The main landing gear wheels sit uncovered after folding into their housing, as seen on the underside of the Boeing 737 shortly after takeoff or in flight. On most other planes, it’s hidden behind closed doors. Since the introduction of the first 737, this has been the case. The most obvious reason, you guessed it, is the limited space underneath the fuselage.
The 737’s primary landing gear wheels are elevated into a cavity within the main fuselage after takeoff. However, rather than being covered (like they are on most planes), they are left uncovered and visible. They aren’t protected by any doors; however, the nose landing gear is. The main landing gear struts are covered by partial doors, but the wheels are not. The 737 has a cavity called the “hole” in which the gears fit in. Smaller planes such as the Embraer jet family and the ATR turboprop share the same characteristics to the 737. These are all short-range, domestic/regional aircraft with short landing gear and little space between the fuselage and the ground.
This aircraft was made to fly low to the ground. The decision was made to make the 737 more adaptable to smaller, regional, and remote airports. Air bridges and baggage loading systems were unlikely to be available at such airports. Lowering the plane to the ground would make it easier to load passengers and cargo, as well as service and fuel the plane with little resources. The trade-offs of a lower fuselage were worth it because this was an important market that Boeing sought to capture with the 737. However, landing gear doors were not possible because the fuselage was maintained low to the ground. When used, these require extra clearance and may come into contact with the ground. Of course, they might be configured to close after the wheels have been stretched before landing. But what if this doesn’t work and the doors stay open, or they have to deploy on the ground? They were not included because they would pose an unnecessary safety risk.
However, with the wheels exposed, several more adjustments were required. The external-facing side of the wheels has smooth hub cabs, which helps with aircraft aerodynamics. A rubber seal also surrounds the fuselage aperture. This protects the landing gear enclosure from foreign objects or water.
The landing gear was not the only part of the 737 that had to be changed to accommodate the lower fuselage. The engine housings on many of the 737’s engines are flat rather than circular, as they are on most other planes. This, too, may be traced back to the aircraft’s initial design. It was planned to be low to the ground, but its motors were hidden beneath the wing. This was in contrast to many of the competing aircraft at the period, which had engines positioned on the tail. Boeing considered it for the 737 but decided against it in favor of wing mounting. It allowed the fuselage to be wider and the engines to be more accessible for maintenance. However, larger engines were immediately developed to handle larger turbines and fans. Because these would not fit in the 737’s limited underwing room, the bottom of the engine housing was flattened. The design was quickly dubbed the ‘hamster pouch’ design.
Finally, the lack of landing gear wheel covers on the Boeing 737 is mostly due to its initial design. Because of the constraints and limits of tiny domestic airports in the 1960s, it was designed to be a short-haul, regional airliner with low ground separation, allowing ground employees operating in those airports to readily service and prepare the aircraft.