Earth’s rotation and Space shuttle launches


Last week we were talking about wind patterns and how they affect flight time. But it is also worth mentioning that Space shuttles are launched almost at all times from West to East to take advantage of the earth’s rotation

How does earth’s rotation affect shuttles ?

Earth is a spherical body rotating with some angular velocity. And as a result of this, the equator is rotating at a higher velocity than the poles. By launching a space shuttle from the equator you are getting a ‘speed boost’.  


This means that if a shuttle is launched from the pole, it has to accelerate from 0 to 17000mph to reach orbital velocity.

But if a shuttle is launched from the equator, it only needs to accelerate from 1025 to 17000mph. (that 1025mph initial velocity is given by the earth free of charge)

This saves valuable amount of fuel required for propulsion


Polar Orbits


Not all rockets are launched from the west to east and the direction is determined by the purpose of its payload.

The satellites that are used for mapping for instance follow a Polar Orbit i.e they move from north to south or vice versa and therefore during launch they cannot take advantage of the earth’s rotation.

Florida or California


Another characteristic of launching satellites is that the launching
stations are generally located near the coast just in
case of failure of the launch, the satellite falls in an uninhabited area.

NASA primarily uses Kennedy Space Center, Florida for east-west launches and Vandenberg Base California for polar orbits for the very same reason. ***


Rocket science is just truly breathtaking.

* How fast are YOU spinning on Earth’s axis right now?

** Also check out about Retrograde motion

*** This statement holds true for most launches.


The Physics of the ‘Stall’

The proposition that more the angle of attack, more the lift does not hold at all angles.


At about 14 degrees, something weird happens and the aircraft instead of soaring the skies starts to plummet to the ground.

When this happens it is known as a stall.



What causes Lift ?

The main thing to know is that a difference in pressure across the
wing–low pressure over the top and higher pressure below–creates the net
upward force we call lift.


Upon reaching a certain velocity, the aircraft’s lift is more than its weight and as a result, the aircraft takes off .


The Concept of a Boundary Layer (BL)

There is a high chance that you might have heard this word even in a casual conversation about wings and that’s because its an important concept in the context of aerodynamics and associated fields.

To understand the physics of a stall, lets consider the interaction of a moving air on a flat plate.


The nature of airflow over a wing/plate is the result of stickiness or viscosity of air. 

The first layer sticks to the wing/plate not moving at all.

The second layer in frictional contact with the first moves slowly over it.

And the third layer moves somewhat faster than the second

Thus layer by later the flow builds up to the free stream velocity or airspeed. These layers of flow are known as boundary layers.


What happens to the BL during a stall?


                                              Source Video

During a stall, these successive tiers of air that form the boundary layer lose their gripping on the surface and break away into turbulence.

( what i mean by turbulence is the chaotic wiggling of the test leads attached to the wing in the animation )



It takes a pressure difference between the top and bottom parts of the wing in order to produce lift. But when the flow of air becomes turbulent ( i.e during a stall ), this pressure difference is no longer established.

As a result of which, the lift drastically decreases and the aircraft starts dropping to the ground.

How to get out of a stall ?

Stalls can cause problems only when the pilot is not aware that the aircraft is stalling. ( Unlikely but has caused accidents in yester times )



As the airplane loses altitude, its nose dips down and airspeed picks up quickly. This restores the lift and the pilot would be able to regain control and bring the aero-plane into level flight.

How are stalls detected ?

On light aircraft there is a reed (much like used on a musical wind
instrument) mounted on one wing root, which is angled such that at the
Angle of Attack which would cause a stall, the reed “plays” which can be
heard in the cockpit.


Here is a view of where this system is mounted on a Cessna

On some aircrafts, it is a similar principal, however instead of a
reed, it uses a fin which at critical AoA pushes a micro-switch which
activates a buzzer/horn inside the cockpit.


Here is the assembly on a Beech 18

Large commercial aircraft typically rely on either Angle of Attack (AoA) Vanes or Differential Pitot Tubes  to supply input to flight computers for the purpose of calculating AoA.




A lot of important stuff regarding aerodynamics in this post. Here’s a summary of the post:

Boundary Layer concept  — >  Why do aircrafts stall ? — >  How to get out of one  — > How are stalls detected ?

That’s all folks!


Hope you enjoyed today’s post and learnt something new.

Have a good one !

This post covers the fundamental principles from which the subsequent posts queued up for this weekend are derived from. Stay tuned.. It is gonna be wild ride.

On Taj Mahal and Lift in airplanes

This is an interesting story that is probably popular among those in the aerospace community on how flaps help provide lift.


During the World War II, a C-87 cargo plane (pic above) was all set to take off from Agra airport, India. The pilot had specifically asked for a small load of fuel for takeoff.

(because the C-87 did not climb well when heavily loaded  )

But the ground crew accidentally filled it to its full capacity and  forgot to tell the pilot about it.


The pilot realized this only halfway through the runway and was already committed for take off.

With a three ton overload on the plane, the plane was heading for a fatal crash with one of the towers of the Taj Mahal which was being repaired at that time and was swarming with workmen.


The pilot gave full throttle but it still refused to rise up.

And in a desperate attempt, he lowered the flaps fully and instantaneously the plane ballooned upwards.


Surely, it lost some of its forward speed due to the increased drag. But it comfortably cleared the famous tomb, averting an impending disaster. So yeah, flaps on an airplane are no joke.

Have a great one!

* Why does lowering flaps increase lift?

** Physics of stall

*** Stories are great at linking words with experience. And this aids a lot in the learning process.


What Is That Hole in the Tail of an Airplane?

When it comes to aviation, you just cannot take anything for granted. Everything serves a purpose, even the hole in the tail of the airplane.

APU ( Auxillary Power Unit )

The primary purpose of an APU on an aircraft is to provide power to start the main engines.

You gotta get them started and provide sufficient air compression for self sustaining operation, right ?


For smaller jet engines, one can accomplish this by electric motors.

But when the engine is a colossal giant, you need something much more than a quotidian electric motor to get it to start running.


What is it ?

The APU is essentially an air turbine motor, i.e a turbine that is used to produce power by using the air as a fluid

It is attached to the rear end of the aircraft. The hole in the rear end is used to direct the exhaust out of the aircraft i.e APU exhaust.


The APU is started by a battery or other means. But once the APU is running, it provides power (electric, pneumatic, or hydraulic, depending on the design) to start the aircraft’s main engines.

What other purpose does the APU serve?

APUs are also used to run accessories while the engines are shut
down. This allows the cabin to be comfortable while the passengers are
boarding before the aircraft’s engines are started.



Electrical power is
used to run systems for preflight checks. Some APUs are also connected
to a hydraulic pump, allowing crews to operate hydraulic equipment (such
as flight controls or flaps)
prior to engine start.


This function can also be used, on some
aircraft, as a backup in flight in case of engine or hydraulic failure.[

GPU ( Ground Power Unit )


Many a times you can also find the aircraft connected by some wires. This is the Ground power unit
and supplies the aircraft with electricity while the generators or the auxiliary power unit (APU) are not running.

airports reduce the use of APUs due to noise and pollution, and ground
power is used when possible.

What we behold as merely a small hole on the tail has so much depth to it .Pretty cool eh?

Have a good day!