With the advent of new technology and the fast paced research and development of obscure concepts many new ideas are becoming a reality in the Aerospace world. Already highly prevalent amongst military aircraft, variable wings have come to the forefront of consideration for its potential application in commercial airliners.
Variable wing geometry is the ability of an aircraft to change the physical configuration of its wings during flight.There are many different ways an aircraft can do this, including but not limited to: variable sweep (a means by which the plane can change the angle at which its wings are pointing, first used in the Bell X-15), oblique (meaning the wing can pivot horizontally about a centre point), and telescoping (an inner portion of the wing slides out of the outer portion much like a telescope). Obviously all of these variable geometry design choices come with both advantages and disadvantages, which we will go on to discuss. First of all let’s look at some general disadvantages to the application of variable geometry in commercial airliners.
With the huge amount of stresses and strain placed on commercial aircraft and the added weight needed to contain forces against the aircraft without variable geometry the extra structural reinforcement needed to put these systems in place could outweigh the benefits. Let’s, for example, look at a telescopic wing design in terms of moments about a vertical axis. As we know a moment is a turning force; doubling the length of the wing by means of a variable wing geometry would increase the moment about the wing root meaning more structural reinforcement, hence weight, on the aircraft.
This brings us very nicely onto the next point, the cost of implementing such ideas onto commercial airliners. Many manufacturers of commercial aircraft and the owners of the companies who run them are less concerned about innovation and more concerned about saving as much as possible. Although the safety of their customers and their reputation remains paramount, every little bit of money that can be saved will be. This goes for additional unnecessary weight which may come as a result of increased structural integrity, the fuel loss due to drag caused by new external features, as well as the cost of research and development for new ideas which are unlikely to be of any practical use in the future.
Although many variable geometry wing concepts have been tested and analysed for use in military aircraft, use in commercial aircraft is still a bit of a grey area with regards to safety. Development and testing would cost millions, which may seem a somewhat pointless investment to make considering the current level of design and safety. Research and development performed on military aircraft doesn’t necessarily translate well over to a commercial product. It only takes one major incident to put a company in the red both financially and reputability.
Variable geometry wing design does however have some benefits, the main one being the way that they give an aircraft the ability to change its take-off and landing speed. The overall aim when it comes to take-off and landing is to be able to do so with the minimum possible speed; certain types of wing geometry allow this to happen without sacrificing overall cruise speed. Variable sweep wings are extremely useful for this, as they allow the aircraft to travel at low speeds when the wing is fully extended (ideal for taking off and landing), and high speeds when the wings are swept back. Changing the cruise speed and reducing the drag of the aircraft will have a positive impact on overall fuel consumption, reducing the cost of running the aircraft. But does this small increase in efficiency outweigh the cost of research and development? This type of variable geometry has now been mostly replaced by computers, able to do the same thing with regards to controlling the aircraft at low speeds and high cruising speeds.
In conclusion, the use of variable wing designs show very little promise for use on commercial aircraft, as the risks and costs involved outweigh the benefits a company may gain by choosing to implement them. The increase in structural integrity needed to support such wings would add weight which increases fuel consumption. With health and safety being an increasingly large part of today’s world, the amount of money which would need to be put into research and development would be inconceivably high, especially with efficient, safe, and proven to work designs of many modern airliners, and would likely outweigh the benefits gained for many years to come. Is there really a reason to fix something which isn’t integrally broken? For the sake of innovation, maybe, but when all of the different previously discussed factors come into play it seems that there really isn’t.