Sendary effect of rudder

[west1218]

Hi all, I am little confused about this phrase.
I do know what happens but do not know why...in details...

The secondary effect of yaw is roll due to the outer wing travels faster than the inner wing.

But how does it travel faster?? Is it because of the outer wing is more exposed to the Relative Airflow than the inner wing? If so, what is exposing got do with increase in velocity?

Anyone who can explain this??please? The simplest way?

[dubbleyew eight]

I can see why you are confused.

the term is actually "the secondary effect of rudder"

ok lets give you a mental word picture to help you.

you are cruising along in straight and level flight, ok.
you pull back the throttle and the aircraft slows down, you trim in a little bit of up elevator to maintain altitude.
ok so you are now flying at a speed well below the manoeuvring speed for the aircraft, that is important for the following.

the centreline of the aircraft is aligned in the direction of flight, everything is in trim and you can take the hands off the controls and the natural stability of the aircraft will keep it flying along just peachy for a while.

ok you hold wings level and very quickly apply a boot full of rudder.
what happens next is that the deflection of the rudder creates air pressure changes to the fin and rudder which causes a force to be applied to the tail of the aircraft. conceptually the force is at the centre of pressure of the fin/rudder and acts horizontally. this horizontal force slews the body of the aircraft about the centre of gravity but the aircraft, at least momentarily, continues along in the original direction.
during this moment the aircraft is flying with one wing a little more forward than the other wing.
a number of things are now changed in regards the wing.
the fuselage will slightly blanket the trailing wing making the forward wing seem slightly longer and thus generate slightly more lift.
as well on wings that have dihedral the forward wing will be at a slightly higher angle of attack than the trailing wing and this will also slightly increase the lift from the forward wing.

you can see this for yourself next time you go flying. slow the aircraft to about 20 knots faster than the stall, get everything trimmed out and stable. then apply a boot full of rudder while looking out along the wing.

the secondary effect of rudder is worth understanding because on a lightie you can use the technique to pick up a dropping wing at the stall.

[john_tullamarine]

on a lightie you can use the technique to pick up a dropping wing at the stall.

Not a good practice, I suggest.

Standard rule with stalling is not to permit yaw ... stall+yaw leads to spin.

[Intruder]

Yaw is rotation about the vertical axis. For this example, push the left rudder pedal.

As the airplane yaws to the left, the right wing is temporarily pushed forward, and the left wing is temporarily pushed aft, relative to the yaw axis. The temporary increase in speed of the right wing causes increased lift, while the temporary decrease in speed of the left wing causes decreased lift. Therefore the right wing rises, the left wing drops, and the airplane rolls. When the rudder is released, the opposite happens, and the airplane rolls upright again.

[mad_jock]

I hope none of you that are spouting this rubbish about the outside wing going faster are teaching it.

If you absolutely hoof the pedals you may get a little effect but most of it is due to a change to the angle of attack. Which direction depends if the wing is anhedral or dihedral.

[Intruder]

If you "absolutely hoof the pedals" you will get an enhanced visual confirmation of the effect -- especially effective in a long-winged sailplane.

The OP asked for a simple explanation. Anhedral/dihedral, wing sweep, blanketing, and a host of other details complexify the explanation.

[1234554321]

Not sure what a boot full of rudder is. But anyhow dont try that with an airbus.
And I am also interested to know why it is rubbish?

Hoof the pedal= is that english?

[Intruder]

Scottish, apparently...

[Dan Winterland]

As the airplane yaws to the left, the right wing is temporarily pushed forward, and the left wing is temporarily pushed aft, relative to the yaw axis. The temporary increase in speed of the right wing causes increased lift, while the temporary decrease in speed of the left wing causes decreased lift. Therefore the right wing rises, the left wing drops, and the airplane rolls.

If anyone actually believes this, go and try it in an aircraft with no dihedral and straight leading edges perpendicular to the fuselage - like an Extra 300. A 'boot-full' of rudder will create mostly yaw and hardly any roll. Then try it on an aircraft with dihedral such as a PA28 and see the difference.

