Comments interspersed below WRB
On Dec 28, 2008, at 12:14, Ed Burkhead wrote: > > Dan wrote: >> I'd be interested to hear what the actual experiences have been of >> others who have had a trim wire failure without the spring & trim >> stop. > > In 1994, as editor of Coupe Capers, I had a long talk on the phone > with the > accident investigator of a disintegrate in flight Coupe accident. I > did not > see the final report to see if it confirmed what he said on the phone. > > He said he was leaning toward ruling it as elevator flutter as a > result of > trim tab flutter. > > The specifics were, for no other apparent reason, the tail broke off > the > airplane, the nose pitched down abruptly, the airflow on the top of the > wings caused huge negative g-loads and the pilot was ejected from the > plane. > I guess he had a long fall. The trim tab must become unrestrained AND the forward speed of a coupe has to become excessive for the effects of trim tab flutter to cause in-flight disintegration. It is extremely rare for a coupe to be going faster than 130 MPH in controlled flight. It is uncommon for the trim tab wire to break or become disconnected such that the trim tab is "free enough" at flight speed to induce elevator flutter. If the above two circumstances do not occur simultaneously, a pilot's experience of any type of flutter is likely one of relatively slow progression (as opposed to sudden and irreversible progress to such airframe stress as to result in disintegration). If the pilot "preprograms his mind" by being always aware of the best off-field places to land in case of engine failure, he greatly improves his odds of being able to put the bird down without injury or damage should he have to do so. He "knows" what to do with little conscious thought...the crisis has been previously carefully considered without haste, options evaluated, and a number of possible decisions tentatively made. Similarly, the pilot should decide in advance that any unusual in-flight experience can likely be successfully managed. An immediate reduction in power and speed will likely either immediately resolve the problem, whatever the cause, or lessen airframe or engine stress so as to "buy more time" for further thought and action. If a pilot panics at the onset of flutter and dives toward the ground, he actually causes an accident that could have been avoided. It is likely that the great majority of flutter encounters begin slowly (with the pilot wondering "what is going on") and will cease as soon as power is reduced and speed drops. I am advocating that everyone preprogram themselves to "do the right thing". Doing nothing or doing the wrong thing can have fatal consequences. > > (In the Sebring crash, the empennage seems to have broken and the last > part > of the scenario seems the same but the cause may well have been > forward if > the ATP witness's account of fluttering ailerons was correct.) > > Bill makes an entirely correct point that trim tab wire failure must > have > happened many times without flutter and destruction. > > But, thinking about that guy's long, long, fall to the ground, possibly > conscious and alert, I think I will always want a trim tab stop and > spring > on any Coupe I ever own again. I will continue to make sure the > spring is > strong at least at each annual. That's my personal preference. > > Still, I won't be a*al-retentive about going for a ride in someone's > plane > which doesn't have the trim tab stop and spring. Per Bill's point, it > takes > a pretty restricted set of circumstances before a failure of that wire > becomes catastrophic. > > Ed
