Use of rudder during flare

[metar]

Hi All

I'm probably being daft... more often than not when landing there is a need to kick the aircraft straight with RIGHT rudder. Even in still air conditions.

I'm at a loss why it is always to the right. Bring the power back to idle on a katana (clockwise engine) should if anything induce yaw to the right and hence need left rudder.

Any thoughts on why this might be the case appreciated. I probably should know the answer, but stumped on this one!

METAR
It's all about the now!

[Chesty Morgan]

When you flare you increase the angle of attack of the downward moving blade, thereby increasing lift/thrust and producing a yawing moment.

[metar]

Many thanks for that!

[BEagle]

Anyone 'kicking' an aeroplane 'straight' needs a sound kicking themselves....

Treat her gently! Squeezes and caresses work much better than kicks and shoves!

[metar]

the rudder authority on a katana... a caressing, loving application of rudder won't get you very far in those few seconds! ;)

[homeguard]

The term 'kick' or 'caresse' while maintaining wings level would be the action prior to touching down following as 'crab' approach. Still air or without a cross-wind will not require the action described.
You are almost certainly suffering from 'parallax'. The illusion causes you to yaw the aircraft to the left in order to aligne the centre of the nose (spinner) with your line of sight (eye ball) and the runway centreline, you will be sat in the left hand seat remember. Wouldn't happen if you were flying a tandem aircraft. Do you also almost always experience an apparent drift to the left during the approach requiring a repostioning of the aircraft to the right to regain the centre line, another sympton of the same thing.
Answer; look DIRECTLY ahead and do not use the nose as a gun sight.

[metar]

i hope I'm not suffering from parallax... i'm in the right-hand seat, have 600 hours on type and the same thing happens when flying from the left! On that basis I think i'll use the whole angle of attack on downward blade, yawing moment explanation!

Having said that it WOULD explain why students would need to apply right rudder. Perhaps a combined effect of downward blade yaw AND parallax.

Thanks.

[GOLF_BRAVO_ZULU]

Have you got "clutch pedal leg"? This is where driving a car demands more force from the left foot than it does from the right. Many of us don't realise we are pushing asymmetrically from the left.
It could be that you are unwittingly becoming tense during the flare and locking your left foot. Without being aware of it, the nose has yawed left. If there was a diploma for this skill, I'd have a Distinction.

[FlyingForFun]

I have to admit that I think that "you increase the angle of attack of the downward moving blade, thereby increasing lift/thrust and producing a yawing moment" (p-factor, or asymmetric blade effect) is a red herring.

The effect is very well known to tail-dragger pilots, because it does interesting things during the take-off run. (It is very much present at the start of the run, goes away when you lift the tail, and then come back again when you rotate.)

However, the effect which a tail-dragger pilot experiences on take-off is with maximum power. And, in a low-powered aircraft - something like a PA18 with a 150hp engine, not all that different to a typical spam-can - the effect is barely noticeable. So I find it very difficult to believe it could be noticeable to any real extent in the landing flare, at idle power.

Having said that, I don't have any other suggestions!

FFF
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[Say again s l o w l y]

I think in this case the "problem" is that the runway slopes, so in effect when you go wings level, you still seem to have a bit of drift when the wings are level.
I have noticed a similar thing in our 152 and tomahawk. I can't really see anyother explanation other than localised air movements off the surrounding buildings and trees.
Do you notice it on 08?

[metar]

Haven't done circuits off 08 for a while. Will take note next time. If you have a similar problem with the 152 then it might well be a local phenomenon (sp?) at that point on the runway. Strange.

[Capt W E Johns]

Nope, you're all wrong - it's the coriolis effect. Try it in the the opposite hemisphere and you'll see...

[Giams]

Nope, you're all wrong - it's the coriolis effect. Try it in the the opposite hemisphere and you'll see...

:O :) :O This is really nice!!!:E

you increase the angle of attack of the downward moving blade, thereby increasing lift/thrust and producing a yawing moment" (p-factor, or asymmetric blade effect)
Here is the answer.

I've flown C152,C172,PA28,BA33,DV20,DA40, this effect is difficult to observe durring flare.
Then I've tried Tecnam P20002JF, an a/c with MTOW of 580Kg and 100hp. You really need to steep right rudder durring flare even in still air in order to mantain your nose inside the RWY.

[2R]

Go up to a safe altitude
Hasel/Halt check complete
Add power while watching the aircraft attitude's
What does your airplane DO ,Did you notice any change to the aircraft attitude??
Back to straight and level
Reduce power to idle (carb heat as req.)
watch the attitude changes
What would you have to do to maintain the staight and level attitude ???
Any rapid change of power in the flair will do exactly what you practiced at a safe altitude and aircraft attitude control should be easy .Now you can concentrate on another squeeker.:ok:
If you decide to go-around and add full power you know what the airplane will want to do :D make it go where you want it to go smoothly
If you really want to learn how to land perfectly ,learn how to play a tune on the stall horn .Easy to do on the cessna's

[FlyingForFun]

2R,

I suggest you go back and read the original post. When you reduce power (with a conventional clockwise-rotating prop), the nose will yaw to the right, needing left rudder to straighten it. But Metar has observed the oposite - that he needs right rudder during the flare.

Giam's observation that the effect is more pronounced in a high power-to-weight ratio aircraft would probably support the p-factor theory, but I still question how p-factor can have so much effect at idle power. If you struggle to keep the nose inside the runway when you raise the nose at idle power, what's it like raising the nose to rotate at full power???

I like the idea of coriolis effect - if for no other reason that no one I know (me included) understands coriolis effect well enough to argue against it!!!

FFF
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[metar]

I think I'm swinging away from the down-going blade theory, and more towards a combination of local weather phenomena (backed up by Say It Again Slowly) and some student parallax.

Will continue to monitor it (especially when I have control) and let you know the outcome!

Thanks to all - some interesting points raised.

[Craggenmore]

How large is this yaw? Sounds like the prop/wings or fuselage is bent/out of tolerance? Has it been crashed previously?

[GOLF_BRAVO_ZULU]

I still think you are unwittingly commanding left rudder and then having to consciously correct it. Although it refers to differential brakes, look at Posts 2 and 8 of http://www.pprune.org/forums/showthread.php?t=229298&highlight=146+brake+left . It sounds very similar to something I used to do.

[Giams]

What about GYROSCOPIC EFFECT?

Apply a force in a gyro as effect you will have another force 90° apart in the same way of the rotation in opposite direction.
Now think about what happen on a clockwise turning propeller during a flare...
Put this in a light aircraft...

[Tc Matic]

It is definately not a local phenomenon, as I have observed it (as an instructor) both in the States and in Europe. I have wondered about it for years, and this is the first time I see someone else mentioning it. It's not the gyroscopic effect, as for a clockwise turning propellor, that would be the opposite (requiring left rudder during the flare)

[2R]

If the aircraft passes the walkaround .Figure it out at SAFE altitiude so you are not distracted by the proximity of the ground or the unusual contol problem and end up in a pile of doodoo.
If the aircraft is not doing what it should at a safe altitude describe what it is doing to your mechanic and get it fixed .
By doing the above exercise's you should be able to determine whether it is the machine or a pilot problem

FFF I would sugest that you go and do that exercise as what you said is not entirely correct.To tell you would be to easy go try it:8