Page 24 - February 2015 Volume 9, Number 2

applies about 40 pounds of help on the “good foot” side. It activates in an all-or-nothing fashion when the differential between left and right side’s unregulated P3 Air gets large enough. Since N1 speed only reaches about 85 percent in Maximum Reverse – less than 50 percent power – the P3 differential was never great enough for rudder boost to kick in.
In the 300, Rudder Boost uses the autopilot’s electric rudder servo to provide the helping rudder push and instead of being an all-or-nothing device, it increases rudder force as the power (still sensed by P3 Air pressure) differential increases. (The model 350 operates the same except it uses torque sensors in place of P3 sensors.)
Low and behold, when the Beech test pilot experimented with single-engine reverse in the prototype 300, he found that at Maximum Reverse rudder boost was starting to operate. Now stay with me here, because it’s a little hard to grasp. Do you see why rudder boost was now working “backwards?” In flight, with the left engine dead and the right engine producing power, the airplane wants to yaw left, so we, of course, want help on the right rudder pedal. When that same engine is putting out reverse thrust after a single-engine landing or aborted takeoff, now the yaw is toward the good engine and we need to push the left rudder pedal to stay straight. Having rudder boost push the right one is definitely not a good idea!
“Okay,” Beech Test said, “we won’t use Reverse then; we’ll just stick with Beta, getting rid of the propeller thrust but not spooling up N1. We’ll just have the pilot stop pulling back when he gets to the red-and-white stripes.”
“What?!” says Mr. FAA guy. “You cannot expect a pilot to do this by feel alone or to direct his visual attention away from the runway and down to the power quadrant to see when he’s about to leave Beta and enter Reverse. Get real!”
And that, dear readers, is why the 300-series has the Ground Fine stop ... so that the pilots may easily and quickly select the bottom of Beta during aborted takeoffs or following single-engine landings, as necessary. As for why the C90B and after and the 1993 and after B200- series also have it? For commonality of parts. Personally, I would prefer that they still used the old style pedestal with the stripes, not the second lift, but it is what it is. KA
If you have a question you’d like Tom to answer, please send it to Editor Kim Blonigen at kblonigen@cox.net.
About the Author: King Air expert Tom Clements has been flying and instructing in King Airs for over 41 years, and is the author of “The King Air Book.” He is a Gold Seal CFI and has over 22,500 total hours, with more than 15,000 in King Airs. For information on ordering “The King Air Book,” go to www.flightreview.net.
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22 • KING AIR MAGAZINE
FEBRUARY 2015