Flight Computers

By Andrew Herd (15 February 2002)

ne area where flight simulation isn't "as real as it gets" is where route planning is concerned. Flight Simulator is fitted with automatic flight planning software which means that getting from A to B is as easy as selecting Meigs in the departure airport box and Gen. Mitchell Int'l in the destination box, checking "direct GPS" and hittting "find route". In return, you get a neatly annotated flight plan that will always get you to your destination, assuming you have still air and pay some kind of attention to the direction indicator. The really laid-back among us don't even have to go that far - all they have to do is engage the autopilot and read a magazine until the destination shows up. Of course, you can complicate things a bit, by loading real weather and entertaining yourself working out what the heading offset should be to maintain track, but ultimately, in Flight Simulator, getting lost isn't such a big deal.

When you are sitting in a real aircraft, sandwiched in between two layers of filthy stratocumulus, out of sight of the ground and the sky, with nothing but your own company and a basic panel to rely on, the quality of a flight plan takes on a whole different meaning. An altitude of 2500 feet is not the place to suddenly start doing fuel calculations, plot courses to alternates, or worst of all, start worrying about where you might actually be.

Ah yes, you say, but what about GPS? Yeah. Well there are people I know who rely on GPS everywhere they go and who never do a written flight plan if they can avoid it, but there are areas in this world of ours where GPS does not work. This is one bit of reality which Flight Simulator doesn't emulate, bless it, but if I take off from Teesside and fly north-west I can rely on losing the GPS signal not to far north of Carlisle - and that is in the UK. As bush flyers are all too aware, the one thing you can rely on is the signal dropping out on you just when you need it most and in some areas of the world, GPS navigation is not an option. Another reason for not relying on GPS totally is that they eat batteries - four hours is a typical operating time before you need a new set of cells. Just imagine what it feels like to realise that you didn't replace the set you used to power the kid's GameBoy back up...

Neither can you expect to find navaids everywhere you fly and there are peculiarities of beacons which FS doesn't emulate, such as propagation error and coastal refraction. In addition, navaid reception isn't quite the on/off thing that Flight Simulator makes it out to be and it is normal to experience quite long periods when you aren't quite sure whether you have got adequate reception or not, let alone the alarming fact that the best way of identifying the bearing to the nearest thunderstorm is usually to look at where the ADF needle is pointing.

So, my rather long winded point is that if you are looking for ways to make flight simming that little bit more like the real thing, or if you are thinking of learning a bit more about navigation, you might look into the idea of buying a flight calculator. Although the first mantra most PPLs learn puts aviating before navigating, well prepared pilots always plan, unless they are just doing the most local of trips. The reason for this is that if all else fails, a good flight plan can get you home with little more than a compass and a wristwatch. The question "Where am I?" is not one that you should be asking when you are on a collision course with controlled airspace. If you are looking to push the boundaries of your flight simulation a little more, then navigation is a satisfying way to do it and it is a skill that will stand you in good stead if you ever take up real aviation. If enough readers are interested, I will look at the basics of navigation in some later articles.

The most basic type of flight calculator available is the circular slide rule, aka whizz-wheel. For a long while it was the only type of flight calculator available, but in the late seventies or thereabouts, the first truly portable electronic calculators appeared. Whizz-wheels can still be seen, partly because in expert hands they are nearly as good as an electronic calculator, but chiefly because they work come rain, hail or snow. For this reason it is necessary to understand how to use one for the JAR exams in Europe, and for all I know, for the FAA exams too. Search through a wise pilot's flight bag and you will usually find one in there somewhere. The problem with whizz-wheels is that most people find them hard to get to grips with, literally and figuratively. Doing a wind triangle on a circular slide rule requires both hands (my wheel has a tendency to stick, so I have to use my chest to push the wind slide), the ability to make reasonably precise pencil marks and, of course, you need to switch the lights on to see read the result at night. I guess that the days of this long-fabled tool are probably numbered, but if you get the chance to watch a real expert use one, take it, because these guys can work stuff out at a speed that takes your breath away. Sure, there is no way a slide rule can be as accurate as a calculator, but such differences as do arise are always well within the limits of error of flight.

Which brings us to electronic calculators. I can't remember when I first saw one, but I would hazard a guess that it was around twenty years ago. They were bigger then than they are now and they used up batteries faster than a Lear drinks Jet A-1. But even in the eighties, they did pretty much all the calculations you needed. One of the reasons I am writing this is because although twenty years of experience means that all electronic flight calculators should be easy to use, they aren't all born equal in this respect.

