GScholz more ont turbo props:

[Golfer]

To be honest I was hoping that you picked an airplane you had some experience with.  Its not in-game its not something anyone can go out and fly.

[HoHun]

Hi Golfer,

>To be honest I was hoping that you picked an airplane you had some experience with.  Its not in-game its not something anyone can go out and fly.

Well, suggest any other, I'll just follow your lead :-)

Regards,

Henning (HoHun)

[Straiga]

http://142.26.194.131/aerodynamics1/Multi/Page3.html

In this photo it shows a yawing monent not a rolling monent.

Straiga

[HoHun]

Hi Straiga,

>In this photo it shows a yawing monent not a rolling monent.

Hm, that could mean that the influence of the P factor is larger than the influence of torque. (A certain amount of rolling moment due to torque should be there in any case.)

Of course, it becomes even more complicated because angle of attack can vary (and the orientation of the engines' thrust line, too).

To simplify things, could we assume for the moment that the straight and level flight situation of our example aircraft has the thrust line aligned so that there is no P factor?

That would bring us to the situation I suggested:

>>a) we held the rudder centered and fed in aileron to compensate for the engine torque?

>The plane would yaw left because of assemetric aileron in the direction of the torque.

I believe we agree that the yaw (in the no P factor case) is the by-product of aileron application?

>>b) we held ailerons neutral and fed in rudder to compensate for the engine torque?

>This is the correct way to counter torque in a 4 engine airplane and the use of rudder gives you directional control.

What would the stabilized flight situation look like in terms of yaw and bank? This is difficult to visualize for a non-pilot :-)

Regards,

Henning (HoHun)

[Golfer]

I believe we agree that the yaw (in the no P factor case) is the by-product of aileron application?

I can't.

There is something called Adverse yaw.  This is the tendency of the nose to yaw opposite the direction of turn in the application of aileron movement.  This is why you need to use rudder in the direction of turn to maintain a coordinated turn.  Coordinated meaning you keep the ball centered.

This is typically not in any excessive amount (with most modern nosewheel trainers) but it is worth noting because it will require correction.


I'm confused slightly (I understand all the principals you're referring to) about how you might mean to interpret when you say aligning the thrust line and P-factor.  I know how to answer the question, I just want to make sure you asked it this way on purpose.

[Straiga]

To simplify things, could we assume for the moment that the straight and level flight situation of our example aircraft has the thrust line aligned so that there is no P factor?

Hi HoHun, This is true in straight and level flight you do not have any P-Factor only until you change the angle of attack. Then P-Factor is a yawing monent in flight.

I believe we agree that the yaw (in the no P factor case) is the by-product of aileron application?

This is also true the when the right aileron is deflected up this decreases Lift, decreases Drag, and so the wing moves forward.
The left aileron is deflected down the Lift increases, drag increases, and the wing moves aft. This is with no rudder appilcation.

So if you were to counter torque roll by only aileron it would yaw the airplane into the direction of the torque. This would create more problems. An airplane yawing to the left, turning left and rolling to left so how can fly in the direction you want to go in. Only by using rudder and no aileron can you effectivly counter torque roll and maintain directional control too. Plus have less drag on the airframe. No assemetric drag from the ailerons. Remember that in flight at cruise speed rudder is very effective to counter torque roll. You can also turn a airplane by rudder alone.  

When you move the engines out toward the wing tip the torque force is still present but the force it applies is in the form of yaw moment to the airframe not a roll moment. When flying a multi-engine you can see this very clearly, and by doing so it makes this very simple to understand.

What would the stabilized flight situation look like in terms of yaw and bank? This is difficult to visualize for a non-pilot :-)

Stabilized flight at cruise airspeed would be this:

Single Engine Airplane: Right rudder or right rudder trim to the right.

Multi-Engine Airplane: both props same rotation to the right  (same as for the single engine airplane).
MEA: counter rotational props, nuetral rudder

SEA: aileron nuetral, Aileron trim nuetral.

