Why does an Airplane turn?

Justwannafly · Post by **Justwannafly** » Sat Dec 10, 2005 12:24 am

Once an aircraft is in the banked attitude what makes it turn?
Can someone give me a technical explanation please?

I was asked this question today & I responded by explaining The horizontal component of lift. I was told that I was wrong …but I’m not sure why I am….I asked him how he would explain it, he responded with a chuckle that it has to do with Yaw & that he would let me figure it out. BUT I’m going over my notes, books & even the internet….& I’m still not seeing how….Don’t get me wrong I’m not saying that I’m not wrong…infact him being an experienced flight instructor & CFI…..& me being a lowly inexperienced IV, the chances are that I AM wrong…but…I just don’t see it  What am I missing?...Yes the plane has to be in coordinated flight or you will slip, skid, or even not turn…but those are factors affecting the turn NOT making the turn…aren’t they?

Flying Low · Post by **Flying Low** » Sat Dec 10, 2005 12:27 am

When I first saw the title of the thread I figured it was so they don't hit things!

I'm have never been an instructor but I would assume that without yaw, of any kind, the aircraft could be banked, would slip into the bank but would never turn (longitudinal axis would slide sideways but always remain parallel to where it was). As the aircraft slips it naturally acquires some yaw into the turn as it "weather cocks" into the slip. The rest of the yaw is the rudder input. Think of a x-wind vector triangle except with the horizontal component of lift. The aircraft will follow the resultant path of it's forward motion and the horizontal component of lift. The aircraft will now fly slightly sideways (slips) unless you add rudder to keep the aircraft inline with the resultant path.

Remember, in it's purist sense, movement around the yaw axis creates a turn. Movement around the longitudinal axis will only create roll but no turn.

This is just me thinking "out loud". I may be wrong (and I'm sure I'll hear about it if I am...this is AvCanada after all) but it makes sense to me.

Cheers!

duplicate2 · Post by **duplicate2** » Sat Dec 10, 2005 2:46 am

Flying Low wrote:Remember, in it's purist sense, movement around the yaw axis creates a turn. Movement around the longitudinal axis will only create roll but no turn.

Unfortunately nothing in aerodynamics is so simple. Movement around the normal axis will create yaw, but you will very shortly start banking as well. Movement about the longintudinal axis is only roll, but you will very shortly starting turning in the direction of the roll as well and the nose will yaw opposite the turn. They're all mixed together and "pure" yaw or roll don't happen in the real world.

Pandora, I think I disagree with your CFI (and agree with you). An aircraft will turn by banking the wings alone and directing the lift vector towards the inside of the turn. It will be a crappy, sloppy, uncoordinated turn, but it will happen. Rudder will clean it up.

Think about a sideslip on final, the aircraft must want to turn due to the low-wing attitude or you wouldn't need opposite rudder to maintain your track.

I'm also open to other theories/explanations.

Flying Low · Post by **Flying Low** » Sat Dec 10, 2005 3:03 am

duplicate2:

An aircraft will turn by banking the wings alone and directing the lift vector towards the inside of the turn. It will be a crappy, sloppy, uncoordinated turn, but it will happen. Rudder will clean it up.

There is no question that the aircraft will turn with bank only. But is it exclusive to the fact that the aircraft is banked or is it due to the weather cocking of the aircraft as it slips (the slip is the true result of the bank). If by some amazing design feat you had an aircraft with the exact side surface area in front and behind the C of G of the aircraft, would it not just slip to the side with no turn? If so, the aircraft turns due to yaw developed by the vertical stabilizer in the side slip as a result of the bank (cleaned up with more yaw from the rudder). Bank and yaw combine to provide an efficient and comfortable way to turn but bank itself (without the inherent design of the aircraft) only rolls the airframe around it's longitudinal axis. The fact that it is designed into the plane doesn't change the fact that yaw and not bank is causing the nose to turn.

I just know Bede is somewhere with his nose in an Aerodynamics book trying to disprove me!