When explaining this to my students, I used to get a piece of A4 paper and fold it in half longitudinally. Put a slight bend in half way and then point it at the student getting him/her to say which side they can see more of when rotated in the yaw axis. Then explain that's the side with the greater angle of attack, more lift and why the aircraft will roll when yawed - assuming it wasn't the Extra! For those the other side of the Atlantic, letter will do instead of A4, - but the aspect ratio won't be so good!

[mad_jock]

Hoof is rapid application of control input. In English and Scottish.


And thankfully I had already covered the topic in my engineering degree before my ppl faa instructor came out with is over simplistic rubbish.

The whole room of riddle instructors was then slightly disturbed as me and another engineer explained why it was rubbish. Give one his due he did go and read up on it and came and asked sensible questions after the initial shock went through them all that they had spent 100's of thousands of dollars to be taught in correct theory.

[Natstrackalpha]

2ndry affect of rudder.


Secondary Affect of Yaw.


anything on the outside travels faster. If you yaw right tail goes left reducing the airflow over the right wing right wing - Left wing goes faster because it has got its original forward speed through the sir - plus - an additional forward speed relative to the right wing - momentarily - as the aircraft yaws.


As the Left wing is going faster in relation to the right wing going slower - then:


There is more Lift on the Left wing - compared to less Lift on the right wing.


The Left wing goes up and the right wing goes down - - as you are helping things along but making, letting the aircraft Yaw, as well, then the aircraft rolls to the right.


Ok, only kidding - actually - am not - come forth ye critics with yer span-wise airflow and angle of attack - fair enough then.


Listen Dudes and Duedess-esses -


Smite us as ye may for saying its not a case of the left wing going faster and the other wing going slower - but do dive in with the pickys and the numbers - don't just say its ----, get on in there - life is short, right?


In other words: show us what you mean - (or go and make some tea)


Thank you for your time.


Re: Bootfuls - Don`t bootful anything - as JT says.


It is not the Brazilian World Cup - were not scoring for England here. Don`t "bootful" anything until you have been shown by an instructor and an aerobatic instructor at that.


As J.T rightly says - an appropriate, amount of rudder is to be used in the event of a wing drop - opposite rudder to the dropping wing - opposite rudder - so that if the Right wing drops, say, IN A STALL, then one would straighten the aircraft that is level the wings - not with the aileron - not with the aileron, but with opposite rudder, not "booting it in" - that's disgusting but apply sufficient rudder, even full rudder, momentarily, momentarily to recover the dropped wing - this is at the stall (or just after the wings have stalled - if the wing has suddenly dropped during the stall)


I won`t go into it - but the reason we do that is so as NOT to use aileron - why? Well using aileron during the stall to pick up the dropped wing can further stall the dropped wing - leading to a spin. If you are trained in spinning you will recover from an incipient spin - i.e., meaning - you will be trained to recover at the pre-stage or onset of the spin before it develops I mean - you will also be able to recover from a developed spin. In reality - if you get into a fully developed spin by accident then you are naughty to fly through a cyclone or you are half asleep or you should have left her on the ground and gone out for a pizza instead . . . . ?


You will get spin training at your local flying club/school as part of your PPL training.


Some of you fly so well that you are daft enough to go and spin - all on your own - why not?


I`ve spun with a student hundreds of times. Can`t quite get myself to do it solo though - seems like an insane way to fly. Unless you are an instructor or aerobatic pilot or a test pilot or a fighter pilot.


If you are not trained in spin recovery - then go and become trained in spin recovery - it may save your life one day.


Don`t put "bootfuls of rudder in" nobody does it - they are just being silly or un-learned.

[172_driver]

The whole room of riddle instructors was then slightly disturbed as me and another engineer explained why it was rubbish. Give one his due he did go and read up on it and came and asked sensible questions after the initial shock went through them all that they had spent 100's of thousands of dollars to be taught in correct theory.

