to do with how it all behaves through waves. The action of the control system in waves, on the one hand, makes the Moth controllable, but on the other side if you have too much control it makes it slow. So it’s understanding what does what, and that’s the other side of Alan’s modelling.’ Smith continues: ‘Most people don’t really understand stability. The simple example is to think about a pendulum. If you put the pendulum and its weight absolutely perfectly over the top of a pivot point, the pendulum is actually stable, but it’s not going to stay there because any small movement is going to swing it right around to the bottom. And it’s only dynamically stable when the bulb weight is below the pivot.
‘Most people think you’ve got stability if the forces and moments acting on the
38 SEAHORSE
flight vehicle – and foiling yachts are flight vehicles – are in balance, which is not true. You’ve got to look at the dynamics; you’ve got to look at all of the derivatives, the position of the boat, the speed of the boat. All six degrees of freedom of motion have got to be stable for you to have a stable fly- ing machine, or a stable foiling yacht. And it’s only by doing the hard yards of what I call the rocket science part of the process that you get situations where you really understand the things that create stability. ‘If you wind the clock back to 2005/2006 there were a lot of things wrong with Moth design. The flap drive systems had a lot of friction, a lot of backlash; nobody knew exactly what sort of gain you should have between the movement of the flap and the movement of the wand. ‘The dynamic model sorts out these
issues. Today the gain system that’s on the Exocet Moth gives you a range of gain from about 0.1 to about 0.4, about a 4:1 change. ‘It was fairly apparent at the Moth Worlds in Australia earlier this year that not many of the guys even knew what gain change was about. The gain change mecha- nism on the Mach 2s is a very neat engi- neering design, but a very poor system from the point of view of stability. So the dynamic model is the thing that gives you confidence to make design changes in this area. The foiling yacht is in fact much more complex than designing a light aircraft.’ For this reason, perhaps, Smith takes his inspiration much more from the aeronauti- cal world than from sailing. After working at the Department of Defence in Australia, where he helped develop an early guided anti-tank weapons system for the British
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72