BOOM XB-1

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mbeels

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It started with neil_w's "imagination fuel" post, it got me firing on all cylinders, so to speak. I really love airplanes that look like rockets, and rockets that look like airplanes. As he observed:

The challenge with so many of these is making them look good when build around a normal body tube. All the compound curves are tough to execute at small size. The noses tend to be extremely long and pointy, good candidates for 3D-printing. The rest requires some creativity.
and that challenge makes these candidates for an even more fun scratch built project. I started thinking about how to get away from cylinders and recreate the look of some of these exotic shapes. There is a lot that can be done with cylinders and planes (such as @lakeroadster 's slick F-79 Lone Wolf) , but I wanted to do some compound curves.

There are quite a few nice examples of non-cylindrical rockets here on TRF, such as @jqavins Elliptical Rocket, @boatgeek Spruce Goose, the current Steamship Barbicane build by @Ted Cochran , and I'm sure there are more. So this is nothing new, just my attempt at it.

boom.png


This appears to be a concept image of a supersonic jet that is currently in production. There is a website with photos of the current progress as well as some descriptions and a 3D model:


The XB-1 will be a demonstration plane for their future Mach 2+ commercial jet liner ("Overture"), but it looks like a fun build. I don't expect this will be a quick build, there will be some experimentation along the way.
 

neil_w

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Woohoo! Looking forward to this. That is a gorgeous plane.

After fiddling around with the model a bit, I can see that it really has potential to be buildable, with just a few compromises.

:popcorn:
 

Mugs914

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Holy smoke, that is a sexy beast! Thanks for the link.

This is going to be a fun one for sure! Any thoughts on construction techniques?
 

kuririn

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Kudos for taking up the challenge.
More ideas and eye candy here:
 

mbeels

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This is going to be a fun one for sure! Any thoughts on construction techniques?
I have a few things in mind to try, I'm not really sure what will work best. So I'm going to make some attempts, see what happens, and go from there. I'm willing to spend some time on it, I need to slow down my building because my "rocket storage facility" is rapidly filling up!

After fiddling around with the model a bit, I can see that it really has potential to be buildable, with just a few compromises.
Yes, I drew it up in Rocksim (approximately), and I think it will work. I'm going to make some changes, such as putting the center of the nose cone in line with the centerline. It looks like it might want to steer the rocket pointed down like that. I'm also going to droop the horizontal stabilizers to project more area perpendicular to the wings.

I'm not going to go for perfect scale, more like "sport scale" that results in something recognizeable. I want to reproduce the sleek look of the plane so I'll make some compromises along the way for fly-ability.
 

rklapp

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It looks like the fuselage is straight but the wings are curved for high altitude flight.

1592681207042.png
 

neil_w

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I'm going to make some changes, such as putting the center of the nose cone in line with the centerline. It looks like it might want to steer the rocket pointed down like that.
I agree it looks like that, but there have been other rockets with asymmetric noses and it doesn't seem to make any difference (e.g.: Starship Nova, the new LEO Space Train). Particularly on a long pointy nose I'll be it has little or no effect.

Fabricating such a nose, on the other hand, is tough.

I'm not going to go for perfect scale, more like "sport scale" that results in something recognizeable. I want to reproduce the sleek look of the plane so I'll make some compromises along the way for fly-ability.
Sounds good, looking forward to see how you tackle it.
 

mbeels

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It looks like the fuselage is straight but the wings are curved for high altitude flight.
Yeah, that's the Overture, the XB-1 has a fair bit more curve to the fuselage, and some variation to the cross section from the front to back. I'll post some side views that I copied off the 3d models later.

I agree it looks like that, but there have been other rockets with asymmetric noses and it doesn't seem to make any difference (e.g.: Starship Nova, the new LEO Space Train). Particularly on a long pointy nose I'll be it has little or no effect.
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.

Fabricating such a nose, on the other hand, is tough.
Yes, I can't turn this one on a lathe, so it will be more of an art project.
 

rklapp

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The guy who made the mailing tube rocket made it look like an asymmetrical nose cone was easy, however unintentional.
 

Ted Cochran

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Fun project! If you want to replicate the fuselage lines accurately, a stick-and-bulkhead (centering ring) approach using the patterns from the 3-d model on the website should work just fine. Maybe interpolate to get some intermediate bulkheads to help with the curves (and the strength, balsa being a bit weaker than titanium :-D )

May need to build it for a single engine, at least at first, and weight it in interesting ways to make sure the thrust vector is where it needs to be.
 

mbeels

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I was curious to see how far thin wall tubing could be pushed. I didn't expect it to do well for compound curves, but maybe it is possible to do a close approximation. From the 3d model, I estimated the dimensions and cross section shapes at 4 positions. Then, I cut out bulkheads to fit BT 60 and BT-55 tubing.

