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Al Wick wrote:
What's the best fuel design to prevent vapor lock? Copy any auto mfg method. They all use the same method because it's SOOO effective. OEM fuel designs minimize every REAL risk we have in our aircraft. They use self cleaning filters that have around 10 or 20 times more surface area than stupid in line filters. They minimize pressure drop at pump inlet by using large coarse filters there. Submerged pumps. Every car mfg uses the same system. Do you know how rare that is? They do it because the wet design with self cleaning filters eliminates all historical failures.
I recently converted my sys to automotive style. Details at bottom of page:
http://www.maddyhome.com/canardpages/pages/alwick/index_files/Page467.htm
Can you explain something to me on this point? Considering that the in-tank pump has a positive volume, how does it avoid a negative pressure when the fuel level gets near the bottom of the tank? I ask, because most airplanes tend to have very flat tanks, and fuel often gets left on the ground for weight and balance reasons. Pulling that last few gallons off the bottom of the tank can be VERY important. Putting the pump in the tank is going to result in pulling fuel uphill at some point unless you have a flat pump.
I'm going to go out on a limb and say you're wrong. Manufacturers all use the in-tank system because it simplifies design and assembly. They all use pre-assmebled console "clusters", and many other pre-assembled components for the same reason. It is not rare at all. In-tank pumps are not a safety issue. It's an economic one.
The best design for avoiding vapor lock is going to be the one that puts the most pressure ahead of the pumps. Whether this is done by putting the fuel as high above the pumps as possible, pressurizing the tank, or magical pixie dust, positive pressure at the pump inlet is the only answer. The in-tank pump only marginally solves the problem and is a maintenance nightmare.
But, to each his/her own. You build it. You fly it.
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