The Boeing 737 was known by many names, the tin rat and the Fluf jet (fat, little ,ugly ****er) being the ones that spring to mind. It was an attempt by Boeing to cover the market for a short haul jet with a smaller capacity than the three engined Boeing 727, itself designed out of the bigger four engine Boeing 707. The fuselage cross section was the same as the other two and the cockpit closely resembles them except, of course, that it was designed for a crew of two pilots instead of two pilots and a flight engineer on the bigger aircraft. The fuselage as much shorter as was the undercarriage which meant the whole aircraft was much closer to the ground than the 707. The 707 had its engines forward and below
the wing, but what with the ground being in the way the 737’s engines were up tight under the wing. The whole aircraft was a cut down version with even the main undercarriage doors being deleted and the wheels forming the doors themselves with hub caps on the outer wheels. The hydraulic systems were cut down to two with manual reversion for the controls in the event of a double failure. The electrical system was split into two with each engine driven generator powering half the aircraft so there was no need for any form of phase locking between generators; if a generator failed there was a bus tie switch that allowed the crew to run both systems from one generator.
The autopilot was fairly basic, but adequate. It was only two channel (elevator & ailerons) with the crew ensuring that the rudder trim was correctly set. The lack of a rudder channel meant that when Autoland was later fitted there was no way to kick of the drift which meant there was a fairly low crosswind limit and the main undercarriage was only held “fore and aft” by springs and could therefore align itself with the direction of travel in a crosswind landing. It could also result in the aircraft not completely traveling in the direction it was pointing while taxying in a strong crosswind.
Th 737-100 was quickly (after only 30 had been built) replaced by the -200 which was slightly bigger and had better avionics with an advanced option which included Autoland. The -200 still had the Pratt & Witney JT8D engines which being a true jet engine and not a turbofan, were fairly noisy. The cruise speed was also quite low which made it an ideal short haul pilot’s aircraft; too slow to go far and too noisy to fly at night. This is not, of course, ideal for airline management. The later models of -300, -400 and -500 had turbofan engines (with strange shaped cowlings to keep to lower side clear of the ground) and some cleaning up of the airframe to give a higher cruising speed, although the airframe was very similar to the -200 (-500 same size, -400 much longer and the -300 somewhere between the two). The -300 and -400 were considerably over powered, but the -500 with the fin and rudder not being as powerful because they were not far enough aft, had to have derated engines to keep the critical engine out airspeeds sensible.
The 737 NG (for Next Generation) which covered the -600, -700, -800 and -900 had a new wing which improved performance and cruise speed and a range of fuselage lengths to accommodate more passengers (189 in the case of the -900), more, in fact, than the Boeing 707 of which the 737 was originally a reduced size version.
The first 737 I flew was a British Airways -236 (the model number is the first number and the last two are the exact specification, effectively the airline that first bought it). BA had bought a total of 48 -236’s to operate short haul routes and also the German internal flights (until re-unification only British, French and American flag carriers were permitted to operate into Berlin). After the complexity of the Tristar the 737 was a gloriously simple aircraft to operate. The Autopilot, although slightly less able than the Tristar, was very easy to understand and did a good job.
I later flew the -400 and -300. These were more complex aeroplanes with a real Flight Management System (FMS) and slightly different hydraulic systems. The later ones seemed to suffer a bit with “new wine in old bottles” with a lot of the updated systems not really joined up (just as one simple example, if you increased the cruise altitude you had to tell the FMS and the pressurisation systems separately what you were doing, the Airbus was better connected).