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Old Aug 01, 2012, 09:38 PM
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Trim Question

In alot of the build threads you have folks telling you to add different amounts of trim to an aircraft prior to first flight. Say 1/8 R Rudder. 1/4 Up Elevator etc. How do these fractions correspond to the controller or airplane? Do you set the trim on the controller bar up 1/4 of the way or do you adjust the flight surface on the plane up by that much in inches.

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Old Aug 02, 2012, 06:05 AM
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That's a good question Nightstone, I would take it as a measurement on a given surface extreme. So 1/4 UP elevator sounds like 1/4" or 6mm. Mind you that sounds like a huge amount ! My Funbat is flat elevator trimmed, it only moves 8mm total up or down and is manic ! Someone needs to clarify I think, maybe it's 4 clicks up-trim
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Old Aug 02, 2012, 07:13 AM
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For the maiden flight, all the surfaces should be set to zero trim . You never know how much trim in either direction you may need. Even two identical planes may need different trim clicks. CG, slight warps make all the difference.

Gord.
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Old Aug 02, 2012, 08:18 AM
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Like Gord said, all control surfaces should not be trimmed for the first flight. Ideally you want the plane to fly straight and level at 65%-75% throttle, so adjust the in-flight trims likewise. Land and adjust the clevises (or similar depending on what you're plane is equipped with) to these new points.

You'll always need a bit of TX trim adjustment in every flight, and every flight will be a little bit different. If you find you consistently have a trim somewhere (like aileron trim constantly at 20% for example) then adjust the clevis or servo neutral point if you have a computer radio.
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Old Aug 02, 2012, 08:55 AM
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I think op is confusing surface deflection with trim. Trim is measured in clicks, or sub trim on a transmitter. Deflection is usually measured with a protractor or a surface deflection measuring tool.

http://www.rcgroups.com/forums/showthread.php?t=346379

http://www.rcuniverse.com/forum/m_63.../tm.htm#631506
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Old Aug 02, 2012, 10:12 AM
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dedStik, so what's 1/8 or 1/4 ? Now you have me wondering too !
I can say most of my models fly with little or no incidence even on elevator, so 1/4 inch would be massive ! One of my models, max deflection is only 5/16" and that's flying like a nutter
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Old Aug 02, 2012, 10:17 AM
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That's what I'm trying to figure out. I don't know anyone that flies that would fly a plane that you had to have an 1/8th or 1/4 inch surface to control it. Imagine the lack of control in the other direction.
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Old Aug 02, 2012, 10:27 AM
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Quote:
Originally Posted by dedStik View Post
I think op is confusing surface deflection with trim. Trim is measured in clicks, or sub trim on a transmitter. Deflection is usually measured with a protractor or a surface deflection measuring tool.

http://www.rcgroups.com/forums/showthread.php?t=346379

http://www.rcuniverse.com/forum/m_63.../tm.htm#631506
So when I see a design where the Designer has added in 1/8 up elevator. That is 1/8 of the distance the elevator will travel ( Deflection ). Deflection is measured in degrees.

This all came up when I built a snowball. Its a nutball with an elevated motor mount and skids. I had a really bad time getting it to fly. It would take off, flip and crash. Thinking it was the CG I adjusted it. Same results. After 3 crashes I decided to launch it straight up. I managed to get it high enough to where I quickly realized what the issue was. I frantically trimmed it and now it fly's great.

That got me thinking about those fractions I see in the build threads. 1/4, 1/8 etc.

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Old Aug 02, 2012, 10:34 AM
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That 1/8 or 1/4 in. is measured from the furthest distance of the trailing edge of the surface to the hinge line.

Gord.
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Old Aug 02, 2012, 10:58 AM
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Quote:
Originally Posted by flypaper 2 View Post
That 1/8 or 1/4 in. is measured from the furthest distance of the trailing edge of the surface to the hinge line.

Gord.
Thanks Gord

So that measurement would be 1/8 or 1/4 up in inches. Not a fractional value of the deflection. Right? This would make alot more sense than 1/4 of the travel.

Nightstone
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Old Aug 02, 2012, 11:01 AM
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That's right.

Gord.
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Old Aug 02, 2012, 11:03 AM
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By jove I think I have it (the Eureka moment !!!).
These measurements must be the amount of throws at trailing surface edge, so 1/4 will be 1/4" deflection from centre or flat. It's the suggested deflection amount (up or down) for elevator or aileron, well or rudder for that matter when you move full stick in given direction. With control surfaces being different widths, the normal 'measurement' is not in degrees of movement because if the surface width is 2" at 30deg's, that would be a huge amount more than same angle with a 1" surface. So it's the recommended setup deflections, not how much incidence to build-in before you start (this is almost sounding like 'Call-My- Bluff' now).
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Old Aug 02, 2012, 11:17 AM
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Whoo Hoo... This will make some of these first flights on scratch builds alot easier. Thanks Alot.

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Old Aug 02, 2012, 03:51 PM
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re;trim

To start out on a new plane trim setting this is what i do(to be safe).On the TX (if programmable) set all trims to the middle except for the throttle.Set the throttle to little under half way. Set the D/R or the throws to 50%.That will give you just enough to get use to the new feel.As you feel more comfortable with the flying increase the D/R

Almost forgot set the expo to about +40
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Old Aug 02, 2012, 04:13 PM
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Heli... Similar for me, except I dial in 50% expo and no D/R (in case my model needs every bit of help not to nose-in). Most of the time I then have a ground adjust D/R after first flight, since it almost always has more than enough throws. More important I find for elevator. My first elevon model would not have had a second flight if I hadn't had full elevator available.
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