Summer Build Contest 2017 "ENDYMION"

[MCriscione]

It's about time I got around to starting my contest build thread, so here we go. Based on previous sketches, I've started to model the rocket. It's a 2x 24mm parallel cluster, and should fly on D/E power, so I guess it technically qualifies as mid-powered.


At this point, the model is mostly for the body, to grab cross-sections from. I'm not at the point where the fins/aft are really modeled properly yet. The aft section will get some significant additional build up to better match the sketch. The outer fins have the right shape, but I think are a touch oversized. At this point, I've put the motor mount together and started to (perhaps) regret, not throwing in a third central 29mm motor, just to ensure I won't end up too heavy. I'm going to have to take care a bit with weight, I think. Right now the plan is 'rib and skin' for the forward portion. The aft is going to be all bent balsa (I think). I get the feeling this one is going to have a lot of wood filler.

I haven't gotten the actual build too far along. Mostly just the motor mount and a few various odds and ends. I don't have a nice spread of all the parts mostly because a lot of it is going to be made on the fly. None of the balsa is cut (or even purchased) yet, so nothing much to show for that. Here's what I've got so far...




I'm not entirely sure if / how I'm going to port it into OpenRocket, but I've taken a first shot at it, and it looks stable, though a fairly low flight on a pair of D12-3's (around 300').

 

[Daddyisabar]

Very Cool!

 

[rstaff3]

Very nice!

 

[rstaff3]

If you can not sim it, mindsim it...and swing test.

 

[Gary Byrum]

Dood, If you pull this build off, you're gonna blow my sox off. That design is a "hottie". I'll be following this one cuz, me tinks I could build one of dems too!

 

[Nytrunner]

That's a great looking design!

What file format is the 3d file in? No guarantees, but I could try running it through my flow models and get you a tentative CP.

 

[neil_w]

Dood, If you pull this build off, you're gonna blow my sox off. That design is a "hottie". I'll be following this one cuz, me tinks I could build one of dems too!

It's got holey fins, how can you not like it?

Anyway, I'm with you, that's gonna be a real looker, I'm pretty enthused to see this one come together. I must say, the contest does seem to draw out some really good work from a variety of folks.

 

[MCriscione]

It's being modeled in SolidWorks 2014 so far. Pretty versatile export options. I don't have the flow sim package though, so no awesome CFD for me. I'm glad you all like it. An yes, 'holey' fins it does have, though not modeled right now.

 

[Gary Byrum]

I must say, the contest does seem to draw out some really good work from a variety of folks.

You should attend an NSL launch if you wanna see what the mad science designers have been up to. It's like being Cookie Monster in a warehouse full of cookies. So many awesome designs and ideas flying off the racks. BIG FUN!

 

[grapetang]

That's a good looking ship! Very cool! Will we get a companion Selene vessel?
Looking forward to the build!

 

[MCriscione]

It's being modeled in SolidWorks 2014 so far. Pretty versatile export options. I don't have the flow sim package though, so no awesome CFD for me. I'm glad you all like it. An yes, 'holey' fins it does have, though not really modeled properly right now.
If I built a companion vessel, Selene would definitely be the name. I'll have to see, perhaps next year's contest?

In the mean time, I have a question for those of you at home. I took my last pic of the motor stuffer tubes, and didn't notice, but there's a pretty significant 'cant' to the whole assembly, such that I wouldn't be comfortable flying it as-is. It's all put together with wood glue right now. Any thoughts on straightening it out, or should I just rebuild? It's early enough that the loss isn't too hard to bear. I don't have a heat gun, just a blow dryer, which I could try I suppose. Otherwise, the wood blocks make that joint pretty firm.

In the mean time, I finished pulling cross-sections out of Solidworks. I printed them on full sheet label paper, and slapped them on some balsa. So that's done at least. Or at least mostly done. Still a couple cut-outs left to make.

 

[neil_w]

In the mean time, I finished pulling cross-sections out of Solidworks. I printed them on full sheet label paper, and slapped them on some balsa. So that's done at least. Or at least mostly done. Still a couple cut-outs left to make.
View attachment 321493View attachment 321494

Whoa, I didn't realize the body was going to be faceted like that. Extra bonus cool points. What are you going to skin it with?

 

[MCriscione]

The body won't be, but the back side of the skin will be. I'll sand the curves into the 1/16" balsa skin. It'll be a touch thin in some places, but nothing too drastic.

 

[neil_w]

The body won't be, but the back side of the skin will be. I'll sand the curves into the 1/16" balsa skin. It'll be a touch thin in some places, but nothing too drastic.

Interesting. Have you tried that before?

 

[MCriscione]

Nope, this is all new to me. Never done a model anything like this before. First cluster too.

