BOOM XB-1

[Greg Furtman]

Woo measuring pixels! (I use paint though lol)

You know how people say the full moon looks bigger after it has just risen? There is an easy way to refute that. Take a picture when it is near the horizon and another (same lens, same focal length) when it is overhead later and then count pixels. When the moon is overhead we are 1 Earth radii closer to the moon than when it rises.

 

[mbeels]

Also, since there is quite a bit of taper towards the rear, it means that many of the planks will need to be tapered as well. Do you have a technique for calculating the shape of each piece, or are you just eyeballing?

This is a phase of construction that is harder to document and get good photos of the intermediate steps. This was mostly eyeballing with the help of some pencil marks.



I did not spend much time getting it perfect, nor did I attempt to chamfer the edges so the planks would meet up well together, I just tried to get some contact for each piece all the way around. As long as it is glued to the piece next to it, I think it will be strong enough and not *squish.

There is going to be plenty of filling and sanding, that's alright. Just put on some good music, and enjoy it.





I also upscaled slightly from my first hasty attempt. The curves are subtle, but they're there.

I left a gap in the top rear for the vertical stabilizer. The wings will be TTW, so I'll do some cutting later.

 

[Greg Furtman]

@mbeels I think the idea of using a sleeve is a good one. No seam! And it will conform to the different diameters. There must be some lighter weight ones out there, although you'll be using so little that I don't think that cloth weight will matter much.

 

[mbeels]

@mbeels I think the idea of using a sleeve is a good one. No seam! And it will conform to the different diameters. There must be some lighter weight ones out there, although you'll be using so little that I don't think that cloth weight will matter much.

Yeah, that is an interesting possibility. Although I've wrapped tubes before with 0.75 oz cloth, and it is so thin that the seam really disappears. If I did a layer of 5 oz cloth (or heavier) I would wrap it in 0.75 oz cloth anyway, as a veil layer to hide the weave texture.

This fuselage is coming out pretty smooth and strong though, I don't think it will need a heavy layer of fiberglass for strength. I'll probably just do one layer of 0.75 oz cloth purely for cosmetic purposes. It gives a nice, even smooth surface texture, and hides small blemishes.

 

[neil_w]

This fuselage is coming out pretty smooth and strong though, I don't think it will need a heavy layer of fiberglass for strength.

This doesn't surprise me. Are you gluing the planks to each other, or filleting in afterwards?

 

[mbeels]

This doesn't surprise me. Are you gluing the planks to each other, or filleting in afterwards?

A little bit of each. I'm using CA so I can work quickly, and the planks are long enough (I'm no Rachmaninov) that I can't hold the entire plank in place at the same time. I'm not totally consistent, but what worked well was to CA one end of the plank to the first bulkhead (and the end of the adjacent plank), and then go down the strip, using medium CA to glue it to each bulkhead while holding it tight to the adjacent plank. Then, after the plank is completely glued to the bulkheads, I'll go back and use thin CA where the gap to the adjacent plank is small, and medium CA where the gap is larger and fillet the joint.

The last plank in a section was "WIT" (whatever it takes), shove it in, and follow up with thin CA and medium CA fillets.

The whole thing went fairly quickly, and was fun.

 

[SDramstad]

@mbeels I think the idea of using a sleeve is a good one. No seam! And it will conform to the different diameters. There must be some lighter weight ones out there, although you'll be using so little that I don't think that cloth weight will matter much.

Yeah, that is an interesting possibility. Although I've wrapped tubes before with 0.75 oz cloth, and it is so thin that the seam really disappears. If I did a layer of 5 oz cloth (or heavier) I would wrap it in 0.75 oz cloth anyway, as a veil layer to hide the weave texture.

This fuselage is coming out pretty smooth and strong though, I don't think it will need a heavy layer of fiberglass for strength. I'll probably just do one layer of 0.75 oz cloth purely for cosmetic purposes. It gives a nice, even smooth surface texture, and hides small blemishes.

For something this size the fiberglass sleeve may be a little too heavy. Now upsize it to a 38 or 54 mm motor mount and the weight wont matter.

 

[Nytrunner]

I guess I missed the BT-20 part of this. Are you really going for 18mm motors on it? Time to break out the C5's C12's D16's and D20's (Not to mention D13s or 24s if you like eetzy beetsy reloads)

I pegged it as a 24mm at least.

 

[mbeels]

I guess I missed the BT-20 part of this. Are you really going for 18mm motors on it? Time to break out the C5's C12's D16's and D20's (Not to mention D13s or 24s if you like eetzy beetsy reloads)

I pegged it as a 24mm at least.

Yes, before I started laying out parts, I was thinking 24mm motor mount. The decision to go smaller was partly due to tubes on hand and also space. My basement is starting to fill up with rockets and rocket parts! Plus I have a cute little 18mm/20 reload case that I don't use as much as I'd like to. I'm aiming to keep the weight in the 6-8 oz range which should be good for D13 and D24 reloads. So I am paying attention to weight as I go.

 

[OverTheTop]

If you are considering fiberglassing, what about a couple of layers of thin f/g tissue?

 

[lakeroadster]

Yes, before I started laying out parts, I was thinking 24mm motor mount. The decision to go smaller was partly due to tubes on hand and also space. My basement is starting to fill up with rockets and rocket parts! Plus I have a cute little 18mm/20 reload case that I don't use as much as I'd like to. I'm aiming to keep the weight in the 6-8 oz range which should be good for D13 and D24 reloads. So I am paying attention to weight as I go.

