My plane does a roll to the right but not to the left, why?
07-08-2003, 08:27 PM
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My plane does a roll to the right but not to the left, why?
The plane is a Great Planes CAP232. When I´m flying straight I do a roll to the right and it rolls perfectly using the fuselage as the center of the roll, but when I do a roll to the left, it rolls in a corkscrew kind of way... not using the fuselage as the center of the roll- I suspect that this problem has to do with the throws of the ailerons but I´m not sure. Any ideas?- I´ve read that scale planes should use less down throw than up throw in the ailerons for perfect rolls-
07-08-2003, 09:07 PM
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My plane does a roll to the right but not to the left, why?
One of the ways I trim rudder is to do left and right rolls. If one is slow and not axial, trim the rudder that direction.
Try adding a bit of left trim. Also pull verical with no rudder to see wich way it pulls.
Also try veritcal and kill throttle. See if it yaws. If vertical changes with power you may need to change engine thust. Otherwise you may be able to adjust with rudder trim.
You'll be suprised how a little rudder trim will effect rolls.
IF a bunch of rudder trim is needed, you have something crooked.
Try adding a bit of left trim. Also pull verical with no rudder to see wich way it pulls.
Also try veritcal and kill throttle. See if it yaws. If vertical changes with power you may need to change engine thust. Otherwise you may be able to adjust with rudder trim.
You'll be suprised how a little rudder trim will effect rolls.
IF a bunch of rudder trim is needed, you have something crooked.
07-09-2003, 12:38 AM
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My plane does a roll to the right but not to the left, why?
I am going to make a dumb statement.
Are you sure that you are not imparting a little aileron movement when you roll left compared to rolling right.
Are you sure that you are not imparting a little aileron movement when you roll left compared to rolling right.
07-09-2003, 09:43 AM
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My plane does a roll to the right but not to the left, why?
One word: torque.
The engine torque pulls the plane over to the right with no problem but fights the roll to the left.
The engine torque pulls the plane over to the right with no problem but fights the roll to the left.
07-09-2003, 01:10 PM
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My plane does a roll to the right but not to the left, why?
I dunno. I am quite familiar with the theory, have read about flight characteristics of WW1 fighters w/ rotaries, etc, but here's more food for thought. My gws cub slowflyer does beautifully quick snap rolls to the right, but just sorta mushes and stall turns to the left on full deflection. All of this is with the plane set up to fly hands-off dead ahead and level at 2/3 throttle. Of course this plane is vastly different from a cap 232 (understatement of the year 
)
)
07-09-2003, 02:36 PM
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My plane does a roll to the right but not to the left, why?
The wing is definetly not twisted. Could be the rudder, I'll check that this weekend when I fly.
I still think it could be a throw problem, one aileron having more throw that the other... I bought a device called accu-throw from great plane to measure the throw of the ailerons to make sure they both have the same amount of throw.
The plane is balance in both ways... no problems there.
I'm doing both rolls, left and right, with the same amount of stick movement.
I still think it could be a throw problem, one aileron having more throw that the other... I bought a device called accu-throw from great plane to measure the throw of the ailerons to make sure they both have the same amount of throw.
The plane is balance in both ways... no problems there.
I'm doing both rolls, left and right, with the same amount of stick movement.
07-09-2003, 03:38 PM
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My plane does a roll to the right but not to the left, why?
Originally posted by DBCherry
I think you got it backwards. Torque tends to pull left, not right. (If it pulled right, we'd be adding "left" when mounting our engines.)
I think you got it backwards. Torque tends to pull left, not right. (If it pulled right, we'd be adding "left" when mounting our engines.)
Besides, the reason the plane pulls to the left on the ground is because of asymetric thrust and somewhat of torque. Due to the angle of attack of the prop. and the thrust from the prop doesn't flow straight back but rather in a spiral. It hits the left side of the tail and forces over. Also, because the prop's AOA affects its thrust pattern. On take off (typically) the right side produces more thrust because as the blades go down they "pull" more air. Read the book "Stick and Rudder". It's a great book.
07-09-2003, 03:45 PM
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My plane does a roll to the right but not to the left, why?
