1:144 North American XB-70 Valkyrie

[Gearup]

Photos.

[lastvautour]

That is a fantastic method of making those engine intakes. I really enjoy your post and the details contained. True a museum quality model.

Lou

[Gearup]

I've been jumping around a bit on the various bits of the Valkyrie. Carving, priming and pondering next steps.

The major parts are now primed, but still separate from each other. I think I will work a bit of paint detail in the inlets prior to assembly to the wing. With the canard installed and the fuselage primed it looks like a broad-head arrow without feathers.

I have started to prime and fill the components using Zinser B I N white shellac primer. It is really nice stuff to work with. It dries fast and seals and fills the grain quite nice. It sands really well after about 30 minutes. Being shellac it works well over wood or other paint types and acts as a intermediate bond to the top coats.

Rather than working from an open can, I made up a funnel holder from wire and ladled the paint, using a spoon, into a 2 oz self sealing squirt bottle. It keeps things cleaner and does not expose the paint in the can to the air continuously.

I brushed on the paint and sanded between coats and spot-filled as necessary. The paint can be thickened using "fumed silica". This is a filler commonly used to thicker epoxy and such. Its lighter than goose-down feathers and a 1 quart container weighs about 1.5 oz !

The paint from the can is really perfect for brushing, which is the way I applied it. Try to lay the paint down in slightly overlapped passes. Working the paint too much will end up a bit messy as the fresh coating dries fast, but is redissolved by the next pass or two. An even wet coat will dry quickly and allow you to sand it down.

For spot filling add about a teaspoon of thickener to 1/2 teaspoon of paint in a small cup. Its like mixing flour and water: it clumps up at first then disperses into a paste. When it is the consistency of peanut butter it is about right. I used a plastic card as a spatula to apply it to larger surfaces and it fills grain really well. For small low spots I dab a bit on the area and give it a quick wipe with the card (or finger) and sand it back fair.

So between coats and for a change, I thought I would build the tail pipes. I used a hardwood dowel (birch?) and turned them on the wood lathe. Using a large drill chuck to hold the piece, I first drilled the inside of the pipe to diameter. Starting with a centre mark from the lathe tailback, i used a small (1/16") drill hand held in another small jacobs chuck. I progressed up to the final diameter in two more drill steps. I then turned the dowel to the major diameter as measured with a drill gauge. Marking the length from the end of the part showed where to start the curved taper to the exhaust outlet. its only a few 10 thousands reduction but it is easy to achieve with a parting tools (nothing fancy) or it can be done completely with sandpaper. The outlet was checked for size again with the drill gauge.

There's six engines so I made about 10 pipes to get the ones I wanted, some to practice on and some to look for later on the floor.

The tail pipes are actually the afterburners and have many segments to vary the outlet area. I used a small scribing tool SCR-01 from UMM-USA to add the lines to the pipes. It is nicely ground like a graving tool and cuts nice straight lines in wood or plastic. It takes a bit of practice, but it is very satisfying to see it make tiny curled shavings in a straight line.

I held the tail pipes on a slightly tapered dowel fitted to the inside to hold them while forming the segment lines. The tool is not razor sharp and does not take much effort to push along.  Note: The tailpipe shown is a test piece to try the scriber on it. Yes it looks a bit messy, but it was worth testing out the technique first

I have more to do on the wings yet. After all one of the defining features are the outer wing panels which fold down 67 degrees to allow the aircraft to surf its own shock wave at M3!

Fraser

[lastvautour]

That is fantastic Fraser, This is an awesome tutorial.

Lou

[Gearup]

It is fun.I know that others may not have access to a small lathe, but the tailpipes are easy to make using a drill and sandpaper and using as scribe  to mark the lines. That is what I like about making the wooden models; the freedom to try different methods during the construction.

A note on drilling the dowel. Holding the drill bit stationary and spinning the work with the drill allows the bit to self center in the dowels axis of rotation giving a cantered hole for the depth needed.

Fraser

[Boomerang]

I echo Lou's comments Fraser.

Awesome !

Gordon

[K_mars]

Great modeling!

It is difficult to make the same things by hand, but it is the real pleasure of the solid model.

Kenji

[Gearup]

Have been working away on the Valkyrie over the past few weeks.

I've installed the fins and used this method to locate and ensure the proper alignment. I cut a block to space them apart and hold them vertical. Then using a 0.025" drill, i drilled two holes on the root of each fin to fit 0.020" brass pins on the drill press. After clamping the block to the wing. I then transferred the hole location to the top of the wing to match the fins. I did this by using the small transfer points that I made for previous models. They are 0.020" brass by 1/2" long. There is a blob of solder at one end that has been turned against sand paper to create a small point with the solder acting as a shoulder to prevent the pin disappearing into the hole.

