Right rudder on landings

[Ed Cesnalis]

This is CT specific and belongs on this forum.

 

2 Members here are arguing that right rudder is required for landings and even stating that "The CT's here use right rudder to keep straight on landings. The instructors here teach more right rudder on landings."

 

 

Hmmmmmmmmmmm,

 

My thinking:

 

in a CT we use or need left rudder or more left rudder trim for our descent if we want to be coordinated. If the power is reduced or set to idle you need to compensate with left rudder. The actual landing rudder input is dictated by wind direction, if the wind is from the right you need a low right wing and left rudder by touchdown to not side load the gear.

 

Left for descent to be coordinated and right or left as needed for alignment by touchdown. You 'could' use right rudder from the beginning if you slip the approach in a left crosswind.

 

Takeoffs require a lot of right rudder, a left climbing upwind turn might even need right rudder.

 

Teaching right rudder for landings is wrong even if your winds consistently require it, how about when the student lands with a right crosswind, that is right wing low and left rudder to counter the turning tendency and maintain alignment?

 

and

 

 

All phases can be different, are you slipping or crabbing on final? Are you effected by crosswind at touchdown? On rollout are there left turning tendencies that are sometimes greater than right turning weathervaning?

 

There is no doubt that a gust on your vertical stabilizer from the right will turn you right and that will need left rudder.

 

Maybe you use left rudder until the nose-wheel contacts and don't really notice and the correction when steering will by right.

[Jim]

Both of my feet are always busy on final. After the round out and in the flair just before the wheels touch, the airplane usually yaws to the left a little. I wonder if that's what we're talking about?

[FastEddieB]

Jim,

 

May or not be the case, but often if the pilot is looking left, there will be a subconscious tendency to "pull" the plane in that direction.

 

Similarly, if a stick is used, pulling it back with the left hand may also result in pulling it ever-so-slightly towards the left rear.

 

Again, not necessarily what you're seeing, but I've seen pilots do it often enough that it's worth a mention. In a no-wind situation I think it far more likely to see a pilot land left of the centerline than right - again, in my experience.

 

Neither spiraling slipstream, torque, p-factor nor gyroscopic precession, the normal left-turning tendencies, should really be in play in a noticeable way in a power-off or near-power-off landing

[Ed Cesnalis]

I notice left turning tendencies after my nose wheel contacts. They seem to diminish or go away completely if I hold my nose up as long as possible and that makes me think my tendencies are about un-footing the rudder if I drop the wheel when fast. I think the longer I hold it off them more strait I get before contact.

 

Like Jim my feet can be active and I do what I need to do to maintain alignment and I loose track of what amount of rudder deflection and what amount of nose-wheel turn I have.

 

A gopro on the belly might tell a lot.

[sandpiper]

Mine always wants to go left after nose wheel contact unless I don't let it. So, I always anticipate it and make sure it doesn't happen. I'm not talking about running off the runway, it just takes input to keep it on centerline.

[Tom Baker]

With reduction of power in the pattern the nose will swing Right, and you need to use left rudder to counter that. When lining up to land most pilots will have the nose too far Left and need to bring it to the Right. I know I have told several pilots trying to land you need to bring the nose to the Right. This is not about the need for Right rudder, but rather the sight picture and people wanting to bring the nose in front of them. I could see how someone being told they need to bring the nose too the Right thinking that means you need Right rudder.

[FastEddieB]

Let me knock this out as a quick and simplistic summary. These all assume a tractor configuration and the engine turning clockwise as viewed from the cockpit.

 

First, the four “left turning” tendencies:

 

1) P-Factor

 

Results when the relative wind hits the propeller disc at an angle. Then the blade moving down into the wind has a higher angle of attack than the retreating one, hence more lift (thrust). In a climb, that would be the right blade, causing a left turn unless corrected.

 

2) Spiraling slipstream

 

The air pushed back by the prop rotates around the fuselage and hits the tail on the left. This is always the case, but the plane has corrections built in to correct for it in the normal cruise regime. Slower than that it winds up and right rudder is needed. Faster, then the built-in corrections can be too much and left rudder is needed.

