An "R"-powered rocket build

[ThirstyBarbarian]

• You're doing right thinking about the load/weight bearing parts of the structure first. Design the internals to deal with the thrust of the motor and weight of the components. In a huge way, a body tube is mostly aesthetic.
• Your concern of transferring the thrust to the rocket is well founded, but when you think of airframe think of the internal structure unit that comprises the fins, bulkplates, nosecone weight and attachment, etc. all of which you have to get moving upward. We integrated the fins and motor mount assembly and attached the structure to the airframe the entire length of each fin root along with internal stringers going all the way from the motor mount structure to the nosecone. Think lots and lots of surface area for attach points. Construction adhesive and long screws work much better on wood parts than epoxy, is cheaper, and is easier to work with.

This is something I was wondering about. I’ve never built anything of this scale, but I have built some rockets that I wanted to be large in appearance, but very light. For those rockets, the “body tube” was really just a skin and didn’t do much structurally. For example, I’ve used card stock for the skin — it gave the appearance of a more substantial rocket, but it could have flown with just the skeleton which really provided the strength of the rocket.

When I think of a 30” sonotube, 20’ long, wrapped in glass, it sounds like literally hundreds of pounds, if not more. Is heavy reinforced body tube the best way to transfer the loads? Or would it make more sense to build an internal wooden frame to provide the strength, and then tack on a lightweight skin?

 

[Bat-mite]

Well, for a Q motor, if you want to go low and slow, you're looking at at least 1000-pound rocket. The 3/4 Mercury Redstone weight just over 1000 pounds and went to about 2600' on a Q. It took the equivalent of an I motor to ignite it.

 

[ThirstyBarbarian]

Well, for a Q motor, if you want to go low and slow, you're looking at at least 1000-pound rocket. The 3/4 Mercury Redstone weight just over 1000 pounds and went to about 2600' on a Q. It took the equivalent of an I motor to ignite it.

My experience with low and slow is mostly that it’s more about drag than weight.

I’ve got no experience with rockets anywhere near the scale of this project, so I don’t want to speak out of turn here. Maybe with a Q motor, weight is not a real concern in terms of the motor being able to safely lift a 1,000 pound rocket. But weight could be a problem for handling the rocket, assembling it, transporting it, recovering it, etc.

And my question was more about what is the best way to build the rocket to transfer the loads throughout the rocket. Is a heavy “body tube” the best construction? Or is an internal frame better? And if you need an internal frame, is it easier to build that inside a tube or build it naked and wrap a skin around it?

I’m just throwing out ideas and also questions for my own learning about these kinds of projects.

 

[Bat-mite]

My experience with low and slow is mostly that it’s more about drag than weight.

I’ve got no experience with rockets anywhere near the scale of this project, so I don’t want to speak out of turn here. Maybe with a Q motor, weight is not a real concern in terms of the motor being able to safely lift a 1,000 pound rocket. But weight could be a problem for handling the rocket, assembling it, transporting it, recovering it, etc.

And my question was more about what is the best way to build the rocket to transfer the loads throughout the rocket. Is a heavy “body tube” the best construction? Or is an internal frame better? And if you need an internal frame, is it easier to build that inside a tube or build it naked and wrap a skin around it?

I’m just throwing out ideas and also questions for my own learning about these kinds of projects.

I'm in the same boat as you. I can only mention what I've seen. I am no structural engineer, that's for sure.

 

[Rail Dawg]

This is something I was wondering about. I’ve never built anything of this scale, but I have built some rockets that I wanted to be large in appearance, but very light. For those rockets, the “body tube” was really just a skin and didn’t do much structurally. For example, I’ve used card stock for the skin — it gave the appearance of a more substantial rocket, but it could have flown with just the skeleton which really provided the strength of the rocket.

When I think of a 30” sonotube, 20’ long, wrapped in glass, it sounds like literally hundreds of pounds, if not more. Is heavy reinforced body tube the best way to transfer the loads? Or would it make more sense to build an internal wooden frame to provide the strength, and then tack on a lightweight skin?

Good questions.

The tail end with motor will push say 400 lbs. Rough guess until I can get numbers run.

