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Old Feb 16, 2013, 02:11 PM
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Adjusting Trim

I have been flying my mini Supercub for about 10 flights now with moderate success (ok in air, not the best on setting up for landings)... and even went so far as to try flying with the Anti Crash off - seemed to be a little more twitchy??
But, I realized that I never really went through any process of adjusting the trim.
When in the process of flying a new plane should adjusting the trim be done?
And, is there a common procedure/process for doing this?
Thx
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Old Feb 16, 2013, 02:40 PM
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Trimming should start before you even fly, at least insomuch as you check the CG is correct and all the control surfaces are centred and the throws are in the right direction and the right amount of deflection.
Once in the air you should start adjusting trims as soon as you have got to a safe altitude. That goes for every flight not just the maiden as models often goes slightly out of trim between flights (don't ask me why!). On the maiden it's helpful if you have a buddy who can adjust the trims for you while you fly. If a model is really badly out of trim it can be a challenge to take your fingers off the sticks for long enough to adjust the trims, which is where the buddy comes in.

For basic trimming you just set the model up on cruise power and adjust trim until it flies straight and level. A properly trimmed model is MUCH easier to fly.

Steve
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Old Feb 16, 2013, 07:14 PM
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Learn where your trim levers are without looking at them. I teach my students to feel the edges around the sticks as a refrance .

Once you have it trimed in the air, you should retrim it mecanically ( on the ground ) and reset your trim levers to neutral, then do another flight to be sure you have it right . ENJOY !!! RED
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Old Feb 16, 2013, 09:59 PM
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Practice trimming on the sim if you have one.
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Old Feb 17, 2013, 02:51 AM
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Quote:
Originally Posted by redh View Post
Once you have it trimed in the air, you should retrim it mecanically ( on the ground ) and reset your trim levers to neutral, then do another flight to be sure you have it right . ENJOY !!! RED
Of course in these days of computer radios you can centre the trim with 'sub-trim' function... Though the old timers (myself included) will tell you that doing it mechanically with pushrod clevises/turn-buckles is better.
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Old Feb 17, 2013, 02:20 PM
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Quote:
Originally Posted by JetPlaneFlyer View Post
Of course in these days of computer radios you can centre the trim with 'sub-trim' function... Though the old times (myself included) will tell you that doing it mechanically with pushrod clevises/turn-buckles is better.
Is that what sub trim is for? And here I thought it was for trimming the dive planes on submarines. Never could understand why they included it on a transmitter ment for aircraft.

Larry
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Old Feb 19, 2013, 03:19 AM
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Quote:
Originally Posted by JetPlaneFlyer View Post
Of course in these days of computer radios you can centre the trim with 'sub-trim' function... Though the old timers (myself included) will tell you that doing it mechanically with pushrod clevises/turn-buckles is better.
Sub trim is really as you know - for arms that cannot be centred on servos such as when setting up Heli's collective / cyclic. Mechanical trimming - that is resetting the control rods clevis is good practice whatever radio you have old or new. It means that you could bind to another Tx if necessary wuthout any need to set other than default ... which is how we survived multiple models on a single non computer radio.

OK - trimming while flying ... I used to teach newbies to learn to trim with OPPOSITE hand to the stick hand ... based on Mode 2 of course. This meant that you could keep right hand on main flight stick and adjust trims with left hand without letting go and having model out of control for that vital second ... using neck strap of course to carry Tx weight.

You see even experienced RC'rs taking hand of stick to alter trims ... and model going of line !! Frantics !!

Nigel
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Old Feb 19, 2013, 09:54 AM
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I trim all my planes mechanically when I assemble them and use subtrim sparingly to get them exact. Once in the air, if the model needs trimming I have no problem in taking my hand off the stick and using the trim buttons until she flies straight and true; this is of course after she has plenty of altitude and she is flying at cruising speed. I have seen newbies try to trim a model really low and at full throttle. You can imagine the results.
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Old Feb 19, 2013, 12:35 PM
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To fly level at different speeds, I have used elevator trim with throttle changes for years.

It really came home to me when I had a trial flight in a full sized Cessna, (sadly I couldn't afford to go any further). The elevator trim was again used with speed changes, (throttle changes).
The throttle was used to set the speed/rpm, but to continue to fly level you had to apply stick pressure to compensate for increased lift from the speed. So elevator trim was adjusted until no stick pressure was required, i.e you could let go of the stick and she would still fly level, (at least for a while ).

Many beginner RC fliers probably do not realize the usefulness of elevator trim, and the need to adjust it with throttle changes if they want to fly level.

