Pressurant tanks, crude vehicle model

For the vehicle, I’m considering downsizing from 5 gallon propellant tanks to 3 gallon tanks and from 250 lbf thrust to 180 lbf. Low Rider Depot makes a 3 gallon version of the 5 gallon tanks I’ve had success with and I purchased one for burst testing. Assuming engine thrust = 180 lbf, Isp = 140 seconds, O/F = 1.1, and runtime is 20 seconds, I’ll need 1.865 gallons of ethanol and 1.414 gallons of LOX. I’ll need high pressure tanks to hold the pressurant and equations from Sutton Chapter 6 and H&H Chapter 5 yield similar answers for the required volume: 0.79 to 0.92 gallons of nitrogen at 2000 psi per propellant tank (pressurantSupply). Based on the dimensions I could find (OD = 4.3 inches, height = 16.5 inches), the volume of a D size medical oxygen cylinder is ~1 gallon, so I’ll need 1 of those cylinders per propellant tank. Here’s a crude version of the vehicle with the 3 gallon propellant tanks and the D size medical oxygen cylinders. The vehicle is roughly 50 inches (129 cm) tall.


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