Archive for the ‘Automotive’ Category

How a steam loco differs from diesel-electric loco?

2013/09/23

A diesel-electric (DE) loco is a constant power machine. We know that, Power = Force x Velocity. This means, when hauling heavy loads (especially on an uphill), a DE loco can increase draw bar pull by reducing speed. This also shows why most shunting locos are DE locos as they need to haul heavy load but at low speed.

 

However, due to the way a steam loco is designed (i.e. its boiler, piston and other mechanisms), a steam loco behaves as a constant force machine up to cruising speed (usually around 25 MPH or 40 km/h). Beyond that, a steam loco behaves like a constant power machine like a DE loco.

 

This difference is crucial. For a steam loco to haul heavy load (or on an uphill), if it can’t deliver enough draw bar pull, it has no way to increase the force like a DE loco, because for steam loco, force is constant at low speed. So, a steam loco won’t be able to climb a slope like a DE loco. It will literally run out of puff under such circumstance. However, once a steam loco has crossed its cruising speed, it will have no problem pulling heavy trains as it behaves in same way as DE loco i.e. constant power loco.

 

There are obviously other differences between these two types of locos. A DE loco is more thermally efficient than a steam loco. The later requires far more maintenance than the former and needs more crews to operate them.

 

No wonder, due to these reasons, most of old steam locos have been replaced by DE locos in all but heritage routes. Please note that a pure electric loco will also behave similarly as of a DE loco.

 

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Why airbags are marked as SRS?

2013/06/30

Airbags are Supplemental Restraint System (SRS) because they supplement the function of seat belts.

The seat belts are primary restraint system in case of an accident. So you must wear seat belts at all times. If seat belts are not worn, airbags may not be deployed in case of a collision.

Always wear seat belts!

Why most US locomotives have single cab while European ones have dual cabs?

2012/12/17

Most US locomotives have single cab. This creates a visibility problem when operating long hood forward mode (visibility is usually ok while operating short hood forward mode). However, it is quite rare for US locos to operate solo – they mostly work in pair (sometimes upto 3-4 units together as well). As a result, they rarely run as long hood forward mode in real life.

But in Europe, the overall weights of trains are lighter and thus often trains are pulled by just single locomotive. Here both forward/reverse operation is desired. Thus European locos need good visibility in both directions (otherwise they would need turntables which are now obsolete after steam loco era).

Countries which imported American locos (like common WDM style locos in India, licensed from ALCO) but often runs as single units, visibility is indeed a problem while running in long hood forward mode.

Why Euro NCAP ratings can be misleading?

2012/11/07

Euro NCAP test gives ratings to cars for safety of adult occupant, child occupant and pedestrians in case of any crash.

The maximum of 5-star indicates very high safety standard and least likelyhood of injury/death in case of a crash involving that car.

However, this ratings can sometimes be misleading if interpreted out of context.

People often assume that a small car with 5-star rating is as good as a large car with 5-star rating. No, it may not be the case!

The Euro NCAP frontal impact tests simulates crashing a car into another of similar mass and structure. This means that the ratings can only be meaningfully compared between cars of the same type and size.

The following structural categories are used in Euro NCAP test:

Passenger car
MPV
Off-roader
Roadster
Pickup

(In each category, cars which are within 150 kg of one another are considered comparable)

This means, occupants in a 5-star rated small car may suffer more injury, compared to occupants in a larger MPV of 3-star rating, if both cars crash head on.

Why planes can’t land in fog?

2012/10/23

You may have seen that often flights are cancelled due to fog.

But we all know that modern airliners are equipped with sophisticated auto pilot system which can land aircrafts in zero visibility. So even then why flights are cancelled?

Even though auto pilot can land aircrafts in zero visibility, if this method is used, pilots can’t override it (if computer makes any mistake) if they can’t see the runway! At Minimum Decent Altitude, pilots need to see the runway so that they can decide whether to land or not. In case of zero/low visibility, there is no human backup.

Also, even if auto pilot lands the aircraft on runway, it pilots still need to taxi the airport to the terminals. Otherwise other aircrafts can’t land or takeoff. Auto pilot can’t do taxiing. In zero visibility, it is too risky to tow the aircraft to terminal building to align with aerobridges.

Why did Boeing name their airliners with 7xx?

2012/08/31

Boeing did not assign 7xx out of nothing. They have manufactured several aircrafts and associated objects.

