Although the Boeing 737’s recent history has been rather checkered, that doesn’t negate its previous 50 years of stellar service and ever-increasing versatility. What started as a short-range aircraft intended to serve small domestic airports has evolved tremendously over the years. Certain versions now offer long-range transatlantic flights, a far cry from the puddle jumper it used to be.
While much about the 737 has changed (not always for the best), one unique design feature has remained: its main landing-gear wheels are still exposed when the gear is retracted. (Traditional doors still cover the nose wheel.)
The reason for this goes back to the aircraft’s original purpose, service to the less-developed regional airports of the 1960s. Not all of them had extensive repair facilities, so the idea was to keep the 737 as simple as possible. Landing gear doors are big, heavy, complex mechanisms that could be prone to failure, especially back then. A main landing gear design that placed the wheels flush with the underside of the fuselage when retracted eliminated the need for doors.
The low-riding 737
Another way Boeing designed the 737 for small regional airports was to give it short landing gear that placed it lower to the ground when parked, making it easier for maintenance crews to work on the engines and the underside of the aircraft. Although most airports today have belt loaders for luggage and jet bridges for passengers, they weren’t nearly as common at smaller airports in the 1960s. The 737’s low height meant passengers could board by a set of stairs, and baggage handlers loading and unloading luggage by hand could reach the low cargo bay doors.
Some say the 737’s low ride height is another reason why the main landing gear wheels are exposed. They believe there simply isn’t enough room for doors large enough to cover them. Others disagree, pointing out that the BAC 1-11, another short-haul airliner, does have landing gear doors despite its low ride height. It entered service in 1965, two years before the 737 first flew, so the decision to leave the wheels exposed was likely not because of landing gear door technical challenges.
What about aerodynamics?
The main reason landing gear retracts is to reduce drag. It may seem like leaving the wheels exposed would work against this goal, but the way Boeing designed the 737, the additional drag over a completely smooth belly is negligible.
The landing gear’s most noticeable feature is a giant hubcap on the wheel that remains exposed. When retracted, the tire sits as flush as possible to the body, and the hubcap continues that smooth surface across the wheel without falling off like a Cybertruck’s. They’re not there to look good, but to improve aerodynamics. Since the opening has to be slightly bigger than the tire’s diameter to fit inside, a rubber seal presses against the tire to close off the compartment from rain and debris when the gear is up. Cleverly, once the plane lifts off, the brakes automatically apply to stop the wheel from spinning before it enters its compartment.
While there are no landing gear doors, that’s not to say that there aren’t other aerodynamic aids at work. When retracted, a fairing attached to the landing gear struts covers the entire mechanism. It sits flush with the underside of the aircraft, just like doors over the landing gear would. You can see how this works in the video above. It looks a little funny and out of place when the gear is down, but when it’s up, this fairing is the reason why all you see is a smooth belly, with only the wheels exposed.