Build thread: fantasy scale Virgin Orbit LauncherX

[neil_w]

Here is the subject of the build:

You may ask: what is this thing? Well, I stumbled across a 3D model of a rocket similar to the one above that purported to be of the Virgin LauncherOne. As far as I can tell, it was an earlier concept that was later discarded and the rocket ended up with a more traditional four fin design. But I really dig the look of the wings, so I rejiggered it into a flyable configuration, adapted the current paint scheme to it, and redubbed it LauncherX.

Here's a top view in OR:

Front section is BT60, midsection is BT70, 24mm mount. Flight stats above are for an E30-7, which gets it up there pretty good. I might even try that sometime if I get confident enough with my yet-to-be-tried JL Chute Release.

Note: I did a lot of parts prep for this rocket a year ago, but for some reason put it aside to do the Skywriter Deluxe and Plasma Dart first. It is not nearly the most complex or difficult build I have done, but it has its share of interesting bits (I hope).

Standard notes before we start:

1. I like to build in a slow and leisurely fashion. Don't expect a quick conclusion.
2. I promising I will spend Too Much Time fussing and fretting over minor things as I attempt to achieve perfection in my techniques and results. I do this because I enjoy it, not because anyone else is telling me to. Spoiler alert: I will not achieve perfection.
3. Whatever stupid mistakes I make (there will always be some) will be on full display here, along with a healthy dose of self-ridicule. I enjoy this as well.

Onward.

 

[mbeels]

Alright! I like the looks of this one as well. Did this version also launch from the wing of a 747?

so I rejiggered it into a flyable configuration,

How much rejiggering did it take? Something like shrinking the wings and/or moving them back?

 

[neil_w]

Alright! I like the looks of this one as well. Did this version also launch from the wing of a 747?

I think back when the winged concept was still in play, they were still planning to use White Knight Two. They later switched to the 747 "Cosmic Girl".

How much rejiggering did it take? Something like shrinking the wings and/or moving them back?

Well, if I could actually find the original image I used as inspiration, I could tell you. Here's the closest I can find now, shown hanging from White Knight Two:

Yes, I needed to move the wings back and might have shrunk them a bit. I also decided not to have the front part of the strakes follow the transition in front; they are confined to the fat midsection. And I added a proper fincan in the back, although I could swear the original image I saw had some fins in the back. The above image is definitely not the one I used.

I dig that crazy paint job but (a) there's no way I could have reproduced it, and (b) the paint job I chose is closely based off what they're using now, so that's a good excuse I think.

 

[Bruiser]

I thought it looked somewhat familiar. Is it in your "ramblings" thread?

Looking forward to the build. You always pick very appealing rockets!

-Bob

 

[neil_w]

I thought it looked somewhat familiar. Is it in your "ramblings" thread?

Yep. Nowadays all my designs start their lives there.

 

[neil_w]

MOTOR MOUNT

I head-scratched quite a bit about the exact build sequence until I eventually realized that it must be done in fairly strict back-to-front order. So, we start with the motor mount. Here's what it looks like:


The hook is inserted into a slot and the engine block pushed in from the front in standard fashion. The motor mount tube will be used as a TTW mount point, so there can be no tape wrap around the hook. I did a quick sanding of the whole area to take off/rough up the glassine, and went with the epoxy blob method:

Blue tape is there to prevent stray epoxy drips, which has happened to me before. Nowadays, though, I'm usually using 15-minute epoxy, so it's pretty much set up (or at least stopped dripping) before I walk away. Anyway, the hook ain't going anywhere.

The Dual Shroud Support is a very small piece of BT55 that will anchor the ends of two shrouds. I made it about 3/8" long (should have made it a bit longer) and centered it on a single centering ring. Note also the small notch for the hook.

I made a mark on the tube where it needed to go (position needed to be pretty precise, and pushed it into place with a "pusher" made of cardstock wrapped around the tube, to ensure it ended up perfectly straight.

Here it is, completed:

 

[BABAR]

I dig that crazy paint job but (a) there's no way I could have reproduced it, and (b) the paint job I chose is closely based off what they're using now, so that's a good excuse I think.