Throttle isn't just an on or off control, and elevator trim isn't a trim once and forget.
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Old Feb 20, 2013, 01:44 PM
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Personally I set my models up to have minimal trim with throttle changes by adjusting CG and thrust angles.

I fully appreciate that full size planes don't usually do it that way but models are not full size planes.
The big differences are that models are usually vastly overpowered compared to full size, so the trim change with throttle, if set up as per full size, would be extreme. But also because we don't fly models at all like pilots fly full size planes. Full size generally have few changes in power. They use high power to climb which they hold for several minutes or more, when they reach altitude they go to cruise power, stay at cruise for maybe an hour or more with only the odd minor adjustment, then reduce power to descend and land. the pilot might have to adjust trim twice in the entire flight.
A typical model flight pattern is very different, constant throttle is not usually maintained for more than a few seconds, one minute you are flat out, a moment later you have the throttle closed, then a moment after that open again. If your model was set up as per full size you would have to be constantly adjusting trim which would be no fun at all and very distracting.

It's perfectly possible to have any plane set up so as to have minimal trim change over a wide speed range.
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Old Feb 20, 2013, 01:56 PM
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I trim my model to fly straight and level with elevator trimmed to 0 degrees of deflection aned at half throttle. If your model climbs radically at 100% throttle, then you adjust the CG, not the elevator. Jet is right, you really can't compare a full scale plane to a model.
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Old Feb 20, 2013, 02:30 PM
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Jet and chuck, I understand what you mean.

So as this is the 'Beginners Training' forum, how about explaining how beginners should go about adjusting the CG on their trainers to minimize the need to adjust trim. ?
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Old Feb 20, 2013, 03:17 PM
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Well, for the most part, a beginner friendly plane should not have to have the CG set by the beginner. I cite the fact that the HZ Super Cub, FB Stratos and the Ares Gamma 370 mention CG in the manual only as a reference to the beginner. When I started flying a while ago, and I had those planes, I just put the recommended battery in the battery compartment as per the manual and didn't wory about CG. It was that simple. Now trimming roll is a different story. When I was a newbie, I basically put the plane up high, saw which way it was rolling, and dialed in the trim with the trim controls on the TX. Yes, I looked down at the TX for a very, very brief moment while I clicked and got the plane to fly level; I was at a very comfortable altitude though. As far as climbing trim, I dont' recall ever having to trim those planes out for that; it was simply reduce throttle to about half and presto, no more climb. This was how it said to do it in the manual by the way. One issue I find that ALMOST always confuses a newbie is the simple fact that ELEVATOR does NOT control altitude. Throttle does. That is just a fact of aviation. Newbies need to get it into their heads that elevator controls airspeed not altitude,...........period. So you can see why I believe that trimming a model airplane to fly level at full throttle isn't exactly something I recommend.
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Old Feb 20, 2013, 03:51 PM
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"If your model climbs radically at 100% throttle, then you adjust the CG, not the elevator. Jet is right, you really can't compare a full scale plane to a model."

If the elevator is centered at cruise throttle, the CG is likely good. "Radical" is understood, although subject to a flyer's judgement. The engine may need more down thrust, and the throttle/elevator mix fooled with. There are (more or less) three elevator trim positions involved - take off, cruise, and landing. Flaps also come into play, mainly for landing on a model. Full size a/c elevator trim is comparable in some ways, not in others. The full size light a/c usually gets it's trim manually adjusted during a flight in preparation for takeoff, during cruise, and before/during landing. I'm still trying to figure out how to use the flight mode switch on my DX-8 to create the three elevator positions. Actually there is a fourth as well, that might be useful for high speed level passes.
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Old Feb 20, 2013, 05:16 PM
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Quote:
Originally Posted by chuck75 View Post
I'm still trying to figure out how to use the flight mode switch on my DX-8 to create the three elevator positions. Actually there is a fourth as well, that might be useful for high speed level passes.

I do it like this on my DX8:
I set the flight mode switch to control ch. 8 (Aux3) by setting Knob:Inh and F Mode:Aux3 in the Switch Select menu item in the System Setup menu.

Then I select Mix1 under the Mixing item in the Function List, and use these settings:

AX3 > ELE
Rate: -10% (10% up elevator when in FM1)
- 10% (10% down elevator when in FM3)
Offset: 0%
Trim: Inh
Sw: On

This gives me a "launch" trim when in FM1, "cruise"-trim in FM2 and "hi-speed"-trim in FM3. If i need trimming for landing with flaps, I do that with the built-in elevator/flaps mix in the flap system menu...
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Last edited by KaiWE; Feb 20, 2013 at 05:22 PM.
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