tdfsks

Let me just correct an typing error in my previous post: "The bellcrank on which the aileron bellcrank ....." Should have read: "The rib on which the aileron bellcrank ......"

The answer to the original question is no, most LSA's without mass balance cannot be guaranteed to be flutter free with slack control cables. The basic problem is that the flutter requirements in ASTM F2245 are poorly written. Perhaps they were written by those with a vested interest in an easy and cheap path to compliance (remember this is a concensus standard written by a committee including manufacturers) or it might simply be that those who wrote the requirements simply didn't understand flutter. Probably a combination of both. Most LSA's are certificated for flutter via flight test. The evidence is that few of these flight tests are conducted correctly with adequate instrumentation and proper means of exciting the vibration modes of the structure. Also I fail to see how they can do a proper flight test without first doing analysis and a ground vibration test to understand the critical modes that need to be checked during flight test. In the case of a convention light aircraft with a Part 23 certification basis, FAR 23.629 (and in particular the associated AC's) are quite clear that you do need to show freedom from flutter for the case where the control surface natural frequencies tend to zero ... i.e. a failed or slack cable. That is why virtually every Part 23 aircraft has mass balance .. either 100% balanced or some form of product of inertia balancing. Note: that 100% mass balance is usually not necessary. The inflight breakup of at least 8 CH-601XL's was due to flutter caused by this exact problem. No aileron mass balance. The bellcrank on which the aileron bellcrank was mounted bent due to the cable tension and let the cables go slack. The aileron / wing then fluttered .... failing the wing spar in the root area. One of the NTSB recommendations was that the ASTM F2245 committee review the flutter requirements .... who knows if they took took any action or even understood the issue.

Hi M61A1 ...... Thanks for taking the time to do this .... I really appreciate it. No appologies necessary for the drawing - it has all the info I need. RG

Hello, This might seem like a strange question ... but can anyone tell me how wide the sheet metal part of a Drifter fuselage is where the seats are attached ..... Also (but not as important) what is the thickness of the sheet metal. Thanks, RG