Size wise finding the sweet spot can be a challenge. Opinions vary but I'm thinking a rocket that small and that complex will increase the difficulty of the build..

 

[Daddyisabar]

Go small or go home! This isn't in the high power section...right?

 

[mbeels]

If you are considering fiberglassing, what about a couple of layers of thin f/g tissue?

I'm not familiar with f/g tissue, but I've used 0.75 oz, is it similar?

Size wise finding the sweet spot can be a challenge. Opinions vary but I'm thinking a rocket that small and that complex will increase the difficulty of the build..

Yes, I also wasn't sure how well the bulkhead + planking would go, this is as much of an experiment as a rocket build, so I have less material invested.

 

[boatgeek]

Size wise finding the sweet spot can be a challenge. Opinions vary but I'm thinking a rocket that small and that complex will increase the difficulty of the build..

And also increase the glory! [Cue charge into medieval or Klingon battle]

 

[OverTheTop]

I'm not familiar with f/g tissue, but I've used 0.75 oz, is it similar?

Not sure what the weight was as I have never used it. Knew it was light though.

Looks like it is available down to at least 0.3oz
https://store.acpsales.com/products/7731/fiberglass-tissue

 

[mbeels]

After about 2.5+(+) rounds of sanding and CWF, the fuselage is looking alright. My son really wanted to sand, so I let him do some of it.





While letting the CWF dry, I started working on the vertical stabilizer. I decided to do a sort of built-up structure to get the cross section shape how I wanted. It has a vertical spar of 1/8" balsa, shaved down to nothing at the tip, plus 1/16" ribs to help set the profile.



I also sanded down the leading and trailing edges of the 1/16" sheet to get pointy edges. First I glued the trailing edge together with wood glue, and let that dry.



Then I carefully folded it together to meet at the leading edge. The airfoil of the vertical stabilizer should be symmetric, so I used a combination of measuring (the left sheet and the right sheet are the same size, so they should meet together evenly at the front) as well shadows from my shop light and eyeballing to make sure it was coming together symmetrically.

Here it is in the shadow of my shop light to accentuate the cross section.

 

[neil_w]

From here the fuselage looks much better than just "alright".

Great progress!

 

[mbeels]

From here the fuselage looks much better than just "alright".

Great progress!

Thanks, it's hard to photograph a slightly non-cylindrical object. On its own it looks somewhat miss-shaped and odd, but I think that will change once it gets a nose and appendages.

 

[mbeels]

And also increase the glory! [Cue charge into medieval or Klingon battle]

Sons of Scotland, I am mbeels.
mbeels is seven feet tall.

Yes, I've heard. Uses CWF by the ton,
and if he were here he'd consume the sandpaper with fireballs from
his eyes and bolts of lightning from his arse.

Would you be willing to trade all the days from
this day to that for that one chance, just one chance to come
back here and tell our LCOs that they may take our flight cards,
but they'll never take ... our balsa!

 

[dhbarr]

Sons of Scotland, I am mbeels.
mbeels is seven feet tall.

Yes, I've heard. Uses CWF by the ton,
and if he were here he'd consume the sandpaper with fireballs from
his eyes and bolts of lightning from his arse.

Would you be willing to trade all the days from
this day to that for that one chance, just one chance to come
back here and tell our LCOs that they may take our flight cards,
but they'll never take ... our balsa!

:applause:

 

[trialsguy]

You know how people say the full moon looks bigger after it has just risen? There is an easy way to refute that. Take a picture when it is near the horizon and another (same lens, same focal length) when it is overhead later and then count pixels. When the moon is overhead we are 1 Earth radii closer to the moon than when it rises.View attachment 421485

When the moon is rising, it only appears larger because it is near other, familiar objects on the horizon (such as trees, buildings, houses, etc.).

The next time you witness a moon rise, where the moon appears to be quite large, turn your head upsidedown and look at the moon. The moon will appear its normal, smaller size. Really. Try it.

 

[jqavins]

I think it was @jqavins that mentioned using curved #10 blades for cutting balsa since you can use more of the blade than just the tip. I'm going to pick some up & give them a try.

It's not just "more blade" that I like, it's that the belly of the curve is far less prone to snagging that the tip. I like it for balsa, and also for paper and cardboard. But only for straight cuts. It's pretty much impossible to turn corners without going up onto the tip.

 

[Glasspack]

Wow …………. Some amazing modeling skill !!!
Looks GREAT !!!!

 

[mbeels]

It looks like I'm running low on 0.75 oz fiberglass cloth, I've got a bit left, but not much. I can't remember where I got this from, but I'd like to get more. I see that Sig has 0.75 oz, and Hobbico has 1.0 oz. I just want a small amount, not a large roll. Does anyone have any suggestions for what to get, or where to get it from?

 

[mbeels]

Sanding the fuselage is done, I forgot to weigh it before I glued the vertical stabilizer on. With vertical stabilizer, the combination weighs 2.7 oz. I fiberglassed the vertical stabilizer with 1 layer of 5 oz cloth, and the total weight rose to 2.9 oz. The weave of the 5 oz cloth is pretty noticeable, so everything is getting a layer of 0.75 oz cloth. That will give it a bit of durability as well as even out the surface texture.



Fresh after trimming the 5 oz cloth:



And the profile:

 

[Mugs914]

Fantastic...

 

[neil_w]

Beautiful!

 

[jqavins]

Outstanding!

 

[kuririn]

Nice work.
I might be able to use those methods to build some land speed record cars.
Think Blurzz with new skins.

 

[Cape Byron]

The work going into this is quite amazing.

Hey, @kuririn, that sounds like a brilliant idea.