RE: Impact
 

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

RE: Impact
 

Thanks Matt,
I appreciate the reply...and yes, this is important info that needs to be repeated. I am going to examine my two Impacts very carfully, and given your comments and those of David (see above) I think 1.5 ounces of ladder/crutch is definitely worth it.....as you say, strength in the right places! Please post some pictures when you get a chance and tell Brian to keep us posted about how his new one works out.

-Erik

RE: Impact
 

If I continue down my truly conservative road to building Impact number 2, I am inclined to follow the suggestion in another thread of putting three oval formers in the fuz (I think it was Matt's suggestion) to ensure the integrity of the oval shape stays in place, as well as the ladder. This tackles three (likely very minor) risks that may exist with the ladder only if whatever is causing our issues puts the fuz at that point in tension (ie, sides pulling away from the ladder). I would rather have something in compression on the vertical axis stopping the deformation in parallel.
- The first is that I am not 100% confident I can get a really good contact/bond to the inner surface of the composite all the way down the fuz on both sides (and if I do it may weigh more than the ladder!);
- The second is I am not sure of the best glue to use -- I have been sanding and cleaning the inner surface, and using epoxy, but it clearly isn't a full strength bond to whatever the inner surface of the composite is -- any ideas on better glues to use (I am not familiar with some of the ones mentioned above)?
- The third is that when I do get a good bond, on the samples I have been playing with on the broken fuz, I can pull the inner layer off the composite.

You may call me paranoid . . .

RE: Impact
 

Hi David,

Ian Howard sells a polyurathane glue which is the same as the probond mentioned elsewhere in this thread.

I only picked up a bottle the other night and at this stage I only tested it gluing 2 pieces of balsa together. It seems to work very well and you dont need much of it. The beauty is that it is good gap filling properties and it set of by moisture (humidity)
At $10.00 for a 250ml bottle it is not a bad product to have around the work bench. This is the glue I will use to glue in the crutch in the rear of my IMPACT fuse over the weekend.

Peter

RE: Impact
 

Hi everyone, I will get some pics over the week end and post them Monday. Should put some flights on it next weekend and report back, I suspect that it will be fine and should fly as advertised, I hope!! It has been slow going together due to CARF just sent a new fuzz and that is it, no formers, firewall, tubes and sockets, nothing just a empty fuzz. I'm not b**ching though as I feel they treated me better than other overseas companies might have.

RE: Impact
 

David, I would also add a pair of balsa longerons to the formers, tying the formers together. I believe this is the best solution overall, but the ladder brace assembly solution will work okay also.

The inside surface of the fuse is glass/epoxy and probaly traces of mold release, so a thorough sanding and cleaning with alcohol is best. Definitely use Polyurethane glue that Peter found. It will foam up to fill any imperfections in the joints.

Small pieces of the broken fuse will allow easy separation of the glass and foam wall. The epoxy adheres well to the foam, but once the foam is compromised, the foam becomes granular and the bond is lost. Best to remove the inside skin completely and start over. I know it is hard to do.

regards

mattK