Solid Rocket Motors 2: Case Design

[@rocketberger]

Great video Charlie! You may wish to add a comment on heat stress and how it can degrade the AL case strength. Not always important in the short burn motors but can be pretty brutal with the bulges, burnthroughs, etc... Looking forward to the next video!

[@AstroCharlie]

Hopefully this 54mm motor doesn't see high temperatures in the case... If it does I picked a bad liner. This is super important to remember for other designs though, and might be the topic of a future video.

[@rocketberger]

@@AstroCharlie , lol - You nailed it CHEAP LINERS SUCK! Spending $100 for a good phenolic set will save you from LOTS of problems... I learned my lessons

[@AstroCharlie]

Hey Rocketeers! I know I said I designed this case for 1500 psi, but it's really a better idea to limit this case to about 900 psi. To get the full pressure you need to do a few things different, and I neglected to clarify this in the video. Cheers! Charlie

[@guerrerohr5500]

Charlie, you cannot imagine what kind of impact your videos are making on people, seriously, they contain the necessary information to start actually making a rocket engine, more specifically to this series, how to create a solid rocket engine. Your channel has encouraged me to actually learn in detail this kind of stuff, and it has gone so far as to make me want to design and build a liquid rocket engine. So, thank you Charlie, keep doing what you’re doing, because it really benefits the community, again, thank you.

[@CanineDefenseTechnologies]

I love this series! I'm glad my Dad stopped me from following one of those PVC rocket motor tutorials a few years ago! Reading basic solid motor concepts makes it look so easy that people like us who are not engineers know just enough to hurt ourselves. By watching this series, there's so many things I never imagined to consider or might have know otherwise! Not sure if I'm that comfortable with tackling a DIY solid motor myself yet, but still so stoked to see more videos about it! Especially can't wait for the manufacturing part, the fun part!

[@matthewstuart2054]

Finally, someone who gets straight to the point! No stuffing around, well executed tutorial.

[@doom8566]

Mr Garcia, thank you for making your input available for everyone here on KZbin! Rocketeering is such an interesting industry. I hope you will continue this series, as I have learned a lot of that other creators don't cover in their videos. I hope you're enjoying yourself with this project as well. I'll see you in the stratosphere my friend

[@TheBeast-qm4de]

Hey Charlie I was hoping you could continue this series.

[@vedantmomaya1533]

Tyssssm for making these videos, there is literally no in depth practical rocket lectures available on the net

[@xylafoxlin]

thank you thank you for adding a few wrinkles to my smooth rocket brain

[@ShubaMurthy]

Thank you for addressing how PVC pipes aren't worth it! Interesting to know that hand calculations work just fine. All the nuances described here are just what I needed, I look forward to the next video eagerly :)

[@piebrowillo5762]

Just a random tip for working in conceptualise metric pressure. I find it easer to work in bars 10^4 pa which is almost exactly 1 atmosphere of pressure. Makes it easy to visualise for me at least. Love the videos please keep up the good work

[@Unique-Concepts]

Most Underrated channel.....

[@Ameliaross106]

Love that SRB intro thing. Thank you for being such a role model to me, I would likely not be interested in rocketry the way that I am without these very interesting videos. Your videos remind me that I need to engineer stuff to be much safer than they are so I don’t get hurt with engineering and more importantly rocketry. I got a copy of rocket propulsion elements almost a week ago and I probably wouldn’t love rockets as much as I do now without your videos. So thank you for being a role model to me.

[@Ameliaross106]

I think KZbin broke, I edited my comment to make it more clear and KZbin got rid of the heart 😢. idk if that’s a normal thing or not

[@YukonK9]

@@Ameliaross106 he rehearted, also if you edit comments after heating, it auto unhearts

[@Ameliaross106]

@ Yukon, thanks I never knew that. The more I know.

[@michaelnelkin2564]

Can't wait for the manufacturing video! Buying materials and heading to my school's makerspace!

[@bocajnamyerf]

Learning a lot! Super excited for upcoming vids

[@ahmedal-khazraji9112]

CG thanks for the info, I am just starting to build my rocket, and I found your videos very helpful. keep up the hard work!!!

[@GregaJerin]

So, when will part 3 be uploaded?

[@stevenboyce661]

Charlie, This has been just what I have been looking for for years. Fantastic work. Thanks so much for sharing and for sharing your knowledge. I am looking forward to more. Let me know how I can help.

[@Ameliaross106]

You should make a video on liners and propellant adhesion to the liner. Furthermore if you could cover insulators and there adhesion I think that would be very interesting. I haven’t found much on the internet covering this.

