It's a viscosity
Thing. And Ice wasn't a design constraint. IMO.
Sooty - I can't find the GE schematic. The RR has an LP Filter downstream the FOHE, and appears to be embedded in an Oil flow system as is the Fuel. The LP seems to be an Impellor design, the HP a lobed, or geared design. So the Fuel goes unimpeded from Tank to LP to FOHE. (Roughly).
Only in Hindsight, and knowing Pipe Ice is a Real problem, are all these comments pertinent. But it would seem that putting the FOHE as the skinny kid, closer to the Nozzles, may have prevented Trent from taking the flak. But then we wouldn't be aware of the Problem at all. Perhaps never. So far, a totalled Bird, a broken leg and some brown Laundry offloaded Delta at Atlanta. So Far.
RightBase - To be fair, the FOHE wasn't designed strictly for high and cold. Down low, and warm, the Oil is in more need of cooling than up high, where most everything's cold to begin with. To get best exposure to the Fuel (which isn't so cold when low,) the design (IMO) slows the Fuel down, by necking down the cross section and adding surface area F/O.
Gives the transient Fuel more time to soak up some calories. Ice? What Ice. The increase in pressure and slower velocity becomes problematic up high, especially when Pipe Ice can occlude the passage. Which is what is frustrating, where the Oil isn't so hot, and the Fuel is very cold, the need for an FOHE is debatable, especially when Thrust is way short of TOGA or Cl. Hence, why not a (relatively) simple bypass for the Fuel? The Oil has one, it bypasses the FOHE when it cools down, Shouldn't the Fuel bypass at the same time? Or in an Icing regime?
AF
Last edited by airfoilmod; 19th March 2009 at 20:50.