Difference between revisions of "Unequal Collective Pitch"

Revision as of 09:37, 9 April 2018

If you are struggling with achieving equal Collective Pitch range for positive and negative side, then the following procedure is for you. If you have hard times to achieve perfect zero degrees between main blades or there is a Geometry 6° imprecision, we recommend to follow the guide.

1 Transmitter

First it is important if your transmitter was configured correctly in terms of channel travel range. It can be verified in the following way. Start the Spirit Settings and go to the Diagnostic tab.

1.1 Collective Centering

1. Put your Pitch stick at the center as close as possible.
2. Verify what value you can see in the Diagnostic tab at the Pitch bar.
3. Make sure you will see 0%. If value is different by more than +/- 2% it is recommended to use the Subtrim function in your transmitter and adjust Pitch channel to achieve 0%.

1.2 Collective Pitch Low and High position

1. Make sure that your Collective Pitch curve in the radio is configured to be -100% to 100% (Linear curve). NOTE: In some radios the lowest position starts at 0% but this is not a problem.
2. Put your Pitch stick at the lowest position - at this point you have to see -100% in the Diagnostic tab at the Pitch bar. If value is diffrent by more than +/- 2% it is recommended to use the Travel Adjust for Pitch channel in your radio.
3. Do the same verification for the highest position - at this point you have to see 100% at the Pitch bar.
4. If this point are correct and you can see +/- 100% then your radio is configured correctly and you can move at the mechanics configuration.

2 Mechanics and Geometry

Correct configuration is necessary to achieve good flight performance. Especially for beginners it could be unclear what are correct steps to do this well. If steps are performed in a wrong way it will usually lead to an incorrect configuration and eventually some odd behavior in the flight. Correctly you have to start with servo adjustment and go up step by step until you will reach blade holders. After each completed step do not touch what was configured previously.

1. Move to the Servo tab and there toggle the Subtrim (tuning) - in this mode servos should be locked exactly at the center (neutral) position. This mode is recommended to be enabled each time when you are configuring mechanical center, including 0° between main blades.
2. By moving with Subtrims move with corresponding servo to set all Servo arms as close to the center as possible (you can do this also for Rudder). (Servo arms should be usually perpendicular with respect to their servo cases).
3. Put push rods/ball linkages perpendicular with respect to the servo arm and swashplate (as close as possible). This mean you have to select which hole of the servo arm is the closest to the perpendicular position. It is always same hole on all cyclic servos. In some models it is unfortunately not possible perfectly which always mean additional error, but you as pilot can't do much about it. Note that also in this step Subtrim (tuning) option should be toggled.
4. Adjust 3 push rods to the same length (if helicopter manual is suggesting same length for all 3 servos). If not, then it adds usually another imprecision to the geometry. But again you can't do much about it. These models can be usually recognized by a design when servo arms are at a different height.
5. Try to set length of the 3 push rods when swashplate is at the center of its Collective Pitch travel. This can be determined by looking at the Anti-rotation bracket of the swashplate where swashplate should be approximately at the center. Adjust lengths of all 3 push rods by an equal amount (so that resulting length is same).
6. Then use the Cyclic Leveler tool and fine-tune lengths of all 3 push rods (usually to be equal again). Subtrim (tuning) option should be still enabled.
7. Mount the Rotor head and adjust length of 2 upper push rods that are connecting blade holders so that they are again equal and at the same time they are configured to reach 0°. This mean when you mount a main blades there and fold ends together, then both ends must be exactly at the same level. And this level should be held at any angle/position/rotation of the main shaft. If not, usually swashplate is not leveled perfectly precise or there is a big play in the mechanics.
8. At this point, if there is no other imprecision in mechanic your model is configured perfectly. Now you can untick the Subtrim (tuning) option and verify if Positive and Negative angles between main blades are equal. If not, then open the Servos/Servo Travel Correction window and move with a sliders (usually it is enough to move with all 3 values by the same amount). If collective pitch is a higher at one side, move the pitch stick to that side (the lowest or the highest position). Then decrease 3 sliders equally to get equal angle as in the opposite direction. When done correctly, you should get precise angles in both directions. Very advanced pilots can use this correction window even at the step 6 together with Cyclic Leveler but this is usually not necessary.

To change Collective Pitch angles you can simply change value Of the Limits/Pitch range. The angles should be equal for both directions always if above procedure was performed.

If you want to not use full Pitch range, you can change the Pitch curve in your transmitter after above configuration. For example if you are beginner you may not want to use a negative Pitch.