Last week I was in Cranfield participating in the Aerospace Challenge Finals. The challenge this year was to come up with a design for a device to drop humanitarian aid accurately (within 20 metres of a target) from 3000 metres up. Our idea managed to make it to the finals which turned out to be a week of lectures on general aerospace engineering, activities and flying! Photos are here.
Each person got two flying experiences, both of which included some time piloting the aircraft: about 10-20 minutes in a helicopter and about half an hour in a fixed-wing plane.
My first flying experience was with a small Robinson helicopter, which can only really be described as terrifyingly, exhilaratingly awesome. The pilot managed the take-off which was one of the most breathtaking experiences I’ve ever had – in a helicopter you’re literally sitting in a big transparent flying bubble with the engine behind you, so the view and experience is truly amazing as the land falls away beneath you… I later took over and found control extremely difficult – even a tiny movement of the stick causes the vehicle to tilt violently in that direction making a beginner like me very prone to overcorrection leading to a serious case of increasing-amplitude SHM! The actual stick is situated between the pilot and the copilot and a rotating handle is stuck on the end allowing dual control, so my rather flailing and uncontrolled flight was abruptly and expertly rectified when the pilot took control (though not before I turned and prepared to land by erratically lurching towards a patch of grass). The pilot then demonstrated some cool things one can do with a helicopter including skid landing and take-off, going backwards and sideways while spinning etc.
The next day I got in a PA28 – my first fixed-wing experience. The pilot had to go through an enormous list of things to check before taking off and explained a little about what she was doing (mostly checking the engine could rev at certain RPMs and wouldn’t give out in certain situations, flicking on and off various lights and calibrating [and pointing at] instruments). The runway was also ridiculously long so she didn’t even bother with flaps for takeoff. This was much easier to fly than the helicopter and the dials and instruments in the cockpit didn’t obscure the view as much I had inferred they would from MS Flight Sim’s portrayal. I did a few rather ginger turns and pitch adjustments before relinquishing control back to the pilot who then demonstrated some steep banks, a stall (which sounded dangerous and seemed to imply the engine cutting out) and a dive (which was extremely cool). Later that week Matthew and I were inspired enough to ask about possible places to get flying instruction – flying has always been one of those things I’ve wanted to learn but I’ve always ended up not having enough time or money to start…
The week started with some group leadership exercises which consisted of attempting to place 30 cards in the correct pattern (easy) and work out the shape and colour of two missing shapes while blindfolded (hard) – both were much more enjoyable than I had expected from that genre of exercises.
The first engineering challenge we were given was an egg-drop challenge – the idea was to construct a package which will protect an egg from a drop of 4 metres. We were given limited materials and each material had a price; the idea was to make the cheapest package that doesn’t crack the egg. Our attempt turned out to be the most epic non-fail in history – literally seconds before the end of the construction phase we managed to pop two balloons which made us completely change our plan and in the last few seconds and in great haste we crammed stuff into a crumple zone and added a parachute … and it somehow worked and turned out to be the cheapest package (if wastage is deducted)! I guess that really proves the KISS principle: Keep It Simple Stupid.
The second engineering challenge was along similar lines – dropping aid – though it was from a more macro perspective. The game was called ‘airlift’ and sold by Elite – the idea was to plan an air route through several African villages which uses the least fuel, while dropping packages of aid which we had to construct out of wooden blocks, paper and tape while making sure everything fits in the cargo hold. The first thing I pointed out when time started was that both problems were NP-complete: the packing problem was almost exactly the same as the knapsack problem and the route planning was basically the Travelling Salesman problem with fuel added in as a factor. In other words we had to be either very good at intuitive problem solving or somehow get lucky. As it turned out, as perhaps a combination of the two, we somehow managed to come up with both the the optimum packing configuration as well as the best route, and finished literally as the final buzzer went – not bad!
The rest of the week was dotted with things like paper plane competitions (which included an awesome flying paper ring which seems impossible when you first see it fly), a game of (actual) CTF and some sports.