So yours will not be a Virgin? Makes for a challenging Maiden flight.

 

[neil_w]

TAIL NOZZLE

Every build seems to have its own focus. This one was all about transitions. First up is the tail nozzle.

I wanted the tail nozzle to be really strong, because it would likely sustain the full landing force of the 5+ oz rocket most of the time. And so I got to work on paper shrouds made from 110 lb cardstock. I made the first one with two layers, and it was pretty good. Then I made another, and went crazy and added a third layer. These were made with the separate tab underneath the two ends, rather than the overlapping tab that I usually use, because I wanted these to be ridiculously smooth and perfect.

Both were fully soaked with CA on the outside, and the area on the inside that extends past the ring. I decided to go with the three layer version because it came out so good and feels really strong. Note that I always store transitions on a body tube, to keep them properly shaped, which is why those two are so perfectly round. Overall this is probably the best paper piece of any type that I've ever made, which is good considering how much time I spent on it.

If Gary Byrum were here he would be roasting me for the overkill of a three layer shroud. I miss that.

Going back to the diagram in the previous post, there is a nozzle support ring that is to be mounted flush with the end of the motor mount tube. Getting that ring sanded to the exact correct size took some considerable time and attention. The edge was beveled so it would have good contact with the interior of the nozzle.

And of course it had a proper notch filed in to allow for motor hook movement.

I really enjoy working with the light ply centering rings... they're just so easy to modify as needed with sandpaper and files.

The ring is glued just about flush with the tube. I pushed it a fraction of a millimeter off the edge, to allow just a bit of catch for glue filler, but it's not really important since it's not a structural component.

Glue is then applied to both rings, and the nozzle is slid on from the front, and pushed pretty hard against the centering ring so it's really tight in place.

From the side, you can see that the small end of the ring lands just about in the middle of the dual support ring, leaving space to anchor the tail cone in front. Maybe not quite as much as I'd like, which is why I mentioned previously that I should have made the little piece of BT55 a bit longer to give more margin. But it'll be fine.

I measured and remeasured this assembly about 100 times to make sure I got everything exactly correct. I got it all almost right... the only slight miss was that the end of the motor hook was supposed to be slightly inside the nozzle. Instead (not visible in picture) it is almost exactly flush, or maybe the hook extends the tiniest bit beyond the nozzle. This represents about a millimeter miss. No biggie.

 

[mbeels]

Beautiful. Did you free hand the bevel on that centering ring? It looks quite exact.

So, if I follow correctly, the small end of next transition will need to go over the support ring, without the benefit of the taper. That sounds like it will take even more

considerable time and attention.

 

[neil_w]

Beautiful. Did you free hand the bevel on that centering ring? It looks quite exact.

Yup, just holding it at a constant angle and rotating it on a piece of sandpaper on my bench, ad nauseum. The trick was to get it to the right angle as quickly as possible, and then keep making it smaller until it was exactly the right size. I suspect there might have been an easier way to do it, but I couldn't think of it.

So, if I follow correctly, the small end of next transition will need to go over the support ring, without the benefit of the taper.

Well, it's the anchor for the small end of a shroud, which is normally just a body tube anyway, so that's no biggie. The nozzle was the only place I really wanted to get that taper right, because I wanted it to be strong but also to look clean from the rear (where no one will see it ¯\_(ツ)_/¯).

 

[neil_w]

TAIL CONE

Moving forward, next is what I'm calling the tail cone, which will serve as the body for the fin can. This transition will be slotted for the TTW fins, so I again wanted it to be strong. This time two layers would be fine.

A normal overlap seam was used here; most of it would either be cut out or covered. I did sand the top part of it pretty smooth; that's the part that will be exposed in the final model. The entire piece was CAed and sanded smooth, leaving a keep-out area around where the fin fillets will go (paging @BABAR).

Slots were cut, and a papered balsa ring was made for supporting the large end. It fits recessed into the cone by about 1/4".

