Saturday, August 13, 2016

The Transonic Range: Aviation’s Undiscovered Country?

With the Cessna Citation X as the lone example in current production specifically to fly at this speed, is the transonic range still the aviation world’s largely undiscovered country?

By: Ringo Bones 

Specifically designed to operate at around Mach 0.935, a velocity only 80 kilometers per hour or 50 miles per hour slower than the speed of sound, it seems that Cessna Aircraft Company’s Citation X is currently the only aircraft of its kind in current production – military or civilian - specifically designed to operate within the “tricky” transonic range (though Boeing’s Sonic Cruiser proposed back in March 2001 was designed to fly at Mach 0.98 or 15-percent faster than existing subsonic passenger planes at the time but only half as fast as the supersonic Concorde, was cancelled in December 2002 due to post 9/11 aviation slump and was since repurposed into the Boeings rather “conventional” Mach 0.85-capable 787 Dreamliner program). As a high-end private jet / corporate jet, the Citation X can also fly nonstop for 6,000 kilometers or the distance between Moscow to Beijing. But given that some modern high-performance military aircraft can even fly at Mach 1.5 without using their afterburners unlike their fuel guzzling Cold War era predecessors, why is it that most aircraft – military or civilian – tend to fly below or bypass into the supersonic region, instead of cruising continuously into the transonic range?  

Any aircraft in flight displaces the air through which it flies, and produces countless small disturbances. Called pressure waves, these radiate from various points on the aircraft’s surface like ripples from a boat. All of them travel at the speed of sound. At subsonic speeds, these waves are able to move harmlessly out ahead of the aircraft. At sonic speeds – i.e. at the speed of sound 760 mph (1,223 km / hr) at sea level which falls off to around 660 mph (1,062 km / hr) at 25,000 feet and above – these pressure waves can no longer move ahead of the aircraft because it is flying as fast as they are, and so they pile up, reinforcing one another to create a high-pressure shock wave. 

The shock wave buildup starts at about Mach 0.8 for most aircraft. Even though the plane is not then moving as fast as sound, the accelerated air moving over the top of the wing reaches supersonic speed and a small localized shock wave is formed. The region from about Mach 0.8 (525 mph or 845 km/hr) to Mach 1.2 (913.45 mph or 1,470 km/hr) is called the transonic range or transonic region because some of the airflow across the aircraft is subsonic and some have already reached supersonic. 

The swept-back wing design that has since become de rigueur in fast airplanes is a result of minimizing the problem of flying in and beyond this transonic range / transonic region. The fact that even a subsonic plane like the venerable Boeing 707 and its related variants could never operate at the speeds it does unless its wings were swept back. This is because the Boeing 707 and its related variants do in fact cruise at speeds of around 600 miles per hour (966 km/hr) at altitudes of 25,000 feet or over. This is more than 90-percent of the speed of sound. At such speeds, a straight-winged 707 would have airspeed over its wings – due to the acceleration needed for lift – already at supersonic speeds. Assuming such a straight-winged 707 variant had sufficient power to overcome the drag created at these speeds, the shock waves set up could cause severe buffeting and lack of control.

However, by sweeping back the wings, the formation of shock waves is delayed. In flight, the swept-back wing meets the air at an angle. The effect of this is that now the velocity of the wind relative to the wing acts in two directions – one at a right angle to the leading edge of the wing, and the other along the span of the wing. Neither of these components is equal to the original velocity of the wind striking the forward edge of the wing – which, in fact, is the speed of the airplane. It is only that part of the wind passing at a right angle to the leading edge of the wing which is accelerated in its passage in order to obtain lift. Since the speed of this wind is less than the forward speed of the airplane, it becomes possible for the airplane to fly much closer to the speed of sound before shock waves begin to form on the wings.  
Because shock waves so severely affect an airplane’s stability, the greatest problem for a pilot at the “tricky” transonic range is the change in control characteristics. A wing has a slowly moving layer of air called the “boundary layer” that clings to the surface. Near Mach 1, shock waves can interact with the boundary layer to distort the airflow so that lift may be impaired and control surfaces made ineffectual. This disturbance also adds to the turbulent wake which is created by any wing, whatever its speed. 

