Mad (Flt) Scientist
Great post- agree with it all. The CAB report on the crash of NW 705 (described in the opening post of this thread from wsherif1) seems to agree as well:
But what does this mean? Does it mean that the initial response is nose down followed by nose up?
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Could you walk us through the traces below from the same report?
The initial part of the top (altitude) trace is the normal climb, which then increases (according to the text of the report) to three and a half times the normal rate of climb.
I assume that this increased rate of climb is due to an up draught.
The next trace shows a falling air speed - not surprising.
The next traces are deduced from FDR data but are not direct traces.
The first shows a PITCH UP increasing from about 4 to 20 degrees during this climb.
This is not a "weather cocking down into the up draught", but might be what the CAB called “the ultimate effect of the updraft is an altitude and nose up attitude increase“.
The last trace shows an initially unchanging angle of attack.
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So does an updraft initially induce nose down quickly followed by nose up, or what?
The pitch trace shows no sign of nose down, with a climb rate three and a half times normal.
Signed, Puzzled.
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Ignition Override
The same report contained strong words of advice to use the attitude indicator as the primary instrument in turbulence, and even then to go easy on the controls. They didn‘t seem to like auto pilots much.:
"From all the evidence available to the Board, it is abundantly clear that flight on instruments in heavy turbulence can present a difficult problem to any pilot who departs too far from the recommended practice of using the attitude indicator as the main reference instrument for maintaining control. If the pilot places undue emphasis on any other flight instrument during his normal scan routine, a serious miscue with drastic consequences can occur. Similarly, attempts to maintain "perfect" attitude control can be equally hazardous, because of the high loadings induced, the danger of over controlling by the use of large control displacements, and the possibility of inducing an undesirable oscillatory motion of the aircraft. "Loose" attitude control, or moderate counteracting control inputs, appears to be the best method of counteracting the effects of heavy turbulence. ………… Little is gained by trying to maintain rigid. attitude control since this can produce excessive aircraft loadings without appreciably affecting the altitude and airspeed excursions that occur during severe encounters. Large pitch attitudes of 40 degrees nose up can occur in severe turbulence but moderate counteracting elevator inputs will prevent excessive speed reductions that could result in a stall. The use of the autopilot on Manual Mode offers some advantages but considerable stabilizer trim activity can occur in some types of' turbulence and could present a serious danger if the autopilot was disengaged either deliberately or inadvertently at a time when the trim varied appreciably from the in-trim setting .”
Cheers,
