Howdy!

Now that I have come along way with my stryker (all kinds of stunts including puttering around upside down) I've decided to get a 2nd plane. Yes, against recommendations I got a stryker as a first plane...

Anywho, my new plane is a World Models [link=http://theworldmodels.com/para/products/airplanedetails.php?airplaneid=186]F4U Corsair[/link]. I did some reading and the reviews are mostly positive. I like the war plane look and I'm not really interested in a bunch of 3D.

The question is, what exactly do I do to trim it out before the first flight? With the stryker I pretty much do all that in the air after fiddling, but I want to make sure this thing doesn't drop like a rock. I know how to get the COG correct, I'm more concerned with ailerons and the elevator. The elevator especially because it is a split elevator (2 rods from the servo work each side). I can eyeball it pretty well but figured it never hurts to ask a question.

So, any thoughts/hints/ideas? Thanks!

PS: Did some soldering for the first time in my life for this plane. After a couple you-tube videos and burnt fingers things seemed to turn out well!

Well, since you didn't heed to advice for a first plane, I won't say a thing about your choice for a second plane.

Mechanical trim simply involves making sure that at zero servo input, with all sticks neutralized including the trim tabs, that the surfaces are straight and flat with no up/down, left/right in them at all.

The way I do that is:

Before going on, make sure your transmitter, if a computer transmitter, is using an empty model with no mix, no enhancements (dual rate, expo, nothing). If it is not a computer radio, then move on to the first step.

First, disconnect all your control rod clevis’s from the control surface control horns.

Next, center servo’s by turning on the TX and RX and putting the TX sticks in the center, the very center.. not about center, but in the center. Center all trim tabs. This is a real important and an absolute necessity. There is no “about� with this. Get them right. If the servo arms are NOT centered, meaning if the arm you are using is not perpendicular to it’s side or front surface (depending on how your servos are mounted), remove the servo arm screw and rotate them until you find the one that is perfectly perpendicular with the side. See the sketch below. Put the servo arm screw back in and tighten it. All servo arms have one arm that, because of the splining of the shaft, will have one that is perfectly perpendicular to the side or the front of the servo. Make sure you do this correctly or you will introduce unwanted differential. Just push it on and see if it is perpendicular. If not, remove it, rotate it to the next arm and check that one.. do this until you have the right one. Turn off your TX and RX.

Next, make two lengths, say six inches, by four inches, of thin ply. Sandwich the control surface AND the stab/wing then carefully and softly clamp this so that it holds the control surface straight and in line with the wing or stab.

Now, adjust your clevis’s so that when you attach them to the control horns on the elevator/rudder/ailerons, you can do so without moving them (thus the reason for clamping the surface in the above step. Once you are happy with this step, remove the clamps. If you have split elevators with two rods, do one side then do the other side. Make sure they are the same.

Now move on to the next control surface and do this one. When you have all of them done, and have removed the clamps, and

Turn on your transmitter and receiver and check movement. Remember, when standing behind the aircraft, right aileron stick moves the right aileron UP. If it’s reversed, fix it!! This MAY result in the necessity of doing the above steps again. (reverse may cause the deflection to change, so go back to the first step, zero the sticks, zero the servo arms, then re-adjust the linkage.

Once you are done all of this, your initial trim settings should be at zero. You are ready to fly it and do the in-flight trim adjustments.

One thing to add to what CGR said.....

Once you've flown the plane and gotten trimmed out in the air, take another look at the position of your trim settings. The goal should be to have the plane trimmed to fly straight and level with the trim settings essentially at their neutral position, or a click or two one way or the other. If you've got one that is more than just a few clicks off of center, it's desirable to re-adjust that surface with the linkage.

What I do is use some sort of marker to indicate the neutral trimmed position of the surface in question, center the trim and then adjust the clevis at either the servo arm or the control horn to put the surface BACK at that position, with the trim centered. I'm not obsessive/compulsive about it, but I don't like to have a control surface trimmed for neutral flight, and have the trim setting halfway between neutral and maxed out. My goal is usually to have the plane properly trimmed, and all the trim settings no further than 5 clicks from center.

Another thing to remember is to get all of the mechanical linkages talked about in post 2 above correct MECHANICALLY correct first do not ue the electroinic "sub trims" in the radio to correct a bad mechanical hook up in the first place. The reason for this that if you ever hook up a buddy box to your plane, say you want a little dual with an instructor, the buddy box does not hold all those sub trims so you may end up with absolutely no way to retrim the plane from the buddy box. Been there done that

Yeah.. I was going to say all that, but my reply was a tad long as it was. Thanks for filling in the remainder for me.

And I guess one more addition to all of this. There is another long winded procedure to do the in-flight trims to get it to track straight, turn correctly, and to do maneuvers correctly, but that will take a few pages of text because you do each and every surface one at a time for up, down, left aileron, right aileron, right rudder, and left rudder as well as thrust angle. This is not totally necessary unless it is way out of whack, or if you want to do pattern type flying.

If you want more information, let us know and we can surely provide you with a link to get all you need to know.

CGr.

