Airplane turning loads and aerodynamics

[fiveoboy01]

The "other" thread had me thinking and go easy on me because I'm still a noob pilot...

Someone said the elevator does not turn the aircraft.

My understanding is that it's the horizontal component of lift which actually turns the airplane, so wouldn't that mean the elevator is used to turn the aircraft(once in the bank)? Or is the elevator just used to add enough horizontal lift back in to keep from losing altitude through the turn?

Help me understand what goes on in a turn beyond the basics that I've read in the various manuals and handbooks. And guys let's not try to bicker ok? Thanks

 

[poadeleted20]

My understanding is that it's the horizontal component of lift which actually turns the airplane, so wouldn't that mean the elevator is used to turn the aircraft(once in the bank)? Or is the elevator just used to add enough horizontal lift back in to keep from losing altitude through the turn?

Change that "horizontal" to "vertical" and you'd have it nailed.

 

[dtuuri]

Consider this thought-exercise. If there were no gravity there would be no need for lift, no angle of attack, no purpose for an elevator/horizontal stabilizer combination. Unless, that is, you wanted to change direction. Then you could pull back, develop some "lift" with the wing which would start you uphill. Since the new direction would change the airflow over the tail, it would weather-vane into the relative wind and in the process change the direction the nose is pointed even more upward. The continuous tail-chasing-nose effect would result in a curving flight path in a vertical plane, ie, a 'loop'.

The same thing happens in a normal banked turn, so it's the combination of the elevator and horizontal stabilizer (or the stabilator) that makes the plane weather-vane to a new heading. Who says the elevator "does not turn the airplane"?

dtuuri

 

[SixPapaCharlie]

The yoke banks the aircraft. which makes you lean in the direction of the bank. That unequal distribution of weight (from you leaning) forces the plane to drift that direction. Airflow has nothing to do with it.

I 'm pretty sure you can test this by banking left and leaning right and you will fly straight ahead in a bank. This is precisely how they acomplish knife edge flight.

 

[Capt. Geoffrey Thorpe]

Elevator controls pitch which results in an angle of attack.

Ailerons control roll with results in banking

Rudder controls yaw which is typically used to avoid slip / skid.

The forces previewed during operation of an airplane (G loading, side loading) are totally due to the aerodynamic forces and are not a function of gravity.

The acceleration due to gravity effects the aircraft trajectory (which in turn, affects speed and altitude) but does not cause the forces felt through the seat of your pants.

Lift is a function of angle of attack and indicated airspeed.

Velocity is a vector - it has direction.

Newtons laws apply.

A "normal" turn happens due to a combination of the net direction of the lift and the yaw rate. The yaw is controlled to maintain ball in the center coordination and the horizontal (WRT the Earth's inertial frame) accelerates the airplane to fly in a different direction.

You can slip (bank without yaw) and the aircraft will tend to move sideways compared to the center line (change the track) and lose altitude without changing the heading.

You can skid (yaw with insufficient or no bank) and change directions, but it is not efficient and can result in a spin if you stall during the process.

If you want to not have vertical acceleration when you bank and turn, you have to increase the angle of attack so the component of the lift that acts in the direction opposite the acceleration of gravity is approximately equal to the weight of the aircraft. Increasing the total lift generated results in "g loading".

Wings stall at an approximately constant angle of attack.

The total lift generated by the wing just before stall is a function of indicated airspeed. As a result, you can reach higher loading at higher airspeeds. This gives rise to the concept that stall speed increases with G loading.

The assumption that you always perfectly increase the angle of attack to avoid vertical (w.r.t. the earth's inertial frame) acceleration during a turn gives rise to the misconception that stall speed is a function of bank angle.

 

[redtail]

Consider this thought-exercise. If there were no gravity there would be no need for lift, no angle of attack, no purpose for an elevator/horizontal stabilizer combination. Unless, that is, you wanted to change direction. Then you could pull back, develop some "lift" with the wing which would start you uphill. Since the new direction would change the airflow over the tail, it would weather-vane into the relative wind and in the process change the direction the nose is pointed even more upward. The continuous tail-chasing-nose effect would result in a curving flight path in a vertical plane, ie, a 'loop'.

