Superhydrophobic, Drag Reduction & Application in Aviation

Drag is a net force in the opposite direction of flow of a fluid due to pressure and shear forces on the surface of an object. There are several types of drag namely pressure drag, viscous drag, interference drag, lift-induced drag and wave drag. Superhydrophobic is a type of material in which it has the ability to repel water. The name itself shows this property in which hydrophobic means "water hating".

In this case, we will concentrate on the second mentioned drag, the viscous drag. The viscous drag or commonly called friction drag and sometimes also called skin friction drag is a part of drag that is directly related to the shear stress on the object. It is a function of not only the magnitude of the wall shear stress, but also of the orientation of the surface on which it acts. In other words, the viscous drag occurs when there is contact or friction between the particles of the flowing fluid with the surface of the object. That is why it is called the friction drag. The viscous drag creates boundary layer with the thickness of the boundary layer depends on the viscous drag itself.

As the superhydrophobic nano-coating owns ability to repel water, the water molecules will be repelled away from any surface coated with this material. Thus this condition does not allow the water molecules to get in contact with the surface. As a result, the friction between the water molecules and the surface will never occur and friction drag is reduced. Since the superhydrophobic nano-coating just repel water molecules, the friction drag still exist as the other particle in the flowing fluid still able to get in contact with the surface to create friction but the different is, the amount will be smaller.

An experiment conducted by a team of researchers shows positive result. Two discs, one coated with superhydrophobic coatings and the other was left uncoated was allowed to rotate in a water-containing container. The current used to rotate the discs at different speed (Reynolds' number) was considered as parameter to determine the drag. The lesser current means lesser drag. The result also tells us that the percentage reduction in drag is higher for laminar flow (lower Reynolds' number) than turbulent flow.

Source: Experimental Investigation of Viscous Drag Reduction of Superhydrophobic Nano-Coating in Laminar and Turbulent Flows written by Kh.Moaven, M. Rad and M. Taeibi-Rahni. 

     

Malaysia Airlines MH197

 A Malaysia Airlines flight 197 has made an air turn back after take off and made an emergency landing in Kuala Lumpur International Airport. It was due to the landing gear exploded during take off. The aircraft operated in this flight was a B737-800. The flight bound for Bangalore and was carrying 159 passengers and 7 crews. All people on board are safe and no injuries were reported.

A Malaysia Airlines flight made an emergency landing in KLIA. All people on board are safe.

Malaysia Airlines state in a statement: "Malaysia Airlines Flight 192 that departed Kuala Lumpur International Airport (KLIA) at 10.09 pm bound for Bangalore earlier had turned back and landed safely in KLIA 1.56 am, today."

Tyre debris was found on the runway and the control tower alerted the pilot. The flight had few hours circulating above the Straits of Malacca to reduce the fuel in the tank. A spokesman of the Department of Civil Aviation Malaysia said that the aircraft is only allowed to land only when it is nearly out of fuel.

Malaysia Airlines tweeted: "Malaysia Airlines flight MH192 that made an air turn back towards KLIA has landed safely at 1.56am. Alhamdulillah."

Path of flight 192

All passengers were relieved after the landing and they express their gratitude to Captain Adam, the flight captain and all the crews for handling a situation in a professional way. The passengers were placed in a hotel temporarily to wait for the next flight to Bangalore.

Malaysia Airlines Flight 370

The missing Malaysia Airlines flight 370 has entered the day 44th and the mysteries are still surrounding. The flight was carrying 239 people including crews from 14 nations bound for Beijing Capital from Kuala Lumpur International Airport. It was reported that two of the passengers on board was travelling with stolen passports. The flight vanished from radars and lost contact with the control tower at 1.20 a.m. The aircraft used in the flight was a Boeing 777-200 ER and its registration number is 9M-MRO. The aircraft has flown many parts of the world. The pilot was an experienced pilot Capt. Zaharie Ahmad Shah with more than 8000 flying  hours and was assisted by the First Officer Fariq Abdul Hamid.

Captain Zaharie (left) and co-pilot Fariq Abd Hamid (right)

A multinational Search and Rescue (SAR) operation was conducted. At the earlier time the aircrft went missing, the search efforts were conducted on the South China Sea, the spot where it was reported missing. The SAR operation was then moved to the Straits of Malacca after military radar was believed to detect an object flying along the straits. Then, the Malaysian Prime Minister, Najib Razak said the aircraft would probably flew to the northern corridor which extends to Kazakhstan or it might be flying along the southern corridor, extending to the South Indian Ocean, to the west of Australia.

The wreckage of Air France flight 447 was discovered after two years from the day of accident. Yet, the missing of flight 370 was considered as the most mysterious case in aviation history even it has not yet pass 2 years.

On 24th March 2014,  Najib Razak announced that the flight ended in the Southern Indian Ocean. This statement was made based on investigation that was done towards the signal received by a British Inmarsat satellite in which the investigation and analysis method was never being used before. It was assumed that the flight ended with no survivors. Australia was appointed to lead the search operation in this area.

Few days later, four pings was detected by a Chinese vessel Haixun 01 and Australian HMS Echo. The pings was believed not from the nature, but it comes from a man made equipment. Thus, it was believed the pings comes from the aircraft's black boxes.

The search area was narrowed based on the analysis done towards the pings received. The search team faced a very difficult task since the South Indian Ocean is one of the remote places on earth and has a depth of 4500m. The battery of the black boxes can stand up to 30 days or more, depends on the condition. After narrowing the search area, the Bluefin-21 was used in the operation.

Malaysia Airlines Boeing 777-200 ER with registration number 9M-MRO used in MH370