1:144 North American XB-70 Valkyrie

[Gearup]

In the spirit of Lou's mystery aircraft series, here's my new project.  1:48, my scale of choice would be a bit big....
Fraser

[Boomerang]

Mmmmmm .... I'll go with a B-70 Valkyrie.

Gordon

[Gearup]

Yes indeed. XB70 Valkyrie.  Easily identified even with the rough cutout forms and bad photo😀.
It is an aircraft that has to be seen to really appreciate the state of the art in 1964. I was lucky enough to see the only remaining aircraft at the USAF museum in Dayton Ohio. It was late and I had 15 min before the museum closed, but it was definitely worth the trip.

So I'm building a 1:144 model of it as 1:48 would have been too large to display.  Spruce for the fuselage and engine nacelles, birch ply for the wing and maple for the vertical fins and canard. Hopefully I will have the wingtips folded down, so it will likely be in a flying position.

Regards,
Fraser

[lastvautour]

Great start Fraser.  The Valkyrie would be too big in any other scale but 1/144. I look forward to its development.

Lou

[Boomerang]

Even at 1/144 it will be impressive. Looking forward to progress.

Cheers

Gordon

[Gearup]

Pinned major parts together. I like to drill 1/16 dia holes at station lines on centre that I can use as alignment points once the parts are carved. Also major reference points are located with holes such as the wing folding hinge center line.
The wing is not a simple triangle either. There is a significant droop in the leading edge that I still need to figure out. I may have to laminate the leading edge lower surface to increase the thickness for carving the droop.

The first photo show the pinned model with the station contour templates ready. The hinge mechanism fairings are simply there for illustration and argot the correct length.  The second photo shows that I will need to pay a lot of attention to the inlets. They are huge and very open to see into.
Fraser

[Boomerang]

Nicely done so far Fraser.

Gordon

[lastvautour]

Looking good Fraser.

Lou

[Gearup]

Started on the wing. How hard could it be? It's just a triangle..  Well it is, sort of.
I spent a bit of time trying to get a good picture of the wing top and bottom to see the contours. Its not that easy because it is an all white, pretty much featureless surface. Also the aircraft flew in the harsh light of the Mojave desert and was not photographed as an art object. Even on the ground, photographers tended to focus on the entire aircraft (no fine detail) or on cool stuff like engine intakes and exhausts. So from a couple of good photos with oblique lighting I got a better understanding of its shapes on the upper surface. It was difficult to get an equivalent shot from below, but i pieced enough info from material to get an idea of the leading edge cuff shape.

Since there was a significant droop on the leading edge, I had to bond 1/16 spruce to the lower surface and carve and shape it. The upper surface leading edge is sanded down to the point it is below the plywood edge and the spruce starts to thin out to form the curved cuff. The wing is definitely not a typical airfoil. On the lower surface the cut was blended into the wing by carving and 80 grit paper on various sticks. I used the canopy wire test on both surfaces for fun to see how it looked. I still have a bit more shaping to di and then filling.

If you notice on the wing the extreme tip of the triangle is broken away. This is art imitating life. It snapped of during shaping so I will address it later in the build. On the prototype aircraft the tip indeed broke off and damaged all SIX engines to the point of no repair.The aircraft kept going on two engines until the #5 engine was restarted to balance the thrust for landing. Turned out the actual airloads where flexing it down and not upward as thought and it was redesigned. I don't think the problem was cross grain though......

Anyways on to fuselage shaping. Still a bit cool in the shop with the rare code weather here.

Fraser

[Boomerang]

Love your work Fraser.

Gordon

[lastvautour]

Thank you for the posts. Some people have asked me if we gave tutorials. This is a fine one.

Lou

[Gearup]

Thanks Lou. Part of the fun for me is to try and make the process visible for others who are looking for techniques to use on their models. I sometimes think the doing is more important than the end result.

Carving of the fuselage seems to have gone well. It turns out the best tool has been 80 grit sandpaper double side taped to a 3/4 x8 inch block of wood. A knife was used for some of the detail work but the block works great on the circular section of the fuselage.

Maple is used for the canard and vertical fins because of the thin sections involved. Again the 80 grit block was used to sharpen the flight surfaces. I held the fins with a small jewellers hand vise and and worked the edges to a wedge profile. The jaw surface of the vise made a nice edge to guide the sanding block and really helped hold the parts.

I was going to split the canard apart to attach the halves individually to the fuselage with pins. Then I decided to keep the canard in one piece for strength, but I did not want to notch out the fuselage to fit it. So i slotted the  fuselage to allow the canard to slide into place. I used the station holes with a1/16" rod clamped between two blocks to keep the fuselage square to the scroll saw. Once the slot was cut, I sanded it to fit with popsicle sticks  and 220 grit.

Drilling all of the pertinent station holes square to the block before  cutting it out really helps to align the assembly's later and can also be used for positioning parts for machining.  I fill them with automotive glazing putty or plastic wood when I'm done with them.

Attached are a few pictures of progress so far. Next job will to be to form the huge inlets in the lower body.

[Boomerang]

Excellent work Fraser. Looks like it wants to fly now.

Cheers

Gordon

[lastvautour]

I echo Gordon's comments. Excellent indeed. And yes the process is the important part.

Lou

[Gearup]

I have been kept busy making the lower body of the XB70 and working out the inlet geometry. Because of the large size, they definitely need to be hollowed out to look proper on the model.

I estimated the inside shape to cut out and did that with the scrollsaw. It will be critical to get the sharpness of the inlet leading edges and keep them strong.

After i cut the inlets out, i thought i would fix the missing tip on the wing as it was important how the tip worked with the inlets for positioning. I used .010" styrene sheet bonded on the wing with cyano to form the tip and sanded it to shape. Seemed to work pretty good.

To close the bottom of the lower body, i thinned out a piece of 1/8" birch ply. I basically planned, sanded and scraped the first layer of veneer off. Of course it went easy until the under layer was exposed as now it is all cross grain and glue. By sanding and scraping i was able to clean it up. Interestingly the layer showed the teeth marks from the rollers used during the manufacture of the plywood.

I glued the bottom to the body. Also the lower body has a gentle curve aft to the tailpipes and at the tip above the inlets. More planing and sanding to refine the shape.

Once the glue dried I lined the inlet inside and out with heavy card stock (110lb). I used cyano and it had the effect of forming a composite material of the paper so it ie actually quite strong and stiff.

Next I formed the nose landing gear bay fairing from a small block. Mounting it to a popsicle stick with double sided tape made it easier to handle and safer to shape. I then glued to to the lower body plywood and faired and filled with automotive glazing putty. I also applied the filler to the paper inlets and sanded them fair as well.