Correct me if I'm wrong: Torque Roll
09-13-2011, 09:39 PM
#1
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Correct me if I'm wrong: Torque Roll
I think I've messed something up here. Correct me if I'm wrong.
I recently modded my UMX J-3 Cub with a UMX Mustang motor. (I was sick of breaking prop shafts and this is a common mod.)
Most people use a Mustang prop, but I went with a 3-bladed Corsair prop mainly to avoid the prop clearance issues that come with the big ol' Mustang prop. Others have posted that they run the Corsair props.
But ... the prop spins clockwise when viewed from the front. This means - doesn't it? - that the plane will want to respond by rolling to the right.
However, the motor is mounted so that it is angled to the right (and down). In my case, though, this is exacerbating, rather than compensating for, the torque roll. Am I right?
Cuz this thing is a pill. It really, really, really wants to roll hard to the right on launch/take-off.
I want to check my thinking before I cut a bunch of foam out of the motor mount area and screw the plane up forever.
I recently modded my UMX J-3 Cub with a UMX Mustang motor. (I was sick of breaking prop shafts and this is a common mod.)
Most people use a Mustang prop, but I went with a 3-bladed Corsair prop mainly to avoid the prop clearance issues that come with the big ol' Mustang prop. Others have posted that they run the Corsair props.
But ... the prop spins clockwise when viewed from the front. This means - doesn't it? - that the plane will want to respond by rolling to the right.
However, the motor is mounted so that it is angled to the right (and down). In my case, though, this is exacerbating, rather than compensating for, the torque roll. Am I right?
Cuz this thing is a pill. It really, really, really wants to roll hard to the right on launch/take-off.
I want to check my thinking before I cut a bunch of foam out of the motor mount area and screw the plane up forever.
09-13-2011, 09:42 PM
#2
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If the prop spins clockwise when viewed from the front (i.e. opposite to normal convention) then yes, you are going to have to set left thrust instead of the more normal right thrust.
downthrust will remain down though
Steve
downthrust will remain down though
Steve
09-13-2011, 09:45 PM
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That's what it seemed like to me. Didn't think about it much until the plane wouldn't fly.
Does this mean that the Corsair prop is built to spin 'backwards?' I can't have it mounted wrong; it screws on.
Does this mean that the Corsair prop is built to spin 'backwards?' I can't have it mounted wrong; it screws on.
09-13-2011, 09:50 PM
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I dont have a Corsair but according to the photos on this page: http://www.parkzone.com/Products/Def...rodID=PKZU1680 it has a conventional prop that spins anti-clockwise when viewed from the front.
Are you 100% sure that you haven't got the direction that the prop is actually turning in wrong?
Are you 100% sure that you haven't got the direction that the prop is actually turning in wrong?
09-13-2011, 10:12 PM
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Well ... not 100% I guess. I'm looking at it now, and it looks like I *could* screw it on from the other end.
But I've mounted it so that the numbers are in the front. That's how I always mount my props and how I've understood they are always designed to go (unless you're putting them on a pusher.)
But I've mounted it so that the numbers are in the front. That's how I always mount my props and how I've understood they are always designed to go (unless you're putting them on a pusher.)
09-13-2011, 10:20 PM
#6
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That does appear to be a reverse rotation prop.. Strange how the photo on the Parkzone web site shows a standard prop?.. we are talking the same plane here aren't we?
Even if you did mount it reverse (which you haven't) the rotation direction would remain the same for forward thrust.
Even if you did mount it reverse (which you haven't) the rotation direction would remain the same for forward thrust.
09-13-2011, 10:23 PM
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You didn't by any chance get that prop off the starboard engine of a PZ Mosquito did you
Looking at the PZ web site that's the only place they use a reverse rotation prop, and it's a three blader, and it looks just like yours.
Looking at the PZ web site that's the only place they use a reverse rotation prop, and it's a three blader, and it looks just like yours.
09-14-2011, 08:37 AM
#9
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Looks like a reverse prop to me as well. I have used them with no issues but my motor mounts have always been straight so had no issues. Your motor mount is angled to reduce the affect of torque roll with a normal prop. So yes you are compounding the problem. Just buy another $5 prop to fix all issues.