[@avirajpawar7198]

when the manufacturing video will be uploaded, please upload it !!!

[@mayurholla6509]

Hey Charlie, where u been man! great videos

[@oldfridayboy5597]

Yeah I agree he should upload more to keep my Rocket Projects sane😂

[@joegrisham5706]

waiting for part 3

[@joegrisham5706]

I cant wait another 10 months for part-3

[@rocketcello5354]

even though I'm messing around with (hopefully) E-class sugar motors, this is still so useful, as if I design it to be safe using more energetic fuels (such as the mix you're using), then it should work with sugar motors. thanks!

[@mojaverockets]

I've built both sugar motors (up to Q-class) and apcp motors. The chemical composition of the propellant does not determine what pressures your case will experience...I've blown cases apart with both propellants. Good design and propellant casting are important for both.

[@rocketcello5354]

@@mojaverockets thank you. how would you recommend to cast sugar prop? ATM, I have a 3d printed mould that peels away on the sides, and pulls out for the grain geometry (ATM just a simple BATES). Would that work, or am i just stupid? should I cast it into the liner, and only have a 3d printed BATES mould?

[@studywithme8055]

What kind of filament do you use? You need pretty high temp in order to use 3d printed material as a jig for sugar motors.

[@rocketcello5354]

@@studywithme8055 was planning to do it with PLA, realized how bad that idea was, and now using cardboard tubes for the shape and a jig that centers the BATES tube.

[@studywithme8055]

@@rocketcello5354 Did you think about carbon fibre nylon filament?

[@stekra3159]

50 minutes of rocket science yay!!!

[@zog9850]

I know I'm coming to this 4 years after-the-fact, but is there more to this series? I'd really like to see how you machined the case, the forward closure, and the nozzle

[@joegrisham5706]

I Want to learn more.Waiting for part-3

[@enternal_sly5443]

Ok Charlie, doing the calculations you mentioned about case loads, for a case of 2.00 inches ID, and for a pressure of 1500 psi, the axial load is 4712 lbs, like you said. Then you mentioned the tensile stress in the cross section of the case is 13.5 ksi, or 13,500 psi. How did you get this number??? By my calculations, the tensile stress should actually be 11.6 ksi, or 11,635 psi, this was by dividing the 4712 lbs by 0.4050 inches which is the cross sectional area of the case. Please explain your calculation. Thanks

[@VikingRocketeer]

One thing I would Change Charlie. You are using a term explode. This can invite regulatory response as it would be treated as a explosive. The correct terms are CATO or Rapid disassembly.

[@AstroCharlie]

Hi Conway, my choice of language was very deliberate. NAR/TRA have lawyers and money to respond to regulatory challenges, and in fact, have already done so. The is legal precedent for propellant being considered non-explosive. People getting started in this hobby who do not understand the significance of the phrase 'CATO' or 'RUD' have no protection for the possibility of hot gasses and shards of metal beyond the instruction they get. Weasel words have no place in safety critical discussions.

[@mojaverockets]

I think Charlie's use of explode as a verb is correct. Here is one definition of explode: "burst or shatter violently and noisily as a result of rapid combustion, decomposition, excessive internal pressure, or other process, typically scattering fragments widely". That is different than the noun 'explosive'

[@POLY_Explains]

Hello to you visiting the comments section! I've just started KZbin videos on the space theme and I'd love to get your feedback. So if you have 5min don't hesitate to give me a little comment!

[@shere_kan8329]

Have you given up on that project ? It would be great to see you back for that awesome project !

[@bluc0bra]

thumbs up from me, look forward to the next one!

[@yottaplex2239]

could you do a video explaning expansion waves and method of characteristics for a bell nozzle please?🤩

[@MichaelLloyd]

Great series but I I don't see the rocket motor machining video. Thanks to this series the plans for me building a "sorbitol motor" are on hold.

[@hudsonkortus7463]

Where can buy ammonium perchlorate?

[@hudsonkortus7463]

I am trying a hybrid rocket engine, is the pressure equasions used in the lase video the same for a hybrid motor as a composite motor?

[@artashesharutyunyan3693]

Very good video Charlie, thanks a lot. But I have a favor to ask from you and from all other rocketeers)))) Here in Armenia there are only 3 guys that are in this hobby, so everything comes really hard. We had a lot of Chinese rocket engines (for single use) that used up very fast and new once nobody is shipping anymore cause it is hazard. So we decided we make our own. Now I have a rocket that is about 1.8kg, how much thrust do i need to push it to 2000m height. (that is 300m from sea level, my city is on 1000m mark). Based on this info then I would try to make an engine that is large enough to get that thrust. Or any specific engine you can recommend that we can learn its data online

[@MrChuckmason]

Great video! Is there anymore on this series?