While doing some dry fitting, I could see that the fin slots were a tad loose, and even the double-layer, CAed cardstock felt a little floppy there. I became a bit nervous (probably without justification) that the fins wouldn't be strong enough, so I decided to borrow from the HPR playbook and try some half-assed internal fillets. I poked a couple of holes in the ring, and threaded through a piece of Kevlar.

White blue was applied to the exposed part of the support ring shared with the nozzle...

... and the tailcone was slid into place, with the Kevlar-ed ring friction-fitted in the large end. Note that the motor hook and it's big epoxy blog is centered between two fin slots.

The ring will stay in place while the fins are installed.

 

[rharshberger]

Looks great so far!

 

[Nytrunner]

I take a rockets break and you finally start the Launcher-X! Nice to see the 3-fin variant win out for building (I think I have your 3 fin concept in one of our emails from......the past?)

 

[neil_w]

I take a rockets break and you finally start the Launcher-X! Nice to see the 3-fin variant win out for building (I think I have your 3 fin concept in one of our emails from......the past?)

You're the one who talked me into the 3-fin variant, way back when...

 

[Nytrunner]

I know! That's why its nice to see it

 

[neil_w]

FINS

I only paper the exposed part, leaving a bit of additional gap at the base where the external fillet will go. I do this on the theory that it is better to glue directly to the wood rather than the paper (remember this is adhesive label paper). I'll bet it doesn't matter.

For me, TTW fins are by far the hardest things to cut by hand. It always involves a lot of test fitting and sanding. I usually bring the tab all the way to one edge of the fin (the front edge, in this case), which makes the fit a bit easier.

Now I set up my good old 3D-printed fin jig. First I dry-fit my BT60 onto a couple of rings on the motor mount tube, to raise the jig up high enough to clear the large end of the tail cone. Then I strap it on, and line it up with the slot. I extended the fin slot lines all the way to the front, making it even easier to line this thing up.

Then I put in the two pieces of aluminum angle, clamping only once all the way at the end. The angles are spread a bit to allow insertion of the fin.

The fin is inserted, and the piece of angle are squeezed into position. In the past I would apply multiple binder clamps around the jig, and then another clamp around end of the two pieces of angle, but this time I realized there's no need. There's more than enough friction + clamping force to hold the angles in position, and it's not like the fin is trying to push them out of the way or anything. So I just move the angles into position and leave it there for 10 minutes or so until the glue is set.

In the above pic you can see that the BT60 was just large enough to allow the angles to clear the tail cone. That worked out well.

A small TBII fillet is applied immediately, to secure the fin to the tail cone and fill the gap. A larger fillet with Quick and Thick will come later.

After all three fins were done, I pulled out the front support ring and applied some very minimal TBII fillets to the fin roots with a Q-tip. I didn't get much glue in there, and couldn't get it all the way to the far end (pretty tight quarters) but I got enough in there to mostly seal the joint. Doubtful it was needed; after the exterior fillets it all felt pretty strong. But it made me feel better, and now you can call me Mr. Hot Shot Internal Fillet Guy.

I decided I wasn't happy with the homemade ring I had in there before, it was recessed too far from the front of the cone. For most precise mating between the cone and the body tube, I think the ring should be as close to flush at the front of the cone as possible. So I grabbed a wood ring, sanded it to fit (with a nice small bevel), and glued it into the end.

Still not quite flush, but close enough I think.

I finished by applying a TBII fillet around the tube/ring joint, and the fin can is done.

 

[modeltrains]

Cool build!

And now, sorry, but I just can't resist ...

If Gary Byrum were here he would be roasting me for the overkill of a three layer shroud. ... This represents about a millimeter miss.

In DJ voice,
"And we now bring you the hip and hit new single from Three Layer Shroud's new album Overkill, Millimeter Miss!"

(with any luck, maybe your friend Gary would have smiled at that)

 

[neil_w]

In DJ voice,
"And we now bring you the hip and hit new single from Three Layer Shroud's new album Overkill, Millimeter Miss!"

Definitely adding "Three Layer Shroud" to my list of band names, into a special category "Names that almost no one will understand".

 

[neil_w]

BODY TUBE PREP

The fat part of the rocket in the middle is BT70; that tube meets with transitions at each end, so I wanted the ends to be really perfectly square. I put a couple of centering rings into the tube right near the end and then rotated my Great Planes (RIP) sanding block around it. This was a good idea, and I shall use it again in the future.

