How to ground an aeroplane…electrically
The Sunday Nation
Nairobi,
26 June 2011
Daniel Kungu asks some interesting questions, starting with a curious one: “How do you ground the electrical system of an airborne plane?” The straight answer is that you use the planes body.
The idea behind “grounding” in an electrical system is to provide a common return path (to the power supply) for all the circuits. The word “ground” comes from the fact that, while on Earth, the common “wire” is usually the physical ground. Yes: the Earth conducts electricity!
If you observe the electricity poles closely, you will notice that they have a wire running all the way to the ground. Grounding ensures that all the components of the system have the same reference voltage…and we can all agree to call it zero volts!
In an airborne aeroplane, there is no electrical connection to the physical ground. So the only common return path is the metallic body of the aircraft. Incidentally, the same design is used on cars: even though they are physically connected to the ground, there have no electrical connection to earth – the rubber tyres are no good conductors.
Sticking to flying objects, Daniel asks his next question: “A rocket does not have wings [so] what keeps it in the air?” Now, one of the distinct differences between aeroplanes and rockets is the way they take off. Aeroplanes race down along a horizontal runway while rockets shoot vertically upwards from the ground.
The lifting force on an aeroplane comes from the wind moving over the wings, but a rocket is lifted by its engines blowing out exhaust fumes downwards at very high velocity. By the law of equal and opposite reactions, when the rocket blows out exhausts downwards, they will push it in the opposite direction – upward.
The third question sound quite theoretical, but her it is: “What does the logarithm of a number mean and how is it calculated?” Before answering it, it is important to point out that logarithms have a base. Usually, we use base 10, but in some instances mathematicians use different bases.
So the correct question should be: “what is the logarithm of a number, X, to the base of Y?” This is the same as asking: “To what power should we raise Y to get X?” That power is the logarithm.
For example: if we raise 2 by the power of 3, we get 8 (2 x 2 x 2 = 8). Therefore, the logarithm of 8 to the base of 2 is 3. Get it? However, the logarithm of 8 to the base of 10 is NOT 3; so, don’t go checking in the math tables and say that I was wrong!
Lastly, Daniel is concerned about the population of a country: “is there away of getting the actual number of people in a country because I do not agree with the census report we get?” My response is two-fold. First, I would ask why anyone doesn’t agree with the census results. Secondly, my answer is no, there is no other way of getting the population – you have to count the people…in a census!
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