Secondary effect/s of aileron

[Guest Cralis]

I am trying to go over all the primary and secondary effects of the main controls. I'm battling with Aileron.

 

Primary effect = roll.

 

Secondary effect = slide.

 

Another secondary effect is yaw.

 

I can understand why we roll. I can also understand why we slide down towards the lower wing (Lift effect is now leaning towards the lower wing?). What I can't get is the yaw. I read in a book that you get 'adverse' yaw, meaning the plane actually yaws towards the higher wing. (If we're banking left, the nose yaws to the right). This is what I read in my BAK... but I'm pretty sure I was told the nose yaws to the downward wing...

 

The reason for the adverse yaw is that the upper wing's elevator is pointed down. Down into the more dense air (Lift: dense were below the wing... less dense above). While the lower wing has the aileron pointing up, and into the less dense air. So, the side with the higher density has more drag, thereby causing a yaw effect.

 

I just spoke to another RA pilot who frowned saying that no.. the yaw is down towards the lower wing, and hence the spiral dive possibility.

 

If the yaw is down towards the lower wing, then why does the plane yaw? Because the slide causes a pressure against the down facing side of the aircraft/fin, pushing the fun upwards, and therefore the nose downwards towards the lower wing?

 

Can someone clear that up? What is the secondary effect of aileron, and why?

 

 

[Guest Macnoz]

quote "the nose downwards towards the lower wing"?

 

The nose aspect to the wing is fixed unless you have exceed Vne!

 

ADVERSE YAW

 

Since the downward deflected aileron produces more lift, it also produces more drag. This added drag attempts to yaw the airplane’s nose in the direction of the raised wing. This is called adverse yaw.

 

Not sure where you are getting the term "slide"

 

slip and skid are more commnly used -- although they mean entirely different things

 

 

[Ewen McPhee]

Initial adverse yaw - due to increased lift and drag on the rising wing, followed by yaw in the direction of the roll as the roll continues due to slip away of the lower wing and increased lateral force on the tail.

 

 

[motzartmerv]

Ok..i'll try and clear this up. You have a grasp of whats called aileron drag, the upward going wing has a downward facing aileron, and pretty much like you said, this causes more drag on that side, so the nose yaws towards the upgoing wing. But then the acft describes a new path through the air as it begins to turn.. now the airflow is coming from an angle to the acft, becasue it is turning.. So say we rolled left, the nose first yaws to the right slightly, then the acft begins to turn towards the left, so the relative airflow is now coming from the left. That airflow strikes the keel surfaces of the plane ie, the fuselage and tail and the aeroplane "weathercocks" into the wind... So the chain of events is as follows.

 

1 You apply aileron to bank the wings left.

 

2 as you do this the aileron drag causes the nose to yaw to the right slightly

 

3 the acft begins to trun to the left

 

4 the airflow striking the left side of the plane causes it to weathercock or yaw into wind..

 

Thats why if you apply same side rudder and aileron you illiminate the the adverse yaw, so it wont yaw away from the turn..

 

phhhewww...hope this helps..

 

 

[Guest Cralis]

Thanks guys. 100% clear now.

 

 

[Tomo]

Wow just checked out your Blog, it is Awesome, Well done... I will be, know doubt a frequent reader of it...:big_grin:

 

Cheers,

 

 

[Guest Cralis]

Thanks Tomo.

 

Yeah, hoping some of the experienced guys can read it sometime and maybe crit it. Tell me whats missing or if there's something incorrect. :)

 

 

[Guest ozzie]

When flying my Lazair with the ruddervators (v tail) and the ailerons interconnected via the little lever on the forward strut i can start a shallow banked turn and complete a 360deg turn at about 5deg bank with the nose pointing 15deg in the opposite direction. This is caused by the, as i find it, induced drag of the lowered aileron creating extra lift (by changing the camber of the wing section) and the result of lift is drag creating the adverse yaw. And possibly highlighted by the 38 ft wingspan. It will stay like that feeling quite stable with no tendency to race into a spiral dive. If i apply more stick into the turn the nose will come around to the direction of the turn and the nose will start to drop so a little backstick and opposite aileron here. Most aircraft will require a little aileron in the opposite direction to stop the angle of bank increasing and off to a spiral dive. the final effect of unbalanced aileron use.

 

With the controls inter connected the turn is initially being led with the aileron, as the angle of bank is increased the ruddervators will come more into play and BALANCE the turn preventing slip and yaw. If i unlatch the interconnector and split the "rudder" and aileron i can lead the turn with just a little bit of rudder and almost remove the effect of the initial adverse yaw.

 

I think what that person was explaining was the affect of aileron (Slip) in an established turn that leads to a spiral dive, the aircraft will tend to yaw into the turn caused by the increased speed of the outer wing, other forces on the fuse and tail also come into play and if not corrected by applying backstick and opposite aileron and balanced with rudder will increase so the final result is a spiral dive not to be confused with a spin.

 

The adverse yaw in the opposite direction is the initial (first) effect of applying aileron with the initial result being induced drag from the increased lift. As the turn rate increases the increased speed of the outer wing will overcome this initial effect and the angle of bank will increase and the second effect is slip and yaw into the turn.