P6170572.JPG

Near the cockpit area it is somewhat oval, slightly egg shaped, near the middle it is almost square with rounded corners, and round at the back.

P6170573.JPG

P6170575.JPG

P6170574.JPG

But the results are not what I'm looking for. The individual sections of tubing look fine, but the transition from BT-60 to BT-55 doesn't work. Long transitions are hard. This might be a useful way to distort tubes at a particular location, but it was not going to give me the smooth shapes and curves I'm looking for.

P6170576.JPG

Ugh. Abort, Retry, Fail?

R
 

mbeels

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Fun project! If you want to replicate the fuselage lines accurately, a stick-and-bulkhead (centering ring) approach using the patterns from the 3-d model on the website should work just fine. Maybe interpolate to get some intermediate bulkheads to help with the curves (and the strength, balsa being a bit weaker than titanium :-D )
That is my next plan! One length of BT-55 stuffer tube, with sticks and bulkheads.
 

rklapp

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Video has a lot of interesting background on ramjet drones, old school. Probably 3D printing.

 

OverTheTop

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It looks like the fuselage is straight but the wings are curved for high altitude flight.
Hard to tell from the image, but I would almost bet the front of them curve down, just like the Concorde does. This was done to shift the CP of the wing rearward during supersonic flight. The front of the wings at normal cruise AoA actually produce a downforce. Concorde also changes the CG during flight regimes by pumping fuel fore and aft.

That was one of the design constraints that caused the need for a very long front wheel strut. It had to be long to get the front of the wing producing lift as well during takeoff. Due to the delta design there were no other "high lift" devices, like flaps, available to increase lift during takeoff. So by using a very high take-off speed and a long nose wheel it could actually get off the ground.
 

mbeels

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I turned off the scroll saw, put down the X-acto knife, and stepped away from the work bench.

Instead, I needed to sit down at the computer and come up with a plan. Between the website and 3D model, I picked out some views that would be helpful for getting more careful measurements.

boom_side_crop.png


With GIMP, I scaled a top view and side view to match, and then used the measure tool to get dimensions in units of pixels. Then I played with the scaling to figure out what size I wanted.

boom_top_side.png


I placed purple lines on the side view where I'm going to put bulkheads. The forward most section will be a solid balsa nose cone, and behind that will be a BT-55 stuffer tube transitioning to BT-20 at the tail cone.

I then used the 3D model to infer what the cross section shape looked like, and sketched those shapes in boxes drawn to the dimensions I determined. That sets the height and width of each station.

P6180583.JPG

I cut out half of the shape, and used that to get symmetric bulkheads drawn on 1/8" plywood by flipping it over a centerline.

P6180584.JPG

Then I traced out a BT-55 hole through the middle, and cut them out on a scroll saw.

P6180585.JPG

Ok. This seems more promising.
 

mbeels

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Hard to tell from the image, but I would almost bet the front of them curve down, just like the Concorde does. This was done to shift the CP of the wing rearward during supersonic flight. The front of the wings at normal cruise AoA actually produce a downforce. Concorde also changes the CG during flight regimes by pumping fuel fore and aft.

That was one of the design constraints that caused the need for a very long front wheel strut. It had to be long to get the front of the wing producing lift as well during takeoff. Due to the delta design there were no other "high lift" devices, like flaps, available to increase lift during takeoff. So by using a very high take-off speed and a long nose wheel it could actually get off the ground.
Very interesting!
 

mbeels

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Today was mostly Father's Day related activities, but this is what the fuselage looks like partially planked. The white tube is BT-55, and there is a length of BT-20 out the back end.

The bulkheads are cut from 1/8" plywood, and they will be covered with strips of 1/16" balsa. The 1/16" balsa is thin enough to easily twist and conform to the shape of the bulkheads. I'm cutting strips between 1/16" wide (so square), and 1/4" wide, depending on the contours. I'll see what the strength is like after sheeting, I suspect it will be strong enough once it is all glued together, but if it needs additional reinforcement I could do a layer of fiberglass.

P6190587.JPG
 
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Greg Furtman

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Today was mostly Father's Day related activities, but this is what the fuselage looks like partially planked. The white tube is BT-55, and there is a length of BT-20 out the back end.

