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Trimming your plane

Old 10-02-2009, 01:13 AM
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Default Trimming your plane

AEAJR has opened this thread to a WattWiki entry.

Thankyou for the i said on your other post..very informative.....I'm in no hurry to crash this plane.will doas you said for trim and at least1 to 2 hrs of easy flying just to get used to the controls..take-off and landing circuit's
Entry: Trimming your plane

Posted by: AEAJR

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.


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.


More tips on balancing

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

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!


Forces in Flight


Stall and Spin

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Old 06-24-2011, 08:25 AM
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Here is another step by step trimming chart that can take you from where Ed left off.

Some of the maneuvers are a little advanced for beginners, but the basic steps will take you a long ways toward a well trimmed model.

Here is another excellent tutorial on trimming that goes even further.

Then agree to the legal stuff
then download which ever tutorial your interested in. There are several good ones, but #9 is specifically for Trimming.
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Old 06-24-2011, 08:34 AM
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By the way, I agree with Ed on the importance of trimming your model. It is the single most over looked way to quickly improve your flying.

Trust me on this. Spend just a little time properly trimming your model and you will suddenly be a much better pilot.


It works
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Old 06-25-2011, 06:50 AM
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I flew free flight for many years. Trmming is the main skill involved. You just can't bypass it.
Always make sure the C.G. is correct before going to the field and remember this is just a starting point. Most times you will find that the stated C.G. needs a little extra nose weight adding. For some reason most plans / kits seem to have models tail heavy causing stalling.

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Old 07-08-2011, 09:00 PM
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Where can I find troubleshooting for poor flight characteristics? I'm trying to hone my skills and I noticed I was making mostly left turns. I was doing this because my plane turns horribly with right rudder. Anytime I hit right rudder it dives dramatically. What would cause this?
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Old 07-09-2011, 02:40 AM
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Thats not something Ive run across before.

My first suspicions are either a warped wing or an unwanted control mix in the tx..... or in your hands

First - do a couple of tests on the ground.

1)Look very carefully at each wing half and see if they have the same amount of twist or no twist as the wing goes out from the center to the tip. You can block the model up level front to back and set each wing tip trailing edge at the tips the same height from the table. Then carefully measure several places along the trailing edge and leading edge down to the table surface. Each wing half should have very close to the same measurements.

For the next tests its safest to remove the prop

2)With the model on the bench, move ONLY the rudder stick left and right while you watch the elevator very carefully. Does it move at all? Do the ailerons move at all?

2A)This next test is difficult to do (honestly) for most people. Try the same test again but holding the tx like you normally do in flight and imagine your making a left turn and then a right turn. Watch the elevator again and see if your adding some elevator input without realizing it.

3)Remember we needed the prop removed? Bet you didnt do it before Do it now for sure!

Run the throttle up to about 1/2, then give the model left rudder then right rudder. Did the motor speed change? If so, you are probably doing that even more in flight. That could cause significant speed changes. if your motor thrust line is off (up or down) that could cause your problem.

What does the plane do when you abruptly give it full throttle in flight from say 1/4 or 1/2? What does it do when you cut the throttle abruptly from full to zero? Any tendency to dive or climb with throttle changes? If so, you may be adding throttle when you turn left and reducing throttle when you turn right (or the reverse depending on how you hold your tx). That would then cause a dive or climb depending on which way things are off.

I would check for warps first and fix any you find. Then do the above tests and correct as necessary.

Then go back and do Ed's "trimming" thing above in the first post.

When thats pretty close, then go to my post #2 above and do the steps in the first link.

By the time your finished with all that the plane will be flying great
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Old 07-09-2011, 04:07 AM
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Thanks for the troubleshooting tips, looks like I definitely have some warpage. My right aileron bows about 3mm in the middle and my left wing is about 5 mm lower on at the tip. I also found my elevator was not centered. Now, how do I straighten warped EPP.

I definitely know where to pay more attention on my next build!

Last edited by M@!; 07-09-2011 at 04:25 AM.
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Old 08-04-2011, 03:33 PM
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Hankg just showed me this link. Hope it helps.
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Old 11-10-2015, 12:42 AM
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Default Trimming engine or wing

I have a scratch built Lazybee, 50 inch wingspan, electric motor Hacker 30. When it takes off it climbs, stalls, dives, climbs, stalls etc. sort of a scallop pattern. It is probably overpowered. But would it fly like this as a result of incorrect wing incidence, or wrong engine thrust?
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Old 11-10-2015, 12:57 AM
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Usually a combination of CG and incidence/trim settings.
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Old 11-10-2015, 03:53 AM
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Originally Posted by fhhuber View Post
Usually a combination of CG and incidence/trim settings.
Those are the most likely plus thrust line might be contributing to the problem if its doing it at hi power settings.

Here is a series of tests you can do to get the model dialed in.

You will need to go through these steps several times. Each time you make a change in one thing (CG, thrust line, trim settings etc etc), that change effects all the other settings. So its NOT a one time and you're done sort of thing.

The first time through, you will change one or more things like CG or thrust line or trim. Then you have to re-do the tests to see how the model responds with the new settings. Then you make more changes and then re-do the tests.

Keep going till you are happy with how it flies. Some models you get there very quickly and some take more flights to get truly dialed in.

