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BACKGROUND OF A PROBLEM:

The Canard type aircraft (VariEZ, LongEZ, Cozy, etc.) use a castering nose wheel and differential braking for ground handling/steering. This works quite well, and when properly aligned and adjusted the airplanes handle quite well on the ground with only a slight touch of the brake on either side to keep the aircraft tracking the taxi way center line. Experience has shown that this excellent ground handling deteriorates with age and number of landings on the aircraft. The aircraft refuses to track straight, even on a flat runway with no wind. The corrections needed become more numerous and more severe until main brake wear and heating become a problem on long taxi trips at large airports. The cause of this has been traced to side to side play in the nose gear at the wheel. In turn this play has been traced to wear or damage to the bronze bushings in the NG6 nose gear pivot. These bushings wear and often fail in bearing due to side loading during landing and takeoff. Due to the long nose gear the play in the bushings result in 1 to 2 inches of play at the wheel. The result is the aircraft weight cause the nose gear to seek one side or the other. The pilot must apply heavy braking on one side to raise the aircraft and force the nose gear to seek the opposite side. The temporary fix is to replace the bushings. This requires nose gear removal. This problem is more severe in the heavier aircraft.

SOLUTION TO THE PROBLEM:

The tapered roller bearing NG6A and MKNG6A is the permanent fix for this problem. Tapered roller bearings were chosen for this application because they can handle both radial and thrust loads and have the ability to stand high shock loading without peening the bearing races. Angular contact ball bearings would not work because they fail under high impact loading due to their point contact on the races. Tapered roller bearings need to be lightly preloaded to insure zero clearance. In the canard aircraft the composite structure allows deflections under landing loads that can cause clearances to increase and decrease on the bearings if the pivot bolt is not tight. But full torque on the bolt would over preload the bearings. The NG6A/MKNG6A assembly solves this problem by mounting the bearings on a precision split spacer (NG7A\MKNG7A). The spacers are length adjusted for a light zero clearance preload. This allows the pivot bolt to be fully torque without over preloading the bearings.

The NG6A AND MKNG6A utilize a custom aluminum sand casting which is stress relieved prior to machining. The tapered roller bearings are fitted with a machined spacer for bearing preload. This preload ensures proper movement of the bearing no matter how tightly you tighten the pivot bolt and assures that the installation will maintain zero play.

Last Updated on Monday, 28 February 2011 12:23
 
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