Oh the instructors worst nightmare when the student actually knows more than him/herself.. and on top of it, is smug about it :p

I was always very humble when having students with deeper knowledge than myself and tried to use them as a resource in teaching for the benefit of myself and other students.

There are lots of myths out there still being taught as reality by thouse who should know better. The danger of downwind turn springs to mind..

[BOAC]

There is great tendency always to 'compartmentalise' this sort of thing and say "It ia just X" or "Just Y" rather like the pundits on the topic of what controls airspeed and RofD and as with everything it is nearly always a combination of effects.

I appreciate the OP asked for 'simple', so faster wing is the best, but yes, there are several factors, and no-one has yet mentioned roll due to fin sideslip yet:uhoh: (and to get really technical, there is the small roll moment generated by rudder displacement alone...) An a/c with anhedral WILL experience a rolling moment in yaw due to differential wing speeds but it may well be masked by other effects.

[foxmoth]

NATSTRACK - not sure where you are, but certainly in the UK picking the wing up on stall went out years ago, current teaching is to prevent further yaw with rudder, but you do NOT pick the wing up, wings are rolled level - with aileron, once OUT of the stall.

[john_tullamarine]

Putting aside very old certifications, most reasonably recent designs are required to be able to accept aileron input during stall activity.

Indeed, some, for example the larger KingAirs, generally require lots of aileron activity to achieve the required certification sequence during a stall recovery.

For those of us mere mortals (ie not aerobatic experts) it is not essential to get the wings level in an instant .. more important to unstall and then worry about the other niceties, I suggest.

See, for instance, in FAR 23.201 -

(d) During the entry into and the recovery from the maneuver, it must be possible to prevent more than 15 degrees of roll or yaw by the normal use of controls except as provided for in paragraph (e) of this section.

(e) For airplanes approved with a maximum operating altitude at or above 25,000 feet during the entry into and the recovery from stalls performed at or above 25,000 feet, it must be possible to prevent more than 25 degrees of roll or yaw by the normal use of controls.

[dubbleyew eight]

john tullamarine the original poster is a newbie asking a basic question.

so I ask you who in hell does basic training in a king air??

in the strident effort to be top dog you guys loose the plot sometimes.

the aircraft I had in mind with the explanation was the Cessna 150. the Cessna 152 will perform the manoeuvre as well as will a piper cherokee.
back in my training days the pick up the wing exercise was used as a skill builder.

[mad_jock]

And now it's actively discouraged in flight training.

There absolutely no problem what's so ever using full rudder deflection on an Airbus as long as your in the envelope to do so. What you can't do is cycle it max deflection from either side trying to lift the wing in a flight upset. Exactly the same as Boeing and any other aircraft type. Including c150 pa28 and other training types.

The problem with teaching rubbish is that it becomes the default rubbish which everyone believes. If you teach people the correct thing from the beginning then there is never any problem. Just like this pick the wing up with the rudder pish an aircraft and pax is also dead because of it. And people still think it's because of a defective design and not a defective method of controlling an aircraft.

The fact that nothing could have survived a cyclic load input that was applied to that tail doesn't matter.

And we were not smug at the time, genuinely confused because it was such a load of rubbish. The rate of application and the amount of yaw to get a significant induced roll moment is huge. And sail planes are the aircraft which you can get it to work in due to the span of the wing acting as a displacement amplifiyer and the relatively powerfully rudder.

Thinking that a 5 deg yaw squeeze by a student is going to give anything like the amount of roll effect that happens is just stupid.

The amount of control input should be appropriate to get the effect you want. Fixed wing powered it's going to be small, glider not so small in fact it feels huge some might say boot full compared to a light training aircraft.

[Mach Jump]

I was going to keep out of this one, because I knew it would turn into a pxxxxxg contest, but I can't help but chip in and say that I am entirely with MJ and JT on this.

