building thread

[cjl]

Yep, I'm working on a 4" by 9' Black Brant X (scratch, not pml), and it will be my first rocket with dual deploy. It is most definitely not small, or inexpensive, although with the right motor it will be fast.

 

[jraice]

I am leaving today for two weeks, I just placed an order for slotted tubes, coupler, 54mm and 38mm motor tubes and some recovery stuff. When I get back my dad will cut some ring's and fins, then I will begin assembly and probably order the timer. After it's built I will get the final weight and descide on a chute to use. It's got a pretty roomy 7.5" by 12" alt bay for just a MAWD and a timer.

 

[jraice]

I spent two week's thinking about the project and have some new idea's. I think pro38 motor's might be useful, easy to light and clean, easy lighting black smoke motor's, e-match ignition (easier on the timer). We will either use large 38mm I's or maybe J400SS's. Timer will be a micro timer (perfectflight) and will be set off by the an opening of the circurt (aligater clips attached to two threaded rod's sticking out the side of the rocket). The L730 burns for around 3.77 seconds so I was thinking 3.5-4 seconds would be best for visual apperance (number of second's until the outboards light). I am also considering glassing the tubes, I could go with aerosleeves but I have seen a few people using other things, I want to use a sleeve and aerosleeves are used commonly on rocket tubes so that may be best. I was thinking one layer with a hobby grade laminating epoxy. How much added weight would you expect from using one layer covering 96"s of 7.5" tubing?

 

[jraice]

Well, just checked, I would need 3 yards of aerosleeves, $60.... more then I wanted to spend, any other option's? What about the GLR easy glass sock? Cheap, but I havent heard great thing's.

 

[jraice]

I have three main issues, or conncern's with this rocket. First off, will it fly? Rocksim method say's 1 caliber while rocksim barrowman says unstable. Second, should I glass it? I really dont want to spend the money or the time. Shouldn't go any more then 550MPH and will come down at no more then 16FPS. I am not super worried about zipper's, 1" TN and it is non brittle phenolic, a little worried about flight stress but I don't think it will be much of a problem. Handling and landing damage worry me a little also, would you glass it? Lastly, what should I use to launch it? Larger rail guides? 1" rod?

 

[rocketkyle]

stay away from rods...

 

[jraice]

Even a 1" rod with a 25 pound bird? So how about those larger sized rails?

 

[daveyfire]

Originally posted by jraice
Even a 1" rod with a 25 pound bird? So how about those larger sized rails?

Do you *really* want to add a 1" launch lug to the outside of your bird? Think of the drag. Think of the... ugliness. Then there's also the matter of transporting, installing, and loading a rocket onto a 1" launch rod. 1" x 8 feet of solid steel is HEAVY!

I highly recommend doing a rail system. You don't even need to go to a 1.5" rail for something like this if you're keeping it light (as the intention seems to be). I flew my 30 lb 7.5" QuikTube rocket off a blacksky ("1010" series) rail with no troubles. You just have to support the aft end of the rocket on the launch pad so the weight of the rocket is not resting on the guides. That way, the rail only has to point the rocket in the direction necessary.

Just use some standard size buttons anchored into 8-32 tee nuts in blocks of wood or some other method to back them up on the other side of the airframe and spread out the force. It'll be fine.

 

[jraice]

So that is the standard type of rail button? That many smaller rocket's use? I may use delrim button's then, or the metal surface mounted acme guides, if my club doesnt have a problem with them being used.

 

[daveyfire]

Originally posted by jraice
So that is the standard type of rail button? That many smaller rocket's use? I may use delrim button's then, or the metal surface mounted acme guides, if my club doesnt have a problem with them being used.

Yes.
And aluminum guides give me the heebie jeebies. Aluminum guides on aluminum rails have high coefficients of friction, are subject to galling, and as such do nasty things... https://photos1.blogger.com/img/2/3089/1024/r805 039.jpg Notice the launch pad leg in the flame behind the rocket.

 

[rocketkyle]

https://photos1.blogger.com/img/2/30.../r805 039.jpg

access denied...

 

[daveyfire]

...and I JUST realized I can attach stuff to posts in this forum. Duhhhh.

This is the point where I stopped taking pictures to make sure it wasn't pointing at me.

 

[rocketkyle]

holy cow poop!!! that would scare the bejeebies out of me!!!

 

[jraice]

Was that the M1315 incedent at lucerne?

 

[daveyfire]

Yup. Word travels fast, it seems

 

[jraice]

I am on the mailing list, didnt read details, just heard some sort of rail incident with a M1315 powered rocket

 

[jraice]

I may go with a lighter version of the main chute (CR12) and that makes the rocket less stable, with four fins it is still not 1 caliber but with 8 ounces of nose weight I can get the rocksim method to 1 caliber but the rocksim barrowman calc says it is under .5 caliber's. Still stable but to close for safety. But from what I have heard rocksim method is best, but most of my rockets had 1 caliber barrowman and 2 for rocksim (stable either way). After getting the final build CG I will try to get the rocksim method up to 1.5 caliber's, then barrowman will not be 1 caliber but still within a safer regain, I may even change the fin design for a more stable rocket. EDIT: I was playing around with the fin design, got it to be rocksim 1.15 and barrowman .51 without any nose weight. Would this be considered a standard diameter/length rocket? I have heard longer rocket's need more caliber's, while shorter ones dont. I may still add the .5 pound's of nose weight and get barrowman to stable, rocksim to even more... here is the new rocksim file, play around with it (L730 and two J400SS's in the motor tubes).