Design
Source Material
I described in the introduction how Daniel Simon's images were excellent starting points for the design of the plane. But three-views they ain't. In fact there are no good three views available that I could find. So I decided to use some of Daniel's original artwork and screen captures from the movie to establish the profile, plan, and front views that I would need.
I can use this profile picture from Daniel Simon - not 100% straight on profile but I can make it work.
Then I took to Youtube to grab some screen captures from videos of the Light Jet scene.
This one will work for a plan view...
...and this one will work for a head on view
Of course, those of you who have seen my earlier posts know that I already had started on a Sketchup model of this, so I already know these pics will work (-ish). But the images are not perfect and there are some inconsistencies between some of the concept art drawn for the model and how the model actually appeared in the film.
Initial Drawings
Plan View Drawing
So this is the plan view drawn in Sketchup using the screen capture image. The wing, v-tail, and pylon are drawn as simply as possible. Only one half of the plan view is needed. The pic shows the panel in solid form (top) and using the "x-ray" view (bottom) so you can see the original plane in the background. Ignore the dimensions shown for now. These were added so that I will be able to scale the various views (plan, profile, front) with each other, a step you would not normally have to do if using a regular three view.
Front View Drawing
The front view was mostly used to establish some basics around angles for the v-tail and wing. Although the picture is not 100% from-the-front, it will work and I can make modifications later as the design progresses. So I have ~25 degrees (from Horizontal) for each of the v-tails (making the v-tail angle 130 degrees, which is probably a little on the large side from what I have read about v-tails). But it's a good starting point. Also figured about ~6 or 7 degrees down angle on the root section of the wing. I am assuming the remaining wing is level. Lastly, I can use this view to establish a shape for the "grill". Again, solid and x-ray views are presented in the pic.
Profile View Drawing
The initial profile drawings mostly help capture the shape of the "fuselage" for want of a better term. It also provides a second look at the v-tail and pylon setup which will help establish the positions of these parts in the final model.
Wings and V-tail modeling.
Next up was to take the wing and v-tail panels from the plan view and set the angles in 3D space. To to this requires making a new panel that can be rotated to the desired angles and then transform the points from the original flat piece onto this surface.
The same approach was used on the v-tail section. A symmetrical airfoil model was added to both mostly to improve the looks of the model in SU. That being said, I am very impressed with the construction and performance of the FT Edge airfoil so using this as a template is a possibility.
These airfoil objects are grouped with the original flat panels in Sketchup so I can view or hide either part depending on what I am trying to model.
Next up was to map these pieces onto the plan view again to that their spatial position in the model can be established. When the original flat panels were drawn I kept the center line of the pylon in the panel so following the adjustment of the angles the parts could be aligned exactly with the pylon and be in the correct position. Here is the plan view with the parts added back and you can see how they now fit in 3D space.
With a simple cylinder model of the pylon made, and the wing an v-tail aligned, the mirror image can be copied into the model to get a feel for how she is going to look.
Although this looks okay, I am a little concerned at this point that the V-tail is too flat. So I made another one at +10 degrees (bottom panel in the next pic). This would reduce the v-tail angle from 130 degrees to 110, which is more typical but to keep the same planform its a lot longer. I needn't lock into one or the other yet, changing later in Sketchup should be pretty easy.
Fuselage
Back to the profile view, this time tracing out the fuselage. I left the pylon center line in place to help with alignment with the 3D model.
At this stage its okay to use all manner of curvy bits to get the shape right but ultimately, to convert this to foamboard, some of the curves will need to be "averaged out" to straight sections.
Cues to the 3D shape can be taken from a couple of images. A screen capture of the jet being formed in the movie shows that the basic shape is composed of oblong/circular/elliptical type rings and they are all pretty much the same shape (which makes things easier).
From one of the images of the rear of the craft you can get an approximate view of the shape. So a simple circle shape was added, then the width was reduced and finally a slight further narrowing of the lower portion of the ring was completed. This will be the cross sectional former to model the fuse in Sketchup. Hard to tell if this is a really accurate representation of the whole fuselage cross section but I think this will do the trick.