Justwannafly · Post by **Justwannafly** » Sat Dec 10, 2005 4:37 am

The airplane must be banked because the same force (lift) that sustains the airplane in flight is used to make the airplane turn. The airplane is banked and back elevator pressure is applied. This changes the direction of lift and increases the angle of attack on the wings, which increases the lift. The increased lift pulls the airplane around the turn. The amount of back elevator pressure applied, and therefore the amount of lift, varies directly with the angle of bank used. As the angle of bank is steepened, the amount of back elevator pressure must be increased to hold altitude. In the average training aircraft at banks at or above (aprox) 30’ require more power. The reason for this is that you have pulled up more on the elevators to increase your lift…this also increases the speed that you turn as well as the amount of drag. Now if I wanted to turn even quicker I suppose I could also push the opposite rudder to make my tail fly around even quicker….(btw DO NOT DO THIS! This will also cause the upper wing to stall easier…& do you really want to enter a spin during a turn?
At least that’s my thoughts…. Maybe we should try addressing this question from a different angle. Instead of trying to figure out if yaw affects our turn we should look at what yaw does to keep you flying in a strait line while in a banked attitude…though even there…I don’t see the correlation. Yaw effects a turn…but doesn’t really have anything to do with the turn it’s self…

I’m looking forward to some really technical answers coming here tomorrow from some of our experienced flight instructors 

BTD · Post by **BTD** » Sat Dec 10, 2005 5:32 am

I pretty much agree with everyone here.

The horizontal lift component pulls the aircraft sideways in the air. The resulting pressure on the vertical stab will tend to weather cock the airplane into the turn.

As was said before you needn't use rudder at all to get an airplane to turn. I suppose it is true that the aircraft is yawing around the horizon in a turn, but I always tend to think of yaw existing whenever the aircraft is in unco-ordinated flight. Only very little rudder (if any) should be used through out the turn, rudder is really needed when rolling to prevent aileron drag causing yaw. Yaw is something that should be controlled, not induced.

Pandora
"Now if I wanted to turn even quicker I suppose I could also push the opposite rudder to make my tail fly around even quicker…"

I think you mean too much inside rudder. Opposite rudder will put you into a slip (not such a bad thing if you want to) Inside rudder will put you into a skid (cross-controlling, very bad situation may lead to a stall spin). If you have a slightly less stable training airplane with a good sized rudder, try entering a stall/spin this way at altitude. Its pretty crazy.

Justwannafly · Post by **Justwannafly** » Sat Dec 10, 2005 6:22 am

@BTD:

I think you mean too much inside rudder. Opposite rudder will put you into a slip (not such a bad thing if you want to) Inside rudder will put you into a skid (cross-controlling, very bad situation may lead to a stall spin). If you have a slightly less stable training airplane with a good sized rudder, try entering a stall/spin this way at altitude. Its pretty crazy.

yea thats what I was talk'n about...I was think'n cross control but your right I said the wrong rudder.....oh & yea I have done that B4 for fun @ a high alt...its quite the entry (though my fav spin I think is still 152 @ full Power )....BUT I dont' recomend training pilots to do either one of those spin entrys unless they are with an instructor

Cat Driver · Post by **Cat Driver** » Sat Dec 10, 2005 8:54 am

I really should stay out of the instructors forum but ocassionally a subject comes up that I must comment on.

The most important lesson in flight training is attitudes and movements.

If the student does not clearly understand attitudes and movements his/her flying skills will suffer and their aircraft handling skills will be sloppy.

When I trained for my instructors rating it was on a Cessna 140 and the Fleet Canuck, both of these aircraft were quite satisfactory for explaining the effects of control movements.

For instance from straight and level flight have the student watch the horizon and you demonstrate the banked angle like this.

Using aelirons only we roll the aircraft to the banked attitude and check the bank angle at approximately 30 degrees, note the airplane will sideslip towards the down wing and the nose will move towards the down wing, this movement you see is a yawing movement.

You then explain why the yaw was produced when bank angle was checked or stopped during the rolling manouver.

We then went on to demonstrate what a yawing movement looks like by maintaining wings level and yawing the airplane with rudder only.

Yaw can be produced in several ways, rudder normally is used to control yaw.

I just woke up and will quit now because I am still half asleep and must go to the airport.

Tonight I may re explain this if I have written it in a poor manner.

Cat

SuperDave · Post by **SuperDave** » Sat Dec 10, 2005 9:36 am

I just turn the wheelee and the plane rolls right over for me like magic!!

But you're right, it is lift...one of the most important forces of flight...

frog · Post by **frog** » Sat Dec 10, 2005 9:37 am

once the plane is banked it will slip inside the turn, this will cause the nose to drop, to compensate you will pull the nose up...and you will turn!

BTD · Post by **BTD** » Sat Dec 10, 2005 12:02 pm

Thats true, but you will still turn even if you don't pull back. Once the aircraft is moving through the air sideways, it will turn into the relative wind, due to the vertical stab.

Cat was headed off with a good explanation, then just cut out.

Meh.

Doc · Post by **Doc** » Sat Dec 10, 2005 12:26 pm

weather-cock?

wannabatp · Post by **wannabatp** » Sat Dec 10, 2005 3:32 pm

Hmmm, stab in the dark in here. Moving the aileron changes the camber of a wing causing more lift on one wing and less lift on the other. All else being equal, once an aircraft wing is higher than than the other, it is at a higher angle of attack and generates more lift, causing the aircraft to turn.

