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How to Determine the Lift Buoyancy of Heated Air

Air that is hotter than the surrounding air volume will tend to rise. If this air is trapped in a volume, then the volume of air will generate lift. This the principle of hot air balloons and is the same as the buoyancy principle of the objects submerged in water.

Instructions

- 1
  If the known values of temperature for the ambient air (Ta) and the lifting air (Te) are in Fahrenheit, convert to Celsius by subtracting 32 and dividing the result by 1.8. Likewise, convert cubic feet of the lifting volume (V) to cubic meters by dividing by 35.315. If the air pressure reading (P) is in inches of mercury, convert to hectoPascals (hPa) by multiplying by 33.86.
- 2
  Compute the lifting force of the heated air with the formula:
  
  Fb = V * (P/2.87) * [(1/Ta) - (1/Te)];
  
  where V = Volume in cubic meters, P = pressure in hPa, Ta = ambient air temperature in degrees Celsius, and Te = temperature of lifting air mass in degrees Celsius. The force of buoyancy, Fb, of the heated air is in kilograms.
- 3
  Compute the value of Fe, which is the downward acting force of the envelope enclosing the heated air mass, plus the weight of the loads carried by the lifting mass. Total these weights in kilograms. If the weights are in pounds, convert to kilograms by multiplying by 0.45359. The total lift of the heated air and the envelope is then:
  
  Lift = Fb - Fa; where Lift is in kilograms, and Fb and Fa are described above.
  
  If lift is negative or zero, then the buoyancy of the lifting mass, Fb, is insufficient to make the system ascend.

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