Guys. Please stop telling people (especially students) that they should 'pick up the downgoing wing with the rudder', during and beyond the stall.

The rudder should be used to prevent further yaw, whilst, at the same time, stopping the wing drop by un-stalling the wings.

Then, after you have un-stalled the wings, level the wings with co-ordinated use of aileron and rudder!

[john_tullamarine]

so I ask you who in hell does basic training in a king air??

.. methinks you may have missed the point of my post .. ? if so, my apologies for any confusion arising from my text.

The KingAir just happens to be an example for which I know, specifically, the requirement applies. Indeed, you won't achieve the OEM's stall figures without aileron input and some knowledge of the relevant certification technique ..

The concern with this thread is not the training/competence/licence level of any given pilot .. rather an outdated, and generally incorrect, belief that applies as much to the 20,000 hour pro as to the 10 hour first solo trainee ..

[BOAC]

John - it would seem this thread is going to 'run wild' away from the OP so I will take the opportunity to askIndeed, some, for example the larger KingAirs, generally require lots of aileron activity to achieve the required certification sequence during a stall recovery..

How is this achieved? Are the basic rules of aerodynamics (use of aileron on a fully stalled wing causes that wing to drop) re-written or is, perhaps, the King Air 'stall' for certification purposes not a 'stall' as such but an incipient stall? One of the essential exercises in training is (used to be!) to demonstate wingdrop if aileron is used on a stalled wing. Does the KingAir have roll spoilers perhaps? A 'standard' basic aircraft will definitely enter an incipient spin if aileron is used and this lesson needs to be re-inforced. It will be highly dangerous if the new pilots go away with the idea that aileron is 'ok'.

[john_tullamarine]

Are the basic rules of aerodynamics (use of aileron on a fully stalled wing causes that wing to drop) re-written

Refer to the FAR requirements and the relevant AC - state of the art design has moved on somewhat since Austers and Tigers ...

King Air 'stall' for certification purposes not a 'stall' as such but an incipient stall?

I suggest not

One of the essential exercises in training is (used to be!) to demonstate wingdrop if aileron is used on a stalled wing.

There are various disconnects betwixt certification and operational views of life, death and the universe. This one, I suggest, is a carry over from the days of Austers, Tigers and those wonderful old military piston Types.

Does the KingAir have roll spoilers perhaps?

No

A 'standard' basic aircraft will definitely enter an incipient spin if aileron is used and this lesson needs to be re-inforced.

Depends on the certification basis - perhaps we should just agree to differ ?

It will be highly dangerous if the new pilots go away with the idea that aileron is 'ok'.

As above. I note that

(a) use of the control doesn't necessarily require full deflection for recent certifications, only that the bank and heading requirements can be met with normal sense use.

(b) the main concern of the discussion relates to using more rudder than is necessary to control yaw in the stall.

[BOAC]

state of the art design has moved on somewhat - intrigued to know more.................can you expand on that? It certainly held good on Cessnas and the Jet Provost (ie unswept planforms). I understand from your last line that you believe it ok to teach use of alieron on a fully stalled wing?

Anyone know how it is done? Differential aileron? Black magic? S&M?

Anyone confirm that you will not get a wing drop with aileron at the full stall on a 'standard' puddle jumper?

[john_tullamarine]

Points to be noted - one needs to know

(a) the certification basis to have an idea of what might have been what

(b) the OEM's history for particular certification FT work so that one knows just what was what

For some aircraft, the certification stall work indeed involved the use of aileron to control bank angle within the required limits for the stall demonstrations.

Reference to a "standard" puddle jumper misses the need to check what the certification basis might be for the particular Type/Model.

I fear you are endeavouring to generalise from the particular, perhaps ?

[Lightning Mate]

"Anyone know how it is done? Differential aileron? Black magic? S&M?"


Black magic mate.............................


WTF !!