Next is to "cut" the profile view of the fuse into manageable sections. Given that I am going to use the score cut / gorilla glue / fold / frame approach, I need to average out some of the curves with straight lines keeping in mind that I would like to keep the fuse to four, maybe five sections.
Okay - that ended up being 6 sections.
Now this profile and the cross sectional profile are combined to build out the 3D fuse. The former is copied to each section of the profile keeping the centers aligned (1) . Then it is re-sized so that the top of the former meets the profile and the center of the former stays on the center line (2). The former is then resized again, this time pulling only on the bottom of the former so that it aligns with the bottom of the profile (3). Finally, the formers are planked
in-silico (4).
This planking piece is a little tedious. Although Sketchup has an extrusion type of tool (called Push/Pull) I find that the slower "join-the-points-by-hand" method gives me better control over how the part turns out.
With one half planked, its mirror image can be made so that the whole fuse piece is now modeled. Using the pylon lines as a guide, this piece can now be inserted into the wing/v-tail/pylon part of the model. Lookin' purdy good at this point.
To finish the fuse the front needs to be sculpted. The part highlighted in the following image is what needs to be removed from the front of the fuse.
This portion is copied, cleaned up, and extruded into a 3D shape that can be subtracted from the fuse.
Here are the two pieces joined....
Then the faces of the two pieces are intersected and the intersection line produced is used to remove material from the front of the fuse.
Next up is the light engine intake. Taking the shape from the head on screen capture, a 3D element was drawn in the same way described for the fuse. Then it was inserted into the existing model and scaled to fit.
This pretty much covers all of the main elements for the design and there is more than enough detail here to build a chuck glider. Next up on the design front will be adding details to the existing parts and thinking about what the internal structure is going to look like. But first....
Scale Issues
One of the challenges for the build is to be able to balance the plane appropropriately. Online CG calculators put the balance point roughly where the two tapered leading edges intersect (ignore the actual lengths here, this is before the model was scaled appropriately).
The plan was to use batteries placed in the pylons to help achieve this balance. This means that the pylons need to be large enough in diameter to hold the battery. If I go 4S EDF approach, then the pylon will need to be ~2.8 inches in diameter to hold the 4S 2200mAh batteries that I have on hand. I can get away with smaller pylons if I drop the EDF and use a prop instead but this would have to be a "ducted prop" placed far forward in the fuse to avoid additional balance problems. So if I scale the current model down to have a 2.8 inch pylon diameter, how big will it be? Well, the wingspan would be 116 inches! That's almost 10 feet - way bigger than I intend to build the model. I was hoping to build at the 40 to 50 inch wingspan scale.
Okay - plan B was to add extensions to the pylons that were larger in diameter to hold the batteries in the hope that this would not destroy the look of the plane. I put together two of these, a cylindrical one and a rectangular one which looks like some of the concept pictures. So how does a 40 inch wingspan version look with these extensions? Pretty bad.
And it gets worse, because at this point I recognized that the fuse seemed narrow compared to the batteries - so would a 70mm EDF fit in there? Nope!
Eventually, after a number of rounds of scaling and squeezing components in, I figure that a 72 inch wingspan is doable, not so huge that it won't fit in my car (I think) and just about big enough to get everything in. But I will need to ponder this some more.
A little later....
Okay - I think I will go with the 72-ish inch version (I might trim a little off the wings and widen the fuse slightly). Rather than take my fat rump out to the Prius to confirm it would fit, I drew up a quick model of the Prius and checked the fit that way.
(nope - I didn't draw this, I downloaded it from the Sketchup 3D Warehouse).
After a little bit more tweaking and resizing I think I finally got everything to fit. The fuse was scaled 5% larger and I reduced the angle of the v-tail so that the EDF could fit. From the pic you can see that the thrust tube for the EDF still interferes a little with the rear of the fuse but I think this will be okay. The battery pods don't look too bad at this scale and I think I will ultimately go with the rectangular prism
version because they have a little more room.
