37’s is not common here in Philippines, but some international airlines are operating their 737 is the country. Before, Philippine Airlines once operated 737 a long time ago. Over the time, airlines here in the Philippines gradually switch to modern, fly-by-wire Airbus A320.
But if you look closely, when they take-off, notice that the main landing gear door is missing, but the front nose wheel has door in it.
We need to keep it low
After they take off, 737 landing gears are directly retracted into main fuselage. Most of the commercial aircraft have main landing gear doors present, but in 737 there is none. But it does have partial doors to cover the struts but not the wheels.
The reason for that is to keep the aircraft low on the ground. Let’s go back in time. This is related to a design issue way back to the development of 737-100 in 1968, where the first aircraft is introduced. This was to make 737 more usable at smaller, regional or even remote airports.
Because unlike the main international airports, they have unlikely to have air bridge or baggage load systems. So keeping the aircraft lower to the ground would be economical and practical, because it easier to embark passengers and cargos. It is also easier for service and fuel the aircraft with limited equipment.
This is also the key for the Boeing to capture the market, and it was pretty successful. They also went for further modifications such as landing on gravel runways to land in some remote regions. Boeing made an optional Unpaved Strip kit made available for 737-100 and -200 series in 1969.
Oops! There’s no space left
It is reasonable to opt out the landing gear doors because of the fuselage being low. This will also make sure that the aircraft will have sufficient clearance to land on the ground. Engineers at Boeing thinks also the safety both of the passenger and the aircraft. So landing gear doors is not added.
It is not a bad thing to remove the doors. It can save also the operator from maintenance and repair, apart from that, it is much lighter and freed up more space in the middle section of the aircraft.
With the wheels are being exposed, changes we made too. The wheels have smooth hub cabs to aid its aerodynamics on the external side of the wheels to avoid unnecessary drag. They added also a rubber seal around the fuselage opening to prevent any undesired objects, or water entering the landing gear enclosure.
Oh, Look at the engines!
They also apply these changes to the engines. That is why some engines has this unusual, non-circular design. This was different compare to other competing aircrafts at that time. Boeing considers also to install engine at the tail, but they prefer wing mounting. This enables them an increase in fuselage width and made more accessible to maintenance people.
Larger engines such as jet turbine comes through, and to accommodate this, they flatten the bottom engine housing. This design would later be known as ‘hamster pouch’ design.
Similar designs follow through
Brazilian aerospace manufacturer Embraer adapted the landing gear design to their E190 and E-jet aircrafts.
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China’s COMAC jets has one too! The Chinese build ARJ21 has also the same landing gear door design.
What are your thoughts in this article? Please let us know through the comments.
Source: Hayward, J. (2020, December 15) Why Aren’t The Boeing 737’s Main Wheels Covered In Flight? Simple flying.
https://simpleflying.com/why-arent-the-boeing-737s-main-wheels-covered-in-flight/
