Formula: **{Fuel_xi = LH2 (Liquid Hydrogen}**

**Liquid hydrogen (LH2) fuels Xi at remote theaters for agile, aggressive & autonomous manoeuvres.**

**Xi dimensions:**

~ **L**_{Xi} = 231.648 cm - the length of the Xi

~ **D**_{Xi} = 33.538 cm - the diameter of Xi

**The challenge is to fit the LH2 tank inside Xi and keep it light enough:**

~ **L**_{LH2Tank} = 46.3 cm - the length of the LH2 tank

~ **D**_{LH2Tank} = 26.6 cm - the diameter of the LH2 tank

~ **R**_{LH2Tank} = 13.3 cm - the radius of the LH2 tank

~ **V**_{LH2Tank} = p × **R**_{Tank}^{2} × **L**_{Tank} = 25 717 cm^{3} = ca. 25.0 liters = ca. 6.6 US gal - the volume size of the internal LH2 tank

**Weigh of LH fuel fitting inside LH2 tank:** - LH2 as a fuel is light 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:** - LH2 tank is not too heavy and thanks to new composite materials will be lighter

~ **c**_{LH2} = 0.11 - LH2 mass presents typically 11% of the total mass of the LH2 tank

~ **w**_{LH2} = **c**_{LH2} × **w**_{LH2Tank} <=> **w**_{LH2Tank} = 15.9 kg = 35 lbs

**Total Weigh penalty LH2:** - not too bad and these figures are pessimistic, see XCopter

~ **w**_{LH2Total} = **w**_{LH2} + **w**_{LH2Tank} = 17.66 kg = 38.85 lbs

**Efficiency of LH2 as a fuel:** - offers performance for aggressive and agile manoeuvres

~ **b**_{LH2} = 4 - constant depicting the fact that four times more LH2 liters are needed compared to benzin

~ **e**_{LH2} = 1.33 - constant depicting the fact that LH2 fuel is 1.33 times more efficient than benzin

~ **E**_{LH2Tank} = **V**_{LH2Tank} / **b**_{LH2} × **e**_{LH2} = 8.3 liter - the benzin energy provided by the main LH2 tank

**Requirements for Xi:** - are being met

~ Maximum_Flight_Time_xi

~ Maximum_Speed_xi

~ if Xi consumes LH2 50 l/h = 13.2 gallon/h, that equals to two LH2 tanks

~ above means that Xi can fly 100 kilometers in one hour (ca 60 miles/hour) with two tanks of LH2

~ due to it's aerodynamic shape Xi needs one external LH2 tank for one hour mission

**Specifications:**

~ Hydrogen power @Xi

**Information:**

~ LH2!

catch ~Fuel_XCopter
~Xi!