Al Wick <alwick@...>
Let me piggy back on what Marc describes. Just because it illustrates how easy it is to permanently improve flight safety.
I’ve always been enamored with how ignorant I am. This leads me to test and measure things. I needed to be real thorough with fuel delivery as that’s our highest risk item historically.
Bottom line, I discovered that my system appeared pretty low risk of vapor lock.....unless..... If I flew for 1 hour or more (heat soaked components in engine compartment), landed and parked for 5 minutes, then restart engine. I would hear that distinctive fuel pump rattle, rough running engine. Vapor lock. Worse on hot day, high altitude airport. Marginal design. Only partial vapor lock, it occurred for only 5 seconds or so. If I parked the plane longer or shorter period, it didn’t occur. Keep in mind that rattling is very destructive to pumps.
So what’s happening? My fuel pump was installed low in engine compartment with around 6 inches of fuel line in that same area. Parking heat soaked plane allowed engine heat to transfer to “cool” pump and fuel line. This was enough to cause vapor at pump inlet.
Solution? Wow, there are so many. Is it really that painful to tape an oven thermometer to the fuel pump? Measure it’s temp after a few taxi tests. Watch it climb after shut down. Then install a thin little aluminum shield between pump and exhaust? Remeasure temps to verify I really did affect pump temp. I’m just trying to encourage heat to move to other objects. Of course, insulating that 6” of fuel line exposed to heat is a no brainer. Nice permanent safety benefit.
Over the years, as I researched fuel delivery failure patterns, I realized that no one was flying with the modern low risk fuel designs. Both airplanes and lawnmowers are trapped in old high risk designs. So I converted my plane to design that in theory drives all the fuel risks to near zero. Ironically, when I flight test it, I assume it will fail. Always a risk of design oversights.
Cozy IV powered by Subaru 3.0R with variable valve lift and cam timing.
Artificial intelligence in cockpit, N9032U 240+ hours from Portland, Oregon
Glass panel design, Subaru install, Prop construct, Risk assessment info:
Todd Carrico wrote:
Well, as Tim A. pointed out, sometimes it gets pretty crowded there. I've seen a number of planes with both the filter and pump on the hot side, and as long as you keep them down low, near the NACA scoop opening, they're in cold air and there shouldn't be an issue (as long as you have the normal updraft cooling). But you DO end up with the pump/filter warmer than it otherwise would have been, and more exposed and susceptible to damage, at least somewhat.
So, no major worries, but unless there's some really good reason not to put them on the cold side, I'd say at least that _I_ prefer them there.