down. 30 stages will almost certainly end with a powered descent.

Moreover, each stage carries with it a chance that it will fail to ignite the next stage, and if any one of them fails to ignite then the upper stage (with the ejection charge and parachute) won't ignite either. The more stages you add, the greater is the chance that one of them will fail to ignite and the rocket will come down ballistic.

mollwollfumble said:

I'm recently retired. I've had a long-standing interest in space telescopes, and met someone who invited me along to the Tripoli (Australia) rocket launch last month. That got me thinking about the mathematics of minimum fuel usage to space.

Click to expand...

Someone has already worked out how many model rocket motors would be needed to get to space:
https://what-if.xkcd.com/24/
(The fact that you mention 30 stages makes me wonder if you've already seen this. Being as it is on XKCD, I doubt it was meant for anyone to actually try it. )

First, welcome to the great hobby of rocketry!

Second, I agree with the others that you need to gain experience in rocketry before going into the more complex stuff. As a retiree, you have plenty of time to gain the knowledge required to build and fly many different designs. You never know which one might teach you something new.

Third, try using Rocksim or Open Rocket to simulate some of your designs. Simulation software will keep you from choosing a design that will be unsuccessful.

Forth, join a rocketry club. There is a vast amount of knowledge among its members, and they are great people as well.

sooner.boomer said:

One thing to keep in mind is the total amount of propellant. You might get it to fly, but you can go over the 62.5 gram limit. Of course, if you're flying alone, or at an unsanctioned event, or are a "certified "Level" flier" then this might not apply.
From Thrustcurve.org

Estes BP motors
18mm C6=11gr

24mm D12=21gr
24mm E12=36gr

29mm E16=40gr

Click to expand...

The FAA Class 1 model rocket limit is 125 grams total propellant in all installed engines with a lift-off weight not to exceed 1500 grams .......

Bob

First off, as I forgot to say this earlier, Welcome. I hope you enjoy this place, and learn from it as I have. Below I try to answer your comments and questions to the points that were contained in my original post. I

mollwollfumble said:

> Keeping your CG in front of your CP is going to be a challenge as the initial weight will be high back end.
I don't understand this because the staging extends the effective length of the motor towards the top of the rocket. With multi-staging the CG moves forward towards the half-height of the rocket which should help stability rather than hinder it.

Click to expand...

I phrased that poorly. I meant what others have said that you're putting a lot of weight at the back which will make your initial CG toward the back. Doing this rack rocket style will help with keeping the CP near the same place as the rocket stages, but the initial weight/balance issue is still there. Rack rockets are a proven design and I am intrigued now...I may have to build one too.[/QUOTE]

mollwollfumble said:

> As for attaching fins; for low/mid power with wood/paper - Titebond II is your friend, and fillets with Titebond molding and trim
Thanks. Will look for this, I'd never heard of it. It seems to be only available from a single specialty distributor (Carbatec) in my city.

Click to expand...

I didn't realize you were in Australia, and Titebond may not be immediately available. What you want is a aliphatic wood glue (yellow stuff) in place of Titebond II, I don't know quite what Titebond molding and trim is other than magic, but you can use Titebond II and make really strong filets. Just don't make them too big or they will have some unatractive gaps, but these heavily staged rockets can be seen as single use anyway (as your experience shows) so maybe a perfect finish isn't a big deal.

mollwollfumble said:

> Everything I've said assumes you are planning to use bp motors, if you are planning on composites everything gets harder by orders of magnitude.
Why?

Click to expand...

Up front disclosure: I have not staged composite motors, but I've been looking into it lately. That said, there are serious differences in the way these motors light and burn that makes staging different. First off, it requires more "pop" to light composite motors, they need to initialize/maintain a certain pressure to operate properly so there can be a delay between ignitor and the motor really getting going (get an E20, guaranteed to chuff). Most importantly for staging is that you don't just tape them together head to foot and they light each other (I assume there are exceptions, but not any I have at hand). Therefore, people use some kind of on board electronics (timers, altimeters, g-switches, etc.) to control the staging. These set off low current ignitors under predetermined conditions to ignite the stages. There are often seperation charges, recovery deployment charges, etc. It can be really interesting, and expensive. See: https://www.rocketryforum.com/showthread.php?56808-(Another)-Comanche-3-Upscale&highlight=Comanche and links therein for a beautiful example.

mollwollfumble said:

Am planning to use both. Will not start on composite until I have a thorough understanding of bp. I calculate that a 12-stage composite motor rocket will be able to get past 100 km altitude, for a total motor cost of about $500, but there are a number of assumptions and subtleties in that calculation that may not be valid.

