first cluster

[radiO]

getting ready to make my first cluster. all the pictures i see the engine holes are touching. does it have to be that way or can they have gaps inbetween? was thinking of doing 3 C's. what is the smallest tube size these will fit in?

 

[GL-P]

The motors don't have to touch. The closer the motors are together the better because if all the motors don't light, the drag effect won't be as extreme. A picture would do now... If you leave a little gap it should be okay.

3 C's fit into a 1.5 inch airframe quite snugly without gaps. I have one rocket exactly like this which is very light and goes quite high on 3 C6s.

 

[radiO]

awesome, thanks!

 

[GL-P]

Get yourself a book called something like Model Rocket Design & Construction by Timothy S. Van Milligan. Good book for modelling. I have it and use it. Got some good solid techniques in it.

 

[radiO]

i'll check it out! so, are 3 C's close to the same thrust as an E?

 

[GL-P]

3 C6 I think equal an E18. The 6 is the intial impulse. 6 times 3 motors equals 18. A C6 has 9 ns of total thrust times 3 motors equals 27 ns which falls into the E category.

Check out I think NAR's site. They have data on all the certified motors.

Do you have wRASP? It's a free simulation program for altitude. It's easy to use and has a database of kits, and motors. It can be added on to easily.

https://www.wrasp.com/

 

[radiO]

thanks again. the wrasp downloads don't say anything about windows over 98. will it work in windows 2000?

 

[GL-P]

I have windows XP. It works just fine. Another program that is free is VCP. It calculates center of pressure so your scratch built models are nice and stable. Includes a great description of stability. Pretty simple also. Works on my XP also

https://v-serv.com/vcp/

Rocksim is the next stage. It costs money (quite a bit) but is an integrated program that is quite versatile. It's one of the most common programs

https://www.apogeerockets.com/rocksim.asp

Honestly. Wrasp and VCP are all I've used for most of my rockets, one of which is 6 feet tall, 4 inches in diameter and weighs 4lb.

Sorry for the wait. was talking to a girl on the phone.

 

[radiO]

"Sorry for the wait. was talking to a girl on the phone."

understandable! hmmm, is that a word? anyways, thanks for all the help, i'll check out that software....

 

[Elapid]

are cool!
Good Luck!

 

[radiO]

well here it is so far. went with the 1.5" BT-60. didn't need any centering rings, kinda nice. learned from this forum about maing a paper mache paste. used elmers and paper towel to fill the gaps between the motors. i had already used CA for putting the tubes together and then CA again for gluing the tubes inside the BT. then to make her look nice and finished i used contour putty. i'm pretty excited so far! i used an old used C engine cut into 3/4" rings as engine stops. this is an all scratch build. the length when the nose cone is on should be about 42". i think 3 C6's should get her off the ground? especially if that is close to the same as an E. i have flown an E one time and it was pretty sweet. i'll ell you though, 3 C's are a lot easier to come by and CHEAPER than 1 E. i had to mail order my pack of 3 E's and with hazardous handling and everything it was over 20 bucks. we all know how much you can get a pack oF C's for, from you know where....


....any advice so far???

 

[radiO]

another picture:

 

[GL-P]

Nice rocket! Mines a lot shorter and has smaller fins! Our club has a cluster weight lofting competition. My rocket is stable with the weight. (and unstable w/o) On my last flight only one motor lit so the rocket did a little spiral and rammed itself into the ground. I destroyed the shoulder on the nosecone and a little of the tube. I'll go get a pic for ya! How heavy is she?

Sorry slept in!

 

[GL-P]

This is my cluster rocket. It's about 20 inches long. It weighs 3oz w/o trim or motors. Probably 4oz full

 

[GL-P]

This is my newest rocket. It's a 24mm minimum diameter rocket designed to hold Ellis Mountain's G37-10. Should go beyond mach and should go above 4500 feet. It needs a little glass reinforcement and a new nosecone. I don't expect to get her back! I have a 38mm minimum diameter rocket which holds a RF locator. It's not done yet! I want her back though!

 

[radiO]

woah!

..not sure on the weight yet. what did you use on that first one to fill the gaps between the engines?

 

[GL-P]

I cut centering rings because I thought they'd stay in one piece. Big mistake. But I glued the mount together using the remains of my centering ring as filler.

Did you glue your fins on so that they wedged through between the cluster tubes? Too late now but something to think about.

Yeah, problem with em clusters is they need a lot of stability to balance the motors in the back end.

The next impotant thing is how to wire the igniters together. Just make sure you have no shorts in he circuit. I'd also suggest maybe if you got some 1/4 A to spare that you can test your skills at wiring them together in a stand (like a cluster motor mount) and seeing if they all fire. Expensive but a good way to make sure you do it right that doesn't cost you a rocket.

Oh yeah, my rocket went high (like really). Paint your rocket maybe in a flame pattern with red, orange and yellow. That pattern is cool and is quite visible. For a chute try mylar. The stuff glitters in the sunlight so it is visible high up.

