Build Report for PaperArts 737

[knife]

Continuing the build, next on the agenda is the wing spars and skins. The wing spar is composed of a series of boxes glued together. The only end piece is at the wing root, so the boxes once glued together are able to twist a little. If I was to build another model, I would probably put some reinforcement around the engine mount area to reinforce it. The instructions show a straight spar, but once glued together they form a Z shaped section.

Once the spars were constructed, I decided to add a wood spar through the fuselage to connect with the cardstock spars. The spars are then glued to the fuselage. Since I had not yet joined the fuselage halves together, it was easy to press the spar and fuselage parts together for a strong joint. If the fuselage was joined beforehand, I think it would have created a week point likely to collapse over time.

The end of the box spars line up with the end of the front fuselage section.

After the wing spar glue joints dried, I fastened the the fuselage sections together.

 

[knife]

Now comes the hard part, the wing skins and flaps.

 

[knife]

On my 737 design, the wing skins are joined together to form an envelope, which is then slipped over the wing spar and glued to the fuselage. No so on the PaperArts version. The wing is designed to have all it's flaps slats and spoilers out. As the photo above shows, there's not much wing left when everything is hanging out.

The individual pieces making up the wing skins from all kind of origami looking pieces and the instructions are not clear. An exploded view of the wing structure would sure help. I hope I have enough German blood in me to decypher this engineering puzzle.

I started by gluing the inboardmost skin to the fuselage, using a lamination of the wing root glued to the fuselage to provide a form. The excess material in the back of the wing skins forms a flap.

I then continued gluing the pieces together, bending the pieces where it looks like it will form the right shape. Strictly going by gut instinct on how the pieces are folded and fit together.

If you are planning to build this model, these are the photos you will want to reference.

 

[knife]

I've completed the basic structure of one wing. Lessons learned so far:

The outer skin is glued directly to the wing spar outboard of the engine pylons. This means the spar must be built straight or the outer skin will have a warp. If I was to build this kit again, I would not use the tabs on the spars to glue the pieces together. I would cut off the tabs and use a small strip of paper under the spar boxes to glue the boxes together. I would then cut a small rectangle of cardstock to seal off the box ends, making them unable to twist. In the photos you can see the leading edge twist that I ended up with.

I started off gluing the wing skins at the fuselage. This induced a twist in the second wing skin panel. I think I would build the second panel first, then glue the first panel to it, then glue the whole assembly to the fuselage. The second skin section is the critical piece, if it warps the outer wing sections develop a twist, and the engine pylon will not fit correctly. The photos show the gap I ended up with between the third and forth wing sections.

I think the front of the wing spars are a little too thick, it doesn't take into account the thickness of the wing skin. When folding this section, I would fold it slightly undersize.

I've included a photo of where to pre-crease the parts prior to cutting them out. Hopefully the next wing will end up better.

 

[knife]

After completing the wing, the next project is the flaps and slats. Here's how they are supposed to look.

 

[sjsquirrel]

Thanks

An excellent build thread knife. I've been wanting to do a 737 for some time so it's great to see a build/review of a kit like this.

Keep up the good work.

Steve

 

[knife]

When I built the second wing, I glued the first three sections together before slipping them over the spar. This seems to create a straighter wing, but there is a gap around the landing gear wells when it is assembled. I then assembled the engine pylons and the flap actuators. None of these parts have crease lines, so it's pretty much cut them out and see how they will fold together. I would recommend NOT to use the triangular tabs on the engine pylons around the leading edge of the wing. Just cut them off and use a light bead of glue around the curve.

 

[knife]

Today I found a major mistake in my build. When I built the wing, I thought the inboard section of the wing included a flap, and built it accordingly. However, what I thought was the flap, if inverted, is actually the inside walls of the flap well. I guess I will have eventually make another model, incorporating the lessons learned from this build.

After completing the wing, the next area is the inboard flaps. Once again, the instructions could have been better. It shows the wing flaps retracted, while the instructions cover shows the model with them deployed. I built them in the landing configuration.

