This long read answers all those questions you had about airplanes but were afraid to ask. Firstly, how does the toilet work in a plane. Short answer: a toilet in a plane works in a completely different way to the toilets in our residence. Julia Buckley of CNN writes: “Using water to flush airplane toilets is a no go because of aircraft weight restrictions. No biggie; instead, planes use air.
The standard evac (evacuation) system uses differential air pressure to empty the bowl, in a design originally patented by James Kemper In 1975.
Waste tanks – where everything that goes down the toilet ends up – are usually located at the back of the plane, and often at the front, too.
When you press the flush button, a valve opens at the bottom of the toilet bowl, connecting it to a pipe below. That pipe – and the waste tank – are pressured, which means that opening the valve creates a vacuum that sucks out what’s in the bowl.
“It’s like your vacuum cleaner – it sucks,” says Nigel Jones, an aircraft engineering expert from Kingston University in London who also sits on the accreditation committee of the UK’s Royal Aeronautical Society.
“As you press the button, it opens the valve – and as soon as the valve opens, the suction draws it all out. Then the valve closes.”
That vacuum effect is going on continuously while the plane is in the air, says Jones – we just don’t hear it until we open the valve and connect the toilet to the system. When the plane is on the ground, however, the differential pressure isn’t there – meaning that the toilet flush is operated by a pump, which creates a vacuum in the tank. As the plane climbs into the air, and the differential pressure in the tank builds, the vacuum naturally forms and the pump stops.”
We learn from Ms Buckley’s article that an airline gets to choose how many toilets it wants on the plane and where. So, the next time you find yourself standing in a long toilet queue mid-air, you know who to blame.
Secondly, how do airlines manage to serve us hot and cold food mid-air. Short answer: by using two completely separate electrical systems. Ms Buckley writes: “Prepping food to be served on a plane is a complex process with stringent hygiene regulations to be adhered to.
Dishes are prepared by catering companies usually based at the airport, before being loaded onto the aircraft. So far, so simple – until you think about having to heat hundreds of meals at the same time. Add in the fact that meals for longhaul flights are often frozen and it becomes even tricker.
Most airplane ovens can either use convection or steam to heat, says Jones – and can contain as many as 40 or 50 meals at a time. “On a large aircraft you could have maybe 10 or 12 ovens.” he says.
Overnight maintenance crews check that ovens are working as the plane sits on the ground overnight. One time they are kept completely off is during take-off.
“The aircraft needs all the power it can get from the engines to take off,” he says. “They don’t put the ovens on till they’re airborne because of the load on the electrical system. Once it’s cruising, it’s fine.”
Chillers and freezers run on a different circuit – so they never turn off. Just as well, since that would be a recipe for food poisoning.”
Thirdly, how does the wi-fi system on-board a plane work given that the plan is flying at 800 kmph? Answer from Ms Buckley: ““It’s pretty easy technology – you have an antenna that sits on top of the aircraft and continually points at satellites in what’s called the geostationary arc,” says Don Buchman, general manager and vice president of commercial aviation at Viasat, which provides Wi-Fi for almost 10,000 flights per day at up to around 100 MB per second.
What sounds like easy tech for him – Buchman has an engineering background – sounds rather more complex for the rest of us, though.
Planes equipped for Wi-Fi with Viasat are receiving from satellites over 22,000 miles (36,000 kilometers) above the Earth, located along the equator.
Getting them up there – to levels called the “geostationary arc” or orbit – takes anything from 30 days to six months. But as Buchman says, once they’re in orbit, it’s simple. That high altitude means that each satellite can “see” about a third of the Earth, meaning you could technically fly around the globe connecting to just three satellites – although Viasat has 18.
Because each satellite covers such a vast area, it means that planes aren’t constantly disconnecting and reconnecting as they fly. Buchman says that a transcontinental US flight, for example, might use anything between one and all five of the Viasat satellites positioned nearest North America.
“Today we can do London to New York City on one, but it depends on the algorithm,” he says, referring to the algorithm Viasat uses to connect aircraft to the best satellite for the flight – bad weather might make the signal from one be better than another, for instance.
A Madrid-Rio de Janeiro flight, on the other hand, might cross two or three satellites, as it dips from the northern to southern hemisphere and crosses the Atlantic.”
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