Last but not least, there is another variable, this is the thrust-line of the engine. This is impor-
tant, and should be measured in relation to the wing. It makes things easy, and we will refer in
this section all angles of attack to the wing as a zero point.
Get the plane on your table, and first set the wing incidence to Zero. Then the stab should be
negative (nose down) about 0.2 - 0.3 degree. You will need an incidence scale to measure this
correctly. In relation to the wing, the engine down thrust should be -2°. And the CG should be
then exactly at the back edge of the wing spar.
With these basic settings you can get on with you first serious trim flight. First setting adjust-
ment will be down thrust (and right thrust at the same time). Take the plane to a high level, and
push into a vertical down line, throttle AT IDLE. At exactly vertically downwards release all the
sticks. The plane should now continue to dive exactly vertical. If the plane goes towards the
belly, you need to uptrim, if it goes to the canopy, you will need down trim on the elevator. Do
this manoeuvre several times, and set the trim so that the plane goes exactly vertically down.
Note: In this manoeuvre there is only the incidence difference of wing of stab influencing the
flight. No thrust line is involved as engine is at idle, no centre of gravity in relation to centre of
lift is involved, as there is a vertical downline without any momentums of both at all.
With the trim setting you found, the plane might dive or climb a little bit in horizontal flight, but
please completely disregard this for this trim flight. The next step is, to fly vertical uplines with
the SAME TRIM SETTING. At full throttle pull vertical up, and see if the plane goes to the belly
or to the canopy. If it goes to the belly, you have to add upthrust, if it goes to the canopy, you
have to add down thrust. It is that easy, and you cannot fool it. Do not change your trim setting
at this time, land, and adjust the thrust line accordingly. After adjustment, make another test
flight, to see if it improved. You should stop when the plane in vertical up AND down lines goes
absolutely straight, without trim changes from your side. Then your down thrust (or up thrust) is
set right. Of course at the same time you will find out about your right thrust, and you can cor-
rect at the same time, too, in exactly the same manner.
Now the effects of the thrust line are eliminated, and the angle of attack issues relative to the
thrust line and relative to both wing and stab are eliminated, too. Now you can continue to find
the right CG settings.
Fly horizontal, and NOW change your elevator trim so that the plane flies straight and level. If
your CG is close, you should only need one or 2 clicks of up trim. If you need more, this is a
hint for a nose heavy setup. Flip the plane inverted, and see if it now dives to the ground
severely. If it does, your CG is definitely too far forward, and you should move it backwards.
Try the same manoeuvre again, after you moved your CG, and you will find an improvement
already. Set it so that the plane only dives very little bit inverted, when if flies with the same
setting absolutely straight when upright.
Regarding the momentums, your plane is now set and ready to go! Now you will have to test
the snap capabilities, and the rolling capabilities, especially for rolling circles (of course, if you
can do it….). In the snaps the plane will need a lot of aileron, and only little of elevator. Make
sure that the snaps track nicely. If you do not get the plane to snap in line, if it “barrels” a lot,
you might have gone to far back with your CG. You can then adjust it a little bit to the front.
Also, if you slow the plane down, and you feel that you almost have to hold the plane with
down elevator to stay flyable, this is another hint that you went to far back with your CG. Move
it a bit forward then.
Do not worry if the elevators are not 100% neutral for all this testing. After you confirm every-
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