BOOM XB-1

[mbeels]

I fiberglassed the fuselage and vertical stabilizer with 0.75 oz cloth. For the fuselage, I cut a slit for the vertical tail and held the cloth in place with two dabs of medium CA on either end of the vertical stab. Then it was just a matter of spreading the resin and mopping up the excess.



The cloth lay down like silk and easily conformed to the shapes involved. It results in a hard surface and smooths out small surface imperfections and irregularities. Everything has an even texture. The seam is practically invisible, without my sharpie marker leftovers, it would be hard to find. There are a few whisps of thread laying about, but they'll disappear with a few swipes of sandpaper.





I now encountered an issue, and that is how to put a centerline down the sides of the fuselage for the wings. There is no straight or flat surface. I first attempted using a coupler to connect a section of regular BT-55 body tube with lines marked on it and extend those lines back down the fuselage, but that was not accurate enough.

So instead I made a jig consisting of two cradle pieces which I could measure and mark, and flip around right to left to make sure that the line was in the same place on each side of the fuselage.



That worked well, I now I have markings to guide cuts for the TTWW (through the wall wings).

 

[Greg Furtman]

That is looking really good. Nice fiberglass job!

 

[jqavins]

So instead I made a jig consisting of two cradle pieces... That worked well, I now I have markings to guide cuts for the TTWW (through the wall wings).

And if you connect the two pieces with a couple of sticks then you've got a handy cradle to hold it during later work.

 

[mbeels]

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

Yeah, it'd work well for something like that. And if you have cross sections for templates, it'd make it quite a bit easier.

And if you connect the two pieces with a couple of sticks then you've got a handy cradle to hold it during later work.

Yes, I think when it is time to glue the wings in place, I may trim the cradle and turn it into a support jig.

 

[mbeels]

After fiberglassing the fuselage and vertical stabilizer with 1 layer of 0.75 the weight is up to 3.1 oz, so all that added only about 0.2 oz. Barely measurable with my scale.

Time to start on the wings. I'm happy with the way the vertical stabilizer came out, so I'll take the same approach with the wings. I cut out 4 sheets of 1/16" balsa with the grain along the sweep. I had to glue 3 planks together to get a complete sheet.



To get the thickness and taper I wanted, I decided to do a single 1/4" square piece of balsa at the thickest point of the airfoil, and then two more 1/8" pieces of basswood on each side. I slit these spars to get a straight taper from root to tip. A #11 Xacto blade worked well for this, but the longest 1/8" basswood was a bit tricky, I had to pay attention to the grain and clean up the cut with some trimming and sanding.

Before sanding:



I took the same approach to sanding, putting a taper on the edge of the 1/16" balsa sheet so that it would come to a nice thin edge. Here I'm trying to use the shadows to show the shape again.



I also added 1/16" ribs to help stiffen up the wing. I still want this to fold up symmetrically when I put the tops and bottoms together, so I did not glue where the ribs meet the spars (red arrows). There is a small gap there, I want to allow that joint to bend slightly to the airfoil shape. If I glued that flat, I'd end up with a flat bottomed airfoil. (right and left wings shown below)



After a bit more sanding and clean up, I'll be ready to join the top and bottom.

 

[mbeels]

Prelude to a nose cone:



I scaled the top and side views of the nose, printed them out, and glued them to 1/8" plywood. I then cut it out and traced out the outline onto the balsa block. Fortunately, the block just fit in my scroll saw, so I could zip it out pretty quickly.



I had thought that I could use the negative template as a shaving guide, but it turned out to be useless because I ended up just cutting right to the perimeter line on the scroll saw, so the only thing left to do was round it out. For that I mostly used the Master Airscrew plane that arrived today (yay!), thanks to @Mugs914 for reminding me about that tool.

Progress pics:











At this point it is close enough that I'm going to stop for tonight. I'll look at it with fresh eyes later and sand a bit more.

That was fun.

 

[Mugs914]

This build is just stupifyingly cool, Beels!!!

Isn't that little plane a fun tool?

 

[mbeels]

Isn't that little plane a fun tool?

Yeah, it planes a consistent cut per pass, so it makes it easier to keep things symmetric. I think I've wanted one of those since I saw it in a 1991 issue of R/C Modeler, back when $10 was too much money!

 

[BABAR]

That's good to know! I'd rather try and duplicate the nose of the plane, as it is. The Starship Nova is really quite asymmetric, so if it works for that rocket, maybe the XB-1 will be ok.

Symmetry is overrated

 

[mbeels]

Symmetry is overrated

Maybe! Both our rockets have one plane of mirror symmetry.

But yeah, there are lots of asymmetric rockets that look great and fly just as well. It surprises me sometimes to see what works.

 

[mbeels]

I started work on the upper scoop by first printing out a 1:1 side view. It will be a simple balsa box from 1/16" sheet. I added a 1/16" square stringer along the top corner so I could sand a larger radius.



I plopped it on, sheeted (is that a verb??) the top, trimmed, and started sanding.







I'll do more sanding later. Boy that looks very prominent. Currently this is a very odd and lumpy looking rocket/airplane.

