Aileron Linkage

2006 Apr 2

Table of Contents:

Caution: Disconnect all linkages from the servos. Failure to do so will result in mechanical binding which can damage your servos.

Introduction:

This a Step by Step guide to setting up the Aileron Linkage. The steps are outlined in a chronological order. Use the Table of Contents to get a visual perspective of the setup.

The instruction manual on page 14 directs you to install a set of balls on the servo control horn; approximately 10.5mm from the center of the servo. This is the ideal setup for the beginner.

If using the Futaba predrilled servo control horn, select the second hole out from the center (10.5mm).

As your flying skills develop, you will begin to notice that the cyclic control / response rate is sluggish.

Repositioning the servo ball on the aileron control horn will change the angle of the linkage geometry. Therefore, you must redo the Linkage Rod Alignment and Servo Mechanical Binding Verification steps.

Servo & Swash Plate Direction Verification:

Note: Any servo that is reversed after completion of the linkage alignment will be off centered and will require a realignment. This is primarily due to the internal workings of the radio's software program when switched from normal to reverse or vice versa.

Turn on the radio transmitter and receiver. Extend the radio's antenna to dissipate the RF energy.

I would advise on disconnecting the aileron linkages from the servo to avoid mechanical binding when the transmitter stick is fully deflected.

Move the transmitter's right stick to the right and observe the aileron servo's control horn.

A right input stick command will yield a clockwise servo rotation as viewed from the top. See photo at left, right image.

If the linkages are connected, the swash plate should deflect towards the right side of the model as view from the tail towards the nose or, the side without the engine's muffler. See photo at left, left image.

Access the radio's servo reversing program menu and change the corresponding channel to reflect the correct stick input command as required.

Servo Control Horn Alignment:

Turn on the radio and receiver and verify the radio's programming menu parameters are as follows:

Aileron Front Panel Trims = CENTERED

Aileron Sub Trim Menu = 0%

Aileron End Points (ATVs) = 100% / 100%

Disconnect both aileron linkage rods from the aileron servo horn.

Note: When checking the servo control horn for perpendicularity, move the radio's aileron stick in either direction. This process will mechanically re-center the servo eliminating any mechanical hysteresis. For repeatable readings, perform this process each time when checking mechanical center.

Rotate the servo control horn on the servo output shaft's spline and select the BEST control horn that will be perpendicular to the collective pitch control arm.

Verify that the aileron control horns are perpendicular by using an "L" shape ruler or note card placed on the edge of the balls or aligned with the holes (see photo).

Adjust the Sub Trims in the radio's programming menu screen as necessary to obtain perpendicularity.

The use of excessive sub trims to establish perpendicularity will adversely affect the symmetry of the servo travel.

It would be recommended to use a blank servo wheel and custom drill the holes required using a servo wheel drill gage as a template.

If sub trim is needed, select the best control horn position that will yield the least amount of % sub trims required to obtain a perpendicular setup. The less the percentage, the better.

Move the radio's aileron stick in one direction then release. Verify that the servo's control horn remains perpendicular. Repeat this process in the opposite direction.

If hysteresis is present, error should be "equally" on both sides of center. If the error is "not equal", adjust the radio's sub trims.

Linkage Rod Alignment:

Refer to page 22 of the manual and verify that both aileron linkage rods connected to the servo control horn and the linkage rods connected from the swash plate to the aileron bell cranks are equal in length.

The length of the linkage rods connected to the servo control horn are not important as it will be adjusted accordingly due to the different servo dimensions per manufacturers. However, they must be equal in length.

I highly recommend purchasing a ball link duplicator.

If a ball link duplicator tool is used, use only "one set of balls" and the "same set" to obtain repeatable measurements. I have found variances in the distance between both sets of balls yielding unequal measurements.

Superimposed the linkage rod's ball link over the ball link duplicator. Do not snap the linkage rod's ball link on to the ball link duplicator as this will force the measurements.

Do not be alarm if a half turn of the ball link is needed to obtain an equal length. The manual shows that the TT Tiger name should face outwards for correct installation. I have had no issues with a ball link disconnecting in flight due to a ball link orientation.