Over the week there were daily lectures. Much as I would love to discuss them all here in depth I haven’t got that much time / space and besides most people aren’t as interested as I am in the effect of negative angles of attack… But I’ll go a little into some of the most interesting lectures.
Fly by Wire (FBW)
The problem for a long time had been that when going sufficiently quickly, adjusting the controls from the cockpit was really quite hard work – the air going past has so much momentum and the mass flow rate is so high that to change its direction by (for example) adjusting the ailerons requires a lot of force. To make things worse, at supersonic speeds a shock cone is developed (some awesome videos of this are on Youtube) – if this touches the aileron the stick can be wrenched out of the pilot’s hand. Some of these controls were partially solved by making the stick adjust small tabs in the wing instead of the entire aileron, reducing the force required to steer, and by making controls non-reversible (force on the aileron doesn’t affect the flying stick). There are of course some problems with these such as lack of ‘feel’ of the controls. So recently manual stick-aileron transmission was replaced with an electronic motor which receives instructions from the cockpit and adjusts the ailerons itself. Not only does this take all the strain off the pilot, but it also allows a computer to neutralise bad judgements on the part of the pilot such as initiating a sharp dive at 50 feet, implemented by a feedback mechanism from the aircraft to the computer. It also simplifies the cockpit – instead of filling the area with controls, dials an instruments, a computer screen with a joystick and throttle suffices to fly a FBW plane. I asked whether, since FBW significantly reduces the pilot’s direct control over the aircraft, FBW might actually make complicated manouevres more unsafe or indeed completely impossible. John Farley, who was giving the talk, said that, from his vast experience, pilots, however experienced, cannot really be trusted to fly planes safely all the time, and in fact he would feel safer trusting a computer’s judgement and letting a computer do such manouevres than a pilot. That talk also proves that a Boeing 747 probably has non-reversible controls so that scene in Snakes on a Plane (I think it was that film) in which the pilot asked the co-pilot to help pull back on the stick very hard was probably a load of rubbish. Not that you needed to be told that.
One of the interesting things from this talk was the reasoning for why helicopters don’t go fast. There is always one part of the rotor going forwards, and if the helicopter moves forwards sufficiently quickly that part of the rotor travels at supersonic speeds generating a shockwave that could rip apart the rotor. In addition, even at lower speeds, there is an imbalance between the airspeed of the fowards-going part and backwards-going part of the rotor meaning a gimbal has to change the angle of attack of the blade depending on which way it’s going: the angle of attack of the rearwards-going blade has to increase to increase lift on that side otherwise the helicopter would just roll over. Of course, there is a maximum angle of attack this blade can be set to before it stalls which is about 20°. This limits the helicopter’s speed at subsonic speeds.
Automation and the future
This was probably the most interesting talk of the week; unfortunately it was cut short for us owing to a jetstream flight. Apparently currently pilots of Euro Fighters get sensor fused info presented to them in the form of advice as to what to do and they simply act upon that, which means half the time the plane is telling the pilot what to do: it is telling the pilot how to control it: semi-automation. Even in commercial aircraft a system called TCAS (Traffic Collision Avoidance System) senses other aircraft and advises the pilot on how to manoeuvre. There is clearly room for improvement: unmanned aerial vehicles are coming. This of course led to the whole humans v computers discussion but for every example of a pilot doing something heroic and saving the plane, there are several examples in which pilots screwed up and computers would have saved lives – Chris Roberts, the speaker, asked whether it *really* is desirable to have a pilot flying the plane, and whether the problem of pilots becoming de-skilled from letting the autopilot take over really is such a problem after all. I also found it very interesting and surprising that currently many landings of commercial aircraft are performed by the autopilot in low-visibility situations.
Anyways overall it was a fantastic week. Whatever the results of the competition turn out to be, I for one got a lot out of six days in Cranfield. I learnt a lot, made some friends, made some good contacts in the industry, and had some great fun relaxing in the English countryside!