Landing gear is one of the most significant contributors to parasitic drag on an aircraft during flight. While essential for ground operations, its exposed structure presents a substantial aerodynamic penalty. Designing landing gear that minimizes air resistance is therefore a critical objective for aircraft manufacturers seeking to improve fuel efficiency, extend range, and reduce environmental impact. This article explores the principles, technologies, and challenges involved in creating aerodynamically efficient landing gear.

The Drag Penalty of Landing Gear

When extended, landing gear components such as struts, wheels, brakes, and retraction mechanisms disrupt smooth airflow, creating turbulence and pressure drag. This drag can account for up to 5–10% of total aircraft drag during takeoff and initial climb, and remains a factor during cruise if the gear is non-retractable. In addition to aerodynamic drag, landing gear is a major source of airframe noise, particularly during approach and landing.

Minimizing this penalty requires a multi-faceted approach that blends streamlined geometry, smart retraction systems, and advanced materials. Engineers rely heavily on computational fluid dynamics (CFD) and wind-tunnel testing to optimize every surface exposed to the airstream.

Core Design Principles

The following principles guide the development of low-drag landing gear.

Streamlined Shapes and Fairings

The most direct method to reduce drag is to shape components so that air flows smoothly around them. Landing gear struts are often enclosed in aerodynamic fairings—smooth, rounded covers that reduce the frontal area and delay flow separation. Wheel wells are designed to be flush with the aircraft skin when closed, and doors are contoured to match the fuselage or wing profile.

Fairings are not limited to struts: brake assemblies, hydraulic lines, and torque links are all potential drag sources. Modern designs use sculpted covers that integrate these components into a single, clean shape.

Retractable Mechanisms

Retracting the landing gear into the fuselage or wings eliminates most drag during cruise. The retraction sequence must be precise to avoid mechanisms snagging or protruding. Engineers design actuation systems—hydraulic, electric, or electro-mechanical—that stow the gear completely behind doors that seal flush with the aircraft surface.

Retractable gear adds weight and complexity, but for high-speed aircraft (above roughly 150–200 knots) the drag savings far outweigh these penalties. For slower, lighter aircraft like general aviation trainers, fixed landing gear with carefully designed fairings is often preferred for its simplicity and lower maintenance.

Lightweight, Durable Materials

Weight directly affects drag because heavier aircraft require more lift and thrust. Landing gear must be exceptionally strong to absorb landing loads, but engineers select materials with high strength-to-weight ratios. Aluminum alloys, titanium, and high-strength steel have been traditional choices. Increasingly, carbon-fiber-reinforced polymers (CFRP) are used for non-structural fairings and some load-bearing components, reducing weight without sacrificing durability.

Advanced composites also allow for complex aerodynamic shapes that are difficult to manufacture in metal, enabling more efficient fairing designs.

Surface Finish and Micro-Geometry

Even minute surface imperfections can trigger turbulent flow and increase skin friction. Landing gear components are polished and coated with smooth paints. Some designs employ surface treatments like riblets—microscopic grooves that reduce drag by directing airflow—though these are more common on aircraft skins than on landing gear due to wear and dirt accumulation.

Fixed vs. Retractable Landing Gear: A Design Trade-Off

Fixed landing gear is simpler, lighter, and more reliable, but it creates constant drag. For slow-flying aircraft like crop dusters and bush planes, the drag penalty is acceptable. Retractable gear dominates commercial and military aviation because cruise speeds are high enough that the drag reduction significantly improves fuel economy.

Modern airliners such as the Boeing 787 and Airbus A350 have advanced retraction systems that stow the main gear into the wing-body fairing, minimizing exposed cavities. The landing gear doors themselves are designed as part of the aerodynamically smooth outer mold line. External links like Boeing’s 787 Dreamliner page show how fairings and precise door alignment contribute to overall efficiency.

Advanced Materials and Manufacturing

New materials enable lighter, stronger landing gear that can be shaped more aerodynamically. For example, Airbus uses titanium and aluminum alloys in the A350 landing gear, while composite fairings reduce weight. Additive manufacturing (3D printing) allows for complex internal lattices that reduce weight while maintaining strength, and can produce optimized fairings with integrated cooling ducts for brakes.

Ceramic matrix composites (CMCs) are being investigated for brake components, which can operate at higher temperatures, reducing the need for cooling louvres that create drag. These advances are detailed in papers from organizations like AIAA (American Institute of Aeronautics and Astronautics).

