Originally Posted by dubbleyew eight
in the case of the air france flight I have often wondered if the aircraft didn't accrete a few tons of ice on the fuselage. if the pilot flying was convinced that the tailplane was stalled then pulling up elevator, which would reduce the elevator angle of attack, would be an entirely logical move to try to get it flying again.
but of course we'll never know.
if the fuselage had accreted a few tons of ice in the flight it all melted in the sea leaving no evidence.
The normal function of the tail is to push the tail slightly downward to counter the tendency of the center of gravity (CG) of the airplane (normally forward of the wings) to pull the nose down. In those situations where the tail no longer is able to provide sufficient “lift” in that downward direction, the effect of the airplane’s weight (centralized at the CG) will result in the nose moving down.
Therefore, with any aircraft condition approaching an aerodynamic stall, should the pilot initiate pulling back on the controls (i.e., pulling the elevator “up” with respect to the horizontal tail surface) there would be an increase the “lift” generated on the underside of the horizontal tail, thereby moving the tail downward and the nose upward,
increasing the AoA, and compounding the problem. With an ice accretion already on the airplane, likely already having decreased the stall AoA, any successful pulling-back on the controls would result in further raising the nose, and moving the airplane closer to the stall or moving it more deeply into an already present stall. How could that be even close to logical?
Also, I think we need to keep the estimates we throw around just a bit more within the realm of possibility, even when realism is totally disregarded. With little doubt, there has been a serious misunderstanding about the weight of ice accretion on an airplane. The idea that an airplane can accumulate “several tons” of additional weight (where several tons ... 4 tons? ... 8 tons? ... would be 8,000? pounds ... 16,000? pounds) is, at best, extremely unlikely.
In fact, recent regulatory/industry working groups focusing on the operations of airplanes at or beyond the normal flight envelope, have described the additional weight accumulating on an airplane of “average” size, likely being about the same as adding the weight of a couple of additional passengers – and on the largest of airplanes this estimate reaches up to 10 to 30 additional passengers – where the average weight of passengers is routinely estimated to be between 180 and 200 pounds, including their carry-on baggage. And ... this is the accumulation that might occur on the ground prior to takeoff - and much less accumulation when already airborne. Therefore, this means an accumulation of less than 400 pounds of ice for airplanes with a maximum takeoff gross weight a bit under or over 200,000 pounds and as much as 2000 to 6000 pounds for airplanes with a maximum takeoff gross weight approaching (and some now that exceed) a million pounds.
While it is true that ice accumulation has an effect on airflow over and around an airplane, and of course we simply cannot dismiss that fact … we must understand that the actual weight of the ice accumulating on an airplane is relatively
insignificant when compared to the airflow disruption it causes.