The Art of Building a Complex Hollow Carbon Fibre Drone Fuselage

David Jones -

In this comprehensive guide, we explore the intricate world of composites, focusing on the step-by-step process of creating a complex hollow carbon fiber drone fuselage. From selecting materials to the final paint job, this blog will delve into the techniques and tools used to achieve a high-quality finish.

Crafting Composites: A Deep Dive into the Parts of a Carbon Fiber Drone Fuselage

The Parts

Creating a drone fuselage from composites is not just about aesthetics; it’s about structural integrity. The fuselage is the heart of the drone, housing all internal components and ensuring stability during flight. Each part must work in harmony to achieve the desired performance.

In our project, the fuselage includes several key components:

  • Fuselage Shell: The outer structure that provides the aerodynamic shape and houses the internal components.
  • Internal Structure: This includes floors, ribs, bulkheads, and spar tubes, all crafted from lightweight carbon fiber sandwich panels to maximize stiffness while minimizing weight.
  • Spar Tubes: These are critical for connecting the wings to the fuselage, providing the necessary strength to support aerodynamic forces.
  • Motor Mount: A robust component machined from solid carbon fiber, designed to withstand the forces exerted during flight.

Each of these components plays a pivotal role in the overall performance of the drone. The internal structure, particularly, is designed to distribute loads evenly, ensuring that the fuselage can handle the stresses of flight without compromising integrity.

Cutting Templates

Before diving into the actual construction, creating accurate templates is crucial. Templates ensure that the carbon fiber prepreg is cut to the precise dimensions needed for each component of the fuselage. The old-school method of using masking tape provides a straightforward approach to capturing the contours of the mold.

Here's how it works:

  1. Apply masking tape over the entire mold surface.
  2. Mark the cut positions directly onto the tape.
  3. Carefully transfer the tape to a flat backing material to create your cutting templates.

This method allows for a quick and effective way to ensure that all pieces will fit together seamlessly, which is essential for maintaining structural integrity.

Cutting Materials

With templates in hand, it’s time to cut the carbon fiber prepreg. This material is known for its strength-to-weight ratio, making it ideal for drone construction. The process of cutting the prepreg is straightforward but requires precision.

Here’s how to cut the carbon fiber prepreg:

  • Use a sharp scalpel or scissors to follow the templates closely.
  • Ensure that each cut is clean to avoid fraying, which can compromise the quality of the layup.
  • Handle the prepreg carefully, as it is sensitive to temperature and must remain within the specified conditions until ready for use.

Once cut, the prepreg should be stored in a cool environment until ready for application, ensuring that it retains its properties until the layup process begins.

Layup

The layup process is where the magic happens. This is the stage where individual plies of carbon fiber are layered to create the fuselage structure. The method of using lap joints is particularly effective, as it enhances the strength of the seams.

To perform the layup:

  1. Begin with the lower surface, laying down the first ply and trimming it to the parting line.
  2. Add the second ply, ensuring it stops short of the parting line to create a lap joint.
  3. Repeat the process for the upper surface, extending the last ply to overlap the lower half, ensuring a strong bond.

This overlapping technique not only reinforces the structure but also simplifies the vacuum bagging process, as it creates a clear path for the vacuum to consolidate the layers without bridging.

How to Use Intensifiers

Silicon intensifiers are a game changer when it comes to vacuum bagging complex shapes. These flexible silicone inserts fill gaps where the vacuum bag might struggle to conform, ensuring a tight seal and proper consolidation of the laminate.

To use intensifiers effectively:

  • Prepare the mold surface with release film to prevent sticking.
  • Press the silicone intensifier material into complex areas of the mold.
  • Vacuum bag the intensifiers along with the prepreg to ensure they cure together, providing a seamless finish.

Using intensifiers not only simplifies the vacuum bagging process but also enhances the final quality of the composite part by eliminating voids and ensuring full consolidation.

Vacuum Bagging: The Secret to Seamless Composites

Vacuum bagging is an essential technique in composite manufacturing, particularly for achieving high-quality finishes on parts like our drone fuselage. The process involves enclosing the layup in a vacuum bag and removing air to compress the layers tightly together, which ensures proper consolidation and eliminates voids.

