Notice Non Sums: Fill & Download for Free

Ooo… pick me!The A330 is a prime example which you can see if the aircraft is an older generation (built in the 90s) or a newer generation (built in the 2000s and after). But how?Easy. Look at the interior:The first photo is an early generation A330 airframe. The second photo is a later generation one. Just look at how different they are.No? Still can't notice?Ok, notice the overhead bins. Early versions of the A330 have rigid contour overhead bins with rectangular opening latch. The later generations ones use smooth contour with an oval shaped latch.Also, look at the sidewall panels around the windows. Older generations ones have rectangular recesses around the windows. Later generations one don't have rectangular recssses.Look at the overhead panels. The no smoking sign on older generations ones are a straight bar. Later generations ones are smooth contour.Other stuff include, the cabin crew call button sound different. The electrical hydraulic pump sound different too (if you listen very carefully before pushback or after arrival, when they open the cargo doors). The older generations pumps make an E-flat (yes, the musical note), while later generations ones make a B-flat.But for the average passenger, in the above two photos they won't find much difference. It's because airlines refurbish their interiors, seats and equipment. This is what most non-avgeek passengers care about after all. But most of the time the overhead bins, sidewall panels and overhead service units (no smoking signs, oxygen contains etc) won't get replaced. They are just relocated to fit the new configuration.Then again, what does it mean if an aircraft is old? As long as it has been maintained in accordance with the required standards, they behave the same as a newly delivered one 30 years apart. Sure, there may be some visible differences and wear and tear, but most passengers aren't really bothered as long as their inflight entertainment works.(In addition, as mentioned by another answer: yes, you can try to find the aircraft’aircraft's registration mark and google it to see how old it is.)EDIT: A lot of comments mentioned about looking up the registration plate and google it. Absolutely true.Aviation legislation requires a civil transport aircraft to have a registration plate and serial number at the L1 or R1 door. It needs to withstand 1,100 deg Celsius heat for a certain amount of time.Alternatively, look for the registration mark on the tail and google it.

Firstly, take a look at this…(Source: General Electric)You see a series of holes along the walls of this engine’s bypass duct. This is the acoustic liner. The worst of the engine’s noise is shielded by this porous liner which has pockets of air inside. Noise causes the air inside the air pockets, rather than the wall, to vibrate, thereby dissipating the acoustic energy before being transferred to the wall, then to the outside, then to your ears.You’ll notice the acoustic liner’s effect, however, on a rainy day when the holes are blocked by water. You’ll hear the engine noise quite a bit louder than on a dry day.Second, it is in the exhaust:Everyone’s familiar with this schematic. A turbofan engine works by sucking in air, accelerate it and throw it out from the back as a higher speed jet.Now, if hot air meets cold air, and if fast moving air meets slow moving or still air, you get mixing. And mixing causes turbulence. And turbulence causes noise. You notice every time when you can hear wind blows on you.The exhaust jet is fast moving and hot. This mixes with the surrounding air in the atmosphere and causes a lot of noise trailing behind the aircraft. Even worse, since a turbofan has a core stream (hot) and a bypass stream (cold), they also mix and cause even more noise. Throughout the years manufacturers have done various things to lessen these noises including:Common nozzles, like this one on an A330. And this weird thing:(Exhaust muffler/mixer, still being used on Airbus A340s)… or more commonly, as also raised by other answers…(747–8 engines)These 3 different designs serve the same purpose: to increase the mixing of the flows immediately after the engine so that the turbulence can’t go too far, thereby reducing the noise from going too far behind the aircraft.EDIT//The increase in mixing also shifts the exhaust noise frequencies higher. Higher frequency noise dissipates more quickly and have shorter ranges.This results in a mild noise which fades almost immediately (e.g. Boeing 787), rather than a deep rumbling noise that trails behind the aircraft for miles and remains around for 30 seconds (e.g. MD11).//EDIT endsBut the most important reason is: jet velocityThrust = (mass flow rate of air) * (jet velocity)For the same thrust you can choose to have either:A small engine that takes a little air and propels it relatively quickly, orA bigger engine that takes a lot of air and propels it relatively slowlyIf you recall, a faster air flow causes more turbulence, hence more noise. The reverse is also true.You’ll notice that aircraft engines have gotten quite a bit bigger these days. We have made engines bigger to accommodate higher bypass ratios. This effectively increases the air flow but decreases the jet velocity. Therefore, we cut a lot of noise while saving enormous amounts of fuel by increasing the engine bypass ratios.Lastly and briefly, maintenanceRoutine maintenance ensures the engine components—bearings, rotating blades—are in good conditions to reduce vibrations and therefore noise. Regular internal inspections ensure good conditions of the hot section, as non-uniformity in the combustor and turbine can cause uneven thermal distributions which cause, you guessed it, more vibrations, noise and damage.

People talk about colonialism a lot nowadays and most people know that countries such as France, Britain, Spain, Portugal, Germany, Belgium etc. had colonial empires.What you probably didn’t know, however, is that the small German city of Augsburg also had a colonial empire.For those who don’t know, Augsburg is a small city of ~280,000 citizens in southern Germany:What you may notice is that it is entirely landlocked.So how did it end up with a colonial empire?In 1528, the leader of Augsburg loaned the Habsburg Emperor Charles V a large sum of money. The emperor, however, did not have the money to pay back so, instead of giving a cash settlement, he gifted Augsburg the colony of Venezuela (which was renamed Klein-Venedig). Unsurprisingly, they were unable to maintain this colony so the Habsburgs took it back 18 years later.For 18 years, however, the German free-city of Augsburg was a colonial power.