The same thing happens in a normal banked turn, so it's the combination of the elevator and horizontal stabilizer (or the stabilator) that makes the plane weather-vane to a new heading. Who says the elevator "does not turn the airplane"?

dtuuri

I thought if you rolled into a bank without using any elevator back pressure, the airplane would still turn due to the horizontal stabilizer weathervaning into the relative wind. You just wouldn't be maintaining altitude, you'd be spiraling down. So the turn is a result of a combination of the horizontal component of lift from the wings AND the horizontal stabilizer/stabilator.

In other words, if you locked the pitch control neutral (no elevator), the airplane would still turn. Correct?

 

[overdrive148]

Correct me if I'm wrong:

1) Straight and level flight: All forces in balance, lift is purely vertical.

2) Roll into a bank w/ailerons: Changed lift to two components, horizontal and vertical.

3) Since you can't maintain the full vertical portion of lift after removing some of it for the addition of horizontal, the vertical component becomes less than it was straight and level flight.

4) Since there is a loss in the vertical component of lift, you re-add it into the equation with elevator to maintain the turn.

 

[ifconfig]

Correct me if I'm wrong:

4) Since there is a loss in the vertical component of lift, you re-add it into the equation with elevator to maintain the turn.

How to explain a stable, hands-off 30° bank?

 

[Lindberg]

The elevator does not add lift.

Because the vertical component of lift from the wing is decreased in a bank, you use the elevator to increase the angle of attack of the wing, which then produces more lift (and drag).

If you don't use the elevator to increase the angle of attack of the wing and thereby restore the vertical component of lift, you'll still turn, but you'll descend as well.

Because you're banked, the pitching moment also has a vertical and horizontal component.

 

[overdrive148]

How to explain a stable, hands-off 30° bank?

Trim?

The elevator does not add lift.

Because the vertical component of lift from the wing is decreased in a bank, you use the elevator to increase the angle of attack of the wing, which then produces more lift (and drag).

If you don't use the elevator to increase the angle of attack of the wing and thereby restore the vertical component of lift, you'll still turn, but you'll descend as well.

Because you're banked, the pitching moment also has a vertical and horizontal component.

The elevator restores the component of lift through that process is what I meant. Thanks

 

[dtuuri]

In other words, if you locked the pitch control neutral (no elevator), the airplane would still turn. Correct?

Correct, you will turn. That's because in real life there is gravity and there is an aerodynamic down force on the horizontal stabilizer all the time to offset it. If you could switch gravity off, while trimmed for level flight, the plane would do a loop. When you bank, gravity comes more from the side, so there isn't enough to offset the amount of lift the wing is aerodynamically trimmed to produce--and the result is a turn similar to the thought experiment, only in a horizontal plane rather than a vertical one.

dtuuri

 

[txflyer]

They're all wrong OP.

The yoke/stick turns the airplane.

And keep them flaps up!

 

[EdFred]

Gravity free planets? Relative wind?

You guys make this way, way, way more complicated than it actually is.

 

[redtail]

Gravity free planets? Relative wind?

You guys make this way, way, way more complicated than it actually is.

How about relative-wind free planets, with gravity

 

[Skylane81E]

How about relative-wind free planets, with gravity

Think "brick"

 

[MAKG1]

How to explain a stable, hands-off 30° bank?

Trim.

 

[MAKG1]

Change that "horizontal" to "vertical" and you'd have it nailed.

It seems strange to me that so many folks would miss something, so maybe it's me....

Your elevator is not an altitude control unless you're straight. If you pull the yoke to correct for a descent in a steep turn, you'll correct it. But you'll also tighten the turn. In equal quantities for a 45 deg bank. This suggests rather strongly that the elevator does participate, though it clearly isn't the only player.

I think just about every student pilot has tried this at one point or another.

 

[redtail]

It seems strange to me that so many folks would miss something, so maybe it's me....

Your elevator is not an altitude control unless you're straight..

I think you mean pitch (attitude) control.

 

[MAKG1]

I think you mean pitch (attitude) control.

Well, it certainly is that. But I was responding to statements about altitude, not attitude.

 

[lr60plt]

I use the elevator to turn sometimes.

 

[Everskyward]

Maybe this will help people??

