The CG was about 1/2 inch forward to the center of the envelope.  I abandoned the test plan and let the fuel burn down in the header tank to see if that would help and then returned to the airport for a no flaps landing.  The chase plane reported that with the flaps at 1/2, the top of the elevator balance horn was at the bottom of the cutout (up elevator).  With the flaps up, the top of the balance horn was about 1/2 way down in the cutout.

Rick,

 

It is not unusual for the reflexed flap winged Lancairs to require nose up trim at slow flight in order to increase the AOA to maintain level flight.  As the flap is extended to take-off position (about 10 degrees, -7 to +3), the wing creates a strong nose-down pitching moment requiring even more nose up trim to maintain level flight even though the AOA is reduced.  Further flap extension requires even more nose up trim. The AOA I am referring to is certainly the aircraft deck angle if not the wing AOA also.

 

Conversely, as speed is increased nose down trim effort is increased (or anti-nose up trim).  At cruise speed (say 170-175 KIAS, perhaps less for a 235/235), the designer would have expected the elevator horn to be at a neutral position - neither up nor down.

 

I use the short elevator bell crank (3" instead of 4"), heavy duty springs and the geared trim wheel arrangement on my 320/320.  The spring to elevator push rod connection is located so that at 200+ KIAS (race speeds) full nose down trim (horn slightly above cutout) is required and I still have to push ever so lightly on the stick.  I have never run out of nose up trim at various weights and CG's and full (45 degrees down) flaps.  I have an empty weight of 1210 pounds and the empty weight CG is at or .1 inch forward of the recommended fuselage station.  My small stab incidence is about -.8 or -.9 degrees.  Generally, it has been shown that 320/320s and 320/360s tolerate forward CGs quite well as indicated by those with small tails and the long engine mount that moved the CG 1.5" forward.  Solo flight with a 200 pound pilot, no baggage and header only fuel puts my plane at the fwd edge of the suggested CG envelope.

 

As mentioned, at takeoff the flaps are set to 10 degrees and elevator trim is set to neutral.  At rotatation (75-80 KIAS) I must pull back some to fly off the runway.  As I retract the flaps in climb (passing thru 100 to 120 KIAS) I must trim out the nose up pitch caused by the flaps going to reflex.

 

1. Are you sure of the empty weight CG and the fuel, seat and baggage arms.  Some people have used the "plans" wheel axle locations and arms when weighing the airplane and have miscalculated the true W & B info.

 

2. Check the horizontal stab incidence.  For the 320/320 the allowable range -.5 to -.1 degree as measured against the leveled longeron.

 

3. The trim "tab" might very well be too small.  Less aerodynamic force at slower speeds?