I gave the tail cone a similar treatment (being double-layered and CA-treated it was very easy to sand), and the end result is two pretty darn square ends, which hopefully will join nicely.

As is my new habit, I applied thinned CWF to the entire exposed body tube areas, to fill the spirals and smooth out any other bumps:

I wasn't super happy with the way this went this time, at least with the BT70. I feel like the CWF was too thick (needed more water), but at the same time it felt like the tube was getting a bit soggy by the time I was done. Seemed fine once it dried, but still I'm not thrilled. I'll keep an eye on this in the future.

After sanding, they look... well, about like you'd expect:

The CWF areas feel incredibly smooth, especially noticeable on the BT60, where I can feel a *huge* difference between the coated and non-coated portions.

I think in the future I might try sanding the glassine a bit before applying the CWF, to give it more grab. It mostly seems to stick OK, but there are occasional small areas where the CWF clears away. Maybe a roughed-up surface will adhere a bit better.

 

[neil_w]

BODY TUBE ASSEMBLY

With the fin can finished, it's time to start assembling the body tubes. Three centering rings are mounted on the motor mount tube:

I want the rings for the BT60 to have absolutely no slop, to guarantee a straight join with the motor mount. The front ring was a bit loose, so I gave it a wrap of cardstock and then sanded it down to a perfect fit. A pencil line marks where the end of the BT60 needs to go. There's a 3" overlap between the two tubes.

Glue is applied, and the BT60 is slid into place.

Next, a second ring for the BT70 is glued to the BT60.

I love body tube/centering ring jigsaw puzzles like this.

And now, I realize that I've made my first bonehead mistake, which should be obvious. I knew I was going to make this mistake, but did it anyway.

Fix to come.

 

[mbeels]

Hmm... not obvious to me.

Sliding the BT-70 over the two rings and getting glue on the upper ring? Shock cord mount?

 

[Bruiser]

Took a minute but I understand. I was wondering where the break would be, nose cone or at the back of the transition and the picture answers that.

Btw, that aft assembly looks sweet!

Refresh my memory... Do you "seal" the leading edges of the label paper with thin C/A?

-Bob

 

[neil_w]

Sliding the BT-70 over the two rings and getting glue on the upper ring? Shock cord mount?

Refresh my memory... Do you "seal" the leading edges of the label paper with thin C/A?

Nowadays, yes, using thin SuperGold wiped on with a Q-tip (god I go through a lot of Q-tips). In the past I used TB2 but I have mostly switched over since the SuperGold is fume-free and I can work safely with it at the bench. Both work fine, each with its own pluses and minuses.

 

[neil_w]

SHOCK CORD FIX

So as shown in the previous post, I forgot to attach my shock cord to the front ring on the motor mount tube. I *knew* I was going to forget it, and sure enough....

Before I start: I know there are many different ways I could have fixed this. I chose this way.

I needed to glue a shock cord anchor 12" down into the BT60, which I think is farther than I've ever had to go. I made an anchor out of a 1/2" piece of BT55 and two centering rings about 1/8" apart. Using two rings would help ensure that the anchor would stay straight in the tube, and also provide more surface area for gluing, since perfect glue coverage would be tough to guarantee all the way down in there. I chose BT55 because, being larger than the motor mount tube, I knew it would be able to slide all the way down against the next centering ring, and around the end of the motor mount. Also it is out of the direct blast of the ejection charge, for what it's worth.

For the first time ever, I decided to tie the loop on the Kevlar before installation, because I knew it was going to be iffy to pull it out the back afterwards (I've run into this problem before when the anchor is close to the center of the rocket). Here's the finished piece.

The Kevlar is looped between the two rings, which made it easy to glue it in by just filling the channel between the rings with a bead of glue.

That's actually my second piece of Kevlar; the first one somehow got frayed:

Once I saw that I ripped it out and put in the new piece. That is not what you want to see in your Kevlar before it's even flown once.