Click to expand...

I'm not looking at your spread sheet, but I can confidently say you have missed some variable because you are off by at least one to two orders of magnitude on the cost. 328,000 ft is A LONG WAY UP. This is a seriously lofty goal, but work up toward it. You will undoubedly learn and refine the goal as you go, and build some really cool stuff along the way.

-Chris

You might want to try this with 13mm mini engines first (A10-A10-A3-A3-1/2A3), minimum diameter, with a long sustainer stage to help stability. Very long rockets tend to be very stable because the length moves the CG forward, especially if you have a little nose weight, and the CP gets moved back in relation to the CG. If you do this as a scaled-down minimum diameter test first, you can get an idea of what challenges you may have if you make it bigger, and if it goes badly it's not going to be as much of a safety threat as it would be if you started big. Anyone doing any scratch building needs to be using a sim program, OpenRocket is free and works very well for most rockets, you should download it model your flight first.

sooner.boomer said:

One thing to keep in mind is the total amount of propellant. You might get it to fly, but you can [not?] go over the 62.5 gram limit. Of course, if you're flying alone, or at an unsanctioned event, or are a "certified "Level" flier" then this might not apply.
From Thrustcurve.org

Estes BP motors
18mm C6=11gr

24mm D12=21gr
24mm E12=36gr

29mm E16=40gr

Click to expand...

Forgive the nitpicking, but the limit is 125g total. The old 62.5g limit - which is no longer in place - applied only to a single motor.

The A10-3T was suggested elsewhere as the upper stage motor, but I think the delay's way too short for an upper stage motor in all but the draggiest of rockets.

S5: A8-5 : 3.3g
S4: B6-0 : 5.6g
S3: C6-0 : 11g
S2: D12-0 : 21g
S1: E12-0 : 36g

Considering the stack above, I get 77g. That's a moderate impulse. Even raising it to all C's in the upper three stages only increases the total propellant mass to 90g, still well under the limit. So I don't think the total propellant mass will be an issue using only 24mm motors and smaller.

OTOH, the 60g in an F15-0, in place of the E12-0, starts getting much closer to the limit (and requires a 29mm mount).

All that said, my experience flying BP stagers is that none of the booster motors have particularly high thrust. The weight of the upper stages, loaded with motors, can result in the rocket crawling off the rod and weathercocking badly. Sometimes, it's better to use a higher thrust composite in the first stage (and electronically air start the 2nd stage) or use a cluster on the first stage. Of course, both these solutions introduce new problems

Doug



.

hpreric said:

Third, try using Rocksim or Open Rocket to simulate some of your designs. Simulation software will keep you from choosing a design that will be unsuccessful.

Click to expand...

But whatever you do, don't ever use these simulations as the Holy Bible. "It worked in the simulation so it's gotta work in real life" doesn't cut it. I have simmed a rocket and it said it's it hit the ground at almost 300 feet per second...and it said it was a good flight.

Thanks all. I had written a detailed reply to you all but lost it when OpenRocket crashed the computer.

You mentioned "rack rocket" which led me also to website:
https://members.tripod.com/tripoli_rocketry_pgh/rackrocket.html
That website mentions heaps of multistage (to a maximum of seven-stage) flight tests that failed as well as those which worked. Extremely useful for me. Pity it doesn't mention the need for a more powerful first stage motor or cluster.

> The fact that you mention 30 stages makes me wonder if you've already seen this ... XKCD

I hadn't, but had actually done the same calculation independently. What XKCD says is perfectly true for black powder rockets. I calculate that composite multistage rockets can do much better, but require careful tuning of either the delay, the burn time, or both.