 

[Cabernut]

Wow this looks like a fun build!

 

[MCriscione]

Here's a quick update. I did end up scrapping the existing body tube/motor mount. I wasn't able to straighten it out, not that I expected it would work. I strapped that down pretty well using some aluminum angle. It just happens that the aluminum angle fit nicely right up the edges where the body tubes were slit to interlock. After reconstructing that, I finished up the ribs and got those mounted up too. It's coming along slowly but surely. The stringers are 1/16 square basswood, and I'm using them to help keep all the ribs square to the tube.



I think I've mentally wrapped my head around what I want the back end to look like. Not sure if I'm going to have time to model it after all, but we'll see. I need to take another shot at it in OR too, now that I've a bit more info on shape. Nose cone will be a custom job, but I haven't touched that, other than to make a couple. I'm also considering throwing a baffle into the body tube. I have one from Sunward that should fit. I'll admit, I was a bit surprised by the 'flimsy' cardstock that it's made out of. Do these things hold up? I feel like I need to coat or maybe even supplement the aft side with some balsa.

 

[Gary Byrum]

I'm also considering throwing a baffle into the body tube. I have one from Sunward that should fit. I'll admit, I was a bit surprised by the 'flimsy' cardstock that it's made out of. Do these things hold up? I feel like I need to coat or maybe even supplement the aft side with some balsa.

Honestly, you'd prolly fair better to make your own. I've been using this thick hard poster board I get from Wally World. Makes hundreds of them and custom CR's for that matter. Pretty cheap in the long run. You can use a hole puncher to knock out as many holes as you think is necessary and keep the strength going. I learned a long time ago, that there are too many LPR kits out there that have poor or substandard quality parts. CR's being one of the many. Never bought a baffle, ever!

 

[TangoJuliet]

This is gonna be great! And it looks like you've got a good start on it.

 

[MCriscione]

It's been about a week since the last update. I had high hopes for this last weekend's work effort, but family stuff took priority and I ended up missing most of the weekend's work window. All in all, only minimal changes, but it's starting to come along. I've finalized the 'primary' rear fin/wing shape, and cut both that (1/8" balsa) and the curved 'outrider' fins (3/32" balsa). The outrider fins have been curved (as of last night). I was stumped for a while trying to figure out where I would find a 10-12" diameter cylinder to wrap the fins around to bend them. Turns out our largest cook pot was just right (10") It should suffice for the upper wing fin's bend too, but for that I'll need to build a jig. (you'll see...) Bending was accomplished with a generous soak of windex, followed by a tight overwrap of paper, which was subsequently taped down. This worked well, and given the large radius of the bend, didn't require much effort to accomplish. I've also installed the 'slotted' portion of the main body skin. A portion of the outside edges will end up sanded down to be flush with the rest of the skin, but it's fine for now. Next up is starting to fit the skin onto the body and finalizing the rear / fin design. I'm starting to think that it will be a bit 3D CAD and a bit of real world shaping on the fly. Now, what everybody cares about; Photos!:

 

[neil_w]

That is looking beautiful, I'm really looking forward to seeing this one finished.

I was debating whether your balsa bending merit badge should be denied, since you bent the pieces with the grain, but we'll wait and see what happens with those wing fins.:marshmallowbeing serious for a moment: is there a reason you oriented the grain like that? I'd be worried about strength. Are you gonna paper them?)


[edit: I hope it's clear I'm joking up above there]

 

[MCriscione]

I was debating whether your balsa bending merit badge should be denied, since you bent the pieces with the grain, but we'll wait and see what happens with those wing fins.:marshmallowbeing serious for a moment: is there a reason you oriented the grain like that? I'd be worried about strength. Are you gonna paper them?)
[edit: I hope it's clear I'm joking up above there]

Joke received, loud and clear. I understand your thought though, the 'inside' of the curve is already papered. Actually, I printed the fin shape on full sheet label paper and then used it as a guide to cut it out. I think it's a bit more obvious in the first picture there with the main body, as one fin is flipped paper side up. I choose the grain direction with 'some' thought, mostly towards ease of bending, rest assured, most of the bends will be at least partly against the grain, with the upper wing-fin being totally perpendicular. The outside of the fin will get some detail work, including a partial layer of 1/32 inch birch ply, which should add some reinforcement and strength and hopefully reduce the chances of snapping a fin on landing. It's certainly a concern of mine though... In addition, the rather, umm, tenuous appearing connection to the main fin will also have quite a bit of additional support there. It's another 'detail' in the works, but without more to go on, it would look like a really weak connection.

I just realized that my planned pre-paint test flight date, July 8th, with CMASS is quickly approaching. I gotta get my butt in gear...

