Ugendar | Aviation Management System

Flight Automation – what you really don’t want to know

Summary – as this technology advances and nominally improves, even where man remains ‘in-the-loop’, he is less and less in control.

It’s no good winging about it. In all forms of transportation, natural intelligence (manual skills) will soon be ‘out’ and artificial intelligence (nerdie skills) with full automation will be ‘in’. There is no question of ‘if’ – just when (the Author’s guess, in 10-15 years). How often in a day does one feel frustration and stress at the failure of digital systems that impact our lives? Now lift them 15 km into the air and the impact is exponentially greater. This is an opinionated review on the need for concern in this regard (Note – the views are personal to the author alone).

Actually, in aviation (and astronautics) automation is a very mature technology. The author first flew in a fully automated helicopter some 50 years ago. Space ships have always been almost fully automated – Yuri Gagarin in the Sputnik in 1959, did not have any controls to touch ! In a general context there are three levels of automation.

The simplest are Pilot-Assist technologies, otherwise referred to as auto-pilots. All commercial aircraft have this aid. It has been around for longer than the biblical three score years and ten. The automation is limited to the maintenance of height, heading and speed, and more recently, aircraft attitude. In addition, the engine responses to Pilot power demands are now also fully automated. But, on airliners (sic Fixed Wing) thus fitted, using hydraulic assisted controls (power steering if you will) the pilot remains in full control of the aircraft and can over-ride the automated elements at the flick of a switch and fly it manually. For Helicopters (sic Rotary Wing), the same is essentially true but limited to the aircraft’s guidance – it’s stabilization (whereby any control movement in one dimension impacts control in the other two) is a more complicated issue as discussed in the previous feature under the heading of ‘Safe but not Sure’. This latter can be switched-off but few of the current generation of pilots have flown unstabilized aircraft and would find themselves juggling to maintain level flight, so it is generally left on. (The author’s generation learned their trade on unassisted aircraft and so instinctively had to develop the necessary coordination and so have no problem in this regard).

Cockpit automation – ‘archaic’ Computer Assisted vs. cutting-edge Computer Controlled

Then there are automatic flight control systems (afcs) with man-in-loop. These aircraft are flown by computers with pilot inputs. There are separate programs for take-off, climb, cruise, descent and landing – in truth to fly from A to B, highly paid pilots need do nothing more than enter a flash-drive with the flight plan into a computer port in the cockpit and select the 5 buttons that run these programs. All these aircraft use Fly-by-Wire (FBW) control input technologies – and here is the scary part. The so-called ‘joy-stick’ that pilots have traditionally used to fly aircraft, is replaced in FBW aircraft with a dinky side-arm controller (see right-hand photo). This is actually not a control at all – it is a computer mouse. As such, any control movement (say to turn left or right) is no more than a mouse telling the computer what the pilot wants the aircraft to do. Unlike with the above hydraulic control systems (left-hand photo), he has no direct access to the control surfaces. Indeed, neither does the aircraft computer. It just sends a digital signal to an analogue sub-system at each control surface which then drives an electric motor to move it as required. So, a pilot may be ‘in-the-loop’ but he is no longer ‘in control’ and can do no more than monitor the computer performance. Were it to fail, there is nothing he can do except to scream “Mayday, Mayday” on the radio and into the aircraft intercom to “brace-brace-brace”! He cannot switch off the afcs and fly it himself (as in the above autopilot) because he has no access to the control surfaces. (Incidentally, as an amusing digression, why scream “Mayday”? It’s those frogs again who just will not accept that international speak is now in English. In the 1920s when aviation was maturing, the language of international diplomacy was still French. It took the late arrival of the Yanks in two World Wars, for it to be changed to English, so that they would better understand what was going on…..! But with international civil aviation being based in Montreal (a francophone town) that linguistic aberration lingered on: hence m’aidez, m’aidez – help me!! (Zat accen’ has always been a challenge for we anglophones…………).

