designing a model rocket, proportions of components

[alessia]

I am designing a model rocket and need to know the proportions every component needs to have. For instance, i saw somewhere that the nose cone length must be about 3 times the diameter of the body tube, is this true? where can i find this information so i can cite it in my project and where can i find the proportions for the rest of the components? It would be great if someone could give me specific links and not just say look in forums and such.
Thank you so much

 

[SolarYellow]

You could do worse than reading everything here to start:

http://www.ninfinger.org/rockets/EstesPubs.html

 

[neil_w]

Design of rockets varies very widely. There are no fixed proportions that any particular part must have. The only thing that is ironclad is that the CG/CP relationship must yield a stable rocket.

If you download a copy of OpenRocket you can look at the various built-in examples (File -> Open Example) to see just a bit of the variety that is possible. If you look at the Part Library for nose cones you'll see a bewildering variety of shapes and sizes.

Looking through old Estes catalogs as suggested above will show you even more.

 

[Antares JS]

For instance, i saw somewhere that the nose cone length must be about 3 times the diameter of the body tube, is this true?

No, that's not true.

I would recommend Harry Stine's "Handbook of Model Rocketry" for source material on this. Experimenting in OpenRocket as suggested above is also a good idea.

 

[SolarYellow]

Looking through old Estes catalogs as suggested above will show you even more.

Not catalogs, tech pubs:

• Estes Industries Guide for Rocket Clubs
• Estes Industries Technical Report No. TR-1 - Rocket Stability
• Estes Industries Technical Report No. TR-2 - Multi-Staging
• Estes Industries Technical Report No. TR-7 - Front Engine Boost Gliders
• Estes Industries Technical Report No. TR-8 - Model Rocketry Study Guide
• Estes Industries Technical Report No. TR-9 - Designing Stable Rockets
• How Cold Propellant Rockets Work
• Model Rocket News
• Ad Insert (date unknown, but late 1960s or so)
• Vol 3, No. 4 (August/September 1963)
• Vol 4, No. 1 (February 1964)
• Vol 6, No. 2 (December 1966)
• Vol 7, No. 1 (December 1967)
• Vol 8, No. 2 (November 1968)
• Vol 9, No. 1 (February 1969)
• Vol 9, No. 3 (November 1969)
• Vol 10, No. 1 (February 1970)
• Vol 11, No. 1 (January 1971)
• Publication Aids Available for Model Rocketry
• Suggested Projects in Model Rocketry

 

[neil_w]

Not catalogs, tech pubs:

Whoops, my bad. Those are good resources.

Looking at the catalogs will, though, show the variety of designs that are possible.

 

[lakeroadster]

The only thing that is ironclad is that the CG/CP relationship must yield a stable rocket.

Awesome name for a tractor motor rocket....

 

[PDawg]

I don't use open rocket much but none of my designs are radical or extreme. I often look up the specs of a production kit and try to stay close to what the Pros have designed. Almost all of my 50+ designs flew great.

 

[bjphoenix]

I am designing a model rocket and need to know the proportions every component needs to have. For instance, i saw somewhere that the nose cone length must be about 3 times the diameter of the body tube, is this true? where can i find this information so i can cite it in my project and where can i find the proportions for the rest of the components? It would be great if someone could give me specific links and not just say look in forums and such.
Thank you so much

"nose cone must be..."
No there aren't any absolute rules about that, it is strictly up to your preferences and the goal for the rocket. For instance if you want maximum altitude then some proportions would be better than others.
I'll say there are 2 absolute rules in rocket design- it has to be aerodynamically stable and the weight has to be below the limit for the motor being used.

 

[SolarYellow]

... and the weight has to be below the limit for the motor being used.

A problem is that that is variable depending on flying conditions. What is GTG in still air may be a problem with a breeze, even well below the 20 mph launch cutoff.

 

[Titan II]

...