Merely banking the airplane into a turn produces no change in the total amount of lift developed. However, as was pointed out, the lift during the bank is divided into two components, one vertical and the other horizontal. This division reduces the amount of lift which is opposing gravity and actually supporting the airplane's weight; consequently, the airplane loses altitude unless additional lift is created. This is done by increasing the angle of attack until the vertical component of lift is again equal to the weight. Since the vertical component of lift decreases as the bank angle increases, the angle of attack must be progressively increased to produce sufficient vertical lift to support the airplane's weight. The fact that the vertical component of lift must be equal to the weight to maintain altitude is an important fact to remember when making constant altitude turns.

http://avstop.com/ac/flighttrainghandbook/forcesinturns.html

You are increasing the angle of attack with the elevator but that doesn't mean you are turning with the elevator. It you didn't increase the elevator you would still be turning but also descending.

 

[Lindberg]

Well, it certainly is that. But I was responding to statements about altitude, not attitude.

The elevator is not an altitude control, it's an angle of attack control.

 

[PilotAlan]

In level flight, the elevator is generating lift through sufficient angle of attack to offset the force of gravity. So when you bank, a component of that lift is being directed horizontally to create a turn.
If you put the aircraft into a zero G/zero AOA condition (like an arc, or straight down), then there is no lift. Rolling one or the other generates no turn, as the wing is not generating any lift.

The ailerons do not generate any turning force (with the exception of adverse yaw in some aircraft as a side effect of asymmetrical drag, not lift), they generate roll. The lift generated by the wing causes the turn (which is caused by forces from the elevator).

 

[Everskyward]

The ailerons do not generate any turning force (with the exception of adverse yaw in some aircraft as a side effect of asymmetrical drag, not lift), they generate roll. The lift generated by the wing causes the turn (which is caused by forces from the elevator).

But there would be no turn without the ailerons putting the airplane in a bank.

Of course you could turn with rudder but that is not what we are talking about here

 

[Pilot Nick]

Watch out, the over thinking of the dynamics will not help on the FAA written!

 

[Everskyward]

It probably won't help with flying the plane either!

 

[Pilot Nick]

In level flight, the elevator is generating lift through sufficient angle of attack to offset the force of gravity. So when you bank, a component of that lift is being directed horizontally to create a turn...

Most airplane stabilizers generate a downward lift force to counteract the moment/torque of that heavy engine out front. Could you say that the horizontal component of lift generated by the tail is actually hindering the turn? The elevator increases this downward (away from the level turn) force when applying back pressure on the yoke!

 

[drotto]

Watch out, the over thinking of the dynamics will not help on the FAA written!

The FAA written will say the horizontal component of lift turns the plane, and you create horizontal force by rolling the plane. As simple as that.

 

[Everskyward]

The FAA written will say the horizontal component of lift turns the plane, and you create horizontal force by rolling the plane. As simple as that.

Glad someone thinks it's simple.

I think where people may be getting confused is that in a steep turn you can tighten it with the elevator. But you wouldn't be turning in the first place if you didn't use ailerons to roll into the bank.

 

[Tarheelpilot]

The yoke banks the aircraft. which makes you lean in the direction of the bank. That unequal distribution of weight (from you leaning) forces the plane to drift that direction. Airflow has nothing to do with it.

I 'm pretty sure you can test this by banking left and leaning right and you will fly straight ahead in a bank. This is precisely how they acomplish knife edge flight.

is this an attempt at humor? Just asking before I respond as if you are serious

 

[Capt. Geoffrey Thorpe]

Most airplane stabilizers generate a downward lift force to counteract the moment/torque of that heavy engine out front. Could you say that the horizontal component of lift generated by the tail is actually hindering the turn?

No. .

 

[Fearless Tower]

is this an attempt at humor? Just asking before I respond as if you are serious

I think he was trying to see if he could out do the silliness of the other thread.

 

[RoscoeT]

The yoke banks the aircraft. which makes you lean in the direction of the bank. That unequal distribution of weight (from you leaning) forces the plane to drift that direction. Airflow has nothing to do with it.

I 'm pretty sure you can test this by banking left and leaning right and you will fly straight ahead in a bank. This is precisely how they acomplish knife edge flight.

LOL. Lean into it and shift your weight around -just like in a hang glider. That was funny. I assume you are not being serious. I hope.

