It's also wise to look at the engine power required column (in the spreadsheet). For the table 2A route, the highest engine power required is 1487 hp on segment 1. If your engines can't put out that cruising power at cruising altitude, then you can't fly the route with the conditions given. (And of course you actually need more power, because winds could be worse than the average values placed in the spreadsheet.) If your power is inadequate, you need more powerful engines, more efficient transmission, or a less power-demanding route.
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Now let's examine a wind-friendly route Table 3B). The simplest assumption is that we fly directly south from Cadiz through the westerlies and variables to 30oN (this is the shortest route to the trade winds zone), then fly directly (rhumb line, although great circle would be shorter) to Havana (completely within the trade winds zone), then directly north through the NE trades and variables to 35oN, and finally directly (rhumb line) to Cadiz (completely within the westerlies zone).
If the wind is unfriendly (segments 1 and 4), then we fly low (300 feet). If the wind is favorable enough so that the down-course component is greater than 30 mph (segment 6), we take advantage of this and set the ground speed accordingly. On segment 6 it's disadvantageous to fly a ground speed less than 52 mph, we want to "free balloon."
This time, the fuel requirement is 7.9 tons, only one-seventh that for the "brute force" strategy. While the route is longer, the total travel time is only 282 hours.
I experimented with the effect of flying NW, rather than N, in segment 4 (out of the NE trades). While this reduced the power requirement, it increased the distance even more so, and the net result was that it was less energy efficient.
Segments 1 and 4 have the least favorable winds, and we can reduce fuel consumption even further by reducing ground speed for those segments. If they were both reduced by 50%, the travel time would increase to 301 hours, but the fuel requirement would drop to 9.6 tons.
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Is it helpful to fly a great circle route? I replaced (Table 3C) segment 3 of the last example with a great circle approximation, four smaller segments (3-6), with intermediate waypoints at 25%, 50%, and 75% of the great circle route between where we entered the NE trades and Havana. This reduces the total distance to 10,178 miles.
For segments 1 and 7 (old 4), the wind direction is unfavorable, so it's advantageous to reduce the strength of the wind aloft, and hence we fly low. And for segments 6 and 9 (old 6), winds are favorable enough to mandate a ground speed higher than our 30 mph default.
The route is 75 miles shorter, 4 hours quicker, but less energy-efficient (8.4 tons fuel). Why? On segment 3 in table 3B, the CWV angle was a constant 39o. On the corresponding segments 3-6 in table 2C, it was 54, 44, 33 and 25o. Because of the nonlinear nature of drag, the higher angles on segments 3 and 4 hurt more than the lower angles on segments 5 and 6 helped.
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What if we replaced the return passage with a great circle approximation? Segments 1-5 are the same as for table 2B, whereas segment 6 is replaced with segments 6-9. On those segments, the ground speed is increased (48, 51, 51, 49, respectively) in view of the high down-course winds. Segments 1 and 4 are still flown low to minimize unfavorable winds.
The travel distance is 10,141 miles, and the travel time is 283 hours. The least efficient segment has a propulsive power of 363 hp and the best a mere 0.5. The total propulsive work done is 11,340 hp-hr. With the assumed overall efficiency, fuel consumption is 8.4 tons.
Why? The CWV angle for segment 6 on the table 2B route was a mere 1o! So the great circle return route, while shorter, will certainly experience more drag. The CWV angles aren't bad-5 to 20o-but they can't beat 1o.
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If those fuel requirements are still too high, then you need to bring down the speeds, increase the altitude, and/or shorten the route.
If you can't find a workable combination of route, set air or ground speed, and altitude, then you have to reexamine your airship design. In essence, use a more efficient engine (diesel instead of hot bulb, hot bulb instead of steam) or find ways to increase the propulsive efficiency.
Remember, the calculations above assume overall efficiency of 10%, so the fuel requirements are ten times what they would be with an ideal (100%) system. (Of course, an ideal system is impossible, but you can do better than 10%.)
Other Routes
There isn't space to discuss alternative routes in the same detail that I did Cadiz-Havana.
What I can do is give some idea of the magnitude of the task they present.
Spain-Peru. This is quite tricky. I imagine that the outward flight would feature a refueling stop at a Spanish holding in the Caribbean, possibly Hispaniola or Puerto Rico.
The obvious continuation is to take the northeast trades over the Amazon and on to Peru. There are two considerations here. The first is timing. Northern South America has a monsoon and the winds are from the northeast in January but from the east or southeast in July. The other problem is, how to you get over the Andes?
So, you say, let's cut across Central America. Fine. Now what? All along the South American coast, the winds blow north up the coast. Sailing ships had to beat down, but an airship will have to pour on the power (and consume a lot of fuel).
The return isn't much easier, because you're fighting across the entire north-south extent of the northeast trades.
Whether this airship route is worth it, to avoid the long watership haul around Cape Horn, remains to be seen. The Spanish didn't try; they shipped gold and silver up the coast to Portobello and then moved it overland across the isthmus for pickup by an element of the flota.
Europe-India. By way of example, the great circle route from Amsterdam to Chennai is almost entirely overland, although it does cross the Caspian Sea. Unfortunately, while it avoids the Himalayas, the Elburz Range and even the Plateau of Iran, not to mention the southward extension of the Hindu Kush, are quite high enough to cause problems. Hence, it's likely to be necessary to head south first, skirting the Alps, then follow the Mediterranean eastward, cross the Saudi Arabian Peninsula to the Persian Gulf, and then follow the coast to Gulf of Gambay. If the airship has sufficient cruising altitude, it can cross the Deccan Plateau, otherwise it must work its way around India. Timing will be important because of the Indian monsoon; the winter is the best time to be crossing the Arabian Sea if you need to make southing; however, if you must round the southern tip of India, the winds of the eastern (Coromandel Coast) are more favorable in April on. Winds aren't favorable for a return until November, and then you want to work your way over to the Red Sea and back to the Mediterranean.
India-China. Unfortunately, the great circle crosses quite a few mountain ranges. So we'd need to take a mostly oceanic route, which subjects us to several monsoon belts.
Europe-China. We probably would need several refueling stops for this to be feasible, but I can envision an overland route, more or less the great circle route from Amsterdam to Beijing. It passes north of the major Russian and Chinese mountain ranges. The winds on this route are mostly light, on the order of 4 m/s. Fly high on the way eastward (to maximize the westerly wind) and low on the return (to minimize it).
Mexico-Philippines. This would follow the standard Manila galleon route.