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How much trim is to much?

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Old 11-04-2012, 05:33 AM
  #1
KW_Counter
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Default How much trim is to much?

When you put a new plane in the air and get it trimmed out,
how much trim do you allow before you go in and mechanically
change the linkage?
Keeping in mind that changing it will require re-trimming the next flight.

I put a WM Mach II in the air yesterday and have about 20 clicks of aileron trim.
Trying to decide if it's worth adjusting to try to get closer to -0-.

Thanks for your opinions,
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Old 11-04-2012, 05:47 AM
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Default RE: How much trim is to much?

I would say yes. 20 clicks is a lot. Normally, it may take several flights to get things close to "center". You probably know this, but I'll say it anyway. The first flight of the day is usually a trim flight, meaning, going up, setting the throttle, then trimming for straight and level. This should take no more than a few clicks to accomplish. So, I would take those 20 clicks out mechanically, then refly and do it again.

My Skylark 70 took several flights to get right. In fact, my former instructor, a Master level Pattern pilot, helped me out to get things as close to perfect as possible. Now, as I said, on the first flight, once airborne, I set the throttle, usually slightly over half, then trim out for straight and level - hands off - then enjoy the rest of the day.

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Old 11-04-2012, 06:38 AM
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Default RE: How much trim is to much?

i'll agree with CG, if both balances are set, then i'd start over with your set alieron set up, i have a mach II and love it, it's my second one, first one got retired anf had to have another, niether one took much trimming, three or four clicks at the most on all surfaces. i'll also add they didn't take much if any weight to balance.
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Old 11-04-2012, 08:24 AM
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Default RE: How much trim is to much?

The amount of trim is telling you the plane isn't set up correctly, balance, thrust angles, warps but it shows how much off things are. After the maiden trim you change things on the plane then fly it again for trim. I have spent days getting a plane into trim. Once I have the plane set up I then will set all the trims manually if needed. With time and use the planes tend to change a bit, then I just use the radio to trim. My favorite plane right now could use some right engine thrust but I have too many things going on to bother taking off the cowl and moving the engine so I just have some right trim in the rudder until I get round to making the correction.
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Old 11-04-2012, 10:55 AM
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Default RE: How much trim is to much?

All the above are correct, anything over three clicks is adjusted with the linkage when back on the ground.[8D]
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Old 11-04-2012, 12:19 PM
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Default RE: How much trim is to much?


Quote:
ORIGINAL: biam

All the above are correct, anything over three clicks is adjusted with the linkage when back on the ground.[8D]
+1, Also I do everthing possible to have 0 sub trim in a plane.

Bruce
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Old 11-04-2012, 01:01 PM
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Default RE: How much trim is to much?

If you're new to this, then there probably are a couple of possible answers to your question, and most address issues 'before' the question.

If your ailerons are aligned properly with the wing and that much trim is needed for the model to cruise level, there is probably a good/bad reason.

The reason could be as simple as you didn't align each aileron with the wing. If you did, then the wing is warped or the two wing panels are misaligned. When the ailerons are straight and true and aligned with their part of the wing, and the wing isn't warped, and is glued together in alignment, there is nothing left on a simple airplane like yours that can overpower that straight and true wing that would require a lot of trim.... unless....

Unless the ailerons were rigged out of alignment.

Everything about the problem can be seen by an experienced modeler from the rear of the model, that is, if it's an alignment problem. If it's not an alignment problem, probability is it's a rigging problem. That's what you've got if an experienced eye sees a perfectly aligned model from the rear.

If it's a rigging problem then it's amazingly simple to adjust the rigging so the TX has very little trim in it. It's worth doing that. It takes very little time for an experienced modeler. It's something worthwhile for any new modeler to take the time to do.

Here's the angle to look from. Notice you see as much of the left side of the fuselage as the right side. You hope to align your eye up and down so you see as much of the top of the wing as the bottom. If you don't there is a twist or warp or misalignment.

With 20 clicks of trim needed, there is a probability there is one of the things mentioned above in that model.
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Old 11-04-2012, 01:07 PM
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Default RE: How much trim is to much?

BTW, the model in the picture is a foamy. It's wing has a problem. It's vertical tail has a problem. The elevator shows the flight trim needed. That really isn't a problem. It's actually sorta normal.
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Old 11-04-2012, 02:00 PM
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Default RE: How much trim is to much?

