Harry, where in my post did I say I was doing a flat turn? What I said it that it is common place to hold rudder to maintain ground track. Maybe you should understand what is being said before posting. Let's also take your comment about aileron differential not being of any use on a zero G up line. Do you have anything that would support that statement other then continuing to brow beat us into believing you? IMO one really can't argue with success, the fact that I have won multiple SW region IMAC contests using these methods illustrates success.

If the wings are level and the airmass isn't changing it's speed, then holding in rudder to maintain a ground track isn't right.

But on a typical crosswind landing we tend to need to lean on the rudder to get the plane to weathercock into the wind as it slows for the landing. The main difference between full size and RC is that windspeed is a much more significant component of our airspeed, so a 5kn crosswind is going to require a much larger change in yaw to maintain a groundtrack as the model slows down than for a full size.

That change in yaw has to be rudder induced because we all know planes don't weathercock into a crosswind as they slow down, they just change groundtrack.

Lowering the upwind wing (ie initiate a very gentle turn) will also help maintain the ground track as the airspeed drops for landing, but if you "must" keep wings level then rudder does the job.

When flying in a cross wind the plane flies no differently than it does in any other wind or no wind at all. But just at the moment the plane is about to touch the ground you certainly want to use the rudder to straighten the path of the plane relative to the ground, otherwise the wheels will hit the ground with a sideways component. If there is any positive roll coupling you might need a brief shot of opposite aileron at the same time. Model or full size makes no difference, except that you might get away with not doing it with a model, whereas a full size will be damaged if you don't straighten with respect to the runway.

Jim

My post wasn't clear but yes, only referring to using rudder to counter adverse yaw.

Interesting that adverse yaw with anhedral actually accelerates the roll rate.

Lots of other factors too, body shielding of the wing, sweepback on anhedral creating "dihedral" effect. No end to variety with aerodynamics which is why it is always a great topic of debate.

Now how does a Bee fly?

Because in a vertical climb, in nil wind so not compensating for wind, the wing must be at its zero lift AoA. For a symmetrical section, there is then no "top" or "bottom" to the wing. If the ailerons on each side have different travels due to differential, they will generate different lifts and drags, thus the differential will actually cause adverse yaw, and a roll axis that is slightly off centre.

I took you to mean that if your model wasn't flying parallel to the runway, you used rudder alone to change the line and avoid being easily seen to be making a turn. Are you actually saying that you hold on into wind rudder all the way along a "straight line"?

Differential is used for two reasons. One to reduce adverse yaw created by the downward aileron producing more drag then the aileron moving up. The second is to counteract the the aileron moving down will result in more gained lift then the wing with the aileron moving up has lost. So by introducing differential you fix both situations. I do agree that for full scale it's not an issue as one can feel the slip and simply lean on the rudder. Our models are a little different as for competition aerobatic pilots we strive to get our airplanes to fly as pure as possible. This means getting rid of as much control cross coupling as possible. Everything is a compromise, while aileron differential will help rolls on the verticals and upright it does do the opposite while inverted. Most guys find that more manageable then having the nose wander on up line rolls. Imagine trying to do 1/2 of an 8 point roll followed by an opposite 3/4 roll on an up line and pulling to an outbound cross box travel 90 degrees to the runway when the airplane is not rolling axially. This can be farther proven by different setups required when ailerons are hinged at center Vs. top hinged on some all composite models. The center hinged requires that through the TX you set positive differential. On a top skin hinge aileron your TX would be set to negative differential because the mechanics of the top hinge actually has you ending up with too much differential.

Correct, when trying to fly a parallel line to the runway in a cross wind blowing inbound I would be holding rudder outbound.

Harry,

A lot of these pattern people think they do that. I think what they're really doing, possibly without being consciously aware of it, is crabbing, and entering the crab by making a skidding turn, which makes the judges happy because the plane doesn't bank. They may even be keeping the plane cross-controlled all the way along. Sort of a Chinese pass, but with the wrong wing down, and then a crab the other way to keep the sideslip from taking them off line. Either that or they aren't really "holding" rudder, they are just using enough rudder to keep the plane where they want it to be (which turns out to be none, but with your mind on other things they may not notice that).

There may be some pattern fliers who are also full-scale pilots, but I've never met one. No full-scale pilot could possibly believe that holding rudder can either cause you to yaw or keep you going straight, depending on what you want it to do.

Al this may be quite true however I think it's because full scale airplanes have roll and pitch coupling when rudder is applied. On a high end pattern or IMAC airplane we strive to eliminate these tenancies. On a well set up aerobatic airplane when you give a rudder command you get yaw and nothing else. This is why when you look at an Extra 300L competition model you will notice some scale deviations. Most have the engine lowered, all have the stab lowered and it's usually on the thrust line, the rudder has more cord on the bottom and the wing has been raised. All these things contribute to the goal of having no control cross coupling. As far as not holding rudder but thinking we do, not buying it. There have been times when the wind is strong enough I can see my airplane 15 degrees off from path of flight. If one does not hold rudder in a cross wind then with each pass he would be getting blown inward or outward. Some can be corrected in the turn around maneuvers, but eventually you would either have the judges looking strait up or squinting to try to figure out what the dot 200 yards out is doing.

