Ed - You're lucky. As you know, flutter is often a high altitude, high speed event. Since the air is thinner at altitude, you have less aerodynamic dampening. Loading the surface was a good idea, as it provided dampening thru the loads you imposed.
As I said earlier, in most light airplanes, flutter margin determines where Vne is set. Sometimes other factors will control Vne, such as windshield strength, but it's normally a function of flutter margin. And we have to remember that the science of aero engineering wasn't in the 1930s and 1940s what it is today. After all, that was just 3 or 4 decades after the Wright Bros. first flew. Lots of principles that were only scantily known then are basic today. Look at the airplanes that have had ADs to install mass balance weights on control surfaces, like the Piper Comanche line. When they were designed, the engineers didn't mass balance those surfaces, and after a few flutter events, later study recognized the problems and solved them by adding weights ahead of the fulcrum to balance the control surface. Balance is extremely important in flutter prevention. For instance, a V tail Bonanza is very susceptible to flutter of the ruddervators when they aren't balanced. More than one has met its end after a paint job, when the ruddervators were hung, trailing edge down, to dry. The normal running (invisible, but there) of the paint as it dried made the surface trailing edge heavy, and out of balance. The ruddervators have to be hung leading edge down to dry after being painted. Just another reason never to skimp on any maintenance, and if you get the idea that the A&P doesn't pay attention to these matters, find another one. Jerry E. -----Original Message----- From: [email protected] [mailto:[email protected]]on Behalf Of Ed Burkhead Sent: Saturday, December 27, 2008 11:43 AM To: [email protected] Subject: RE: [ercoupe-tech] Sebring crash, NTSB preliminary report > NTSB Identification: ERA09FA087 > 14 CFR Part 91: General Aviation > Accident occurred Saturday, December 13, 2008 in Sebring, FL > Aircraft: ERCOUPE 415-D, registration: N99154 > Injuries: 2 Fatal. > . . . Another witness, who was also a certificated airline transport > pilot, stated that while outside working on his house he > observed the accident airplane flying overhead. . . . He > additionally noted that while the airplane was banking, > both ailerons were "fluttering" at a high frequency. . . . The mention of aileron flutter in the accident report brings me to recount my encounter with aileron flutter in a Coupe. At high altitude, in perfectly smooth cool air, I needed to descend to go under clouds far ahead. Rather than do a cruise descent, I decided to do a gentle dive to touch the Vne of the Coupe. I was still a few mph short of Vne when I felt a vibration very much like hitting the washboarding on a gravel road. For some strange reason, I deduced the cause in a very short time - between 1-3 seconds - and correctly figured out I needed to load the aileron to dampen the flutter. A sudden turn of the yoke instantly dampened the flutter and I slowed the plane gently, doing S-turns to keep the aileron loaded till I was down to normal cruise speed. The plane checked out, there in the air, so I continued on to home base. Testing on the ground showed that the aileron system had excess play. It's already part of the Coupe instructions how to check the aileron control system play. My recommendation to everyone is to DO IT! Check that aileron system play. Soon! Please! I'd also recommend a thorough inspection of the components of the control system. Perform the integrity test on the aileron push rods (is the ice pick actually the correct method?) and make sure all the parts of the control system are corrosion free and in good condition. And, consider that it's not necessarily a good idea to approach Vne in a 60+ year old airplane. Ed Ed Burkhead http://edburkhead.com/Ercoupe/index.htm ed -at- edbur???khead.XXX change -at- to @, remove ??? and change XXX to com
