Concept design: Alien atmospheric probe

[Bill S]

I'm working on yet another design, an alien atmospheric probe. It's supposed to have an organic look to it, borrowing the concept of long body strakes from the Arapaho-E (Squirrel Works), and using the long multi-section nosecone from the Estes Dark Energy kit. The fins are planned to be sanded a little more eliptical than shown in the picture, and Rocksim can't handle the multi-sectional nosecone. I'm cutting down the nosecone a bit, removing the rear section. It'll have 6 strakes.

Its 29" long, flies on a variety of 18mm and 24mm motors (up to D12-5, then Aerotech D22 or E26 motors). Weight is about 3.33 oz, allowing 15% for glue and paint. Tentative idea for paintjob is basecoat of turquoise, with perhaps a stripe or two, not sure yet.

 

[neil_w]

Very sleek.

You can approximate the nose cone with a series of transitions. I just whipped this up, dimensions are very approximate but it gets the idea across, if you'd like a better visualization.

 

[Bill S]

That's pretty nice, Neil. Not sure how to get Rocksim to recognize it as a nosecone though.

 

[neil_w]

That's pretty nice, Neil. Not sure how to get Rocksim to recognize it as a nosecone though.

It's not a nose cone and won't be recognized as such. It's a whole series of components. You would need to be able to copy the whole set from one RKT file to the other. I'm not a Rocksim user so I can't advise too well. Is there a way to group components, and then you could copy/paste the group?

The other, less appealing possibility is to start with that and then copy over the other stuff from your design. There aren't that many components to move.

Anyway, just some thoughts.

 

[Bill S]

I was able to import it, and tweak Rocksim to use the proper body diameter as a reference for stability. I then pasted the entire body assembly from my version of the rocket onto the nosecone, and fiddled with it a bit, and it seems to work. Have to tweak the weight a little, but its close. Thank you VERY much for the image.

Updated picture:

 

[neil_w]

Looks like you’re missing the last few segments of the nose assembly but you’re on your way.

 

[Bill S]

Looks like you’re missing the last few segments of the nose assembly but you’re on your way.

I deliberately took those out, as I don't like the look as much when they are there.

 

[Bill S]

I've got some in progress pics...

Pretty basic body tube with coupler in the middle, with the 3 main fins and 24mm motor mount installed:



I had to cut out and sand 6 long thin fins. The issue was cutting out the strips as close as possible to the correct width, then sanding down the ends to maintain the elliptical look. I put them on a piece of painters tape and ruler to keep it aligned.


Rocket with the 6 side fins attached:

 

[Bill S]

To my irritation, I discovered that despite my efforts at ensuring the final design is stable, the sheer amount of glue/fillets needed for the strakes has changed the Center of Gravity enough that stability is marginal. (1.01). After tinkering with the main fin shape, I discovered that had I merely increased the span of the fins by a mere .25" all would have been well. I guess I cut it too close. May have to add .1oz of noseweight, which I hate doing, but things are at an advanced stage and I'm not ripping off the main fins and re-doing them.

Lesson learned: ensure that the fin span is more than the body tube diameter, and leave more stability margin when designing.

 

[Woody's Workshop]

What kind of chute was you using on you using?
If it was plastic, you can add some stability by using a heavier chute, solid brass snap swivels, etc.
It might reduce the amount of nose weight needed for an acceptable stability factor you want.
And if you have access to the nose cone interior you can give it a coat of epoxy for a little additional weight.

 

[Bill S]

I am using a Top Flight 15" parachute.

I did re-test the CG with the shockcord attached to the inside of the tube, and with wadding and parachute inserted where they would be when flying the rocket. Stability increased to 1.11, some improvement, but we'll see.

My plan was to put in some 30-min epoxy in the nosecone tip if needed.

I'm going to re-evaluate when I get the rocket primed and painted; that will be a while, as we are forecast for a week or more of tropical humidity levels and I don't want to spraypaint under those conditions.

 

[Bill S]

Making progress... painted but needs decals still.

I am probably going to do a combination of waterslide decals and decal sheet spraypainted with purple and cut to size.

Interestingly enough, stability improved to 1.29 on a D12 motor, after painting it and rechecking weight of some parts. Strange. Usually painting doesn't affect the CG much in my limited experience.

 

[Tom Howe]

Two words: Nice Job!

 

[Bill S]

I'm in the midst of putting on decals now. Of course, since I was using clear decal paper, the color I was working with darkened up since the basecoat is showing through the decals. There was no way I was going to mess with printing the decals on white backed paper and then try to touchup with the basecoat (I've tried this before with awful results).

Should have pics up tomorrow or so. Rocket is ready just in time for a Saturday launch.

 

[Bill S]

The rocket is done, pictures and etc are here:

https://www.rocketryforum.com/threads/scratchbuilt-alien-atmospheric-probe.168503/