In my calculations, a two-stage rocket running at optimum velocity (i.e. minimum fuel usage) to space would require a burn time of about 76 seconds. Hence my playing around with multistage. So far as possible I'm taking baby steps. An Arduino microcontroller has been suggested as a timer.

The one variable most likely to have been missed by my calculations is an energy loss due to stage separation. I'm trying to calculate what that would be, perhaps 11%?

Ditto Verna Post,
By the time the 3 stage has finished it's trusting MOST Mod-Roc Staged bird are flying Horizontally or nearly so. Because we don't know where the additional stages will send the model it's just NOT WORTH THE RISK to other people and property to fly such things.
I did a 4 stage Farside ONCE many years back D13-0, D13-0,C6-0, C6-7. The only thing I recovered was the 1st stage. and the model was flying horizontally as mentioned above by the third stage in almost 0 winds.

From the link to the Triploli rack rocket I posted above, the following looks promising for 6 stages:

"Ken Good was eager to give the problem of massive multi-staging a shot. He liked the idea of a single piece rocket, and came up with the concept of "open hull" construction. Accordingly (in November of 1969) he built the KG-4 Achilles, a six-stage open hull single-body rocket. It was a clear success, flying so well that it was not recovered; its initial flight on February 1, 1970, saw it disappear into the gray clouds over Tripoli Irwin’s “Launch Site A." The Achilles utilized four 3/16" wooden dowel rods to enclose the motors, and yet leave them open to outside air to eliminate the Krushnik Effect. It was this rack-like structure that had caused the term “rack-rocket” to be coined. The rack contained a motor stack, the uppermost stage of which was inserted into a conventional body tube that was joined to the rack and contained the recovery system. As each motor ignited the next, it was blown out between the dowel rods and clear of the rocket. Each motor's stability, as it cleared the rocket, was guided by the dowel rods so that no chance of unbalance could occur. Also, since the structure was one unit and maintained a consistent alignment through all stages, there was no chance of inter-stage misalignment to induce flight aberrations."

But I see possibilities for improving these rack rockets:
1) There's no allowance on that website for clustering the first stage or for using a larger diameter motor for the first stage.
2) The rack rockets have a considerable amount of drag from the gas jet generated by the motors on the rack and on the fins.
3) The first rack motor built was also the most heavily staged, with 6 stages. Nothing since has improved on that.
4) There needs to be some way to track the real high fliers so that they aren't lost. I suggest VHF trackers similar to that used on small animals.

> By the time the 3 stage has finished it's trusting MOST Mod-Roc Staged bird are flying Horizontally or nearly so. Because we don't know where the additional stages will send the model it's just NOT WORTH THE RISK to other people and property to fly such things. I did a 4 stage Farside ONCE many years back D13-0, D13-0,C6-0, C6-7. The only thing I recovered was the 1st stage. and the model was flying horizontally as mentioned above by the third stage in almost 0 winds.

By the time (long distant) that I want to try a real high flier I'll be able to fire it off with the Tripoli Rocket Club, which has a launch site a long way from everywhere (including where I live, unfortunately). Other people there have more dangerous rockets (such as rockets that weigh more than 100 times as much and have motors 200 times as powerful as my four-stage). My first home-built launch weighed only 138 grams was still flying up all through the fourth stage, so that at least is not just possible but easy. I guess and hope that it was the "Krushnik Effect" that limited performance of stages above the first.

Practice has shown that sequential ignition of more than four stages is problematic and becomes more a matter of sheer luck than operational success.

The 'rack rocket' things basically just prove you can tape 5 or 6 (or more) motors together and get 'em to light.

Handbook of Model Rocketry (by G. Harry Stine and Bill Stine) very highly recommended...they go into a great deal of explanation of staging and the practical problems/limits you run into. I have no staging experience myself but the book helped me understand the challenge.

My local library will borrow materials from other libraries on borrowers' behalf...ask yours if they can do that for you. Otherwise, I don't think you'll be disappointed buying one.

From a weight perspective I’d think the best motor combination for a five stage rocket would be;
D12-0/C12-0/A10-0T/A10-0T/A3-4T. This would allow for very short and lightweight 3rd and 4th stages and the rocket should be going fast enough at that point stability or lack thereof, wouldn’t be a problem.

