In aviation, fuel quantity and fuel consumption can be expressed in:
Conversions between volume (litres, USG, or Imp. gallons) and weight (kg or lbs) is a necessary skill as you will find, for example, American aircraft flight manuals using US gallons but the European refuelling equipment using litres. This is covered in the next lesson.
Specific gravity is a term used to describe how much a certain liquid weighs. The standard aviation fuel for piston engines is known as AVGAS. The specific gravity of AVGAS changes slightly with temperature but we typically assume AVGAS has a specific gravity of 0.72.
This means that 1 litre of AVGAS weighs 0.72kg or 720 grams.
So to calculate the weight of your AVGAS, you can multiple the quantity in litres by 0.72. For example, if you have 75 litres of AVGAS on board, the weight is:
Fuel requirements for PPL flying are found in the regulations under Part-NCO (non-commercial operations). Specifically, NCO.OP.125 says that for non-commercial operations we are required to carry sufficient fuel to fly to the aerodrome of intended landing plus fuel to fly at normal cruising altitude for an additional 30 minutes during the day or an additional 45 minutes at night.
“Fuel to fly to the aerodrome of intended landing” includes all the fuel required for engine start, taxi, takeoff, climb, cruise, descent, approach, and landing.
However, the above is an absolute minimum requirement and many flight schools will follow the good practice of requiring:
Each flight school’s policy varies so make sure to check with your instructor!