Part 6 of this series of articles describes the 737 model differences after the origin of the 737-100 and -200 models, up to the birth of the 737 Max.
The success of the B737-100 and -200 models
The 737 First Generation proved to be a resounding commercial success. This would lead to the next (second) generation of aircraft, garnering the name Classic. This Second Generation involved the 737-300, -400, and -500. The differences in these variants are as follows:
Second Generation of 737s
Engineer Mark Gregoire was tapped by Boeing to lead a design team to explore the possibility of modifying the existing 737 Airframe to accept the newest turbofan engines available. This involved the CFM 56-3B-1 which offered a quantum leap in power, fuel savings, extended range, and payload capacity.
How the engine was fitted to the airframe on the second generation of B737s
Here again, this would require modification to the existing airframe in order to properly place these engines under the wing.
CFM International engineers reduced the engines’ initial fan size (diameter) in order for it to properly fit, allowing sufficient ground clearance to occur. This was due to the lower ground clearing allowed in the original design.
This engineering marriage of the engine to the underwing pylon took place resulting in its rather distinctive distorted engine nacelle (engine cover).
It was flat on the bottom and often referred to the hamster pouch “air intake”. This was further facilitated by placing the engine slightly ahead of the wing while mounting the engine accessories to the side of the engine nacelles.
This singular engine upgrade prompted Boeing engines to stretch the fuselage nine feet six inches allowing additional passenger capacity up to 149.
The Second Generation’s 737-300 also featured improved aerodynamics:
- The wingspan was extended one foot nine inches, allowing for wingtip extensions of nine inches.
- The leading-edge slats and trailing-edge flaps were adjusted to work in concert with the re-designed horizontal stabilizer. This was required to improve the aircraft’s trim pitch due to the forward repositioning of the new CFM 56 engines. Two airframes were produced allowing for the nine-month certification program.
Two airframes were produced allowing for the nine-month certification program.
Boeing made a special announcement in June 1986 introducing the development of the Dash 400 model in the ever-evolving 737 family of aircraft. It featured an additional ten-foot extension in the fuselage length. This allowed for additional passenger payload totaling 188 seats in all.
The first test flight occurred on February 19, 1988. Extensive flight testing took place for seven months/500 hours, culminating in serviced entry with Piedmont Airlines that October.
The 737 -500 was developed to replace the 737-200 airframe. This decision was heavily influenced by Southwest Airlines. The 737-200 was lengthened by an additional one foot seven inches. This was facilitated in order to meet the increased demands regarding payload capacity afforded to this airframe by the newer, more powerful CFM 56-3 engine.
This upgraded turbofan produced a 25% increase in fuel efficiency over the older original Pratt & Whitney engines.
Southwest Airlines placed an initial order for 20 aircraft in 1987, flying for the first time on February 28, 1990.
Successful airframe and engine improvements of the B737
It became obvious that these airframes could be successfully upgraded through the constant improvements of these turbofan engines that were under constant and continuous development. This was further facilitated by the savings achieved through the spike in fuel prices (15%) in 2000 to 40% by 2008.
Third Generation of 737s
These relentless upgrades in turbofan engine design as well as Air Buses’ ascendency as a major rival to Boeing through its A320/A319/A318 series of aircraft motivated Boeing’s upper management to the further development of the 737 families of aircraft.
Next Generation (NG) 737s
This would result in the third series of aircraft better known as the Next Generation (NG). NG aircraft included the 737-600, 737-700/700ER, 737 -800, and 737-900/900ER.
The 737 Next Generation of aircraft offered a redesigned wing utilizing a longer wingspan and increased wing chord allowing for greater wing area and fuel capacity.
The newest rendition of the CFM 56-7 enhanced series of turbofan engines was also incorporated in this variant. This along with a glass cockpit (full automation) as well as a larger fuselage, accommodating up to 215 passengers.
Some 737 NG variants were also used by the US Navy as the P-8 Poseidon.
The 737 Max model difference
These constant and relentless series of upgrades would finally culminate in the 737 MAX.
This is the straw that broke the camel’s back. Boeing would cross the line, with some people feeling that Boeing was compromising its company’s moral ethics and reputation as a trusted aircraft company.
This concludes the description of model differences of the 737, up to the beginning of the Max. The 737 Max will be discussed exclusively in Part 7 of this series of articles, entitled B737: Stretched to the MAX. You will learn how Boeing’s development of the 737 Max series of aircraft came about in an attempt to keep up with Airbus.
Featured image: Boeing 737-300. Photo: Eturbo.
- Wikipedia: The Boeing 737
- Boeing.com: The 737 Family of Aircraft
Story: ©2020 Thomas E. Gardner. Renowned Aviation Journalist & Author Thomas E. Gardner has spent months on his investigative report. The author has based his story on facts that he has learned in regard to the 737 Max-8 engineering disaster during his in-depth investigation process of the article.
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