 

[86mustang408w]

I started using OpenRocket for the first time 2 weeks ago, they all the pre-selected parts, and you can enter your values with them. Check it out, watch a few YouTube tutorials like I did. BYU has good one I think it was. Ill post more info if you're interested.

 

[Pem Tech]

"nose cone must be..."
No there aren't any absolute rules about that, it is strictly up to your preferences and the goal for the rocket. For instance if you want maximum altitude then some proportions would be better than others.
I'll say there are 2 absolute rules in rocket design- it has to be aerodynamically stable and the weight has to be below the limit for the motor being used.

Yeah, what he said.
Outside of those limitations you are free to create the most terrifying and wonderous rockets imaginable.
A Sim program? Yes, it would be a great idea, OpenRocket is very popular. It will help you with CP/CG relationships. However, don't let the program limit you.
It is just a tool to check your Mark I calibrated eyeballs and mind-sim. After several builds, crashes, fires and personal tragedies you will start to develop an "eye" for what may and may not work. It is the ability to mind-sim designs and it comes with experience.
Now go forth and build imaginative rockets that don't spear wildlife or initiate international incidents!

 

[SolarYellow]

Heck, I'll answer the question "as asked" - sort of.

Build a scale Little John with the clipped-delta prototype fins. It's perfectly proportioned.

 

[BABAR]

What are your goals for YOUR first rocket? How many kits have you built and flown?

Above posts include a lot of good advice

If goal is a simple basic rocket with three or four fins, a tube, a nose cone (probably a good way to start for a first shot), so long as it looks roughly like most of the rockets you see in catalogs or on this forum (ironically NOT in the scratch build section) you should be good. Stay away from designs by @neil_w , @lakeroadster , @Daddyisabar , and especially @BABAR , you need a few simple successful design and launches before you go bat ———— crazy.

Once you have a design planned, feel free to post it here and you will get lots of (mostly helpful) feedback.

Aside from the CG/CP rules, only other rules are

Be Safe

Have fun





Straight trails and short walks.

 

[86mustang408w]

I am designing a model rocket and need to know the proportions every component needs to have. For instance, i saw somewhere that the nose cone length must be about 3 times the diameter of the body tube, is this true? where can i find this information so i can cite it in my project and where can i find the proportions for the rest of the components? It would be great if someone could give me specific links and not just say look in forums and such.
Thank you so much

I bought a good book that goes from level one stuff to level 3. There's no "set" rules but you can build horrible designs that could hurt someone or damage property. OpenRocket is great, definitely helps with flight sims and stability, YouTube has many videos on beginners model rocketry.

 

[bjphoenix]

I'm starting to design a couple of new builds and was thinking about this to get a starting point. I'm usually buying off the shelf nose cones so I'm stuck with what I can find but most LPR nose cones that I find are more like 4:1 or 5:1 length to diameter. I was trying to think what body tube length to start with and so I went through photos of various rocket designs that I liked and found that length to diameter of the body tubes ranged from 8:1 to 11:1. Actually I was thinking I was going to go up in tube diameter so I needed to be on the shorter side regarding the tube diameter so I was picking out the shorter rockets that I liked that I didn't consider to be short rockets. Something like the HiFlier XL or the Vapor have length to diameter much higher than 11. Anyway this gives me a starting point so I can start putting things into OpenRocket.

 

[BABAR]

photos of various rocket designs that I liked

picking out the shorter rockets that I liked

key phrases.

draw up what you like, then play with it in the sim.

 

[bjphoenix]

key phrases.

draw up what you like, then play with it in the sim.

Sim programs are a lot of fun. I'm more interested in fine tuning rocket size, weight and motor choices to get the performance envelope that I want. My club has a large field and a small field so I'm continuously trying to find the combination I like best for each field.

Long ago I used to sketch rockets a lot. In my profession I use autocad so I've stooped to drawing them in autocad, even to the point of coloring in the areas to test different paint schemes. Open Rocket and Rocksim have taken all of that to a whole different level.