True, it wouldn’t be setting any altitude records with that combination but it would probably give the rocket the best chance of actually flying.

boomtube said:

From a weight perspective I’d think the best motor combination for a five stage rocket would be;
D12-0/C12-0/A10-0T/A10-0T/A3-4T. This would allow for very short and lightweight 3rd and 4th stages and the rocket should be going fast enough at that point stability or lack thereof, wouldn’t be a problem.

Click to expand...

Stability will be a concern regardless of how fast the rocket is going. If the CP ended up ahead of the CG when one of the boosters detached, the rocket will become unstable and cartwheel, and the only positive thing that can be said is that it will do so a few hundred feet in the sky. That won't help if it's any but the last stage which does it because the next stage will ignite while pointing in a random direction, which will have unpleasant consequences if that random direction is somewhere downwards...

The point about stability I was trying to make is that with so little weight in the forward three stages the D12-0 would have enough thrust to get the rocket moving fast enough the rocket would leave the rod stable.

As for ditching the lower stages; that does change the CP/CG relationship but again having light weight 3rd and 4th stages those shifts would be minimized. This minimization could be further helped along by having a small dia. for the 3rd, 4th and 5th stages and using correspondingly small fins.

Personally I think it would be very difficult to build a conventionally styled five stage rocket and achieve a successful flight. Like you I think at some point the rocket is going to have a hard separation and things will go downhill from there.

mollwollfumble said:

From the link to the Triploli rack rocket I posted above, the following looks promising for 6 stages:

"Ken Good was eager to give the problem of massive multi-staging a shot. He liked the idea of a single piece rocket, and came up with the concept of "open hull" construction. Accordingly (in November of 1969) he built the KG-4 Achilles, a six-stage open hull single-body rocket. It was a clear success, flying so well that it was not recovered; its initial flight on February 1, 1970, saw it disappear into the gray clouds over Tripoli Irwin’s “Launch Site A." The Achilles utilized four 3/16" wooden dowel rods to enclose the motors, and yet leave them open to outside air to eliminate the Krushnik Effect. It was this rack-like structure that had caused the term “rack-rocket” to be coined. The rack contained a motor stack, the uppermost stage of which was inserted into a conventional body tube that was joined to the rack and contained the recovery system. As each motor ignited the next, it was blown out between the dowel rods and clear of the rocket. Each motor's stability, as it cleared the rocket, was guided by the dowel rods so that no chance of unbalance could occur. Also, since the structure was one unit and maintained a consistent alignment through all stages, there was no chance of inter-stage misalignment to induce flight aberrations."

But I see possibilities for improving these rack rockets:
1) There's no allowance on that website for clustering the first stage or for using a larger diameter motor for the first stage.
2) The rack rockets have a considerable amount of drag from the gas jet generated by the motors on the rack and on the fins.
3) The first rack motor built was also the most heavily staged, with 6 stages. Nothing since has improved on that.
4) There needs to be some way to track the real high fliers so that they aren't lost. I suggest VHF trackers similar to that used on small animals.

> By the time the 3 stage has finished it's trusting MOST Mod-Roc Staged bird are flying Horizontally or nearly so. Because we don't know where the additional stages will send the model it's just NOT WORTH THE RISK to other people and property to fly such things. I did a 4 stage Farside ONCE many years back D13-0, D13-0,C6-0, C6-7. The only thing I recovered was the 1st stage. and the model was flying horizontally as mentioned above by the third stage in almost 0 winds.

By the time (long distant) that I want to try a real high flier I'll be able to fire it off with the Tripoli Rocket Club, which has a launch site a long way from everywhere (including where I live, unfortunately). Other people there have more dangerous rockets (such as rockets that weigh more than 100 times as much and have motors 200 times as powerful as my four-stage). My first home-built launch weighed only 138 grams was still flying up all through the fourth stage, so that at least is not just possible but easy. I guess and hope that it was the "Krushnik Effect" that limited performance of stages above the first.

Click to expand...