[BOAC]

....and I fear, John, you are trying to extrapolate from certification testing to 'normal' aviation. I have yet to see a stall accident where the pilot approached the stall at 1kt/second, not trimming beyond Vs1g + x%. Further, I never managed to watch or achieve a proper 'stall' on 737 airtests since back stick ran out before stall. My concerns lie with the 'average' pilot, not cert/airtesters who should know better.

I would like you to try your next KingAir in approach config in a descending turn (at a safe height please) pull through any buffet until a wing drops and then 'pick it up' with aileron. I would be amazed (and impressed) if you did not over-speed the flaps....

I agree with (a) the certification basis to have an idea of what might have been what

(b) the OEM's history for particular certification FT work so that one knows just what was what and wonder whether our OP will understand. I would include in a) what the definition of the stall is, and of course how 'normal use of controls' is defined, since your quote mentions roll and yaw.

We have discovered to our cost that perceived attempts to re-write basic aviation 'lore' - eg Airbus - 'will not let you stall - just keep pulling back on the stick and she'll look after you' - have come to a sad end. I am concerned that it is just possible that west1218 might (if still reading) go away with the wrong concept of 'normal use of controls at the stall'. You have not answered "I understand from your last line that you believe it ok to teach use of aieron on a fully stalled wing?". It is important to clarify.

[mad_jock]

Unfortunately I think most if not all modern planes have washout designed into them so they do work.

But if we go back to the OP's initial question.

Hi all, I am little confused about this phrase.
I do know what happens but do not know why...in details...

The secondary effect of yaw is roll due to the outer wing travels faster than the inner wing.

He is confused because it is over simplistic and pretty much rubbish.

For any one with even a milligram of engineering sense it is obviously :mad:

So why are people even mentioning this rubbish?

[keith williams]

This thread has long since departed from the OP's original question, which was:

But how does it travel faster?? Is it because of the outer wing is more exposed to the Relative Airflow than the inner wing? If so, what is exposing got do with increase in velocity?


So any reply which cannot start with the words "The outer wing goes faster than the inner wing because" is probably heading in the wrong direction.

[Lightning Mate]

Black magic innit..................


If you are not qualified professionally to fly aeroplanes then please stay off this thread.

[foxmoth]

So any reply which cannot start with the words "The outer wing goes faster than the inner wing because" is probably heading in the wrong direction.
Well, it is true that the outer wing goes faster - rotate a stationary aircraft and the outer wing goes forward and the inboard backwards, thus the outer wing has speed added to it and inboard subtracted, but the real question IMHO was about why you get secondary effect of rudder and, whilst the above comes into it in a small way, most of the secondary effect is other factors, as discussed.:rolleyes:

[Natstrackalpha]

I am with fox moth on this one. Guys - per favore! On his last post, the one above this one. but I don`t like the bit about:


"""but you do NOT pick the wing up, wings are rolled level - with aileron, once OUT of the stall."""


You see fox moth - I don`t like recovering from a stall when the aircraft is banking to the left, with the nose down at the same time, say, because I have been too damned lazy to pick the wing up with the rudder as I so irritatingly put it. I would like a nice straight aeroplane - then when the speed picks up as I have applied forward pressure to lower the nose and make the aircraft go down hill thus increasing the airflow over the wings due to an increase in airspeed then I can raise the nose to/or above the horizon applying full power and climbing away (at the proper speed). Putting it simply.


Your way - taught `today` or not - making me do all that with a dropped wing and a low nose, uh uh - I wanna recover from a stall first - and catch it first - if that means applying opposite rudder to the wing drop then so be it - I will do that, because I was trained to do that - it works, beautifully, and I have trained others to do it this way - and neither of us are dead yet, ok? Anyway, it seems nicer (and saner) to go hurtling downhill in order to recover from the stall Straight -


Taking it a stage further - if the wing dropped nastily - as they sometimes do - then we hardly have time to p--s about with e"enough rudder to prevent further yaw - what in Jesus`s name is that going to do - well, I`ll tell ya! You wing is low so is your nose - you may very well be picking up speed so - by your theory or modern training techniques - you leave the wing where it is - we are descending in a descending turn which is quite a loo-loo as you have insisted on letting it stay there- ah well - lets wait for your "stall recovery" - ah, there is the nice juicy airspeed that you need - brilliant - we are now hurtling down at the start of a spiral dive due to our attitude, due to our attitude - which you put us into as you could not be bothered to pick up the wing.


