Trimming your plane
by Ed Anderson
aeajr on the forums

Your having problems flying your plane. Your problems may be your flying or
it may be that the plane is out of trim. If it is out of trim or if any of
the components can move around inside the plane, all your skills will be
used fighting these problems, not flying the plane. Here is how we will
find out. If you have an experienced pilot to help you with this, all the
better, but you can do this on your own if you have patience.

When I coach new pilots, we spend a lot of time trimming the plane first. I
may fly it 10 times before I give them the sticks. It must fly properly or
they have little chance of success.

Balance

If the plane is not properly balanced everything else is a waste of time. I
want you to recheck the balance of your plane. This must be done at home
where there is no air movement. All components, and especially the battery
you are going to fly, need to be in the plane to check the balance. If you
don't know how to check balance, tell me, but I am going to assume you know.
This link may help you confirm you are doing it right.

Balancing
http://www.rcuniverse.com/magazine/article_display.cfm?article_id=84

More tips on balancing
http://www.rc-airplane-world.com/balancing-rc-airplanes.html

Make sure all components are in the proper place and well secured. If the
battery or any other components can move around, they can move the CG of the
plane enough to throw off the handling, especially in a turn, on climb or in
a loop, etc. Stuff has to stay put. NOTHING is allowed to move! Balance it
to dead center of the recommended point. Dead center. Not nose heavy, not
tail heavy. Dead center! Good enough is NOT good enough. Get it right on
that spot!!!

You might need to add tiny amounts of weight. Or you might remove weight by
ripping a bit off a piece of foam you are using to hold something in place.
Whatever you do, I want that plane balanced dead center of the recommended
range. This is normally a very conservative spot and may actually be
slightly nose heavy. It usually is, but that is the starting point we will
use. Dead center! ( OK Ed, Dead Center! I get it! )

Surface trims

If you have flown the plane already, then I want you to look at where you
set your trims on the radio. With the plane is the air, all trims on your
radio should be centered. If they are not, then I want you to adjust your
surfaces at the control rods before you fly again so that you can center all
your trims. Remember this MUST be done with the battery connected and the
radio on.

If you have three clicks of left rudder trimmed on your radio to get the
plane to go straight, then measure how much the rudder moves when you move
the trim to center. Now adjust it back at the control rods/lines so that it
sits in that position with the trim centered. This will give you maximum
trim capability in the air.

If you have not flown it, make sure all surfaces are aligned with the fixed
parts with the trims centered. The plane and radio MUST be on to do this.
Trim centered and all surfaces aligned.

Take your balanced and correctly trimmed plane to the field. Do a range
check! If you don't know how to range check, look in your manual for your
RTF plane or in your radio manual for all others. If you still don't know,
tell me!

Check all surfaces and all components again to be sure all is well. Now get
ready to launch.

I want you to pick as calm a day as you can find but at least on a day when
the wind is under 5 mph and not gusty. For a slow stick or anything like a
slow stick, under 3 mph please.

Put a freshly charged battery in the plane, preferably the one you used to
balance it. Check for smooth motor operation. Make sure the prop is on
tight and turning in the right direction.

If you are hand launching, launch it into the wind, at full throttle with a
good solid level throw ( not up ) and get your plane out at least 50 feet
before you touch any up elevator. Always hand launch into the wind and
level.

Now fly it up slowly and get it to height, at least 100 feet ( say double
tree height where I live) and preferably higher. Get it well up wind from
you. At no time do I want the plane over your head or behind you. Keep it
at least 50 feet in front of you, upwind. No stunts today. Do this by
making gentle turns around the field till you get it high and flying into
the wind and going reasonably straight.

Now, smoothly take the throttle back to HALF throttle. Be sure the plane is
flying straight and level, and take your hands off the sticks and watch the
plane. It should proceed fairly straight and either hold height or lose it
in a graceful/gradual fashion. Unless this is a 3D aerobat, it should not
be climbing!

Visualize it as a small boat on a river of water. It will bob up and down a
little, and shift left and right as the air currents and waves float by, but
it should continue to fly. Let it float on the river of air. It will bob
left and right as the waves of air come past but it should not dive, or snap
left or right into a roll. The wind may push it into a gradual turn, let
it, but it should continue to fly with little or no input from you. Resist
the temptation to correct it unless it is going out of control. Let it fly!

If this will not work, if the plane can not maintain flight without your
constant input, your plane is out of trim. All your efforts to learn to fly
it will be thwarted by this. You need to work on the balance and trim of
the plane or it is going to behave badly.

Land it, adjust surfaces and do it again. See how she flies. This is your
"gold standard" for making sure the plane is right. Spend at least a couple
of hours on this. Looks good? OK, move the CG slightly forward and do it
again. Better? Or does it tend to dive now? Move it back slightly.
Better? Or does it tend to climb and stall?

You may get it right very quickly but be prepared to spend some time with
this. I have spent 2-3 hours trimming till I was totally happy. Do it
until the plane no longer needs your constant attention to fly. Your plane
knows how to fly if you set it up right. It does not need you to fly it!

How are you doing? Is the plane flying on its own? Good!

Now! Do the same but turn the motor completely off. The plane should still
fly in an unpowered glide. If it stalls immediately and starts to dive,
power up and save it. You probably have too much up elevator trimmed into
the tail. This will cause the plane to want to climb all the time. With
the motor off, it can't climb, so it will stall and drop. The motor will
mask this situation. That is why we are doing it in a glide now. You need
to trim a little down into the elevator and try it again.

To what extent it will glide depends on the plane but the Easy Star, T-hawk,
EZ400, the e-starter, slow sticks, Magpie, Aerobirds, and other light wing
loaded planes should be able to still fly straight and lose altitude in a
graceful manner. Even if you are flying a high wing loading plane, you
should still be able to do this. After all, the 5, 10, 20, 40+ pound glow
and gas planes can be landed "dead stick" with no motor. Boeing 767s can be
landed with the motors off. Your small electric should glide very well and
practically land itself!

Now that you have spent a day at the field trimming your plane, now that it
can fly without you, now you can learn to fly your plane. Now it will
behave as it should.

This exercise may not seem like the fun you had planned for the day, but it
will teach you more about your plane, how it flies and how you can fly it
than anything else you will do. Trying to learn to fly a poorly trimmed
plane is frustrating and typically hard on plane and pilot alike!

When the plane is in a glide, you should still be able to exercise full
control. The only thing you can't do is climb. The response may be sluggish
as there is less air moving over the control surfaces, but you should still
have control!

When I started to fly gliders I learned more about flying electrics because
I learned not to depend on the motor to power me out of trouble and to
overcome a poorly balanced and poorly trimmed plane. Also during this
trimming process you will convince yourself that you do not need to
constantly interfere with the plane and thus you will tend to overcontol it
less and less. The plane "knows" how to fly. Let it fly!

This is what I am suggesting you do, for just a little while. Get that
plane flying so well that you don't need the motor to fly it. Then, and
only then, will you know that the problem is you and not a poorly trimmed,
poorly balanced plane. At that point you can make progress and become
master of the skies!

I hope you find this helpful.

Clear skies and safe flying!

OTHER RESOURCES

Forces in Flight
http://adamone.rchomepage.com/index4.htm

Stability
http://adamone.rchomepage.com/index5.htm

Stall and Spin
http://adamone.rchomepage.com/index6.htm

Balancing
http://www.rc-airplane-world.com/balancing-rc-airplanes.html