Build Tips for 5" rocket?

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Well-Known Member
May 10, 2011
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Well, I scored some 5.345" tubing from a build site... Its pretty good spiral wound paper, strong enough for me to stand on and not bend... I have two of these tubes, each 36" long. I have the coupler made, the fins and CRs cut, and the motor mount right here in front of me (54MM) Rocsim says the rocket will be about 11 pounds, which includes a pound of weight near the fins for epoxy. I dont really want to use expanding foam, so I am thinking internal tip to tip glassing like Ryan tol me how to do... Cut the fin slots all the way to the end of the tube, so you can tack the fins to the MMT with epoxy, then slide it all out, put big fillets on it, and glass the whole thing tip to tip, then stick it back in the tube and put regular fillets on it. How much weight should this add, if I use 6 OZ glass and US Composites resin? This will be strong enough to take a K1275R, right?

Heres the rsim model for this bird... I could really use some suggestions here, I have never scratch-built a rocket this big before... The Nike Smoke is just about this size (I just finished that one, BTW), but that came with easy instructions... :rolleyes:

Thanks in advance!
are you overbuilding or actually going to fly it on that motor?
what happened to the 5.5 nike, and that big 2 stage one .. and the sono tube build know... all them other rockets?
Well, I would like to fly it on a K1275... :rolleyes: And, in the future, after I get a set of 54MM hardware, I proabably will... So yea, I might as well build it to hold up with that motor...
Nike Smoke was finished yesterday, sono-tube rocket is postponed untill next year, and big two-stage rocket has been downscaled to 2" diameter... :rolleyes:

And I had already been planning on making this rocket, but I found another tube to make it longer, and itll need to be a little stronger to take the bigger motors I want to put in it now... :D


And I plan on making the 2 stager and this rocket at roughly the same time... It might take me a little longer to collect the parts for the 2 stager though... (I just got that Perfectflite timer in the mail... :D Fun stuff :D)

If you are worried about the fins being distroyed by fluttering during high speed flight then go to Rocketry Online and look under Rocketry Design then select Fin flutter

You can download a fin flutter estimation spreadsheet for MS Excel:

Also look under rules of thumb here is a quote:

"Reinforcing the Airframe

The larger the rocket, the more important reinforcement becomes. Two layers of a lighter fiberglass fabric work better than a single heavy layer. Two layers of 4oz fiberglass works well for 3-4 inch rockets, 2-3 layers of 6oz for 5-7.5 inch rockets. A final wrap of 2 oz glass provides a good sanding veil.
Glass a rocket measuring 2.56" or greater that will reach equal or greater than 0.85 Mach. "

You could also purchase Finsim software for $30.00 from AeroRocket at:

The RockSim file looks great to me; what are the particular issues you are concerned about? Stable to 8000' on an L1500, Mach 1.1!

Bruce S. Levison, NAR #69055
lol... Mach 1.1 with a 5" paper tube... Naw, prolly not :D

Im just worried about fin strenth in general.... Do you think it would need the tip to tip? Proabably so if I plan on flying it on the biggest motor I can shove in the back end of this thing...

Would it be a good idea to glass the tubes, as well?
I wouldn't glass the tube. I would do internal fillets like PML does and then a layer of external tip-tip fibreglassing for final strength. That tube sounds plenty strong.
Even for a K1275R? Sounds like a pretty punchy motor to me... :eek: Does that motor go in the 2560 case, or am I thinking of something else? Sounds like one heck of a motor to me...

But, if I were to glass it, should it be two layers of 6 OZ?
Yeah, then a layer of 2oz so you get a smooth layer.
no do not do 2 layerrs of 6 oz, do 1, and youy dont need the 2 0z, you can do it though.

this rocket must be pretty long right? maybe 8 feet

I suggest flying Js and then flying Js with dual deploy and then flying Ks before you build a rocket for a K1275, that is a big motor
Yea, maybe I should... Should I just stuff all the stuff in a box and store it untill next year?
It's called a winter project! No other launches to worry about. Great to do on cold winter days!
Originally posted by Neil
Should I just stuff all the stuff in a box and store it untill next year?

Store it until you've flown every rocket you've built for large 38mm or 54mm motors at least once on a motor of J or greater. Surprisingly, complexity seems to increase as the square of the level... it's a lot different flying a J-powered dual deploy rocket than it is flying a H powered minimum diameter rocket with apogee motor deploy...

Get some experience stepping up in the power levels. You'd be surprised at how different a J350 and a K1275 are. Work your way up there. Fly a K550 before you build a rocket for a K1275. Test it on a K700. See what works and what doesn't. Enjoy the ride... that's what rocketry is about.

You probably wouldn't believe how many projects/ideas I've come up with over the years that are still in the planning stages, half-built, or I lost interest in for the time being. It is perfectly OK to come up with an idea then shelf it for the time being until you know it'll work with your experience.

if you wait you will be amazed at the number of things you will pick up and the things you will do differently
Dave Reese and Ryan are right on the money. Have fun; it's not a contest.

An unglassed rocket will take a K1275. An unglassed rocket will take an L1500. An unglassed rocket will take an M2000.

