Scratch build first high-power?

[Saint_Tiki]

Hello again!

Been looking into some good Level 1 cert kits and started thinking about designing my own! There are a few good looking kits but nothing has exactly what I have in mind. I have some questions though about materials, weight, etc.

I know there will be some naysayers and I understand that a scratch build is probably not the best idea for most people coming into the hobby. However, I’m quite engineering oriented and my other hobby is combat robotics which is all about designing things from scratch, sketching, graph paper, CAD'ing, parts lists, weight sheets, etc so I’m pretty confident in design and building from scratch as a general process. I just think it would be a lot more satisfying to fly something of my own creation and get certified that way and have total control over each aspect of it. I’m also not really worried about failing my L1. Don't get me wrong, I’d prefer not to! I’m fortunate to have two clubs nearby that appear to do monthly launches so there will be plenty of opportunities to fly and try again if something goes wrong. And I’m planning on designing and building something that I can fly on mid-power at a nearby site and do some local testing before I go high-power for cert so the rocket should have a few successful flights already before I take it out for a cert attempt.

1. Total parts. With all of that being said, I need a little guidance. From what I can tell, a high-power L1 attempt kit is usually two tubes (airframe and motor), 3-4 fins, 2-3 centering rings, motor retention, nose cone, eyebolt, shock cord, parachute, lugs/buttons, and a few other nick-nacks. So designing my own rocket would essentially be decisions on airframe diameter/length/material, motor tube diameter, fin shape/size/number, nose cone shape/size, etc. That sound about right? All simulated first of course for stability.

2. Tubes. I'm looking at BT-80/66mm so I have some room for future options and these seem easy to source. Slots seem a little trickier though. My first thought was to CAD and 3D print a cutting guide/jig, tape it in place, then I could cut out fin slots in the exactly correct spot. I feel like I could probably do this in paper tubes with a hobby knife and some patience but I’m also leaning towards going fiberglass. I want to keep my build pretty light so I can launch on G or even F motors at home, and also so I have the option to add an e-bay and altimeters in the future without getting too heavy.
(EDIT: I realized fiberglass tubes seem to actually be heavier than paper tubes. The BT-80 "kraft paper" tubes certainly are not meant for high power? They seem a bit thin.)
I'm a tinkerer so I know L1 is just the beginning and I'm gonna want some payloads. How hard is it to cut slots in fiberglass? Dremel and particle mask? Do you recommend I go for it with a fiberglass tube? Can I order one from somewhere pre-slotted to my design spec? I’m more concerned about time invested than money. If I put a ton of hours into making it and it explodes, it doesn’t matter to me that it cost an extra $50 for the tube at that point, lol. But if fiberglass is going to be significantly harder to cut, glue, paint, etc, then that changes the equation. Also, if I do go fiberglass for the body, should I fiber the motor tube as well or is that unnecessary?

3. Fins. I found a few places that sell pre-cut plywood fins. I don’t love the shapes though and that’s kind of part of designing my own, right? Looks like G10 is the go to fiber material for fins. I have some good cheap CNC contacts through combat robots and I’m thinking I could probably get a few fins CNC’d for relatively cheap. What kinda thickness should I be considering for G10 fins?

4. Centering rings. Looks as simple as buying a couple plywood rings sized for my build (probably 66mm to 38mm) and drill a hole for an eyebolt, anything I’m missing here? Worth going fiberglass on these as well?

5. Nose cone. There are some really cool looking nose-cones out there in some of these kits but I can’t find them as standalone parts, only a few generic BT-80/66mm nose cones. Any other options besides a friend with a lathe?

I think that’s it for now. Thanks for any help or advice!

 

[Neutronium95]

You can get thick wall 2.6" cardboard tubing from various sources, it's pretty much the same size as BT-80. If you do go with fiberglass, I would strongly suggest buying from a vendor that can cut the fin slots for you. Good quality plywood is going to be fine for fins on a level 1 rocket.

Madcow makes good options for parts in both Fiberglass and cardboard. Loc Precision makes good cardboard and plywood parts.

 

[thzero]

mach1rocketry is also a good source of fiberglass tubing.

Personally Id go with the 2.6" tubes from madcow or loc p (depending if you are closer to california or wisconsin). But the other thread is right, the bigger the tube, the higher the weight and drag, therefore lower altitudes for same motor. So a lot of it depends on how high do you want to go for a given range.

