rudder or engine thrust

[bigalrc]

What is the best way, during flight trimming ,to tell if a plane needs an engine thrust adjustment or a slight rudder adjustment. They give very similar results.
Thanks, Al

[Dan Baker]

Al: For the most part, engine thrust is set by establishing a vertical upline (your plane must have unlimited vertical). Hold the line and let your thumbs off the transmitter. Adjust thrust until the plane tracks straight up "hands off". Rudder trim is done on horizontal flight. Of course thrust to weight has a lot to do with it. If you don't have unlimited vertical, upline testing is useless. What plane is it? Engine size? Weight? What type of flying are you into?

Dan,

[bigalrc]

Thanks for your response Dan. Right now I'm practicing 3-D flying and getting comfortable with all the maneuvers with a dw yak foamie. I have read the flight trimming charts , but it seems to me that on an upline if your rudder is off slightly you could get the same results. Not to argue against the charts it just seems to be a fine line between slight thrust and slight rudder problems. So I was looking for different ways to distinguish between the two.

[Dan Baker]

Most trimming charts say what to do, but they do not say WHY we do it that way. Let's take one example of using rudder to trim for thrust changes that are needed. If you need right thrust and decide to put in right rudder trim instead, then the right rudder trim is there ALL the time. Your plane will always be wanting to yaw to the right in all flight attitudes, at all throttle settings. Even at idle on landing approach your plane will want to yaw away from the center line. It's best to trim thrust with thrust changes. Most all thrust habits are involving 3/4 to full power. So your thrust changes only affect the plane when the power is up, just what we want.

Hope this helps,
Dan Baker

[zoomer260]

Me thinks I have wondered about this a little too. Most planes I have had required a little rudder imput on the uplines. But the plane does not "yaw" when I feed in a little rudder, it just goes up straight.

Seems I had at least one kit that the vertical stab was actually built with it in on the plans ?

Next season I am going to do more of what most seem to do these days and really try to get a plane to fly as completely neutral as I can.

[SportFlyer]

I worry about this as well as I have yet to go through a complete in-flight trimming process. I don't have a lot of experience trimming and sometimes I second guess my findings then just end up flying around them, so much that if someone wants to fly my plane ( because it seems to be flying really well) and I hand it to them they can hardly keep up with it and I have to end up taking the transmitter back.

So how long does it take you guys to fully flight trim an out of trim plane...and what seems to be you method to the madness ???

[tomatocan]

On my larger gas planes I prefer 0 thrust angle, and then I use a throttle to rudder mix to offset any thrust. I began doing this after reading an article by Chip Hyde that extolled the virtues of such trimming. It works better in almost all situations for me. With point mixing, I can have a plane that acts neutrally in virtually every throttle setting. It takes me roughly 10 brief flights and landings to get the mix near perfect.....I then leave it alone while I work on my other trimming. I will usually come back to it after a while and fine tune it a bit more. I have yet to use more than 3% on my gassers.

On my smaller 4 stroke 3d planes, I have been using about two degrees of right thrust , and then finishing out the trim with the throttle to rudder mix. It seems that the torque of the four stroke needs more compensation than I want to use in just the radio. If I try to get it all in the radio, I end up with a mix closer to 12% in areas, which I really don't like.

I have gotten very used to my radio, so I can usually get my plane to about 90% happy in just about ten short flights....this includes a rudder to elevator mix, a rudder to aileron mix, and the thrust mix. It took a lot longer at first. I have been starting with just a linear mix for pitch coupling to get in the ballpark, then after everything else is good, I use a point mix to get it perfect. I have noticed that if I don't take the time right away to do this, it never gets fully done.

I do the cg first, since it will affect the other adjustments... then the thrust, then any pitch or roll coupling.

[Tired Old Man]

Final trimming never really stops, though 60-80 flights is fairly common to get things real close to where you want them. I start with center of gravity and move forward from there. I'm another that favors an initial zero-zero engine thrust angle. Never any right thrust, with a change in up or down thrust determined after flying to establish any need.

[tomatocan]

BTW....adjust the rudder trim to neutral first before you try to make thrust adjustments.....fly the plane at a medium cruise throttle setting directly away from yourself and into any wind. You should be able to see if the plane is yawing to one side or the other. Use your rudder trim to get it straight.....then after you are satisfied with that......work on your thrust. You are right in thinking that if the rudder trim is off, you wont be able to get a good thrust setting.

[Tweaker]

One chart I read said go to full power level flight (not an extended bonzai run, just get it level and throttle up) Pull to an upline. If it yaws right away it's rudder, if it slowly pulls to the side higher in the climb it's the thrust. I don't know the accuracy so take with a grain of salt. All Basic CG, lateral balance and trimming has to be done first as well. Just trying to give you more info to work with, sometimes different methods work better for different people.

If you have anyone around that trims their own planes for IMAC, they can probably get you on the right track.

Addendum: This method will be inaccurate if the rear stabs are not square with the wings/fuse.

[SportFlyer]

Good info keep em coming guys.

[bigalrc]

I agree with Sportflyer, the more responses the more useful information we will get.
Al

[pipercub123]

	Quote: Originally Posted by zoomer260
	Me thinks I have wondered about this a little too. Most planes I have had required a little rudder imput on the uplines. But the plane does not "yaw" when I feed in a little rudder, it just goes up straight. Seems I had at least one kit that the vertical stab was actually built with it in on the plans ? Next season I am going to do more of what most seem to do these days and really try to get a plane to fly as completely neutral as I can.

I agree, pilot that plane sonny and use the rudder stick to make corrections! For pure contest like IMAC I can see going the extra to trim it out, but what has happened to the good ole days where flying a straight line was merely how well the pilot can feed in the inputs?

I too would like to get my plane to fly as neutral as possible so I'll likely be doing the same. I can't afford to wreck up a plane and I'd rather fly than build so I feel I'll have it longer by doing more IMAC flying and only careful 3D a few mistakes up!

[zoomer260]

I agree, it's getting interesting. Seems my planes back when had no built in right thrust but did have built in right vertical stab.

These days they all (I think) come with about 3 degrees right thrust and a straight stab. 'Course I've forgotten most of what I used to know back when. Quite a few times I "re-learn" something and remember that I used to know it already.

[nate428]

i do this thrust angle on maiden flights, i will only trim ale and start doing vertical climbs till i get a good read on what its doing. i want both elv and rudder centered and thrust angle on the motor adjusted to achieve near straight climbs. afterward i can worry about cg by flying canopy up, trim it, and then inverted. since i know my thrust angle is ok the planes reaction is probably going to be cg related only.

i found that if my rudder isn't centered it will cause wing rock in harriers.