PPRuNe Forums - View Single Post - Turn Rate Indicator / Turn Coordinator / Looping Error
Old 24th Feb 2014, 22:54
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flyer101flyer
 
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PS I spoke to a former USAF instructor pilot (T-37's) yesterday, whose military and civilian career also spanned through C-130's and MD-11's. He was completely unfamiliar with any need to reduce G's before reading the needle-and-ball turn rate indicator, and was also completely unfamiliar with this scenario where under heavy G's, the turn rate indicator may continuously be deflected to one side even as the direction of bank and turn actually goes through a reversal, as the aircraft is rolled through wings-level and beyond. He said "sounds like something from the dustbin of history".

Sounds to me like the designers and manufacturers of these instruments eventually realized it was best to use stiff centering springs, to cut this "looping error" to a minimum.

And I also suspect the issues that have been observed re oversensitivity of the "turn coordinator" in flight conditions close to straight-and-level have nothing to with "looping error", or with the direction of spin of the gyro. "Looping error" should be zero when the aircraft is near wings level and plus 1G. The "wrong" direction of spin should give you something analogous to "looping error" when the aircraft is engaged in a nose-down pitch rotation, producing less than 1 G, or even minus G -- but except for a few very exotic cases, it's impossible to sustain a substantial nose-down pitch rotation for more than a few seconds without heading for something like a downward vertical dive (or sustained inverted flight, in which case any sustained turn will have a nose-down pitch rotation) ... that doesn't have much in common with flight near wings-level at approximately +1 G.

S
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