Something almost never mentioned is the radio itself. Most the better radios have an item I think it's called trim value?? Don't quote me on that, I didn't feel like looking at my radio instructions and it's almost never used. It just has a numbered value as to how much trim each click or beep adds to the trim. I think {again} most of the factory default is set at #4 but mine goes up to 8 or 10. Only time I change it from the factory default is on bigger planes like 80 inches or bigger. On them when I hear a beep I want the controls to move a lot more then normal. Others will have a different idea about that. Not all beeps are the same!
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Old 11-04-2012, 04:55 PM
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Default RE: How much trim is to much?

Do a Google search for "Dean Pappas trimming". You will find 3 downloadable pdf files that will help you understand static trim (what ya do on your bench before you go fly) and dynamic trim (what ya observe while the plane is in the air performing specific trim maneuvers). Then you can make your own decisions. The more you know the better it gets.
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Old 11-04-2012, 05:04 PM
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Default RE: How much trim is to much?

Old habit of pre computer radios. Always mechanically adjust the control surfaces back to center trim after the maiden !
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Old 11-04-2012, 05:17 PM
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Default RE: How much trim is to much?

Another old habit from back then...

Immediately after the maiden, look at what trim your model needed. (Do that from the perspective illustrated in the picture above.) Considering what trim the model required, look again to see where your rudder, elevator and ailerons are trimmed to. While looking at them, look again at the wing to see if you can now see a warp or misalignment. And look at the tail for the same.

Every new plane teaches you something. Keep in mind that before the maiden, you had rigged the ailerons, elevator, and rudder just where you thought they should be.
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Old 11-04-2012, 05:53 PM
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Default RE: How much trim is to much?

Your horizontal stabilizer is not zero to the wing. Not a problem if the stab is not hard mounted. If it is than your SOL unless you can shim the wing.
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Old 11-04-2012, 06:16 PM
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Default RE: How much trim is to much?

Quote:
ORIGINAL: SeamusG

Do a Google search for "Dean Pappas trimming". You will find 3 downloadable pdf files that will help you understand static trim (what ya do on your bench before you go fly) and dynamic trim (what ya observe while the plane is in the air performing specific trim maneuvers). Then you can make your own decisions. The more you know the better it gets.
+1. I use this trimming chart for every model I build. Most of my planes require very little adjustment since I began doing this.
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Old 11-04-2012, 08:23 PM
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Default RE: How much trim is to much?

There is no real need to correct the trim mechanically. Enjoy the perks of a computer radio and fly, fly, fly.

Kurt
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Old 11-05-2012, 01:13 AM
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Default RE: How much trim is to much?

Quote:
ORIGINAL: Bozarth

There is no real need to correct the trim mechanically. Enjoy the perks of a computer radio and fly, fly, fly.

Kurt

There are actually two reasons to correct your trim. Both have something to do with the rigging. Remember the rule that your pushrods should make a right angle to the hingeline?

When you've got a large amount of trim required to bring any surface into alignment, that screws up the right angle at the servo arm. That means you're introducing differential deflection at the servo arm. How much? Depends on the reason the surface was out of adjustment.

The other reason is your radio is also going to go differential on you. It'll have one of two problems. It'll have fewer 'cycles' to divide up your stick travel one way and more the other way. Or it'll actually send fewer 'cycles' one way than the other. Even a computer radio can't read your mind. It won't know that you are considering that trim as a permanent setting in your mind.

You will need to adjust the radio no matter what, so take about a minute longer and unplug the connector to the horn on that surface, screw it in or out as needed, and connect it back. It'll take you about a minute for each surface that's not centered. There are a couple of good reasons for having your rigging setup correctly. If you're lazy enough that you'd rather not take that time, you might have found the reason the plane took so much trim.

It really is worthwhile to make the plane right by the old rules. And it doesn't take but a minute or two.

But the decision about using the radio or adjusting the rigging REALLY should come after inspecting the plane to find out WHY a 'perfectly aligned' plane would need so much trim. If you're new at this game, you really should figure out if you missed something while assembling the ARF, or if something else is wrong that is actually what needs to be corrected.

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Old 11-05-2012, 02:00 AM
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Default RE: How much trim is to much?

