Formula: {Minimum_Tank_xi = 25 liters = ca. 6.6 US gal}

The main (internal) LH2 tank 25 liters = ca. 6.6 US gal i.e. minimum tank here depicts the situation, where external LH2 tank is not being used

Volume LH2 tank = V_LH2MainTank = p×13.3²×46.3 = 25 717 cm³ = ca. 25 liters = ca. 6.6 US gal - main tank volume

Weigh of LH fuel itself: - LH2 as a fuel is not too heavy for Xi
~ d_LH2 = 0.07 kg/l - the density of liquid hydrogen
~ w_LH2 = d_LH2 × V_LH2Tank = 1.75 kg = 3.85 lbs

Weigh of LH2 tank: - the internal LH2 tank is not too heavy for Xi thanks to new composite materials
~ c_LH2 = 0.11 - LH2 mass presents typically 11% of the total mass of the LH2 tank
~ w_LH2 = 1.75 kg = c_LH2 × w_LH2Tank <=> w_LH2Tank = 15.91 kg = 35.0 lbs

Total Weigh penalty LH2: - the weight of LH2 liquid plus LH2 tank required is not too high and these figures are pessimistic
~ w_LH2Total = w_LH2 + w_LH2Tank = 17.66 kg = 38.85 lbs

Efficiency of LH2 as a fuel: - liquid hydrogen offers performance for aggressive and agile manoeuvres
~ b_LH2 = 4 - constant presenting the fact that four times more LH2 liters are needed compared to benzin
~ e_LH2 = 1.33 - constant presenting the fact that LH2 fuel is 1.33 times more efficient than benzin
~ E_LH2Tank = V_LH2Tank / b_LH2 × e_LH2 = 50.0 / 4 × 1.33 = 16.625 liter = 4.39 gal - benzin energy offered by LH2

Requirements for Xi: - are being met
~ Maximum_Flight_Time_xi
~ Maximum_Speed_xi
~ if Xi consumes LH2 25 l/30 min = 6.6 gallon/30 min, that equals to one tank of LH2 in 30 minutes
~ above means that Xi can fly 50 kilometers = 30 miles in 30 minutes with internal LH2 tank

catch ~Volume_Tank_xi ~Minimum_Tank_XCopter ~Xi!