Showing posts with label THEORY OF FLIGHT. Show all posts
Showing posts with label THEORY OF FLIGHT. Show all posts

Sunday, May 27, 2012

A380 PUSHING TECHNICAL BOUNDARIES

Srinivas Rao | 11:01 PM | | | | | | Best Blogger Tips

Airbus has always been at the forefront of pushing technical boundaries in aviation and excelling in aircraft design and technology. Airbus says efforts to lower the weight of the world's largest airliner lay behind recent A380 wing cracks and pledged to learn from mistakes that lay dormant for a decade, as repair costs looked set to climb towards 500 million euros ($A642 million).

Friday, May 11, 2012

A380 SUPER AND WAKE TURBULENCE

Srinivas Rao | 12:05 AM | | | | | Best Blogger Tips

Airbus.com

Wake turbulence is turbulence that forms behind an aircraft as it passes through the air. Wingtip vortices occur when a wing is generating lift. Wake turbulence exists in the vortex flow behind the wing. The strength of wingtip vortices is determined primarily by the weight and airspeed of the aircraft.Wingtip vortices make up the primary and most dangerous component of wake turbulence. This is the reason the separation criteria had to be written out for A380.

Tuesday, May 8, 2012

BOEING WINGLET DESIGN FOR 737 MAX

Srinivas Rao | 12:05 AM | | | | | | | Best Blogger Tips

B737 MAX
In continuation of our coverage on WINGLETS and FUEL SAVING A320 SHARKLETS, we bring the news about Boeing announcement and breakthrough on new winglet design concept for the 737 MAX. The new Advanced Technology winglet will provide MAX customers with up to an additional 1.5 percent fuel-burn improvement, depending on range, on top of the 10-12 percent improvement already offered on the new-engine variant.

Sunday, May 6, 2012

FLIGHT AT EXTREMELY LOW SPEEDS

G R Mohan | 12:05 AM | | | | Best Blogger Tips
S tall speed is defined as the lowest airspeed at which 1 'G' level flight can be achieved. However it is also possible to fly the airplane at speeds below the defined stall speed. This regime is outside the certified flight envelope. There are several important factors that a pilot must know when the airplane is at extremely low speeds.

Friday, March 30, 2012

KUCHEMANN'S CARROTS

G R Mohan | 12:37 AM | | | | Best Blogger Tips

A


s we do the pre-flight walk around , and inspect  the wing underside we rarely give a second glance at the canoe shaped flap track fairings under the wings. Some are slender but many appear somewhat oversized to accommodate just  the flap fairings. Or do they serve some other function?
The physics of airflow alteres violently as it expands from subsonic to supersonic speeds. As the aircraft passes through the transonic speed range, local airflow approaches sonic speeds over the wing and body of the aircraft and leads to the formation of shock waves and consequent large increase in drag.
At transonic speeds, it was found, that the time-honoured principle that the drag of the individual elements of an airplane could be added in a linear manner to give the approximate drag of the entire configuration could no longer be relied upon.
Researches by Dietrich Kuchemann in the UK and Richard Whitcomb of NASA , in early 1950s, established that this wave drag can be minimised by a fuselage wing configuration synthesis, where the cross sectional area changed smoothly along the length of the aircraft. Known as the Area Rule, its basic tenet postulates that the wave drag of a simple equivalent body of revolution would be the same as a more complex wing body arrangements.
Initial  application of area rule designs can be seen in the   “Coke Bottle” or “Marylin Monroe” indented fuselage body shapes to reduce the effect of the presence of wings as in F-102 and F-106 aircraft. This, however had practical limitations and alternate efforts to address the local discrepancies in cross sectional areas led to the concept of attaching conical and pod shaped bodies along the wing , nacelle and fuselage. First successful application of this principle to combat wave drag effects was in Convair- 990. Following applications of the local area rule, several pylon, nacelle, and wing fairings were embodied, to smooth out the area distribution and facilitated in raising the cruise speed from 0.8M for the basic aircraft to 0.89 M for the modified airframe.
 These anti shock bodies  christened as ‘Whitcomb After-bodies’ or ‘Kuchemann’s Carrots’ are widespread in today’s designs.
Anti shock bodies were also apparently developed by the Soviet Designers during the same time , as seen in their installations in TU-16 and through subsequent designs such as the TU 154.

On most modern designs, the mechanism for deploying the wing flaps are encased in canoe shaped pods , which serve as anti-shock bodies and can be seen in A300/310, A 380 and Boeing 757 to name a few. Known to most as flap track fairings, garnering little attention, these pods nevertheless have an important role in transonic drag reduction and fuel economy.

Tuesday, March 27, 2012

WINGLETS

Srinivas Rao | 1:22 AM | | | | | | Best Blogger Tips

It’s a nearly vertical airfoil at an airplanes wingtip that reduces drag by inhibiting turbulence.
( Merriam-Webster dictionary)

First known use of winglet dates back to as early as 1611.


EVOLUTION OF WINGLET

NASA’s pioneering research in the 1970’s as part of energy efficiency program to conserve energy in aviation resulted in Winglets finding acceptance with airplane manufacturers and airlines alike.
Richard Whitcomb was instrumental in conducting test to explore hypothesis that a precisely designed vertical wingtip device could weaken wing tip vortices and thus diminish induced drag which translates into less fuel burn and better cruise efficiency.(NASA website)

American, Southwest, Ryanair, and others took advantage of fuel efficiency that comes with winglets and partnered with Boeing –Aviation Partners group(ABP) to have winglets installed.
Wing Tip fence
Wingtip fence is the preferred device of Airbus to tackle and reduce induced drag on wingtip.Airbus also has ambitious project in introducing Sharklets, akin winglets on its A320 neo and also an active proposal for the same to be introduced on A330.





