Does down elevator indicate a tail heavy condition?

[Joel K. Scholz]

I am working on a flying hyrofoil in pusher configuration. The plane is stable enough to fly hands off, but has a fairly significant down elevator. Is this an indication of tail heaviness? Would too positive downthrust be responsible?The airfoil is a symmetrical one 14" chord at around 9 percent.

[BMatthews]

If your hydro thingy has positive pitch stability as shown by it wanting to pull out of a hands off dive or recover normally from a stall then no it does not mean that it's tail heavy. And similarly if there is too much downthrust then the model will show that by reacting differently in pitch as you add and remove power. Too much downthrust will show as the nose trying to tuck when you apply full throttle and lift when you go to idle. With normal downthrust the model should try to lift the nose slightly as power is applied.

[Sparky Paul]

Lots of down elevator for trim says the horizontal is on at too low an angle of incidence.
Raise the leading edge some. Or, more easily, raise the trailing edge of the wing a bit.
We do this on our Kadets to get rid of the normal down elevator trim for level, and it adds a bit of speed to the plane.

[Tom Harper]

What do you mean by "positive downthrust"?

[Joel K. Scholz]

When I say positive downthrust, I mean the rearward facing prop is angled downward to add positive uplift. Does that make sense?

[vintage1]

No. Dowmnthrust like that introduces a nose down moment that would need UP elevator to compensate.

If its stable, its just a question of the stab needs to be glued on at the angle you seem to need the elevators at...and hey presto...no down elevator? :D