Would Carbon Fiber Rods work in place of the wooden dowels for the "rack" structure? Thinking they would be smaller, just as strong, and (here is the question) less affected by the blast/heat. Smaller rods would impose less drag/effect on the nozzle jet. Could also mount them to a "ring fin" that would be completely outside the jet blasts of the upper engines.

As for stability, seems like for a rack rocket stability only gets better with stages, as you are progressively jettisoning your tail weight with forward weight constant and CP presumably constant.

Here's a 5 1/2 stage idea you could probably kitbash 2 Mini-Comanche 3 kits (plus a few oddball parts) into:


STAGE 1: A10-0T
STAGE 1.5 (parallel stage pods mounted at the nose): 2x C6-0
STAGE 2: A10-0T
STAGE 3: C6-0
STAGE 4: C6-0
STAGE 5: C6-7


The parallel stage pods would jettison about .2 seconds after stage 3 ignition.

The 2 C6-0 motor pods up front along with lightweight A10s in stages 1 and 2 would probably fix your CG/CP situation.
Liftoff speed should be fine since you are lifting off the pad under power of 2x C6 plus an A10.

Watching this thing fly -- even if it worked correctly -- would be one of the hairiest things you ever saw because you would have 3 separate pieces fly off the rocket within .2 seconds of each other at stage 2-3 staging and then the "SRB Sep."

I would take a wild guess that the chances of some 'anamolous event' at that point (a parallel stage burning .1 second long or short) that would kick the rocket off a vertical flight path would be pretty high. If ONE of those parallel 'SRB' pods drops off a tenth of a second early or late, the remaining stack veers off at about a 60 degree angle.

Then you would continue with essentially a conventional C-C-C 3-stage rocket.

If you built the whole kaboodle with minimum-diameter BT-20, that top stage would be going pretty good by burnout.

mollwollfumble said:

What works and what doesn't?

The second reason I'm on the forum is that I want to work up through a series of tests to massively multistaged (eventually to at least 12 stages and possibly as many as 30 stages).

Click to expand...

NASA limits itself to 3-4 stages for a reason

Bazookadale said:

NASA limits itself to 3-4 stages for a reason

Click to expand...

Wimps!

Technically the Apollo was a 6-stage vehicle:

S1: S-1C
S2: S-II
S3: S-4B
S4: SM
S5: LM (DS)
S6: LM (AS)


That said, the time-honored rule-of-thumb of 4 stages as a practical max has worked out pretty well for model rocketry.


The 5 1/2 stage 'Double Mini Comanche' thing I proposed above MIGHT work (at least in theory it should), but my gut feeling is you would probably only get full 7-motor ignition about every other launch, plus as noted a good number of those 'all-go' flights would probably careen off crazily at one of the staging points.

(Needless to say if you don't get perfect 3-for-3 ignition on both outboard parallel-stage booster C6-0s and the center S1 A10-0T, you are FUBARed from the get-go. :shock: )

Not to mention 'unforeseen' problems such as what would happen if the parallel-stage 'SRBs' were coasting along at the fairly low sustainer thrust of the C6-0s (the long leveling-out section of the thrust curve) just as the center-motor Stage 3 C6-0 lights and spikes up to max thrust, depending on the pin-and-slot arrangement you used to mount the parallel-stage boosters, the core vehicle could accelerate right out of those pins and take off before the boosters burn out.

In such a scenario my bet is the separation of the boosters would probably not be nice, neat and symmetrical, so you'd have these boosters peeling off one at a time and the rocket veering sharply under 2-motor off-center thrust when one booster peels off before the other.

So theoretically it should all work perfectly, but if you have variances of even something like .05 of a second (which could start on the pad when you hit the ignition switch -- as we know there are no guarantees all motors of a cluster will light precisely simultaneously) that could be enough to send the rocket off in pretty crazy directions.

I'd bet also on the top couple of stages you might be running into 'speed of balsa' problems too.

And finally -- if you are launching this 5 1/2 stage BT-20 rocket under the power of 2x A10 and 5xC6, that top stage is going to go for "miles and miles." If you're out on Black Rock you might get it back but otherwise you'll probably be lucky to see anything above stage 2 ever again.