Roger Mellema, Ray Ward
Newsletter #14 (May 84)
Ray also gave me a reminder about take-off in the BD with low fuel in the tanks. One of his early test flights resulted in a complete engine stoppage at about 500 +t. He had taken of+ with the fuel selector in a single tank position and had about 9 gallons of gas in that tank. The tremendous acceleration because a+ the 300 hp engine and probably steeper climb angle caused the front fuel line to unport which resulted in a loss of power. Ray switched the selector to both tanks and leveled of+ which allowed the engine to restart. Ray had changed the fuel system to incorporate the "rear tank feed line goes behind and under the door" method. He now has some other thoughts on ways to further improve the system. He believes that what he has is alright but the position of the "Y" where the lines from one tank become one is at the wrong place. He thinks that the system can be improved if the "Y" is placed at the bottom of the fuselage. He justifies this with figure 1, and explains it in this way- With aircraft sitting tail down, fuel level was checked with stick gauge (1) before +light. It shows fuel (about 9 gal) level at about (2). Throttle advanced wide open at 20 mph, aircraft accelerates to 120 in about 10 seconds. This figures to about 0.5 g acceleration (176 ft/sec/10 sec). One g is 32 +t/sec/sec as recalled from physics. The vector seems to show new fuel level (3) which not only uncovers fuel tank forward drain, but also the "T" where rear line joins. In a few seconds, air enters the "T" while acceleration causes fuel in lower line (4) to be drawn aft. Engine starves since no fuel is available from either line. I've thought of several fixes. (A) Placard the plane against take of+ with less than 1/3 tank. (B) Put in a header tank like my other BD-4. (C) Move "T" from position called out to position (5). If this is true, then it will solve the problem plaguing all BD-4s on steep pitch-up attitudes. I don't remember anyone proposing moving the "T", but it looks like a good idea for BD-4s.
Steve Craigle
In an email to Holger Stephan from 2001-06-06:
Yes, you need to get the fuel line connection down as low a possible. Even better if you can figure a way to get them in is to use .50" dia fuel lines. In experiments with a mockup of the fuel system, Jim Huber and Roger Mellema found that bubbles entering the fuel lines when a pickup point was uncovered acted as plugs when the fuel recovered the port. With .50 lines, the fuel goes around the bubbles and keeps of feeding. I used an electric pump (vibrator type) on the downstream side of my fuel selector valve. It's very handy for restarting the fuel flow in my .375 dia lines after switching tanks. The pump allows gravity feed through it with only 18 in. of fuel head.