Letter-size Helicopter (fits in an Envelope!)

One of my nephews lives in a rural area halfway across the globe, so sending gifts there is a challenge. Given the distance and complications involving multiple postal systems, I didn't want to risk sending something expensive or paying a lot for postage for his birthday in case it got lost along the way. As a result, I designed this helicopter to fit in a regular letter-size envelope and weigh less than 50g/2oz, which only costs a few dollars to send internationally ($4.17 from Canada as of the time of this writing). The cost of the plywood used is minimal as well. If the helicopter got lost or damaged along the way, I could easily send another one! Thankfully the first one that I sent made it with no issues :)

This helicopter features (relatively) freely spinning rotors, a swiveling hook on the bottom, and a cockpit that a Lego minifig can just squeeze into. In this Instructable, I'll share my design process and challenges. If you just want the design files so you can make your own, the svgs are attached in Step 16.

Wood - For this project, I used 3mm poplar plywood*. Baltic birch works as well, but it is heavier, so you'll need to cut out some areas of the wood surrounding the helicopter if you want to get it under 50 grams.

Bamboo skewers (and something to cut them with) - Used for the rotor shafts. The diameter of the skewers that I'm using is approximately 2.8mm as well.

Glue to hold everything together! I've recently been using superglue for a lot of my laser cut projects and it works great for most things, but can be a challenge if you need a bit of time to get things perfectly aligned before the glue sets.

Laser cutter - this would be a tricky project to cut by hand, so a laser cutter comes in handy here! I'm a member of my local makerspace, so I am fortunate to have access to a laser cutter through that. Check if there's something similar in your area!

Envelope and stamps to send your helicopter across the city, country, or world!

As far as software requirements, I used Inkscape for the design and Lightburn to set up and send the file to the laser cutter.

*The poplar plywood is actually closer to 2.8mm thick, but everything is designed for 3mm thick wood.

The first image here just shows a profile view of the helicopter, while the second shows a marked up version, with each part labeled.

The whole helicopter design needs to fit within a standard letter envelope, which is 4.125" x 9.5" (105mm x 241mm). However, since the wood is thicker than a few sheets of paper, the dimensions need to be smaller than that to give the envelope room to fit around the wood. I did a bit of testing, and a size of 3.5" x 8.5" (89mm x 216mm) fits well in the envelope and leaves enough space to add a few sheets of paper as well.

I started by drawing a rectangle of this size in Inkscape. Everything has to fit in this box, so it's important to think through the most important components of the helicopter and where they might need to fit in:

• Fuselage - this is obviously going to be the largest individual piece, so most other pieces will need to be designed to fit around this.
• Main rotor - this is the longest individual piece of the helicopter, so it needs to stretch almost the entire length of the envelope.
• Landing skids - these are both relatively long as well, so they definitely need to be accounted for.

All of the other pieces of the helicopter are relatively small in comparison, so if we can get this initial list sorted out first, we'll be in good shape!

Helicopters come in all shapes and sizes, so I started by searching for some images that I could use as a starting point for my design.

This Wikimedia Commons page shows a lot of 3-view drawings of helicopters that can be used as a starting point for a design. I used Inkscape to trace one of the helicopter designs, then heavily modified it to a shape that I thought looked nice.

One thing that's handy to make in the design is a flat section on top and a flat section on the bottom of the fuselage. These aren't completely necessary, but will make it significantly easier to design and attach the landing skids and main rotor shaft/mounting assembly. Some tweaks to the design may be necessary to fit it all within the envelope footprint, but this is a good starting point!

Helicopter rotors aren't purely rectangular and usually have a bit of a swept design, so I drew up something that I thought looked good, as shown here. A hole is put in the center of the rotor for the rotor shaft to go through. The hole should be slightly larger than the diameter of the bamboo skewers so that the rotor can spin more freely.

For the tail rotor, I decided to just use a scaled down and slightly adjusted version of the main rotor. However, scaling down the tail rotor makes it too narrow to put a hole for the rotor shaft through. To remedy this, I add a buffer of 1mm around the hole that the shaft goes in and merge that with the rest of the rotor. The hole for the shaft in the tail rotor should be roughly equal to the diameter of the shaft, since the tail rotor will later be glued to the shaft.