09-26-2011, 07:50 PM
#13
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And a bit of advice, couple actually. Don't always believe the rule of thumb.
Not all props have the numbers on the front. The one used on the Parkzone Corsair, the park size, not the micro, is one that can bite you. Properly installed the numbers are on the back of the blade.
Ask me how I know.
#2 don't confuse torque roll with P factor.
Prop P factor is the forces (on a normal rotation prop) that makes the prop pull to the left and up. That's what your down and right angles on the motor are used to compensate for.
Torque is the force used to turn the prop, bigger the prop, the more torque it takes to turn it. And in turn, the more the airframe has to counter it.
You'll see torque roll as a type of condition, where the torque of spinning the prop is used/fought to make the plane roll on the prop axis. Do a roll to the right and it's easier as the torque is helping roll the plane over. Try it going left and you have to over come the torque to roll.
Prop P factor (again normal set up)is always trying to pull the nose up and to the left.
Torque is trying to twist the airframe to the right/clockwise, when viewed from the rear.
Not all props have the numbers on the front. The one used on the Parkzone Corsair, the park size, not the micro, is one that can bite you. Properly installed the numbers are on the back of the blade.
Ask me how I know.
#2 don't confuse torque roll with P factor.
Prop P factor is the forces (on a normal rotation prop) that makes the prop pull to the left and up. That's what your down and right angles on the motor are used to compensate for.
Torque is the force used to turn the prop, bigger the prop, the more torque it takes to turn it. And in turn, the more the airframe has to counter it.
You'll see torque roll as a type of condition, where the torque of spinning the prop is used/fought to make the plane roll on the prop axis. Do a roll to the right and it's easier as the torque is helping roll the plane over. Try it going left and you have to over come the torque to roll.
Prop P factor (again normal set up)is always trying to pull the nose up and to the left.
Torque is trying to twist the airframe to the right/clockwise, when viewed from the rear.
09-26-2011, 08:36 PM
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If we are getting technical then it's not actually P-factor that's responsible for most of the yaw experienced due to the prop rotation. P-factor is not a cause at all of nose up pitching, that's a different issue altogether and related to stability, trim and other factors.
Most of the left yaw you might experience and the main reason for right thrust is helical prop wash creating a sidewaws force on the vertical stabiliser. P-factor is only an issue where there is a large difference between the line of the prop axis and the direction of travel, like in high alpha flight or on a taildragger during the take off run. In normal level flight P-factor isn't an issue.
From Wiki:
Most of the left yaw you might experience and the main reason for right thrust is helical prop wash creating a sidewaws force on the vertical stabiliser. P-factor is only an issue where there is a large difference between the line of the prop axis and the direction of travel, like in high alpha flight or on a taildragger during the take off run. In normal level flight P-factor isn't an issue.
From Wiki:
This is an attempt to answer the frequent question "Why is my airctaft turning left all the time?".
This occurs only in aircraft with propellers at the front of the aircraft. And yes, it does occur in real life. Four distinct phenomena cause the effect, all causing the aircraft to turn in the same direction. They are:
Prop wash
A propeller pushes air not just horizontally to the back, but more in a twisting helix around the fuselage (clockwise as seen from the cockpit). As the air whirls around the fuselage it pushes against the left side of the vertical tail (assuming it is located above the propeller's axis), causing the plane to yaw to the left. The prop wash effect is at its greatest when the airflow is flowing more around the fuselage than along it, i.e., at high power and low airspeed, which is the situation when starting the takeoff run.
Propeller torque effect
Torque effect is the influence of engine torque on aircraft movement and control. It is generally exhibited as a left turning tendency in piston single engine propeller driven aircraft.
According to Newton's law, "for every action there is an equal and opposite reaction," such that the propeller, if turning clockwise (when viewed from the cockpit), imparts a tendency for the aircraft to rotate counterclockwise. Since most single engine aircraft have propellers rotating clockwise, they rotate to the left, pushing the left wing down.
Typically, the pilot is expected to counter this force through the control inputs. To counter the aircraft roll left, the pilot applies right aileron.
