TM 1-6625-724-13&P0071 000071 00-27TASK 3 - TRACK AND BALANCE MAIN ROTOR IN FLIGHTTrack height should be given only minor consideration during the track and balance process. It is recommended tokeep an eye on track and perhaps use it as a delineating factor when choosing between two otherwise comparablyeffective solutions, but to not use track for picking adjustments. If the AVA adjustment set is not manipulated tooerratically, track willremain under sufficient control. This is because minimizing vibration requires only two blades.The third blade is used to control track with little compromise to vibration. The AVA will always use the third blade tominimize track spread, as needed. The only mechanism available for having a severely out-of-track condition whilehaving vibrations in limits is the split tip path plane in which two opposite blades are flying in one plane and the other 2opposite blades are flying in another plane. It is possible to end up with this configuration if one manipulates orrestricts the adjustables too severely, however, the AVA will itself never drive the rotor to this configuration.In a perfect world, zero track height would correspond to zero vertical vibration. However, in the real world, eachblade (including lead lag links and pitch cases and pitch links, etc.) is far from identical to the other. Therefore, in thereal world, perfect track usually does not mean zero vibration. The more mismatched the blades, the larger the trackspread may have to be to obtain minimum vertical vibration.Hub WeightsHub weights are turned off as a default and must be manually turned on (i.e., Edit Adjustables) if needed.If the ground lateral and hover lateral points on the polar chart need to be brought closer together, hub weights will notbe effective. A hub weight adjustment will essentially move the two points around the polar chart without significantlychanging the distance between them. This is evidenced by the closeness of the sensitivities both in magnitude andphase angle, for the two conditions. Therefore, if both the ground and hover lateral points need to be brought closertogether on the polar chart, pitch link adjustments are generally required.The sensitivities of vertical vibration in forward flight to hub weight changes are included in the sensitivity matrix in thescript file. Due to the relative weighting of the vibration measurements, which more heavily weights the total of allvertical vibrations as compared to the total of the two lateral vibrations, the hub weight solutions will often be renderedless effective for reducing lateral vibration, since weights will be more effective in reducing vertical vibration. Forthese reasons, it is important to get hover and ground lateral under control early in the track and balance process,when potentially pitch link, weight and tab adjustments are being called for. The AVA will generally not be effective incoming up with a weight-only solution to minimize lateral.Pitch LinksThe AVA may give large pitch link adjustments (2 flats or more) and use a corresponding tab adjustment to counter it.Usually, these are uncalled for and are not recommended. If the AVA is giving pitch link moves of 2 flats or more, it isrecommended to try other combinations of adjustments (including no pitch links at all) to try to come up with a morereasonable solution. Rarely would such relatively large pitch link moves be justified as long as ground and hovertrack spreads are reasonably small.TabsTabs are triggered by blade track height. When the blade relative track height changes 0.5 inches or more from itshover value at a given speed, a particular tab region is turned on, depending on that speed. The correlation betweenspeed and tab region is as follows:4-10 tab: Track exceeds 0.5-inch difference from hover at 60-80 knots6-10 tab: Track exceeds 0.5-inch difference from hover at 100-120 knots8-10 tab: Track exceeds 0.5-inch difference from hover at 140 knotsIt is recommended to avoid tab bends of 2 degrees or more, if possible. If a 6-10 or 8-10 tab is triggered, but theadjustment calls for a 2 degree or more bend in that region, turn off the 6-10 or 8-10 tab and turn on thecorresponding 4-10 or 6-10 tab. This distributes a smaller move over a larger span and will serve the same purposewithout requiring excessive tab bending. A 4-10 tab bend of 2 degrees or more cannot be avoided in this manner.However, a 4-10 bend in excess of 3 degrees is potentially an indication of some other problem. If this happens,check to see if there is any bend in pockets 0-3. If so, they should be zeroed and a new measurement set taken. Ifthere is no bend in 0-3 and the large 4-10 bend is required, make a 1/2 degree bend in 0-10 instead, take a newmeasurement and go from there. If a large 4-10 is still called for, another 1/2 degree can be put in 0-10 instead, butdo not exceed 1 degree total in pockets 0-3.
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