The wings of most airplanes are left unpainted, which often surprises people when they first notice it. Aircraft wings have a smooth, bare metal appearance rather than being painted like the rest of the plane. There are important reasons why this is done.
Leaving the wings unpainted improves aircraft performance and efficiency in several ways. It reduces weight, drag, maintenance needs, and corrosion. The metal material of the wings is also designed to be strong, smooth, and aerodynamic. Let’s explore why aircraft designers choose to leave wings mostly unpainted.
Weight Savings
Every extra pound on an aircraft requires more fuel to fly. Paint adds weight that provides no structural or performance benefit to the wings.
A typical passenger jet may have over 3,000 pounds of paint on its fuselage and tail. Painting the wings could add another 1,000 pounds or more of dead weight. Over the thousands of flights an aircraft makes, that extra weight becomes very costly.
| Aircraft Model | Max Takeoff Weight | Fuel Capacity (lbs) |
|---|---|---|
| Boeing 737-800 | 174,200 lbs | 6,875 lbs |
| Airbus A320 | 171,000 lbs | 6,400 lbs |
As the table shows, a Boeing 737-800 has a maximum takeoff weight of 174,200 pounds. With a full passenger load, 1,000 pounds of extra paint could mean 5-10 less passengers could be carried. Over thousands of flights a year, the reduced payload capability is a major cost.
The fuel capacity of airliners is also limited. Extra weight reduces the amount of revenue cargo and passengers that can be carried for each pound of fuel. Airlines choose light but strong composite materials for wings to maximize fuel efficiency.
Winglets Reduce Induced Drag
Winglets have become common on large airliners like the Boeing 737 and Airbus A320. Winglets reduce induced drag at the wingtips by smoothing the airflow. Adding paint over winglets would disrupt the smooth airflow they are designed for.
Reduced Drag
The minimalist, smooth design of an unpainted aircraft wing improves its aerodynamic efficiency. Even “smooth” paint creates slight surface roughness that increases skin friction drag across the large surface areas of the wings.
Research by NASA and aircraft manufacturers has shown that polishing and coatings can further reduce drag and friction. Drag reduction of up to 10% has been achieved. Unpainted wings already have an optimal smooth surface.
Laminar Flow Wings
Newer wings are being designed for laminar flow that maintains smooth airflow over more of the wing surface. Paint would trip the airflow and disrupt laminar flow, causing turbulent flow and increased drag.
Lower Maintenance
Paint needs regular maintenance as it degrades over time from jet fuel and fluid leaks, sun exposure, rain erosion, and foreign object damage. Repainting large aircraft is very costly.
For example, it may cost $50,000 to repaint a typical business jet, and over $100,000 for a large airliner. Frequent repainting of the wings would be required if they were painted. The bare metal requires little maintenance other than occasional polishing.
Aircraft Paint Stripping and Repainting Costs
| Aircraft Type | Paint Stripping and Repainting Cost |
|---|---|
| Small business jet (Learjet) | $50,000 |
| Large business jet (Gulfstream) | $70,000 |
| Narrow-body airliner (Boeing 737) | $100,000 |
| Wide-body airliner (Boeing 777) | $150,000 |
As shown in the table, repainting costs can be very high for large jets. Avoiding paint on the wings saves enormous maintenance expenses over decades of operation.
Preventing Corrosion
Aluminum aircraft wings are susceptible to corrosion from water penetration. Special protective coatings help maximize smoothness and prevent corrosion.
Most airliners use a system called Alodining that forms a protective oxidized layer on the surface. It provides excellent corrosion protection with minimal increase in surface roughness.
Adding layers of paint would seal off the metal and trap any moisture, promoting corrosion underneath the paint. This occurred in early aircraft and still does on painted wing surfaces. The unpainted metal alloy wings can withstand moisture exposure better.
Alodined Layer
Diagram showing the thin Aladined layer that protects unpainted aircraft wings against corrosion.
The Painted Leading Edge
The front section and sometimes rear of aircraft wings are often painted. This is because paint or tapes are added to the leading edges to prevent erosion.
The leading edge takes the brunt of raindrop and insect impacts as the wing slices through the air. High-speed impacts can gradually erode the metal, called rain erosion, if not protected.
Thin metal strips or plastic tapes are added to the front of wings. These are then covered with a smooth paint for extra protection from impact and moisture ingress.
Leading Edge Protection Methods
| Protection Method | Description |
|---|---|
| Metal Erosion Shields | Thin metal strips on leading edge |
| Plastic Tape | Taped plastic strips |
| Paint Coating | Smooth durable paint over other protections |
The metal and tape strips prevent erosion. The paint provides a moisture barrier and smoothes the airflow over any surface irregularities. This allows most of the wing to remain unpainted.
Why Not Paint Colorful Wings?
With all the colors and liveries used on fuselage paint schemes, why not paint colorful wings? Wouldn’t they look great?
While attractive, paint on the wings provide no technical benefit and has several drawbacks:
– Added weight reduces payload and fuel capacity
– Increased drag decreases fuel efficiency
– Frequent repainting would be needed, increasing costs
– Trapped moisture could speed corrosion of metal wings
– Applied paint fillers smoothness and laminar flow
Airlines gain no advantage from painted wings. For all white or color liveries, the bare metal provides an elegant, distinctive look. The smooth metal is left unpainted for technical reasons that benefit safety, efficiency and costs.
Conclusion
Aircraft wings are left largely unpainted because the bare metal surface provides engineering benefits. Weight savings, drag reduction, corrosion prevention, and lower maintenance are all advantages of bare metal wings.
Only the front and rear wing edges may be painted and taped for extra protection from erosion. The special aluminum alloys and treatments used resist corrosion and maximize a smooth surface. This allows the rest of the wing to be left unpainted for optimal performance.
So while painted wings might look visually striking, the bare metal is better engineering. The raw technical aesthetic of unpainted wings reveals the innovation and performance capabilities built into modern aircraft.