AERODYNAMICS OF WINGLET

Winglets
Lift is the force that makes the aircraft fly. Lift is a result of unequal pressure in a wing as air flows around it with positive pressure underneath the wing and negative pressure above.
Drag is the resistance encountered while moving through the airflow. Considerable amount of drag is also generated from the high pressure under the wing, which causes air to flow up over the wing tip and spin off in a vortex.. These vortices produce what is called induced drag which hampers aircraft fuel consumption, range, speed and so on.





Sharklets
 Hence, the primary aim of winglet is to break the wing tip vortices and reduce the induced drag and increase aircraft performance. Fuel savings are estimated between 4-6% by employing winglets.  Initial results as released by airbus for A330 program indicate fuel saving in excess of 3.4% and increased take off weight. Also, the noise footprint will be reduced along with better carbon footprint in light of emissions being the centre stage of aviation policies.
(Acknowledgements: Airbus, NASA and Merriam-Webster)












Tuesday, January 31, 2012

BUFFET BOUNDARIES- COFFIN'S CORNER

G R Mohan | 12:17 AM | | | | | Best Blogger Tips
Stall speed is defined as the minimum airspeed required to maintain 1g level flight. Any further reduction in speed will result in the lift produced by the wings to be less than the weight of the aircraft and leads to a loss of altitude. The increase in angle of attack will in turn cause flow separation from the upper surface of the wing . In a swept back high speed aerofoil, this flow separation and associated pitch down will not be a marked phenomenon. Instead the aircraft enters into a descent. The descent rate further tilts the relative airflow downwards and leads to an increase in angle of attack further driving the aircraft into the stall regime. Any attempt by the pilot to raise the attitude by aft pressure on the elevator will cause a further increase in angle of attack and further loss of altitude.


The lift, however, depends on both air density (kg/m³) and on the plane’s velocity, and air density decreases with altitude. So, the higher you go, the faster you have to fly to stay above the stall speed. As you go higher, temperature also decreases, at least in the troposphere were commercial planes are flying. As the temperature decreases, so does the speed of sound.
Similarly, the critical Mach number is the maximum speed at which the airflow can sustain over the wings without losing lift due to flow separation and shock waves,. Any increase in speed in will cause the airplane to encounter stall effects. When the critical Mach number is exceeded, there is an abrupt rise in drag rise as well as a pitch down due Mach tuck. This can result in aircraft upset, altitude loss and loss of control. As the aircraft descends, the airspeed increases. Excessive pull forces during recovery may lead to further loss of control or structural damage to the airplane.
Modern commercial jet aircraft may suffer both high and low speed stall buffet. The associated boundaries are depicted in the FCOM of the aircraft.  The high speed buffet is caused by flow separation from the wings as occurs behind a shockwave at high altitudes and/or Mach numbers. The low speed buffet is caused by the same airflow separation as the aircraft approaches the stall angle of attack. With stall speed increasing with altitude and sound speed decreasing, the velocity window in which an aircraft can operate becomes narrower and narrower.
Turning manoeuvres at these altitudes increase the angle of attack and results in stability deterioration with  a decrease in control effectiveness. The relationship of stall speeds to critical     Mach number (Mcrit) narrows to a point where sudden increase in angle of attack , roll rates and disturbances cause the limits of the airspeed to be exceeded.


The Coffin corner or the Q corner is the altitude at or near which a high speed fixed wing aircraft’s stall speed is equal to the critical Mach number.  Coffin corner exists in the upper portion of the manoeuvring envelope of an aircraft, for a given gross weight and G – Force.
VMO is an aircraft’s indicated airspeed limit. Exceeding the Vmo may cause aerodynamic flutter and G load limitations to become critical during recovery. Structural design  integrity is also not predictable at airspeeds greater than Vmo.
A deeper understanding of the stall characteristics and recovery procedures are important proficiency issues.  When flying at high altitudes, the crew needs to be aware of the margins of safety available, especially when manoeuvring and while riding out turbulence.
To recover from a stall, the attitude needs to be decreased to reduce the angle of attack. The old maxim of Power for ROD or altitude control and Attitude for airspeed control holds good. A burst of power is not the solution for a stall recovery. In all cases, remember  “attitude before power” when you are in a stall.

Monday, January 23, 2012

WING LOADS

Srinivas Rao | 12:23 AM | | | | Best Blogger Tips
In the aftermath of wing root cracks appearing on A380, lets refresh ourselves on how the wing loading and wing root cracks surface.


Lift produced by a wing is not linear across the wing surface.As a matter of fact,lift is produced by the wing as a result of pressure differential between the top and bottom side of the wing.The pressure differential gives birth to wing shear force and a bending moment, which is the highest where the wing meets the fuselage.
However, aircraft like A330,whose engines are wing mounted, their weight is near the area where maximum lift is being produced.This reduces the total weight, thereby reducing the shear force and the bending moment at the wing root.
Wing loads are also subject to the fuel distribution in the wing.Aiming to achieve lesser moment at the wing root is the objective in effectively managing the wing loading.