New Wings

The most serious issue with the current set of wings is that they are way too heavy, at ~ 2.4 kg each. They also have a high center of gravity — about 500 mm above the deck. As a result, we need to put over 12 kg in the keel to keep the boat upright. As a result, it sits low in the water and is much slower and less responsive than it could be. Their construction (bent plywood over laser cut plywood frames with printed ABS fittings) is also not representative of the the sort of wing we’d like to build for ocean going vessels.

Therefore, I embarked on designing and building a new, lighter set of wings. The core design objectives were as follows:

  • Cut as much weight as possible

  • Lower the center of gravity

  • Remove potential interference between counterweights and tail surfaces

  • Make the tail dismountable for easier transport and storage

  • Eliminate the difficult wire routing from the servo to the controller.

  • Improve cover attachment for the electronics box

  • Leverage the capabilities available at The Facility Makerspace to produce a light, strong, and inexpensive wing.

The construction method I selected for the wing is a laser cut plywood frame filled in with router-cut foam blocks and covered with epoxy-glass fiber composite. These choices leverage three things available at the Facility — laser cutting, the CNC router, and the composites lab. They can also be scaled up for the wings for the Microstransat boat, which are twice as large in every dimension.

Pathfinder boat wing sail

Pathfinder boat wing sail

This design is a kilogram lighter than what it replaces with a center of gravity a full 200mm lower, on a wing that’s only 1000 mm tall in the first place. Additionally, the box support for the tail mounting provides a convenient place to mount the electronics with no twisty passages for the wiring to snake through. It also makes it easy to make a fitted hatch cover for electronics access. It does put the servo off center a little bit, but I don’t think that will be significant in the final analysis.

Initial calculations show that removing a kilo from each wing while lowering the CG by 200 mm will allow us to remove 6 kg from the keel, for a total weight loss of 8 kg. The boat only weighs 21 kg in the current configuration, so this is a major reduction in weight; I look forward to a corresponding improvement in speed and responsiveness on the water.

The tail attachment is simple — a pultruded carbon tube is fixed into the structure, and a smaller tube slides neatly into it. A stainless steel bolt match drilled in Dragonscale makes both the tubes and a line of bonded-in fittings for them that allow me to create a convenient hinge for the tail. The spine of the tail is another piece of carbon tube glassed into the laser cut plywood that forms the blade of the tail.

Like the last iteration of the wings, the counterweight is a stack of fender washers on a piece of 3/8” all-thread. The all-thread is passed through the main spar and both bolted and glassed in for extra strength.

The following gallery contains a visual history of the assembly and painting of the wings. Click on the images to expand and see a description for each one.