To actually get the anchor glued in down there, I'd need two tools: a pusher, to give it a firm and *straight* push into the tube, and a long glue applicator.

The pusher is a long piece of cardboard rolled up, with a piece of larger-than-BT55-but-smaller-than-BT60 tubing glued onto the end:

This would apply straight and even pressure around the perimeter of the ring, ensuring a smooth and straight installation.

White glue was applied around the body tube with the dowel, and the anchor was pushed into place successfully:

You can see that the Kevlar loop ends about 1/2" from the edge of the body tube, which is perfect. When I pulled it out the back of the rocket...

...it only stuck out about that much. Which means it's a good thing I pre-tied the loop, because I wouldn't have been able to do it at the desired length out the back. That is more than enough exposure, though, to attach the elastic, which I'll do at the very end so it doesn't annoy me for the remainder of building and finishing.

If I ever have a Kevlar break in a rocket in the future, I'll probably use this exact method to anchor in a new one. It's probably a bit more complex than needed, but it worked well, was pretty much foolproof, and only cost me a couple of rings and a sliver of BT. I'll take it.

 

[Bruiser]

Quite a fix you came up with and like you wrote, it can also be used if one needs to be replaced. Way to go!

-Bob

 

[Daddyisabar]

Coolness!

 

[neil_w]

FINISHING THE AIRFRAME ASSEMBLY

As mentioned previously, I did a splendid job squaring off my transitions and body tubes Nonetheless, a dry fit is *always* a good idea:

Apparently I put a bit of an angle on one or the other. I bit more sanding yielded a much more satisfactory dry fit:

Glue was applied to the ring, and the edge of the transition, and then inside the other end of the body tube:

And the body tube is slide into place.

Several rounds of CA/sanding/CWF/sanding/more CA smoothed out the joint. This is something that I struggle with every single time; I still don't have what I would call a good, repeatable way to smooth out those joints.

The front transition was made like the tail cone: two layers, lots of CA and sanding. Like that one, it's also not smoothly round, due mostly (I think) to the use of liquid glue to joint the two layers. I may switch to glue sticks in the future; I'm experimenting with one now. A ring was glued into the end.

Glue was applied to the edge of the transition, and to the BT where the ring would sit...

...and it is slid into place. A wipe of CA with a Q-tip is all that is used to seal down the small end.

And now the airframe assembly is complete, other than some CWF work to smooth out the front seam.

 

[Bruiser]

Really taking shape and looking great!

-Bob

 

[neil_w]

BT MARKING AND LAUNCH LUG

I made this marking guide for the main body:

Everything is clearly marked so I can't possibly make a mistake.

First I made a mark along the top, using the seam on the tail cone for alignment. Then the marking guide went on, aligning the seam with the top mark. I was happy I got the size just about right on the first try.

Then I made the marks as indicated on the guide. Lately I like to make two marks for the fins, finding it easiest to center the fins between the lines. Especially useful here, with the very thick wing assemblies.

I sanded down/scuffed up the fin and lug attachment areas with my 220 grit sanding stick. Maybe not necessary but how could it hurt? Also, have I told you lately how much I love my sanding sticks?

I then cut, CWFed, sanded, and attached the lug (a 2-incher, centered on the BT70, on the bottom.) As I went to sight down the tube to get a good visual on lug straightness, I was confused by the fact that.... a fin was in the way? What? Ah: I had put the lug on top instead of the bottom.

Remember how I said up top that I labeled everything on the marking guide so I couldn't get anything wrong? That's called "foreshadowing". Also, perhaps I should actually pay attention to what I'm doing once in a while.

Fortunately the glue was still wet, so I pulled off the lug and wiped off the glue with a wet paper towel. Then I applied another bit of thinned CWF to cover over sanded-and-scuffed are for the lug to smooth that over, and put the lug in its correct place on the bottom.

Since TVM published that article on launch lug drag, I've been following his results and angling the front, and leaving the back square. I did a better job than usual getting a clean cut this time. And hey, I remember to attach the lug before painting! That's gotta count for something in life.

 

[Bruiser]

If it were me, I would have continued on my moment by putting the slant to the rear on the re-glue

-Bob