 

[SolarYellow]

I'm starting to design a couple of new builds and was thinking about this to get a starting point. I'm usually buying off the shelf nose cones so I'm stuck with what I can find but most LPR nose cones that I find are more like 4:1 or 5:1 length to diameter. I was trying to think what body tube length to start with and so I went through photos of various rocket designs that I liked and found that length to diameter of the body tubes ranged from 8:1 to 11:1. Actually I was thinking I was going to go up in tube diameter so I needed to be on the shorter side regarding the tube diameter so I was picking out the shorter rockets that I liked that I didn't consider to be short rockets. Something like the HiFlier XL or the Vapor have length to diameter much higher than 11. Anyway this gives me a starting point so I can start putting things into OpenRocket.

I might have said it earlier in this thread, but the Little John, to me, is just the perfect rockety-looking rocket. Its payload is pretty short. Lots of other sounding rockets are only a little longer aspect ratio when you consider just the motor. Payloads on sounding rockets can vary greatly, which is where you get the range of forms and long, skinny shapes.

Estes makes most of its bigger designs much longer than optimum for performance. It's super-low-cost, once you have all the other elements of the kit in place, to include another tube and coupler in the bag and have a bigger ("better"/more/higher value) rocket. Also, they are selling to the general consumer, where finding a good-size field to fly from may be challenging. So a bigger, cooler-looking rocket that's less likely to fly away and be lost is a win for them and their typical customer profile. Just for an example, the Star Orbiter is a much better rocket if you leave out one of the body tubes and add just enough nose weight to ensure it's stable.

If you play around in OR and believe what it says, you'll typically find that for a 3/4FNC rocket above a minimal power level, apogee increases when you shorten the body tube as much as practical and add whatever nose weight is required. Long and skinny looks zoomy, but skin friction drag is a thing. Also, long and skinny bends and ultimately buckles more easily, so as you push the rocket harder, it is far more likely to shred than a shorter one made with otherwise the same specs. See Star Orbiter...

 

[neil_w]

I'm usually buying off the shelf nose cones so I'm stuck with what I can find but most LPR nose cones that I find are more like 4:1 or 5:1 length to diameter.

Have you looked at BMS and eRockets? Between them they have about a billion LPR nose cone profiles. They're balsa, which some folks object to (I don't), but for me the priority is generally getting the shape I want, in whatever material.

 

[ljwilley]

For instance, i saw somewhere that the nose cone length must be about 3 times the diameter of the body tube, is this true?

Ummmm.... yeah probably don't believe everything you read because I've never heard that in my life. You should probaly make sure it is stable using a program like openrocket or do a swing test, though to make sure it is stable.

I'm usually buying off the shelf nose cones so I'm stuck with what I can find but most LPR nose cones that I find are more like 4:1 or 5:1 length to diameter.

And for you, check out ASP rocketry, they have TONS of balsa noses, all shapes and sizes. Lot's of transitions and other supplies too!

 

[bjphoenix]

Have you looked at BMS and eRockets? Between them they have about a billion LPR nose cone profiles. They're balsa, which some folks object to (I don't), but for me the priority is generally getting the shape I want, in whatever material.

I've been looking at things on eRockets, and I've been on BMS before but haven't looked for specific things recently. Right now I'm focused on BT70, BT80 and BT101 sizes. I've found 2 plastic cones for BT70, and one each pointed cone for BT80 and BT101.

They way I do my recovery systems I have snap swivels on the ends of the shock cords so I can switch nose cones around at will. I have a BT80 rocket (Executioner) and BT101 rocket (Big Daddy) so technically I can build more designs in those sizes without needing to buy another nose cone.

I'm still contemplating my designs, then I'll decide what to buy, so I'll check BMS and eRockets again.

 

[neil_w]

Yeah, the selection in those sizes is a lot more limited, but IMHO those are really pushing into MPR rather than LPR.

 

[bjphoenix]

Yeah, the selection in those sizes is a lot more limited, but IMHO those are really pushing into MPR rather than LPR.