More lift also equals higher drag (upper wing tends to drag behind the aircraft) so rudder is used to counteract adverse yaw (and thats ALL a rudder is ever used for).

I do remember it had nothing to do with how the relative wind hits the ailerons or control surfaces forcing changes in the axes.

I had to look that up for a CFI years ago and it made sense at the time.

Comments?

Cheers!

Edited for bad grammar/spelling.

Airtids · Post by **Airtids** » Sat Dec 10, 2005 3:52 pm

Pandora, I agree with what has been posted here by the Avcanada experts. I would now like to hear what your CFI had as an explanation. My guess is it is some approximation of the above.

Cat Driver · Post by **Cat Driver** » Sat Dec 10, 2005 4:03 pm

To try and dissect the aerodymanics and the lift vectors that are at work during a turn is interesting from an acedemic point of view.

Where this need to know falls flat on its ass is observing the end product, the pilot, not knowing how or when to move the controls to make the aircraft go in the direction he/she wants it to go.

I find it frustrating that so many pilots think they understand the physics involved, yet the airplane flys them.

Crosswind take offs and landings are a typical area where sloppy and or improper control inputs are common resulting in very ropy crosswind take offs and landings.

Give me a pilot that can thread his airplanne through the eye of a needle effortlessly and doesen't understand jack shit about the aerodynamics involved and I will let him/her fly my airplane. Rather that the paper expert that can write a doctorate on aerodynamics and physics but I have to run and hide everytime they semi crash the airplane because they never learned to fly.

Cat

SuperDave · Post by **SuperDave** » Sat Dec 10, 2005 4:18 pm

Well, I guess a short answer like: "cause I want it to!!!" aint gonna cut it.

As the ailerons deflect to roll the plane into the turn, the lowered aileron on the "up"-wing creates increased drag. This causes the nose yaw slightly in a direction opposite the initial turn. So we step on the rudder to compensate for this yaw.

As the plane banks, some of the lift, that until now has counteracted gravity in order to maintain level flight is vectored to the inside of the bank..."lifting" the plane into the turn.

There is some inertia involved, but it's only a factor for a little while. The aircraft maintains level flight until the vertical component of lift decreases enough and allows gravity to take over, causing the aircraft to descend. This is where we have to apply back pressure on the schtick to increase the angle of attack, as someone already mentioned, and thus producing enough added lift to maintain the desired altitude. As we know lift causes drag, so some power has to be applied to overcome the increase in drag and keep all four forces in equilibrium.

Amen.

SuperDave · Post by **SuperDave** » Sat Dec 10, 2005 4:25 pm

Give me a pilot that can thread his airplanne through the eye of a needle effortlessly and doesen't understand jack shit about the aerodynamics involved and I will let him/her fly my airplane. Rather that the paper expert that can write a doctorate on aerodynamics and physics but I have to run and hide everytime they semi crash the airplane because they never learned to fly.

Excellent point. Just like some pilots try to impress you with knowledge of air regs that are completely irrelevant to their operation, but somehow knowing all this useless shit makes them feel good about themselves.

Luckily I have not met too many off them, but the ones I did run into that tried to intimidate me with that stuff left a bit of a scar. Once bitten, twice shy I suppose.

No knowledge in the world can replace good hands and feet coupled with sound decision-making.

Cat Driver · Post by **Cat Driver** » Sat Dec 10, 2005 6:11 pm

" As the ailerons deflect to roll the plane into the turn, the lowered aileron on the "up"-wing creates increased drag. This causes the nose yaw slightly in a direction opposite the initial turn. So we step on the rudder to compensate for this yaw. "

In all airplane designs?

Cat

Doc · Post by **Doc** » Sat Dec 10, 2005 6:47 pm

I turn zee wheel to the right...the airplane turns right! I turn zee wheel to the left.....the airplane turns left! I is happy wit dis, no?

Justwannafly · Post by **Justwannafly** » Sat Dec 10, 2005 7:02 pm

Cat Driver wrote: " As the ailerons deflect to roll the plane into the turn, the lowered aileron on the "up"-wing creates increased drag. This causes the nose yaw slightly in a direction opposite the initial turn. So we step on the rudder to compensate for this yaw. "

In all airplane designs?

Cat

yes its call'd aileron drag....there are a number of different aileron designs out there that work on comensating for it...but I don't think any of them have completely resolved the issue...afterall drag is a byproduct of lift...you can't have lift without drag

When we figgure that stuff out we will have spaceships