 

[radiO]

no, the fins don't go through the BT. **** good idea though! do you think mine will have enough stability with those fins? i shouldn't need any nose weight, should i? i read here on the forum that nose weight is needed with short and fat rockets??? i am also all about mylar! if you notice in the second picture i posted, i love my rockethead chutes! funny you should mention that color scheme, i'm thinking the same colors. i'm not going to do the fade thing though. i'm just thinking red nosecone, orange fins, white BT and maybe some yellow in there....

...thanks for all the great advice! i'll post more pictures when it is done....

 

[GL-P]

That rocket should be perfectly fine for stability wise. I suggest using VCP to find the Center of Pressure. Then you can mark that with a marker. All you have to do then is test the Center of Gravity when it's fully loaded at the field by balancing it on your finger or a ruler. The CG should be 1.5+ body diameters ahead of the Cp.

If the rocket really is 42 inches long it's not short and fat. It's quite long. My nosecone was quite light and my fins were small so I needed nose weight. Yours should be fine.

Whenever you have rockets where you can use through the wall fins, do so! In the bigger ones I have it's absolutely necessary.

Try VCP. It's easy and useful on these kinds of rockets

 

[radiO]

....can't wait to fly her. guess i'll have to give her a name. i gues i better wait to see if it flies, or even comes back first. sure don't want to get too attached now.....

....this is my biggest rocket so far. should also be my most powerfull. i spent about 4 hours of sanding time on this baby. as much as i know this is a hobby and is meant to take up some time, i sure wish at times that body tubes had no lines and bals was smooth. also guess it's more rewarding this way....

....anyways, here are some pictures, i'm pretty stoked. i'll report back after she flies on 3 C-6's......

 

[radiO]

that is suppose to read "balsa", above. i really need to start proof reading my posts!

 

[radiO]

..and picture number three:

 

[GL-P]

Awesome. She should really burn rubber er... BP! What paint do ya use? I always have a problem with paints.

I'm working on my two rockets now. I made one bad epoxy batch on my minimum diameter G rocket and cuz of it it took forever to dry. Other rocket should be flying without w/o electronics in about 2 weeks time. Still got the recovery stuff to do and some fibreglassing.

Yeah, I build all of my rockets with cost in mind. Mine are all very cheap and I don't cry if I were to lose it. (Except some of my new stuff!)

It's an orange bottom right? Just in one of the photos it looks red. Nice paint job! Just take ur time with the igniters and you'll have one great flight! You going to fly with a tower? I saw no launch lugs.

Maybe next time scale her up to 3 Ds with thru the wall fins!

Can't wait for pics!

 

[radiO]

yeah, orange bottom. there are two launch lugs, they just don't show in the picture. i would love to make a rail setup! i use krylon paint most of the time. i also use the high temp stuff, it lays down really nice and there some cool colors. i heard the high temp stuff fades fast though because there isn't as much UV protector in it. i primed and sanded three times before i painted. when i paint, i put on a light coat and then a really nice heavy coat. you spray the paint till it gets glassy/waterey looking and then back off. krylon these days is amazing! that stuff dries so darn fast and is had to make drip if you try.

 

[jflis]

oh, THAT is a fine looking rocket! Can't wait to hear the launch report!

 

[radiO]

thanks! i can't wait to get some of your kits, they look amazing. it's next on my list, promise....

 

[scadaman29325]

Originally posted by GL-P


The next impotant thing is how to wire the igniters together. Just make sure you have no shorts in he circuit. I'd also suggest maybe if you got some 1/4 A to spare that you can test your skills at wiring them together in a stand (like a cluster motor mount) and seeing if they all fire. Expensive but a good way to make sure you do it right that doesn't cost you a rocket.

you could just fire the igniters without the engines to test your wiring abilities.

Estes and Flis have good info on wiring clusters...

 

[GL-P]

ur right, much cheaper!

 

[Fore Check]

Awesome job RadiO! You should be proud! My first "scratch" rocket was not nearly as cool or good looking.

Well done!

I'd slap 3 c6-7's in that baby and let 'er rip. WooHoo!


It kinda looks fast just sitting on the bench!


A couple of tips:

1) make sure you get a nice, snug fit on your motors when you put them in your mounts. A wrap of masking tape around each, about 1/4" up from the nozzle end, should do the trick. If they aren't snug, the multiple ejection charges could eject your motors rather than your recovery system!

2) Don't forget to put about 1/2 sheet of recovery wadding mashed down on the clay retainer cap on the ejection charge end of the engine, just in case. It's a long story, but this can prevent serious mishaps if one of your engines doesn't work right.

3) TAKE LOTS OF LAUNCH PICS AND POST THEM HERE!

Again, well done!

 

[radiO]

awesome advice! i'm such a newbie, i really do appreciate this. i hope to launch her next week.....