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|16th December 2009, 19:22||#1|
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How commercial aviation safety has transformed passenger car technology
Born from Jets
Ever wondered that spending a six-figure tag on purchasing a car is akin to investing in a life support system? A car, above all, is designed to be powerful, efficient, good looking, with optimum bias towards ride and handling and above all, safe.
Safety is a factor that can make or brake an automobile company's reputation.
Ask Toyota. No less than 3.8 million group cars have been recalled for a design defect in the accelerator pedal which can get stuck due to floor mat design not being compatible. 4 persons died of this.
Ask Ford about the number of lawsuits it has faced due to its explorer SUV rolling over due to defective tyres.
Well, in many western countries, Safety is valued as one of the topmost priorities in car purchases, as is engine tech and comfort and style.
However, in India, safety, unfortunately, is not given paramount importance. Only major factors that sell a car are 3, primarily:
We need to understand the importance of safety over cost factors and despite a zillion attempts to educate Indians about safety, they seldom care the hell about it.
Now, coming back to the topic, in the 1950s, the global economy boomed, people's pockets got fatter and the desire to fly frequently meant that commercial aviation era was on the rise.
Now why I am talking about commercial aircraft in this thread? That's because when I start to correlate some of the technology that's similar to those in airplanes and cars, you all will get the essence of this thread and I hope, that you all will like it interesting to read too.
Fortunately, the airplanes that we fly in today are infinitely safer than airplanes that used to fly back in the 50s.
Safety has progressed tremendously but the aviation has learnt lessons in a rather tragic way. Only when planes started to crash taking lives of passengers on board did the aviation realize the importance of safety and improvements were carried out in design, technology, build and aerodynamics to make planes better and safer to fly.
Similarly, cars that were designed way back in 70s and 80s were lacking safety as compared to cars of today.
Mercedes-Benz invented some pioneering safety features like ABS, ESP, EBD, BAS, airbags, seat belts, collapsible steering, pretensioners etc heralding a new era in automobile safety. That was way back in 1960s, and so these gadgets continuously evolved and today's updated technology means that passengers are more likely to be safer in an event of a crash as compared to cars of yesteryears.
While I do have interest in automobiles, an area of interest that has always attracted me is commercial aviation safety, and how tragic lessons were learnt by airplane makers when their marvels of engineering crashed killing innocent passengers.
By watching a groundbreaking programme in Nat Geo TV, Air Crash investigation. Truly informative, and easy to understand even for a lehmann, it educates the frontiers of aviation safety.
Just in case the car driver is responsible for the life of himself and his/ her family in the way he/ she drives and controls the car, similar duties lie in understanding the relationship between the pilot and the aircraft.
Some accidents are caused due to design defect, some are caused due to driver/ pilot error, some are caused by negligence and so on.
Back in 1950s, UK introduced its first commercial airplane-the Havel land "comet".
Capable of carrying 50-60 people and their luggage, it made transatlantic flights in a matter of just a few hours and suddenly, connection between mainland Americas and the rest of the world became a lot easier than even Amelia Earhart thought it would be.
However, while the plane was making great headlines and the rich people were enjoying every moment of jet age travel, the plane's basic design had a dark side to it: the rivets that were used to join the windows with the plane's fuselage (the aircraft's outer aluminum skin) were prone to failures due to constant fatigue that the aluminum body of the aircraft was prone to as a result of cabin pressurization and as a result it disintegrated into the air without any reason whatsoever, instantly killing its occupants. When the design defect was uncovered by performing a pressurization test in an artificial submerged water by giving extreme stress to the fuselage in pressurization tank, it was already too late and 4 planes crashed, killing more than 250 people.
Boeing incorporated all these changes and designed windows to be of curved nature rather than the rectangular ones that the comet had, which contributed to the structural failure.
These new window designs, launched in Boeing 707 in mid 60s, made that aircraft much safer than the comet, which was history that time. Additional riveting only helped matters. More progresses will be discussed as the thread progresses.
Now, how does an aircraft really fly and how is it related to the driveability of the car?
In Lehman terms, there are 4 basic things that a plane is equipped that keep it flying in a controlled manner.