Contrary to popular belief, the position of the arm related to the servo has
absolutely no effect on control surface differential. the only parts of
the servo arm setup that has to be on a 90degree angle is the pushrod to
the arm. A servo travels the same distance no matter what angle it is
installed, but if the pushrod to arm angle is off it will induce a
differential of the control surface deflection. On most of the planes
we see the pushrods are parallel to the servo case, so CGretired's sketch
is very accurate. but I have played with small electrics and a few poorly
built planes that the pushrods were set at wierd angles to the servo
and on a deflection meter you could see that a differential was present.
this was easily fixed by setting the servo horn at a 90degree angle to the
pushrod. I made a slight modification to CGr's sketch to show what I
mean (the blue lines represent the pushrod and the red lines show the angle
between the pushrod and the servo horn).

This same principal applies to the control horn at the control surface.
an optimal setup is a 90degree connection of the pushrod and control horn
continuing down through the hinge line. I have added a picture (I am no artist)

You have to consider that the servo is square in the servo tray which would make it square with the movement of the pushrod at the center or zero point of the servo arm (note Overbored's sketch). That's why it's important to square the servo arm up at zero or the center point as my sketch showed. If it is not square, the arm starts off with plus or minus of the zero point so the arm will move more in one direction than the other, thus differential. So, with the servo zero'ed, and the servo arm square with the servo, the pushrod becomes square with the servo arm and it will move equally as much forward as rearward from center.

So, yes, it matters.

Note that on trainers, with one servo in the center, the servo arm on the ailerons are not square, but they are angled forward (uses the five part servo arms where the two in use are not square with each other but are at an angle to each other, more forward of center). This intentionally induces differential which helps prevent adverse yaw.

My my, we're getting technical.
CGr.

Just trying to show that if the servo doesn't sit parallel or at a 90 degree angle to the control rod
it can still be setup properly with no differential if the control rod and horn are at 90 degrees.
I guess I spend too much time with the setup masters.

The difference is incredible when a plane is properly setup comapared to the old good enough setup.
that is the reason Ken, Minn, and others else post technical details and pictures. Because if the job is worth
doing it's worth doing right, even on a trainer or sport model (second plane)

Another pic with proper angles

Yep, I agree totally, but it's easier and looks better (apperances are something) when everything is square and connected correctly. Mechanical trim is easier because your frame of reference is square and that makes everything else square when set up. And, as you know very well that the slightest irregular offset causes differences in the sky that are sometimes quite profound.

And, yes, of course, it flys much better once the trim is done right.

Were you there when Ron and I set up the Skylark 70? We spent quite a bit of time adjusting then flying then adjusting then flying. It was amazing how nice that plane flew once everything was right. AND, I spent some time when assembling that plane on making servo's square in the servo tray. You can fly it next time I'm out at Straw with you. It is clearly my most favorite sport plane.

CGr.

CG this is Saturday what are you doing up so early???

G'Mornin, Irish.

Yeah. I am going to the Stockton State College this morning to be a judge in a middle school science fair. I've done it for the past several years. Lots of fun seeing what these kids, a lot of them quite talented, are doing with their projects.

CGr

you are right some are very talented. I enjoy seeing what the young people are capable of.

It will be interesting what the group leader will assign me today. I usually get about 10 or so kids to judge, usually in the 12 - 13 year old agegroup. No one has done anything with RC aircraft yet. One of these days... ha..

CGr.

get a hanger 9 acro-throw

Thanks for all the replies. Yes, now I know about the stryker as a first plane being a mistake but I wasn't on forums at that time and the LHS certainly didn't argue that I wanted to buy it. So, I really didn't have anyone to tell me to start with something else.

But, it has gone exceptionally well even though I know it was stupid to start out. Since I see something like a stryker as a 2nd plane, and I'm very comfortable flying it, I see this as a third and next step up. Oh, I have flown a Super Cub a couple times but I just didn't want to go from the Stryker back to a Cub. Possibly another stupid idea but I do have trainers at my field who I've already spoken with to help with my first couple flights (and to trim it in-flight).

From this advice I now know I do need some work. Not all my servos are set at the 90 Degrees. I came as close as I could without using electronic centering. I've played around a bunch and just can't seem to get it to set right. Perhaps I'll turn the servo around and see if the links will allow it on the other side. I knew to do that when flying heli's so did it first when setting up the plane.. I will so what I can but the angle of the control rod is such that it wants to come out of the plastic tube very close to the center of the servo and it will require some modification to have everything working perpendicular as in the drawings...

Thanks!

CWHFSR

This exchange of information was just that. Keep in mind that none of this is difficult if you just sit down and do it right. Think about what you are doing and then set things straight (meaning, square as I repeated a few times) and work from that. Most of all, start out fresh by selecting a new model from your model selection (if using a computer radio) or reset everything to zero before starting out. If not a computer radio, then make sure you zero all trim tabs and zero all servos.

Do this by plugging them in your receiver and then moving your sticks and trim tabs to center. Yes, even the throttle, which is the toughest because it does not normally go to the center when released. But, you can work that out easy enough, I'm sure.

Then find the right servo arm by removing the servo hold-down screw and rotate it until the right arm is in the right place and it shows the square (perpendicular) setting on the servo then put the screw back on and tighten it. Remember that when tightening it, it will tend to turn... so turn on your transmitter again and things will center for you.

Then go forward as I discussed above. Above all, take your time and do it right. This will make things a lot easier at the field on that maiden day.

CGr.