Last Saturday I was helping one of our new members. He had just soloes about 2 weeks earlier so he put together his "second plane" The plane was an old Seagul Plasma ARF low wing sport plane that apeared by all counts to be a good choice for him since he trained and soloed on a 40 size Space Walker. This was however his first complete assembly. Anyway, we are at the feild going ove the build and checking controls for proper direction and movement. I noticed the elevator halves were not aligned properly (one was up the other was down) so we made the adjustment. I then asked him, "You did balance the plane right?" He assured me he did. He wanted me to maiden the plane for him. Satisfied with my inspection I agreed to take it up for him. As soon as the plane broke ground it started climbing. elevator input was very touchy and to make things worse the ailerons needed an excessive amount of trim and were sluggish to respond. Knowing altitude is my freind here I get the plane up as best I can and trim the plane as well as possible. I finally get straight level flight but still have a very sensitive elevator. Many here have already guessed. The plane was very tail heavy. I managed to get the plane on the ground in one peice and said, lets check the ballance. We drained the tank and I flipped the plane inverted to see where it ballanced. It was then that I discovered it was about 1.25 inch behind cg and he told me he ballanced the plane upright, not inverted. After adding about a half of pound to the nose the plane flew great. He did not fly the plane this day. Sunday he's back, with the plane ready to fly. He makes a few warm up flights with his Space Walker then puts the Plasma together. He takes off like a warbird with a long roll out on the mains with the tail flying. Beatiful enough to make his instructors eye tear up. He flys for about 20-30 seconds then during an aileron roll one wing seperated from the rest of the plane. It was horrific watching the plasma spiral away to the ground while the wayward wing panel fluttered aimlessly down. Upon crash recovery it was observed that the main spar channel in the wing that seperated in flight had no significant damage. The spar itself seperated cleanly and had a nice shiney coat of epoxy thinley spread over it and no evidence that it had adheared to the spar hannel in the wing. The wing halves were joined with too little epoxy and was only held on by the epoxy between the two root ribs of each wing half. The plane only lived for a day and a half. It only had 2 and a half flights. But it tought the owner and this guy a few things

That's a tough one because, as an instructor, you can only check so much. Who would ever think of checking the spar for proper glue.. how would you do that, anyway.

One thing I learned from my instructor was to slobber in the epoxy until you can't get any more in (the spar slot in the wing) then push the spar in. The glue oozes out so it's just wiped off then the wings are joined, aligned, and the glue allowed to set up.. I let them go for 24 hours.

That must have been really tough to see that fine plane go in like that with that helpless feeling you get when you know it's to late to do anything.

CGr.

I like Gorilla Glue for joining wings. Wet the socket in the wing halves and paint a light coat of Gorilla on the dihedral brace/wing joiner. The Gorilla glue foams up to fill all the space. You do have to tape the wing halves together and check every 30 minutes or so and wipe the excess glue foam off. It will push the wing halves apart if the socket isn't tight. I have never seen one of these fail. I have seen failed epoxy joints where the glue was only stuck on one side due to a loose socket.

Buy a small bottle of Gorilla and after you use it, squeeze all the air out and replace the cap. It lasts longer this way.

Getting back

No, there is no way to check the wing spar but I described the process to him for next time pretty much as you just did. As for Gorilla Glue... I will have to try it some time. I've never had an epoxy job fail on me (knocking on my wooden head) But I'm not afraid to try new meathods.

I have found that in situtions such as these, hitting the joint with a heat gun after slathering on the eopxy makes it flow like water. You can control its flow with the heat, and becuase while it is hot and flowing like water, it penetrates the wood better and fills the gaps more fully. A by-product seems that the heat shortens the curing time without losing any of the strength of a good epoxy joint. All pros with no cons.

That would work well with a kit built plane but to get the epoxy hot enough in an ARF your covering would be destroyed.