Van's Air Force
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bank when lowering flaperons
- Thread starter John Foy
- Start date
I have flown 5 different RV-12's and none of them have behaved this way.
That leads me to believe that it is possible to make adjustments to resolve it
That leads me to believe that it is possible to make adjustments to resolve it
I was unable to make it fly level by pinching until it starts to look ugly.
Added a little trim tab on one flaperon and its perfect around 100 knots and i can let go of the stick.
When i put flaps in the first detent or second it starts rolling and needs some stick correction, but its not annoying to me as it is not a lot.
I checked for any differences in angles and pivot points but cannot see any.
I would have thought it is pure related to engine torque.
Added a little trim tab on one flaperon and its perfect around 100 knots and i can let go of the stick.
When i put flaps in the first detent or second it starts rolling and needs some stick correction, but its not annoying to me as it is not a lot.
I checked for any differences in angles and pivot points but cannot see any.
I would have thought it is pure related to engine torque.
Effects of Controls
Ours roll too when flying "hands off" and selecting flap.
Only noticed when I was running through an "Effects of Control" lesson with my passenger prior to my instructor renewal.
In normal "hands on" flying the pilot simply corrects for it automatically.
John.
Ours roll too when flying "hands off" and selecting flap.
Only noticed when I was running through an "Effects of Control" lesson with my passenger prior to my instructor renewal.
In normal "hands on" flying the pilot simply corrects for it automatically.
John.
Last edited:
yankee-flyer
Well Known Member
143WM rolls, too
But it's more noticeable with one notch of flaps than with 2. It's not a big deal unless you let go of the stick. Now on takeoff with full power and one notch of flaps there's a lot of left stick needed, but that's to counteract the right rudder.
I'm betting that those of us with left roll with one notch of flaps at approach speed also have quite a bit of rudder trim tab-- I have almost 1 3/4 Avery tabs. Tabs move ruder to the right, airplane yaws, and rolls left. I'll have to see what happens at 65 knots without flaps next time I fly.
My semi-educated guess is that the whole roll/trim tab issue is a function of bot getting those &*^%&^$^$&^%&^ longerons bent just right and having the whole aft fuselage just a hair out of alignment.
Wayne 120241/143 WM
But it's more noticeable with one notch of flaps than with 2. It's not a big deal unless you let go of the stick. Now on takeoff with full power and one notch of flaps there's a lot of left stick needed, but that's to counteract the right rudder.
I'm betting that those of us with left roll with one notch of flaps at approach speed also have quite a bit of rudder trim tab-- I have almost 1 3/4 Avery tabs. Tabs move ruder to the right, airplane yaws, and rolls left. I'll have to see what happens at 65 knots without flaps next time I fly.
My semi-educated guess is that the whole roll/trim tab issue is a function of bot getting those &*^%&^$^$&^%&^ longerons bent just right and having the whole aft fuselage just a hair out of alignment.
Wayne 120241/143 WM
I used a tab for awhile until I got tired of looking at something I was told, I should not need. I tried and failed with numerous attempts at pinching the trailing edges of the flaperons, I started thinking about how we are to measure the rod end bearings and decided that I had not done this with any degree of precision. I had a very heavy right wing and through trial and error, found that by threading the bearing out 1/2 turn on the left wing (Light Wing) it was now perfect. I just considered that there are too many -12's flying straight and level for there to be no answer to the issue I had.
Another thing you can do is remove the bolt from the middle bearing and if the flaperon springs up or down, I believe it tells you if the flaperon is straight or bowed. I think this was also part of my problem.
Once you get this resolved, you will be amazed with how well and refined this airplane flies.
Another thing you can do is remove the bolt from the middle bearing and if the flaperon springs up or down, I believe it tells you if the flaperon is straight or bowed. I think this was also part of my problem.
Once you get this resolved, you will be amazed with how well and refined this airplane flies.
OK - here's a stab.
My airplane has not flown yet, so I cannot ascribe as to the in-flight characteristics. But, I did notice that when I lowered the flaps, the stick moved laterally. It did that very noticeably if I was not holding the stick. If I held the stick, it didn't do this. I noticed that I naturally resisted the movement - it only took very little force to do so, and was almost un-noticeable.
During my 2 - 4 AM serious think time I contemplated this. I recalled that it did not used to do this. I pondered what had changed. I finally figured out that I had installed the autopilot servos. After I hooked up the servo pushrods, there was a very noticeable change in the stick force in both axes. This stands to reason as the servos have a built in torque which can be readily observed by just moving the servo torque arms with your fingers while on the bench. (There's also a sound - ratcheting of the slip clutch, or some servo internal, I assume.)
When I was installing the roll servo and had the flaperon pushrods removed, the flaperon torque arms could be flopped up and down with little force. When I hooked up the RH pushrod to the torque tube, the resistance changed only a little. But, when I hooked up the LH pushrod WITH the roll servo pushrod hooked up, there was a significant change. With the pushrods disconnected at their forward ends, the RH moved easily, the LH required much more force due to rotating the autopilot servo.
So - with everything all hooked up, you can feel the added roll force in the whole system, although it is being generated only by the added servo torque connected to the LH flaperon.