Now, in a car, two similar things are controlled and driven by hydraulic fluids.
In simple terms, power steering means that depending upon the speeds of the car, the handling and control of the car with respect to the driver input is sensed by the on board sensors and accordingly, the hydraulic power steering fluid acts as a vital tool in steering the car at varying speeds.
Speed sensitive power steering is another innovation inspired by the airplane technology where varying levels of handling are achieved according to the sped ad the limits to which the car is driven.
Last edited by sidindica : 16th December 2009 at 19:24.
|16th December 2009, 19:40||#2|
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1. The Plane's rudder and the car's power steering
As mentioned before, the rudder steers the plane right and left at varying levels of pressure by using the plane's hydraulic fluid, in a similar way the power steering in a car varies the amount of feedback required to the driver in order to steer the car left and right, make quick or long turns, negotiate sharp bends and curves easily, controllable handling in twisties etc.
It uses the hydraulic steering fluid controlled by a power control unit that is installed inside a steering column to steer the car.
That's why when the ignition is turned off, the steering does not move lightly, it does only when the ignition is turned on, and the ECU senses that the car is ready to go.
Similarly, the aircraft has a PCU (power control unit) which helps in steering the plane left and right.
To simplify, a coke bottle shaped unit called the dual servo valve directs the flow of hydraulic fluid to the rudder to move it left or right when the pilot presses the rudder prdal located beneath his feet at the controls. Failure of movement of the servo valve can jam the rudder, making the plane uncontrollable and hence, crash. It was a major design defect in Boeing 737 that caused 2 major crashes in mid 90s an it took the company 10 years and billions of dollars to redesign and retrofit the new bigger design in thousands of 737s, the most popular commercial airplane on earth.
Now, in case the fluid levels go down in a car, it too can jam the steering and cause accidents, which could have been avoided in the first place. So regular inspection of PS fluid is necessary in every service.
Nowadays many cars come equipped with electric power steering systems in which a small servo motor located under the steering column steers the car with varying levels of power according to which the driver drives the car and handles it. In fact, it was the aircraft's dual servo valve that inspired the design of EPS, a little known but interesting fact.
It works in a similar manner as an aircraft, but without the use of hydraulic fluid.
The next correlation will be discussed in my next post.
The diagram is a simple illustration of how the rudder helps a plane to steer at varying levels of flight, taken courtesy Wikipedia.
(PS: I have tried to put my best effort here. Any aviation expert here is more than welcome to correct/ modify any terms used in this thread, or correct me if I am wrong. This will only add more value to it)
Last edited by sidindica : 16th December 2009 at 19:54.
|16th December 2009, 20:15||#3|
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2. Aircraft tyres and the car's "runflat" tyres.
Yes, both are actually co related to each other. In fact, the runflat tyres used in many European high end cars is inspired by aircraft tyre technology.
In simple terms, whenever a plane takeoffs and lands, the maximum pressure is on tyres. Any tyre burst and a plane can either crash land or disintegrate.
However, tyres also help to save lives, just as in case of air transat 236 airbus A 330 (shown below) which landed at 400 kmph on an empty fuel, gliding for 8 hours. All its tyres burst but its design played a pivotal role in saving the lives of more than 334 passengers.
However, tyre blowouts can also lead to tragic crashes, just in case of Air France Concorde crash in 2000, killing all 113 people on board. In this case, a small metal strip on the runway had blown the tyre which in turn ruptured the concorde's fuel tanks, causing a fire. After this crash, tyre design became an area of prime importance in commercial aviation safety and more reinforced runflat tyres were developed as a result.
Now coming to cars. tubeless tyres are infinitely safer as they run on low temperatures and slowly dissipate air in case of a puncture, making the car controllable and easy to stop in case it was traveling at high speeds. Lower unsprung weight also plays a vital role, so does the stiff sidewalls.
Tube type tyres are a thing of the past and their notorious properties of running almost instantly flat in case of a puncture have made it more irrelevant. That why many manufacturers are providing tubeless tyres as standard equipment, even in small cars.
