USTP Ornithopter

January 2026

The goal here is not merely to build an Radio-Controlled Ornithopter that flies, but to understand why it flies and how to do it in a principled, engineering-driven manner.

1. Introduction

An ornithopter is a flying device that mimics the flight of birds. At face value, the concept is simple; in practice, it is anything but. Unlike fixed-wing aircraft, an ornithopter generates lift and thrust through the periodic flapping of its wings, closely replicating the biomechanics observed in nature. This makes it an ideal engineering problem—deceptively straightforward in description, yet mechanically and analytically complex in execution.

Leonardo Da Vinci's Work

This project serves as a practical engineering challenge that bridges theory and application. It demands an understanding of aerodynamics, kinematics, structural mechanics, and energy transfer, all working in concert. Designing an ornithopter from scratch requires reasoning from first principles rather than relying solely on empirical replication. It is well known that numerous ornithopter designs are readily available online. Hobbyists have refined workable configurations for decades, and public demonstrations—such as early TED Talks showcasing flapping-wing flight—clearly prove that the concept works.

However! this blog is not about copying an existing design. Instead, it focuses on what happens under the hood: the assumptions, trade-offs, and physical constraints that govern flapping-wing flight.

Interestingly, ornithopters remain popular among hobbyists due to their versatility in material selection and mechanical layouts. This flexibility, however, often masks the underlying complexity of the system.

2. Assumptions and Constraints

The first question that must be addressed is fundamental: how do birds actually fly? At its core, bird flight requires two things—lift to overcome gravity and thrust to overcome drag. Birds generate both primarily through the flapping motion of their wings, which are highly specialized, cambered aerodynamic surfaces.

The curved (cambered) shape of a bird’s wing produces a pressure difference between its upper and lower surfaces. As air flows around the wing, the pressure above the wing is lower than the pressure below it, resulting in an upward force—lift. However, lift is not produced by wing shape alone. The flapping motion actively accelerates air downward and backward, and by Newton’s third law, this momentum change produces an upward and forward reaction force on the bird.

Key Insight: air must be moving relative to the wing for lift to exist. Once relative airflow is established, the air passing over the top surface of the wing generally travels faster and over a longer path than the air beneath it. This velocity difference contributes to a pressure imbalance: lower pressure above the wing and higher pressure below. The rushing air beneath the wing helps sustain lift, while the pressure deficit above prevents collapse

Flapping does more than generate lift—it also produces thrust. During the downstroke, the wing acts much like an oar moving through water. By pushing air backward and downward along a diagonal path, the bird generates a forward component of force. This effect is enhanced by a carefully controlled angle of attack, where the leading edge of the wing is slightly angled downward relative to the incoming airflow. This orientation allows the wing to generate thrust while maintaining lift, overcoming aerodynamic drag.

In simplified terms:

Downward force component → lift
Backward force component → thrust

The coordination of wing motion, deformation, and angle of attack is what makes sustained forward flight possible. To translate biological flight into an engineering system, assumptions are necessary. These assumptions reduce design complexity, constrain the solution space, and enable first-order analytical estimates before committing to hardware.

Flight Regime

Low-speed, low Reynolds number flight
Subsonic, Incompressible flow
Quasi-steady Aerodynamics (unsteady effects are acknowledged but approximated)

Mission Profile

Short endurance flight
Ground-assisted launch
Operation in calm air or light wind conditions

Structural

Elastic wing deformation is intentional and aerodynamically beneficial
All structural components remain within elastic limits
No plastic deformation under nominal flight loads

While real bird flight is highly unsteady, adaptive, and nonlinear, these assumptions allow the ornithopter problem to be treated as an engineering system rather than a biological imitation exercise.

3. The CAD

The flapping mechanism uses a crank-slider driven directly by a coreless motor Wing spars are light wooden material.

3D model of an ornithopter

4. Analysis and Observations

At peak motor speed, the flapping frequency reached approximately 6 Hz. Significant torsional oscillation was observed in the wing spars, indicating under-designed stiffness.

Ornithopter Test

Key Insight: Structural compliance dominated aerodynamic effects, masking any lift gains from increased flapping frequency.

5. Results

Short hops achieved (< 1 second)
No sustained flight
Mechanism reliability acceptable

Ornithopter prototype

6. Lessons Learned and Next Steps

Future iterations will prioritize wing torsional stiffness and introduce passive twist via compliant joints rather than rigid spars.

The team behind that made this project possible!