Design Round 2: Lockheed P-38 Lightning (Part 4)

The last two parts include what is arguably the simplest, and one of the most complicated.  The wing support is an important part which adds to the structure of the model.  That being said, it is essentially a plank of paper which spans the engine booms.  On the other hand, the canopy is mostly decorative (it does partially act as a vertical stabilizer), yet it is one of the more complex parts of the model, requiring careful design considerations.

Wing Support

The wing support is a simple structure intended to give the wings some added strength.  Normally it's used to help hod the wings up when they're heavy and long.  In this case, I feel the extra support is necessary because of the triple-fuselage configuration.  As an added plus, it will add more weight to the front of the plane, which will hopefully mitigate some of the tail-heavy traits of the previous version.

It's a really simple part--a double-thick rectangle with a V in the middle to fit into the cockpit nacelle structure.  Measuring the spotter card from the cockpit nacelle to the engine boom, I find the distance is roughly 2 1/2 inches.  This is good enough for me.  Because the engine nacelle is 1 7/16 inches deep, I add this onto the one side of the support.  Because there are obviously two sides, the total length becomes 7 7/8 inches.  I only need the support to be about 1 inch wide, double thickness.  This makes the final dimensions of the part 2 inches by 7 7/8 inches.

Canopy

The canopy is the smallest part, and can be a tricky part to design. By measuring the spotter card, I get 1/2 inch tall and 2 1/2 inches long.  Because the canopy is folded in half the long way, its final dimensions are 1 inch by 2 1/2 inches.

The tricky part is designing the canopy so that it not only looks like a canopy, but that it also has structures to attach it to the model.  It's a teardrop-like bubble, with a peak around 1 inch from the front.  I made a mistake in the first design where the peak of the bubble was the same distance back from the front as the canopy was tall.  This means no structural tabs extended from the bottom of the canopy.  It's time to check that this design will offer enough of those structures.

First, I create a plane in Sketchup whit the dimensions of the full part.  I draw a line down the length of the part, indicating where I will fold it in half.  The next mark goes along that center line, 1 inch from the front.  This is the peak of the bubble.  I draw lines from this point to all of the corners.

The next step might seem odd at first, but you'll understand where I'm going with it once you see it.  I delete half of my drawing along the center line, then rotate it so the peak is aligned in a vertical direction.  The canopy gains its shape by folding the inner triangles in the opposite direction of the original fold, so I have two options to emulate this: Figure out a way to rotate the smaller triangles along the diagonal lines, or use measurements and geometry to create new triangles with the same end orientation.  I choose the latter.

Using the protractor tool, I make a guides along the same plane as the part, perpendicular to the diagonal lines.  Then, knowing that the height of the part is 1/2 inch, I draw a 1/2 inch lines along the guides.  From the endpoint of those lines, I draw new lines to the peak.  I can then remove the upper small triangles, since the new triangles are really just the upper triangles, folded over.  Finally, we can see that there is plenty of structural material to attach the canopy to the model.  Not only that, but you have a very god idea of what the canopy will look like!
Looking at this one, I'm not completely convinced it will look quite right, I may end up adjusting the peak point or the overall length of the canopy, but I'm going to go with it until I can see it on an assembled model.

Speaking of assembling the model, now that the canopy and wing support are done, we have all of the measurements needed to construct a (hopefully) working plane.  Actually, I will be assembling it virtually in Sketchup first, so I can make other part placement measurements important to the construction phase.  That being said, the design part isn't done yet--there are still a few details to add, like the rounded wings, which will add that realistic flare to the model.