Hi Gordon,
It would be interesting to measure fuel consumption with and w/o the FOD by placing the fuel tank on a scale when you are running the turbine and calculate the consumption as weight/min.

In some cases the FOD will generate a pressure drop in the compressor inlet. Even a marginal pressure drop will have significant effect of the efficiency and fuel consumption. In general the FOD should have as large area as possible and be as far away from the compressor inlet as possible. The size of the grid is of course also a critical factor. If it is large enough the distance and area may not be so critical. The speed of the air increases exponentially the closer to the compressor you get. The higher airspeed over the FOD the greater pressure drop in generates.

I tested once a custom made FOD and the fuel consumption increased by almost 0,75 litre in 5 minutes flying. This is my safety margin when I land but this time (twice) I had to dead stick after 5 min because of no fuel left. In this case the FOD had a grid that was too fine.

I also find it quite amazing that the FOD distributed by a world known turbine manufacturer has a price of 45Euro when anyone can se that is a conventional tee strainer made in China and some Festo connectors. A total value of less then 10Euro!

/Johan