I did my level 1 with a scratch built fiberglass rocket, but I had specific goals as I wanted to launch it at my local club launch (or at least the local closest one) that has a tight field and certain restrictions (max of G, 3000' ceiling, etc). So it was actually built with fiberglass tube, a spare Aerotech 2.6" nose cone, and wood centering disks, a carboard 29mm tube, and fiberglass fins. Worked really well for my level 1 - it was approx 2400' (well someone forgot to turn on the altimeter correctly...:|). Run off a 72"+ rail, but designed to have min. velocity 50f/s off 72" rail.

But yes, basic rocket would be
nose cone
tubing
motor tube
centering rings (at least two)
fins

Fin slots on carboard is pretty easy. Just make your fin guide marks. Grab a piece of aluminum angle iron. Draw 3 (or 4 or 5 or however many fins you have) lines on the tube. Then I like to measure out the width of the fins from one of the lines, twist the fin guide to that new mark, and repeat the process. Now measure your top/bottom marks for the fin. Then using the angle again and sharp xacto knife cut out the slots!

I've done similar on a fiberglass layered carboard tube but using a dremel. But certainly for fiberglass if you know the dimensions of your fin before you order tube, its certainly easy to take advantage of their services.

 

[prfesser]

Fiberglass tubing is great! Can be wet-sanded, and you don't have to worry (much) if the rocket lands in mud or a puddle.

I cut nicely straight, neat fin slots in CF tubing with a setup as shown.


Tube is taped *firmly* to a flat surface (e.g., countertop). Dremel is taped *firmly* to a flat spacer. Spacer+Dremel is free to slide to and fro on the work surface. Diamond bit of the right diameter---got a set of a dozen cheap diamond bits at a flea market for $8. Turn on Dremel, slide lengthwise to cut the slot. Repeat after turning the tube 120 or 90 deg (3 or 4 fins) and re-taping it down.

 

[HHaase]

The core concept of scratch building your own, I'd say go for it. If you have the construction skills and design skills I'd have zero hesitation endorsing such a build. In fact, please do a build thread here! This way we can help steer you along in case we see a safety issue. I'm glad to see you're not afraid of failures, as they will happen from time to time, just as long as you understand the difference between an unsuccessful flight and an unsafe flight.

Materials choices are pretty wide open too. Cardboard body tubes, of sufficient weight and durability, are used all the time for L1 and L2 flights. Probably far more common than fiberglass to be honest. Yes, fiberglass is significantly heavier for a given diameter rocket. Both are valid choices as long as you understand how to confirm a safe design and safe motor choice.

That being said, I'd probably say you should look at larger tubing for the airframe. Lightweight 3" rockets with an H motor easily hit about 2,000ft. 2.6" might not seem that much smaller, but its cross-sectional area is 30% less than a 3" rocket. It's gonna really scoot!

-Hans

 

[Saint_Tiki]

I see what you're saying about the 3". Makes sense. Here's something I whipped up.

It's a 3" G10 airframe with G10 fins and a 38mm paper motor mount. I love the fin design of the Athena so that's my inspiration for those. I stole some other concepts from the MadCow Tomach kit. It essentially has an optional payload/e-bay for a dual-deploy Long configuration (future goals), or can be removed and flown with simple ejection charge main chute in a Short configuration. It's stable in both configurations even with big motors and gives me options to tinker with electronics/dual-deploy and stuff after L1. This also lets me fly off a G motor or even an F (with a long launch rail or calm day) at home in the lighter configuration.

Thoughts?

One thing I'm not super sure about is the dimensions/proportions for the front airframe tubing versus the rear tubing. Here I've got 15" in the front and 24" in the back, plus a 1" section that would be part of the e-bay/coupler. Just don't know how much space I need to fit the chutes in and if part of the nose-cone cavity can be used for that as well.

 

[boatgeek]

I scratch built my L1 rocket, which was the second rocket I built after returning to the hobby as an adult. That rocket is easily my most-flown airframe. It's definitely doable if you have some fabrication skills and an engineering mind. Review some build threads here--the process will be much the same as for a kit, just with slightly different shaped materials.

1. You're on the right track. fin shape is the biggest variable in how the rocket looks, so that's where you're really going to customize it. The nose cone is in second place in that regard. In an ideal world, you want your rocket to land on the motor nozzle and not the fins for cert rockets--less chance of breaking a fin in an off-nominal flight.