My response to the original poster here in the beginners forum: You don't have to, but you could. Go fly, fly, fly. and then decide.

Kurt
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Old 11-05-2012, 07:15 AM
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Default RE: How much trim is to much?


Quote:
ORIGINAL: Gray Beard

Something almost never mentioned is the radio itself. Most the better radios have an item I think it's called trim value?? Don't quote me on that, I didn't feel like looking at my radio instructions and it's almost never used. It just has a numbered value as to how much trim each click or beep adds to the trim. I think {again} most of the factory default is set at #4 but mine goes up to 8 or 10. Only time I change it from the factory default is on bigger planes like 80 inches or bigger. On them when I hear a beep I want the controls to move a lot more then normal. Others will have a different idea about that. Not all beeps are the same!
The current crop of computerTX's will allow one to set the sensitivity of the trim as GB has pointed out. Most radios come with a default trim sensitivity or resolution of 4 ms which means every beep or click of the trim lever will apply 4ms worth of signal to the servo. Truth be known, most servos available today will barelyrespond to this level of signal; they just can't resolve anything finer..... Consider that a servo's full travelresults froma signal strength of around +/-1000 ms thereforea single trim click is around 0.4% of the full travel. Very very small

Futaba and JR servos are about the only ones that are designed to accept more sensitive input than that, making them higher performing than most of the others. Airtronics and Hitec also have some servos capable of higher resolution as do some other brands such as Savox and Spektrum....

Nevertheless, a trainer will practically never need more sensitive trim setting than that, even if the servos couldresolve the signal.Still, 20 clicks or beeps of trim is significant no matter what and it should be something the OP should correct mechanically at some point. No, it isn't critical that the mechanical correction be done immediately; it won't crash the model or anything like that. Except one should always have the maximum amount of trim range available, and as beginner, it's a great habit to get into from the start.... The higher performing models in his future will benefit
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Old 11-05-2012, 07:32 AM
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Default RE: How much trim is to much?

Being a beginner is the best time to listen, learn and do things the proposed correct way. Even though the radio will allow the plane to be flown with surfaces so far out of adjustment doesn't mean it's the "right thing" to do.  You won't be doing yourself a favor once you move into larger more advanced planes if you let the radio do everything for you.
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Old 11-05-2012, 09:29 AM
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Default RE: How much trim is to much?

If your plane is needing a bunch of up elevator trim to fly level then you know the CG is too far forward. Instead of fly fly fly why not move the battery pack back a little or remove some lead from the nose and start making corrections while you are there at the field and can fly the plane. Just a thought? The field is even a good place to do some prop testing to find that perfect magic prop all new pilots ask about.
Fly fly flying a plane out of trim isn't the smartest thing you can do. Trim work begins on maiden day at the field. That's also where you locate a good instructor to show you how it is done. It isn't hard but it is something you should do before you fly fly fly.
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Old 11-05-2012, 09:56 AM
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Default RE: How much trim is to much?

So you are assuming the elevator trim was required because of an aft cg. That's ok. Just a thought; what about a poorly installed stab, incorrect wing incidence, incorrect thrust...And where was his elevator prior to trimming.

I think a beginner wants to fly, fly, fly as opposed to searching for the perfect cg spot, or better yet, finding that magic prop.

Go fly, fly, fly. And when you come home, tinker with the plane in the shop all night long. Then go fly, fly, fly all day again.[X(]

Kurt



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Old 11-05-2012, 10:02 AM
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Default RE: How much trim is to much?

Yes , you are suggesting to fix the problem which is good as opposed to someone just saying don't sweat the small stuff, just fly it and don't worry about it. They don't have to fix it at the field but that is where most of the knowledge is and the help to get it corrected properly.
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Old 11-05-2012, 11:07 AM
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Default RE: How much trim is to much?

Agreed. But responders need to use something more than "Flying a plane out of trim isn't the smartest thing you can do." "Do things the proposed correct way." "You won't be doing yourself a favor,,," "You will need to adjust the radio no matter what."

None of these statements technically back up anything.

Kurt
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Old 11-05-2012, 11:13 AM
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Default RE: How much trim is to much?

What ? Did you actually read any of the responses here?  Reasons were given as why someone should correct these issues.
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Old 11-05-2012, 11:27 AM
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Default RE: How much trim is to much?

Yes, and I'm exhausted.

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