It is important to understand that torque is a movement about the roll axis. Aileron controls roll. Prop torque is not countered by moving the rudder or by setting rudder trim. It is countered by moving or trimming the aileron.
This correction induces adverse yaw, which is corrected by moving or trimming the rudder (right rudder).
On aircraft with contrarotating propellers (propellers that rotate in opposite directions) the torque from the two propellers cancel each other out, so that no compensation is needed.
Further Reading: Propeller Torque Factor
P-Factor
P-factor is the term for asymmetric propeller loading, causes the airplane to yaw to the left when at high angles of attack.
The descending right side of the propeller (as seen from the rear) has a higher angle of attack than the upward-moving blade on the left side and provides more thrust. This occurs only when the propeller is not meeting the oncoming airflow head-on, for example when an aircraft is moving down the runway at a nose-high attitude (i.e. at a high angle of attack), as is the case with tail-draggers. Aircraft with tricycle landing gear maintain a level attitude on the takeoff roll run, so there is little P-factor during takeoff roll until lift off. In all cases, though, the effect is weaker than prop wash.
According to What You Need to Know About Aerodyanics... by Franklin Gutierrez.
Gyroscopic Precession
This is the tendency of a spinning object to precess or move about its axis when disturbed by a force. The engine and propeller act as a big gyroscope. However, gyroscopic precession is likely to be minimal in a typical aircraft.
Gyroscopic precession is frequently confused with p-factor.
This occurs only in aircraft with propellers at the front of the aircraft. And yes, it does occur in real life. Four distinct phenomena cause the effect, all causing the aircraft to turn in the same direction. They are:
Prop wash
A propeller pushes air not just horizontally to the back, but more in a twisting helix around the fuselage (clockwise as seen from the cockpit). As the air whirls around the fuselage it pushes against the left side of the vertical tail (assuming it is located above the propeller's axis), causing the plane to yaw to the left. The prop wash effect is at its greatest when the airflow is flowing more around the fuselage than along it, i.e., at high power and low airspeed, which is the situation when starting the takeoff run.
Propeller torque effect
Torque effect is the influence of engine torque on aircraft movement and control. It is generally exhibited as a left turning tendency in piston single engine propeller driven aircraft.
According to Newton's law, "for every action there is an equal and opposite reaction," such that the propeller, if turning clockwise (when viewed from the cockpit), imparts a tendency for the aircraft to rotate counterclockwise. Since most single engine aircraft have propellers rotating clockwise, they rotate to the left, pushing the left wing down.
Typically, the pilot is expected to counter this force through the control inputs. To counter the aircraft roll left, the pilot applies right aileron.
It is important to understand that torque is a movement about the roll axis. Aileron controls roll. Prop torque is not countered by moving the rudder or by setting rudder trim. It is countered by moving or trimming the aileron.
This correction induces adverse yaw, which is corrected by moving or trimming the rudder (right rudder).
On aircraft with contrarotating propellers (propellers that rotate in opposite directions) the torque from the two propellers cancel each other out, so that no compensation is needed.
Further Reading: Propeller Torque Factor
P-Factor
P-factor is the term for asymmetric propeller loading, causes the airplane to yaw to the left when at high angles of attack.
The descending right side of the propeller (as seen from the rear) has a higher angle of attack than the upward-moving blade on the left side and provides more thrust. This occurs only when the propeller is not meeting the oncoming airflow head-on, for example when an aircraft is moving down the runway at a nose-high attitude (i.e. at a high angle of attack), as is the case with tail-draggers. Aircraft with tricycle landing gear maintain a level attitude on the takeoff roll run, so there is little P-factor during takeoff roll until lift off. In all cases, though, the effect is weaker than prop wash.
According to What You Need to Know About Aerodyanics... by Franklin Gutierrez.
Gyroscopic Precession
This is the tendency of a spinning object to precess or move about its axis when disturbed by a force. The engine and propeller act as a big gyroscope. However, gyroscopic precession is likely to be minimal in a typical aircraft.
Gyroscopic precession is frequently confused with p-factor.