Connect both linkage rods to the aileron bell cranks leaving the opposite end disconnected from the aileron servo's control horn.

Use a swash plate leveling tool and level the swash plate. It would be a good idea to review the information on the Swash Plate Level Tip page.

If you do not have a swash plate level tool, use two wooden blocks or similar material and of EQUAL dimensions placed above the upper frames, (see photo).

The size (length / width) of the wooden blocks are not important as long as you are able to insert it underneath the swash plate and and the upper frame. They must be equal in dimensions.

Apply a slight downward pressure on the swash plate to ensure that the swash plate remains level during adjustments of the aileron control surface.

With the radio on, superimpose both aileron linkage rods over the aileron servo balls and adjust both linkage rod's ball links in EQUAL amounts of turns so that the ball links are centered over the balls.

From experience, I have had no issues with a ball link coming out in flight as a result of the Thunder Tiger name facing in due to half turn adjustments. What is important is that both links are equal for a symmetrical setup.

If one of the linkage rod's ball link does not line up on the aileron servo's ball, recheck that both linkage rods connected from the swash plate to the aileron bell crank are equal in length and also both linkage rods connected to the aileron servo are equal in length.

If they are equal in length, recheck the Servo Control Horn Alignment for mechanical center.

If the servo control horn alignment verifies accordingly, check for servo backlash (mechanical slop / play). Compensate for this error by rocking the servo horn back and forth and adjust the linkage rod ball links equally so that they are centered on the aileron servo balls.

Remove the swash plate level tool.

Do not connect the aileron ball links to the aileron servo until mechanical binding verification is complete.

Servo Mechanical Binding Verification:

Depending on the placement of the ball on the servo control horn, binding may not be present. You must understand the Equal Throw Method as this is the basic key element on a symmetrical mechanical setup.

The objective of this setup, is to obtain an End Point value of +/- 10% with BOTH end point percent values EQUAL.

You may have to play with the aileron servo ball placement so that you find the BEST percent value closer to 100%.

Keep in mind that if you go further out on the servo horn, you gain mechanical speed and lose resolution and torque or, if you go closer in on the servo horn, you gain torque and resolution but lose mechanical speed. Refer to the Cyclic Rate Tip page.

Apply full aileron stick deflection with the transmitter and superimposed the linkage rod ball links over the servo balls.

It is important that at maximum aileron stick deflection, there are no mechanical binding.

The ball links should either be aligned on the center of the servo balls or extend beyond the servo balls for a no mechanical binding condition.

If this is not the case, and mechanical binding is present, move the balls on aileron servo horn closer to the center of the servo's rotational axis or adjust the radio's End Point value.

If the balls have been relocated from its initial alignment, you must repeat the Linkage Rod Alignment steps to ensure that the ball links are aligned with the servo horn balls at center.

Verify that there are no mechanical binding on both sides of full aileron stick deflection and at center position.

If one set of linkage rod ball link aligns on the center of one servo ball and the other set of ball link does not align on the center of the other servo ball, then the servo horn is not perpendicular to the collective pitch control arm, the radio sub trim value is too excessive, the aileron trim is not centered, or the linkages are not equal.

If all the above mentioned mechanical and electronic criteria's are met, then this is normal.

This out of alignment or unsymmetrical issue at full deflection, is caused by the interaction of a push pull configuration system having the servo control horn balls inline with the center of rotation.

To eliminate this interaction of the push pull system, the servo control horn balls must be offset 2- 3mm from the center of rotation, or reduce the radio's end point value until binding is eliminated.

Verify that the binding errors are equal in both directions at full aileron stick deflection. See also Equal Throw Method. If the errors are equal, adjust the radio's end points EQUALLY so that there are no binding in each direction at both full aileron stick deflection.

Connect the aileron linkage rod's ball links to the balls on the aileron servo horn.

NOTE: Binding of the collective pitch arm travel will be verified upon completion of both Aileron and Elevator control surfaces. Refer to Swash Plate Binding Verification.

Swash Plate Level Verification:

This step can ONLY be accomplished after completing the Elevator and Aileron Linkage Rods setup.

