Project Overview

UWaterloo WatArrow Design Team

Growing up, I have always been a huge fan of planes or aircraft in general. After being personally selected by a recruitment process for the WatArrow student design team, I was given one objective: Redesign their current plane from scratch with the following objectives in mind:

Shortest take-off distance
Easy re-manufacturability
Strength and stability during flight
Able to withstand repeated crashes/impacts
House all electrical components, and servo motors

About WatArrow

WatArrow Plane Before I Joined

1

WatArrow is a new design team that builds small RC-airplanes from scratch. Everything that we produce is in-house. This means we design, machine, and do our own wind-tunnel testing.

2

The competition WatArrow competes in, is called the SAE Aero Design Competition. WatArrow competes in the micro-class, where scoring is dependant upon things such as: wingspan, take off distance, payload weight.

3

Because of the scale of the project, WatArrow needs individuals specialized in certain areas, hence the reason why there is an application process where I had to submit my resume to join the team

Project Overview

Solution Generation

Because I was designing this plane for a competition, I thought it would be important to know how the competition works. I knew roughly what things would increase our score, however the information was very limited. After doing my own research I found exactly how the scoring worked. Using the equation provided alongside excel, I ran tests to see which scoring criteria would maximize the amount of points we gained. I found out that the criteria which would lead to the most point gain was having the shortest take off distance. From there, the plane design was geared towards being as light as possible.

The next thing to do was to research aerodynamics, and how planes actually fly in the first place. This would help in making design choices for the actual shape of the plane itself. After taking into consideration the resources available to me, budget restrictions, and how the plane control surfaces were operated, I chose the conventional plane tail shape.

The last thing to do was adjust the actual body of the aircraft. The initial plane had a large, heavy body, which increased stability and durability. It also acted as housing for all the electronics, greatly increasing the visual appeal of the plane which was its main purpose. However, this was at the cost of a greatly decreased take off distance. I thought about it, and realized that aesthetics weren't a design criteria. What was stopping us from having all our electronics on the outside, and all our motors exposed? The body itself had no reason to be as wide and heavy was it was now. In the end I decided that a carbon fiber rod with a diameter of 1cm would be the best solution. Not only would we have a weight reduction of over 500g, it would be even more impact resistant due to the strength of carbon fiber. The wires could simply wrap around the rod, and the motors would be embedded into the wings. The idea was quickly approved by the team leads, but the next challenge would be actually mounting the wings to the rod without making holes in the carbon fiber rod. Drilling holes wouldn't work because it was extremely difficult and would make the carbon fiber lose its strength...

Plane Sketch & Scoring Equation

CAD Designs of Prototype 1

Prototype 1

Prototype 1 in Action!

First Idea

The next step was prototyping. Before we started ordering carbon fiber rods, I wanted to try a different design first. The first prototype involved 4 wooden rods spaced apart to form a square-like shape.

I then designed a wing mount with 60 degree arms, turning the conventional tail into a v-tail with hopes of reducing weight even further. The mount would sit on top of the wooden rods, and a screw would be screwed through the hole in the top, securing it, and the wings to the body. It was also 3D-printed.

At this time the front part of the fuselage remained large as I wanted to balance the center of gravity and center of pressure to maintain stability. (The tail was still considerably heavy compared to the front.)

The intention behind this prototype was to resolve the issue of mounting the wings while not being able to drill any holes, while also heavily reducing the weight. However, the wooden rods experienced too much torsion which lead to steering and stability issues. In the video it is clear to see the tail not remaining in line with the rest of the plane, causing it to crash.

Second Idea

After realizing the wooden rods wouldn't work, I decided the best course of action would be to pursue the carbon fiber rod idea, despite the cost and complications. How would I mount any wings on this extremely thin rod without using any screws? Well, when life gives you un-drillable carbon fiber rods, use epoxy. This adhesive would not only solve the issue of drilling holes into the rod, it would also reduce the weight even further because epoxy is lighter then physical screws.

Then came the adapter idea. I realized I could simply slot an adapter over the rod, and use epoxy to secure it in place. Then either epoxy or screws could be used to hold the wings to the adapter.

Iteration 1 was an adapter that took on the shape of the airfoil (created by me using the Curve Through X-Y-Z Points feature in Solidworks to create the complicated geometry). The wings would slot into the sides and the top, and be held in place with adhesive. This idea didn't work due to the 3D-printer not being able to replicate such complicated geometry

Iteration 2 was an adapter that would slide onto the rod and provide a flat surface for the wings and rudder to sit on, and be screwed to the adapter with wood screws. This idea was also insufficient as the wings would often fly off.

All of the wings were made using a homemade wire foam cutter. A current would be ran through a wire, causing it to heat up and easily cut the foam. I opted for Foamular NGX C-200 as a material for the wings, as it was an extremely light weight foam but also stiff and brittle.

Adapter Iteration 1

Adapter Iteration 2

Wing Manufacturing

Final Prototype

Final Idea

Finally, the last iteration of the adapter idea was developed. This adapter is purposely made from PETG filament allowing it to flex and bend easier. This is because the wings are meant to be slotted in between the arms. Once they have been slotted, a screw is placed through the holes, causing the arms to bend and clamp onto the wing whilst the screw also holds it in place. This new design solves both problems of wings flying off, and un-manufacturability.

Due to the new foam wings, and the adapter alongside the carbon fiber rod, the new plane reached a weight reduction of over 70%!

As seen in the video, the plane takes off in a much shorter distance, while maintaining stability in the air. It is also extremely faster, boasting a speed of 15 m/s.

All the electrical components are wrapped around the rod, with the servo motors being embedded into the rudder an each individual wing.

In the end, I was simply happy to see my design work lead to improvements in functionality. We hope to get a podium place in the upcoming 2025 SAE Aero Design Competition!

Final Iteration of Adapter

Return

Results

Although there is still a lot of work to be done, the concept is there and has been put in practice. For future work I will try further optimizing the design, as well as make it aesthetically pleasing. Some positive outcomes from my work on this team were:

Weight reduction of over 70%
Take off distance less then 7 meters
Take off time split in half
Speed of 15 m/s
Aerodynamics knowledge/experience
Rapid prototyping experience
Learning intelligent ways to CAD
General material knowledge