Maybe have the rocket weighing under 1000 lbs is the goal.

Need enough altitude to allow large cargo chute to deploy.

What about carbon fiber? Expensive yes but if it can eliminate the internal structure it’s worth it.

Curious how many wraps it would take.

Thoughts?

Chuck C.

 

[OverTheTop]

For the full scale V2 we used an aluminium frame and skinned it with styrofoam. The foam was sculpted as necessary, and a final vinyl overwrap added to the strength. Nice and big and relatively light. 46' tall and about 880 pounds with motor loaded. This method should easily adapt to smaller scales (we did a 1/4 scale as proof-of-concept) as long as the flight speed is not too great. If you want big and draggy this might get you there! Here are a couple of pics with details of the skeleton and construction:

 

[Rail Dawg]

A 100 yd roll 50” wide of 2x2 3k carbon fiber twill delivered is $1650.

That’s a LOT of carbon fiber.

Seems if I could get 3 wraps of carbon on the tube...

Chuck C.

 

[Rail Dawg]

For the full scale V2 we used an aluminium frame and skinned it with styrofoam. The foam was sculpted as necessary, and a final vinyl overwrap added to the strength. Nice and big and relatively light. 46' tall and about 880 pounds with motor loaded. This method should easily adapt to smaller scales (we did a 1/4 scale as proof-of-concept) as long as the flight speed is not too great. If you want big and draggy this might get you there! Here are a couple of pics with details of the skeleton and construction:

Great work!

So many unique designs that do the job.

Chuck C.

 

[BDB]

Nothing says it has to be round....

If you are looking for speed and ease of construction, it's be easier to build something big and square.

Just a thought....feel free to disregard.

 

[llickteig1]

The KloudBuster MAX was about 675#. External airframe tube had two wraps of fiberglass. If you tie all the members together internally, the exterior airframe "skin" will gladly go along for the ride.

Design and construction decisions were made through gut experience by team members. Not a lot of sitting down and "engineering" per se but plenty of ingenuity.

--Lance.

 

[CzTeacherMan]

I can model on Open Rocket really easily... Just shoot me a list of parts, right dimensions, and materials. As the build occurs, I can tweak to exact weights, etc
For fin design, perhaps simple trapezoid, nothing rest swept to reduce damage on landing

 

[boatgeek]

OK, I'm going to riff on BDB's suggestion and step outside the box. So far outside the box, I'm back in a box. In my industry, we use a fair amount of molded and pultruded fiberglass grating. You could easily use those to use as stringers for a square rocket. The pultruded gratings are basically a set of linked I-beams. You'll have to work out the corner details and bulkheads, but otherwise you have a very strong and stiff side that you just need to skin with something thin and light. Plywood doorskins would probably work if you like. If you put the grit side to the inside, you'd even have a smooth gluing surface on the outside. Molded gratings are basically a laid up grid of square openings. They're probably not quite as stiff and strong, but they'd be easier to bolt bulkheads to because they have flat surfaces. Either way, if you choose the rocket outside dimension to match a standard width, you'd have an easy construction process. Here's a couple of links to a local manufacturer, though the same basic gratings are available all over:

Pultruded: https://www.gratingpacific.com/fibe...pultruded_safe-t-span_pedestrian_grating.html
Molded: https://www.gratingpacific.com/fiberglass_gratings/fiberglass_molded_fibergrate.html

A square rocket is a heck of a lot easier to fit into a truck for transport, plus your nose cone and coupler setups are quite a bit easier to fabricate. If you used the lightest pultruded grating in the first link, weight is 1.9 lbs/square foot, call it 2.5 lbs/sq ft including a skin and corners. For a 30" square rocket, 20' long, your skin is about 500 lbs. That's well along toward your goal of ~1000 lbs all up.

 

[Rail Dawg]

I can model on Open Rocket really easily... Just shoot me a list of parts, right dimensions, and materials. As the build occurs, I can tweak to exact weights, etc
For fin design, perhaps simple trapezoid, nothing rest swept to reduce damage on landing

That would be great!

A huge help and I can concentrate on supplies and build.