So - next time you go stalling for exercise - you just go and see if you can live with a wing dropped - and leave it there (in your descending turn - and you WILL be descending like the clappers!) - and then proceed with stall recovery - and then . . . . roll your wings level. - So why do it all pointing down there at the ground in a steep banked turn to the left, which is what it would become. Why dramatize a simple, but simple wing drop with a mess. When, all you have to do is to P I C K U P the dropped wing by applying opposite rudder - slight me as ye may - but I am right.


the OP was:

"The secondary effect of yaw is roll due to the outer wing travels faster than the inner wing"

Then we all (me included) go on about stalling, incipient spins and recovery or prevention thereof -sigh, (sorry):rolleyes:


Excuse my impromptu launch into logical thought, but: why not? Why is it not, simply that:


When you do cause a yaw, due to pushing on a rudder pedal the aircraft - as you are forced to agree - will rotate around the normal axis or neutral axis - by mere physics of leverage and direction and rotation the (right rudder pedal pushed) aircraft . . will yaw to the . .right and subsequently the left wing travels comparatively faster than the right wing which is now travelling comparatively slower than the left wing - stand with your arms outstretched, just as you did in the school playground when you playing at being aeroplanes. If you rotate your body to the right the left arm goes forward and the right arm goes back - its not NASA!

The same thing happens when you apply rudder to cause a yawing . . . moment around the neutral axis . . of the aeroplane.


So - it figures that the left wing has more lift than the right wing -


and by the same point


the right wing has comparatively reduced its forward motion somewhat, and therefore has less lift, slightly, but there is more, oh yes, by the mere application of the right rudder (say) you have in fact accelerated the left wing anyway because you have pushed it forward - more, into the relative airflow = more lift - (if only due to the acceleration)


left wing lifts, right wing does not, (. . . .have this increase in lift)


- da da!!


= Roll.


Its not pish.


Grab a b------g aeroplane and go and try it out yourself then.


Everyone else comparing Provosts and King airs - I was not referring to you guys who obviously have previous more technical experience with these types.


-(nor was I referring to an A320, watch this space - under construction)
Thank you for your call, Nats is not here right now, if you would like to leave your name and number, I`ll get right back to you as soon as I can:)

[Andy_P]

I decided to have a look at what my BAK books says. IT says the adverse roll is due to difference in wing speed. However after a lot more research on the engineering side I would Have to say that mad_jock is on the money with this one, and my book is technically incorrect.

Here is some simplified explanations of the reasons: 9 Roll-Wise Torque Budget (http://www.av8n.com/how/htm/roll.html#sec-roll-budget)

[john_tullamarine]

I'm not persisting to prove a point at all .. but this thread has a very pertinent training value ...

you are trying to extrapolate from certification testing to 'normal' aviation

Not at all. Indeed, the more the two diverge in critical areas, the more risk we accept.

(a) the relevant certification Standard for a particular Type puts a line in the sand regarding what the aeroplane should, and should not, be expected to do. Unfortunately, it is a well-known observation amongst the FT community that whatever capability is possessed by the aircraft offered to the Industry .. the Industry often, in ignorance, expects something different

(b) the Standards have evolved with Industry capability so one MUST review the particular set of Standards pertinent to a particular Type/Model rather than generalising in the usual operator manner

(c) the philosophical approach to stalling protocols amongst the operator fraternity often tends to ignore the delta between what the OEM provides and what the operator industry presumes.

