Sunward Star Watcher Question

[Solomoriah]

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?

[Solomoriah]

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.

[Gus]

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.

[pantherjon]

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...

[Solomoriah]

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?

[pantherjon]

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 ;)

[Solomoriah]

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).

[pantherjon]

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 :)

[pantherjon]

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 ;)

[chanstevens]

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.

[Solomoriah]

So, 1/2 ounce is 14.235 grams... I use computer screws for nose weight, and have previously determined that they weigh 0.77 grams each on the average, so that's about 18.5 screws.

I still don't know what epoxy weighs. In the past, I have used a "rule of thumb" that a screw and the epoxy to hold it weighs about a gram. That is nothing more than a guess though.

In effect, I need at least 15 screws, but almost certainly no more than 18, with epoxy to hold them in. I'm thinking 16 screws is a workable guess.

Thanks for the information, pantherjon. Most likely you'll get yours launched long before me, as I'm in NE Missouri... cold and wet here today. I considered a launch on Sunday when temperatures were around 65 F here, but the ground was too wet for reliable recovery.

[Skippy]

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.

Errm... I was the guest who wrote:

"SPECIFIC ROCKET TIP:
10/06 - "The Star Watcher was my first Sunward kit. I e-mailed Angelo Castellano about extra nose weight needed for the X wing configuration, he suggested about a cubic inch of clay if flying in wind. Interestingly he said that in light to no wind, no extra nose weight should be necessary. A quick swing test had my Star Watcher stable, but flying aft about with a C6-5 in place. The CG was 90mm from the rear of the body tube. Time for a quick burst of nose weight. Twelve size 00 split lead sinkers gave me an even 10 grams of nose weight. These were dropped into the nose cone and secured with 4ml of polyurethane (Gorilla) glue. A quick check showed the CG had moved to 135mm from the rear of the body tube. Stable flyer, and one of my favorite rockets until I parked it high in a tree." (M.M. )"

Sorry, talking to the manufacturer and swing testing seems a pretty logical progression of thought to me. Perhaps I should go back to divining the CG with chicken entrails... :)

I have built four Star Watcher kits in the 'X-wing' configuration and they all fly well on B and C motors.

YMMV, as may your nose weight. :rolleyes:

[Solomoriah]

Sorry... perhaps I should have said that there seemed to be no math to it, rather than no science.

I'm personally surprised that the manufacturer hedged so much on this. I'd think that they, being in the business and all, would have coughed up for RockSim and would have had a solid figure for the suggested noseweight.

[Skippy]

Angelo doesn't (or didn't) use Rocksim when I spoke to him about the Star Watcher. He said he used experience to guide him, and to be fair, the instructions do have details of how to perform the recommended swing test.

Do Estes use Rocksim?

As for math, gee I counted to twelve, what more can you ask for? :p

[PunkRocketScience]

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.

Hi guys-

Actually, I do poke my head in here from time to time... Just not very often! Too many rockets to build so I have to pick and choose which forums I frequent...

I didn't actually weigh the amount of nose weight that I added, I just did swing tests and kept adding small bits until the rocket swung stabily. Sorry I couldn't give you a more clear cut answer!