2. The BT-80 kraft paper tubes don't hold up well under HPR type loads without a bunch of reinforcement. Personally, I'd go with heavy wall cardboard tubes from LOC or Madcow. They'll be light enough that the rockets will be easier to fly on F-G motors at your home field. Fiberglass tubes are fine as well, though a bit heavier. You can buy tubes pre-slotted if those slots suit your fins, or you can cut your own. I use a hobby knife for cardboard and a dremel cutoff wheel for fiberglass. I am paranoid about fiberglass dust, so I use a half-mask respirator when cutting FG.

3. Buy 1/8" baltic birch plywood stock from Rockler or another better hobby shop and cut them yourself (or get a friend to NC them). A basic jigsaw will be fine, though you can go up to bandsaws and scroll saws if you like. If you use a FG tube, you can probably buy some sheet stock from the same vendor that you buy the tubes from.

4. You can get your centering rings laser-cut if you're going that way for fins, or you can just buy them direct from whoever you buy your tubes from. Whatever you do, buy both tubes (motor mount and body tube), couplers, centering rings, and maybe the nose cone from the same vendor. Then you're reasonably sure everything will fit.

5. If you see a nose cone in a manufacturer's kit line that you don't see as a standalone part, ask them if you can buy one off the line. Most rocketry vendors are pretty small shops and are pretty accommodating that way. If you're asking for a favor, then it would be polite to give them your business too.

One last piece of advice--make your body tubes the length they come from the vendor as much as possible. That saves you cutting an end off. My tubes cuts are never as good as the manufacturer's.

 

[JamesS]

I also say go for it! l too scratchbuilt my L1 and even upscaled the same rocket for my L2 cert flight. It is a fun (even the butterflies in stomach are fun!), rewarding experience and definitely a really good feeling upon success. It also looks like you are already in a good mindset to do this - confident that you'll be able to figure things out, nonetheless by asking for help here on the forums. Great you're also already throwing some ideas at sim software. Playing around in sim software is a great way of understanding and seeing how the physical aspects of a rocket affect flight and will help guide and fine tune your particular design. Even though the software does CP/CG calculations, for my L1 I did the exercise of also calculating these by hand and it was good to see what's behind the math with these calcs. I'm not saying you should also do this (I certainly wont ever do it again, lol) but getting a brief understanding of the relationships in the equations can help inform designs with particular goals.

Definitely create a build thread. With all the helpful eyes here, it will be difficult for you to be steered down a bad path toward executing your idea(s).

4. Centering rings sometimes have small cutouts that engage/lock with through wall fin designs. You can see examples of this technique in some LOC kits; check them out if you're interested.

 

[MikeyDSlagle]

Yep, another that says go for scratch build.

I did my L1 with a scratch build 2.6" fiberglass, dual deploy. 1248' on an H123 and 2000+ on the I245G. I fly it fairly regularly and the durability of the fiberglass has been a huge bonus. I did my L2 on a 4" paper bird and the paper shows some wear after just two flights. There is a story about some damage but not going off on that tangent. Glass is easier to paint and finish than the paper/wood is. I do wet sand paper models but glass is much less worrisome. You can mix/match materials no problem. Wood rings, Quantum tube, canvas fins and glass nose. Rat rocket. LOL.

Most vendors will do custom work for you. Not sure how long you have been in the hobby but check out the resources thread and check out our many good kit producers and vendors. Some you may not be aware of. https://www.rocketryforum.com/threads/rocketry-resources.110/

Two more materials you may not be aware of, both are waterproof:
Quantum tube from Public Missiles (PML) https://publicmissiles.com/secure/
Quantum tube is plastic and easy to work with. Not meant for trans-sonic flights. Don't let the haters dissuade you. The stuff is more durable than paper, lighter/cheaper than glass. For sport flying it is great. Their kits come with pretty much everything. Ditch the piston and build it as normal.
PML is great to work with. Doesn't splinter and produce a lot of dust when drilled or cut.
Send them your sim file and they can (pretty much) spit you out a kit. It helps keep the price down if you find fins on their site (from one of their kits) that you like.
https://publicmissiles.com/custom_work.html
Their Endeavor has split fins. - https://publicmissiles.com/kits/sportfliers

Canvas phenolic from MAC Performance (MAC) https://macperformancerocketry.com/
It is slightly lighter and cheaper than glass but nearly as durable. Easy to work with as well. Mike does custom work but always talks me out of it because the cost is quite high. But his kits are great.