Well, the engines in our planes turn clockwise (from the pilot's perspective). Now picture the prop held still, the plane would spin counter clockwise, which is why I'm assuming torque would assist in a left roll, but.... ??
Well wait. I just re-thought this. The plane WOULD try to follow the spinning prop, so unless there's something (ailerons) holding it back, it would.
So, mea culpa, I believe you ARE correct. Torque. :stupid:
Dennis-
Well wait. I just re-thought this. The plane WOULD try to follow the spinning prop, so unless there's something (ailerons) holding it back, it would.
So, mea culpa, I believe you ARE correct. Torque. :stupid:
Dennis-
07-09-2003, 03:56 PM
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My plane does a roll to the right but not to the left, why?
read the book "Stick and Rudder". It explains it a lot better than I do.
The increased roll rate to the right is caused somewhat by torque but mostly by the asymmetric thrust of the prop. The thrust coming off the prop does not flow straight back but rather spirals back. Since that's true, it's essentially "packing" air under the left wing and pushing down on the right wing.
Ok. I change my original post:
Three words: torque and asymmetric thrust.
The increased roll rate to the right is caused somewhat by torque but mostly by the asymmetric thrust of the prop. The thrust coming off the prop does not flow straight back but rather spirals back. Since that's true, it's essentially "packing" air under the left wing and pushing down on the right wing.
Ok. I change my original post:
Three words: torque and asymmetric thrust.
07-09-2003, 04:04 PM
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My plane does a roll to the right but not to the left, why?
The right roll in my experience is always faster due to torque. I think it's probley aileron difference and possibly combined with wind direction.
No one has mentioned this but if you roll into the wind it will be faster rotation than with a tail wind. You may want to think about that before adjusting surfaces etc.
No one has mentioned this but if you roll into the wind it will be faster rotation than with a tail wind. You may want to think about that before adjusting surfaces etc.
07-09-2003, 10:58 PM
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My plane does a roll to the right but not to the left, why?
Gian:
What you mentioned in your first post about one aileron moving more in one direction is referred to as aileron differential. The downward travel of the ailerons is set to move less than the upward travel. This is because there is drag associated with generating lift. It is called induced drag. The downward travel of the aileron changed the angle of attack for that wing, which causes that wing to generate more lift. The reverse is true for the upward traveling aileron. What happens is that you get a drag differential that causes a yaw in the opposite direction to roll, often called adverse yaw. HOWEVER, if your plane is setup well (i.e. up/down aileron travel is equal, straight wing, etc.) this effect typically only seen on non-aerobatic planes with flat bottom airfoils. While technically this happens on aerobatic plane, the effect is so small it rarely need correcting. I seriously doubt this is your problem on the CAP.
What I would verify first is that you are not pushing/pulling a little elevator when you roll. This will cause the corkscrew. If this is not the case, I'd agree that you got something out of wack.
Check your ailerons carefully. Note first if each line up the same with the wing when at neutral. If they are not the same, you have trimmed out something you need to fix. Look for a wing warp or crooked rudder/fin or even the stab/elevator. Also verify that movement of both ailerons is identical. Make the up travel equal the down travel.
Check your stab carefully. It should be perfectly in line with the wing. A crooked stab usually shows problems in loops but it can effect rolls too. Verify both elevator halves have the same movement and sit at the same location at neutral.
Check the rudder close. Site plane from behind. The rudder should be perpendicular to the wing and stab and it should be lined up with the nose of the plane.
I'm pretty sure one of the above will solve you problem, but if all else fails, you might be getting a funny with propwash. Try a different prop or even roll at idle to see if the problem changes.
Torque: Assuming you are using a standard engine, torque causes a LEFT roll, thus the need to offset the left roll with right thrust. The plane rolls OPPOSITE to the propeller rotation. Torque rolls are always to the LEFT. Planes roll quicker to the left and snap more violently to the left. However, torque does not cause non-axial rolls. There is NO way the above posted problem is due to torque.
RCAeroguy: The P-Factor on takeoff really only effects takeoff and would not effect the roll issue that started this post. The effect is very small in models and is really only seen on 1/4 scale and larger.
