View Full Version : weights of different fluids

leeschaumberg

06-04-2008, 10:36 AM

Trying to find actual weights of fluids is very difficult unless you weigh them your self. As an example - What does 20-50 oil weigh? Whats the differance between mineral and synthetic? What does LL100 weigh a gallon? Having a good chart showing the weights of all fluids would be nice. Weights should be x.xx per (unit). If any body can answer some of these please feel free. Thanks Lee

John Clark

06-04-2008, 11:39 AM

Trying to find actual weights of fluids is very difficult unless you weigh them your self. As an example - What does 20-50 oil weigh? Whats the differance between mineral and synthetic? What does LL100 weigh a gallon? Having a good chart showing the weights of all fluids would be nice. Weights should be x.xx per (unit). If any body can answer some of these please feel free. Thanks Lee

The general rule is 6.0 pounds per gallon for 100LL and 6.8 pounds per gallon for engine oil. These numbers are close enough for most weight and balance issues. If you want to get technical you need to know the temperature of the fluids at the moment of the calculation. Gasoline weighs 6.15 pounds per gallon at 60 degrees F but can vary from 5.8 to 6.5 depending on the temperature. Motor oil weighs 6.8 pounds per gallon. For practical purposes, I just figure 2 gallons (8 quarts) in the BOW (basic operating weight ) of the airplane. Again, to know the true weight you would need to know the exact amount of oil in the engine and the temperature at the time of the measurement.

John Clark

RV8 N18U "Sunshine"

KSBA

Auburntsts

06-04-2008, 12:11 PM

If you really want the true weight you also have to factor in the pressure as density is affected by both temp and pressure. On a standard day 20W-50 weighs 7.34 lbs/gal. 10W-30 weighs a tad less at 7.26 lbs/gal and SAE 60 weighs a bit more at 7.49 lbs/gal. I derived this by taking a gander at the MSDS's of a number of brands (Aeroshell, Exxon, Castrol, and Phillips). To compare, water weighs 8.3 lbs/gal on a standard day.

Transporter

06-04-2008, 12:20 PM

For planning purposes, you can estimate using (these are US Army planning factors):

Gas: 6.103 lb/gal

Oil: 7.434 lb/gal

Water: 8.33 lb/gal

More accurate estimates for your specific brand/weight of oil, fuel, etc. can be derived by digging up the tech data for the product. Gotta do some math, since weight must be derived from the product density (usually expressed in kg/cubic meter or kg/liter at a specific temp.).

As an example, Aeroshell lists .892 kg/liter as the density for 40W at 15 degrees C.

Convert this into kg/quarts (using 1 quart=.9464 liter) giving 0.8441888 kg/qt; convert kg to lb (using 1 kg=2.2046 lb) giving 7.444394514 lb/gal. As always, YMMV.

Formula (formulae?) can be found on the web.

Good hunting,

Mike