21 Rules that effect Gas Balloons Lift

Rule 1:  Lift of a balloon varies with volume if all other conditions affecting  lift remain constant.

Rule 2:  Lift of a given volume of gas increases if barometric pressure increases.  Lift decreases if barometric pressure decreases.

Rule 3:  Lift of a given volume of gas will decrease if atmospheric temperature increases and will increase if temperature is decreased.

Rule 4:  The higher the atmospheric humidity the less lift you will have.

Rule 5:  There is no change in equilibrium due to a change in barometric pressure when the gas is free to expand.

Rule 6:  Where air and gas temperature change an equal amount there is no change in equilibrium if the gas is free to expand.

Rule 7:  A balloon in equilibrium at any altitude will be in equilibrium at the Surface, providing no weight is lost or gained and the superheat value is not changed in the decent.

Rule 8:  A balloon rising from the surface in equilibrium will be at equilibrium at any altitude below pressure height if no weight is lost  or gained and the superheat value does not change.

Rule 9:  Barometric pressure will decrease approximately 1 inch for every 1000 feet of ascent in the lower atmosphere.

Rule 10:  Atmospheric temperature will decrease approximately 1 degree F for every 300 feet ascent, or 3.5 degrees for every 1000 feet ascent.

Rule 11: Gas volume is changed 1% for every 5 degrees F change in gas temperature.

Rule 12:  Gas density is changed 1 percent for every 5 degrees F change in gas temperature.

Rule 13:  One percent in gas density or specific gravity for hydrogen changes the lift 1/10 % when at pressure height.

Rule 14:  One percent change in gas density or specific gravity of helium changes the lift 2/10 % when at pressure height.

Rule 15:  At pressure height the lift will change only 1% for 20 degrees F superheat with helium and 1 % for 45 degrees F superheat with Hydrogen.  This shows the danger in going from maximum daytime superheat conditions to zero superheat value at night if not properly understood or counteracted.

Rule 16:  Lift is changed 1% for every 5 degrees F change in superheat in flight if the gas is free to expand.

Rule 17:  (1) 5 degrees F superheat will lower pressure height 360 feet at  altitudes below 7000 feet.   

 (2)     5 degrees F superheat will lower the pressure height 400 feet  at altitudes above 7000 feet.

Rule 18:  In an ascent under average atmospheric conditions the gas volume will increase 1 % for every 360 feet of ascent rising to 7000 feet and will increase 1% for every 400 feet above 7000 feet.

Rule 19:  In going above pressure height lift is reduced 1% for every 360 feet below 7000 feet and 1% loss for every 400 feet when above  7000 feet.

Rule 20:  1 % of the original mass of gas is lost in going 360 feet over pressure height when below 7000 feet and 1 % is lost for every 400 feet when above 7000 feet altitude.

Rule 21:  If, when full of gas, 1 % of lift is thrown over as ballast, equilibrium will be reached when 1 % of the gas has been valved.

Rules are from the Technical Manual of Aerostatics - TM 1-325 - War Department 1940.