If we were to design accurately scaled landing skids for this helicopter, they'd be way too skinny, so a thicker design is used. To create this in Inkscape, I simply drew a single angled line as shown. I then increased the stroke width on the line until it looked good enough to me. I then used Path>Stroke to Path to trace around the stroke and create a new path.

For mounting the skids, I drew one half of a basic rounded shape and adjusted the curve until I thought it looked good. This will be modified later for it to connect to both the fuselage and the skids, but I wanted to have an overall idea of how it should look at this point.

Note that for now, I'm not adding any of the holes or tabs in the pieces that will be used to fit them together. I'll only go through that process once I make sure that everything will fit within the footprint of the envelope. It would be a bummer to do all of that work, then test the fit on the envelope, only to find that things need to be adjusted!

The swivel hook on the bottom of the helicopter is created in a similar way to the landing skids - a basic shape is drawn, the stroke is adjusted, and the Path>Stroke to Path tool is used to convert the outline to a path of its own. A circle is added and merged to the hook that will be mounted in the fuselage of the helicopter. A matching circle is cut out near the bottom of the helicopter.

Make sure that the hook doesn't extend past the bottom of the skids! I messed this up initially so I had to redesign it to be a little shorter.

The hook will also need to be held in place somehow, so I drew up a plate that will be mounted on either side of the hook so it can swing back and forth but not fall off!

As mentioned in the Introduction, the cockpit of the helicopter is designed to fit a Lego minifig, so a little seat needs to be constructed for that (you could potentially put a 2x2 flat Lego plate on the seat to lock the minifig in place as well!). My minifig measures 15mm from the tips of its feet to its back, so that's the dimension that I used for the seat. After testing the fit, I modified this measurement to 14.8mm so the minifig fits a bit more snugly.

I also decided to put an "instrument panel" in the cockpit, so I drew up a simple trapezoid with some circles on it that will be mounted in front of the seat. The circles on the instrument panel are sketched in a different color because they'll be engraved into the wood rather than cut.

The overall shape of the cockpit was fairly arbitrary. I needed to fit the seat and instrument panel in, but other than that, just tried to match the curves of the overall fuselage as much as possible to make it look nice!

I added holes to the seat parts and instrument panel and tabs to the inside of the cockpit so that the pieces will fit solidly together.

At this point, it's a good idea to confirm that everything that's been designed will fit within the footprint of the envelope. A few more parts need to be designed (namely rotor mounts and "bushings", but those are relatively small and it shouldn't be too hard to find a place for them. Here I've laid everything out and it's tight, but seems to fit! Note that the skid mounts aren't finished yet, but they won't take up too much more room than their basic outline.

There is also a bit more wiggle room than this image might indicate. The lines that are drawn to show all of the shapes in Inkscape are much thicker than the kerf of the laser cutter beam, so each shape has more space around it than the image shows!

The side panels that hold the swivel hook in place could probably just be glued onto the side of the fuselage, but I thought it would be nice to have them better aligned and fixed in place more securely. The plywood that I'm using is 3mm thick, so if I cut a 3mm tall rectangle, I end up with a 3mm square "rod". I used this measurement to put square alignment holes in the fuselage and mounting plate. The rods are cut to 9mm long, since they need to go through 3 layers of plywood.

The main rotor shaft needs to be thoroughly supported, so I sketched up a mounting bracket that slides into a slot at the top of the helicopter. The bracket and the helicopter top each have a notch cut in them as well that holds a square bearing surface. This surface is used to support the main rotor so that it doesn't rub directly on the top of the fuselage, but instead is shifted up slightly to spin more freely as shown in the enlarged inset image. Note that this enlarged image isn't entirely accurate. It shows that the main rotor shaft sits on the bottom of the slot cut into the fuselage. In the actual model, the rotor shaft mount slides that slot, and the main rotor shaft sits in the shaft mount instead.

All that the tail rotor needs to mount it to the helicopter is a hole somewhere through the tail! From looking at images of helicopters, it seems like there are a lot of different locations that can be chosen, so I just picked a spot that looked good and went with it!

