The British R 38 class, at present building, with a capacity of approximately 2 3/4 million cubic feet has an estimated endurance at 45 miles per hour of 211 hours or 8.8 days, which is 34 hours greater than the German L 70 class. It is evident that for a ship of this calibre the crossing of the Atlantic will possess no difficulty, and as an instance of what has already been accomplished in the way of a long-distance flight the exploit of a Zeppelin airship based in Bulgaria during the war is sufficiently remarkable. This airship in the autumn of 1917 left the station at Jamboli to carry twelve tons of ammunition for the relief of a force operating in German East Africa. Having crossed the Mediterranean, she proceeded up the course of the Nile until she had reached the upper waters of this river. Information was then received by wireless of the surrender of the force, and that its commander, Von Lettow, was a fugitive in the bush. She thereupon set out for home and reached her station in safety, having been in the air 96 hours, or four days, without landing.
It is therefore patent that in R 33 and R 34 we possess two airships which can cross to America to-morrow as far as actual distance is concerned, but various other conditions are necessary before such voyages can be undertaken with any prospects of commercial success.
The distance between England and America must be roughly taken as 3,000 miles. It is not reasonable for airship stations to be situated either in the inaccessible extreme west of Ireland or among the prevailing fogs of Newfoundland.
Weather conditions must also be taken into account; head winds may prevail, rendering the forward speed of the ship to be small even with the engines running full out. In calculations it is considered that the following assumptions should be made:
1. At least 75 per cent additional petrol to be carried as would be necessary for the passage in calm air, should unfavourable weather conditions be met. This amount could be reduced to 50 per cent in future airships with a speed of upwards of 80 miles per hour.
2. About a quarter of the total discharge able lift of the ship should be in the form of merchandise or passengers to render the project a reasonable commercial proposition.
We will consider the commercial loads that can be carried by the German airship L 70 and our airships R 33 and R 38 under the conditions given above. Two speeds will be taken for the purposes of this comparison: normal full speed, or about 60 miles per hour, and cruising speed of 45 miles per hour.
L 70.--At 60 miles per hour a distance of 3,000 miles will be
accomplished in 50 hours.
Fuel consumption about
13 tons + 9.75 tons (additional for safety) = 22.75 tons.
Available lift for fuel and freight = 27.8 tons.
Fuel carried = 22.75 "
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Balance for freight = 5 " about.
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At 45 miles per hour, distance will be
accomplished in 66.6 hours.
Fuel consumption about
10 tons + 7.5 tons additional = 17.5 tons.
Available lift = 27.8 tons
Fuel carried = 17.5 "
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Balance for freight = 10 " about.
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R. 33.--At 60 miles per hour.
Fuel consumption
14.25 tons + 10.68 tons additional = 24.93 tons.
Lift available for fuel and freight = 21.5 tons.
Fuel carried = 24.93 "
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Minus balance = 3. 43 "
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At 45 miles per hour.
Fuel consumption
9.66 tons + 7.23 tons (17 tons approx.)
Lift available for fuel and freight = 21.5 tons.
Fuel carried = 17 "
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Balance for freight = 4.5 "
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R. 38.-Estimated only. At 60 miles per hour.
Fuel consumption
20 tons + 15 tons additional = 35 tons.
Lift available for fuel and freight = 42 tons.
Fuel carried = 35 "
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Balance for freight = 7 "
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At 45 miles per hour.
Fuel consumption 12 tons + 9 tons additional = 21 tons.
Lift available for fuel and freight = 42 "
Fuel carried = 21 "
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Balance for freight = 21 "
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It will thus be seen that at the faster speed small commercial loads can be carried by L 70 and R 38 and not at all in the case of R 33, that is assuming, of course, that the extra fuel is carried, of which 75 per cent of the total does not appear at all excessive in view of the weather continually experienced over the Atlantic.
At the cruising speed the loads naturally increase but still, in L 70, and more particularly in R 33, they are too small to be considered commercially. In R 38, however, the load that can be carried at cruising speed is sufficient to become a commercial proposition.