You need to use the propeller that flies the plane.
You use lead to balance the plane, As much as
it takes, and as far forward as you can get it.
Using a bigger battery puts the weight farther
back than a chunk of lead all the way up in the nose,
so it doesn't do as much for balance. This makes t
he plane heavier than it needs to be. Use the right
size battery, and use lead to balance the plane, as
far forward as you can get it.
You can use really long screws on the engine
mount and put the lead under the engine on
the extra length of the screws. You can screw
it to the front of the firewall.
Don't select the propeller because it is heavy
and helps balance the plane. Don't choose the
propeller that gives the most thrust on the ground.
Select the propeller that translates the engine torque
into the most thrust at flying speed.
A 14x7 three blade is way WAY too much propeller.
Sure it will blow a lot of air on the ground, but the
engine will not get up to its proper running speed.
The engine MUST run fast enough to produce its
maximum power. PERIOD. Running it with too
much propeller is like driving a loaded truck uphill
in high gear. (In the truck you need to downshift
so the engine runs faster and produces enough
power).
On your plane, a 14x7 two blade propeller will
turn faster and produce more thrust at flying speed
than the 14x7 three blade. A 14x6 two blade will
turn even faster. A 13x7 propeller will turn faster still.
You don't want to get too light, though. The engine
will have a "sweet spot" where it performs well. You
need to try different propellers IN THE AIR to find
the sweet spot.
About the weight issue, the plane can get pretty
heavy and still fly with a reasonably small engine.
Planes fly at half throttle quite often. A heavier
plane will have a higher stall speed, which is
really only an issue in landing, They also need
a bit more power for climbing aggressively.
The biggest problem with weight is pulling it
through grass on the takeoff run. Since your
plane did get off the ground, it will probably
be OK once you get the right propeller on it.
One plane I have started off weighing 9
pounds, Now after modifications and repairs
it is up to 12.5 pounds. That is over a 25%
increase. It still has the same engine, which
was on the small end of the scale when I
installed it. That plane still flies great.
That said, losing unnecessary weight always
helps. Light wheels are an easy first step,
especially the tail wheel. Removing the
retract servos and locking the retracts in
place should be possible. Removing any
wheel covers could also help. The pilot figure
can be removed if it isn't too difficult. (It may
be easy to cut it out from the bottom of the
cockpit.) You might be able to remove 1/4
pound of weight this way. Its not a lot, but
it could be noticeable.
Jenny