Disconnect the collective pitch linkage rod and reconnect the aileron and elevator linkage rods to their respective servo control horn's ball.

Turn on the radio transmitter and receiver. This is necessary to maintain a level swash plate.

Reinsert the swash plate leveling tool and ensure that the swash plate is resting on the leveling tool.

With the nose of the helicopter facing you, slightly raise the swash plate with the collective pitch arm so that a small gap can be visible between the bottom of the swash plate and the swash plate leveling tool.

Sight between the bottom of the swash plate and the top of the swash plate leveling tool.

There should be an "EVEN GAP" between the two surface if the swash plate is level. See photo at right.

If an out of level condition exists, raise the swash plate with the collective pitch arm just enough to clear the swash plate leveling tool.

Move the aileron stick on the transmitter and release. Gently lower the collective pitch arm and take note of the gap for an un level condition.

Raise the swash plate again and move aileron stick in the opposite direction. Gently lower the collective pitch arm and take note of the gap for an un level condition.

The swash plate should remain level in both directions or should have an equal amount of error (hysterisis) in both direction.

If this is not the case, then check for friction or play within the control surfaces by isolating the linkages from the swash plate to the head assembly and repeating the above.

Check all bell cranks for a smooth rotation. Friction can be eliminated using ball link resizer tool.

If the swash plate remains level or there are equal amounts of error (hysterisis) the Aileron Servo Setup is complete.

Aileron Control Lever:

(aka, aileron bell crank)

Let me just say that there are many ways to setup a helicopter. There is no such thing as a wrong way! What matters is that you understand the mechanics of your setup and you follow the guidance set forth that you are comfortable with.

If you follow the linkage dimension per the manual, you will note that the linkage rods connected from the swash plate to the aileron control lever, will not be at 90 degrees to the aileron control lever.

The aileron control lever is engineered for a 70 degrees angle and not 90 degrees and therefore angles slightly downward from the pivot point.

My current setup follows the linkage rod dimensions as stated in the instruction manual for a couple of reasons. To minimize the binding caused by the interaction of the linkages when configured as a push pull system, the angle of the linkage rods at the swash plate and aileron servo in relation to the bell crank.

I have also tried setting up the aileron control lever so that the linkage rods from the swash plate to the aileron control lever are at 90 degrees and found a higher degree of interaction at full swash plate mechanical deflection and at maximum servo travel.

You will also note that one set of linkage rod from the bell crank to the aileron servo horn will be aligned to the ball's center axis at full deflection and the other linkage rod will be significantly off centered.

This is the interaction of the push pull system as seen when the servo horn and the swash plate are at their full deflection.

I have found that this interaction is more noticeable when the linkage rods are set at 90 degrees to the aileron control lever then when set using the stated linkage dimension per the instruction manual.

Currently, I do not have a concrete knowledge as to why the aileron control lever was designed with a 70 degree angle verses a 90 degree angle.

However, I can assume that this 70 degree angle design of the aileron control lever may have been engineered for simplicity of the setup when using standard servo horns. Keep in mind that when using a standard servo horn for a push pull configuration, the balls will be mounted inline of the servo's center of rotation.

Also consider the angle of the linkage rod from the swash plate to the bell crank and the angle from linkage rod from the bell crank to the aileron servo.

In due time, and with your assistance, I will attempt explore this area mathematically.

End Results:

Sub Trims:

Least % value, preferably 0%.

End Points:

Both Sides Equal.

Avoid using excessive end point values if resolution is a factor.

Swash plate:

Level and 90 degrees to the main mast.

Tilts according to respective stick input command (left / right).

Linkages:

All linkage rod lengths are set per the manual's dimension except the linkages connected to servo horn.

Zero mechanical binding at full servo deflection.

Mechanical movement is friction free with linkage rod disconnected from servo and moved manually.

Paired linkages are Equal measurements (same length).

Fly Bar Paddles:

Level to the Datum Reference Line

References:

Hysteresis is a property of systems (usually physical systems) that do not instantly follow the forces applied to them, but react slowly, or do not return completely to their original state. http://en.wikipedia.org/wiki/hysteresis.

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