Rider
I would like to do something a little more "3D" for the rider on this model, but it will still be pretty simplistic as a fully 3D rider will hamper the EDF inlet. Tried to draw a profile based on the pics I have and then positioned this flat rider in the center of the model.
Added some depth to the torso and angled the limbs....
... and it fits reasonably well in the craft.
Not going to spend any more time on this for now but I am going to have to fix the head so it looks less like a Star Wars battle droid.
Dec 12th, 2018
Man - last update on this was the beginning of September, need to get my bum in gear.
Since September I have been thinking about how to put this together and also thinking about the scale, wingloading, weight etc. Right now I expect her to be in the 3.5 lb range which would put the wing loading (WCL) at around 15-ish. This is a worry because the scale only allows for one 70mm EDF from which I expect to get 2 - 2.5 pounds of thrust. To add to my worries, I have decided to see how far I can go without using any wood or carbon fiber reinforcement partly as an exercise in frustration and partly to keep the weight down.
Pylon / Fuse Mount.
Did a little work on the pylon mount. Essentially it will be a two component deal - an DTFB square section spar and the shroud that connects the pylon to the fuse. When I looked closely at the some of the pictures, the piece between the fuse and the pylon is a lot beefier than I had originally thought so I took advantage of that. This pic shows how the pieces come together. The spar will be joined to the spar on the other side at the base of the fuse where the two will be braced with some foamboard. This bracing piece might fill the whole fuse cross section so I can use it as a mounting plate for the EDF also.
V-tail Simplification and Pylon Elongation
Now that I am not going to use some sort of airfoil for the V-tail, I replaced it with a simple flat panel which I imagine will be a double layer of foamboard. While I was working on the pylon I also shortened the main pylon and added really long extensions which will hold the battery pods. Hopefully these are way too long but I thought it best to build them this way until I can confirm that I can balance the plane properly. Because these extensions will slide into the main pylon, it will be easy to progressively shorten them until they are the correct length, at which point I will glue them in.
Next up I will need to work on the wing and how it will mount to the pylon.
Update 20th December 2018
Started to try to design the wing. First decision is whether the wing "goes through" the pylon or whether the pylon goes through the wing. From some of the images I have it seems that the pylon is completely enclosed by the wing.
I like this in concept because the thicker wing root could be stronger and I might have more surface area for gluing. Additional spars could be shoved through the pylon from the inboard side to provide additional strength / support. I used a plugin that I have developed for making wings in Sketchup. You provide a file containing the airfoil coordinates and then you can define four different sections including chord, percentage thickness, taper, and dihedral for each section. The plugin then models a wing half in 3D and also unfolds the sections. Here is the wing produced for the light jet using a NACA0010 profile.
Then I can take the 3D wing and fit it up to the plane
This is the 175% root chord version - doesn't quite enclose the pylon
And this is the same model with a 200% thickness (which ends up being 20% because I am using the NACA0010 airfoil).
This does a better job but could probably be a bit thicker
22nd December 2018
Eventually settled on a wing thickness and modified the airfoil to be a little simpler but symmetrical, kinda like the FT Edge wing. Modeled a box spar for the wing taking the foamboard thickness into consideration. The spar is modeled all the way to the tip but I will shorten this to about 50 - 75% of the outer wing panel to save weight. I like the way the pylon will go through the spar but its gonna be a tight fit, which is probably not a bad thing.
Then modeled a second spar which will "pin" the wing to the pylon.
Getting close to generating a first draft set of plans. Just a couple of small parts to add to the Sketchup model and and I should be ready to start unfolding the 3D parts to plans.
7th January 2019
Added an upright post to provide additional strength to the spars that will support the pylons. Also modified the "seat" part to extend further into the fuse. As drawn it will interfere with the EDF inlet, soI will remove some of the foamboard when it is installed. Also decided to make the circular feature in the front of the seat section its own part which will be suspended from the roof of the seat part.
8th January 2019
Tidied up the rest of the 3D model to the point where I was happy that I had covered most of the stuff needed to create a set of plans. Unfolded the pieces (I was a little shocked at how many there are). These will be converted to a DXF file and assembled for printing in DoubleCAD XT. Should start building real soon.