[@joeymurphy2464]

Looks like your Patreon link is missing from the description! :)

[@AstroCharlie]

Self promotion fail. It's fixed now - thanks!

[@CUBETechie]

8:20 should 8.8 Bolts be enough? 800N/mm² and 640N/mm² is the stable strength to come back before damage.

[@akosmaradi5281]

Where do you buy the material for your graphite nozzle from? As far as I can see they are extremely expensive.

[@ThisGamerAlex]

Great serie of videos about making your own solid rocket motor! But I'm afraid that you won't continue uploading more videos about this, since it has been almost a year and a half since this one.. Is that the case, or you plan to continue the serie? I'm thinking of making my own rocket as my final project on high school and this would be really really helpful to learn about it from someone that actually knows what he's doing! Hope you see this comment, and have a great day.

[@gregh3729]

hello when I try to run the code it tells me that "matplotlib" is missing, I try to install it on the command prompt but the result doesn't change; does anyone know how to do it?

[@tomh2628]

Great job on the video. My friends and I have been trying to build a rocket engine using potassium chlorate as the oxidiser, silicone as the binder/fuel and a 3d printed case. They keep exploding. Do you think this is because the case isn't strong enough or because the fuel has a spike in burn rate as the pressure increases.

[@tomh2628]

We a actually just got out first solid rocket motor to work today!

[@briansimons2703]

@@tomh2628 what was the problem?

[@tomh2628]

@@briansimons2703 we found that surface area on the grain had a big effect on burn rate (which in hindsight was kind of obvious) so we just used end burners instead of cored rockets. With a potassium chlorate oxidiser the rockets are much more likely to explode so if you want to make a large cored rocket KClO3 isn't really an option. Were working on making potassium perchlorate (KClO4) by electrolysis but for now the potassium chlorate end burners work well enough.

[@firstnamelastname.7749]

@@tomh2628 when you use silicone as a binder, do you have problems with glass slag sticking to the nozzle?

[@tomh2628]

@@firstnamelastname.7749 Sort of, the residue stuck to the whole combustion chamber but it never actually clogged the nozzle. We've since switched to using nitrocellulose as a binder with acetone as a solvent. We haven't had much success yet because the consistency isn't ideal and it forms big sticky clumps that aren't great for forming complex cores but it doesn't leave the residue that the silicone did. We've also tried dextrin as a binder and we've been able to fly a rocket using it but when dry the fuel is pretty brittle so we could only really do end burners. As a side note we've just figured out how to make potassium perchlorate so we'll be using that as our oxidiser in the future because of its superior stability and oxygen content to the potassium chlorate.

[@Nammaooruscience]

Awesome Charlie 👍 Can u give some reference about endplates thickness calculation?

[@bencoman]

Hi Charlie. Those links to onlinemetals.com appear broken. They seem to have a "new site". Could you update the links. Also, perhaps include descriptions of item parameters in your text, in case links break in the future. This video is going to be useful to people a long time into the future. For my own future reference... Case Tube: Aluminium Tube 6061T6 OD 2.25" ID 2" Closure: Aluminium Tube 6061T6 OD 2" ID 1.5" Clearance Drill Bit: 1/8" Tap Drill Bit: 3/32" Tap: 4-40 Screws: 4-40 Thread Size, 3/16" Long, Black-Oxide Alloy Steel Hex Drive Flat Head Screw Countersink: for Screws, 82 Degree, 1 Flute, 1/4" Body Diameter

[@marlowp5234]

Excellent work, friend. Thank you for this. I have to ask, what do you think of the simulator "Kerbal Space Program"? You seem the most qualified to ask.

[@CUBETechie]

What about an normal drinking can with an hole in the ground? It has a very interesting geometry.

[@Andres-gr3us]

How do you protect the aluminum case from the very hight temperature of the combustion?

[@mojaverockets]

adding an insulating liner (cardboard, phenolic, etc) between the propellant and the case.

[@SevenDeMagnus]

HI. I think I'm also a rocketeer, a solid motor- roman candle rocket:-)

[@redfive9559]

Are you going to use potassium nitrate?

[@joeymurphy2464]

Potassium nitrate is often used by beginners as an oxidizer, since it's readily available as stump remover. However, it's really not that good as an oxidizer, and the sugar it is usually paired with as a fuel yields a propellant that doesn't perform nearly as well as modern composite propellants. Charlie touches on this in the video. I expect that he will use ammonium perchlorate as his oxidizer, rather than potassium nitrate.