The one exception to this is the modern airship (known as a Hybrid Air Vehicle – HAVs) which, using a combination of gas-lift and aerodynamic lift, are very large (some 100m in length and almost 20 stories high). They also use the same afcs principal except using fibre-optics (fly-by-light – FBL) instead of electrical wiring (FBW). Essentially they are very similar but FBL allows some 10 times the data rate. Because of its huge size, in the HAV there is the space (and lift) to put in a duplicate system allowing the pilot mouse (side-arm controller) to directly access the analogue actuator and messily get the gargantuan balloon back to base in the event of complete afcs computer failure. Airliners instead have duplex critical sub-systems, triplex safety-critical systems and five computers. It is thus very unlikely to go wrong, but that is not to say it ‘never’ fails. It has so on several, but not frequent, occasions and each time everyone died. However with a frequency of such event being very small (less than the regulatory standard of 0.002%), it is correctly perceived as an acceptable hazard – after all, every day folk use their cars where there is almost a 0.1% chance of a major incident.

Nonetheless, the thought that the so-called man-in-loop cannot actually assume direct control when computers cease to properly compute, is scary. A nice anecdote demonstrates this lack of pilot control. In a demonstration to client airlines of a new type of FBW airliner by a senior test pilot (ie a guy with vast experience), he decided to end the demo with a very low, high speed pass (as one does on such occasions). It was impressive not least because he over-cooked it and realised he was going to have a problem clearing the trees at the airport perimeter. So he slammed the power controls fully forward and heaved up the nose – except the aircraft responded to neither. His dinky side-arm controller could only tell the computer what he was seeking to do to not hit the trees at the end of the runway but the computer (which could not ‘see’ the looming disaster) knew better. Realising that to fulfil the (Chief) pilot’s demand would overstress (and damage) the engine and airframe, the compute opted instead to increase engine power and use control movements that would stress neither. The result was that the aircraft clipped the tree-tops, filling the engines with scrub (thus writing them off) and seriously damaging leading edges of the wings to say nothing of the hull the paintwork. Fortunately the only casualty was a bruised pilot ego and a few millions of dollars of repairs (which the subsequent sale of many aircraft to the very impressed client airlines, fully compensated!!).

From this it can be seen that the next step, to fully automated passenger aircraft with no man-in-loop (ie unmanned aircraft), technically speaking, is incremental – the main issue preventing this change is not one of technologies but simply a matter of perception. Even if pilots can do very little to control a FBW aircraft, not having one (indeed two) up-front would not be good for ticket sales. In the military, the remote piloting of long range killer drones all over the world controlled from a hangar in California is now well established. Airliners may eventually follow, ultimately with a single pilot sitting at an airline HQ, from where he could control multiple aircraft. After all, in the cruise, automated vigilance will suffice – only for brief periods at take-off and landing will dedicated pilot surveillance be required. What will he do if something goes badly awry? Probably exactly the same as those today in any FBW aircraft cockpit – issue a mayday and politely invite the unfortunate passengers to brace themselves for the final curtain – then, no doubt, go to a bar to console himself.!

The driving force for this change will be the new generation of E-Vtol Tupperware, so-called, air taxis (in the AMS view a technology bubble which will burst in a year or two and about which we will also write soon). Notwithstanding their small size and limited Pax. payloads, their automated flight profiles are similar to any airliner, but in a much more challenging flight environment. Bubble or not, these platforms will be required to achieve the same level of certification as a 400-seat airliner (called ‘Transport Category’). Once they have done this, the door will be opened to the full automation of the airliners themselves. Hence our guess that such is not more than some 15 years away……