I’ll post some data later on that you can start with.

Appreciate your efforts!

Chuck C.

 

[Rail Dawg]

Waiting for some input on 3-4 wraps of carbon over sonotube and that’s it for the airframe.

Stuff is pretty dang strong lol.

The motor mount and fins will be heavy duty.

Huge parachute near the nose cone to help with CG.

CZ TeacherMan will let us know if we have a CG/CP issue.

Thanks!

Chuck C.

 

[troj]

I may come to regret this, but I'll chime in...I've got a "bit" of experience with this. Delta III (twice), Redstone (twice), a Pershing on a Q, and I'm not sure what all else. I was the main instigator on all of these, and Pat G built all of our motors except 1.

Edit: As a friend reminds me, the Safety Rocket. A lovely CATO 2.3 seconds into the burn.

Not all worked perfectly. Projects like this are not trivial undertakings.

Based on what you're giving for dimensions, you're building a BDR - Big Dumb Rocket. Go find yourself some quality 1/4" plywood - baltic birch is your best choice, but if you can find something else that's truly good quality, it'll work. Two layers of that with a layer of 6oz fiberglass in between. Trust me, it's plenty strong enough for what you're building.

If you have a router, you can make a jig to cut all the centering rings you need. Paying a custom woodworker to do it is possible, but you're going to need lots of rings and you can build your own jig (and own a nice router) for a lot less. Source 3/4" baltic birch plywood, and make your load bearing rings from that and any other rings that are just alignment from 1/4" plywood.

Trying to make a 30" coupler that will reliably separate is difficult at best. Plus if you're using sonotube, it's very humidity sensitive and prone to jamming because of that. We went 100% with flat plates at the joints and used explosive bolts to split them apart. They never failed us.

Lance is 100% correct that any project like this is a 1-off. We did the Delta III first and it was a huge learning experience. From there, we built the Redstone next and refined our build approach. All of our large projects were built the same way and one key component is that we built an internal load-bearing structure with the tube being removable and being nothing more than an aerodynamic fairing. Our rocket would've flown if we left the tube off.

How big is your team and how big is your budget? You're going to be spending a chunk of change on this. The launch pad alone is an undertaking and an investment.

You also have to think about logistics. You are going to spend quality time out at the pad. You're going to need a crew to do so and a plan for how to get your rocket vertical. You're talking a lot of weight. If you don't have a dedicated crew of 6 to 8 people who are going to help build, transport, prep, etc, you're asking for frustration. Those need to be 6 to 8 people who can spend a lot of time together without bickering. Design by Committee will be the death of your group and your project.

-Kevin

 

[OverTheTop]

^^^ What Kevin said. The logistics of these large projects are complex and take a good team effort. Not exactly what you would call a relaxing launch day (or two, or three).

 

[saadzmirza]

More details on the motor? Looks very cool

 

[OverTheTop]

More details on the motor? Looks very cool

Me or the OP? Ambiguous. Ours was an O25000. Long way from a Q.

 

[kalsow]

I'm a relative beginner to big rockets, but I'll add my $0.02. I've been trying to build and fly large, lightweight rockets. I'll leave the flying of 2x4s and Porta-potties to others. Here''s my story. Enjoy.

<flame throwers off>
The largest rocket I've built was called "Good Enough". That was also our mantra and the full extent of our engineering abilities. The rocket was a 2' x 30', 100lb rocket constructed of paper, foam, a bit of fiberglass, and a jug or two of Gorilla Glue. It flew on a Dave Leininger Smokey Black N3400 to about 2000ft. Loaded on the pad it was 140lbs. We planned to recover it in garbage bags, but it all survived!

