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 Post subject: Re: Well the MU2 is a nice ride, especially the Crossno expr
PostPosted: 07 Jul 2018, 20:55 
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Ahem. What's the T in PAST? :)


Ya got me...(?)


PAST is a common "memory aid" in multi-engine training. P-factor, Accelerated slipstream, Spiraling slipstream and Torque. Factors that affect engine criticality. Torque is a factor there.


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 Post subject: Re: Well the MU2 is a nice ride, especially the Crossno expr
PostPosted: 07 Jul 2018, 21:36 
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____________________________________

Sandy,

Yes, torque is used as a measurement of power, but with the loss of an engine it's asymmetrical thrust that creates a yaw requiring rudder, not torque, just to be clear. :cheers:


Ahem. What's the T in PAST? :)


Torque created along the longitudenal axis creates a rolling moment, countered by roll input, ailerons or MU2 spoilers. The rolling moment in most pronounced when the torque axis is on the longitudenal axis of the plane, like single engines. Any torque roll on a twin would be much less, but still countered by ailerons or spoilers, not rudder.

In a twin with both engines rotating to the right there is a pronounced yaw when the angle of attack of the props is increased because the down swinging blade on the right engine has a greater arm about the vertical axis causing more yaw than the down swinging blade of the left engine causing the plane to yaw and maybe roll, but the roll is from momentary differential lift increase on the right wing as it yaws, not from torque.

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 Post subject: Re: Well the MU2 is a nice ride, especially the Crossno expr
PostPosted: 07 Jul 2018, 23:25 
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Username Protected wrote:
Torque created along the longitudenal axis creates a rolling moment, countered by roll input, ailerons or MU2 spoilers. The rolling moment in most pronounced when the torque axis is on the longitudenal axis of the plane, like single engines. Any torque roll on a twin would be much less, but still countered by ailerons or spoilers, not rudder.

That may seem logical to you, but its not the way it is done.

This video explains it:

https://www.youtube.com/watch?v=o8sc3VlZPUc

Namely, rudder is used to counter engine torque because of the undesirable side effects of using ailerons to do it.

This also talks about rudder trim changes with speed and power, an example at top of climb shown:

https://www.youtube.com/watch?v=rTrhAkTLHCY

One way to think about the rudder causing torque reaction is that it is best to use the entire wing to counter that torque than just the small aileron. A small rudder input does that.

Basic take away: engine torque is addressed by rudder primarily.

Even when there is no roll, say a P-51 on the ground at the start of takeoff roll, you need rudder to counter engine torque. If the pilot doesn't do that, they will be off the runway. This occurs even though the main gear prevents any roll.

Mike C.

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 Post subject: Re: Well the MU2 is a nice ride, especially the Crossno expr
PostPosted: 08 Jul 2018, 00:48 
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Even when there is no roll, say a P-51 on the ground at the start of takeoff roll, you need rudder to counter engine torque. If the pilot doesn't do that, they will be off the runway. This occurs even though the main gear prevents any roll.


You need rudder to counteract "P" factor and as the tail comes up, gyroscopic precession.

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 Post subject: Re: Well the MU2 is a nice ride, especially the Crossno expr
PostPosted: 08 Jul 2018, 11:11 
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Username Protected wrote:
You need rudder to counteract "P" factor and as the tail comes up, gyroscopic precession.

You need rudder well before the tail comes up, and before P factor is significant (which requires significant airspeed).

P-51 gyro forces are minimal due to very little attitude change in takeoff and that change in attitude occurs slowly.

[youtube]https://youtu.be/3dvuTAJq-iQ[/youtube]

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 Post subject: Re: Well the MU2 is a nice ride, especially the Crossno expr
PostPosted: 08 Jul 2018, 11:15 
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Username Protected wrote:
Torque created along the longitudenal axis creates a rolling moment, countered by roll input, ailerons or MU2 spoilers. The rolling moment in most pronounced when the torque axis is on the longitudenal axis of the plane, like single engines. Any torque roll on a twin would be much less, but still countered by ailerons or spoilers, not rudder.

That may seem logical to you, but its not the way it is done.

This video explains it:

https://www.youtube.com/watch?v=o8sc3VlZPUc

Namely, rudder is used to counter engine torque because of the undesirable side effects of using ailerons to do it.

