I think I have talked about Brian's explanation of the failure in the other IMPACT threads, but this is important and is worth repeating. Brian explained that he had just made one circle around the filed and wanted to enter the box to start his routine. As he started to pull out of the ESS, he noticed the whole tail group shaking in a strange, unexpected manner, and he immediately chopped the throttle and landed. The plane had suffered a buckle on its right side, just forward of stab LE. The whole right side had developed a crack through the TAVS, around the bottom and about 1/3 the way the left side.
He eventually brought the plane to my house and asked how it could be fixed. In the mean time, over a span of about 3 months of phone calls, emails, and other assorted contacts with his rep, he was finally told that they were going to replace the fuse free. He brought the new fuse to my shop and asked me to do the critical installs, and to keep the broken fuse. I have the broken one in my shop and have started repairs.
The new fuse was completed and delivered to Brian. Just about the same time, I started fileding more emails from fellows whose models had failed in similar fashion, so I talked with Brian about adding the extra bracing in the tail. I saw his ladder brace last night and it will definitely do the job. His is about ready to fly and, as he gets air time, I would hope that he would come on and explain how things are going.
Hopefully he can post a couple photos on the brace design: if anyone saw the History of Flight series on the Wings Channel last year, and particularly the episode on the Wright Flyer's wing rib design, that's the same concept we employed on the brace. Simple, slightly flexible, extremely light (<1 1/2 ozs) but very strong both in compression and torsion.
And BTW any of the European rubber ducky fuselages could benefit from such a structure. Not that these have the same problem as the Impact, no, not at all. Just that these are flexible and the tail surfaces tend to shake all over the place. Undesirable in my view
regards
MattK
ORIGINAL: ERichard
Matt,
I absolutely agree that one is too many....even for the guy that doesn't own the plane. I hate to hear about these kind of crashes, especially like the one that happened to Brian. I think that you will agree that the Sportsman split ess is not a particularly violent maneuaver, so something was definitely wrong. I now see why Brian is beefing his second one up...I don't blame him one bit and would do the same.
If your estimates about the total number of Impacts flying is correct (which I would agree with, maybe 50 at the most) then these are abo****ely unacceptable statistics......13% failure rate! And that just includes the ones you know about. I am going to try to investigate this further....but if anybody out there has experienced an impact failure like Brian's, then please chime in and tell us about it.
As far as my statement about just strong enough, what you are saying is implied in my context....they key phrase in your statement being ..."that we can afford". We all want our planes as light and strong as possible, to a point. I (like many) spend a lot of money on this hobby/sport/disease, but I'm not Boeing or Lockheed Martin so I'm not going to spend a fortune on exotic materials that will make my bird light and withstand loads that it will never experience...that's what I meant by just strong enough. I think at least in spirit we are saying the same thing...if not then okay, so be it.
Back to the Impact problem....Did you witness Brians failure? If so, can you describe what happened? For example, do you think something (rudder or stab) fluttered? I suspect that it was probably all over in an instant, so it is hard to tell. However, inspecting the damage after the fact may have some clues....any ideas?
-Erik