If you get yaw and nothing else when you apply rudder, then applying rudder and holding it would cause you to keep yawing, and you'd be making a flat turn. That would not keep you flying in a straight line.

Sure it would, we are only holding enough rudder to counteract the force of the wind. Imagine driving in a strong cross wind. You have to hold the wheel slightly towards the wind but your not doing a constant turn. Sailboats also do the same thing. If it were under clam conditions you would be correct.

The wind doesn't make a plane yaw. It just carries it in the direction the wind is blowing, without changing its heading at all. The car and sailboat analogies don't work, because they are not moving in a mass of air. The better analogy with a boat is a boat moving in a stream with a current. say you point the boat due east on a north-south stream with the water flowing south. If you row without turning, the bow of the boat will keep pointing east, but the boat will move sideways (relative to the ground) at tem miles an hour. It doesn't turn. A plane flying in a mass of moving air behaves the same way.

An airplane in coordinated flight "sees" wind only from straight ahead. Once off the ground, a plane in a steady wind handles absolutely the same way as a plane on a calm day. (For much, much more on this see the "downwind turn myth" thread in the Jets forum.)

Again, this is something full-scale pilots appreciate but modelers can easily get mixed up about. Full scale gliders use yaw strings (strings attached to the plane at the bottom of the center of the windshield). Whether the glider is flying upwind, downwind, or in a crosswind, the string goes straight up the center of the windshield. A string like that on a car or boat would behave very differently.

Al you are missing a couple points, one on a full scale airplane you really would not care about the ground track, the and a 15 knot wind is not going to have as much effect on a full scale airplane as it has on a model. You seem to believe that without any any type of correction that the airplane would drift with the wind direction. So let me ask this question of you. How would one control the drift while keeping wings level? And let me state once again, I have won numerous pattern and IMAC contests using this technique, I'm not just blowing smoke here.

I do agree that airplanes do not see wind, they only see airspeed but they also drift with the wind direction if in a cross wind. If your statements were true then landing in a cross wind would be the same as landing in a head wind correct?

+1

Speedracerntrixie, you do not hold on rudder into a crosswind, as Al described above there is no crosswind as far as the aerodynamics of the plane is concerned. As Al also pointed out, a lot of people think and say they are holding in rudder when they aren't, or used it just for a moment to yaw onto a different heading without doing it properly by banking and turning which comes right back to my original point about it being done as a deception to judges. If you hold on rudder all the time, no matter how little, the plane will yaw and change direction, it won't go in a straight line

If you want to follow a particular track over the ground, and normally we do (and full-size pilots care very much about ground track!), and there is a wind blowing from a side of that track, you turn the plane slightly into that wind and then put all the controls back at the centre. You do not hold on any rudder or aileron. The plane is flying head on into its headwind, it doesn't feel any wind on its side. The plane appears to be crabbing slightly across the ground, but aerodynamically the only wind it feels is its own head wind straight on. Landing in a cross wind is the same as landing in any wind or no wind, you turn the plane until its track is straight down the runway and then put all the controls in the centre. If there is a cross wind you may notice the plane appears to be crabbing slightly along the ground. You don't come down the approach with rudder or aileron held on, the controls are in exactly the same place as if there was a headwind or no wind. At the flare just an instant before touchdown you use rudder away from the wind side to yaw the plane along the runway line so that the wheels don't get a side load, but with prop planes you often have to be using rudder anyway as the throttle is brought to idle and the rudder position for balanced flight promptly swings a little due to the change in the spiral flow.

Many model fliers have been wrongly told that you side-slip down the landing approach in a crosswind, and the error is further worsened by almost always being taught to side-slip the wrong direction! There are two ways to make an approach in a side wind. Fly normally as you would for any required track with the controls at the centre, as I described in the paragraph above, or do a side-slip. Flying normally is by far the easier and safer, side-slip is more difficult and raises the stall speed and means that if you do stall it will probably flick into a spin instantly. But if you must do a side-slip, please do it properly. Model fliers apply their misunderstanding of rudder, and put rudder into the cross-wind and then bank away from the wind, e.g. cross wind from the right, they rudder right and bank left. But this is to muddle the processes that should happen. You don't yaw into the wind to compensate for it. You bank into the wind and let the huge power of the wing compensate for the wind drift. But that would make you turn, so you then apply rudder away from the turn, i.e. away from the wind, to stop the plane from turning. So with a cross wind from the right, you bank right and rudder left.

Therefore in both methods, the normal albeit crabbed approach, and the side-slip approach, the rudder when applied will be away from the wind, not into it.

