Originally Posted by
Tandemrotor
Is anyone able to tell me what the practical difference would be between a HIGH unusable fuel figure, and a LOW unusable figure?
Isn't the significant term in both cases the word 'unusable'?
Thank you for paying attention - yes there is a huge difference between a high and a low unuseable quantity - surprisingly.
Try this parallel:
Imagine 'sucking' water out of a swimming pool with a (fixed) straw compared to the same process with a a thimble. When can it be said that you can't get anymore water up the straw? In the case of the thimble it would be well defined, but for the swimming pool there would be a very long duration with
some degree of air introduced.
So if the 'sump' were shot-glass sized the 'out of fuel moment' would be very well defined. (as in small unuseable)
If it were
fuel being blown up a partially submerged tube orifice there would be air and fuel pushed up the pipe (by the atmosphere) - the pump would foam it (?) and push a fuel foamed mixture onward - I would be surprised if the engine
would just stop cleanly at the first hint of slightly aerated fuel - like fortyodd and zorab are so sure it would - I don't think so - it could be a drawn out period of very odd power delivery and perculiar characteristics, perhaps difficult to control or interpret,
if the unuseable quantiy is high compared to the flow rate.
I had an obscure fuel system issue previously and it turned out to be caused by foaming JetA1 - nearly caused
me a major problem.
Maybe this problem does not apply here for some reason - I don't know (do you?)