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Aviation History
1985
1985 - 0096.PDF
occurs to me that it was only right and proper that they were awarded the propfan flight-test contract together with Lockheed. Between them they know everything there is to know about propeller noise. Nobody talks; nobody moves much. The facility for either activity is severely limited. Everyone just smiles and tries not to get in anyone else's way. Half an hour passes. I open a Cadbury's Peppy—a curious chocolate bar with peppermint marshmallow inside it. Another hour passes. It is now about 14.00. I resume my education on page 16 of A visitor's guide to Antarctica, issued by the New Zealand DSIR, by whose cour tesy I am to visit Scott Base in the south ern continent's Ross Dependency. "Sperm whales are polygamous", it says, "but Petrels and Skuas nest with the same mate every year"—all 100 million of them. The Royal New Zealand Air Force has only five Lockheed Hercules, whose longevity obviates the necessity to pro create. Twenty per cent of the fleet is still churning through the skies, headed due south at 210kt indicated (about 330kt true) some 28,000ft above the ocean. Navigational niceties I head for the spacious cockpit, to find that it is not much quieter than the back end. I glance at the instruments and discover that the aircraft commander, Sqn Ldr Murray Sinclair, is flying due south, while the copilot's panel indicates that we are flying due north. I shout and gesticulate to navigator Fit Lt Paul Simpson in an attempt to reconcile the paradox. Apparently, it is all to do with convergence of longitude, "grid" maps, inertial navigation systems, precessing gyro compasses, dip errors, star shots, and pressure patterns. Dozens of 747s fly across the North Pole every day of every week with their autopilots plugged into their infallible triplicated black boxes, but down south in a Hercules it is real polar navigation. So, back to basics. As you get close to the poles, the compass tries to point up or down to north rather than round to it, and the lines of longitude to which it might be related start to converge, with alarming rapidity, to the point of navigational impossibility. The best way round the problem is to cheat with your cartography by drawing a convenient map grid in which all lines of longitude are parallel, then distorting the land to suit. That way at least you know which way is south, even though the map may say it is north. Confused? Don't be; it is simple. I only had to ask four times before I understood it. The so-called "grid" maps are produced as lengths taken from a single strip which goes right round the Earth pole to pole. They have magnetic variation taken out, so they are related to true north. The one used by the RNZAF on its Antarctic runs just happens to be centred on the "Zero" Greenwich meridian which makes things easier to explain. The map starts at Greenwich and heads south down the "zero" line of longitude to the South Pole, but then continues south all the way back over the North Pole to London. If you are flying "real" south from New Zealand using one of these continuous strip "grid" maps, you will be flying north with respect to the map's convention. So there is no inconsistency between the captain of our Hercules flying "real" south with his instruments slaved to the INS, and the copilot flying north with respect to the map. The navigator faces both ways at once except when he is looking up to take a star shot with the sextant. The RNZAF Antarctic resupply flights all start from Christchurch, using a single inertial navigation system referenced to the captain's instruments and coupled to the auto-pilot. This prime reference is supplemented by air-to-ground radar fixes taken on various southerly islands at up to 230 miles range from the aircraft. Immediately after reaching top of climb the gyro compasses have their magnetic inputs removed, because the magnetic anomalies to be encountered later will be counter-productive. This gives the navi gator plenty of time to assess the gyro precession rates with reference to the INS and astro-navigation inputs. The gyros are then fed with instructions which coun termand their precession as the flight progresses. Dunedin VOR is the last usable short- range navigation aid. The next fix is by airborne radar on the Auckland Islands; then Campbell Island. There follows a leg where there are no terrestrial features, and starshots are needed to back up the INS (with a fall-back option to pressure pattern interpretation using a high-range altimeter). The Omega gradually becomes useless because its VLF ground-hop transmissions are absorbed by the approaching Antarctic ice. It is at around 65° south, however, that the critical decisions are taken. To go or not to go. The criteria are stringent, because the wrong decision will probably put the Hercules in the ocean through lack of fuel. Survival kit is carried, but the drill is simple—hold on to something heavy and get it over quickly. Before going beyond the point of safe return to Christchurch or Dunedin the captain must have HF communications with his destination at McMurdo, and all valid onboard navaids must be working and in agreement. The Hercules also needs to be mechanically perfect, because Antarctica is no place to have an unserviceable aircraft. The Balleny Islands must be on radar; and not only must the weather be good at McMurdo, but the trends must also be favourable. Antarctic weather can be fickle, blow ing up into intolerable conditions within hours, sometimes minutes. So, every hour for six hours before departure the weather comes in from McMurdo on the HF radio. Visibility from cruise altitude to the horizon is given when possible, as well as the surface visibility, to alert pilots to "white-out" conditions. "White-out" means white snow, white clouds, white sky, white everything. It can be totally disorientating and fatal. The Hercules is still three hours from McMurdo when it reaches the point of safe return. Paul Simpson takes a wind reading, as he has done every 15min for the last several hours. Besides providing trans- Chrislchurch Dunedin : I: Auckland Is (N.Z.U---" Campbell I (N.Z.) ROSS DEPENDENCY \ ' (N.Z.) | / Balleny is 24 Flight time for the 2,000-mile trip between Christchurch and McMurdo is usually 7hr to 9hr, depending on wind. Southbound, the point of safe return is at about 65° south. Crews use "grid" maps with convergence of longitude removed. Fourteen round trips were made in 1984 port, the crew is collecting statistical data for one of the atmospheric research teams. Outside it is -46° at our 28,000ft cruise altitude. I see a classic practical demon stration of what I learned from a textbook years ago—the upper air is warmer at the poles than over the tropics. Paul puts it another way—the tropopause has dropped from 36,000ft over New Zealand to 22,000ft as we cross the Antarctic coast at 14.50 to head over the frozen promentory of Victoria Land. The white is so bright that it throws the cockpit into silhouette, and it takes goggles to distinguish any geographic features. Victoria Land lasts for 40min. Then there is to be another l hr of pack ice before we land on the frozen Ross Sea. Paul produces a graph showing the „ tropopause descending. The air only gets progressively colder up to the tropopause; i thereafter—in the stratosphere—it stays at roughly constant temperature. This is * why we have not climbed to the normal ^ temperate-latitude cruise altitude of 30,000ft. There is no point; the air will not > get any colder up there, so the engines will not become any more efficient. They will * still burn about two tons of fuel per hour. ,. I leave the crew to prepare for their descent, and return to the artificial gloom ' in the economy cabin. In Georgian , England there was a window tax which was quite lucrative until people started 4 bricking up their windows. I begin to -> wonder whether Lockheed works under similar legislation. About 160 miles out from its desti- * nation the Hercules will pick up the 4 McMurdo Tacan beacon. In the back there are now signs of movement—people ' FLIGHT International, 12 January 1985*
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