My first at home scratch build. Input please.

[soxfan121]

So I have designed a small rocket but it's the first scratch build that I'm doing by myself. Normally I build my rockets with three of my buddies. I just decided to get into true Hobby rocketry, unfortunately I don't have a job so i can only get parts occasionally. I will be able to get some from my school where I normally build rockets. Also it will be going somewhat slow because I am also currently near done building my TARC 2013 rocket. Any input on the design of this rocket would be GREAT, normally I have my mentor and a teacher to give me and the other club members guidance. I have built high powered rockets in the past and probably 10 other medium powered rockets besides that. Been doing this for nearing 3 years and never plan on stopping. Thank's in advance for reading and providing me with any guidance and support!
Specifications
Mass: 289g or 10.19oz
Length: 61.3cm or 24.134
Diameter: 6.6cm or 2.6 in.
Stability 1.57in.

Simulation Results
Apogee: 384m or 1260 ft
Max Velocity: 119 m/s or 390 fps
Max Acceleration: 169 m/s^2
Time to Apogee: 7.54 s
Flight Time: 53.8 s

 

[les]

Nice design. I assume the altimeter just to measure the altitude?

The diffusion bulkheads are a baffle, right?

If you want a little more fin strength you could do through the wall to the motor mount. You would want to lengthen the motor tube so you could move the centering ring forward. Probably not really required for the selected motor (but could help with landings)

 

[soxfan121]

Nice design. I assume the altimeter just to measure the altitude?

The diffusion bulkheads are a baffle, right?

If you want a little more fin strength you could do through the wall to the motor mount. You would want to lengthen the motor tube so you could move the centering ring forward. Probably not really required for the selected motor (but could help with landings)

thank's i'll give that a try, yea they're baffle and yes the altimeter is just to tell altitude.

 

[Coop]

I'd suggest elongating the MMT and going TTW with the fins. With the swept-back design, these will be taking the brunt of landing forces.


Later!

--Coop

 

[T-Rex]

Looking at you specifications, you need to add a little nose weight to bring you stability to 1 caliber, or in you case, 2.6inches.

 

[soxfan121]

can anyone tell me a good store to buy tubing like bt80-50-20 tubes? no online stores i'd prefer somewhere i can go in person. Home depot? Lowes? i was at micheals for a hour and a half today buying balsa and a few other materials for my rocket.

 

[soxfan121]

Looking at you specifications, you need to add a little nose weight to bring you stability to 1 caliber, or in you case, 2.6inches.

I had my nose set as hollow but i just set it as solid balsa and it's at 2.50 i was used to rocsim where 1.50 is a good stability margin and was thinking this was the same. Someone care to explain the difference?

 

[soxfan121]

I'd suggest elongating the MMT and going TTW with the fins. With the swept-back design, these will be taking the brunt of landing forces.


Later!

--Coop

I was thinking the exact same thing about the fins i just wasn't sure it was going to be a big deal on this rocket, but i have no problem changing it if someone think's it'll be a problem. Thank's!

 

[soxfan121]

Here's the new and improved design, don't like the look of the fins but they did improve the stability as well as won't be taking the full force of the landing. I've included the parachute specs (both are the same so only 1 pic), fin specs, and rocket specs. (motor is still F20W-7) I'm beginning construction of the internals today. Can you guys embed some pictures of you're favorite motor mounts for MPR's? I'd like to see some other types of mounts.

 

[soxfan121]

sorry did a quick redesign and here it is, i increased the length of the Booster tube and gave everything a bit more room in between and remembered to add on launch lugs
-Stability: 2.58
-Length: 66.2 cm
weight w/ motor: 346g

 

[Bubba02STi]

Can you post the .ork file... it will helps us to better help you

As far as i know michaels and hobby lobby dont carry just body tubes.... htusa does carry some... i suggest using apogeerockets.com and going to their building supplies page... they have all dimensions and weights available...