The bulkheads are cut from 1/8" plywood, and they will be covered with strips of 1/16" balsa. The 1/16" balsa is thin enough to easily twist and conform to the shape of the bulkheads. I'm cutting strips between 1/16" wide (so square), and 1/4" wide, depending on the contours. I'll see what the strength is like after sheeting, I suspect it will be strong enough once it is all glued together, but if it needs additional reinforcement I could do a layer of fiberglass.

View attachment 421377
That's pretty much how cedar strip canoes are made. I built a solo strip canoe about 35 years ago & it is still going strong. The wood strips are covered with fiberglass & WEST System epoxy inside & out. The nice thing about this is that it still lets the beauty of the would show.
 

mbeels

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That's pretty much how cedar strip canoes are made. I built a solo strip canoe about 35 years ago & it is still going strong. The wood strips are covered with fiberglass & WEST System epoxy inside & out. The nice thing about this is that it still lets the beauty of the would show.
A good friend of mine built a cedar strip canoe (2 person), and it is gorgeous! He had to do some repairs when he scraped some rocks on a river, but it is still beautiful. He did the planking in a careful and deliberate way so it makes a nice pattern. My planking is not nearly so nice, but I'll cover it all up and hide it.
 

neil_w

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I'm cutting strips between 1/16" wide (so square), and 1/4" wide, depending on the contours.
Wow, cutting 1/16" strips is a non-trivial exercise. Do you have any particular technique?

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?
 

mbeels

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Wow, cutting 1/16" strips is a non-trivial exercise. Do you have any particular technique?
Not particularly, I have a long, wide aluminum straight edge, and press it down firmly on the balsa sheet with one hand, and cut with a sharp #11 blade using the other hand. This particular sheet of balsa is particularly light and soft, so it is cutting very smoothly and easily. Some of the harder sheets tend to pull the blade with the grain, but this sheet isn't doing that.

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?
With the strip laying on the surface, I'm using a pencil point to approximately mark the intersections with the adjacent plank, slicing it off with a sharp blade, trimming if necessary, and then counting on some sanding and filler to cover everything up 😄. The last piece in a section take the most time, it has to wedge against the top and bottom plank. So it takes some fiddling with a blade and swipes of sandpaper. There will be some sanding. Ok, there will be a lot of sanding. I'm starting at a corner (the bottom edge has a pretty well defined corner), and working towards the centers. More photos tonight.
 

Greg Furtman

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Not particularly, I have a long, wide aluminum straight edge, and press it down firmly on the balsa sheet with one hand, and cut with a sharp #11 blade using the other hand. This particular sheet of balsa is particularly light and soft, so it is cutting very smoothly and easily. Some of the harder sheets tend to pull the blade with the grain, but this sheet isn't doing that.
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.
 

mbeels

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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.
Yeah, I remember that, it seems like it is worth trying. I can also see how more of the blade is against the straight edge. It seems like it could have some advantages.
 

SDramstad

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Today was mostly Father's Day related activities, but this is what the fuselage looks like partially planked. The white tube is BT-55, and there is a length of BT-20 out the back end.

The bulkheads are cut from 1/8" plywood, and they will be covered with strips of 1/16" balsa. The 1/16" balsa is thin enough to easily twist and conform to the shape of the bulkheads. I'm cutting strips between 1/16" wide (so square), and 1/4" wide, depending on the contours. I'll see what the strength is like after sheeting, I suspect it will be strong enough once it is all glued together, but if it needs additional reinforcement I could do a layer of fiberglass.

View attachment 421377
If you are thinking about covering with fiberglass look at this.
I have been thinking about using this to make a bodytube with a non constant diameter like this build of yours. Should go on easy and no edges to deal with.
Steve
 

mbeels

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If you are thinking about covering with fiberglass look at this
That's an interesting possibility, I've seen those products used in other build threads with good results. Based on the "Min - Max" diameters, it looks like it accommodate a body tube with variable diameters and shapes. Is that stuff really heavy, though? I'm used to cloth in the 0.75 oz to 5 oz /sq yard range, and these are 10-30 oz! I see that they also have Kevlar, and the carbon / kevlar patterns are interesting.
 

SDramstad

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That's an interesting possibility, I've seen those products used in other build threads with good results. Based on the "Min - Max" diameters, it looks like it accommodate a body tube with variable diameters and shapes. Is that stuff really heavy, though? I'm used to cloth in the 0.75 oz to 5 oz /sq yard range, and these are 10-30 oz! I see that they also have Kevlar, and the carbon / kevlar patterns are interesting.
They have fairly light weight carbon fiber sleeves. I made a 1.25 inch diameter body tube out of just the lightweight carbon sleeve and it is still quite strong and quite light.
 
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