MEA: Airleron nuetral, Aileron trim nuetral (same rotation props and counter rotational props)

SEA: Elevator nuetral or nose down, elevator trim nuetral or nose down.

MEA: same as in the SEA (same rotation props and counter rotational props)

You have a good understanding so far. HoHun good points.

Straiga

[HoHun]

Hi Golfer,

>There is something called Adverse yaw.  

Yes, I should have said "adverse yaw".

Then the situation would be: Clockwise turning propeller, anti-clockwise (left) torque-induced roll, we feed in right aileron in order to keep the wings level, producing adverse (left) yaw. So we end up wings level, ailerons deflected, rudders neutral, in a left yaw.

Does that sound plausible?

>I'm confused slightly (I understand all the principals you're referring to) about how you might mean to interpret when you say aligning the thrust line and P-factor.  

Let's say that in our cruise situation, the free airstream hits the propeller disk perpendicularly so that the propeller blade angle of attack is symmetrical and we have no P factor effects.

(Thinking about it, P factor would also induce a left yaw for the situation described above, so we seem to have two factors adding up.)

Regards,

Henning (HoHun)

[HoHun]

Hi Straiga,

>Stabilized flight at cruise airspeed would be this:

>Single Engine Airplane: Right rudder or right rudder trim to the right.

>Multi-Engine Airplane: both props same rotation to the right  (same as for the single engine airplane).

The thing I haven't fully understood yet: If you're flying with a slight right yaw, does that mean you have the left wing down a bit?

In any case, the left wing gets a bit more lift due to the dihedral effects Golfer mentioned, compensating the (as I assumed, rolling) torque without the necessity for an aileron deflection?

I assume the slight right yaw trim is preferable above the wings-level, left yaw, ailerons deflected situation described in my post above?

If I manage to score 2 out of 3 here that probably means I'm getting real close ;-)

Regards,

Henning (HoHun)

[Straiga]

The thing I haven't fully understood yet: If you're flying with a slight right yaw, does that mean you have the left wing down a bit?

When your flying straight and level with rudder input to the right th ball is centered wings level. No right yaw at all.

The vertical stabilizer is set at an angle of attack to the left of the center line of the airplane. Also the left wing sets a higher angle of incidence then the right wing this is rigged to counter torque roll as the vertical stabilizer is.

Angle of incidence is the fixed angle of attack position of the wing to the fuselage.

In any case, the left wing gets a bit more lift due to the dihedral effects Golfer mentioned, compensating the (as I assumed, rolling) torque without the necessity for an aileron deflection?

Dihedral is set into both wings as the plane rolls in one way the lowest wing is at a greater angle of attack and will create more lift then the other wing and will roll the plane level again.

Then the situation would be: Clockwise turning propeller, anti-clockwise (left) torque-induced roll, we feed in right aileron in order to keep the wings level, producing adverse (left) yaw. So we end up wings level, ailerons deflected, rudders neutral, in a left yaw

Yes exactly.

Let's say that in our cruise situation, the free airstream hits the propeller disk perpendicularly so that the propeller blade angle of attack is symmetrical and we have no P factor effects.

When the relative wind is perpendicular to the prop disk the prop has equal lift through out the prop disk. But when you change angle of attack of the main wing up the prop disk on the right is at a higher angle of attack the left side of the prop disk yawing the plane to the left. Now when the airplane is nose down the left side prop disk is now at a higher angle of attack and yaws the plane to the right.

There are two types of wind that affects the airplane. 1 the wind that blows around the trees and 2. relative wind which is the oposing wind which is oposite to the flight path of the airplane. It is not oposite to the way the airplane is pointing but the direction its is traveling. ie nose high but moving forward.

Straiga

[hitech]

The vertical stabilizer is set at an angle of attack to the left of the center line of the airplane. Also the left wing sets a higher angle of incidence then the right wing this is rigged to counter torque roll as the vertical stabilizer is.