This also talks about rudder trim changes with speed and power, an example at top of climb shown:

https://www.youtube.com/watch?v=rTrhAkTLHCY

One way to think about the rudder causing torque reaction is that it is best to use the entire wing to counter that torque than just the small aileron. A small rudder input does that.

Basic take away: engine torque is addressed by rudder primarily.

Even when there is no roll, say a P-51 on the ground at the start of takeoff roll, you need rudder to counter engine torque. If the pilot doesn't do that, they will be off the runway. This occurs even though the main gear prevents any roll.

Mike C.


Rudder and rudder trim is for movement about the vertical axis. Ailerons (or spoilers) is for movement about the longitudenal axis.

Your P-51 example with the tail on the ground on the initial takeoff roll is P-factor - asymmetrical disc loading. As was stated, when the tail is raised it's gyroscopic precession.

Any trim is for steady state conditions; change speed, power, or angle of attack, and trim forces change, i.e. reaching top of climb and transitioning to cruise.

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 Post subject: Re: Well the MU2 is a nice ride, especially the Crossno expr
PostPosted: 08 Jul 2018, 15:20 
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Username Protected wrote:
Rudder and rudder trim is for movement about the vertical axis. Ailerons (or spoilers) is for movement about the longitudenal axis.

That's an idealism that doesn't work in practice.

Rudder trim is used to counter engine torque because it uses the entire wing to counter the torque, not just the aileron.

Watch the video again. Note the slide that says when increasing power causes a left roll, apply RUDDER. They wrote it in RED to emphasize it.
Attachment:
torque-slide-1.png

Quote:
Your P-51 example with the tail on the ground on the initial takeoff roll is P-factor - asymmetrical disc loading.

There is no P factor if there is no airspeed. It takes appreciable airspeed before P factor becomes a factor. You need rudder well before that.

Quote:
As was stated, when the tail is raised it's gyroscopic precession.

Gyro precess is tiny due to very little attitude change and smooth changing of attitude.

Mike C.


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 Post subject: Re: Well the MU2 is a nice ride, especially the Crossno expr
PostPosted: 08 Jul 2018, 16:42 
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Quote:
There is no P factor if there is no airspeed. It takes appreciable airspeed before P factor becomes a factor. You need rudder well before that.


Obviously your definition of "P factor" is only known to you. For the rest of us, speed is not necessary for the down swinging blade to exert a left turn in a tail wheel airplane. ( tail low, with a right turning prop) .

Torque , at cruise power is countered by washing in the left wing ( clockwise props) this increases lift and drag which an offset fin counters, on light airplanes.

You may yaw a wing to counter roll, but only for the moment, holding the rudder does not stop a rolling moment, it will pick up a wing....won't hold it though.

However...you know wayyyyy more than I, I have thousands of tail wheel hours, but none in a P-51.... Or the MU-2.

How did you do on the treadmill take off problem.

Edit. Found this.
http://wiki.flightgear.org/Understandin ... d_P-Factor

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 Post subject: Re: Well the MU2 is a nice ride, especially the Crossno expr
PostPosted: 08 Jul 2018, 17:16 
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Username Protected wrote:
Obviously your definition of "P factor" is only known to you. For the rest of us, speed is not necessary for the down swinging blade to exert a left turn in a tail wheel airplane.

P factor is caused by the airspeed not being aligned with the prop rotational axis.

No airspeed, no misalignment.

Not clear what you think P factor is if you think it exists with no airspeed.

Quote:

P-Factor
...
This occurs only when the propeller is not meeting the oncoming airflow head-on


No airflow, no P factor.

Mike C.

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 Post subject: Re: Well the MU2 is a nice ride, especially the Crossno expr
PostPosted: 08 Jul 2018, 17:50 
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You really need some tail wheel time.

If you believe that the spinning prop does not create asymmetric thrust sitting still under power tail low..... I guess there is no thrust until you release the brakes...



Video says, use rudder to counter torque (pick up a wing) when at minimum air speeds. No one argues that. when at minimum airspeeds.

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 Post subject: Re: Well the MU2 is a nice ride, especially the Crossno expr
PostPosted: 08 Jul 2018, 18:27 
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Username Protected wrote:
You really need some tail wheel time.

My first 480 hours are tailwheel time. I'm one of the few flying today who did their primary training in a tailwheel airplane.

