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Old 5th Sep 2003, 02:39
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Lu Zuckerman

Join Date: Sep 2000
Location: The home of Dudley Dooright-Where the lead dog is the only one that gets a change of scenery.
Posts: 2,132
Thumbs up Which pitch is which?

The Robinson has a seven-degree negative pitch in the blades. Prior to start of the rigging process assuming everything is normal if the blade root has a pitch angle of seven degrees the tip has a setting of 0-degrees. The blade pitch settings are set with the protractor at approximately 75% span and under the conditions stated above the pitch angle would be 1.75 degrees.

From this point forward everything gets confusing. I have been working in various aspects of helicopter maintenance since 1949 and I have never seen a rigging procedure as confusing as that of the R-22 and by extension the R-44.

One point of confusion is that the cyclic stick has limited travel in all directions with these limits established by the cyclic control stop plate. This is contrary to FAA guidelines but I wonít go into that. The rigging procedures start with the cyclic in its neutral position relative to fore and aft and lateral control. This means that the travel for fore and aft is the same relative to neutral. However when the cyclic is moved forward the required pitch setting for the basic R-22 is 8.3 to 8.8 degrees. I have never been associated with a helicopter that had a range in the pitch setting but there may be more than the R-22. Back on track, the aft pitch setting is 8.5 to 9.0 degrees.

If the desired aft range canít be achieved the mechanic must adjust the push pull tubes attached to the swashplate. This will change the setting for forward pitch and the mechanic is told the following.

NOTE: If adjustment is required to obtain aft cyclic control blade angles, the forward cyclic must be rechecked.

Two points to consider: 1) The mechanic is not told what to do in order to change the forward cyclic angle because if he does he will also change the aft cyclic angle and the whole process starts all over again. And, 2) If the cyclic is moved from the center of travel forward and aft from the center of travel how can they have different pitch settings for forward movement and for aft movement.

The rigging procedures are very vague and this includes the rigging procedure for the tail rotor. The rigging procedures for the R-22 are totally contrary to the procedures used to rig any other helicopter. The R-22 rigging procedure can introduce excessive pitch into the blades. If the blade angle readings are taken at the 25% span and the readings are 8.5 to 9.0 then the reading at the root would be around 14.25 degrees and this is with no collective. The collective reading with the blades in the neutral position is 11-12-degrees. With maximum cyclic input the pitch reading at the root could exceed 25-degrees which is quite high for most helicopters. This angle will in most cases increase with adjustments for autorotation.

My hat is off to the mechanics that maintain these helicopters and to the pilots that trust that their mechanics have a full and total understanding of the procedures.

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