The landing skid mounts connect to both the landing skids and the fuselage. To accommodate this, three parts need to be modified:

1. The mounts need to have notches in the top to attach to the fuselage. They also need tabs and notches on the sides to mount into the skids.
2. The skids need holes in the sides to accommodate the tabs from the mounts.
3. The fuselage needs notches in the bottom to align with the notches in the mounts.

I adjusted the thickness of the skid mounts to make room for the notches and tabs and ended up with the shape shown.

A few additional parts need to be cut out to fully assemble the helicopter. The main rotor and tail rotor shafts are made out of bamboo skewers, so some space in the overall layout needs to be cut out to put the skewers in for shipping.

Additionally, to hold the rotors on to the helicopter, I cut out some round bearing/bushing pieces that will be glued onto the rotor shafts to hold them in place. These will be detailed more in the assembly steps!

With those changes to the overall layout, it looks like everything fits! You'll notice that there are duplicates of some of the smaller pieces. I like to do this in case they get lost or broken during assembly. They fit in the layout without causing any issues, so it's always nice to have a few spares!

*This isn't actually be the final layout! After assembly, I had to make some changes, but the final version is shown in the next step.

It's always fun to see a design finally get cut out! Once it was done on the laser cutter, I assembled it and discovered a few issues that needed to be resolved:

1. As shown in the second photo, the landing skid mounts stick out just above where the bottom of the pilot seat should be, so the seat can't be glued into place.
2. The landing skids themselves weren't quite long enough or weren't mounted far back enough, so the entire helicopter tilted back instead of sitting flat.

To remedy these two issues, I adjusted the location of the seat so that there was more clearance above the landing skid mounts. In addition, I extended the landing skids toward the rear to improve the helicopter's stability. This required moving a few things around in the layout, but nothing significant.

With those changes in place, the model fit together and balanced perfectly after it was assembled. The updated layout is shown in the 3rd image here.

The images attached here show the basic order of the steps that I take to assemble the helicopter. Most things are pretty straightforward, but the assembly of the rotors in particular needs to be done correctly so that they can spin relatively freely.

For the main rotor, this is how I do it:

1. Glue the rotor mount into the slot in the fuselage.
2. Glue the square bushing into place.
3. Squirt some glue into the fuselage/mount slot and put in the main rotor shaft.
4. Set the main rotor on the shaft.
5. Dab a tiny bit of glue into one of the circular bushings and stick that onto the rotor shaft, making sure not to get any glue on the shaft.

For the tail rotor:

1. Glue one of the circular bushings onto the end of the shaft.
2. Slide the shaft through the tail rotor hole.
3. Slide (but don't glue) a circular bushing onto the shaft.
4. Glue the tail rotor onto the shaft.

Also be sure not to get glue on the swivel hook when you're installing the side plates, otherwise the swivel hook won't swivel!

Here are some photos of the finished helicopter, complete with Lego minifig! The svg design file for the helicopter is included in the next step.

Attached is the final SVG file for the helicopter. I've set it up so that black lines are cut lines and blue lines are engrave lines (only used for the instrument panel). Please let me know if you experience any issues with these files.

I designed the helicopter for 3mm plywood, so that's what is in the files, but the actual wood that I used was closer to 2.8mm thick. If you are also using thinner wood, you can just scale down the file to match the size that you need, but you need to watch out for a few things:

• The holes and notches for the rotor shafts need to be adequately sized to fit whatever you're using for those shafts.
• If you want a Lego minifig to fit, you need to ensure there's adequate room for it to sit in the cockpit.
• If you're wanting to send the helicopter to someone, I recommend keeping the overall envelope dimension at 3.5"x8.5", otherwise there's too much empty space surrounding the model in the envelope, and I don't think the postal service likes having significant variations in thickness for mail being sent in an envelope!

To send the model to someone, I'd recommend putting painter's tape on one or both sides of the laser cut frame to hold the pieces in place! Don't forget to include the bamboo skewer for the rotor shafts, and ensure you add enough stamps to cover the weight of the model that you're sending. My overall weight (wood pieces, tape, and envelope) was only 22 grams using 2.8mm poplar plywood. Baltic birch would be significantly heavier, so you may need to cut out some sections of the frame to get it down to the desired weight if you decide to go that route.

Thanks for reading! Please share a photo if you decide to make one of these helicopters. I'd love to see some modified or decorated designs!