Hydroman400
To me, the way fuel ice is addressed via FOHE is backwards, and under conditions that were 'tested' by Boeing, show the concept lacking. Now the inability to 'de-ice' ice laden fuel is patent, per the reports and the extensive work done by the manufacturer, though it too is not dependable. Delta rolled back at 35k feet and lost 5k to regain thrust. At those frigid temps. the FOHE is shut down, and the oil is 'cooled' by air cooler. At take off under high demand, the oil heats rapidly, and the fuel cools the oil. Let down or cruise are the problem, under these conditions, the Exchanger is inop. In other words, even a spill valve would be putting frigid fuel back to the face. The engine operation for the Trent does not mention "fuel de-icing", not in the a/c manual.
You have a most valid point, though I disagree with the ability of the unit to perform to RR's expectations, via its manual. A long discussion, but what we have here is an enhanced demand due to a surprise in fuel performance. This new demand is addressed by trimming tubes back to face sheet, instead of re-engineering a new unit (architecture); although a 'new' FOHE wouldn't necessarily be expected to mitigate the problem well, if at all, given that the fuel performance is still "mysterious".
bear
Last edited by bearfoil; 20th Jan 2010 at 15:01.