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Old 21st Jun 2016, 19:05
  #91 (permalink)  
Join Date: Nov 2015
Location: Seattle area
Posts: 213
Several pilots have said that any information about the flight dynamics will have to come from a simulator. I've loaded X-Plane, which is the best one for my purposes, and am using a L188C model written by David Starling. The manual says the Electra at the conditions for Flight 706 should stall about 110 knots, and the model does. The maintenance manual says the rudder can deflect 30 degrees right and 25 left, and the model has it exactly.

The model appears to be an accurate representation, and we can probably take its behavior to be correct within a smallish percentage of error. I'd be interested in hearing from pilots about the feel of the model.

One of the questions is whether an Electra can knife-edge fly. Turns out it can at any speed over about 250 knots. At lower speeds there isn't enough airflow over the rudder to get the nose up. I've run a number of tests, all starting at 1k feet over Puget Sound, since Flight 706 got to 300 feet tops and ORD elevation is 680 feet. My tests start at 160, 200, 250 and 300 knots, and I throttle up as needed as soon as the bank goes vertical. At 160 knots the plane has no chance, and is essentially in free-fall for the first 500 feet. At a starting 200 knots after a few tries I could get to 250 knots about 50 to 150 feet over the water. Starting at 250 or faster the plane had no trouble at all.

There will be some discussion of this in the next version. The answer for now is that knife-edge flying was not possible for Flight 706 because it was about 100 knots too slow.

My next step is to write a program harness for X-Plane so I can run turn and bank trials and collect more rigorous numbers. The questions to address are (1) what bank can the rudder induce, or what unwanted bank can it counter, and (2) what do rudder inputs do to turn radius calculations.

Hand-flying suggests that the rudder alone can turn the plane completely over, which impressed me. I'll be interested in seeing how the data turns out.
BRDuBois is offline