The Wing’s The Thing

How Wing Design Affects Your Ride, and How to Preflight for Safety

By Jennifer Caron

Source: FAA Safety Briefing Jan/Feb 2020

Admit it — there are things you don’t know, but should know, about aircraft wings. In particular, do you know how their shape or design determines the type of flying you experience, or pros and cons of different wing types? Although wings are the “heart of the aircraft,” too often they do not receive a proper pre- or post-flight examination. Critical parts such as pitot tubes and aileron balance weights are often overlooked.

Read on to learn more about your aircraft wings, the pros and cons, and how to properly inspect them before and after your flight.

1. Wing Placement

Some might argue that the difference in wing placement (high versus low, etc.) is chiefly a personal preference, but there are some important variations in aircraft performance to consider. Here are some general pros and cons of each.

2. Wing Structure

Many high-wing airplanes are semi-cantilevered, meaning they have external bracings or struts attached to the fuselage. Positioned halfway out on the wing, they help support the wing and carry aerodynamic and landing loads. A few high-wing and most low-wing airplanes have a full cantilever wing that’s designed to carry loads without external bracing. Aircraft with a full cantilever wing structure are much stronger than aircraft using external braces.

Strut-braced wings, in general, stiffen and strengthen the airframe while allowing a lighter overall aircraft. For example, a biplane with its two, strut-braced stiffened wings is lighter and stronger than a single-winged, braced monoplane. The downside to external bracing is additional drag, reduced speed, and less fuel economy, whereas a monoplane is more efficient with the lowest drag.

One key part of a wing that is often overlooked or unknown is balance weights (Figure 2).

Pilots know about the two control surfaces attached to the rear or trailing edges of the wings: ailerons and flaps. Ailerons extend from about the midpoint of each wing out-ward toward the tip. Flaps extend outward from the fuselage to near the midpoint of each wing. However, many pilots are not familiar with the function of balance weights, which are used to balance out an aircraft design in the ailerons (as well as elevators, propellers, and engines) and eliminate or reduce excessive vibration (flutter). If not controlled, flutter can result in damage or failure to not only the stabilizers and the wing itself, but also to the ailerons and elevators, as they’re more prone to this type of dangerous vibration.

Aileron balance weights are teardrop shaped and are located at the leading edge of each of the ailerons ahead of the hinge line (typically three on each aileron). It is important to check balance weights at each and every preflight, as flying without balanced controls can spell disaster.

3. Wing Shape/Planform

The shape and size of a wing greatly affect an aircraft’s performance. Three factors are used in wing design to modify the overall aerodynamic characteristics of flight: aspect ratio, taper ratio, and sweepback.

Aspect ratio, the length and breadth of the wing, has an important effect on a wing’s lifting capabilities and drag (Figure 3). An increase in aspect ratio with constant velocity will decrease drag (induced drag), especially at high angles of attack, improving wing performance in a climbing attitude.

A thin, long wing for instance has a high aspect ratio and therefore a better lift to drag ratio. It’s more aerodynamically efficient, generates more lift with less drag, consumes less fuel, and is ideal for sustained flight in subsonic aircraft. Longer wings are not as maneuverable as shorter wings, but they’re best at low speeds and high altitudes, and are usually more forgiving of improper pilot techniques. Most training and GA airplanes are operated at high coefficients of lift and require high aspect ratios.

Low aspect ratios are seen in thick, wide wings. A decrease in aspect ratio provides a corresponding increase in drag. Very low aspect ratios result in high wing loadings, high stall speeds, and higher fuel consumption. They provide greater maneuverability than wings with high aspect ratios, but what you get in movement, you lose in speed and fuel.

The majority of typical GA aircraft have aspect ratios that range anywhere from 5-9 (gross Aspect Ratio); home-builts: 4-7; gliders: 20-35; and supersonics: 3-5.

4. Wing Design

Taper ratio and the sweepback, or rearward slant of a wing, are two other design ratios used in wing design. Tapering (decreasing the length of chord from the root to the tip of the wing), causes a decrease in drag (most effective at high speeds) and an increase in lift.

Aspect ratio, taper ratio, and sweepback can be mixed to create different flying experiences. In Figure 4, you’ll see some typical GA design configurations and their pros and cons.Other wing designs, such as the elliptical and swept wing planforms, are observed on military aircraft, specifically the Supermarine Spitfire and the Dassault 3G.

5.Wing Pre-and Postflight Checklist

Preflight inspection is one of the most important steps you can take to ensure that your aircraft is fit for flight — and that includes inspection of your aircraft wings. Use this checklist as a guide in developing your own personalized system to inspect your wings before and after each and every flight.

Wing Pre- and Postflight Checklist:

• Wing tips for cracks, loose or missing rivets; bolt security; general condition of wings and covering for torn fabric, bulges, wrinkles; aircraft at unimproved airports: prone to erosion on wing leading edges.
• Staining, dripping, puddles of fuel, oils anywhere on the wing or where a fuel tank is mounted, no matter the age of stains; rivet lines for fuel leakage on wet-wing fuel tanks.
• Wing strut attachment points for bows, bends; external bracing attachments and spar lines for distortion, cracks, security; internal brace fittings at wing attachment.
• Deicing: weeping wings, hot wings, inspect boots for leakage, attachment.
• Landing gear that retracts into wing, nacelle — clean, check frequently.
• Position lights on wingtips for operation right, left.
• Aileron, flap hinges, actuators for cleanliness, lubrication, dents, cracks, excess play, hinge pins, bolts for security, condition; movable surfaces for full freedom of movement includes full aileron, elevator, rudder deflection in all directions (which is often overlooked). In low-winged aircraft, bend/crouch to inspect under wings, flaps, ailerons.
• Aileron balance weights for cracks, security; lift up aileron to check security of the rivets holding balance weight in place.
• Pitot or pitot-static port(s), check drain holes for blockage, insects, water, never blow air into tube to clear; check both holes large (in front), small (in back) for blockage.
• Postflight: inspect under wings and other fuel tank locations for fuel stains.•Post-storage: inspect for bird nests inside wings, control surfaces, and damage to rib stitching from mice.
• Winter: inspect wings, control surfaces for snow — it can melt and freeze inside controls.

Jennifer Caron is FAA Safety Briefing’s copy editor and quality assurance lead. She is a certified technical writer-editor in aviation safety and flight standards.