 

[soxfan121]

View attachment thepunisher.ork
there's the .ork file (thepunisher.ork)

 

[Bubba02STi]

id suggest using loc 2.56 tubing as the bt80 may be a little difficult to get centering rings for... 1/4 ply is a little excessive for bulk head discs and centering rings as well... i cleaned it up for you a bit... i changed your 2 motor hooks to the estes 29mm retainers

View attachment thepunisher.ork

 

[soxfan121]

id suggest using loc 2.56 tubing as the bt80 may be a little difficult to get centering rings for... 1/4 ply is a little excessive for bulk head discs and centering rings as well... i cleaned it up for you a bit... i changed your 2 motor hooks to the estes 29mm retainers

I usually build everything (except centering rings and tubing) myself including my engine hooks, I will however take some of your changes into account, i should try other things than what i always do.

 

[aditat2]

If your looking for body tubes that you can get locally I would suggest either the local postoffice or business supply store such as Staples. I use mailing tubes all the time for scratch build projects. They're a bit heavier but work quite well for most MPR builds. The biggest problem is finding NCs that fit properly because a 2" shipping tube is 2" ID not OD, etc. LOC does make some really nice NCs that fit a 3" mailer perfectly - but they are a bit expensive.

 

[soxfan121]

not a bad idea i'll stop at staples tomarrow, i was looking at LOC tubes like bubba suggested, i think i'm going to go with that for this particular rocket. again thanks for the help guys! keep it coming! can never have to much help/guidance/suggestions

 

[JordanT]

Looks fun! Good choice in getting those fin tips further away from the landing impact. I missed what you were making them out of, but having replaced one-two balsa fins on a stretched Big Daddy every. single. landing. I'm always wary of how much force gets put into the first part of the bird to touch the ground.

Have you considered rolling your own tubes? There are relatively few BT-comatible sizes off the shelf. Kraft paper (virgin kraft, not recycled) is good - just roll it up with paste or very light glue - though you might want to put a sheet of regular bond on the outside for finishing. If you graduate to HP 3" designs, find your local architectural print house - they might be listed under techincal printers or large format printers - and ask for some empty cores. They'll have 36" long, 3" ID / 3.18-3.20" OD spiral tubes. They'll probably give 'em to you free, but get ready to fill some grooves!

BTW - If you're on a Windows machine and want to post a screen shot you might do a screen capture by pressing either Ctrl-PrtScn to get the whole screen or Alt-PrtScn to get just the window you're working in. Then you can paste it into any program using Edit|Paste or pressing Ctrl-V. You're adding graphics so I assume you have something to paste into that can save a jpeg, of course.

 

[soxfan121]

Looks fun! Good choice in getting those fin tips further away from the landing impact. I missed what you were making them out of, but having replaced one-two balsa fins on a stretched Big Daddy every. single. landing. I'm always wary of how much force gets put into the first part of the bird to touch the ground.

Have you considered rolling your own tubes? There are relatively few BT-comatible sizes off the shelf. Kraft paper (virgin kraft, not recycled) is good - just roll it up with paste or very light glue - though you might want to put a sheet of regular bond on the outside for finishing. If you graduate to HP 3" designs, find your local architectural print house - they might be listed under techincal printers or large format printers - and ask for some empty cores. They'll have 36" long, 3" ID / 3.18-3.20" OD spiral tubes. They'll probably give 'em to you free, but get ready to fill some grooves!

BTW - If you're on a Windows machine and want to post a screen shot you might do a screen capture by pressing either Ctrl-PrtScn to get the whole screen or Alt-PrtScn to get just the window you're working in. Then you can paste it into any program using Edit|Paste or pressing Ctrl-V. You're adding graphics so I assume you have something to paste into that can save a jpeg, of course.

Thank's! I'm not abandoning this design but i realised how overdone this type of rocket is so i think in a week or two i'll decide to either do a build thread on this rocket or on a cluster rocket i'm currently designing. I'll post a new thread for it because i've never done a cluster before and think it'll be fun. Thank's for your ideas and especially the screen cap...can't believe i never knew about it...thanks!

 

[T-Rex]

I had my nose set as hollow but i just set it as solid balsa and it's at 2.50 i was used to rocsim where 1.50 is a good stability margin and was thinking this was the same. Someone care to explain the difference?

I think the confusion is coming from calibers and inches. The general rule is that you need at least 1 caliber of stability. A caliber is the diameter of your body tube. If it is a 2.6" tube then the CG must be at least 2.6" in front of the CP. If it is a 4" tube, then you would need 4" for a stable rocket. Some folks say that you need 1.25 calibers, just adds a little safety factor.

I apologize for causing confusion.