The spoilers are glued to the top of the wing. Since they are made out of doubled cardstock, they look too thick. Also, the undersurface of the spoilers is printed on the top of the wing, so the spoilers look like they are just glued on top the wing. If I was to remake this model, I would cut out the undersurface and rebuild it sunk into the wing for a more realistic 3D effect.

 

[knife]

The outboard flaps are next, same problems as the inboard flaps and spoilers.

 

[knife]

The ailerons are pretty straight forward, but it looks like the design didn't take into account the thickness of the cardstock. If your paper has no thickness, I'm sure the parts would fit perfectly. But here in the real world, paper has thickness, so if you build the parts exactly as printed, they will not fit in the area provided. All the flaps and the ailerons should be smaller than the design has.

The leading edge slats are made from cardstock folded in halve, so you end up with a lamination two thick. It could (and should) be made just from one piece formed into the leading edge shape. You can't see the inside surface once in place so there's no need to use the printed part.

As suspected, the leading edge of the wing should be warp free and have no slant to it for the slats to fit properly (my model has both). Once again, I think this is because the model doesn't take into account the paper thickness. In the virtual world of 3D design, all skins have no thickness. The slats also bring out the importance of having a straight leading edge on the wing.

This build is not meant to be the picture of the week, just a quick throw together built stock to see how it goes together. I'm already making a list of changes I want to make to the design before I build another one. Next assemble will be the engines.

 

[knife]

I choose to build up the engine from the inside to the outside. Thus, I first made the internal intake and exhaust pieces. The internal exhaust cones have a bulkhead designed to be bent up to form the end pieces. It's best to cut these bulkheads off from the side pieces, and glue them back on once the sides are formed.

 

[knife]

Continuing the engine build, the only major problem I had was the fit of the internal exhaust parts into the exterior exhaust shell. I ended up cutting off the bulkhead and trimming the internal parts until they fit properly. I then glued the internal side parts to the external shell, then glued the bulkhead back on the end of the internal parts.

 

[knife]

I finished the engine by gluing the front half to the back half. Everything fit well and the completed engine mates with the engine pylon with no problems.

 

[knife]

Here's some comparison photos of the PaperArts engine and my own design. The PaperArts engine is much more complex, using 10 pieces to form the outer shell compared to 5 pieces in my design. The only real complaint with the PaperArts model is the black disk representing the turban fan blades. This piece should have been made much lighter to see the individual blades.

 

[knife]

The final engine bits are the engine reverser guides and the fence. The fence is made up as a box, and is way too thick. Just cut the two sides out and glue together for a more realistic model. The thrust reverser guides must be for an old model of the engine. Modern CFM engines have a single box structure.

 

[knife]

I started modifying the pdf file to make the changes I think should be made before making my final model. I was thinking about a repaint, maybe like this:

 

[knife]

Here's a quick repaint of the horizontal stab and elevator. The original is upper right, my repaint is lower left. I just cut and pasted off a texture file from FlightSim.com

 

[knife]

I've completed the second engine. I cut the bulkheads off the side pieces, and didn't use the tabs. The assembly went together easier and quicker than the first one. One problem was the engines hung too far down when mounted on their pylons. I ended up cutting the front of the pylons down so the engines would mount flush.

 

[knife]

Next on the agenda is the landing gear. For all you Polish and German craftsmen, those who like to make actual wheel spokes on your 1:200 scale SE-5 model, these landing gears are for you. For all others, make sure you have a LARGE bottle of wine before beginning. I spent about three hours making the front strut and one wheel, and that was doing a quick (and dirty) build. I'm using a q-tip as an internal strengthener. I either cut it down or build it up depending on the radius required. Since q-tips are made out of paper, this isn't cheating on the build and should make the gear much stronger.

 

[knife]

I should mention that I printed the page with the landing gear parts on both cardstock and regular printer paper. I use the cardstock pieces for structural parts such as the tires and wheels, and printer paper for all other parts. The instructions don't necessarily match the parts, so here is my best guess on how the nose gear goes together. It looks a little too tall once mounted, I will continue the build with the main gear to see how it looks when the main gear are attached.