Lemme give ya redneck Scott's answer to all of this: The sumbitch ain't right, get ya a new one!!!
Scott --- Robert Morrissey <[email protected]> wrote: > Serge: As a former "Liaison Engineer' for a big > aerospace company that > was bought out by Boeing I will give you the SOP > (standard operating > procedure) for your aircrafts 'non conformance' that > occurred during > 'manufacturing' or 'depot level overhaul". (My text > book answer) > FOR THE; > a. original WAFs with the oversize 3/8 inch > hole---are they a standard > oversize? Let us assume they are not a standard > size. > > Looking at FWD WING ATTACH FITTINGS, drawing no. 18 > in my RR book pg.23 > dated january 1990 the WAF is 1 1/2 inch wide and > has a 3/8 dia. hole > drilled 3/4 inch from the end. In my working days > I would go to a stress > engineer, show him the part drawing, identify the > 3/8 hole is oversize > and tell him what my method of repair was to be. > The stress engineer > typically went to his books and evaluated the over > size hole condition as a > 'lug analysis' with reduced edge distance (tear out) > and 100% of the time > went along with the installation of a larger > diameter fastener. For really > critical lugs, with really screwed up damage, I > actually had inspection > record > the tear out as well as the actual part thickness > and provided this data to > the > stress engineer. The hole could be drilled to an > oversize such as 1/64 > oversize, > 1/32 oversize or even a next full size standard size > as was required by the > part condition.. > Any hole increased in size must have the same > fastener/hole assembly > tolerances > as the rest of the WAFs. If there was a > possibility of the oversize bolt > being removed in the > future the area was marked to denote the hole and > special size fastener. > For those parts that would undergo constant bolt > removal and replacement > then a minimum 0.016 inch wall thickness bushing > would be pressed fit into > the discrepant part. The bushing would have a 0.0005 > to 0.001 inch press fit > and > be of the same material. This would bring the > discrepant part back to > blueprint. > > b. for your new WAFS-- my drawing referenced above > shows a series of 3/16 > inch diameter holes located 1/4 inch from the long > edge of the part. If I > take half of the 3/16 inch and subtract it from the > 1/4 inch we have 5/32 > (0.0156inch) of an inch for tear out. That is not > much edge distance. > As an intelligent guess, if you are looking at > tear out of less than 0.140 inch I would not use > them. > > I am going to ignore the fact that the WAF drawings > used are not to > aircraft standards. I have never seen fractions used > on such a critical > machined part. > Standard sheet metal tolerances are +- 0.030 inch. > Can you see what would > happen > on the WAF if that tolerance was used > indiscriminately during manufacture? > How about checking your WAF holes to see what kind > of assembly tolerance > your fittings have. > > I never did get involved in reliability engineering > during my work career > but I do love redundancy. I hope the above info > gives you a feel for what > you have on your hands > Do you have any friends that are stress engineers > that you can pass this by? > Regards > Bob Morrissey, New Bern NC > > ----- Original Message ----- > From: "Serge VIDAL" <[email protected]> > To: "KRnet" <[email protected]> > Sent: Wednesday, September 14, 2005 5:16 AM > Subject: Réf. : RE: Réf. : KR> RE: Dual Ignition > Systems, it Saved My > Bacon - CORRECTION > > > Well, as a former reliability expert, I can give you > the text book answer: > > - Reliability is risk management; > - The universally accepted method of managing that > risk is what gives > birth to aircraft safety standards; > - The authorities (like ICAO) are supposed to define > what is your > acceptable level of risk for the activity (roughly, > basically, deaths per > X flight hours). > - At designer level, you then find what is likely to > cause these risks, > and define "unwanted events" (example: power loss, > flight controls > failure, etc.) > - If failure of one component that is likely to > cause an unwanted event is > so unlikely that it is less than the acceptable risk > level, then you don't > have to do anything about it. You assess that by > estimating the > probability of failure (occurrence) and its > consequences (severity), to > define the level of CRITICITY. A part can be non > critical because it is so > unlikely to fail, or because .. If it is not the > case, then you have to > improve the reliability. You have many ways to do > that, (can be better > technology, better part design, monitoring, > maintenance, you name it.). Of > course, one method is redundancy. It is seldom the > correct answer, but it > is generally the easiest, and that's why it is so > popular in aviation. > > Now, this is the rule for expensive designs > (airliners, jet fighters, > nuclear power plants, space shuttles or whatever). > In general aviation, > the trouble is it is not affordable to calculate > exactly all the risks > attached to all the parts and equipment. So, we > apply a rule of thumb, > which is: no single failure may lead to an unwanted > event. That is what > you do with your ignition or fuel system. > > But we also apply criticity, through return of > experience of 100 years of > designing and flying. We know that single engine is > an acceptable > solution, so we don't make the engine redundant. But > we make the engine's > most critical components redundant. The ignition, > but not the carb... > > Likewise, we know that control cables are unlikely > to fail, provided you > rig them properly and inspect them regularly, so we > don't make them > redundant either. > > In my opinion, the statistics of engine failure in > aviation are an > absolute shame, and the ignition is the main > culprit. So, I go for a > better technology, and ultimately, as soon as it > will become practical, I > will go for an engine technology without ignition: > the Diesel engine. > > Serge Vidal > KR2 "Kilimanjaro Cloud" > Paris, FranceSent: Tuesday, September 13, 2005 9:13 > AM > To: Corvair engines for homebuilt aircraft > Subject: Re: CorvAircraft> Dual Ignition Systems, it > Saved My Bacon > > > > > _______________________________________ > Search the KRnet Archives at > http://www.maddyhome.com/krsrch/index.jsp > to UNsubscribe from KRnet, send a message to > [email protected] > please see other KRnet info at > http://www.krnet.org/info.html > __________________________________ Yahoo! Mail - PC Magazine Editors' Choice 2005 http://mail.yahoo.com
