Sunward Star Watcher Question
 

I'm building the Sunward Star Watcher right now, and in fact I'm pretty much done but for the painting; but I've run into an "issue" with it. I've used the alternate "X-Wing" layout for the fins, and the instructions say that nose weight may be needed... but not how much.

I don't have RockSim, but looking online it appears nobody has yet done a RockSim file for this rocket anyway (not even on EMRR), leading me to wonder if there is some reason for this. Does anyone know how much nose weight this beasty needs?

Hmm... I'll partially answer my own question. One reviewer at EMRR said he used "several ounces" of clay for nose weight, while a guest reported using 10 grams of lead sinkers plus 4 ml of Gorilla Glue. There seems to be no science to this, though.

I haven't built one but I just checked out what it looks like and it appears like it should be fairly simple to swing test.

I built mine in the x-wing configuration as well...I could take some measurements and put together a quick and dirty RS file for it...

Aha! I have questions for you:

Did you add any noseweight? If so, how much?

Have you launched it on a C engine?

Did it fly right?

I have launched it, yet don't remember how it flew:o Still in one piece so it must have flown fine..Almost done with the Q/D RS file...Will post in a couple here...

Ok, done with the RS..Flies fine in the sim with no nose weight..HOWEVER, I couldn't figure how to put the fins in the x-wing configuration-and the nosecone isn't exactly right in the RS file but close enough, and I did a 'mass override' using the weight of my finished one..I also couldn't figure out how to put the fin tips in the sim as well..

Like I said I have flown it(I can smell the burnt BP), I just don't remember how well it flew or what motor I used- I am sure it was a B as the field locally is fairly small..

RS file attached, so if anyone cares to tinker with it and correct the inaccuracies, feel free to..And post your results ;)

I know the answer to one question... to get the X formation, create two fin sets, each with two fins, and set the radial position to 30 degrees for one set, -30 degrees for the other (at least, that's what my protractor says).

Ah-ha! That works! Got the fins in the right orientation! I also went ahead and took the mass override OFF of the sim..Yeah, with a C6 loaded the stability is shown as 'marginal' with a margin of 0.54..Add 1/2oz weight and margin goes to 1.85..Flew it in the sim on a C6-5 altitude reached was 836 with a DV of 24ft/sec..

So, I guess the answer is 1/2oz of nose weight :)

Cg
 

Just an added note: On my built and painted Star Watcher, the unloaded CG is located 8.5" from the tip of the nosecone..Like I said before I have flown mine in the x-wing config with no nose weight, but am going to add 1/2oz just to be on the safe side when I launch it Saturday on a C6-5..Will let you know how it goes, unless you fly yours before I get back then you can tell us how yours did ;)

FWIW, the EMRR reviewer you're referencing is Todd Mullin, who probably doesn't troll here but lurks in rocketryforum.com as punkrocketscience. You could hop over there and PM him for details.