Good luck!
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Old 11-10-2015, 04:06 AM
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Originally Posted by bgchip View Post
I have a scratch built Lazybee, 50 inch wingspan, electric motor Hacker 30. When it takes off it climbs, stalls, dives, climbs, stalls etc. sort of a scallop pattern. It is probably overpowered. But would it fly like this as a result of incorrect wing incidence, or wrong engine thrust?
One more thing - its important to realize that no single aspect of model setup is independent. Every detail effect every other detail as far as model "trimming". When we talk about trimming a model or setting a models "trim" we dont just mean elevator trim settings.

CG, thrust line, decalage and trim setting all work together. Each one effects the others.

For example, haveing the CG to far forward forces you to add more UP trim on the elevator with in turn means you need more down thrust to keep the model from climbing under power and diving with power off. Having too much elevator down trim would make you want to move the cg back and or add UP thrust, etc etc.

Thats why you need to run through the tests above more than once.
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Old 11-10-2015, 05:16 AM
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Thank you. My grandson has the Bee right now. I will go through these steps.
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Old 11-10-2015, 01:20 PM
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I grabbed the wrong copy of the trim chart above. This one is basically the same maneuvers but has more details.

If you Google this you can find other variations with different maneuvers but they all work basically the same way.

I posted a link to this same info in post 2 by the way
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Old 11-10-2015, 02:24 PM
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Note that the dive test in most of these charts assumes a symmetrical airfoil. With a flat bottom airfoil the dive test might say you have the CG too far forward until you have pushed the CG back beyond where its possible to recover from a spin.

Do a second check of level flight just reducing speed without re-trimming. The plane should not have the tail come down. (unless you are doing 3D... they often push the CG back that far)
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Old 11-10-2015, 07:22 PM
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FWIW and to the best of my knowledge, the dive test was originally devised for sailplanes, and it actually works best on sailplanes or at least models that are quite clean and efficient aerodynamically (more draggy models need a very steeper dive angle for it to work)...
Anyway, sailplanes rarely if ever have symmetrical airfoils and it works 'as advertised' on them.

It's always worked well for me though for aerobatic models I prefer to use the inverted test to set CG i.e. trim the plane for level upright flight, roll inverted and observe what it does 'hands off'
  • For 3D it should fly level or very gently arc downward.
  • For pattern and sports type acrobatics it should arc down a little more.
But personal preference comes into play too. Trimming for 'hands off' level inverted flight does make the plane a little tricky in some aspects of flight, like the ballooning up when you slow down that fhhuber mentioned.
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Old 11-11-2015, 03:02 AM
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Good advice from both of you.

This particular trimming chart was designed for and by IMAC/pattern/power flyers. This particular "dive test" is different from Mark Drella's sailplane version in that it calls for a banked turn or inverted test under power rather than dive to set CG. Their "dive test" is to set decalage instead of CG. The two settings are so closely interrelated that I look at it like 3 different ways to dial in CG/trim/decalage.

They want a very neutral responding model as far as inverted flight and up/down lines are concerned. Not quite but almost 3D settings for CG and almost equal inverted/upright flight and zero coupling in knife edge flight. Actually they like as little coupling in all axis as possible.

Its comes down mostly to how far you take each adjustment = personal preference and skill level.
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Old 11-11-2015, 03:19 AM
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The goal of this series of tests is to end up with a model that does ONLY what YOU tell it to do.

In other words, when you change throttle only the speed changes - no pitch up/down and no yaw and no roll.

When you tell it to roll the rolls are perfectly axial with no pitching or yawing or barrel rolls. When you yaw the model it doesn't roll or pitch, etc etc.

When you do a climb or dive it climbs or dives in a perfectly straight line with no need to correct with elevator, rudder, throttle or aileron.

Loops stay in the same plane with no tendency to roll out or yaw off line, etc.

Inverted flight is almost hands off.

In other words a model that is easy to fly perfect pattern/IMAC maneuvers.

Turns out that also makes for a model that is easier to fly well once you get beyond the basics in skill level.

Just dont go toooo far for your skill level with a rearward CG.
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Old 11-12-2015, 03:54 PM
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I just want to say thank you for all the help that has been given. This has all been very helpful.
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Old 11-12-2015, 05:16 PM
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Even with all of the above...

Trim it so it flies the way you like.
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Old 06-25-2017, 02:24 AM
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Default Trimming your plane... a video

So, if you have the time to spend, this was a talk given at our club by Tim Attaway. Tim is AMA District X AVP, and he has been writing the IMAC routines for years. He is an accomplished competition pilot, and I have learned bucketloads from him.

Grab a drink... its almost an hour.

Enjoy, and learn something... maybe.
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Old 06-27-2017, 04:18 AM
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I have enjoyed reading this thread...all of great importance, with regard to trust.
The airplane 'wants' to fly. Some of my favorite memories are from frustrated students and instructors who have overlooked the basic skill of trimming the airplane - mostly instrument students who just cannot keep up with the airplane because all of their focus is on controlling (over) the craft. Once they learn to let go of the airplane...the mind is freed for other tasks. The airplane is flying itself - pilot just gives it suggestions! Then and only then all of the pitch and power settings work with only small adjustments. While a real airplane is truly easier to fly, the same principles must be respected.
Hats off all you guys and gals if applicable!
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Old 09-23-2017, 05:14 PM
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if no one has said it, I like my plane trimmed so that at 50% throttle, I've got level flight, but above that I'll start to climb.

Otherwise straight and level for everything else.
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