Are commercial electric planes possible?

      Are commercial electric planes possible?

commercial electric planes
Electric Plane - Wikimedia

You may have heard about Tesla cars which run on electricity and have zero emissions. Ever wondered can the same be possible with planes? Well, the concept of electric aviation is not new. You may be astonished to know that the world’s first electrically powered flight took in 1883. Albert and Gaston Tissandier showcased the world’s first electrically powered aircraft by coupling an electric motor to an airship.


Why are electric planes needed?

The main reason for the development of electric planes is the adverse impact on the environment caused by conventional plane emissions. It is found that out of total Global Greenhouse emissions aviation CO2 emission is 2%. The amount of CO2 emission from aviation is growing by 3-4% per year. US-based aircrafts are responsible for 29% of all greenhouse gas emissions from commercial aircraft worldwide according to EPA. Also, the penalties on greenhouse gas emissions are increasing and stricter emission regulation standards are pushing electric aircraft development.

The European community has set pollution reduction targets of 75% CO2, 90% NOX, and 65% for noise. Electric planes are better because they have no direct emissions. Electric planes are also quieter in operation. There will be no noise produced by electric planes in airports and inhabited areas. The other fact is that the optimum performance of a jet engine is decreased when there is an increase in altitude and temperature. Electric plane’s performance does not depend on environmental factors. Since electric planes work on electricity they don’t carry flammable fuel and thus are safer than conventional planes.

How electric planes work?


In conventional planes, the jet engine sucks the air which is compressed or squeezed in a compressor. This increases the temperature and pressure of air which makes it suitable for mixing with fuel. The fuel is injected from injection holes in the combustion chamber which mixes with the incoming air. This air-fuel mixture is then lit. Now, this high-pressure, high-temperature mixture (fluid) passes through a turbine which reduces its pressure. Due to the reduction in pressure of this fluid, it's velocity increases and it leaves the jet engine with high velocity. This high velocity is responsible for generating the thrust and makes the plane move forward.
Jet Engine
    Jet Engine-Wikimedia
On the other hand, the working of electric planes is rather simple. When it comes to electric planes the power source need not be compulsory batteries. Solar power can be used as power source. In case of battery powered planes, the batteries run an electric motor that spins a propeller. This spinning produces the thrust required. Yup as simple as that! Electric engines are thus mechanically simpler than the jet engines. This reduces their maintenance and performance monitoring requirements.


Problems with electric planes

            The question now arises that even though electric planes have so many advantages why don’t we see any flying over our heads? The main problem is weight. Let me put it in this way. When you travel by train you don’t have limitations on the weight of luggage you carry. In the crowded country like India, people travel by sitting on train roofs. Although you cannot travel by sitting on plane wings, the fact is there is a limitation on the maximum weight of luggage for traveling through planes. Why is this so? 

Planes have a maximum takeoff weight. If the weight is more than this it cannot take off and will keep running on the runway (actually it may damage the plane and is dangerous). So how is this related to electric planes? As mentioned earlier electric planes can be powered by


  1. Battery Power
  2. Solar Power


The thrust required for the plane is very large and thus will require more numbers of batteries. This concept is related to energy density. Energy density is the amount of energy stored per unit volume. The energy density of batteries is far less than fuel. It means that for the same amount of energy generated more numbers of batteries will be required than the fuel. As more battery packages are needed to be installed the weight of plane increases. Li-ion battery energy density is 300 Wh/kg or 1.08 MJ/kg while the energy density of typical aviation fuel is 44.65 MJ/kg. Research is being done to develop batteries having energy density of 400 Wh/kg.

The other problem is that airplanes also have a maximum landing weight. In conventional planes the fuel is burnt till it reaches its destination and thus the weight of the plane is reduced. Also a plane on its way to the destination burns fuel due to which the weight of fuel carried by the plane gradually goes on reducing while in air until it completes its journey. This reduction of weight due to burning of fuel also increases the efficiency of jet engines.

This is not possible in case of batteries. Batteries once used remain in planes and contribute to the overall weight of the plane and as a result of this the plane has to fly with the weight of used batteries.

The other method of powering the electric plane is by solar power. The batteries generate power by solar energy and thus drive the motor. But we cannot fully rely on this as weather conditions are different throughout the year.


Attempts made by companies for electric planes

The disadvantages of electric planes haven’t stopped some companies to develop one. Although electric planes do exist but their weight carrying capacity is less which is mostly upto 2-4 persons per flight only. This no is far less than that of commercial conventional plane flights which has a to take on an average 150 passengers per flight.

German company Siemens has developed propulsion system for Extra 330LE electric plane. The plane has a very powerful drivetrain. The motor which weighs only 50 kilograms develops a power of 260 kw which is equivalent to 350 horsepower. The aircraft is able to reach a world record breaking speed of 340 km/hr. Although these numbers don’t sound impressive but the important thing is the plane burnt no fuel and emitted zero emissions.
  Siemens Extra 330LE electric plane
  Siemens Extra 330LE electric plane - siemens
Solar Impulse 2 is another such aircraft financed by Swiss businessman and pilot Andre Borschberg. As the name suggests this aircraft runs by power generated through solar cells. The batteries are used to store the power generated. It is a single seater aircraft and contains 17000 solar cells. These cells are mounted on the wings of the plane. The plane is still under testing.

 Solar Impulse 2 - Wikimedia
 Solar Impulse 2 - Wikimedia
The Airbus Group’s E-Fan is a two-seater electric aircraft and first took flight in 2014. It has a top speed of 220 km/hr. The E-Fan has been upgraded to E-fan Plus version which has a hybrid configuration for longer flight endurance. Hybrid implies that it uses an internal combustion engine in addition to its on-board lithium-ion batteries.
           