Quote:
If you believe that the spinning prop does not create asymmetric thrust sitting still under power tail low..... I guess there is no thrust until you release the brakes...

You have confused P factor with other effects. P factor can only occur with airspeed. With no airspeed, the AOA of the blades are the same all the way around, thus the P factor effect is absent. The prop, when sitting still, does not create asymmetric thrust from P factor.

What you are sensing is the swirling prop wash exerting forces on the tail which you counter with right rudder. In effect, the fin has AOA due to the prop wash hitting it that you have to remove with the application of rudder.

Quote:
Video says, use rudder to counter torque (pick up a wing) when at minimum air speeds. No one argues that. when at minimum airspeeds.

I think you have mischaracterized the video as saying to use the rudder to correct prop effects only at minimum airspeed. It does say prop effects are more significant at lower airspeeds, but that's not the same as saying the rudder is only use at minimum airspeeds. They say to use the rudder to correct torque roll effects.

Mike C.

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 Post subject: Re: Well the MU2 is a nice ride, especially the Crossno expr
PostPosted: 08 Jul 2018, 20:36 
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I will agree with one thing, Jim Bixby is right.... The EMB120 takes a lot of rudder trim fidleing when you change pitch or power. ( I liked that airplane ).

for the rest of this... :bang: :deadhorse: :btt:

Edit:
Quote:
The prop, when sitting still, does not create asymmetric thrust from P factor.
I have to give you that, it has to be moving, but not a whole lot.... :hide:

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 Post subject: Re: Well the MU2 is a nice ride, especially the Crossno expr
PostPosted: 09 Jul 2018, 11:18 
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Username Protected wrote:
Rudder and rudder trim is for movement about the vertical axis. Ailerons (or spoilers) is for movement about the longitudenal axis.

That's an idealism that doesn't work in practice.

Rudder trim is used to counter engine torque because it uses the entire wing to counter the torque, not just the aileron.

Watch the video again. Note the slide that says when increasing power causes a left roll, apply RUDDER. They wrote it in RED to emphasize it.
Attachment:
torque-slide-1.png

Quote:
Your P-51 example with the tail on the ground on the initial takeoff roll is P-factor - asymmetrical disc loading.

There is no P factor if there is no airspeed. It takes appreciable airspeed before P factor becomes a factor. You need rudder well before that.

Quote:
As was stated, when the tail is raised it's gyroscopic precession.

Gyro precess is tiny due to very little attitude change and smooth changing of attitude.

Mike C.


So in the diagram advocating rudder to counter torque roll, the torque is present as long as the flight is at minimum controllable airspeed, power on, but they advocate right rudder to counter, which means they are speeding up the left wing by yawing it to create more lift, which means to maintain that the plane would be in a constant skidding turn. Now stall it and over you go into a spin.

You say there is no P factor if there is no airspeed. Untrue; think relative wind, in other words when the prop is spinning with the tail wheel on the ground but the plane not moving, the down swinging blade has a higher angle of attack than the up swinging blade, and therefore creating asymmetrical thrust without aircraft movement, i.e. "airspeed." Spiral effect on the rudder is also present as part of the P factor.

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 Post subject: Re: Well the MU2 is a nice ride, especially the Crossno expr
PostPosted: 09 Jul 2018, 11:25 
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Username Protected wrote:
Obviously your definition of "P factor" is only known to you. For the rest of us, speed is not necessary for the down swinging blade to exert a left turn in a tail wheel airplane.

P factor is caused by the airspeed not being aligned with the prop rotational axis.

No airspeed, no misalignment.

Not clear what you think P factor is if you think it exists with no airspeed.

Quote:

P-Factor
...
This occurs only when the propeller is not meeting the oncoming airflow head-on


No airflow, no P factor.

Mike C.



airflow - relative wind. The prop blades are moving through the air as the prop turns with the plane stationary; relative wind, not aircraft airspeed. Just like a wing moves through still air.

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 Post subject: Re: Well the MU2 is a nice ride, especially the Crossno expr
PostPosted: 09 Jul 2018, 14:52 
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Username Protected wrote:
airflow - relative wind. The prop blades are moving through the air as the prop turns with the plane stationary; relative wind, not aircraft airspeed. Just like a wing moves through still air.

No aircraft movement and there is no difference in relative wind between either side of the prop. It’s a circle - things are pretty even across it. Up vs down is irrelevant.

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