I will add this:
Build the thing to fly on L1 motors. And build another rocket to fly on F and G motors. Of course you can always do the old "Fly the booster on F and G then add a payload section and fly it on H motors." 2.6" or 3" glass, paper, quantum or canvas will work in that case.

 

[mo2872]

FYI, Saint, Tulsa’s launch for this Sunday scrubbed to the 25th if you haven’t been following on FB. If you had planned on coming, anyway! Always a good time, and tons of knowledgeable folks to help with your L1!

 

[RobertH3]

Designing your own is good - one of the people in my club encouraged it. You will learn to cut TTW slots and do good measurements. What did they say..."a kit is just a collection of standard parts."
I would go with cardboard first. Why?
Low cost of parts
Less Weight - if you are careful and use 2.6" thick wall tubing, you'll easily be able to keep weight low enough to fly on mid-power. Handy when conditions aren't optimal
Less motor cost for same performance - see less weight
Smaller, lower cost parachute - see less weight
Cutting out your own plywood fins - good experience and less cost
Less recovery harness cost - see less weight - heavy duty recovery harnesses and D-Rings are expensive and add weight.
You can use Titebond II for a lot of the work, with epoxy on the heat-sensitive joints like TTW tab to motor mount and centering rings to motor mount. Less weight and less toxicity, less mess.
Better safety - again, less weight. 6 pounds of fiberglass lawn dart is more scary than 2 pounds of cardboard lawn dart : )
I have done several cardboard HP rockets and while filling spirals and dealing with the slightly pebbly finish on HP tubes is a little annoying, if you mess up a 2.6" thick wall tube it is only about 9 bucks to replace.

In my humble opinion, another piece of advice I got from my L1 cert attempt was very good. Don't try to break Mach or go super-high - if there is a failure, you won't be able to see what happened.

Also, if it crashes, you won't feel as much like you received negative karma! Renegade's first flight failed due to a DMS delay tool being improperly adjusted from the factory, and she ripped her chute and went into the corn. Next month I got her back (thanks for the drought - positive Karma) and for 11 bucks and some glue and paint, ready to fly again!

Saving money means a really kick-butt fiberglass kit when you are certed.
I have a 260.00 Mach 1 Nike Artemis kit I am putting together (glass) and I will snivel if it crashes, though it will likely survive anything short of a full lawn dart.

Below is the 75mm cardboard Renegade upscale I scratch-built - less than a hundred bucks.
You can download kit instructions with TTW tabs to see how they go together. Measurements are pretty important.

Cheers / Robert

 

[HHaase]

In my humble opinion, another piece of advice I got from my L1 cert attempt was very good. Don't try to break Mach or go super-high - if there is a failure, you won't be able to see what happened.

Yup, L1 certification is really really simple in theory. Goes Up , Comes Down, Not Broken.

I usually see one of three things go wrong on an L1 attempt.
1. Bad timing on the ejection, causing a zipper or bulkhead failure.
2. No chute, for various reasons.
3. Went too high, probably still up there.

I keep refining my idea of a perfect L1 certification rocket kit, and one of these days I'll build it to test the theory.

-Hans

 

[Kelly]

Agree with the others, if you're an experienced builder then doing a scratchbuilt L1 is no big deal. Couple things I'll add:
1) Most HPR rockets are overbuilt, IMO. Paper & plywood is plenty strong for an L1, so no need to go to more exotic materials (unless that's what you prefer working in!)
2) Get yourself a simulator - OpenRocket is great and free, RockSim is another option for $. This will allow you to play with your design in terms of materials, size, fin shape etc. and see what tradeoffs you will be making in terms of weight/stability/cost/altitude/etc., and see what range of motors your rocket will be flyable on.

 

[Saint_Tiki]

FYI, Saint, Tulsa’s launch for this Sunday scrubbed to the 25th if you haven’t been following on FB. If you had planned on coming, anyway! Always a good time, and tons of knowledgeable folks to help with your L1!

Yeah just saw that, too bad. I'm planning to come up from OKC for the next one.

 

[Saint_Tiki]

Thanks for the feedback, everyone. I'm going to move forward with the scratch build!