I have yet to see a stall accident where the pilot approached the stall at 1kt/second, not trimming beyond Vs1g + x%

Quite so .. but that ignores the purpose of that requirement. Furthermore, the certification program does examine less benign protocols and, for the military, much more formally and rigorously.

since back stick ran out before stall

This is quite acceptable under the certification requirements .. same thing, for instance, applies to the KingAir as a matter of interest (and seeing we had mentioned that machine previously).

I would like you to try your next KingAir in approach config in a descending turn (at a safe height please) pull through any buffet until a wing drops and then 'pick it up' with aileron. I would be amazed (and impressed) if you did not over-speed the flaps....

Actually, I don't fly the bird .. I only used it as an example. However, the certification requirement for its stalling work does require appropriate introduction of aileron input. More importantly, there is no requirement to pick up the wing .. only to constrain the bank angle within the required certification demonstration parameters.

since your quote mentions roll and yaw.

FTG ACs are the place to delve into this material for the detail .. as well as privileged conversation with NAA certification/FT and/or OEM certification/FT folks. Keep in mind that, for the certification exercise, the bank and yaw limits permitted are modest as in FAR 23.201 (http://www.ecfr.gov/cgi-bin/text-idx?SID=44f26a5ff7f310ea0a29a343cd091a52&node=14:1.0.1.3.10.2.65.39&rgn=div8)

You have not answered "I understand from your last line that you believe it ok to teach use of aieron on a fully stalled wing?". It is important to clarify.

If the relevant frozen Design Standard so requires, I would expect use of aileron to be conventional through the stall. For some aircraft, whether you might wish to accept that or not, aileron use is required to obtain the OEM AFM stall data.

I don`t like recovering from a stall when the aircraft is banking to the left

That's perfectly fine .. but it might put you at odds with what the OEM FT team did during the development and certification of the wee beastie. That, in turn, might erode some of the fat built into the certification and intended to look after the line pilot's tail in the heat of the moment.

For instance, I can recall a presentation by a very experienced TP trainer who related a tale concerning a military (not that that is important - it could have just as well been a civil) student who wished to push a particular twin well into a stalled condition, contrary to the certification basis.

All went well until the aircraft departed into an inverted spin .. apparently somewhat to the surprise of the student. The TP instructor, on the other hand, had seen it all before I guess.

I would like a nice straight aeroplane

Might I suggest the best way to do that is to use just sufficient rudder to constrain yaw ?

and my book is technically incorrect

There are many not-quite-right pilot training explanations in this Industry. However, to be fair, as with any technical arena, it is appropriate to pitch an explanation at a level suitable for the student. Sometimes, that might best be done by using an explanation which is a tad simplistic. Post grad engineering stuff really is not necessary for a pilot to gain sufficient understanding of what's what for the purpose at hand. Then again, the occasional book content is just plain wrong when the author is not up to it.

[BOAC]

(Have to run, will complete this later) - thanks, John, but not for me.

[tow1709]

Trevor Thom Volume 1 (my copy is the 2005 edition) on p 37 presents two bullet points under the heading of Yaw causes Roll summarised below:


the outer wing moving faster than the inner wing, and
the stuff about dihedral

They are presented in that order. It also goes on to say the inner wing will be somewhat shielded from the airflow by the fuselage and produce less lift.

Both bullets seem entirely plausible to me as a non-expert in aerodynamics. But my inference, because of the order in which they were presented in the book, was that the first bullet was the more significant one, and that (first bullet) was how it was explained to me when I was briefed on effects of controls - no mention of bullet 2.

I note that the OP has not reappeared - probably even more confused now!

[mad_jock]

The speed thing is a constant battle due to people not wanting to leave go of it because its nice and easy for them to visualise.


That fact its transitory and very little effect is neither here nor there.

And it is the correct order. Initially there is a very small effect due to a slight difference in wing speed.

As the yaw comes in it is superseded by the main effect.

Now that's not to say the speed thing can be ignored. In situations like dutch roll it needs to be taken into account because this is a dynamic situation not a static one like when a aircraft is setup in a sideslip.