Well I know various people who push the Big Daddy well into high power but that's not me. But yes I intend for the BT-80 and BT-101 sizes to go slightly into MPR.

 

[BABAR]

Well I know various people who push the Big Daddy well into high power but that's not me. But yes I intend for the BT-80 and BT-101 sizes to go slightly into MPR.

I do intend to mean well here, but this last line is making my spider sense tingle.

My apologies if you are experienced in ALL of the following:

building mid-power
flying mid-power
SUCCESSFULLY RECOVERING midpower.

if so, build away and ignore the rest of this (or just ignore the rest regardless, unasked for advice is usually ignored anyway.)

First, "mid-power" itself isn't an official level, and no certification exists nor is required for E, F, and G motors (well, I think maybe there are some G motors that may be technically high power, but I digress.)

Second, just from you initial question I suspect (again perhaps wrongly) that you do no have a whole lot of experience with LOW POWER. A logical and I believe likely successful pathway is to build, fly, and successfully recover a number of low power kit rockets first. At that point you can either move into mid-power kits, or scratch design some LOW power builds. In any case, while your enthusiasm is wonderful, I'd recommend at least building some mid-power kits before scratch building mid-power rockets.

I'd also like to know more about your flying field. I believe that ALL rockets should be launched with a "reasonable" probability of recovery WITHIN a safe recovery field. I cringe every time I read about somebody saying they are going to put in a Z motor and "yeah, I know I probably won't get it back, but......"

From Trip Barber's Safety Lecture 2020. Attached is the PDF. Good read with good pics.

"Both parachute recoveries and ballistic trajectories can land farther away than vertical-flight apogee altitude. It is unacceptable for these to occur outside the boundaries of the launch site."

Nearly 75% of failures were recovery issues. Bigger rockets don't always go to higher altitudes, but often the temptation is to fly them higher. And bigger rockets are more likely to have unpleasant consequences if they land in unintended areas. start small and work your way up.

 

[bjphoenix]

I do intend to mean well here, but this last line is making my spider sense tingle.

My apologies if you are experienced in ALL of the following:

building mid-power
flying mid-power
SUCCESSFULLY RECOVERING midpower.

I'm not sure what gives you that idea but I've been launching rockets since 1965 and I'm level 1. I have 4 rockets with 29mm and 38mm mounts and 2 more in construction but it is easier for me to get Estes motors than Aerotech so for most of my casual launching I stick with black powder motors. My club has a large field and a small field so I try to optimize designs for both. This is where the proportions come into play. My strategy is to keep the rocket where I can see it at apogee. I've been running sims to play with different rocket sizes and motor combinations.

For a small field- I like BT60 size tubes. Consider a Big Bertha- it will launch well enough on a B6-4. Now consider an Estes ESAM. It is roughly the same size but enough heavier that it is barely acceptable on a B6-4. It will fly higher on a C6 but the problem is it is slow enough off of the pad to weathercock and if you weathercock a rocket with a long burn motor you have a long way to walk. So there is a limit to how big you can go and get reasonable flight. To some extent the answer to this is to use a C5 or C11 motor and I've done that too but those aren't sold in HL so those launches become much more expensive. And if you put a D12 into a BT60 rocket you get more altitude than needed for a small field. I've noticed in our field we seem to have about 3 in 4 chance of successful recovery and I've waded out into a nearby lake to recover 2 D112 rockets owned by other people. So my conclusions are to build BT55 rockets for that field, or simple BT60 rockets such as the Baby Bertha or Estes Patriot Missile. This got me interested in how a BT70 rocket would work with a D12. I already have a Big Daddy and an Executioner and launch them frequently with D12 so I know how they fly, I'm looking for something a little higher.