However, the runflat tyres takes safety to an entirely new level. Its stiffer sidewalls and specially designed compounds does not dissipate air easily, more so than the tubeless tyres and evenly distributes air pressure in the manner the car is driven, so that it can be driven for a distance before it is repaired. In fact, cars with RFTs can be driven to a maximum of 200 km smooth roads at speeds upto 80 kmph, making it as easy to drive as normal car.
But, the RFTs have some limitations like harsh ride, tyres getting bulged in case of poor roads like ours and the cost of tyre is in fact pretty high, making it virtually unviable for our roads. Just ask BMW owners here.
Better infrastructure and service support with some changes to suspension technology will be needed to make this invention a success.
Despite its drawbacks, this tech has great potential in saving lives of countless passengers.
Illustrations taken courtesy Michelin, Bridgestone and Continental tyres, and familycar.com website.
The first two diagrams show the aircraft tyre design and the rest illustrates a passenger car's RFT tech.
Correlation # 3 will be discussed in my next post.
Last edited by sidindica : 16th December 2009 at 20:20.
|16th December 2009, 20:44||#4|
Join Date: Mar 2009
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Flaps NOT Rudders
- You have got the basic aerodynamics a bit mixed up! The diagram you have put up is actually of the cross-section of a wing depicting spoilers (airbrakes in Red) and FLAPS - in Green (those are flaps and not RUDDERS).
- Flaps are extendable and moveable surfaces used to 'change' the aerofoil section - or the contour of the wing cross-section (simply put). With the flaps extended, the wing is able to produce more lift at lower speeds that are used for landing the aeroplane. However, the wing then also produces more drag - the reason why one typically hears the pilot of an airliner opening power on the engines when the flaps are extended for landing. Flaps are also used for take-off although to a lesser degree (lesser angles of extension).
- Rudders are moveable surfaces on the trailing (rear) end of the vertical fin Contrary to popular perception, aeroplanes do not primarily use rudders to turn - you gotta bank the 'plane to the desired direction of turn - somewhat like on a high-speed banked road. If you only press a rudder pedal hoping to turn, the 'plane will initially respond by only yawing its nose. You need to initiate the turn with bank, and then follow with an appropriate amount of rudder to balance the turn. In this context most modern jets with good sized vertical fins hardly need any rudder inputs at all.
- Regarding hydaulics there are some important differences between aircraft and cars-
- aircraft hydraulics usually have multiple (at least dual) channels for redundancy. The systems are also built to closer tolerances and higher specs.
- Aircraft hydraulics usually operate at far higher pressures (typically 3000 psi). This helps make the hydraulic actuators smaller and lighter.
- Aircraft controls are usually fully powered - hence the use of servo valves as you pointed out. Incidentally, it also means that if the hydraulics fail - you cannot move the controls manually - hence the need for back-up systems. Cars usually use power-assisted hydraulics operating at a lower pressure - hence as you pointed out, even with the engine (and hydraulics switched OFF), one can still turn the wheel with extra effort. There are other important differences - such as aircraft hydraulics using pressurised accumulators and being either of constant-presure or constant volume types.
Lastly, the De-Havilland Comet's crashes were caused due to metal fatigue . This was the first jet-powered airliner put in service across the Atlantic. The Comet had a pressurised cabin (like modern jetliners). Due to routine pressurisation (in-flight at altitude) and de-pressurisation whilst descending for landing, its cabin was subjected to stresses. The critical flaw was the design of its windows - they were square shaped and the corners were points of stress concentration during the pressurisation cycles of the cabin. The stress concentration was higher than what it was designed for and as a result of accumulated pressurisation cycles, fatigue cracks initiated and spread which were aggravated by the type of rivets used in the immediate area. The aicraft literally boke apart in-flight. Incidentally, all pressurised aicraft today have oval or round windows - never square shaped and you know why!
Good initial effort, keep up the good work Sids
|16th December 2009, 22:35||#5|
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It's de Havilland not Havel Land
Disc brakes and anti lock braking tech too originated from its use in Aircrafts.
Last edited by mmmjgm : 16th December 2009 at 22:38.
|16th December 2009, 22:46||#6|
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Not to forget using 'Nitrous Oxide' for boost!
But, I see more features from Formula 1 cars getting into passenger cars.
Even the KERS that was in use this year will eventually make it into passenger cars.
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