Flying my Dolphin I notice it requires a bunch of rudder to do something like a loop or an Immelman turn or something. Is this pretty normal? It always wants to pull to the same side. I just tried laterally balancing the plane but I'm not sure I know what I'm doing (rested plane on vertical stab and held prop blade. Never got it to balance, but it seemed to fall to either direction an equal amount). What are some of the causes of this? I think if I had a better understanding of the cause, I'd be better at compensating for it during flight.

Thanks guys...flying again today if the weather holds up

gaRCField,
Yes, the rudder is used to keep a plane tracking straight through a loop or any manuever that has a portion of a loop as a compenent. Usually the wind is the cause of throwing the plane off of track in a loop, and the rudder is used to correct for this. If you plane is always not tracking straight then the setup of the plane is incorrect and needs to be fixed. It's not only the lateral balance that will affect it. The location of the CG can affect it as well. Also, if the plane isn't trimmed properly it can affect how the plane will track through a loop.

Ken

Thanks Ken.

If the main cause is the wind, wouldn't this cause the plane to turn out of the loop in opposite directions at opposite ends of the pattern?

I am still currently working on finding the right CG. The plane balances according to the directions, but I was told a good test for sport planes is inverted flight, and the amount of 'down' elevator needed to fly it straight.

Sounds like it's a normal phenomenon, though, and that I plainly need more practice. Thanks for the help!

Yes the rudder is the primary control to maintain tracking during a loop and the most common off tracking occurs during the pull up and normally to the left is propellor (P) factor (most conventionally configured airplanes will yaw to the left during the initial pull (yaw not roll).

P factor is the production of more thrust on the right side of the propellor disc than the left when ever the propellor disc is being pulled to a high angle of attack to the relative wind. It is not torque. Torque reacts in roll not yaw.

This can be minimized somewhat with a small amount of right thrust.

John

Not necessarily. Any crosswind will push the plane from the side while in the loop and require the use of rudder to keep the plane tracking straight.

Ken

Often, as I have found anyway, our control and the way we handle the transmitter has a lot to do with the attitude of the plane as you enter a maneuver, such as a loop. It takes practice to add elevator without ANY aileron influence. Practice and focus. Try to do a loop and focus on your straight back pulling of the elevator. If the plane is set up properly, your and your input is straight back, the plane will do a nice round loop without any roll. And of course, it helps to start out by flying directly into the wind.

As I said, practice and focus works every time. And as my 'instructor/mentor' always tells me, burn fuel. Period. Burn fuel and practice practice practice.

CGr.

If you find that this is not wind related there are two likely causes. One is lateral balance, and the other is too much right/left thrust on the engine.

I've found that slightly higher spring tension on the aileron control than on the elevator in the TX helps quite a bit in this regard. (Mainly for heli's, but it also helps a lot for planes too.)

You're right. My mentor/instructor suggested that I tighten up the tension as tight as I could get it. So, I did. And I feel that alone improved my handling of the aircraft. I was no longer, unknowing, pushing aileron while pulling elevator.

Nathan.. It contributes, but it is by no means the answer. Many times, people just don't know how or why they should do a lateral balance so it does not get done. As for thrust, well, adjustments to thrust angles can be a pain in the butt, and again, most don't know how or why, so they leave it the way it came in the kit/arf. But thanks for pointing that out. It adds more to what I have to do to my Super Star 120.. []

CGr.

One more possibility is that your elevator is not stiff enough. This usually happens with a wire connection between an elevator in two halves. When you pull up one half goes further up than the other giving you a roll component.

Quite common on artfs

If your airplane is in perfect trim with zero wind, then it takes right rudder for inside loops and left rudder for outside loops.

Thanks Highplanes.

Yeah, can 'ya tell I'm a pattern pilot?

I spend months on airplane setup after each flight to get things "just right."

Well I'd love to know how and why, and did I mention how...to do a lateral balance. I believe a 6lb, 60mph flying model spinning a prop at 13000rpm should be balanced as much as possible. I am very interested in pattern flying to boot.

Thanks.

Be sure to make sure your plane is trimmed correctly and that the two elevator halves are parallel. If the elevator halves are not even, the plane can roll slightly when you apply it.

When I do a lateral balance, I attach a string from the engine drive hub to the tail wheel. I then suspend this from a hook in my garage ceiling. I may loop the string around the hook a few times so the plane doesn't slide for and aft. You'll immediately see if one side is heavy. I tape weights on the high wing tip until it is balanced. You can remove some wing covering and permanently epoxy the weights inside or just screw them on the wing tip if it isn't too much. Another option is to sink screws or nails into the wing tip for weight. It is also a good idea to recheck the CG after the lateral balance unless you put your weights right in line with CG.

Pattern fliers use to check the thrust by flying their models in a straight up line, if the model tends to go to the left then you need right thrust and vice versa. As has been noted I also would check the elevator halves to know if they move accordingly, the use of an incidence meter here is a must if we are thinking that the problem resides here. On some models like Cap and Sukhoi (to name just a few), at certain level of throw of the elevators the plane will tend to roll or even to snap (Do you have heard Snap-Cap?), so you have to be very careful on adding throw on any model and stick with the recommended throws by the manufacturer.

