Why Are Biplanes and Triplanes No Longer Being Produced

During the 1920s and 1930s, biplanes and triplanes were the dominant types of aircraft. A biplane has two wings stacked one above the other, while a triplane has three. These aircraft were particularly prevalent during World War I. Classic examples include the Albatross D.Va, the Sopwith Pup, the Royal Aircraft Factory S.E.5, the Fokker D.VII, and, notably, the Fokker DR-1 triplane. These models were among the most popular biplanes and triplanes of that era. But why have biplanes and triplanes fallen out of favor, and what advantages did they offer over monoplanes in their time?

Advantages of Biplanes and Triplanes

One of the most significant advantages of biplanes and triplanes is their ability to produce more lift for the same wingspan, thanks to their greater wing area. This results in lower wing loading, which translates to shorter takeoff and landing distances and lower stall speeds. In practical terms, this means these aircraft can operate in smaller airfields and have better low-speed handling characteristics, which were particularly valuable in the early years of aviation.

Biplanes and triplanes boast better roll rates due to their reduced roll inertia and roll damping, a direct result of their shorter wingspans. This improved maneuverability was a critical factor during World War I, leading to a surge in triplane designs. Fighter aircraft and aerobatic planes, especially those used in the years following World War I, often utilized biplane designs to capitalize on this agility.

Despite their advantages, biplanes and triplanes do face certain challenges. Aerodynamic interference between the wings can reduce the efficiency of lift generation. The high-pressure air under the top wing and the low-pressure air above the lower wing can cancel each other out to some extent. This means that a biplane doesn’t achieve double the lift of a similarly-sized monoplane. However, increasing the spacing between the wings can reduce this interference, though it requires longer spacing struts.

Transition to Monoplanes

The primary reason for the decline of biplanes is their inefficiency compared to monoplanes. Biplanes create a significant amount of drag relative to the lift they produce. This means they consume more fuel to cover the same distance as a monoplane. In an era where fuel efficiency and environmental considerations are paramount, this drawback is a major disadvantage.

Another issue is visibility. Biplanes typically offer poorer visibility than monoplanes, which is a significant drawback for pilots. In aviation, visibility is not just a matter of convenience but a critical safety factor, especially in crowded airspace and complex flight operations.

Limited Advantages in a Modern Context

While biplanes do have certain advantages, such as a good roll rate and low stall speed, these benefits are increasingly overshadowed by the capabilities of modern monoplanes. Biplanes can fly slowly and are quite maneuverable, which is beneficial in aerobatics. However, advances in wing design and composite materials have allowed monoplanes to perform aerobatics effectively, negating one of the few niches where biplanes had an edge.

In terms of practical applications like travel and cargo transport, biplanes fall short. Their complex design and inefficiency make them less suitable for these purposes compared to monoplanes, which can achieve higher speeds and carry loads more efficiently.

As engine power and aircraft speeds increased, particularly towards the end of World War I, the advantages of thick cantilever wings became more apparent. These wings, with their inherently lower drag and higher wing loading, made monoplanes more attractive. They helped solve structural problems associated with monoplanes and offered little improvement for biplanes. This shift marked the transition to the monoplane as the standard design in aviation, especially for high-speed and high-altitude flights.