Space ships have almost always been thus full automated – although the Apollo-series of moon landing fame maintained a man-in-loop capability (which was lucky as, on the big day in 1966, it soon became apparent that NASA has got it wrong and Neil Armstrong had to land the Eagle module manually, which he miraculously did with just some 10 seconds of available fuel remaining !!). Today we watch in awe as space ships do increasingly amazing things both in earth orbit and to the very edges of the solar system. But the fact is that, being subject only to the simple principals of Newtonian laws of motion established some 400 years ago, space ships are far easier to control than aircraft operating in the unpredictable atmospheric conditions on Planet earth. In space, there are just two main forces – one generated by man-made power plants and the other gravitational pull. These can be calculated to the micro-Newton and never change thus making precision control, almost literally, childs’ play. (Helicopters, as you may have seen in the last dissertation, are anything but……!).

Conclusion – based on media prognostication, full automation is typically presented as a futuristic projection, but in aviation (rather than the automotive milieu) it has effectively been there for a generation or more. The technologies are fully understood as is the reliability of computers – we each have our own experience in that regard !! But, as stated in earlier essays, notwithstanding all the negatives highlighted above, the chances of a flight accident are minimal. Travel on roads is significantly more dangerous. So take a deep breath, double your beverage of choice and sit back, (try to) relax and enjoy your automated flight………!!

Helicopter Flight – safe but not sure

by Ugendar | Pause for Thoughts

fulfilling a unique and invaluable niche in remote area logistics, helicopter flight defies gravity and mechanical practicality and yet are surprisingly safe. This is how they work

Helicopter Flight – safe but not sure

Travelling through any medium, an aerofoil with a positive angle of attack ‘α’ with respect to the horizontal, will cause a medium deceleration below the aerofoil (thus increasing pressure) and an acceleration above it (thus decreasing pressure). The pressure differential generates a lift force. The amount of lift generated depends on the size of the aerofoil, its speed through the medium and the density of that medium. When the lift generated by the aerofoil is greater than that of the body to which it is attached, that body will rise. Let us start by looking at each of these elements impacting lift generation.

Medium Density vs Aerofoil Size – the baseline properties of solids, liquids and gasses are very similar. Almost every substance has the three states. The change in state is a simple function of atomic vibration. The level of vibration is a dynamic of energy. Available energy is a factor of temperature. At Absolute Zero (-278°C), atomic vibration ceases altogether so (typically) everything is in a solid state. As the temperature rises, energy levels increase and with it atomic vibration, causing a decrease in substance density and the associated changes in state (solid > liquid > gas). In higher densities, aerofoils are more efficient. So in liquids it only requires a small aerofoil (of a couple of meters) to lift a 300 tonne hydrofoil out of the water while, in the lower density of air, to lift an equivalent aircraft, it requires an aerofoil (wing span) of more than 50 meters. Air density similarly varies with temperature. So, in cold climates aerofoils are more efficient than in tropical climates, which has a fundamental impact on aircraft operation.

As one would expect, the way aerofoils work on aeroplanes and helicopters is exactly the same: what differs is the way the causal airflow is generated. Aeroplanes have fixed wings and so need a very long straight road (runway) to get these very large and heavy trucks up to a speed of some 200 km/hr where the lift generated by its aerofoil equals its weight and it flies. Helicopters are more subtle, generating the airflow to realise the required lift by simply rotating the aerofoil blades at some 2-300 rpm. The larger (heavier) the helicopter, the larger the size and number of its aerofoils (blades). The biggest chopper in the world is the Russian Mi-26 with roughly 100 tonnes of Lift provided by 7 huge blades – and that must be somewhere near the limit of what is possible.