Wing shape is obviously important in controlling airflow, but other design solutions have been found. Some are ingeniously simple – i.e. Boeing’s cancelled Sonic Cruiser which flies deep into the transonic range by having a cruise speed 15-percent faster that existing subsonic passenger jets, resorted to having a “supersonic ready” flight control surfaces. Tail surfaces, for example, may be moved up or down to get these out of the wings’ troubled wake. But providing supersonic-ready flight control surfaces to transonic planes may prove to be a not-so-brilliant engineering solution because since the advent of the aviation world’s mastery of flying faster than the speed of sound around the middle of the 20th Century, supersonic ready flight control mechanisms / flight control surfaces weigh two and a half times than their subsonic counterparts and cost on average four times as much. 

Wednesday, April 13, 2016

The 18-Rotor Volocopter: The World’s Safest Helicopter?

Its aerodynamic design was said to be inspired by the inherent aerodynamic stability of quad copter drones, is the 18-rotor Volocopter VC200 the world’s safest helicopter? 

By: Ringo Bones 

Ever since Igor Sikorsky “perfected” the main rotor and small tail-rotor type helicopter near the end of the 1930s, it has since become the favored configuration of helicopters in military and civilian use since. And despite its inherent safe record, accidents still happen, but is there a better aeronautical engineering design out there that’s much safer than the “Sikorsky Configuration”? Fortunately, a bunch of Germans got inspired by the inherent stability of quadcopter drones and believe that a safer helicopter design should involve increasing the number of rotors, so they designed and built a helicopter with 18 different blades.   

It’s called the Volocopter VC200 and the German engineers have been working on it since 2010. They’ve done manned flights before, operating the craft like a gigantic 18-rotor man-carrying drone, but this time, E-Volo Managing Director Alexander Zosel got behind the controls and flew the craft himself. 

One of the biggest problems with helicopters is that they’re extremely difficult to fly in comparison with conventional fixed-wing aircraft. Helicopter configuration that’s in widespread use – the Sikorsky Configuration – only has one main source of lift and when it fails the results are usually disastrous. Multi-rotor flying craft like the popular quadcopter drones are more stable in the air, and more importantly, much easier to handle aerodynamically for inexperienced pilots. The Volocopter team wants their flying craft to bridge the skill gap between everyday transportation like cars and human flight. The Volocopter’s controls are incredibly simple – a single joystick with a few buttons – and a giant canopy of independent rotors mean it can hover almost perfectly with very little effort or skill required.  

Using current battery technology, the battery powered Volocopter VC200 only has a flight endurance of 25 minutes but if its batter runs out in flight, the Volocopter can automatically lands itself safely even with a student pilot at the helm. Currently the Volocopter VC200 costs around UK£200,000 each but E-Volo Managing Director Alex Zosel hopes that demand from interested affluent buyers and flight schools could generate enough funds for additional research and development funding for a Volocopter version with an increased flight time and greater payload. With its inherent safety and low carbon footprint are multi-rotor battery powered helicopters the future of helicopters? 

Sunday, April 3, 2016

Steam Powered Aircraft: An Aeronautical Engineering Impossibility?

Even though mid 19th Century accounts of their flight attempts are notable for their “comical failure” are those steam powered aircraft still an aeronautical engineering impossibility in the 21st Century?

By: Ringo Bones 

Maybe we should be “blaming” the Mythbusters for doing those proof of concept experiments in their shows – especially ones pertaining to “aeronautical engineering impossibilities” – like the lead balloon and the concrete glider, which more or less, they managed to successfully flew on their shows and confirming them that they are not an aeronautical engineering impossibility after all. But has the Mythbusters ever tried to build and fly a steam powered aircraft? After all, if one managed to successfully fly back around 1850, the Wright brothers would probably have given up designing and building their first successful gasoline-powered aircraft. 

The steam powered aircraft gained legendary status probably because the press-at-large became very intrigued by William Samuel Henson’s publication of the design of his “Aerial Steam Carriage” back in 1843 after it was patented in 1842. Although a full-sized model was never built, illustrations of this “remarkable aircraft” were given world wide publicity and did more than anything else to establish the modern airplane configuration of fixed monoplane wings, a fuselage, a tail unit, and propulsive airscrews – features that became standard in many airplanes some 65 years later. 

Another intriguing possibility that a steam powered aircraft – like William Samuel Henson’s Aerial Steam Carriage and those like it – could have successfully flown back in the middle of the 19th Century is that Henson hired a very skilled mechanic named John Stringfellow to design and build an extremely light steam engine that could have flown the first ever steam powered airplane. Stringfrllow’s steam engine achieved a power-to-weight ratio of around 20 pounds of engine weight per horsepower produced – which was comparable to the power-to-weight ratio of the engine used by the Wright brothers during their first ever successful flight. Sadly, neither Henson nor Stringfellow managed to design a propeller that is as efficient as the one designed by the Wright brothers in converting mechanical rotation into forward thrust – i.e. the Wright brothers’ propeller has a 66-percent efficiency rating. Given that today’s modern propeller designs can now achieve 90-percent efficiency, will the Mythbusters or any other daring aeronautical engineer be building their own flyable steam powered aircraft anytime soon? 