Actually, I know a pattern guy who flies the Masters sequence that checks his elevator halves using the same technique I described above. I wouldn't go so far as to say an incidence meter is a must for this task, although it is still nice to have one around. [8D]

I didn't write this, and I don't remember where I got it, but it seems fairly concise.


Starting with a model that has been built and balanced as per the kit instructions then it should fly quite well. Some simple trimming will help remove any minor building errors and generally take the model to a relaxing hands off type of flyer.

The following is a basic trimming process and as long as it is done in the order below it does not need to be an iterative and long drawn out procedure. Generally a couple of evenings will take you through the process.

All checking will be started with the model trimmed to fly straight and level (hands off)at a low to medium power setting. All checking will be done flying into the wind.

A couple of control facts need to be understood.
Control surfaces are more effective at higher speeds and less so at low or take off/landing speeds.
Engine thrust lines (sometimes known as the effect from prop wash) are very predominant at low speeds( landing/take-off) and are negligible at flying speeds.

Step one: Set Balance Point.

The starting balance point should be marked on the model.

Trim out to fly hands off straight and level into the wind at a low to middle throttle setting.

For a low wing aerobatic model:

Roll inverted, release the sticks and observe.
Severe dive ..... nose heavy.
Slight dive..looks good.
Straight and level..perfect.
Climb..bit tail heavy.

For a high wing or non aerobatic model.

Go rapidly to full power and observe the flight reaction.

Climb..nose heavy.
Very slight climb to no change..ok.
Dive..tail heavy

Add or remove weight as required and then repeat the test until you get the right balance point is found.
The plan balance point is usually quite conservative as a nose heavy model is sluggishly stable. As the true balance point is approached the model will become more lively and sensitive to elevator input and may require less elevator throw for normal flight. (low rate on the transmitter).

When the balance point is found mark it on the fuse as a future reference point.

Step two: Correct Thrust line.

This step is quite sensitive to the wind direction and extra effort should be made to always fly straight into the wind.
The objective of this test is to fly a shortish vertical line and observe what direction the nose of the plane falls to as the speed falls off and the plane comes to a halt.

Before taking off set the rudder at the neutral position and do not touch the rudder trim.
Trim out to fly hands off straight and level into the wind at a middle throttle setting.
Pull to the vertical and fly a half throttle vertical line with no corrections and observe.
Two things can happen:
if the model immediately starts to pull to one side then it is likely that the rudder is not straight. Go back to the straight and level flight and add a couple of clicks of opposite rudder trim (ie model pulled left...add right rudder trim) then repeat the test.
The model climbs reasonably straight and then pulls left/right etc as the speed falls to zero. This pull to the left or right is caused by the thrust line of the engine being incorrect.

To confirm this the test should be repeated a couple of times just to make sure its not the wind causing the problem. Typically the model will pull to the left as it comes to a stop. The model may also try to ā€œfall on its backā€ or fall to its landing gear in combination with going left or right. The first step in correcting the thrust line is to shim the engine in the opposite direction to the way it falls. For example; pulls left then add some right thrust. It is usually best to correct the side thrust first before correcting vertical thrust lines.

With the side thrust corrected you should see a noticeable improvement during take-offs and landing overshoots. The quick application of power should now have the model tracking straight dwom the runway with no tendency to pull/roll left.

The test can then be repeated to check for down thrust correctness. If the model ā€œfalls on its backā€ then you need some down thrust. If it falls to the landing gear side then you need less down thrust. Unless you are planning to do hovering type maneuvers or some advanced aerobatics it is probably not worth worrying about getting the down thrust angle correct.


Step three: Aileron Roll correction.

This is a very easy test to do and corrections can be made at the field.

Climb high and throttle to idle speed.
Push down to a vertical dive give full right aileron and observe.
If it rolls axially then no corrections are needed.
If it rolls as if in a barrel then you need less 'up' aileron throw on the right side.

Repeat the exercise for the left roll.

If you have a computer radio and one servo per aileron per channel, ie left servo on ch2 and right on ch6 with 2 and 6 mixed then you can adjust the aileron travel individually on the radio. If the servo's are joined with a Y harness or a single servo is used then you will have to adjust the throws mechanically.

I have found that mid wing type planes usually do not need any aileron differential. High wing and low wing models typically need some differential so that the down aileron travel is about half of the up aileron travel.

Step four: Remove rudder bad habits.

This is not worth doing if you are flying a trainer model as the rudder on a trainer is not very effective.
Also if you do not have a radio with mixing capabilities then this step can not be done.

Fly straight and level and give full right(or left) rudder and watch.

If the plane dives then mix some up elevator trim into the rudder.
If the plane rolls rapidly then correct correct with some aileron mixing.

Remember to check and correct for both left and right rudder.


Step five: Loop trim.

Straight and level, medium power.
Pull up and do three reasonable tight loops in succession. Do not add any corrections.
If the plane tracks well but drops a wing then it is heavy on that side and you need to add a balance weight to the other wing tip.
If the plane tries to corkscrew ie each loop is progressively further left (or right) than the other one then you have a aileron that is not in alignment to the wing. If the plane tracks left then the leading edge of the left aileron is either high or low in relation to the trailing edge of the wing and is causing the plane to skew to that side. You need to correct the aileron alignment.


END

Thanks, that was really helpful. I had some difficulty aligning my ailerons, and it sounds like this could be related to my plane corkscrewing through loops. I'll check it out on Saturday.