Thanks for all the quick responses. Here’s what I have so far:

 

...very high descent rates with not much fuel in the selected tank, lots of air. Could be that tank vents didnt keep up?  Low air press in tank temp impeded flow? A IVP guy reported that he had to modify his andair vent check valves to allow higher backflow during rapid descents.

I distinctly recall blowing in both directions through the Andair check valves before installation. They behaved as expected – no restriction for air entering the tank and some restriction for air leaving the tank. I looked at the descent rate from my flight data. The vertical speed was around 1000fpm, which doesn’t seem excessive.

 

Bob Pastusek pointed me to his article in the LOBO newsletter about Lancair fuel systems. I have to confess I performed some of the steps in his articles but not all. The fuel bays in the Legacy wing are pre-built. I verified that all the inter-bay passages were clear (both top and bottom) and the flapper doors were working both before and after wing closing. I sloshed the wing tanks before installation. A tiny amount of debris and a few bug bodies came out but the fuel samples have been immaculate since then. My DAR required that I perform the high-angle-of-attack fuel flow test, and both tanks provided fuel with the tail resting on the ground and less than 5 gallons per side.

 

Bob also pointed out that prolonged uncoordinated flight will cause fuel to flow outboard and away from the fuel pickup. I added lateral g’s to my graph and bingo! You can clearly see a lateral acceleration during the descent. We’re all used to adding right rudder for takeoff and climb, but I had forgotten that most planes need left rudder during descent. This is perfectly normal. The canted motor mount that compensates for left turning tendency works against us during descent so adding left rudder is to be expected. I just have to remember to step on the ball both on the way up and the way down!

 

From Scott Kreuger: During the build when it is easy, almost everyone fails to test "usable fuel" quantities in wing-main-tank systems.  That is, the wing can be tilted up and down in pitch whilst measuring how much fuel it takes to keep the pickup covered.  It seems that usable fuel in a nose down pitch is wing capacity less 10 or more gallons in each wing.  Hard to tell what the pitch reading means - was that merely down by 5 or 6 degrees? - only for 2 minutes?  The high fuel reading meant the fuel had gone up higher on the probe - was this an uncoordinated descent?  Where did the left wing fuel hide during the pitch over or was that in a steep bank?

Sorry, the pitch scale is degrees/5 so the maximum descent angle was 12deg nose down. I had never heard of testing unusable fuel before wing closing. It certainly would have given some good insight into how the pickups behave at various flight angles. The fuel probe is a 6’ metal tube with an open end and some holes drilled around the base so fuel can flow in and out. The fuel probes angle up diagonally from wing root to tip. I suppose if all my fuel ran to the outboard end of the left wing and the inboard end of the right wing that could explain the fuel level readings.

 

This was only my second flight with the Dynon so I’m still tweaking it. You can bet I’ll configure that low fuel pressure alarm before my next flight!

 

 

Adam,

 

If you didn’t correct the asymmetry of the vertical fin, as shipped in the kit from Lancair, it’s more likely you unported the fuel pickup because the aircraft was flying in a skid (the ball not centered). Most Lancairs have a fin that generates considerably more lift on one side than the other, resulting in the airplane’s yaw trim changing dramatically with changes in both power setting and speed. This, combined with the very small amount of dihedral in Lancair wings will unport the fuel pickup easily with large changes in speed until you get used to harmonizing the rudder.  This would be my first guess as to your problem.

 

I’d also recommend you set alarms on low fuel pressure and low fuel flow. These, and other alarms, are really life and equipment safety precautions. Play with the settings until you get a reliable warning of trouble without them being a blithering nuisance…it takes a while.

 

Bob