To begin vacuum bagging, ensure that the surfaces of your mold and prepreg are clean and coated with a suitable release agent. This will facilitate easy demolding later. Once your layup is ready, carefully place it into the vacuum bag, ensuring that no bridging occurs. This is critical, as any air pockets can lead to weak spots in your finished product.

After securing the vacuum bag, connect it to your vacuum pump. Monitor the vacuum pressure closely to ensure it remains consistent throughout the curing process. A well-executed vacuum bagging not only improves the structural integrity of the part but also enhances the surface finish.

Demolding: The Big Reveal

Demolding is arguably the most exciting part of the composite fabrication process. Once the curing cycle is complete, carefully remove the vacuum bag and breather fabric. The moment of truth arrives as you separate the mold halves. If done correctly, you should see a perfectly formed part with crisp edges and no voids.

After demolding, inspect the part thoroughly. Any flash or excess material can be trimmed using a perma grit wheel and sanding block. This step is crucial for achieving a clean finish and preparing the part for the next stages, such as painting and assembly.

With the main fuselage component complete, it’s time to move on to the internal structure. This includes floors, ribs, bulkheads, and spar tubes, all designed to maximize stiffness while minimizing weight.

Internal Structure: The Backbone of the Fuselage

The internal structure of the drone fuselage is critical to its performance. By utilizing lightweight carbon fiber sandwich panels, we achieve maximum stiffness with minimal weight. The sandwich panel consists of a single ply of 210-gram prepreg carbon fiber on either side of a sheet of three-millimeter Roacel PMI foam.

This combination offers an excellent strength-to-weight ratio, making it a preferred choice in UAV construction. The panels are then vacuum bagged against a sheet of glass and oven cured following the standard XC110 cure cycle. This process ensures uniform curing and optimal material properties.

After curing, the profiles are cut from the material using a three-axis CNC machine, resulting in incredibly light yet surprisingly stiff components. The motor mount, which bears a significant load, is machined from solid two-millimeter sheet stock, ensuring robustness in this critical area.

Painting: Finishing Touches for Aesthetic and Protection

Once the internal structure is bonded into the fuselage, it’s time to consider the paint job. While typical UAVs are painted in solid colors, opting for a satin clear coat allows you to showcase the carbon fiber weave while providing protection. The Phantom Clear paint used here is specifically designed for carbon fiber and offers excellent adhesion and finish.

Applying a high-quality satin or matte finish is generally quicker than achieving full gloss, requiring just a single coat followed by a finishing coat. While this additional layer adds minimal weight, the aesthetic improvement and surface protection are worthwhile.

The final result is a stunning fuselage that not only looks incredible but also weighs only a few hundred grams—provided the motor isn’t included. This balance of aesthetics and functionality is what makes working with composites so rewarding.

Conclusion: The Art and Science of Composites

The journey of crafting a complex hollow carbon fiber drone fuselage is a testament to the intricacies of composite materials. From the meticulous design and preparation stages to the final touches of painting, each step plays a vital role in the overall performance and appearance of the drone.

Composites may seem daunting due to their complexity, but they offer unparalleled benefits in strength and weight reduction. For those passionate about engineering and innovation, the world of composites presents an exciting and fulfilling challenge.

If you're looking to dive deeper into the world of composites, consider exploring additional resources and guides on our website. Whether you're a seasoned expert or a newcomer, there's always something new to learn in this dynamic field.

FAQ: Your Burning Questions About Composites

  • What are the benefits of using composites in UAV construction?
    Composites offer a superior strength-to-weight ratio, allowing for lightweight structures that maintain excellent structural integrity.
  • How do I ensure a successful vacuum bagging process?
    Ensure all surfaces are clean and free of any contaminants, and monitor vacuum pressure throughout the curing cycle to avoid air pockets.
  • What types of adhesives work best for bonding composites?
    Methyl methacrylates (MMA) and structural epoxies are commonly used, with MMA often providing a good balance of performance and cost.
  • Can I paint over cured carbon fiber?
    Yes, using a clear coat designed for carbon fiber will enhance appearance while providing protection.

This article was created from the video Making A Complex Hollow Carbon Fibre Drone Fuselage

All of the contents above was scrubbed from the video link mentioned above, we take no credit for the exception work which Paul and the team from EasyComposites have done here, but rather offer a brief overview of the subject with the hope that it will inspire you to pursue similar projects. Please do have a look at the full video, Paul explains hard to grasp concepts with exceptionally simple and easy to follow videos.