By Donald Cooney, EAA 523904

Being awarded an honorable mention at EAA AirVenture Oshkosh 2025, followed by an article in the January 2026 issue of EAA Sport Aviation magazine was both a humbling and gratifying experience that prompted me to look back on my flying experiences and the design decisions that led to the Carbon Prowler trike.

I began building trikes in 1982 with a group of hang gliding friends I had been flying with for the previous decade. Those early years of ultralight aviation were an extraordinary time. We could hardly believe we were being allowed to build our own aircraft and fly them without a certificate. For the first time, we were no longer at the mercy of the prevailing winds and confined to ridge soaring the cliffs along Long Island’s north shore. We all exchanged ideas and made sure nobody was taking unnecessary risks.

Several members of the group had prior experience with two-stroke engines, gained through their involvement with dirt bikes and snowmobiles. This background enabled us to identify and evaluate potential engine failure problems. Most of us did not have any formal flight training. However, those who did passed on their knowledge to the rest of the group. My first trike was powered by an 8.5-hp engine and equipped with a Manta Fledge hang glider wing following the original FAR Part 103 rule of 155 pounds’ maximum empty weight for an unpowered vehicle. My Prowler trikes are a compilation of design ideas gathered over the years from all of my flying buddies.

In 1995 I established Concept Aviation as a platform for the design, development, and production of ultralight trikes, initially operating from my one-man workshop. Early design goals focused on minimizing empty weight while maximizing structural integrity, handling qualities, and overall flight performance.

Aviation journalist Dan Johnson mentioned my Prowler trikes in several articles.

“The smartly styled and Part 103 legal Prowler trikes are some of the highest performance single seat trikes made in the U.S.A.,” Dan wrote.

At AirVenture, my Prowler trikes earned a Reserve Grand Champion award in 1999, Grand Champion awards in 2000 and 2003, an honorable mention in 2005, a Bronze Lindy in 2007, and an honorable mention in 2025, for my Carbon Prowler trike.

I was compelled to build this latest trike after becoming aware of revised British rules for ultralight aircraft, known as single seat deregulation rules. It is similar to our Part 103 regulation, except that the critical factor is wing loading, which is set at 10 kilograms per square meter. In the United States, that equals 2.05 pounds per square foot. Using one of my 108-square-foot wings, the maximum allowable empty weight could not exceed 221.4 pounds. That immediately became a challenge.

Over the past decade a new type of lightweight trike, known as a nano trike, has begun to appear. To reduce weight, most designers of these trikes end up using very small engines. I wanted to take a different approach and use a 40-hp Rotax 447, resulting in a trike with a high power-to-weight ratio.

I began the design process by researching carbon fiber properties, machining processes, and product availability. What I found was that carbon fiber has a tensile strength approximately 3.8 times that of aluminum and a specific stiffness about 1.7 times greater than aluminum. When strength-to-weight or stiffness-to-weight matters, carbon fiber is the obvious choice.

Machining carbon fiber requires high-quality tools, as the material is abrasive and rapidly accelerates tool wear. I used carbide drill bits and carbide saw blades throughout the build. I found a number of companies offering a wide variety of carbon fiber products. Although carbon fiber is expensive, it does not require any surface finishing, such as anodizing. As a result the increase in total cost amounted to only a few hundred dollars.

The new trike carriage design retains the same fundamental geometry and overall dimensions as my earlier trikes. The primary structural members were redesigned, replacing 2.25 outer diameter (OD) by 0.125-inch wall 6061-T6 aluminum tubing with 14 feet of standard modulus 2.00 square with a 0.125 wall carbon fiber tubing, weighing 8.4 pounds. The main landing gear struts are made of 1.00 OD by 0.125 wall 6061-T6 aluminum tubing, oversleeved with a streamlined symmetrical airfoil carbon fiber tube. The nose gear struts are fabricated from 0.625 diameter pultruded unidirectional carbon fiber rod. A hydraulic disc front brake was also incorporated. The total weight of all the carbon fiber components is only 9.6 pounds. Carbon fiber materials were sourced from Rock West Composites and DragonPlate.

The aluminum angles, brackets, and plates used in the assembly are made of 6061-T6 and 2021-T4 aluminum. Each part was carefully evaluated to minimize weight, with any unnecessary material machined away. The instrument cluster includes the usual gauges, exhaust gas temperature, cylinder head temperature, and tachometer. For navigation I am using an iPhone running the ForeFlight app. The radio is an Icom IC-A5, with a dipole antenna mounted on the king post. The iPhone and radio are powered by a battery and rectifier mounted beneath the seat. A manually deployed hang glider recovery parachute is installed at the headrest location.

After a few months of working with this new trike design, I introduced several refinements to make it more user-friendly. I designed a folding mast mechanism to simplify setup and takedown. Originally, setup involved lifting the 85-pound wing and wrestling it into place at the top of the mast, a difficult task to perform alone. With the new modifications, the mast folds down, allowing the control bar base tube to be placed into a removable mount. The wing can be rotated back and slid into position, bringing the wing and trike together with ease. Then lift the control bar, releasing it from the mount, and continue bringing the wing up and back until the latch locks it into an upright position.

The resulting aircraft has an empty weight of just 222 pounds (a mere 0.6 pounds over 221.4), delivering outstanding performance. Paired with a 108-square-foot wing and a 40-hp Rotax engine, the trike has an exceptional power-to-weight ratio of 5.5 pounds per horsepower and a strong sea level rate of climb of 1,050 feet/minute.

Donald Cooney, EAA 523904, started a 25-year career in the defense aerospace industry after returning from the Vietnam War. He later applied that experience to his lifelong passion for flight, founding a company building ultralight aircraft. Donald remains actively involved in ultralight aviation today. He lives in Knoxville, Tennessee. Connect with him at aaldon@aol.com.