 

[neil_w]

In that case it sounds like you've got everything accounted for. I'll get back to my popcorn now. op:

 

[MCriscione]

Some progress has been made in skinning the body. I expected the process to be a bit of a trial and error fit-up, but it's gone smoother than I expected. I'll still have some small gaps to fill, but Elmers CWF should take care of that. If anything, the process of determining the proper shape has been easier than I expected. It's just seriously time consuming. It took me about an hour to cut out 4 panels this evening (and attach two). I'll get the other two sometime later tonight before bed.



I've made a bit of other progress. I built that jig I had mentioned. The upper wing-fin needs a 34 degree bend around a 5-6" radius. That pot came to the rescue for me again, but I still needed a jig to ensure I got the proper degree of bend. This one will be against the grain. No pictures yet, but it's still sitting down in the garage 'setting' since last night. I also assembled the Semroc baffle (with added balsa base), which I'll give a quick coat of glue to at some point. I did run into a bit of 'trouble' when I found the outer curved fins had flattened a bit during the first day. They were only under pressure for about 8 hours, and I wonder if they weren't fully dry yet? Or perhaps it was just 'memory'. In any case, I re-treated them with windex and put them back on the other side of the pot. Once I have the re-enforcement ply cut out, I'm sure layering that on will lock in that bend. Enjoy! (more to come...)

 

[MCriscione]

A couple more pics...

 

[MCriscione]

I've been pretty lazy about posting updates, but the build does soldier onward. It's finally starting to look more like a rocket now, abet a half completed one. I can half-envision it sitting in a spacedock somewhere, with little workers jetting around...

Photodump:

before and after body sanding/rounding

Forming the nose cone, 1" balsa blocks sandwiched a piece of .188" basswood, pre-cut with the curved profile. I missed photos of installing the coupler on the back side. It's ok, it wasn't pretty.

Rear fins installed. ROUGH Nosecone fitted for show. Curved outriders are just placed on the tabs for the shot.

Outrider fin details / strengthening plys cut and epoxy bonded. Inner ones are over papering. This was stupid on my part, but I'm hoping the 30 minute laminating epoxy I used soaked through somewhat to enhance the label paper bond. These fins are rock hard now, no chance they'll flatten back out.

 

[MCriscione]

Ten photo limit...

See above for the super rough, bandsaw cuts.

Then used a belt sander to refine a bit. (also some additional fin details/panels

Finally a handblock with 120 >> 220 grit

Still more work to go on it (but it's currently wrapped in bubble wrap after having endured some cosmetic surgery, so no more photos yet)

 

[MCriscione]

Whelp... Had some trouble. My wife ended up getting sick the first week of July and after about a week in bed, she started having too much trouble breathing to get up. An ambulance ride to the hospital, x-rays, CT scan and a bunch of doctor's, and she was diagnosed with serious pneumonia in both her lungs (about 70% reduction in lung capacity). Got put on two strong antibiotics and stayed for 5 days. Thankfully that really seemed to help, but it was another 3 weeks after that before she was back on her feet again, and another couple weeks before she was really feeling 100%. In the mean time, I was fully occupied with care for her and the two kids, so not much work got done on the Endymion. Sadly, time had run out. I truly wish I had been able to find time to finish her, I have some high expectations that haven't yet been met. Regardless, last weekend was my last chance before the deadline to actually fly her, so even in a partly finished condition, I took to the field.

Before:



The flight on 2x Estes D12-3's went very nicely. Video here: https://youtu.be/eVwmAjBloPI

Sadly, I misjudged the chute size a bit. Final flight weight was around 350g, and the day had started off a bit breezy. I wanted to be sure she came back to me, so I only used a 16" TFR chute. I wanted to be sure to reduce drift. Unfortunately, it caused a descent that was a bit to rapid (and spinning) which caused one of the outer fins to snap off on impact with the ground. It's easily repairable, but if I'm reading the rules correctly it probably disqualifies me from the contest. Regardless, the Endymion will fly again, probably after a bit of winter hibernation (repair and significant finishing work) and I'll be continuing to update this build thread periodically.

 

[Gary Byrum]

That's a really killer design man. Musta been pretty tedious. I'm really looking forward to seeing you finish this. The painting alone will require some Picasso tenacity.

 

[MCriscione]

The build actually went along pretty smoothly for the most part, except for the swept/bent transitions. I was trying something that I thought would allow me to get a bit of curve in the third dimension (think saddle shape) but unfortunately, it simple weakened the structure too much, and started falling apart. That's high on my list of items that need to be fixed/finished.

I'm looking forward to finishing her up. I think the paint scheme is going to be fairly simple, at least that's the intent. Something like a Star Trek starship grey with panel lines and some weathering?