“Once you have tasted flight, you will forever walk the earth with your eyes turned skyward, for there you have been, and there you will always long to return.” This quote from Leonardo Da Vinci can be seen to be used tremendously in aviation related topics. It is so rightly true for those who got a chance to taste one of the safest and fastest means of transportation till date and also to those who are willing to travel with it someday. If it’s the anxiety to meet long lost loved ones, reuniting of family during festivals or maybe employees and student with big dreams in heart sailing over oceans and mountains, this flying machine safely bring them to their opted destinations. We are so used to the fast paced technological advancement these days; we hardly take a look back to appreciate and know about it. We take the technology for granted and sometimes this can lead to our habitual ignorance. We don’t need to stuff ourselves with all the technological jargons but still appreciate the basic principle which can be handy for boosting our horizon of knowledge. Furthermore, have you ever wondered how the house like structure of airplanes never fail to perform during the turbulent gust of wind, severe climatic conditions and all those flight loads and yet bring you safe and sound to your destination? How can the cabin pressure maintained inside the airplane don’t give us hint even if we are 30,000 ft. above sea level and still maintain its structural integrity in such pressure difference? So, today we take a quick insight on the basic structure of airplanes and maybe it will be helpful to solve some queries which we might have chewed up with our taking for granted habits. Thanks to those ever diligent and imminent scientists and engineers who sacrificed their whole life on countless experiments in a real to life simulation labs, various test flights and crash tests. They have made our air travel more comfortable and luxurious than ever before. “Even the sky is not the limit” for the endless possibilities of what can be next in the future of air travel. So what is the basic of the structure that makes it so agile and strong, that it can withstand unimaginable load and external forces? Let us discuss the basic of structure types used widely in the aviation.
TRUSS TYPE
Truss type structures were first developed with similar concept of the structure used on the first powered flight of Wright Brothers. Truss type of vertical and horizontal members previously made of woods then later were made up of steel tubes and other light aluminum alloys which were either riveted or bolted together providing structural stability. Further classification is made under truss type they are Pratt truss and Warren truss. Pratt truss happened to be used on earlier air craft’s but the later air craft’s which were more streamlined and lighter made use of Warren truss.
MONOCOQUE STRUCTURE
As advancement took place the need for more streamlined and lighter airplanes gave the stressed skin concept, a break-through. In this concept the structural loads was carried by the skin itself and without any frame truss. The heaviest of these structural members were located at intervals to carry concentrated loads and at points where fittings are used to attach other units such as wings and engines. The problem with this concept was that the strength has to be maintained with accordance to the weight factor. Moreover, those structures were vulnerable to fail even with slightest of dents or cracks.
SEMI-MONOCOQUE STRUCTURE
Now we go through the most important and advanced aircraft structure. It is most widely used in modern airplanes. Semi-monocoque totally eradicated the problems which were faced with monocoque design as it provided a better strength to weight factor. In these structures, the skin is fastened to a sub structure or skeletal framework, which allows the loads to be distributed between the structural components and the skin of the aircraft. The framework consists of sub skeletal individuals like longer ones, bulkheads and stringers mostly made up of aluminum alloys and upon which the stressed skin evenly distributes the load being imposed on it. This structure helped to achieve streamlined, stronger and yet rigid structure which could withstand considerable damage and yet hold together the structure. So now semi-monocoque is the basic foundation of all modern air craft’s structure. The Basic goal for all aircraft basic structure is reaching a Fail-safe design. This concept has a different meaning for structures than for systems. Fail-safe for structures are concerned with residual strength after sustaining damage; fail-safe for systems is concerned with the functional implications of a failure condition and its probability of occurrence. Although both concepts have the same goal, a safe design. In general, the structural components of an airplane (such as the air frame and wings) are designed such that “an evaluation of the strength, detail design, and fabrication must show that catastrophic failure due to fatigue, corrosion, manufacturing defects, or accidental damage, will be avoided throughout the operational life of the airplane. Another factor is the high strength to weight ratio. With different new alloys and materials that has evolved every day, the goal will be to achieve much lighter materials which will overcome aerodynamic loads in flight and withstand various stresses like tension, compression, torsion, hear and bending which aircraft are normally subjected to. Not only the metals maintain rigidity and strength but also allow the cabin pressurization and depressurization when the air crafts flies over different pressure zones with climbing altitude. Most commonly used alloys on air crafts are made up of aluminum and hot areas with titanium and some with composite materials as well. To add up on that, the important part for any structure is its Factor of Safety. The common factor of safety for aerospace structures is 1.5, as required in the U.S. by the FAA (Federal Aviation Administration). The factor of safety is defined as FS = material strength/maximum load. But for the acrobatic air crafts the factor of safety rises a bit as they undergo 2G, 3G maneuvers’ where the gravitational force is felt just double or triple compared to the normal force. Finally to sum up with, Aviation is an ever changing field and has big scope for improvement with each new invention and breakthroughs. The air travel will have countless ways to improve on various factors like passenger’s luxury, noise pollution, fuel efficiency, time efficiency, number of passengers, bio-fuel and many more. But in the end it all depends upon one factor and that is structural feasibility. New advancements can only be made if it can still restore the structural integrity of an aircraft. So next time after you tasted your flight you will held your eyes towards sky with the sense of gratitude to all those pioneers for the structure that hold you together with comfort throughout your journey.