If you teach the thing properly from the start there is zero confusion about the difference between the two situations.

[foxmoth]

NATS
Grab a b------g aeroplane and go and try it out yourself then.

As an instructor I have not only tried it myself but can demo both methods, what you say about
You wing is low so is your nose - you may very well be picking up speed so - by your theory or modern training techniques - you leave the wing where it is - we are descending in a descending turn is not correct, if you put the stick forward the stall is recovered very quickly and the wings rolled level immediately - I think you need to find an instructor who knows what he is doing and get him to show you. I CAN recover using your method of picking the wing up, but it actually takes longer to recover - and there are certainly a number of aircraft where you are highly likely to end up in a spin in the "recovery" direction!

[mad_jock]

just had a look at that link Andy posted.

Well worth a read by everyone.

[Andy_P]

just had a look at that link Andy posted.

Well worth a read by everyone.

I kinda wish he would cover off the wing speed thing. If indeed it was correct, then why does an anhedral wing roll opposite to yaw? I used a model plane to help visualise it, and you can actually see the difference in AoA wrt relative airflow.

[mad_jock]

Another way is a model out the car window with some one else driving then feel the forces.

[Andy_P]

Anyway thanks mad_jock for pointing that out. As a result of investigating that (I guess thats the problem with us engineering types) I have also discovered a lot of other myths from Denker's site.

So now I understand most of the aspects of roll due to yaw, I am stunned at what is written into both of the basic text books I have. I am yet to refer to 'stick and rudder', only because I cant find it due to moving house.

[BOAC]

why does an anhedral wing roll opposite to yaw - it doesn't - it rolls due to sideslip. There is a danger of getting confused here. We must be careful how we define 'yaw' - it is simply a rotation around the vertical axis. In pure aerodynamic terms, an/dihedral have no effect on rolling moments due to yaw. They DO have an effect on rolling moments due to sideslip (motion along the lateral axis) CAUSED BY YAW which is where your 'conundrum' occurs. There, the roll due to sideslip is the greater force. (If we are not careful we will start Dutch rolling....)

The ultimate test would be to rotate two models with an- and di- hedral around the vertical axis - with no forward motion - and see that there is indeed a roll couple due to wing 'speed' difference and this would not differ between the two models.

Conversely, presenting both models at a fixed yawed angle to an airsteam will produce a rolling couple purely due to wing setting with zero 'yaw' input.

Never realised flying were so complukated.....:)

[Andy_P]

Ahh see I thought yaw is rotation about the normal axis in motion, so perhaps my terminology is wrong . However, you are correct. Perhaps the easiest way to describe it is by saying the aircraft is yawed relative to the airflow.

Either way, the myth that the outside wing is travelling faster and generating more lift is plain wrong and is not the reason for the secondary effect of the rudder.

That link I provided earlier is an excellent read. The guy dispels a bunch of common myths that are incorrectly taught to students like myself. I have only just started to read it, but I have already learned a heap from it. Useful given I am about to sit my BAK exam.

[BOAC]

Either way, the myth that the outside wing is travelling faster and generating more lift is plain wrong and is not the reason for the secondary effect of the rudder. - no it is not plain wrong. It is part of the reason. It is that the roll due to sideslip and wing blanking is normally predominant.

You are in practical terms correct about 'yaw' since unless you are in VSTOL mode, there will always be translational motion of some sort and the moment you stat 'yawing' you start sideslipping.

While we are being 'technical', this discussion is about the effect of yaw, not the 'secondary' effect of rudder! The secondary effect of 'rudder' is indeed roll, but caused by the sideforce generated by the rudder being applied above (or below) the roll axis and generally insignificant. The roll we are talking about is generated by both the yaw AND the subsequent sidelsip in differing amounts.

If you flew on a constant heading with crossed control (ie with sideslip) there will be a roll couple of either sign due to an-/di-hedral and any other 'vertical' surfaces and obviously there is no speed difference between the wings.