 

3) Gyroscopic precession

 

Apply a force to a rotating mass and it will react as if you had applied it in a direction 90º in the direction of rotation from the actual force. Only a factor when pitch is changing. (We’ll neglect other axes for now).

 

4) Torque

 

Equal but opposite a la Newton. Engine goes right, plane wants to roll left. Again, corrections built in so at normal cruise it should be no factor.

 

 

Now, each considered per the phase of flight:

 

Cruise

 

P-factor - not an issue. The relative wind should be roughly perpendicular to the propeller disc.

 

Spiraling slipstream - not an issue. Plane is built to be neutral at cruise in all axes.

 

Gyroscopic precession - not an issue. The pitch is not changing in any appreciable amount.

 

Torque - not an issue. Plane is built to be neutral at cruise in all axes.

 

 

Climb

 

P-factor - causes left turning tendency that must be corrected for with right rudder.

 

Spiraling slipstream - causes left turning tendency as the spiral “winds up” tighter than the plane is designed for that must be corrected with right rudder.

 

Gyroscopic precession - not an issue. The pitch is not changing in any appreciable amount.

 

Torque - may be a small issue as the engine is turning faster than at cruise. If there is, correction should be via right aileron since it results in roll, not yaw.

 

 

Landing

 

P-factor - not an issue. Though the relative wind may be hitting the propeller disc at an angle, little thrust is being produced at or near idle.

 

Spiraling slipstream - not an issue. Again, little thrust is being produced at or near idle, and so little spiraling slipstream

 

Gyroscopic precession - unlikely an issue. As long as the change in pitch is gradual, the effects should be small. In fact, rotating the nose up in the roundout and flare is like pushing on the bottom of the propeller disc. Hence the effective force would be felt 90º in the direction of rotation - the left side. If anything, this would cause a right turning tendency.

 

Torque - Again, little thrust is being produced at of near idle, and so torque should be minimal.

 

 

So that’s it - quick and dirty and I expect it to be picked apart.

 

But, if something is causing any given plane to turn left on the landing and need right rudder, I can’t see how its any one of those factors.

 

If it is, please educate me!

[Ed Cesnalis]

I'm going out on a limb here and I am going to say that any tendency to generally go left is pilot induced. If I do a landing and do not try and prevent it the left turning tendency is common for me too however:

• Sometimes the turning tendency is right not left, this is probably a left crosswind condition.
  
• On our long downhill parallel taxi way it is easy to approach 30kts and my CT has no left turn tendency going fast downhill.
  
• If I hold the nose wheel off as long as possible the tendency goes away.
  
• The turning tendency isn't there until nose wheel contact.
  

[Jim]

2100 rpm for idle? I'd get that fixed. No way you'll be able to do an honest short-field landing with the idle set that high.

[FlyingMonkey]

Jim, idle at a 62kt approach is probably right around 2100rpm. I don't think he meant ground static idle.

[FredG]

The rudder trim setting in any given airplane will affect the need for rudder application (left or right) during landing and during other phases of flight. Because this setting is pilot-adjustable, the amount of rudder application needed (L or R) will vary across airplanes and even for a given plane if the rudder trim is moved.

 

Also, the rigging of any particular airplane may affect the yaw tendency during the flare (with the engine at idle power).

 

There may be no one correct answer across the fleet.

 

(I'm not an instructor and my comments are not flight instruction).

[FastEddieB]

I am an instructor and, again, I do not recall seeing right rudder recommended in any official or unofficial publication regarding a normal landing.

 

If it is required in a CT, I would still be curious as to why.

[Roger Lee]

Ed, the easy answer is trim from the factory and the owner.

 

 

My plane will land cocked to the left (calm wind) if I fail to apply right rudder. My plane will yaw left on take off if I fail to apply right rudder. Many of the people that come to my field in a CT that get some additional training all have issues just before touch with a left yaw. I have them always apply a little right rudder just before touch and they land straight.

 

What many are forgetting is each plane is trimmed a little different and each plane's owner has a little bias already on the rudder with the trim wheel. So what works for one may not be the same for the other. Rudder input will also be affected depending on if you land at idle or a little power.

Why do you think so many that have CT's put marks on the windshield for landing? It is because most are cocked to the left some and need to add a little right rudder to be straight so they put lines and dots on the windshield. They have talked about this for 7 years on the forum.

