Wing Loading During Cruise

WING LOADING DURING CRUISE

Wing loading is a measurement that relates the mass of an aircraft to the total wing area. The relationship between wing area and body weight is given in kilograms per square meter(or grams per square centimeter). Wings generate lift due to the flow of air over the wing surface. Larger wings move more air, so a plane with a large wing area relative to its mass(low wing loading) will have more lift at any given speed. Therefore, a plane with lower wing loading will be able to take off and land at a lower speed (or be able to take off with a greater load). It will also be able to turn faster. 2

Maximum wing loading of Boeing 747 is about 730 kg/m . Although it has a huge wing load, it can fly because of its incredible speed. Planes are heavy, but they can move very fast, showing that the ability to fly depends not only on wing size but also on the speed at which the wings move through the air. A plane will leave the runway because the speed at which it travels (for example, 280 kmph for an Airbus A380) allows the wings to develop lift great enough to raise the heavy machine into the air. The faster a plane flies, the more lift is produced by each unit area of wing. So planes with smaller wings can carry the same heavy load as larger winged planes if they travel faster. Aircraft that moves at slow speed is bounded to experience stall performance. At high speed, the aircraft performance is restricted by the available engine thrust , the rise in transonic wave drag and the effects of the associated buffet on the aircraft structure. The stall speed is increasing as air density reduced as defined below:

    [] As the altitude and temperature reduces, the speed of sound and thereby the aircraft speed will reduces too. The speed of sound c an be determined through:

  

Where

 is the speed of sound at sea level, which is 340.29 m/s, 661 kt. The effect can be shown

diagrammatically in Figure 1.

Figure 1 : The g raph of altitude vs aircraft speed

Wing loading is important as it is the only indicator of how “heavy” an aircraft is. The actual

weight of an aircraft is meaningless, as we discuss before. The relationship between wing loading and the performance of take-off, cruise and land is linear. The lighter the wing loading, the slower the aircraft can take-off, fly and land. It will also have a better climb. A larger model can have a higher wing loading and fly comparably to a smaller aircraft having a lower wing loading due to differences in the aerodynamics of different size aircraft. There are two aerodynamic coefficients needed for wing loading during cruise, which are

 and .   is zero lift drag coefficient and equals to 0.015 for a jet aircraft while  is Oswald efficiency factor and equals to 0.8. In or der to maximize the range during cruise, the wing loading should experience high . A jet aircraft can maximize the range when the parasite drag is three times bigger than the induced drag. This statement leads to the formula of wing loading for maximum range of jet aircraft;

  √  ⁄ By substitute the values of

 and  into the equation, we got;  

The wing loading is very important design parameter as it indicates the sizes of the wing of an aircraft. The parameters needed for cruise aircraft is: 1. Take-off weight,



2. Take-off wing loading, 3. Aspect ratio, 4.

 

 



Here the designer faces a real dilemma as these mission requirements are in conflict with one another. For example, good cruise efficiency drives the combat ability requires a low

() to high values whereas good

(). Thus, the designer must consider the requirements of the

aircraft and then decide upon an appropriate compromise.

REFERENCES

http://www.airfieldmodels.com/information_source/math_and_science_of_model_aircraft/formula s/wing_loading.htm http://www.airfieldmodels.com/information_source/math_and_science_of_model_aircraft/formula s/wing_loading.htm http://arc.aiaa.org/doi/abs/10.2514/8.472?journalCode=jans