Why Are Horizontal Stabilizers Not Equipped with Winglets?

Many aircraft designs incorporate winglets to enhance their aerodynamic efficiency, but you may have noticed that not all horizontal stabilizers feature these devices. This article delves into the reasons behind this design choice, exploring the benefits and limitations of winglets, and presenting various aircraft models as examples.

Introduction to Winglets

Winglets are aerodynamic devices designed to reduce drag, thereby improving fuel efficiency and overall performance. They are often found on wings, helping to improve the aspect ratio, which is the ratio of the wingspan to the chord length. Winglets work best when the aircraft is in a region of lift coefficient where the plane operates during long-range cruise, as they can optimize drag reduction in this specific area.

The Role of Winglets and Stabilizers

While winglets can greatly enhance the efficiency of wings with insufficient span, horizontal stabilizers serve a different function. These devices are primarily designed for stability and control, providing lift at the tail end of the aircraft. Their role is to counterbalance the pitching moments caused by the lift generated by the wings. Unlike winglets, horizontal stabilizers operate over a wider range of cruise lift coefficients, including negative lift during certain flight conditions.

Ground Constraints and Operational Differences

Aircraft wings are often constrained by ground operations, such as taxiing and parking, where limited ground space can restrict the wingspan. Therefore, winglets or folding wingtips can be used to increase the effective wingspan without the need for a physically longer wing. This is evident in the Boeing 737 and 777X, with the former opting for winglets and the latter using folding wingtips.

The Case for Raked Wingtips

For military aircraft, such as the Boeing P-8, the freedom from ground constraints allows for the use of raked wingtips. These wingtips reduce the wingspan on the ground but maintain the ideal span in flight, offering the benefits of both ground and air operations. Another example is the Boeing 767, which also employs raked wingtips to balance ground constraints with aerodynamic efficiency.

Economic and Structural Considerations

The decision to equip horizontal stabilizers with winglets involves careful consideration of costs and benefits. Winglets are effective in reducing drag and improving fuel efficiency, but their effectiveness is limited to specific regions of lift coefficient. Horizontal stabilizers, due to their wide range of operation, might not benefit as much from winglets, as they are optimized for different lift conditions.

Additionally, the structural requirements for winglets add extra weight and complexity. The horizontal stabilizer is already subject to vibrations from the wings, and the addition of winglets could further exacerbate this. Therefore, the structural requirements would need to be much stronger and heavier, which might not justify the benefits in terms of fuel efficiency and performance.

Economic Viability and Operational Routes

Many airlines operating on shorter routes have found that winglets do not offer a significant economic benefit. Studies have shown that below 1000 NM, the cost savings from using winglets do not justify the investment for shorter routes. This is especially true for the Boeing 737, where the winglets initially installed were found to be less cost-effective for flights shorter than 1000 NM.

Conclusion

The choice to equip horizontal stabilizers with winglets is not a one-size-fits-all solution. It depends on the specific design goals, operational constraints, and economic considerations. While winglets provide significant benefits in terms of aerodynamic efficiency, their application to horizontal stabilizers is limited due to their operating range and the added structural and economic challenges they present.

Key Points Recap

Winglets are designed to reduce drag and improve fuel efficiency. Horizontal stabilizers primarily contribute to stability and control. Winglets and raked wingtips offer flexibility in ground-constrained environments. Economic viability and structural requirements play a crucial role in the decision-making process.