The core consisted of 4 6' sections that were bolted together before the rocket was skinned. Each section had 4" mailing tube core that was covered with 2 layers of 6oz fiberglass, 6 centering rings cut from 2" pink foam, 2 end-cap centering rings cut from 1/4" cheapo plywood, and a bunch of 2"x2" longerons. The core tubes were joined with couplers glued on only one end and the end-cap centering rings were bolted together. At apogee the rocket separated between the 3rd and 4th sections. Those sections had a 12" sonotube mounted around the 4" core. The parachutes rode in these tubes. The 4" cores were sealed off about 12" above and below this joint. The end-caps at this joint were joined with explosive bolts. At apogee the 4 explosive bolts were blown, then a half second later the short sealed section of the 4" core was pressurized to separate the rocket. All told, we only used a few grams of black powder. There were 2 parachutes, a 20' for the booster and a 12' for the nose. The chutes were tied together with a little velcro at their apex. So they pulled each other out.

The "cylindrical" sections of the airframe were covered with the same heat-shrink plastic that is used to cover boats for the winter. The skin added a little stiffness, but not much! The central 4" core and a 1/2" plywood thrust plate at the bottom carried the thrust.

The nose was similar to the other airframe sections. It was approximately a cone. It had the same 4" core, with varying sized centering rings and longerons to define its shape. It was covered in a couple crude layers of fiberglass.

The fins were made from 2" foam covered with 2 layers of 6oz fiberglass. The foam was punched with small nail holes every 1" or so. The medieval torture device described in the appendix of "Advanced Composite Techniques, Lightweight Moldless Techniques For The Aircraft Homebuilder" by Zeke Smith was used to punch the holes. The holes provided a place for tiny epoxy teeth to forn and to help hold the fiberglass in place.

Duct tape, lots of it, was used to seal the AV bay and for fin fillets.

The whole thing barely hung together. In the videos it appears that the airframe is flexing in mid flight. See

The project required 6-8 people meeting about 25 times for 3 hours at a time. It took about a year of elapsed time to build the beast.

Below are a few pictures.


</flame throwers off>

 

[Rail Dawg]

I may come to regret this, but I'll chime in...I've got a "bit" of experience with this. Delta III (twice), Redstone (twice), a Pershing on a Q, and I'm not sure what all else. I was the main instigator on all of these, and Pat G built all of our motors except 1.

Edit: As a friend reminds me, the Safety Rocket. A lovely CATO 2.3 seconds into the burn.

Not all worked perfectly. Projects like this are not trivial undertakings.

Based on what you're giving for dimensions, you're building a BDR - Big Dumb Rocket. Go find yourself some quality 1/4" plywood - baltic birch is your best choice, but if you can find something else that's truly good quality, it'll work. Two layers of that with a layer of 6oz fiberglass in between. Trust me, it's plenty strong enough for what you're building.

If you have a router, you can make a jig to cut all the centering rings you need. Paying a custom woodworker to do it is possible, but you're going to need lots of rings and you can build your own jig (and own a nice router) for a lot less. Source 3/4" baltic birch plywood, and make your load bearing rings from that and any other rings that are just alignment from 1/4" plywood.

Trying to make a 30" coupler that will reliably separate is difficult at best. Plus if you're using sonotube, it's very humidity sensitive and prone to jamming because of that. We went 100% with flat plates at the joints and used explosive bolts to split them apart. They never failed us.

Lance is 100% correct that any project like this is a 1-off. We did the Delta III first and it was a huge learning experience. From there, we built the Redstone next and refined our build approach. All of our large projects were built the same way and one key component is that we built an internal load-bearing structure with the tube being removable and being nothing more than an aerodynamic fairing. Our rocket would've flown if we left the tube off.

How big is your team and how big is your budget? You're going to be spending a chunk of change on this. The launch pad alone is an undertaking and an investment.

You also have to think about logistics. You are going to spend quality time out at the pad. You're going to need a crew to do so and a plan for how to get your rocket vertical. You're talking a lot of weight. If you don't have a dedicated crew of 6 to 8 people who are going to help build, transport, prep, etc, you're asking for frustration. Those need to be 6 to 8 people who can spend a lot of time together without bickering. Design by Committee will be the death of your group and your project.

-Kevin

Kevin this is awesome stuff.

Was that your Delta III at Argonia back around 2004 or so? If so that was one of the last launches I attended before a hiatus. Helped you guys lift the upper section onto the lower.

That was a real team effort and I was impressed with your leadership.

I've always wanted to learn how to use a router. What's the learning curve and being able to fashion CR's and things like the lower and upper thrust plates?