The market leaders are the Jeppesen TechStar and the Air Classics CX-2 Pathfinder. We will start with the TechStar, because that is what I did. The TechStar measures around 145x75x35 mm - I didn't bother to weigh it, but it is manageable. The machine is thicker at the top than at the bottom, so when you lay it on a desk, the screen is angled towards you, and the calculator comes in a floppy plastic slip case that lasts about ten seconds of normal use. Power is provided by four AAA batteries, held in by a cover which wouldn't shut on the first machine I possessed and won't open on the one I currently own. Power management is good, the batteries last a reasonable time, helped by the fact that the computer shuts down automatically when it hasn't been used for a few minutes. The screen is a generous 48x72 mm, but it lacks any kind of backlighting at all and the display quality seems to vary from TechStar to TechStar. The first one I had was unreadable in any light, the one I currently own is OK, though I wouldn't describe it as bright. There is a small manual - which should not be lost under any circumstances - and a fold out tree view of the menu structure which is enough to frighten most normal people half to death.

The first thing that you will notice about the TechStar is that it is designed to be used lying on a desk and its slight top-heaviness means that it is inclined to take a dive for the footwell and get jammed behind the rudder pedals if you don't keep a firm grip on it in flight. After switching it on, you fire it up by pressing the mode key, then use what I can only describe as a series of line select keys (LSKs) on the right to step through the menus until you have found the calculation you need. All entries are made in a scratchpad area at bottom right of the screen and line selected up - then, once you have filled in all the slots, you press the comp key and after a surprisingly long pause, the TechStar grinds out the answer. You can transfer computed values to the scratchpad by pressing the "rcl" key and then the LSK next to the value - allowing you to store a number and use it in the next calculation. It would appear that a different team designed the conversions section, because this relies on the reverse system used for the nav stuff - to convert nautical miles to statute, you enter the distance in the scratchpad, line select it to the NM line, then press "cmp" and then press the LSK opposite the statute miles line. If this all sounds needlessly long-winded and counter-intuitive, it is. While there is no doubt that the TechStar does the job it is meant to do, the menu system could be vastly improved; the keys are fiddly; the ergonomics need a radical overhaul; and LSK data entry, while it might seem instinctive to jet jocks, is cumbersome, requiring you to use both hands unless you happen to have fingers eight inches long with four joints.

Broadly, the functions of the CX-2 and the TechStar are comparable - some of the extras on the CX-2, like the ability to calculate cloud base from dew point and OAT are of questionable value when you can just go outside and eyeball it, but for me the TechStar wins here, despite its lack of a reciprocal function, because it has much better support for non-US measurements like imperial gallons.

Now for the CX-2. This is a very different animal to the TechStar and appears to have been designed by someone who has actually been in a light aircraft at least once. Overall dimensions are much the same as the Jepp at 155x85x25 mm, weight is about the same, but the CX-2 has a hard plastic case that completely protects the keyboard and screen and which can stand some seriously hard knocks. Push off the cover and you are confronted with a bold keyboard, with finger sized keys and 58x40 mm screen, which has a broad range of contrast adjustment. Display quality is good by comparison with the TechStar, though the viewing angle is narrower than I would like. Power is provided by four AAA batteries, the machine switching itself off after seven minutes without a key press and it will warn you when it is down to an estimated hour of remaining use. The build quality is very good indeed, ahead of the Jeppesen by a comfortable margin, but where the CX-2 really excels is in the ergonomics. This pup is such a delight to use that I am willing to forget that they don't appear to realise that aviation occurs outside the continental US.

There is a single manual, which is extremely well written, but I doubt you will have much need to refer to it once you have used the CX-2 for any period of time. Air Classics say that the machine has been designed to flow data entry the way it naturally would for a paper flight plan and they are quite right. The ergonomics of this computer put the TechStar to shame - the best thing being that calculations are automatically transferred from screen to screen without any need for the LSK shuffle that Jeppesen's device demands. In addition, the keyboard has been carefully designed so that one handed operation is possible, which means that real pilots (i.e. those of us who can't afford autopilots) can use it in flight without clamping the yoke between our knees. For example, when you need a "shifted" function of a key, you press the "2nd" key and then press the key with the superscipt function you need - you don't need to press the two together. There are no LSKs, no "comp" or "rcl" keys and you just go from calculation to calculation by pressing the down arrow or enter. Some genius has programmed the CX-2 so that if you suddenly realise that you need to do a unit conversion, you can actually do it there and then in the middle of the calculation you were doing without going through any kind of a scratchpad, and (no, I don't have shares in the company, but I do like the CX-2) it remembers values from one session to the next, so that you aren't always having to input a cruise speed and fuel burn that never vary. Best of all, when you hit enter, the answer appears, just like that. In short, I love the CX-2 to death and the designers need some kind of award for services to aviation.

I guess my preference is pretty clear. If you have a TechStar, hang onto it, it is a good machine. But the CX-2 is better and even if it doesn't support quite such a wide range of units as the Jepp does, I would put it first on my list if I was buying new. Maybe the release of the CX-2 will spur Jeppesen on to redesign the TechStar - the company has such a reputation for leading the market that I can't see them taking this challenge lying down, but for now, the Air Classics CX-2 is king.

Andrew Herd
andrew@flightsim.com

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