The two round fuel selectors have three positions switching in the following sequence: off, outboard tanks and inboard tanks.
The sequence reflects standard operating procedure for the real Blenheim, which calls for start up, taxi and take off on the outboard tanks and cruise on the inboard tanks.
There are two outboard and two inboard tanks,one of each on each wing. Each engine is fed by the ones on its side of the wing.
The third fuel cock is optional, it is actually a crossfeed valve that allows running the engines from the fuel tanks on both wings.
The only reason to use it is if you have a fuel leak and you want to use as much of the leaking fuel before it runs out, or running both engines from a single tank on one side of the wing if the other one is empty (which would only happen if it leaked, as normally both sides get depleted at an equal rate because each engine is fed from its own tanks). Setting it to on will let the engines be fed not only from the tanks on their side of the wing, but the tanks on the other wing as well.
So for example, if you have a leak in the left inboard tank and you want to use up some of it before it's completely dry, you would switch to inboard tanks with the wheel-shaped fuel selectors and open the crossfeed valve.
Once the left inboard tank is empty you can:
1) either switch to outboard and disable crossfeeed, this will have each engine running from the outboard tank on its side of the wing, or
2) keep running on inboard with crossfeed enabled, this will have both engines running from the right inboard tank since the left inboard tank is empty.
In other words, it's useful for balancing asymmetric fuel weights that are caused by battle damage. Otherwise you might have trouble landing because more weight on one side of the wing will result in a rolling motion and that is more pronounced the slower you go because it can't be easily counteracted with a low amount of airflow over the wings and control surfaces.
|