James Phillips wrote:

O.K. This is from memory which in my case can be somewhat cloudy. But I
remember the F-16 having a Heat exchanger in the fuel system. It used fuel
to cool either engine oil or hydraulic fluid. I don't remember which for
sure. Could a heat exchanger be put in a main fuel tank. Or maybe it could
be installed in  some sort of sump or header tank to keep it immersed in
fuel? Would this work better than having the heat exchanger in the hot oil
pan?

Well, there are a few problems with doing this:

  1. You already *must* run the fuel lines from the tank(s) to the engine, and
     frequently there are return fuel lines from the engine to the tank(s).
     Making the fuel take a side trip to the oil pan is a lot less trouble than
     running oil lines out to the fuel tank(s).  Plus the oil lines to the fuel
     tank(s) are gonna have oil in them, which means your system oil capacity went
     up, which means you're heavier.
  2. When the fuel tank gets low (last hour of gas), the oil will pump just as
     much heat into it.  It seems to me that you'd end up vaporizing (and ejecting
     out the vent line) a lot of fuel that way.  Plus it sets you up for a vapor
     lock problem in the fuel pump (intake cavitation induced vaporization).

Russell Kent

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