I'll make a build thread when the time comes. Still researching materials. Going to read more about MAC canvas. I'm just kind of put off against cardboard. My local launch site has a big pond in the middle... And I have young kids who will wanna mess with all my toys so I don't see cardboard holding up for very long. I also like the idea of being able to hose off the rocket, lol.

I know most people have dozens if not hundreds of rockets so the general recommendation is to build for a specific purpose, L1, +mach, L2, dual-deploy, etc. For me though, I don't have space amongst all my hobbies to have a bunch of rockets, in addition to all my robots, 3D printer, RC planes, quadcopters, CNC machine, etc. I also am more limited on "play time" so I hate having to choose which toy to bring out. That's why I'm leaning towards a rocket I can fly as a booster only or as booster+upper-section. Gives me options to tinker in the future and do multiple things with one airframe. Plus I like the engineering challenge of designing something to fit that bill that can make reasonable altitudes on different motors and be stable.

 

[boatgeek]

Thanks for the feedback, everyone. I'm going to move forward with the scratch build!

I'll make a build thread when the time comes. Still researching materials. Going to read more about MAC canvas. I'm just kind of put off against cardboard. My local launch site has a big pond in the middle... And I have young kids who will wanna mess with all my toys so I don't see cardboard holding up for very long. I also like the idea of being able to hose off the rocket, lol.

I know most people have dozens if not hundreds of rockets so the general recommendation is to build for a specific purpose, L1, +mach, L2, dual-deploy, etc. For me though, I don't have space amongst all my hobbies to have a bunch of rockets, in addition to all my robots, 3D printer, RC planes, quadcopters, CNC machine, etc. I also am more limited on "play time" so I hate having to choose which toy to bring out. That's why I'm leaning towards a rocket I can fly as a booster only or as booster+upper-section. Gives me options to tinker in the future and do multiple things with one airframe. Plus I like the engineering challenge of designing something to fit that bill that can make reasonable altitudes on different motors and be stable.

Once you start down the scratch building path, forever will it dominate your destiny!

This sounds like a good course, and what I do a lot. The one issue with a multi-functional rocket is that it's not too hard to build a rocket that flies well on F-H (and maybe E), or another one that flies well on G-J. It's really hard to build one that flies well on G-J, even if you do shorten it up.

 

[thzero]

I tend to try and leave 6-8" for chutes in my 2.6-3"

 

[thzero]

This sounds like a good course, and what I do a lot. The one issue with a multi-functional rocket is that it's not too hard to build a rocket that flies well on F-H (and maybe E), or another one that flies well on G-J. It's really hard to build one that flies well on G-J, even if you do shorten it up.

Yeah I find that even if I did build for a band of motors (i.e. D-G) or something, I end up flying each rocket on a particular motor that just performs well for it.

 

[Saint_Tiki]

Canvas phenolic from MAC Performance (MAC) https://macperformancerocketry.com/
It is slightly lighter and cheaper than glass but nearly as durable. Easy to work with as well. Mike does custom work but always talks me out of it because the cost is quite high. But his kits are great.

So I called Mike and he was super helpful. I think I'm going to go this route. I love to design, build/assemble, test, engineer etc. I don't really enjoy fabrication. Looks like Mike will be able to custom make me a whole kit and from what I've read, they are really high quality. Being lighter than FG but still strong and waterproof is a big plus for me.

 

[MikeyDSlagle]

So I called Mike and he was super helpful. I think I'm going to go this route. I love to design, build/assemble, test, engineer etc. I don't really enjoy fabrication. Looks like Mike will be able to custom make me a whole kit and from what I've read, they are really high quality. Being lighter than FG but still strong and waterproof is a big plus for me.

I should've told ya to mention me so you could receive a 0% discount and a "Michael who??" response. LOL. I only have one of Mike's kits but I recommend him quite a bit and drum up business for him, I've "sold" more than I own.

 

[ether]

So I called Mike and he was super helpful. I think I'm going to go this route. I love to design, build/assemble, test, engineer etc. I don't really enjoy fabrication. Looks like Mike will be able to custom make me a whole kit and from what I've read, they are really high quality. Being lighter than FG but still strong and waterproof is a big plus for me.

Agree, canvas phenolic is perfect. Only step up is carbon and the cost / benefit only works for high impluse projects