I'll repeat what I've said a thousand times before: IT'S NOT VELOCITY; IT'S AOA!!!!

Since you can't predict AOA (you can only attempt to minimize any deviation from zero degrees AOA), fiberglass (or other laminates) are the way to go to prevent an airframe failure. Lamination also provides ROCKET LONGEVITY.

Best way to avoid fin flutter is NOT tons of fiberglass and monster fin fillets but DESIGN. If you plan on flying a rocket on fast, hard spike motors, then make the fin profile with a narrower semi-span. Too wide a semi-span is a guaranteed way to put way too high a stress load on fins.

The rule-of-thumb quoted from ROL, IMHO, is WAAAAAY overstating the case UNLESS the author is referring to PROPER lamination by way of vacuum-bagging or pressure-bagging. Fact is, the ratio of laminate to epoxy (by volume) is what makes for tensility, NOT gobs of epoxy and yards and yards of wasted and entirely unnecessary cloth (and weight).

I've got a 5.4" rocket that I'm going to start building some time next month. It's LOC tube, peeled down to the penultimate layer (almost to the inner substrate) and ONE layer of OVER-THE-COUNTER 10 oz. cloth. I figure the rocket - which will have a 98mm mount that will hold up to a 15KN-s motor - will weigh around 16 pounds without recovery (2.5 pounds MAYBE) or motor. When it comes to completion, I'll do two flights: one big K for a shakedown pass (K1500?) and an 8000-isn N-s Blue or Yellow M. Have I flown anything quite that aggressive before? No. Am I confident it'll be a safe flight? Yes. Am I CERTAIN it won't vaporize at Max Q? NO, but I'd lay big odds I'll be walking back with that bad boy in one piece. And braggin' rights :)>

Other suggestions: never consider making a payload section more than about 25-33% of the overall airframe length and use a coupler that's 15-25% longer than one caliber. These two things will increase axial integrity even under hard thrust conditions. (Yes, the math may not work out for all airframes but I'm specifically referring to rockets 4 and up.)

Neil, build and fly some smaller rockets. They're fun, too. Remember, it's a hobby that you're supposed to enjoy, not a "who's-got-the-bigger-d***" contest.
Ok... So, should I wait untill after this coming launch (labor day) where I will fly a cluster toataling something like a J677 give or take, or wait untill next year? I dont see the point in waiting untill next year... If I wait untill next spring and build the rocket, with no launches all winter to fly bigger motors at, no point in waiting all winter if you ask me...

So, winter project? Sounds like a good idea to me... I need to buy more epoxys and stuff also... I ran clean-out of everything I need to build a big rocket like this on my Nike Smoke... All my epoxy putty, almost all of my 3:1 epoxy, all my Qcells, all my expanding foam... Geez... All I have now is 5-minute epoxy and 6 OZ fiberglass cloth...

I need to place another order with US Composites soon...
WOW, you must use a ton and a half of epoxy! How'd you run though it? I've done lots of glassing, random building, and other stuffs with the West epoxy, and im not even remotely close to out.
wait until you fly motors that are bigger than H, correct me if I am wrong but you havent flown anything bigger than an H. Just because you fly one J does not mean you are ready to fly a full K
Originally posted by Evil Prince
I'm thinking Neil has the "overbuilding" gene:D

I'm a bit into the overbuilding game too, but at least I know when i'm doing it...:kill: Actually, I don't "over" build, just build stronger than necessary. I firmly believe there's a difference....
Plus it's like the saying, "Just throw a bigger motor in"
Fibreglass is just a way for rockets to have a nice strength safety margin. Extreme overbuilding is just expensive and overkill. A little fibreglass keeps the airframe stress in the tolerable limit with a safety margin so you don't end up with a mushy rocket after a kick @$$ flight or 2. Just don't want your rocket raining down in small chunks! :D :D :D
Your right, I only have 5 Hs under my belt... BUt thats about to change... 2 weeks, and it will be a cluster with a toatal of a J677, and several I motors...

Two 4" rockets, one 3" rocket, one 5.5" rocket (8 sets of fillets. Expanding foam wrecked the first ones), and a lot of smaller rockets, is how I ran through all my epoxy.... I also havnt quite gotten the hang of the 3:1... Im still bad at guessing how much I need... :rolleyes:
measure it out using bottle caps or those ketchup things from Mcdonalds
No, thats not it... I know how to measure it (I use scales for that)

Its just deciding how much I need... I either run out early or have tons left in the cup afterwards... :rolleyes:

Im getting better, though... :rolleyes: :rolleyes:
Where do you plan on flying this? Are you over 18? Sorry to say but you might have a problem flying that at some fields, especially if they knew you were an inexperienced flyer and if you're not 18.

If you're not 18, who flew your H's?
Same way all the other kids do... Certified parents :D

We are all "range assistants", only it turns out we assist a little more than it sounds, especially in the workshop... :rolleyes:
have tons left in the cup afterwards...

My dad can 100% agree with me that i'm horrible at this! I never run out but always have too much left!:rolleyes: