Trimming out your RV-10 for smooth flight

Getting Rid of a Heavy Wing
Proper Aileron Alignment
Watch for this Elevator Trim issue

This section will hopefully develop into a section on how to adjust your flaps and ailerons and things of that sort to get your plane to fly straight and true.

Getting Rid of a Heavy Wing
These posts were taken from the RV list by "LN", and Scott Bilinski...very good info:

I think you will find that the light wing has a larger gap between the aileron and upper wing skin, as compared to the other wing. Some people slot the holes and adjust the aileron so they are even. I know a guy who  did this and he only needed to move it about .032 and then it was on the money. Me personally, I would fill the slotted area with JB weld and then tighten the bolt.
This was the most effective method I found for my RV6. Purchase a new outboard aileron bracket and correct the probable assymetry between the left
and right side aileron. In my case, I had a right wing heavy condition due to a very small rise in the right outer aileron bracket position relative to wing rear spar mounting point. Sometimes you can't even see difference without laying a straight edge across it. In any case, you lower the bracket position slightly relative to the main wing rear spar mounting point to correct the heavy wing. In my case I was running 8 lbs heavy to the right side. 8 lbs of extra fuel in the left tank would balance the aircraft out.   The 8 lb condition was corrected by dropping the right aileron bracket by 1mm. It is strictly a trial and error method. Get 2 new outboard brackets.  Use the first as a test bed by elongating the holes and tweaking the positioning a mm at a time until the problem is nullified. Then measure the spec and drill the second bracket to meet that spec. Some guys just use the elongated hole method as a final fix, but I am too much of a purist for that.

A & P mechanics are taught that all control surfaces need to be balanced before painting and REBALANCED after painting on all certified aircraft.  The phenomena is just as appropriate on kit-built VAN’s products.  This “Just Build It… and don’t worry about it or ask why” needs some improvement.   The alternative is that some builders are going to have finished products with characteristics beyond the statistical mean which are going to skew the insurance claim data and result in the catastrophic rate increases seen with Lancair.

From: The Lancair Mailing List

Flutter is not simply caused by something being loose; that is a gross oversimplification.
Flutter is a complicated science and is sometimes confused with buffeting and vibration. Typically flutter is experienced at or near the Vne speed of the aircraft. It is generally known to happen very quickly and involves a catastrophic failure. But wait, there is more - a lot more; read on.


Flutter is a dangerous phenomenon encountered in flexible structures subjected to aerodynamic forces.

Flutter occurs as a result of interactions between aerodynamic, stiffness, and inertial forces on a structure. For an aircraft, flutter may occur when the aircraft is accelerated to a speed where, when disturbed, the wings flex, and the resultant vibrations do not have sufficient damping. The damping of an aircraft’s vibrations is a function of the speed at which it is flying.

Also at:

Flutter is the resonance of a structure that occurs when the elastic properties of the structure are in harmony with a load being applied. Although pilots normally think in terms of "aileron flutter", flutter can be experienced in the fuselage, stabilizer, rudder, wings, or even propellers.

There are several type of flutter modes that can occur. Most pilots think of aileron flutter as looking out and seeing their ailerons buzzing up and down.

Although an easy answer is "unbalanced control surfaces", you need to understand why. In an unbalanced control surface, there is a positive rotational moment of inertia. In other words, the CG of the surface is not at the hinge point. So if load the aircraft in G (or shake the wing up and down), the aileron will want to rotate up and down accordingly. In my case, the aileron vibration translated to wing vibration, which overloaded the wing attach fitting. Now typically the opposing ailerons will counterbalance this tendency. But importantly, all of the intervening pushrods, slave-struts, hinges, idlers, bellcranks, bolts and bearings add a degree of flexibility. And that's what causes problems.

The independent variables include control surface moment and balance characteristics, but they also include vibration sources (such as the rotating heavy thing up front), turbulence, air density, velocity, G-loading, CG, weight, shock wave formation, etc.


Flutter is the dynamic instability of an elastic body in an airstream. Flutter speed (Uf) and the corresponding frequency (vf) are defined as the lowest airspeed and frequency at which a flying structure will exhibit sustained, simple harmonic oscillations. Flutter is a dynamic instability (self-sustaining and increasing) that may result in failure of the structure. In aircraft, the failure of a main structure generally results in the loss of the aircraft. Aircraft are designed such that their airframe flutter will occur at airspeeds and conditions outside the aircraft envelope by a safety margin of at least 15 percent. Modifications that change the vibrational modes of an aircraft cause the flutter speed to change.

The frequency and airspeed at which flutter occurs generally increases with increased structural stiffness. However, many times increased stiffness in a structural component changes the vibrational frequencies of that component and result in changes of frequencies in the overall aircraft structures. These changes can cause unforeseen consequences such as vibration or flutter, and their effect must be evaluated by analyses or testing. Usually, a ground vibration test is made to determine changes in the vibrational modes of a modified airframe. These modes are used to validate or update the structural dynamic analysis model that determines the flutter speeds and frequencies.

Flutter, buffeting, and vibration can affect handling qualities. This is caused by the uncompensated motion of the flight control surfaces relative to the airflow. For instance, an elevator rotated upward is expected to cause an aircraft to climb. Deflection of the horizontal stabilizer caused by buffet, flutter, or vibration can result in the elevator providing a nose-down rotation. Asymmetric bending of the horizontal stabilizer from flutter, buffet, or vibration can cause a roll or yaw. In general, remedies for flutter, buffet, and vibration are also remedies for these types of handling problems. These are usually high-speed problems.


When aerodynamic forces applied to the wing or a control surface alter the aoa, the dynamic pressure distribution changes. These changes plus the structure's elastic reactions may combine as an oscillation or vibration (probably initially noticed as a buzz in the airframe) which will either damp itself or, as the airspeed is increased, may begin to resonate at the natural frequency of the structure and thus rapidly increase in amplitude if the phase relationships are right. (Pushing a child on a swing is an example of phase relationships and amplification). This latter condition is flutter and, unless airspeed is very quickly reduced, will cause control surface separation within a very few seconds.

Inertia has a role in flutter development requiring that control surfaces – ailerons, elevators, rudder – be mass balanced (i.e. the centre of gravity of the control surface coincides with the hinge line) to limit the mass moment of inertia; and also to prevent them becoming heavier as airspeed increases. It may be acceptable for the control surface to be over-balanced, i.e. the cg is slightly forward of the hinge line.

The critical flutter airspeed [or something akin to it] may eventuate well below Vd or Vdf (See Note at bottom) if wear in control surface hinges, slop in actuating rods/cables/cranks/torque tubes, water or ice inside control surfaces or absorbed within a foam core, mud outside, faulty trim tabs or other system weaknesses exist which alter the structure's reaction.

The following paragraph is an extract from an article by William P. Rodden appearing in the McGraw-Hill Dictionary of Science and Technology; it provides a succinct description of flutter:

"Flutter (aeronautics) – An aeroelastic self-excited vibration with a sustained or divergent amplitude, which occurs when a structure is placed in a flow of sufficiently high velocity. Flutter is an instability that can be extremely violent. At low speeds, in the presence of an airstream, the vibration modes of an aircraft are stable; that is, if the aircraft is disturbed, the ensuing motion will be damped. At higher speeds, the effect of the airstream is to couple two or more vibration modes such that the vibrating structure will extract energy from the airstream. The coupled vibration modes will remain stable as long as the extracted energy is dissipated by the internal damping or friction of the structure. However a critical speed is reached when the extracted energy equals the amount of energy that the structure is capable of dissipating, and a neutrally stable vibration will persist. This is called the flutter speed. At a higher speed, the vibration amplitude will diverge, and a structural failure will result."

NOTE: Flight at airspeeds outside the envelope (or at inappropriate speeds in turbulent conditions or when applying inappropriate control loads in a high-speed descent or, indeed, at any time) is risky and can lead to airframe failure. Vne is the IAS which should never be intentionally exceeded in a descent or other manoeuvre and is normally set at 90% of Vd, the 'design diving speed'. For a normal category aircraft, Vd is required to be 1.4 times Vno and, to receive certification, it must be demonstrated, possibly by analytical methods, that the propeller, engine, engine mount, and airframe will be free from overspeeding, severe vibration, buffeting, flutter, control reversal and divergence. To provide some safety margin, Vne is then set at 90% of the lower of Vd or Vdf. Vdf is a diving speed which has been demonstrated without problem in test flights and which must be lower than, or equal to, Vd.

I hope this has been a help.
Warm regards,
FXE (Fort Lauderdale Executive)

Proper Aileron Alignment

More than one case of ailerons hanging low has been documented on the RV-10.  Ideally, you want the flaps full-up, and align the ailerons to them and have the wingtips aligned with them too, all at the same time.

The tip that I found was that you need to perform the alignment of the ailerons with the elevator completely neutral.  I originally did my alignment with the stick secured, however if you have up-elevator applied your ailerons will both rise slightly and cause them to be low while in-flight.  Aligning them with a perfectly neutral stick will fix this issue.

Watch for this Elevator Trim Issue!

Here is a link to the original post:

Read through the information below, but let me tell you my opinion on it first...
Basically the gist of the issue is that you need to ensure that both sides of the trim tabs go to the neutral, trailing position, at the same time, and that no matter what you do, will you end up with a situation where one trim tab goes up while the other goes down.  It's that simple.  So have someone actuate the trim while you watch...if you have a position where one tab is up and the other is down, fix it.  In normal operation, the trim tabs do NOT move exactly the same.  If memory serves correctly, they both go down together, but as they pass through neutral towards up, only one continues upwards.  There is a small period of time though where the cam action of the actuator may briefly make one side move a small amount down as it's on it's way upward.  At any rate, just inspect your trim and ensure that never is there a time when the trim tabs are opposite eachother.  If you achieve that, you should be set, as long as you're getting somewhere near the listed travel requiremements.  I haven't personally verified Bill's measurements below but I'm sure they're at least close.

Bill's Post
I went through this issue with Vans couple of months ago hoping for a plans revision or service bulletin but those folks seem to be busy in other areas - but I believe it to be important and want to share my findings.

I setup my elevator tabs per the instructions with both left and right 35 degrees below trail position when the servo is at the full up position. It is possible to meet this spec by making adjustments at the servo end of the cable.

During my first cross country I happened to look back at the tail and saw it was twisted. The elevator counter weight was above the horizontal stablizer on one side and below on the other. This bothered me more than a little as the forces would need to be high to cause this twist. I had not noticed this during my test flights because I now had luggage in the back and needed more down trim. After a lot of measurements I determined that the problem was I followed the instructions. If you begin with both elevator trim surfaces down at exactly 35 degrees the port side will never rise to trail position do to the cam action of the two actuators. Yet, the starboard will rise .75 inch above trail causing the twist.

At a minimum effort, all flying RV-10s should check for this condition. The fix is easy.

Highly recommend that you set the trim as follows:
1. Run the trim servo to full nose up.
2. Set the starboard trim tab trailing edge to 3 inches below elevator trailing edge.
3. Run the starboard trim tab to trail.
4. Set the port trim tab to trail.

Using these settings you will be able to trim out all pitch forces during final with the CG forward.

Bill DeRouchey
N939SB, flying straight