 

[dtuuri]

Maybe this will help people??

http://avstop.com/ac/flighttrainghandbook/forcesinturns.html

Actually, that's probably what confuses people. It doesn't 'explain' why an airplane changes heading. It might be intuitive for some, but there's a better way. As Wolfgang Langwiesche states on page 198 in his book Stick and Rudder,

"An airplane is turned by laying it over on its side and lifting it around through back pressure on the elevator."​

The key, as he illustrates with a drawing, is the continual action of the horizontal tail surfaces, much like the feathers of an arrow or as a weather vane, to maintain the selected angle of attack, resulting in curving flight.

dtuuri

 

[Capt. Geoffrey Thorpe]

Actually, that's probably what confuses people. It doesn't 'explain' why an airplane changes heading.

F = M*A

or,

A = F/M

An airplane is a mass, if there is a net lateral Force, the result is an Acceleration to a different heading.

Or, to not accelerate (in any direction) the sum of the forces must be zero.

("Centrifugal force" is a psuedo force - not a real force - if it was a real force, according to the picture posted, an airplane would never turn)

 

[SixPapaCharlie]

is this an attempt at humor? Just asking before I respond as if you are serious

Yes. From time to time I am known to get silly.

 

[redtail]

The yoke banks the aircraft. which makes you lean in the direction of the bank. That unequal distribution of weight (from you leaning) forces the plane to drift that direction. Airflow has nothing to do with it.

I 'm pretty sure you can test this by banking left and leaning right and you will fly straight ahead in a bank. This is precisely how they acomplish knife edge flight.

LOL. Lean into it and shift your weight around -just like in a hang glider. That was funny. I assume you are not being serious. I hope.

That's how the Wright Brothers performed knife edge flight


"The braided cable attached to the hip cradle zigzags through pulleys placed about two-thirds of the way back along the rear wing struts. When you slide the hip cradle to the right, the cable pulls the right wing tips down and the left wing tips up. The left wing tips, with their increased angle of incidence, generate more lift. The left wings rise as the right wings, with their lift decreased, fall. The airplane rolls to the right".

 

[eetrojan]

Maybe this will help people??

Along the same lines...

My flight school taught me that a plane turns in an arc as it moves forward, rather than just flies off at an angle, because the angled flight path associated with the thrust vector and the horizontal component of lift (top view) creates a relative wind - and the airplane constantly tries to face into the relative wind (bottom view, weathervaning).

Bearing in mind that this is just a student's interpretation and all (please correct if wrong), here's a diagram I drew a while back to illustrate the concept to myself.

Joe

 

[Everskyward]

Actually, that's probably what confuses people. It doesn't 'explain' why an airplane changes heading. It might be intuitive for some, but there's a better way. As Wolfgang Langwiesche states on page 198 in his book Stick and Rudder,

"An airplane is turned by laying it over on its side and lifting it around through back pressure on the elevator."​

The key, as he illustrates with a drawing, is the continual action of the horizontal tail surfaces, much like the feathers of an arrow or as a weather vane, to maintain the selected angle of attack, resulting in curving flight.



dtuuri

So we can blame Stick and Rudder for confusing things because it doesn't mention how the airplane gets layed over on its side, or the fact that the airplane would still turn without additional elevator input.

 

[ifconfig]

Each further post reminds me that human beings weren't meant to fly.

Happy New Year everyone.

When the aircraft is rolled into a bank, the lift component tilts with it; the lift is perpendicular to the wing observed from behind. The resulting horizontal lift component pulls the plane parallel in the direction of the bank. The lateral movement creates relative wind that hits the airplane from the side and yaws it into the wind like a weather vane. Yaw is delayed because the plane must be accelerated laterally by the horizontal lift component before the relative wind can act on the tailplane. When the airplane yaws, the sideslip induces a lateral flow around the fuselage.

Depending on the shape of the fuselage this changes the angle of attack on the affected wing or shelters parts of the wing. Furthermore, the speed on the wing going upwind is momentarily increased by the rotational speed of the yaw. These two effects cause the bank in the direction of the yaw. The onset of the roll in response to the yaw is also delayed due to the inertia of the airplane.

When rolling the airplane into a bank, the aileron on the up going wing deflects downwards and produces extra lift and drag. This drag acts opposite the desired turn direction. This is adverse yaw. If this effect is not minimized by design tricks, differential ailerons, or additional spoiler deployment in your handy dandy 737, more rudder in the desired direction has to be applied to coordinate the turn.