From mboxrd@z Thu Jan 1 00:00:00 1970 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me X-Spam-Level: * X-Spam-Status: No, score=1.2 required=5.0 tests=BAYES_00,FROM_WORDY, INVALID_MSGID autolearn=no autolearn_force=no version=3.4.4 X-Google-Language: ENGLISH,ASCII-7-bit X-Google-Thread: fac41,e01bd86884246855 X-Google-Attributes: gidfac41,public X-Google-Thread: 103376,fb1663c3ca80b502 X-Google-Attributes: gid103376,public From: "Ken Garlington" Subject: Re: Interresting thread in comp.lang.eiffel Date: 2000/07/24 Message-ID: #1/1 X-Deja-AN: 650097393 References: <8ipvnj$inc$1@wanadoo.fr> <8j67p8$afd$1@nnrp1.deja.com> <395886DA.CCE008D2@deepthought.com.au> <3958B07B.18A5BB8C@acm.com> <395A0ECA.940560D1@acm.com> <8jd4bb$na7$1@toralf.uib.no> <8jfabb$1d8$1@nnrp1.deja.com> <8jt4i0$18ec7$1@ID-9852.news.cis.dfn.de> <8k5a31$1p61t$1@ID-9852.news.cis.dfn.de> <3966D7B0.5D6475E4@earthlink.net> <396CA5AD.EE955F7A@earthlink.net> <397A5CB4.AF5F6B8A@earthlink.net> <397C29CA.7B445687@baesystems.com> X-Priority: 3 X-MimeOLE: Produced By Microsoft MimeOLE V5.00.2919.6600 X-Complaints-To: abuse@flash.net X-Trace: news.flash.net 964441870 216.215.75.172 (Mon, 24 Jul 2000 07:31:10 CDT) Organization: FlashNet Communications, http://www.flash.net X-MSMail-Priority: Normal NNTP-Posting-Date: Mon, 24 Jul 2000 07:31:10 CDT Newsgroups: comp.lang.ada,comp.lang.eiffel Date: 2000-07-24T00:00:00+00:00 List-Id: "David Gillon" wrote in message news:397C29CA.7B445687@baesystems.com... > > > Ken Garlington wrote: > > > > > > > The gains changed abruptly when the aircraft transitioned from > > > > takeoff-and-landing to up-and-away mode. This produced a sudden > > transient, > > > > triggering the start of the PIO. The transition now occurs more > > gradually. > > > > > > That fixes the primary cause, but not the actual failure mode. Does > > > the stick now > > > have tactile feedback? > > > No -- you don't often get significant tactile feedback from a force-sensor > > side stick connected to a FBW system, such as that on the F-16 or F-22. (In > > fact, the original F-16 stick didn't move at all!) > > IIRC, the YF-16 had a PIO incident during the fast taxi trial and was > only saved by the test pilot lifting off before the oscillation about > the roll axis became severe enough to contact the runway with the > wingtips. Actually, the wingtips DID contact the runway, although the damage wasn't so severe as to make the aircraft unflyable. > He managed to dampen it out once in the air, did a circuit and > landed without further incident. The solution lay in the (analogue) FCS, > not the fixed stick. Correct, although the stick was later changed to move slightly with the pilot's hand, to give it a better "feel". It doesn't provide any feedback from the airframe, however. > There is an undeniable advantage to a moving stick, in that it > immediately demonstrates the last control input if the pilot is > hands-off or in a two crew cockpit. IMO, It tends to be more defensible with respect to throttle, if the FCS can independently select thrust (autothrottle). > However I don't believe tactile > feedback as a solution to PIO is a workable argument for mandating one. > (Stick-shaker operation as a stall warner is a completely separate > issue). Particularly for a relaxed stability aircraft, the whole idea of feedback gets interesting. Should it move in response to the surfaces, which aren't necessaily moving in a way the pilot "expects"? Should the FCS -- which is in the PIO loop -- be synthesizing some sort of artificial feedback? What does "feedback" mean in the presence of thrust vectoring?