Ed, I know you have to remember this?

 

 

Too many factors to make this black or white.

[Ed Cesnalis]

...

Why do you think so many that have CT's put marks on the windshield for landing? It is because most are cocked to the left some and need to add a little right rudder to be straight so they put lines and dots on the windshield. They have talked about this for 7 years on the forum.

Ed, I know you have to remember this?...

 

If they need right rudder to correct because they are as you say cocked to the left then they are correcting for pilot error.

[Doug G.]

I think what Roger is referring to has more to do with the sight picture on landing. There is a bit of, for lack of a better term, "optical illusion" that goes on with the mushroom. It even comes up in the AOI. (For the CTLS anyway.)

[sandpiper]

I don't think I am cocked to the left on touchdown because the turning tendency only happens after the nose wheel touches. As long as I hold it off, the plane wants to go straight.

 

It's not a big deal.Just fly the plane.

[coppercity]

After instructing in CT's the last 5 years I find myself saying "right rudder" and "keep coming down" in my sleep

 

I think the perception of needing right rudder is due to the sight picture during landing approach.

[Anticept]

Ed, the easy answer is trim from the factory and the owner.

 

What many are forgetting is each plane is trimmed a little different and each plane's owner has a little bias already on the rudder with the trim wheel. So what works for one may not be the same for the other. Rudder input will also be affected depending on if you land at idle or a little power.

Why do you think so many that have CT's put marks on the windshield for landing? It is because most are cocked to the left some and need to add a little right rudder to be straight so they put lines and dots on the windshield. They have talked about this for 7 years on the forum.

 

Just going to add a couple things. First, trim is the most significant factor to why each CT is different, as roger said.

 

In single engine aircraft design, rudder longitudinal alignment is offset for optimum cruise. This is why you don't have to keep your foot on the pedal to counter the slipstream in traditional aircraft. Have a look at planes on the ramp. You will notice that in many of them, the vertical stabilizer is ever so slightly tweaked. Piper aircraft take this a step further, and offset their engines! FD has opted to give us rudder trim instead, which makes our planes much more versatile.

 

If you fly your CT at max cruise, you will need more trim to counter the slipstream, than someone like me who likes to fly her nice and slow. I have to make a significant trim change, spinning the trim wheel a few full rotations, when i go from slow to fast cruise. CTs also have very large tails for such tiny planes, so trim and slipstream has a much more pronounced effect.

[Roger Lee]

Exactly. What the others said.

 

And I might add that if you have never flown that persons plane then it would be hard to say what is needed upon landing or take off. That would be like telling me I'm not braking my truck right and I'm too late or too early for my stops.

 

Each plane can be different and each plane may be very similar, but to say the other guy is wrong when he knows he has to add right peddle to keep straight and he fly's his plane everyday (more or less), well is wrong. There is no clear cut answer here because it is aircraft specific.

[FastEddieB]

Got it.

 

But we did have someone saying not just that his plane required right rudder, but implying that all planes of his type did, due to "...the engine at idle (2100rpm) still has the prop spinning, and that means there is still torgue, P factor, gyro, and prop slip in effect."

 

That's what I take issue with, which I believe is in error, not that his particular plane may be out of rig or mis-trimmed or need right rudder on landing for some reason. I addressed my reasoning in a rather lengthy post where each factor was considered.

 

From coppercity's input, I still suspect CT's may be getting subtly pulled left, which requires a bit of right rudder to get things straight on touchdown. I still remain puzzled why right rudder would be needed if the nose was straight and the rudder properly trimmed.

[Ed Cesnalis]

Ed, the easy answer is trim from the factory and the owner...

 

My plane will land cocked to the left (calm wind)... I have them always apply a little right rudder just before touch and they land straight...

 

What many are forgetting is each plane is trimmed ...

Why do you think so many that have CT's put marks on the windshield for landing? It is because most are cocked to the left some and need to add a little right rudder to be straight so they put lines and dots on the windshield....