Aerodynamic Fairings and Surface Treatments

Main Gear Fairings

On aircraft with non-retractable gear, full-leg fairings (sometimes called "spats") enclose the wheel and strut in a streamlined housing. These are common on many general aviation aircraft. However, fairings must be carefully designed to avoid creating separated flow at the wheel opening. CFD studies have shown that small vortex generators or Gurney flaps can improve fairing performance.

Wheel Well Design

Wheel wells are cavities that can cause significant drag if not sealed properly. Doors must close after gear extension to minimize cavity drag. On some aircraft, the well is also pressurized or ventilated to reduce the low-pressure regions that attract drag. Surface treatments like dimpled liners (similar to golf balls) have been tested in wheel wells to reduce friction, though results vary.

Vortex Generators

In some cases, small vortex generators are placed on or near landing gear components to energize the boundary layer and delay separation. These can be found on struts or fairings of specific aircraft, though they are more commonly used on wings and tail surfaces.

Active and Adaptive Technologies

The next frontier in landing gear aerodynamics involves active systems that adapt to flight conditions. One promising concept is morphing fairings that change shape as the gear deploys. For example, a fairing could be flat during cruise to minimize drag, then bulge outward when the gear extends to provide additional space for the wheel.

Active flow control (AFC) using micro-jets or synthetic jets can be used to blow air over a landing gear surface, reattaching separated flow and reducing drag. While still in research, such systems have been demonstrated in wind tunnels. NASA has explored AFC for landing gear noise reduction, which directly correlates with drag reduction. A valuable resource is NASA’s Aeronautics Research Mission Directorate, which publishes findings on landing gear drag and noise.

Computational Fluid Dynamics in Landing Gear Design

CFD has become indispensable for analyzing the complex flow fields around landing gear. High-fidelity simulations capture turbulent wakes, vortices shedding from wheels, and interference between gear and airframe. Engineers can iterate quickly on strut profiles, fairing shapes, and door gaps without building physical models.

Modern CFD tools also predict aeroacoustic noise, which is closely linked to drag. By reducing pressure fluctuations, both noise and resistance can be lowered. The use of lattice Boltzmann methods and detached eddy simulation has improved accuracy for landing gear flows. Designers combine CFD with wind tunnel validation to ensure that real-world performance matches simulations.

Challenges and Trade-Offs

Even with advanced tools, designing aerodynamically efficient landing gear involves significant trade-offs. Key challenges include:

  • Structural integrity – Landing gear must withstand high impact loads during landing. Streamlining often requires hollow or thin shapes that may be structurally weak.
  • Weight – Add-on fairings and complex retraction mechanisms add weight, which can offset aerodynamic gains. Every kilogram saved requires careful optimization.
  • Cost – Advanced materials, actuators, and manufacturing processes increase production and maintenance cost. Airlines must weigh fuel savings against higher upfront investment.
  • Maintenance – Fairings and doors can be damaged during landing or from debris, requiring repairs that affect dispatch reliability.
  • Safety – Retraction systems must have high reliability. A gear failure to extend can be catastrophic. Simpler, less aerodynamic designs are sometimes favored for safety.

These constraints mean that the most aerodynamic landing gear is not always the most practical. Engineers must balance drag reduction with durability, cost, and certification requirements.

The push for more electric aircraft and urban air mobility vehicles (eVTOL) is driving innovation in landing gear design. Many eVTOL aircraft use fixed landing gear with streamlined fairings due to low cruise speeds and the need for simplicity. For larger commercial aircraft, concepts like "blended wing body" (BWB) designs integrate landing gear into the wing-body structure, allowing for larger gear bays that can be more aerodynamically optimized.

Research into smart materials—such as shape memory alloys—could lead to landing gear that automatically smooths its shape based on aerodynamic loads. Additionally, the use of active load alleviation systems can reduce the structural demands on landing gear, allowing more aerodynamic shapes. For a broader perspective on aircraft design trends, see Airbus’s innovation page, which discusses ongoing research into efficient landing systems.

Conclusion

Aerodynamically efficient landing gear is not merely an afterthought in aircraft design—it is a critical element that directly impacts fuel burn, range, noise, and environmental footprint. Through careful attention to streamlined shapes, retraction mechanisms, advanced materials, and computational optimization, engineers can significantly reduce the drag penalty. While challenges remain, ongoing advances in smart materials, active flow control, and manufacturing promise even greater gains. As the aviation industry pushes toward net-zero emissions, every drag reduction matters, making landing gear aerodynamics a field of enduring importance.