Straga: Do we agree that the left wing greater AOA is simply to counter the engine torque. I.E. preforming the same functions as ailarons.

Also:

Dihedral is set into both wings as the plane rolls in one way the lowest wing is at a greater angle of attack and will create more lift then the other wing and will roll the plane level again.

Can you describe how the low wing, in a stead state bank with dihedral creates more lift than the other?

If your just talking about the yaw produced in the bank , and that yaw producing oposit roll then no need to describe the dynamics.

Also: If you do not except that moving engines outboard does not effect there torque on the plane. We are realy going to have a hard time totaling up the forces for stable flight.

HiTech

[HoHun]

Hi Straiga,

>Also the left wing sets a higher angle of incidence then the right wing this is rigged to counter torque roll as the vertical stabilizer is.

OK, let's assume a simplified symmetrical airframe.

In that case, the higher lift required from the left wing would be the result of more favourable aerodynamics on the left wind due to the right yaw?

(Fuselage blanketing the right wing and lots of complex stuff - I guess this is why Golfer asked for a specific aircraft type :-)

Regards,

Henning (HoHun)

[Straiga]

Straga: Do we agree that the left wing greater AOA is simply to counter the engine torque. I.E. preforming the same functions as ailarons.

Yes I agree this is why no aileron is nessasary only in a single engine airplane.

Can you describe how the low wing, in a stead state bank with dihedral creates more lift than the other?

Think of a dutch roll.

If you do not except that moving engines outboard does not effect there torque on the plane.

Torgue does not change true but how it affects the airframe in a multi-engine airplane yes it does change to a yaw moment.
Go ask somebody else if you dont believe me thats all.

Straiga

[rshubert]

Originally posted by hitech
Straga: Do we agree that the left wing greater AOA is simply to counter the engine torque. I.E. preforming the same functions as ailarons.

Also:

 

Can you describe how the low wing, in a stead state bank with dihedral creates more lift than the other?


HiTech

It doesn't, actually.  BUT the more horizontal wing has a higher component of it's lift vector pointed straight down.  One thing to remeber is that in ground school, they always talk as if the wing lift vector in stable cruise flight is straight down.  Actually, it isn't in a plane that has wing dihedral.  It's off vertical by the amount of dihedral, and some lift is lost in a horizontal direction.  Not much, but it is there.

In a plane with dihedral, when a wing drops, the downmoving wing becomes more horizontal, and the upmoving wing less horizontal.  Without dihedral, the falling wing becomes less horizontal at the same rate in the opposite direction as the rising wing.

Back to the plane with dihedral.  As the dropping wing rotates past horizontal, it still has a smaller angle to the horizon as the rising wing, and still has a larger lift vector straight down.  The net effect of this is that when a wing drops, aerodynamic forces tend to right the plane about the longitudinal axis.

[Casca]

A wing does not generate more lift because it is oriented horizontally.  The reason dihedral works is that when the wing drops it induces a slip that moves the relative wind to a greater AoA on the decending wing.

[hitech]

Casca: That has always been my understanding.


Straiga:

Torgue does not change true but how it affects the airframe in a multi-engine airplane yes it does change to a yaw moment.

You keep stating that engine torque is changed to a yaw. But never describe how.

Unless I missed it some where.

Now if your just describing that torque is counter by extra AOA in the one wing, or by ailaron, then because of the extra AOA more inducuded drag, hence that needs to be countered with rudder.

Then im in agreement.

But the fact still remains that moving the engines out board did not in any way change the engine torque in the roll axis.  Nore how those forces affected the airframe. They were just compensated for in the rigging of the plane.

Straga: Also wondering if you have ever done power off and power on stalls in a twin. And noted the difference in stall speeds? Haven't done the calcs but curious how much speed difference in a light twin.



HiTech