Quad 18mm Clustered Rocket

[Silverfish]

Hi all,

Having considered a scratch build cluster in my Saturn V thread, here's my initial design!! It will be powered by four C6-5's or C6-3's, and will have one of Mike Dorffler's altimeters in the forward body tube section. This is my first attempt at a cluster, so I hope it will work. I have included the Rocksim file, but seeing as I am relatively new to using Rocksim, any design change suggestions would be most welcome. I tried to give it that military missile look (the original concept came from the Nike Hercules rocket), but I would like some wraps or decals to finish it, any suggestions? Also, I cannot think of a name for it, so again, any suggestion gratefully received.

Thanks

Silverfish

View attachment Quad Cluster.rkt

 

[dedleytedley]

I like it! The nose has a cool armor-penetrating look. It will probably land hard with all those motors though. You will most likely need to stiffen the fins as they will take the shock of landing. Other options could be adding a dowel to the body to impact first or plugging some of the motor tubes to make them eject(admittedly a safety hazard). I built a 24mm+3x18mm cluster where the 18mm eject at burnout(c6-0) to reduce the landing and coasting weight. Ted

 

[Bill P]

Nice looking rocket, Silverfish.

Working off dedleytedley's "cool armor-penetrating look" comment, I think 'The Penetrater" may be a good name. Unless it is a windy day, I'd stick to the 5 second delay.

I, personally, would move the fins from the motor mount tube to the space between the tubes.

Just tossing out some "paint schemes": Leave what you have,the drab green with yellow nose cone. Toss in some yellow and/or red bands like in the Pershing II and some sort of fin "accent". Decals: Militaristic. An "US Army" decal and some of the standard accompanying ones like "Lift Here".

Again, nice looking rocket.

 

[thunderdog]

Hi,
Looks great:clap: I would go with between the tubes for fin mounting and as far as paint yes olive drab, yellow and how about the quad killer

THUNDERDOG

 

[JRThro]

Looks nice! I like the color scheme.

What is the transition made of? If it's balsa, is the parachute partially inside the aft end of the transition?

Also, it looks like the 4 tubes are held inside the forward body tube by a single centering ring. I would suggest two rings at least 1/2" apart if not more, the forward ring more or less at the forward end of the 4 smaller tubes. That might mean the 4 tubes would need to extend further into the large body tube.

 

[Pantherjon]

Nice design! I would concur with a couple of suggestions..Move the fins mounting to the 'valleys' between the motor tubes, will definitely make the bond a lot stronger..Also, extend the motor tubes a little and use 2 centering rings spaced at least 1/2" apart to assure the upper tube is straight and plumb..Now, with 4 ejection charges going off at once(they won't all 4 go at the exact time, but still) you will have a TON of force pushing out the laundry. Either: 1) Plug 2 of the engine tubes and vent the ejection gases, or 2)have an extremely long shock cord(at least twice the overall length of the rocket) to dissipate the energy from the ejection charges..OR 3) (Wild idea, but just might work), Use 2 motors with the 5 second delay and 2 with the 7 second delay. Also give you a backup in case the first 2 don't get the laundry out the other 2 will...

I like the design..Keep us updated on build progress!

 

[RangerStl]

How heavy is the mass object in the nose?

N

 

[gerbs4me]

Looks great, very cool color scheme

 

[Micromeister]

Silverfish:
Excellent looking design. I'd also suggest giving yourself about 1/2" of tube extending to the rear of your aft centering ring. this will give you area to both internal friction fit your motors and externally as well. I've learned over time this double tape method really helps keep all motors in at ejection.
Moving the fins to the recess v's is a good idea as long as you maintain enough fin area outside the airstream shadow from your chute compartment.
Have you done a Cp CG margin study? as RangerStl suggested with all those motors in the aft end it's often necessary to add a good amount of nose weight to get the margins right.
You don't have to worry about the multi ejection charges, In all the clusters i've flown over the last 5 decades, I've never had more than one go at a time, Counting pops is one of the early indicators of the number of motors in your clusters lit. It's a very good idea to make very sure your laundry is ejectable on a single ejection charge as that all your really going to have doing the work. Once the first pressureizes the chute compartment enough to dislodge the Nosecone if the laundry isn't on the way out the additional charges usually don't have enough pressure to move them along.
If You'll visit Narhams.orgs web site in the library section in the Tech-Tips files #006 Clustering BP motors. Wil give you a ton of very helpful information on successful clustering techniques. Even with the new Quest Q2g2 igniters this information will help make your clustered motor flying much more fun and reliable.
Something I tell all new Cluster Motor flyers: be very sure you check each and every igniter before and AFTER you have installed them in your BP motors. I can't tell you the number of times i've had to change out a BAD igniter that I snapped while prepping the motor. or the increasing number of just plain bad out of the package or motor pack igniters i've found. Bad igniters are a nusience with single motor flights they can be deadly to your clustered models in the Tech tip is a very simple and easy to construct iginter tester that I wouldn't be without on the flying field.

 

[Silverfish]

Taking into account all of your immensely helpful comments, I have made some modifications to the rocket. I have moved the fins into the recesses between the engine tubes, and I have lengthened the engine tubes and placed a second centering ring inside the body tube to hold them rigid. I have also made the fins slightly larger to account for them being recessed, and moves the aft centering ring slightly forward of the back end of the rocket. I was originally going to attach engine hooks to the engine tubes, but having thought about it, wrapping masking tape around the end of the motors to secure them in might be a better option, any thoughts on this would be most welcome.

To answer JRThro, yes, the transition will be made from balsa, and yes, the parachute will have to be partially inside it.

As with the mass object in the nose, it is an altimeter, which weighs about 15 grams (0.5 ounces). I have to admit that this is only the second rocket that I have designed myself (and the first was just a mismatch of bits left from other kits- it was a miracle that it actually flew :S), and so although I am pretty sure that the CP/CG are in acceptable places (having done extensive research on the internet), I may have neglected some factors (see Rocksim file - margin 1.18 with C6's).

Finally, to solve the ejection problem (if it does exist), I could always just use two C6-5's and two C6-0's, and block off two of the engine tubes, but, again, you guys are far more experienced than me, and any of this experience that you are willing to share, I will happily accept.

Thank you again for all your help and advice, I am going to order the parts tomorrow, and so they should be through soon so I can start building!!

Silverfish





View attachment Quad Cluster.rkt

 

[Silverfish]

I have finally started my build .

I've cut all the tubes to size, and filled all the spirals, and while waiting for the filler to dry, started work on the transition, which I have decided to make from paper rather than balsa, and have run into some problems. Having watched this series of videos from Apogee <https://www.apogeerockets.com/Rocketry_Videos/Rocketry_Video_10.asp>, I realized that it would be very difficult to build the shoulders and get them straight within the transition. I cannot extend the upper BT-20 tube down through the transition and glue in some centering rings (as suggested in the videos), as there will then not be room for the parachute, and I also need to have access to the altimeter, which will be stored within this upper tube. I might have to resort to just glueing some couplers to the ends of the paper transition, and then fixing the upper BT-20 on by friction. This would not be ideal, but might be the only way... hopefully you clever people might think of something .

Thanks

Silverfish