I then position the fin at the correct location fore/aft and hold it against the block fixture. A light push down on the fin makes a nice little centre mark on the wing from the pins. When drilled it is a perfect match to the existing pin holes on the fins.

Next I tackled the wing folding hinges. The prototype aircraft used compound planetary gear boxes of a reported 35,000:1 reduction (!) driven by hydraulic motors. It appears there where no locks to hold the wing tips at the selected position as you find on carrier planes. This was accomplished by brakes that held the drive line at the selected 0/25/67 degree positions. Planetary gear boxes do not back drive too easily especially at this extreme reduction ratio.

I chose a simpler method by fabricating hinges from brass tubing and rod. I used 1/8 brass tube for the hinge body and 3/32 tube for the hinge pins.  To ensure that the hinges would not snap off the wing, I soldered 0.020" pins to the tubing. Two on the central piece and one on each small hinge body. The pins are inserted into the brass tubes by cross drilling the tube with the small tool bit used before and soldered.  A small centre drill was used to start the hole on the tube while it was held in a drill press vice. Machinist centre drills are a short small drill on a large diameter shank so they are rigid and don't wander when starting the hole. Once a good "v" point is on the brass tube, the fine drill will try its hardest to stay in that divot and not wander around.

The resulting hinge was really quite strong and rotated freely. Once i determined they would work using a mock up with a test wing, I cut the wing tips off. After all the work to shape the delta wing, it was a bit of a stress to cut them off. Additionally it was not a straight cut and had to be two cuts to provide the correct gap for the hinge when assembled. It went well and I did not have any real problems.

After carefully marking the holes for the pins of the centre hinge on the wing stub, they were drilled this time using a handheld dremel tool. I could not use the locating pins as before because the width of the hinge and length of the mount pins prevented using that method. So  I had to wing it and transfer the hole locations by pencil by laying the assembled hinge in the gap and marking each wing and tip as a pair.

The fit went really well and then I glued the pins into the holes. This was a bit of fun since the cyano glue ran into the hinge joint, which was not good. I had to use acetone to free the joints up, but a total disaster was averted.

Next making the drive fairing to fill the gap.

'Fraser

[Gearup]

Oh yes, before I cut the wingtips free I scribed out the elevons. I used my fish hook tool and it worked out well.

As well here are more pictures of the wing cut apart and locating the hinges.

The wing tip folded down shows the problem created by the cuffed/drooped leading edge. when rotated down the arc of the leading edge starts to interfere early on with the main wing. The original aircraft used a titanium boron alloy fairing to cover the gap. I was fresh out of that stuff so there is a bit of a gap at this point that I could only minimize with filling , but not completely eliminate.

I initially thought a simple tapered dowel would form the spike but again the cuffs were a problem. I built up the structure of the hinge with styrene rod, wood and filler. To prevent the hinge from becoming stuck together, I inserted wax paper at the joint to work with the filler. Many thin layers and sanding to shape ended up with a workable fit, but I did not have a practical solution to completely fill the gap caused by the cuff. That's where squinting and using imagination to fill the gap works. 

SO now it is ready to assemble the fuselage and lower body (engine nacelles) to the wing.

[Gearup]

Joined the blocks together. No real challenge here, but the locating pins and holes I made early in the model sure help it line up.

Starting to look like a Valkyrie!


Now I'll continue on with filling, primer and paint. Currently woking out the color scheme. White with black and maby red somewhere..........plus some grey. I knew it was going to get more complicated.


Fraser

[lastvautour]

You capture the look of the Valkyrie. This will be an excellent addition to your collection.

Lou

[Boomerang]

Fraser ,

In  a word  Awesome ! I can imagine your sense of satisfaction with this so far.

Cheers

Gordon

[Gearup]

Thank you Gordon and Lou. Now working on the markings. The only color, other than white and black, are in the insignia.
Fraser

[Gearup]

Nearly done. Thought I'd take a photo and play with it a bit in photoshop. So here is the Valkyrie nearly complete at the edge of space....

I used an iPhone and one desk lamp. With all the other lights in the shop turned off at night it is possible to get a nice black background.  Just don't illuminate the shop with any other light or have light coloured / shiny stuff behind the model. The wall is about 10 feet behind the model with the light angled towards the camera and I used my hand to shade the lens to avoid glare. The larger distance behind the model makes it darker. I only cloned out the stand. I am experimenting with the design of the stand and made the black background a bit blacker in photo shop.

Fraser

[lastvautour]

A magnificent model Fraser. The white on black makes it come to life.

Lou