So, returning now to the impact of temperatures on aircraft operation. Increasing temperature increases atomic vibration thus reducing air density and decreasing the lift generated by aerofoils at any given airspeed. The operational impact of this is significantly different for fixed and rotary wing types. For aircraft with fixed aerofoils (wings) increasing temperature is of little consequence as all one needs to do is go faster to generate the required lift, thus requiring a longer runway to achieve lift-off. For rotary wing this is not always an option: where a runway is available they can mitigate the reduced lift with increasing temperature in the same way as aircraft with fixed aerofoils by doing a running take-off. But in the absence of a runway – operating from helipads – they have no option other than to reduce the aircraft weight to get it off the ground, typically by carrying less passengers and cargo (rule of thumb – a reduction of 100kg for every 10°C increase). Hence, in Fixed Wing operations, weight calculations tend to be more casual while for aircraft using rotary wings, every kilogram including fluids, fuel and even pilot bulk is accounted for to the point of paranoia!

And then there is the mechanics relating to the aerofoil types. By definition, aircraft with fixed wings are simple with aerofoil length and lift being (essentially) linear: not so for the rotary types. For α start, airspeed at the inner end of a rotating aerofoil is very much less than at the tips, so the generated lift is anything but linear. This is complicated further by the fact that as a rotary wing aircraft moves forward, the advancing blade will generate a great deal more lift than the retreating blade. This is to the point that above some 60 km/hr, the difference is enough to flip the aircraft over. The only way to compensate this is to reduce the ‘α’ of the former and increase it on the latter. Given aerofoil (blade) weights of some 200kg and rotations of some 300 rpm this makes for complex and robust mechanics and explains why it took more than 50 years after the first fixed wing aircraft staggered off the ground, for an equivalent brief flight to be realized using rotating aerofoils.

Then there is the need to compensate the inconveniences engendered by Newton’s Laws and particularly that whereby action and reaction are equal and opposite. So significant is this that one ton of rotating aerofoil at 300 rpm will cause the 4-ton aircraft to which it is attached to rotate at some 75 rpm in the opposite direction – while good for training astronauts, such is unacceptable for normal folk. Hence the small fan put at arms length at the back of the aircraft (the tail rotor) to counter that effect. This all results in the need for multiple sets of complex mechanical devices on rotary wing aircraft which, although Safety Critical, are a simplex installation (typically a ‘no-no’ in electro-mechanics) – any failure is thus always catastrophic and fatal. Such risk is not further mitigated by the need to combine the nominal opposites of robust reliability with lightness of structure. It is a very real measure of man’s ingenuity that this ‘mechanical oxymoron’ has, in the main, been achieved.

No sweat – with thanks to Captain Ed Cooke

And pity the pilot…… Due to said Newtonian Laws, a change in any one rotary wing parameter – airspeed, ‘α’, direction or power – and all the others have to be corrected to maintain the stability in flight. Simply stated, while airplanes with fixed wings naturally want to fly, those with rotating wings are defying nature and do not. As such, any disturbance in the delicate balance of mechanical forces in the latter and it will cease flying, immediately and disastrously! So, while pilots in fixed aerofoil aircraft, once airborne, can relax, those in rotary types are typically brooding anticipators of impending doom.

So, does this mean helicopters are essentially unsafe ? Certainly they are less forgiving. Users must take nothing for granted, be disciplined in following procedures and respect nature. While fixed wing aeroplanes can usually ‘punch through’ bad weather and get above it, Helicopters, in the main, have to live within it. And with the complexity of its mechanics, there is so much more to go wrong in an helicopter, so they tend to be less reliable. A measure of this is that for every hour of flight of a helicopter, there needs to be some 12 technician man-hours on the ground, while typically this is only three for fixed wing. But that said, as a function of its fixed wings, an aeroplane needs to travel very fast to maintain controlled flight so, when things go badly wrong to the point that control of flight is no longer possible, they return to terra firma at fast and furious speeds leading to considerable destruction and high fatalities. Helicopters on the other hand, in the event of complete power loss will experience a slow and undramatic return to earth such that, where the terra is firma and not liquid, passengers may even be unaware that there has been a failure except for the fact that the arrival point is not that desired.

In short, while aircraft using rotating aerofoils are inherently less reliable than those with fixed aerofoils, bottom-line, they are inherently no less benign and even safer.

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