Their model series followed this convention:

1xx – Helicopters
2xx – Old airliners and military aircraft
3xx – World War 2 and post war airliners
4xx – Jet Bombers
5xx – Turbines
6xx – Missiles
7xx – Commercial jetliners (e.g. 747, 777, 787 etc.)
8xx – Other
9xx – Hydrofoils and experimental military aircraft

 

Air-cooled vs water cooled engine

2012/08/01

Most likely your modern car has a water-cooled engine. When an internal combustion engine operates, it creates high amount of heat. Unless there is a mechanism to dissipate the heat, it will damage the engine components. In modern automobile engines, a coolant system is used to keep the engine cool. Usually a chemical coolant is used (although named water cooled, water is not used anymore now as coolant) within a sealed system (you rarely need to top up). The cooling system creates a jacket outside the engine. It also keep the engine in constant temperature. The proof is your car’s temperature gauge which usually stays halfway to H and C mark.

In air-cooled engine, air is used to cool the engine down. Thus, it does not require radiator and cooling system – which makes the whole engine a lot simpler. It uses radiator fins (easy to see in motorcycles) which are used to cool the engine. But there are drawbacks too. Unless there is steady flow of air, the engine may get overheat quickly. They are also very noisy as the radiators fins vibrate when engine is in operation.

Air-cooled engines are used mainly in motorcycles, some 3-wheels (like India’s Bajaj autorickshaws), some cars (classic VW Beetle, old Porsches etc.) and some propeller aircrafts.

For aircrafts, they are not a big problem. Unlike a car, an aircraft does not get stuck in traffic jams. Aircraft engines operate within their 80-100% RPM range most of the time and due to high speed cruising plenty of air pass over the radiator fins to keep them cool. This also explains why old propeller aircrafts with such engine sound so loud.

But problem might happen in air-cooled car engines! If the car is stuck in traffic or moving slowly over extended period of time, the engine may overheat (which may lead to seizure of engine).  On the other hand, they are quite good at cold weather condition as chance of overheating is lower.

 

Why auto stop start is modern cars?

2012/07/16

Many new cars of today feature auto stop start feature. This is also known as Intelligent Stop and Go and similar names.

Cars with this feature, turns of engine as soon as you stop and take your foot off the clutch. Then as soon as you press clutch again to engage the gear, it switches on the engine.

Manufacturers do this because they claim it saves fuel while waiting in traffic.  This also allows them to quote higher fuel economy figures and CO2 emission (on which most cars are taxed nowadays). This makes these cars statistically more attractive (because of lower fuel consumption and tax) to the buyers.

On the other hand, many drivers find it as a psychological challenge. It also requires a stronger (thus more expensive) battery and starter motor. So how much money is saved at the end (for drivers) is open to debate.

Fortunately, if you do not like this feature, it can usually be turned off via a switch on dashboard.

As of now, automatic cars do not have this feature but in future this may be offered in autos as well.

 

Why passengers are not provided parachutes in commercial flights?

2012/07/01

It is a common question asked by many as people believe having a parachute for everyone will save lives if plane crashes!

However, even if parachutes are provided to all passengers, it is very unlikely than anyone will survive if a modern commercial airliner crashes.

Proper use of parachutes requires sufficient training, skill and nerve. If a plane crashes, there will huge panic on board and everyone will rush towards doors to deploy parachutes. Even in military aircrafts, it takes several minutes for every soldier to jump off with parachutes in an orderly manner.

Besides this, all passengers will have to sit wearing the parachutes all the time (you can’t really wear it like your coat). This will be very uncomfortable for long haul flights.

For parachutes to work, the aircraft must slow down to a required speed, otherwise parachuters might hits towards rear of the aircraft.

Leaving the aircraft in the sky often is more dangerous compared to staying inside. A novice passenger even with parachutes are very vulnerable.  It will be very cold outside and you may not be able to breath properly. An expert pilot might manage to land the plane safely even after major trouble.

Modern flights are quite safe although unfortunate incidents do happen, the probability of plane crashing is very low.  For the reasons cited above, providing parachutes to all passengers won’t server any real benefit and that is why they are not provided to passengers.

Some very small aircrafts (usually less than 8 seats) do have parachutes for all passengers. In fact, some small aircrafts have mechanism of having a parachute for the whole aircraft itself. Obviously, large aircrafts can’t have this because of their massive weight.

 

Auto transmission PRND321 vs M+-

2012/06/16

You might have noticed that in some automatic transmission cars the gator shows PRND321 where as some shows manual + – mode. So what dictates which one you will get?

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The PRND321 mode is usually featured when the car has traditional 4-speed torque converter type transmission. Since there are just 4 gears which you can cycle thru, it is convenient to explicitly display which one you have selected.

In many automatic cars, especially automated manuals where there are 5 or higher gears, it will be difficult to show all gear positions because it would make the gator quite longer or wider. Thus, just the manual mode (with M indicator) is shown with gator position for + and -. To up shift you push the gator to + slot and to downshift use the – slot.

The following picture shows how the gear selector would have to travel further if PRND321 style is used for many gears.