GVilleFlyer
Member
Must I drain fuel in my tank to perform W&B, or can I subtract it mathematically from weight and moment ?
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Weight and Balance Question
- Thread starter GVilleFlyer
- Start date
To get an accurate weight that includes however much unusable fuel your particular plane holds, it’s best to drain it. Not hard to do if you remove the sampling cock under the access plate on the bottom of the fuselage (with fuel valve shut off!), and attach a hose on a barbed npt fitting. Then drain into jugs.
GVilleFlyer
Member
Got it. Dump the fuel! Thanks all
BoydBirchler
Well Known Member
It is often accomplished by "doing the math". That way the unusable fuel is already in the empty weight (if you subtract out the useable and start with absolutely full as you can make them, tanks).
If you drain the tanks, at any other place than the fuel pick up going to the engine, it is possible you might underestimate the unusable fuel amount/ weight. (Such that the tank sampling drain is lower than the fuel pickup). I drained my tanks using the boost pump to cans under the firewall where I attached a hose. The assumption being the boost pump would only be able to pick up usable fuel; so any remaining was included in the empty weight.
If you drain the tanks, at any other place than the fuel pick up going to the engine, it is possible you might underestimate the unusable fuel amount/ weight. (Such that the tank sampling drain is lower than the fuel pickup). I drained my tanks using the boost pump to cans under the firewall where I attached a hose. The assumption being the boost pump would only be able to pick up usable fuel; so any remaining was included in the empty weight.
Most people (including A&Ps worldwide) do not appreciate that Unusable fuel quantity is to be tested in the attitudes of flight to be expected in normal operations.
It is not acceptable to do the test by levelling the aircraft. It should be placed at an attitude that would be the worst case....... from my experience with Vans aircraft that would be in a nose down attitude as the fuel pickup point is at the aft inboard area of the fuel tank in most of Vans designs. Then into the empty tank, put in a known quantity of fuel, then pump (from a point forward of the firewall) and measure the quantity pumped....the difference is the amount of unusable fuel.
Refer to FAR 23-959.
It is not acceptable to do the test by levelling the aircraft. It should be placed at an attitude that would be the worst case....... from my experience with Vans aircraft that would be in a nose down attitude as the fuel pickup point is at the aft inboard area of the fuel tank in most of Vans designs. Then into the empty tank, put in a known quantity of fuel, then pump (from a point forward of the firewall) and measure the quantity pumped....the difference is the amount of unusable fuel.
Refer to FAR 23-959.
Not in a RV12. Fuel pickup in the front. POH describes all this