[@mojaverockets]

@@joeymurphy2464 KNO3 isn't just used by 'beginners'. I know people in aerospace that use it for their own personal 'amateur' rockets...it is in fact, the world's most commonly used amateur rocket propellant. I've been using it for years for motors from A thru Q impulse and we are now working on a 360,000 Nsec S-26,000 'sugar' motor. My K-impulse 'sugar' motor reloads cost about $4 and M impulse sugar motors cost about $12 per reload and I now have over 3 million Nsec of 'sugar' propellant to my credit. If you are making rockets for the military or to launch something in orbit, sugar is not the propellant you want to be using. But for student teams that want to experiment with things like electronics, recovery, air brakes, etc, 'sugar' offers them a low-cost alternative for conducting more launches at a lower cost. kzbin.info/www/bejne/Z6bNqX-XlL-Jf68 As for performance compared to an APCP propellant motor? kzbin.info/www/bejne/rnWnY2l8rJiDoNE Full disclosure, I do solid and liquid motors of many different types and often use several thousand dollars of apcp motors a year for different things but don't knock 'sugar' propellant as a viable rocketry propellant...it does blow up on occasion but so does any rocket propellant including apcp but at a much higher cost for ap kzbin.info/www/bejne/e4DCmnqsd71rbcU

[@junuhunuproductions]

The case.py inside Github link seems to calculate O-ring stretch related properties, rather than tensile strength. Was that intended?

[@AstroCharlie]

It should have functions for both - You get a sneak preview of episode 4 where we do o-ring gland sizing.

[@junuhunuproductions]

@@AstroCharlie Got it!

[@robertcook5380]

Charlie! Question- I just downloaded open motor. In a practical sense do end burn motors keep function in longer formats? Like I known it works small scale but do you know anyone doing it at the larger scale?

[@mojaverockets]

"...keep function in longer formats?' The longest end burner I've done was about 60 seconds. The big issue is preventing the case from overheating during that time. A good insulating liner, lower temperature burning propellant and choice of case materials are important.

[@chomkypanda]

This was a great video. Would it be possible for you to make the whole "book" you wrote (xD) on bolt preload and put it in a google docs so that we can have easy access to it and you won't have to make a lengthy video on it and you can move ahead to make a video on complicated things like fuel, how to make the fuel, should we make the fuel ourselves, liners, etc.?

[@Trupal050]

Everyday Astronaut sent here.

[@JuanHernandez-mq2go]

are you going to build the structural fuse? or are you going to buy it?

[@astrofox2409]

I've got to ask where you got the numbers for the 4-40 bolt shear strength, as the numbers at 8:22 show that the bolts should withstand a load of 375 lb, while you mention that the shear strength of the bolts is 940 lbs in the segment right after. It's a bit confusing to me how you end up calculating the 8 bolt requirement to fasten the bulkheads in and wanted to gain further insight on how to calculate that. I'm personally trying to work on a project to measure combustion chamber pressure for solid rocket motors and ultimately I've decided to go from using snap rings to instead using the radial bolt method, though, I'm still trying to figure out the math behind a radially bolted enclosure. The video series has otherwise been a huge help to me in better understanding how to make casings that are potentially better than using a basic old snap ring system. I'm trying to apply this to a 38mm motor so it's definitely going to get interesting, and hopefully I can build up from there to 98mm motor hardware. I'm wondering if switching from 4-40 bolts to say, 2-56 bolts might be more appropriate. This brings me to my next question: how one would incorporate a secondary row of bolts into the casing? What kinds of calculations would be involved with doing so, and what other resources should I look to in order to better understand how this works and possibly even how such expressions can be derived? Thanks for the help! EDIT: I just saw the fine print at 8:22, though, I'm still confused on how one reaches the 940lb number for the shear strength of the bolts.

[@AstroCharlie]

This was an error - I edited the video months after I filmed it. 375 lbs is the correct value. To calculate the number of bolts multiply the chamber pressure by the area of the bulkhead to get the load the bolts need to survive. Divide this number by the strength of your bolts and round up to figure out how many bolts to use. Here is a write up. wikis.mit.edu/confluence/display/RocketTeam/Radial+Bolted+Case+Design

[@astrofox2409]

@@AstroCharlie Ah, alright. I see your comment on lowering the chamber pressure to 900 psi, and running through the math I do get ~7.5, which would round nicely to 8. If I used 2-56 bolts instead, would I use the values mentioned at 8:22 or would I have to find my own shear strength for the bolts? Thank you again

[@aksh_x_]

@@astrofox2409 My design needs to at least withstand the pressure of about 991psi but I will go with 1100psi, I was also confused at the same part of the video and then when he commented to limit it to 900psi it got me more confused bout why he said that. Reading the above convo cleared my doubt. Thanks!

