The necessity to carry more fuel drives size, weight and cost of long-haul aircraft up disproportionally. For example, 2017 Boeing 737 MAX 9‘s flight range is 6,570 km for 144 seats model, which is listed at $129 m. Long-haul 2020 Boeing 777-9X‘s flight range is 13,300 km for 395 seats model, which is listed at $442 m. Accordingly, 777’s seat specific price is greater than that of 737 by [(442/129)/(395/144)], i.e. around 19%.

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This example shows that one seat in a long-haul aircraft is typically more expensive then that in medium-haul airliner. The reason is that the longer the aircraft’s flight range is, the greater the weight of fuel it carries is. To put it simply, a long-haul airliner has to burn more fuel per unit of distance to carry its greater volume of fuel. In order to keep long-haul aircraft’s seat-specific fuel economy within reasonable limits, long-haul aircraft have to carry more passengers, and thermodynamic efficiency of their power-plants needs to be greater than that of middle-haul aircraft.

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It is common knowledge in the industry that developing and manufacturing long-haul aircraft is the risky business. Closed AG-Cycle will mitigate the problem by making contemporary long-haul aircraft irrelevant, by integrating Closed AG-Cycle into power-plants of medium-haul aircraft, thereby doubling their flight ranges without sacrificing useful payloads, and improving their fuel efficiency by around 55%. A more detailed analysis is presented below.

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AG-converted aircraft’s fuel capacity, though, won’t rise proportionally, i.e. by [1/0,55], i.e. 2.25 times, because water recovery unit will take on part of the weight. Almost 100 year ago, the US Air Force made a research on water recovery from exhaust of reciprocal 400 hp IC engine, installed on a helium airship. The experiments revealed the empirical ratio for an airship moving at a speed of 45 MPH in the temperature of 15 C, and having water recovering unit’s capacity of around 90%: 1 lbs (0.4536 kg) per 1 hp.

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Estimates show that for contemporary aircraft this ratio is lower than that in the airship. Contemporary passenger aircraft’s speed is around 12 – 13 times greater, and the temperature at their flying altitudes is around 70 C lower, i.e. heat transfer is more intensive. Thermal efficiency of aircraft’ turbofan is at least twice as high as that of airship’s IC engine, i.e. exhaust has around 30% lower heat energy content per unit of power.

Since combustion of one kilogram of hydrocarbon fuel produces around 1.4 kg of water, exhaust contains around [(1+1.4)/1.4], i.e. 71% more water vapor, which means that 45% recovery rate will suffice, instead of airship’s 90% recovery rate. Estimates show that for contemporary aircraft the ratio at the higher end is [1*0.7*0.45], i.e. 0.315 lbs (0.143 kg) per 1 hp, even without taking into account higher temperature difference, higher speed, and advancements in heat exchange technology during last 100 years, which were remarkable.

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At a cruise speed Boeing 737 MAX 9’s turbofans produce 19,600 hp of power. The estimated weight of a water recovery unit is [19 600*0.143], i.e. 2,800 kg, which constitutes [2,800/25,817], i.e. 10.8% of airliner’s fuel capacity. The core thrust of the up-to-date LEAP-1B, installed on Boeing 737 MAX 9, accounts for around 10% of the overall thrust. Since the large portion of this thrust will be lost due to the back pressure of a water recovery unit, the estimated fuel consumption reduction would be directly proportional to estimated increase of engine’s thermal efficiency, i.e. around [2.5*0.9], i.e. 2.25 times, which is equivalent to around 55% reduction in fuel consumption.

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If the weight of a water recovery unit is included in aircraft’s fuel capacity, its range would increase by [2.25*(1-0.108)], i.e. by a factor of 2, up to [6,570*2], i.e. 13 140 km, which is close to 13 300 km range of long-haul Boeing 777-9X. Flying on such modified Boeing 737 is expected to be more accommodating due to sufficient supply of water for maintaining comfortable humidity in a cabin.

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A typical long-haul aircraft’s average flight time is around 15 hours a day. If 2017 Boeing 737 MAX 9 with fuel efficiency 2.91 kg/km flew long-haul flights for 20 years with a cruise speed of 839 km/h, and the cost of jet fuel would be the same as annual average cost of jet fuel in 2019, $2 per gal,  the cost of the overall fuel consumed would be [15*365*20*839*(2.91 /0.8/3.785)*2], i.e. $176.6 m. If  Boeing 737’s power-plant was enhanced with AG-Cycle, this cost would be around 55%, i.e. $97 m less. Since an actual value price of 2017 Boeing 737 MAX 9 (before grounding in 2018) was less then $97 m, AG-Cycle will reduce 737’s actual value price down to zero.

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Supercritical Carbon Dioxide (S-CO2) power plant is believed to be used on serial hybrid aircraft in the foreseeable future. According to Meridian International Research, S-CO2 would reduce contemporary aircraft’s cruise specific fuel consumption (SFC) to 0.37 lb/lbf/hr, which is around 30% lower than that of the turbofan with the best specific fuel consumption in class, LEAP 1B‘s 0.53 lb/lbf/hr. Accordingly, paring S-CO2 with AG-Cycle would allow for further reducing specific fuel consumption to [0.37/2.25], i.e. 0.164 lb/lbs/hr.