Rudder Trim: Don't set rudder trim on uplines. I suppose it is possible, but technically difficult because of right thrust issues. To hold the upline, you'll have to add rudder, when you throttle back, you'll need to release rudder to maintain the straight upline and then try to estimate if your rudder is off. Too many rudder movements, you'll never see if your rudder is off. It is much easier to set rudder trim on downlines. Fly high, throttle back. At idle point the plane straight down. Plane should track straight down. If you see a yaw, your rudder is probably off. This is also a good incidence/CG check. Rudder trim and right thrust are kinda a catch 22 as they are interrelated and right thrust depends upon speed and power output. In other words, right thrust is always a compromise and can only be set perfectly for one particular speed and throttle setting.
Lateral balance rarely effect flight unless you are WAY off. It really only effects elevator, such as high G corners in a square loop.
What you mentioned in your first post about one aileron moving more in one direction is referred to as aileron differential. The downward travel of the ailerons is set to move less than the upward travel. This is because there is drag associated with generating lift. It is called induced drag. The downward travel of the aileron changed the angle of attack for that wing, which causes that wing to generate more lift. The reverse is true for the upward traveling aileron. What happens is that you get a drag differential that causes a yaw in the opposite direction to roll, often called adverse yaw. HOWEVER, if your plane is setup well (i.e. up/down aileron travel is equal, straight wing, etc.) this effect typically only seen on non-aerobatic planes with flat bottom airfoils. While technically this happens on aerobatic plane, the effect is so small it rarely need correcting. I seriously doubt this is your problem on the CAP.
What I would verify first is that you are not pushing/pulling a little elevator when you roll. This will cause the corkscrew. If this is not the case, I'd agree that you got something out of wack.
Check your ailerons carefully. Note first if each line up the same with the wing when at neutral. If they are not the same, you have trimmed out something you need to fix. Look for a wing warp or crooked rudder/fin or even the stab/elevator. Also verify that movement of both ailerons is identical. Make the up travel equal the down travel.
Check your stab carefully. It should be perfectly in line with the wing. A crooked stab usually shows problems in loops but it can effect rolls too. Verify both elevator halves have the same movement and sit at the same location at neutral.
Check the rudder close. Site plane from behind. The rudder should be perpendicular to the wing and stab and it should be lined up with the nose of the plane.
I'm pretty sure one of the above will solve you problem, but if all else fails, you might be getting a funny with propwash. Try a different prop or even roll at idle to see if the problem changes.
Torque: Assuming you are using a standard engine, torque causes a LEFT roll, thus the need to offset the left roll with right thrust. The plane rolls OPPOSITE to the propeller rotation. Torque rolls are always to the LEFT. Planes roll quicker to the left and snap more violently to the left. However, torque does not cause non-axial rolls. There is NO way the above posted problem is due to torque.
RCAeroguy: The P-Factor on takeoff really only effects takeoff and would not effect the roll issue that started this post. The effect is very small in models and is really only seen on 1/4 scale and larger.
Rudder Trim: Don't set rudder trim on uplines. I suppose it is possible, but technically difficult because of right thrust issues. To hold the upline, you'll have to add rudder, when you throttle back, you'll need to release rudder to maintain the straight upline and then try to estimate if your rudder is off. Too many rudder movements, you'll never see if your rudder is off. It is much easier to set rudder trim on downlines. Fly high, throttle back. At idle point the plane straight down. Plane should track straight down. If you see a yaw, your rudder is probably off. This is also a good incidence/CG check. Rudder trim and right thrust are kinda a catch 22 as they are interrelated and right thrust depends upon speed and power output. In other words, right thrust is always a compromise and can only be set perfectly for one particular speed and throttle setting.
Lateral balance rarely effect flight unless you are WAY off. It really only effects elevator, such as high G corners in a square loop.
07-09-2003, 11:54 PM
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My plane does a roll to the right but not to the left, why?
If you have dual servos (one on each side) have you checked servo travel in the radio? Some times their is a difference with travel when using a computer transmitter. Are they tied together with a y harness? Did you mix the servos in the transmitter?Their could be several possibilities to solving the problem.