Saturday, March 5, 2016

Emirates Airbus A380 Completes World’s Longest Commercially Scheduled Flight

Emirates say the record may be short-lived but did the feat just happened because Emirates is taking advantage of current low crude oil prices?

By: Ringo Bones 

Given that crude oil has lost 70-percent of its value since 2014, it is likely that “adventurous” airline companies could now be exploring world record setting feats as a way to attract new customers, but the world’s longest flight recently set by an Emirates Airbus A380 as it flew from Dubai to Auckland, New Zealand back in March 2, 2016 to complete what is currently the world’s longest commercially scheduled flight promises more than a one-off taking advantage of the current slump in crude oil prices. The 17 hour 15 minute 14,200-kilometer flight cuts 3 hours off the current route that includes layovers. 

However, the record-setting Dubai to Auckland flight of March 2, 2016 is expected to be short lived because Emirates’ upcoming Dubai to Panama City service will take 17-hours and 35-minutes when it launches later this month. Emirates described it as “one of the longest air routes in the world by distance”. “But with the assistance of clever technology and good planning, passengers will get to their destination in the shortest possible time,” it said. 

The inaugural Dubai-Auckland flight of March 2, 2016 was made by an Emirates Airbus A380 which the double-decker super-jumbo has been in service with the world’s leading airline companies for the past 5-years but the regular service will be carried out – according to Emirates – by their fleet of more fuel-efficient Boeing 777-200LR planes. New Zealand Transport Minister Simon Bridges said the non-stop service, which cuts three hours off the current Dubai-Auckland travel times, improved New Zealand’s connectivity to the rest of the world. And to anyone wondering, the previously held record as the world’s longest commercially-scheduled flight route was the Qantas 13,800-kilometer Sydney to Dallas route that was launched back in 2014. 

Monday, February 15, 2016

Do Laser Pointers Pose A Danger To Airline Flights?

Though they are not yet capable of blowing up a plane like those shown in science fiction movies, but can high-powered laser pointers pose a danger to airline flights?

By: Ringo Bones 

A “laser incident” forced a pilot to turn around a flight from London to New York, Virgin Airlines said. Virgin Atlantic Flight 025 was en route from Heathrow Airport on Sunday – February 14, 2016 – when a laser was pointed at the plane, spokeswoman Jamie Fraiser said. “Following this incident, the first officer reported feeling unwell. The decision was taken by both pilots to return to Heathrow rather than continue the transatlantic crossing,” the airline said on its website. The aircraft landed safely at Heathrow with 252 passengers and 15 crew Fraiser said. Virgin Atlantic said its offering the affected passengers overnight accommodation and the flight is scheduled to depart London on Monday. 

The airline is working with authorities to confirm the source of the laser, it said. London’s Metropolitan Police Service said it is investigating, but there have been no arrests. Britain’s Civil Aviation Authority recorded 48 laser incidents at Heathrow Airport in the first half of 2015. Such incidents are on the rise – especially in the United States – as handheld lasers that are several times more powerful than the ones used in a boardroom presentation become more common and affordable. A laser beam has the potential to burn a pilot’s cornea and cause serious injury. Direct hits have put pilots in the hospital. The beams can also temporarily disorient and blind pilots.  

The laser used to “dazzle” pilots and cause near-crashes during “laser incidents” are a more compact version of those bulky helium-neon lasers used in planetarium laser shows during the 1970s. They range in size from those as big as torch-lights to those as big as a mid-sized pair of binoculars. These lasers are legitimately used in stage lighting effects during concerts and other special occasions but due to their relatively affordable cost – they range in price from 10 to 40 US dollars and are widely available on online shops like e-Bay – pranksters have used them to point at planes especially at the cockpit window part of the plane. The green ones pose the most danger because the human eye is most sensitive in this part of the visible light spectrum and they are the most likely to disorient the pilot and the co-pilot and could trigger a tragic crash because “laser pranksters” often point lasers at planes during takeoff. These lasers are so bright that during tests by the U.S. Federal Bureau of Investigation, these lasers are capable of disorienting pilots even if the pointed lasers are located 3,000 feet away from the plane’s cockpit windows.