[@mojaverockets]

@@AstroCharlie You should add the corrected (8:35+) amount in your description for people that don't read through all the comments.

[@intuitivealpha328]

I need an EPP license how do you contain, the motor during construction for safety?

[@karinherrmann637]

Awesome video Charlie. I am working on my own motor. When stainless steel is used as a casing material and the combustion temp. is 1500 C, do I need a liner for thermal protection ? Since I use Bates graines and the burn time is only 1.5 sec. I think I should be fine without a liner since the yield strength isn't really suffering under high temp. like aluminium. Greetings from Germany. PS. the longer the video the better

[@AstroCharlie]

Yes - you always need a thermal liner if you plan on reusing the case.

[@karinherrmann637]

@@AstroCharlie When my outer surface is inhibited is it possible to use the inhibitor ( BT-70 body tube) as a thermal liner.

[@varunahlawat9013]

I was waiting for the follow up videos but this playlist seem to have been out of interest now. I'm soon starting work on a rocket motor having near L class of total impulse.

[@MOBAEsportsCentralMain]

Thanks for sharing see yaa.

[@etstudios]

I am one of those people who happens to use PVC, however in my defense I am continually making sure that what I do is safe and one of the ways I get around the PVC shooting bits of itself at me is to use very low pressure tolerant end caps so it essentially dumps all the fuel inefficiently out the top of the motor if there is even a slightly higher pressure than I would want inside. Side note: the main reason I use KNO3 and Sugar with PVC is because where I live as it is very difficult to come across even some of the more easily found materials many others have access to. Shipping costs being the main concern over here in South Africa when it comes to getting such things as the fuel grain you want to use or get correctly sized aluminium for the motors.

[@timhoksong4396]

I am so glad to know that you also used PVC as the rocket casing material since I am working on the same material as you do. What was your recorded chamber pressure with PVC casing?

[@mojaverockets]

PVC casings for 'sugar' and other type of motors can be just as 'safe' as other materials if designed correctly. I've blown up both PVC, fiberglass, aluminum, and steel cases doing rocketry. PVC cases will often fragment into many pieces (hundreds?) but because of their low mass, they do not travel as far. I've had 6061 T-6 aluminum cases fragment into as many as 14 sharp jagged edge pieces that fly a lot farther than PVC and with more force. I've also had steel cases fragment into just a few, 2, or 3 pieces that don't travel as far because of their mass. After years of experience, I'd much rather be out in the open 200' away from either a PVC or steel case failure than an aluminum case failure. Full disclosure, I use many different types of case materials for my motors depending on the use.

[@ThatRealredheadedkid]

Why not use model rocket fuel and aluminum foil with durable plastics around it?

[@AstroCharlie]

That will no work well, if at all. I have the ability to make a much more effective rocket using materials that are just as cheap if you're willing to purchase from somewhere other than the hardware store.

[@nopea3]

can you add metrics into your simulator. I am not familiar with inches so mm/cm would be much better

[@AlejandroMunoz-ns3dq]

GOAT

[@JoneKone]

Somebody has to start a gofund me and we need to get Charlie a new camera :I I love to watch your videos but it's difficult, cause it's not sharp... and sometimes i miss some reference pictures when my eyes are too stressed to watch... :) I would buy you a new camera, but I'm poor.

[@ruturajyellurkar9588]

If you bolt the motor casing to the body, you won't be able Thrust Vector it right.

[@AstroCharlie]

This motor will not be thrust vectored. It is much larger than the motors that are typically gimbaled and the airframe would be uselessly large.

[@ruturajyellurkar9588]

@@AstroCharlie So do you plan on using RCS thrusters? Since its quite a big rocket, it needs some sort of active attitude control.

[@aksh_x_]

@@ruturajyellurkar9588 Ion think so, basically it'll have fins and won't have any any fancy attitude control systems.

[@timthatshim8037]

Can I keep you😜?

[@rcexpfpv481]

Idk what it was about this video but the vibe was off. Good thing I didn't vibe check this vid

[@barry7608]

If your going to put your vids forward as "professional" don't waffle about PVC and human flesh being of similar composition, its utter bullshit. The reason it may be difficult to see with x ray is x ray opacity and nothing to do with chemical composition!! Other wise your vids are well a touch.....

[@Marusija8]

To much talking and doing nothing...!!!

[@vertex3243]

?????????