Does everybody add trim/adjust right thrust on their engines until the plane goes
up straight at all thottle settings ?

My plane veers left hard at 1/2 and only goes up straight at full,
but I usually only fly at around 1/2 - 3/4.

L

Yes. If your plane consistently behaves that way, you need to take out some right thrust. (move the thrust angle to the left - hardware)(add throttle to rudder mix - software)

CJ

I guess I disagree. He needs to add more right thrust to the engine to overcome this left dirft with power.

Read closely. The left drift is at part throttle. At full throttle he is neutral. That means he has trimmed his rudder to the left to fight excessive right thrust at full power. Adding left thrust will allow him to move the rudder trim towards the right at full power, which will also neutralize his part throttle drift.

CJ

CJ is correct.

He has left rudder trim to fight the excessive right thrust, so at partial throttle the left rudder trim takes over.

OK, I see, thanks

Yeah, It gets confusing. I can't tell you how many times I've gone the wrong way with thrust corrections!........

How on earth did you guys dream up that answer ? If lennyk has an airplane
that holds a straight up line with full power then his thrust line is right where
it needs to be assuming he is running a neutral rudder trim. I didn't read anything
about him trimming thrust with offset left rudder and hopefully that's not what he's
doing. You will never get an airplane to go straight up at all throttle settings all by
itself. You will need to hold some right rudder at reduced power not take out right thrust.
The name of the game is to get it to fly straight at full power by using right thrust not
rudder trim. If he takes right thrust out he'll end up with an out of trim hair ball that
he can chase all over the place.

Actually.. to me this sounds like a crooked airplane. I'd make sure everything is straight before you start messing with thrust line changes.

Well I have checked and everything is straight as I can check.
The plane was involved in a midair shortly after building and the firewall box was replaced/modified so the right thrust may need some adjusting hence my posting.

Note, I have used a smaller prop and the side pulling is much less so I am inclined to think it is not crooked.

JLB, Doug,

Let me ask this this question,
should a plane be able to be trimmed to the point where it will not pull to the sides at any throttle setting on an upline ? Or will there always be a compromise ?

Lenny,

Don't let the last two posts confuse you. Crooked or not, your plane would benefit from a bit of left thrust - as long as your initial post is correct.

If you want to make one more check, then trim the rudder so the plane goes straight in a perfectly vertical up line under full throttle. Check it different directions, as it will tend to weather vane into the wind. Once you are satisfied with your vertical, full throttle, up-lines - now fly directly towards and away from yourself in level flight while using 1/2 throttle. If, with the wings level, the plane slowly tracks left - then your thrust line needs to be moved to the left. (Or, you could add left rudder to throttle mix to accomplish the same thing without messing with the engine mount. I prefer moving the engine, but that's just me.) Make your adjustments and flight check again from the beginning. If your lucky, you'll hit it after one or two attempts.

In answer to your last post........you can trim the plane with thrust angle to fly straight up at all steady power settings, but only for one speed. For most planes the speed isn't really a factor either. It may still pull to the canopy or wheels, depending on CG. But it should not track left or right if the wind is calm and the thrust is steady. As you noticed, changing the prop may alter the thrust angle requirement too. The reason for this is it changes the strength and size of the spiral airflow the prop creates around the fuselage. This airflow impacts the left side of the rudder, causing the plane to drift left - which is why you need some right thrust on the engine to begin with.

Have fun! CJ

Lenny,

You're correct that you can't trim out an airplane to behave the
same in all flight attitudes. You are always dealing with compromises
of one sort or another as many variables are affecting flight characteristics.
Right thrust is introduced to an aircraft to counteract the P-factor (torque)
induced by the engine and not airflow. If you want to see torque very clearly
in action take a look at a helicopter under power or an aircraft doing a hover
and the torque roll that takes place. Leave the thrust line where it is and go
have fun rather than chasing phantoms.

Torque factor is an axial (aileron only) affect when the power is added rapidly. It causes the roll during torque rolls, but does not cause a heading change. In level flight it is only noticed during engine acceleration, not steady power.

P factor is a result of aircraft angle of attack, because the downward travelling prop blade has more angle of attack (bite) to the airflow than the upward travelling blade, it pulls the nose of the aircraft left at slow airspeeds and high power settings - requiring right rudder to negate. Or, it can be a factor at high speeds when pulling high "g's". If you are doing an inverted harrier, the P factor will require left rudder instead of right.

Spiral airflow is a result of the propeller inducing a change in direction of the free stream airflow as it accelerates it. In front engine applications this affect is always a player and is usually to aircraft nose left, regardless of aircraft attitude.

Gryoscopic affect is a result of the gyroscopic stability of the crankshaft and prop as they spin. If you rapidly pitch the aircraft nose up, the Gyro affect will pull the nose to aircraft right. It has no effect unless the aircraft is changing attitude.

So, what does all this mean to a simple minded pilot like myself when in the middle of vertical up-line? Torque is not a factor as the power is constant. There is no P factor as we have zero angle of attack. There is no gyrospic affect as the plane is not turning. So.......we are left with spiral airflow. Fortunately, we can trim the spiral affect out with right thrust. And, when done correctly, the plane will fly straight up under all steady power settings. In fact, if you don't ensure your thrust line is correct, you will always be fight your plane instead of concentrating on your pattern work. The "factory" setting for thrust angle gets you close. Lenny, as you pointed out, there are other parameters. like prop and engine size, that can change your requirement for right thrust trim. Anyone serious about acro should seek to fine tune the factory thrust setting.

Allas...........your plane will fly all day without trimming anything if you are uninclined to do so. And a fortunate few will luck into the correct setting right out of the box, never empathizing with those of us who have to work to get our planes flying straight.

And that is how I "dreamed up that answer."

By the way, I liked my short answer best.

CJ