 

Roger,

 

I will agree the answer is the owner. Strait is hard to see in a CT and the fact that you need a correction prior to and after touchdown isn't the plane's fault. If you go left after the nose settles there is a reason. Most landings have some amount of crosswind to deal with. When landing the aircraft yaws in relation to the relative wind at the pilots discretion either right or left, not always left requiring right rudder. The pilot should maintain alignment with rudder inputs as necessarily, either left or right depending on how much drift he is countering and any gusts. If I have a strong enough crosswind from the right I will need full left rudder to land, how does your need for right rudder work then?

 

I think students and instructors mark their windshields because it is hard to tell if they are strait. Because the marks are a triangulation and the distance to the runway is not a constant the marks lie to the pilot except at one point. If you rely on the marks enough it ill lead you to a continuous yaw because the angles change as you approach. Marking your windscreen could be the very thing that leads you left prior to touchdown.

 

You say most add a mark because they are cocked left? What good is the mark if they are still cocked left? If it could be fixed with a mark how is that the plane's fault and not the pilot's?

 

I'm not saying that many don't use right rudder and or right steering correction on most landings I'm just pointing out that there is no need for it beyond correcting what should have been strait in the first place. On a side-slipped landing its the pilot's job to maintain tracking of the centerline and alignment. Due to gradient and shear the amount of input required changes and if the nose yaws left of centerline the pilot failed to maintain alignment.

 

Saying that all CTs are trimmed different is not an issue, we land with our feet not our trim, we overcome rudder trim forces without a thought on landings.

[Roger Lee]

So see we agree because how can you tell the other guy he is wrong for keeping his plane straight because the debater does exactly the same thing. They use what ever and as much peddle as needed. So the very first post isn't very representative.

 

Here is another difference. i do not need any rudder after touch down. My plane is trimmed at the steering rods to taxi straight. On a calm day I could taxi at 25 mph without any peddle input.

Next time anyone taxi's at 15-20 mph take your feet off the peddles. It should go straight and if it veers either way it's out of trim on the front end.

 

Time to leave.

 

On my way to Copper State Fly-In for a few hours and then back finish up my hose change.

[FastEddieB]

One other thought I had last night.

 

The need for right rudder on landing could be an aerodynamic issue with an individual plane, or it could be something else.

 

If the left brake was dragging slightly, that could pull the nose left on touchdown as well. As could a misaligned nosewheel, as Roger just pointed out.

 

In any event, I think it's important to find out why the plane is doing that - something could actually be wrong with it and the pilot should not just imagine "they all do that".

 

To help troubleshoot, maybe he should try watching what the plane does on an approach to landing stall in the same configuration he normally lands in. Is right rudder necessary there to keep the nose from swinging left? Is right rudder required to keep th ball centered? If so, it would seem to be an aerodynamic problem with the plane's rigging.

 

But if not, then that might point to something going on with the nosewheel or brakes or tracking, since other than ground effect, the aerodynamic forces on a landing plane should be the same as one approaching a landing stall.

 

A video taken of a landing from the runway threshold, even with just a smartphone, could tell us a lot. A better description of when the right rudder is necessary would also help.

 

Again, I'm just trying to troubleshoot and understand, not cast aspersions.

[FlyingMonkey]

I think what Roger is referring to has more to do with the sight picture on landing. There is a bit of, for lack of a better term, "optical illusion" that goes on with the mushroom. It even comes up in the AOI. (For the CTLS anyway.)

 

Sight picture in the CT is definitely something that requires getting used to. There's a huge forward view with very little aircraft parts (cowling, etc) for reference. It's harder to know if the alignment is correct on approach as a result because there is little to align to. I wonder if Eddie's Sky Arrow has the same problem? It seems there's not much structure to see out of that airplane either.

[FlyingMonkey]

I don't think I am cocked to the left on touchdown because the turning tendency only happens after the nose wheel touches. As long as I hold it off, the plane wants to go straight.

 

It's not a big deal.Just fly the plane.

 

Hmm...My airplane seems to want to go left also when the nose wheel is down, but I thought it was just me. I have definitely noticed that this tendency is reduced or eliminated by holding off the nose wheel as long as possible. I wonder if there is some instability or torque effect that creeps in at higher speed with the nose wheel that disappears below some threshold speed...

 

BTW my airplane taxis dead straight.