For a large field- I do more launching of larger BT60 rockets with D12 but depending on the conditions those will go out of sight. I have a stretched rocket based on the HiFlyer XL parts and last weekend I launched it on a D12-5, completely out of sight. I managed to see the cloud from the ejection charge and picked it up well enough to retrieve it. I'm thinking a BT70 based rocket on a D12 would be a bit lower and a bit easier to see so that's why I've been running sims of them. I like the way the Executioner flys on an E12 but it can be a little slow off the pad. My theory is that it needs a cluster of two D12 to get higher initial thrust so I'm doing sims of that too. And extending it to BT101 size and running those sims. It has been some years since I've actually launched a cluster but I did my first cluster in 1968. I still have that Estes Ranger.

 

[SolarYellow]

The Executioner might be happier with a Quest E26. Pretty close to the same impulse as an E12; still far from a full E like the E35, even less than two D12s.
Or even a D22 gets its thrust up a little quicker and holds it there.
https://www.thrustcurve.org/motors/AeroTech/D22W/https://www.thrustcurve.org/motors/Estes/D12/
A Quest might be just right for you, and they're available at ACSupply.

You might also be a candidate to participate in the BT-101 thread I started a few weeks back.

 

[BABAR]

I'm not sure what gives you that idea but I've been launching rockets since 1965 and I'm level 1. I have 4 rockets with 29mm and 38mm mounts and 2 more in construction but it is easier for me to get Estes motors than Aerotech so for most of my casual launching I stick with black powder motors. My club has a large field and a small field so I try to optimize designs for both. This is where the proportions come into play. My strategy is to keep the rocket where I can see it at apogee. I've been running sims to play with different rocket sizes and motor combinations.

For a small field- I like BT60 size tubes. Consider a Big Bertha- it will launch well enough on a B6-4. Now consider an Estes ESAM. It is roughly the same size but enough heavier that it is barely acceptable on a B6-4. It will fly higher on a C6 but the problem is it is slow enough off of the pad to weathercock and if you weathercock a rocket with a long burn motor you have a long way to walk. So there is a limit to how big you can go and get reasonable flight. To some extent the answer to this is to use a C5 or C11 motor and I've done that too but those aren't sold in HL so those launches become much more expensive. And if you put a D12 into a BT60 rocket you get more altitude than needed for a small field. I've noticed in our field we seem to have about 3 in 4 chance of successful recovery and I've waded out into a nearby lake to recover 2 D112 rockets owned by other people. So my conclusions are to build BT55 rockets for that field, or simple BT60 rockets such as the Baby Bertha or Estes Patriot Missile. This got me interested in how a BT70 rocket would work with a D12. I already have a Big Daddy and an Executioner and launch them frequently with D12 so I know how they fly, I'm looking for something a little higher.

For a large field- I do more launching of larger BT60 rockets with D12 but depending on the conditions those will go out of sight. I have a stretched rocket based on the HiFlyer XL parts and last weekend I launched it on a D12-5, completely out of sight. I managed to see the cloud from the ejection charge and picked it up well enough to retrieve it. I'm thinking a BT70 based rocket on a D12 would be a bit lower and a bit easier to see so that's why I've been running sims of them. I like the way the Executioner flys on an E12 but it can be a little slow off the pad. My theory is that it needs a cluster of two D12 to get higher initial thrust so I'm doing sims of that too. And extending it to BT101 size and running those sims. It has been some years since I've actually launched a cluster but I did my first cluster in 1968. I still have that Estes Ranger.

I slouch corrected.

very easy to build a BT-80 rocket that recovers easily on a small field.

https://www.rocketryforum.com/threa...-body-bt-80-horizontal-recovery.166124/page-2

 

[bjphoenix]

The Executioner might be happier with a Quest E26. Pretty close to the same impulse as an E12; still far from a full E like the E35, even less than two D12s.

I have an old Estes Phoenix that was probably last launched 20 years ago. I don't remember for sure- was the D12 available back then? Whichever D engine Estes had back then was pretty wimpy in the Phoenix. I launched it one time on an Aerotech SU E30, it flies really well on that motor, barely in sight under good conditions.
I see very few problems with D12 motors but I see a good number of problems with the Quest composite motors so I'll skip those for now. I have a 24/40 case so I might try that one.