The only way to keep from drifting while holding the wings level is to crab into the wind. Pattern flying consists in part of making the plane look like it's doing something different than what it's really doing. Crabbing just a little bit, so it doesn't much show from the ground. Slipping just a little bit, so it doesn't show from the ground. If you hold rudder in a crosswind, or not in a crosswind for that matter, the plane will yaw, and keep yawing. Let's take a concrete illustration. Your runway is east-west, and a wind is blowing from the north. You want to make the plane look like it is flying straight east or west, with the fuselage lined up straight east or west and the wings level. It is not possible for any airplane to do that. So you come as close as you can to making it look that way. With practice you can do this well. But I am absolutely sure that you can't do it by applying rudder, holding it, and keeping the wings level. Because doing that with the rudder will make the plane yaw, and keep yawing.

Congratulations on your trophies. No number of trophies changes the laws of physics.

Harry's post appeared while I was typing mind. Everything he says is true, with one small qualification. With full-scale taildraggers, some pilots prefer a sideslip on final (with the wing down on the side from which the wind is blowing) to crabbing. The reason is that slipping lets you keep the fuselage pointing straight down the runway through the whole final approach, which in turn reduces your chance of a ground loop. With models, as Harry says, crabbing is much, much easier. (It's not because models fly differently than full-sized planes, its that when you're sitting in the cockpit you can know exactly what your bank angle is and you can tell, much better than with a model, if you are lined up straight.)

As I stated, banking the wings to compensate for a cross wind will result in a down grade, that's why we use rudder. If you doubt this then go fly your model in a cross wind and hold the same box depth while keeping the wings level. I bet you can't do it.

This all reminds me of a conversation I had with Sean Tucker. He was out watching on of our IMAC contests and asked why there were no bi planes. I told him that it's because they flew poorly. The look of horror on his face was priceless and at first he couldn't wrap his head around it but as the conversation went on and he learned about the different perspectives full scale and R/C pilots deal with he got it. Bottom line is that we have to deal with the cross winds otherwise we drift with it. I think we all agree with that one. We get downgraded if we enter or exit a maneuver without wings level. Rudder is the only option. I'm not saying this is proper technique for full scale but is commonplace for R/C pattern and IMAC. This is why full scale pilots usually get to a certain level with R/C and no more. They have difficulty leaving behind what was taught to them as it applies to full scale aircraft and set up and fly their models in the same manner as they would full scale thus leaving much of the airplane's potential performance on the ground.

So do you have an explanation for how you keep the plane from continuing to yaw when you hold rudder while keeping the wings level? You seem to think that applying and holding rudder will cause your plane to move straight sideways, counteracting what the wind is doing to it, without yawing. Rudders don't do that.

Also because some of those taildraggers have engines you can't see over such as Spitfire or Pitts Special which may make a sideslip even in no crosswind just to see where they are going, and also because full size have an airspeed indicator so can be sure they have raised their speed during a sideslip, which model fliers can't be unless speed is raised quite a bit more than required just so you can see the difference from the ground.

We can do it, by using rudder to yaw into the wind direction at the start of each pass, but only holding rudder on briefly until the necessary new heading is obtained, and then promptly putting rudder back to neutral for the rest of that straight leg.
This is just a deception for the made-up rules of that particular competition. If you want to fly parallel to the runway and the wind is blowing from the right, you turn slightly right to point slightly into wind and then centre all the controls. Your comp rules won't allow you to turn properly so you have to cheat at a turn by yawing with rudder rather than banking until the same new heading is obtained as if you had done a banking turn, and then all controls to centre. No rudder, no aileron, the plane will go straight along the runway, slightly crabbing, the end effect is the same in both methods. Straight track, same heading, slightly crabbed into wind, controls at centre. The only difference is that right at the start of each pass you did a flat turn rather than a proper banked turn to set the new heading. You can not hold on the rudder, no matter how little, keep the wings level and go in a straight line, the plane will make a flat turn.

Harry, then I suggest you actually try what you are suggesting here. IMO you two guys are still talking theory and have not actually flown an R/C model with the goal of keeping a constant depth. Perhaps we should agree to disagree until one of you guys actually gives it a try with someone standing behind you letting you know if you are drifting or not and if your wings are being kept level. Trust me it would be a big eye opener. I personally find it hard to believe that you guys want to argue this point when it's obvious that neither on of you guys have pattern or IMAC experience. Personally I would not think about giving full scale pilots advise on piloting their aircraft simply because I am not a full scale pilot and am not qualified to do so. IMO you two trying to convince me that I am flying my models incorrectly is the same, you just don't have that level of experience. As I said gentlemen, agree to dis agree. At this point all 3 of us are just repeating ourselves.

since this is neither the aerobatics, aerodynamics nor any sort of full scale forum, but rather is the RC airplane beginner's forum,
I could not agree more.

+1 You said it. Flying in RNP 1 airspace, ground track is critical if you want to keep your licence.

Fly an ILS with 25 Kts crosswind.. The only thing that matters is ground track. Drift is compensated for by offset heading (crabbing) but in balance.

IE no rudder input held at all until the flare when you apply rudder to straighten the nose so you don't land sideways.