 

[kuririn]

I plopped it on, sheeted (is that a verb??) the top, trimmed, and started sanding.

Looking good, Marten.
Yeah, I think the usage is correct but make sure you pronounce it very carefully.

 

[mbeels]

Looking good, Marten.
Yeah, I think the usage is correct but make sure you pronounce it very carefully.

Thanks, and that's true! Boy, that reminds me of a story that would be next to impossible to properly tell on this forum.

 

[neil_w]

You’re doing a great job on this, and working fast.

 

[Daddyisabar]

KUTGW! Push the envelope on asymmetric design!

 

[mbeels]

KUTGW! Push the envelope on asymmetric design!

Kittens Utter The Good Wisdom?
Karl Undulates Through Gardens Wobbily?
Kool-Aid Unites Thirsty Grand Worms?

 

[BABAR]

Thanks, and that's true! Boy, that reminds me of a story that would be next to impossible to properly tell on this forum.

Hey, if Israel can plop
Beresheet

On the moon, I think your wording is fine for this forum.

https://en.m.wikipedia.org/wiki/Beresheet

 

[mbeels]

Hey, if Israel can plop

Sounds like it did literally "plop"!

 

[Daddyisabar]

Kittens Utter The Good Wisdom?
Karl Undulates Through Gardens Wobbily?
Kool-Aid Unites Thirsty Grand Worms?

OMG, LOL! DOUBLEPLUS GOOD!

 

[jqavins]

Kites Under The Good Wind.
Kentucky Undertakers Think Godlike; Whatever.
Kansas Uberalles; Thank God Wyoming.
Kindness Upward Takes Goodness Wild.

OMG, LOL! DOUBLEPLUS GOOD!

OK, but please answer the implied question: what the heck does KUTGW mean?

 

[n27sb]

Keep up the good work?

 

[BABAR]

Keep up the good work?

Used to be a term used frequently by Luke Strawwalker, IIRC.

 

[mbeels]

I've ordered some more 0.75 oz cloth from Sig, so while that is making its way from Iowa, I have time to come up with a plan for the side engines, air scoops, and horizontal stabilizers. I've been basing my model on the version of the XB-1 shown in the 3D model, but there have been a lot of variations along the way and I'm not exactly sure what the real thing will look like. For example, here is an earlier wind tunnel model showing a central airscoop that is much more rounded than the 3D model.



The square version in the 3D model is fortunately quite a bit easier to make from balsa. But this image is helpful in seeing detail around the side engines. Either way, the main point of this build is not to be a scale model, but to try out some methods for generating compound curves.

 

[Nytrunner]

Used to be a term used frequently by Luke Strawwalker, IIRC.

Before he somehow got banned from the 'Terribly Run Forum' and started complaining about the dangerous high power yahoos that infest it from the safety of Yorf?

 

[jqavins]

Either way, the main point of this build is not to be a scale model, but to try out some methods for generating compound curves.

Hangon hangon hangon. Do you mean to say that you're building this beautiful rocket for a test when you only really needed to build a potato chip? (Sadly there is no emoji for bowing to your greatness.)

 

[mbeels]

Hangon hangon hangon. Do you mean to say that you're building this beautiful rocket for a test when you only really needed to build a potato chip? (Sadly there is no emoji for bowing to your greatness.)

Oh no, I didn't mean to imply that! I should say that the main point is to build a rocket (/airplane) that looks cool by featuring some compound curves. If I take liberties with the scale, that's ok, but it's got to look cooler than a potato chip.

I was pondering which forum to put it in (scale? scratch? LPR?) and decided that I'm more interested in the techniques involved with scratch building than getting a well documented, highly accurate scale model. Scale fidelity is a moving target anyway, because there are so many different examples of this particular airplane between the windtunnel models and website models and illustrations. And the real one isn't even done yet, they just put the wings on. Hence, it is a 'scratch' build, not an LPR or 'scale' thread.

 

[neil_w]

It is in the right place.

 

[Ted Cochran]

I think it's possible that the wind tunnel model is more accurate, as it was created for expensive engineering studies. The 3D model may be an approximation created by social media content creators. So if you want to do compound curves, have fun! You're not constrained by the 3D model.

 

[BABAR]

We prefer you in the craz---i mean creative section

 

[mbeels]

I think it's possible that the wind tunnel model is more accurate, as it was created for expensive engineering studies. The 3D model may be an approximation created by social media content creators. So if you want to do compound curves, have fun! You're not constrained by the 3D model.

Yeah, I bet you're right, the website model is probably the least accurate. There are quite a few variations of the wind tunnel model, it looks like they started with something close to the 1/3 scale mockup which only has two inlet scoops:



and had some design iterations during wind tunnel testing. The 3D website model was the most convenient for me because I could spin it around and get something close to 3-views, but you're right, no need to be constrained by it! The two side engines under the wing are going to be a bit more tricky, so I may take some liberties.

Tonight I glued the wings on and added the pitot tube to the nose cone with a 3/32" dowell.





Next will be the side engines. This is going to be a bit more tricky because I don't have good reference lines or flat surfaces to measure from. It feels all "willy-nilly". So I'll probably resort to some combination of jigs and eye balling.