Weight & balance unusable fuel.

[Will.iam]

Was just curious why you can not weigh the airplane empty and then just mathematically add the 3 gallons of unusable fuel to make the empty weight?

[EricJ]

36 minutes ago, Will.iam said:

Was just curious why you can not weigh the airplane empty and then just mathematically add the 3 gallons of unusable fuel to make the empty weight?

You can, you just need to make sure it's actually fully empty, maybe by removing the sump drains and shaking it a lot.    You can also weigh it full and subtract it down to unusable, which is usually the easiest path.

[Will.iam]

On 12/2/2024 at 10:12 PM, EricJ said:

You can, you just need to make sure it's actually fully empty, maybe by removing the sump drains and shaking it a lot.    You can also weigh it full and subtract it down to unusable, which is usually the easiest path.

Thanks. I figured both fuel caps off and drain plug removed with a shop vac blowing air through the wing would expedite evaporation of any fuel that might still be left in the tanks after the drain. Outside of course with a long shop vac hose to the tank. Don’t want the electric motor of the vac lighting off fuel vapors.