 

think i got it right. I belive that text books like the BAK will give you the nessesary knowledge to understand what is going on and give you the correct answers to pass the exam but can cause some confusion as it is just a little more complicated than what it brushes over. If you really want or need to understand what is really happening grab some books on aircraft design and explore things like the effect of different types of roll control, dihiedral anhiedral, swept wings or even two axis aircraft.

 

Ozzie

 

 

[Guest TOSGcentral]

Damn! I just wish that Stability was part of our syllabus!!!!!

 

It is as easy as this"

 

1. Roll the aircraft (say to the left).

 

2. The canted lift line from the wing pulls the aircraft to the left.

 

3. The aircraft then slips to the left briefly because it is out of balance.

 

4. Weathercock stability in yaw then yaws the aircraft to the left.

 

You now have the components of the spiral dive which is what the aircraft will commence to do.

 

If you are slow enough you also have all the components for entry into autorotation (more commonly known as the spin!)

 

If you do not understand this then I seriously suggest that people stop quacking about technicalities and ground yourselves until you do understand it!

 

Tony

 

 

[Guest ozzie]

OK whilst i am standing in the corner maybe you can explain the terms "stability' and "balance" and any difference thereof.

 

Ozzie

 

 

[Guest TOSGcentral]

OK Ozzie.

 

 

First of all I am not picking a fight with you (we go back too far my friend) or anyone else. I guess I was just a bit frustrated about something so simple being made so complicated (from early responses in this and other threads).

 

 

We do fly very simple aircraft and understanding them can be equally as simple.

 

 

You asked for some definitions.

 

 

STABILITY. This is essentially the property of any certified aircraft to keep itself aligned with the relative airflow and do so automatically if it is in within it’s authorised centre of gravity range and design MTOW.

 

 

BALANCE. Is normally a transient stage where operation of the controls (eg aileron drag or adverse yaw if you prefer) causes natural stability to be temporarily overcome until stability exerts itself again.

 

 

Another way of expressing the latter is if the pilot anticipates aileron drag and uses rudder in the same direction as roll thereby negating the adverse yaw while the ailerons are deployed. Balance is thus preserved before Stability has time or need to step in and reinstate that condition.

 

 

Tony

 

 

[motzartmerv]

Tony, so exactly who are you sugesting should ground themselve's? I was under the impression we had this wrapped up??

 

 

[Guest TOSGcentral]

As I said Motz - anyone who does not understand those fundamentals instinctively has no right to be in command of an aircraft until they do understand! There are a great many who do not!

 

In fact all of the answers above are quite clear, well put and I particularly enjoyed Oz's description of the Lazair control system and behaviour.

 

My rather emphatic (possibly over-stated) remarks were directed more towards the training system than the student, or subsequent pilot. A great deal of confusion and/or uncertainty can be created by the instructor hurrying through the fundamentals because they are so simple to him/her.

 

Personally I do not introduce aileron drag until medium turns are started and I like the student to have a couple of hours on the controls before going into secondary and further effects.

 

On the other hand I do teach Stability as the first flight execise and do it quite thoroughly. I am therefore always working from a firm foundation that I can fall back onto at will.

 

Tony

 

 

[Guest brentc]

Cralis, it depends on the aircraft type too as to how pronounced the adverse yaw is. As an example a short wing Jab doesn't really suffer from adverse yaw or atleast not nearly as much as a long winged Jab.

 

 

[motzartmerv]

Tony, fair enough.. It is a bit of a brushover subject in the syllabus.. I try to revisit it during mdeium turns which we do during the turning sequence..from memory the thrusters have a pronounced effect of aileron drag??..the jabs don't have as much of an effect but do have a savage secondary effect of yaw, so teaching medium turns we need to make sure they have a good grasp of it..

 

cheers

 

 

[bilby54]

Hi Cralis,

 

Try and keep things simple from the start and break the problem down into steps.

 

If the aircraft is flying straight and level, how and why does it roll from a pilot input? Forget about noses chasing wings and and things slipping all over the place until you really understand how the roll is initiated in the first place.

 

I read your blog and the description of what causes yaw bothered me as I think that you are confusing it with stabilty. As Tony has said, it really is better to ignore the secondary effects at the early stages of training and don't try to confuse yourself.

 

If you have a model A/C with movable control surfaces, then use it to describe each step and get it clear in your own mind... ie, if I move the stick to the left then the aircraft ROLLS left.... Why? i_dunno See the explanation by Macnoz after you understand the first bit.

 

Cheers

 

 

[BLA82]

Cralis,

 

From my experience it is a great idea to bring these kind of things up with your instructor first. I know from when I have asked questions everybody has their opinions (all valid) and you end up trying to decipher what you need to know aswell as decipher everyones opinions. It only confuses the hell out of you more an makes a little step a big issue. Everyone here has the best intentions but it doesn 't come close to the one on one instructing an instructor can give you.

 

 

[farri]

Cralis,I know from when I have asked questions everybody has their opinions (all valid) and you end up trying to decipher what you need to know as well as decipher everyones opinions.

Opinions don`t count.

 

Study good theory books.

 

Frank.

 

"Flying is easy,Crashing is hard".