NOW - you pull the flap handle to the first notch. Both push rods want to move in unison, but the LH rod has the added resistance generated by the roll servo and so the system becomes unbalanced. The RH rod moves more (a lot more) than the LH rod, the RH flaperon moves down and the stick moves to the left inducing a LH roll.
This is hands-off the stick. Try it. When you hold the stick - even very lightly - you both resist and inhibit this motion without noticing. John Stamper seems to have confirmed this theory in his comment.
Bob Bogash
N737G
Within days of flying
My airplane has not flown yet, so I cannot ascribe as to the in-flight characteristics. But, I did notice that when I lowered the flaps, the stick moved laterally. It did that very noticeably if I was not holding the stick. If I held the stick, it didn't do this. I noticed that I naturally resisted the movement - it only took very little force to do so, and was almost un-noticeable.
During my 2 - 4 AM serious think time I contemplated this. I recalled that it did not used to do this. I pondered what had changed. I finally figured out that I had installed the autopilot servos. After I hooked up the servo pushrods, there was a very noticeable change in the stick force in both axes. This stands to reason as the servos have a built in torque which can be readily observed by just moving the servo torque arms with your fingers while on the bench. (There's also a sound - ratcheting of the slip clutch, or some servo internal, I assume.)
When I was installing the roll servo and had the flaperon pushrods removed, the flaperon torque arms could be flopped up and down with little force. When I hooked up the RH pushrod to the torque tube, the resistance changed only a little. But, when I hooked up the LH pushrod WITH the roll servo pushrod hooked up, there was a significant change. With the pushrods disconnected at their forward ends, the RH moved easily, the LH required much more force due to rotating the autopilot servo.
So - with everything all hooked up, you can feel the added roll force in the whole system, although it is being generated only by the added servo torque connected to the LH flaperon.
NOW - you pull the flap handle to the first notch. Both push rods want to move in unison, but the LH rod has the added resistance generated by the roll servo and so the system becomes unbalanced. The RH rod moves more (a lot more) than the LH rod, the RH flaperon moves down and the stick moves to the left inducing a LH roll.
This is hands-off the stick. Try it. When you hold the stick - even very lightly - you both resist and inhibit this motion without noticing. John Stamper seems to have confirmed this theory in his comment.
Bob Bogash
N737G
Within days of flying
Good observation Bob, but I don't think it has anything to do with what is being described.
The aerodynamic feedback force from the flaperons, while that airplane is in flight, is far higher than the friction from the autopilot roll control servo. So actions that you see happen with the airplane sitting in the hangar, will be totally different when there is aerodynamic forces on the system.
I have flown RV-12's with, and without autopilots that did not have this characteristic. I am sure it is a rigging or construction issue.
A few comments....
Flaperon shape can have an effect on roll trim. The effect can be significant
if there is a large shape difference between the left and the right.
The aft skin portion of the flaperons should be totally flat cord wise, from the skin lap joint, all the way aft to where the trailing edge radius starts, when checked with a straight edge.
I have corrected roll trim problems on many RV's in one try, just by reshaping the flaperons or ailerons while checking for correct shape with a straight edge.
Once you have confirmed that the flaperon shape is correct. You should confirm that the flaperon vertical position is correct (rod end adjustment).
After confirming that, you should confirm that the flaperon rigging is correct. Flaps retracted and stick in neutral position, each flaperon should be drooped down between 1/16" and 1/8" relative to the wing tip (this is because with a slight amount of elasticity that exists in the control system, the flaperons deflect up about that amount in flight, as a result of aerodynamic loads).
Once all of the above has been confirmed, slightly adjusting the shape of the flaperon trailing edges is very effective in adjusting out minor amounts of roll imbalance.
BTW, I would expect that anyone that resorted to adding an external trim tab to a flaperon to adjust roll trim, would have a change in roll trim when they deploy the flaps. Every time they deploy the flaps, the trim tab angle changes relative to the airflow. It is no different than if someone were changing the bend angle on the tab, every time you moved the flap handle. A tab attached to the bottom of the flaperon and bent downward would be the worse case of this.
RFSchaller
Well Known Member
I put bendable trim tabs on the rudder and both flaperons to get rid of a slight roll and center the ball in cruise. I don't notice any obvious tendency to roll when I deploy flaps. If the effect is there it just be very subtle.
Scott, you can fly mine at OSH this year and you will see this phenomenon, if you're interested. Not really an issue, I have just always just corrected for it automatically I guess.
How to straighten flaperons.
@RVbuilder2002
Good point About the trimtab on the flaperons. Never thought about that.
Checked the flaperon straightness today and they are not very straight from the middle out towards the tip on the heavy wing holding the trimtab.
Its ok on the ribs but oil canning up to 1/8 or so in between.
Problem is how to get these out. When i pinch the trailing edge the bubble pops in but when i release it comes back.
Any other tricks ?
@RVbuilder2002
Good point About the trimtab on the flaperons. Never thought about that.
Checked the flaperon straightness today and they are not very straight from the middle out towards the tip on the heavy wing holding the trimtab.
Its ok on the ribs but oil canning up to 1/8 or so in between.
Problem is how to get these out. When i pinch the trailing edge the bubble pops in but when i release it comes back.
Any other tricks ?
I will try and post some info soon, describing how I do it. If you don't see it within the next week, PM me a reminder.