Am tending now towards aircraft baltic birch plywood for the fins and other internal components like CR's and thrust plates.

Either all-thread or cabling to tighten things up.

This is a work in progress. Right now I'm alone on this as far as build but I'll bet as time goes on I'll get good help.

Please describe more the flat plates and explosive bolts. If it worked for you it can work for me.

Everything you write is being absorbed and put into the equation.

It's appreciated.

Chuck C.

 

[Rail Dawg]

I can model on Open Rocket really easily... Just shoot me a list of parts, right dimensions, and materials. As the build occurs, I can tweak to exact weights, etc
For fin design, perhaps simple trapezoid, nothing rest swept to reduce damage on landing

CZ can we start off with a 7 1/2 ft motor weighing 200 lbs loaded? 9" diameter.

Weight of airframe/fins/thrust plates, etc in lower 4 ft of rocket sure to be 100 lbs. Rough guess.

30" diameter rocket 25 feet tall. More length if needed for stability.

Birch plywood fins sized with what you recommend for stability. Thinking 3/4" but may go Troj's route with inner fiberglass core. You choose a fin design we'll see how it looks.

300 lbs in the forward half of the rocket when counting cargo-sized parachute just under the nosecone. (This is a very rough guess but can get you started?)

Airframe will be carbon-fibered sonotube for now.

If you need more info don't hesitate to ask.

To all of you if I deviate from your suggestions don't take it personally. It doesn't mean I'm not listening. I may very well utilize your ideas. I write everything down and then look at the overall picture.

Thanks CZ!

Chuck C.

 

[rharshberger]

Sonotube brand Sonotube weights 8.8lbs/ft for 30" tube according to one source I found, and that seems about right, so a 12' section would weigh 105 lbs roughly. 12' long sections is the common length carried by concrete/construction suppliers.

 

[Rail Dawg]

Sonotube brand Sonotube weights 8.8lbs/ft for 30" tube according to one source I found, and that seems about right, so a 12' section would weigh 105 lbs roughly. 12' long sections is the common length carried by concrete/construction suppliers.

That's great info Rich.

Thanks!

Chuck C.

 

[DAllen]

I've participated in 2 giganto projects and I find it interesting that no one has mentioned one key element that MUST be present: Y'all have to work well with each other. You have the delegate tasks and ultimately trust each other. If those things can't happen it's going to suck. REALLY suck. This includes the ugly topic of finances needs to come up early and figured out. The money bit WILL come up - and often if it isn't handled properly. Unfortunately, I have the type of personalty where I just can't seem to work well with a big group project like this. As a USLI mentor I feel right at home with college students but when it comes to these big projects it just isn't my cup of tea I guess.

I've also noticed with larger projects you get a lot of "hangers on" as I like to call them where folks who have put little to no effort into the construction want to be considered part of the team. This drives me bonkers. Probably not an issue for others but just an observation you may want to tackle early on so defining who is and is not on the "team" might be important.

-Dave

 

[tomsteve]

anyone ever build a Q motor capable tetrahedron??

 

[DAllen]

anyone ever build a Q motor capable tetrahedron??

That would be one of the coolest rockets ever but holy logistical nightmare Batman. I wonder how many parts you'd have to break it down into just to transport it. Yikes.

 

[Rail Dawg]

OK I've studied how to use a router table to make plywood circles.

I can bang these these things out like nobody's business.

Looks like fun!

Chuck C.

 

[rharshberger]

Use a circle jig and a plunge base router, no need for a router table and its quick.

 

[Rail Dawg]

Use a circle jig and a plunge base router, no need for a router table and its quick.

OK I’m listening.

Will also need to cut the fins and other parts.

I saw the jigs with the plunge router looked easy but can I use the router table for making the other parts?

Chuck C.

 

[rharshberger]

There are several that attach directly to the base of the router, simply set a center pin, set jig over pin, plunge running bit into material, cut.

Milescraft 12190003 CircleGuideKit https://www.amazon.com/dp/B0744PD3VS/?tag=skimlinks_replacement-20

The above is just one of several similar styles.