Solid is Rudder FIXED
Dashed is for Rudder FREE.
effects Rudder Hinge Moments:
Even after George Shairer's design modifications (Dorsal Fin, less area of Rudder aft of the hinge), Boeing decided to install Hydraulic Rudder Boost: to ensure positive control of that Rudder surface (prevent Lock-Over). Below is an excerpt from page 116, _Aviation_, May 1940.
[About two decades later, Boeing proceeded with a similar design-evolution of the Fin-Rudder on the B707 -- see later web-pages discussing the design-errs, mishaps, and the evolution of B-707 Fin-Rudder (size, boost, artificial stability of "Yaw Damper").]
This cognitive battle between "yaw angle" and Sideslip Angle
evolved after Mar'1939.
Schairer wrote this in 1940 --
so his concepts of
"at various angles of YAW"
might have evolved from that
earlier work done aboard NX19901, into a later exact measure of
on the later tests with the
re-designed Fin-Rudder, using his
Beta Vane during testing.
asymmetric, #3 and #4 prop's feathered, yawing moment balanced initially with Left Rudder: with large Beta, excess Pedal Forces due to excessive Hinge Moment, pilot soon unable to fetch balancing-Rudder from the Lock-over position.
Failure - Interactions
TWA B307 Stratoliner /1Jan41 (date from Rummel pg 56) cold wx, T/O from KC with low ceiling, during climbing turn, inflight upset. Recovered control, returned & landed KC. Capt was Harry Cambell, said he came close to "buying the farm". The F/E, Larry Beggs, resigned rather than fly again [this post-mishap resignation of a mishap-pilot also happened in later decades]. Passengers reported looking up at the roofs of buildings along Independence Avenue.
Airplane grounded, inspected, all controls found normal, lack of any identifiable aircraft faults suggested cause of upset was pilot error.
Boeing investigated problem, identified cold soaking as a factor, plane had been sitting on ramp for twelve hours with OAT less than zero degrees F. Hydraulic fluid congealed inside the Rudder Boost System, resulting in discrepant Rudder displacement.
Boeing modified the Rudder Boost system with bleed holes so that warm hydraulic fluid would circulate inside the Rudder hydraulic cylinder after engine start.
[According to Ed Betts, _AAHS_, Fall '93, pg 171; no specific date listed for mishap. No corroborating AAR mentioned, story may be constructed from hearsay, but the F/E's resignation might be verifiable -- no other information.]
Ironically, the Rudder Boost system was an engineering fix, one of three Boeing modifications to the Stratoliner's empennage -- added after the 18Mar39 upset/breakup (that killed men of Boeing and KLM, and Harlan Hull, TWA's Chief Pilot). The post-accident modification to the B307 was Boeing's first use of hydraulic boosted rudder.
This upset mentioned by Ed Betts might be the first mishap in which a hydraulic related anomaly caused discrepant rudder, and induced a yaw/roll upset. Bob Rummel, _Howard Hughes and TWA_, pg 56, cites this exact date for this cold-soak mishap, but Rummel mistakenly states that the upset was a pitch-Elevator hard-over. See AA Flt One/1Mar62.