Airbus Group’s E-Fan - Wikimedia
With the current developments in technology will we be able to travel in commercial electric planes? 

Probably not so soon. As mentioned earlier the Solar Impulse 2 uses solar power. However its flight is made possible only because it is light in weight. The technology is still not ready to power commercial planes which are more heavier. In order to have electric planes in the commercial market, we need better batteries. The current batteries in the market are lithium-ion batteries which have replaced the lead-acid batteries. To power a plane we need batteries which deliver more power simultaneously being small and light in weight. Scientists say that those kinds of power delivering batteries will be available in a decade and only then we will be able to travel in electric planes having tickets cheaper than those running on fuel.

Thanks for reading!  

Why do planes dump fuel?


Why do planes dump fuel?


Why do planes dump fuel
Why do planes dump fuel? - Wikimedia

Fuel cost represents one of the biggest expenses for the aerospace and airline industries. On an average fuel costs account for 29% of all operating expenses. So, why do planes dump fuel? Before answering this let me tell you that this is not done frequently and is done only in emergency situations, like mechanical failure or a medical emergency.

In technical terms, fuel dumping is known as fuel jettison

Aircrafts have two types of weight limits: 

            
The maximum structural landing weight is always less than the maximum takeoff weight. Now one might think that taking off at a heavier weight would be more difficult as opposed to having to land at a lighter weight. However, this is not the case, as landing puts more stress on the plane.


Why do planes dump fuel?

Fuel Jettison Duct
Fuel Jettison Duct - Wikimedia
One of the factors increasing the weight of an airplane is the fuel stored in it. Now when an airplane takes off, its weight is under the limit of the maximum takeoff weight. The amount of fuel in the plane is such that most of it will be consumed as it reaches the destination thereby decreasing the weight of the aircraft and bring it under the maximum landing weight. 

But in the unfortunate situation of an emergency in which the plane has to land suddenly it is not possible to do so without dumping the fuel . This is because the weight of the airplane is higher than its maximum landing weight and hence it is far too heavy for a safe touchdown. Thus fuel is dumped so that the weight of the plane becomes safe for landing.

In certain situations, dumping of fuel will prove to be cheaper than not dumping it. If an airplane is made to land at a weight higher than its maximum landing weight then it can cause structural damages primarily in landing gear and also to the airframe structure. Sometimes planes can suffer severe structural damages that can take months to repair or worse yet, be irreparable. The plane can even break apart on landing. Thus fuel dumping is not as wasteful as it seems.

Fuel dumping is a simple procedure. Fuel is stored in the hollow wings of the plane. The fuel is jettisoned from nozzles which are located in the wings. The pilot performs a three step process to engage the plumbing and start dumping fuel. 


Plane fuel tanks
Plane Fuel tanks - Wikimedia
Sometimes there occurs an emergency in which there is no time to dump the fuel. In such cases, the pilot has to take the risk of overweight landing. Jets flying with US airlines in the 1950s and early 1960s tended to have fuel dump systems. However, most of the planes developed today are designed by considering the maximum overweight landing. 

For example, Boeing 757 has no fuel dump capability as its maximum landing weight is the same as its maximum takeoff weight. Larger, wider body planes like the Boeing 777 and 747 can dump fuel.

What happens to the dumped fuel?


Since the fuel is dumped in the sky, do we need to hide under roofs when a plane goes over us to protect ourselves from it? Well, the answer to this is NO. Fuel dumping is usually restricted by altitude, that is, fuel cannot be dumped below a particular altitude generally 4500 feet (1371.6 meters). Dumped fuel flows behind the plane like a contrail

Most of the fuel evaporates into the atmosphere before reaching the ground. The evaporation of fuel depends on several factors like altitude, air temperature, and dumping pressure .Technical advancements lead to the development of systems which are installed in planes which help to vaporize the fuel stream to a large extent so as to aid evaporation. 


F111 burning dumped fuel
F111 burning dumped fuel - Wikimedia
Air shows sometimes include dump-and-burn which is a type of fuel dump in which the dumped fuel is burnt by using plane’s afterburner. The dumped fuel burns and produces a tail of fire. However, Dump-and-Burn is banned in the USA as fuel costs a lot of money and to dump it would be a criminal waste.

How long is the fuel to be dumped for?

So how does the pilot decide how long the fuel dump is to be performed until the plane reaches appropriate landing weight. This can be explained by an example
Boeing 777
Boeing 777 - Aircraft Nerds
For Boeing 777

Maximum takeoff weight = 247,200 kg
Maximum landing weight = 201,840 kg
Weight to lose = 45,360 kg or approx 46,000 (46 tons)

The fuel dumping rate for Boeing 777 is 2 tons/min

Fuel burn rate = 6 tons/hr
                       = 0.1 tons/min

Thus fuel dumping rate + Fuel burn rate = 2.1 tons/min

To lose 46 tons the time required will be 46/2.1 = 21.9 min

So the pilot will need to perform fuel dumping for approx 22 min to reach the appropriate landing weight.
            
Generally landing with less fuel is better than to land with more fuel. Fuel makes up a very large proportion of its total weight and it’s inefficient and uneconomic to fly around with unneeded fuel. The point of dumping fuel is to decrease the weight of the aircraft to the point where it is safe to land. Large planes with a full load are too heavy to land safely, however, if it is a serious emergency like a fire or something similar, it has to be done.  

So to answer the question, dumping fuel is not routine and though fuel dumping leads to wastage of loads of gallons, it needs to be done in emergency situations to protect the plane from any harm and also the people traveling in it.

Thanks for reading!