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Old Oct 10, 2014, 04:40 AM
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United States, GA, Savannah
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Another question?

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Originally Posted by electrich View Post
I used some 5 minute epoxy. Have everything prepped and measured before mixing, then work swiftly. Or be lazy and use 15 minute. It doesn't take much to get it to stick. Keep it light.
I was lazy and used the 15 min. epoxy that I have been using for everything else. Seems to have gone OK.

Another question. Should I install the balsa tail fin plug with CA instead of epoxy? I'm thinking if I have to get back into the tail I could use CA de-bonder to remove the balsa plug. Although the balsa is so soft it would probably destroy it anyway. Epoxy would mean a permanent plug installation.

Guidance? Curt

(I'm getting closer, running out of parts. Don't think she will be ready for the air today maybe tomorrow.)
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Old Oct 10, 2014, 05:31 AM
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Went with CA.

Sorry for all the questions. You guys are an invaluable source of information.

I'll let you know when I put her in the wind.

Thanks a lot! Curt
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Old Oct 11, 2014, 09:31 AM
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United States, GA, Savannah
Joined Sep 2009
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Wooo! Hooo! Successful Maiden!

My hands were shaking badly but she flew great with the initial setup. Took some of the elevator throw out, better to start with too much than not having enough. I flew her with a 2200mah for power and a 1000mah for ballast the first flight. She was CG'ing about right on the 80mm mark. The next flights I removed the 1000mah ballast which moved the CG back slightly but she still flew great.

I'm excited! My new favorite plane. Thanks you guys for all your help.

Hope to meet up with some of you at HHAEFI this coming week.

Later, Curt
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Old Oct 20, 2014, 05:22 PM
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United States, GA, Savannah
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Right Wing Available?

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Originally Posted by gquiring View Post
I am so upset today. A 25% gasser made a right turn right into my left wing on my Prelude. It was amazing that I was able to fly it to the ground without breaking anything else. This was my favorite sailplane. Do you think EspritModel sells spare wings?
You guessed it. Lost radio communication with the glider at HHAEFI. She went down in a nose down spiral into the pine trees. Amazingly the damage was confined to the right wing. Of course the horizontal stabilizer mounting washers broke free also. I can deal with that I think but, the wing damage is another story.

Hoping after your incident you might have a right wing available?

Curt aka: Crashmaster
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Old Oct 20, 2014, 09:54 PM
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United States, MA, Grafton
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Post a picture. I smashed up the wing on my Grafas (just a bigger Prelude) pretty badly in New Hampshire a month ago but she was back in the air three weeks later. As long as the spar is intact, everything else can be repaired/replaced.
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Old Oct 21, 2014, 03:03 AM
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Prelude wing pictures

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Originally Posted by tom1968 View Post
Post a picture. I smashed up the wing on my Grafas (just a bigger Prelude) pretty badly in New Hampshire a month ago but she was back in the air three weeks later. As long as the spar is intact, everything else can be repaired/replaced.
Tom, Thanks for the reply. I'll take some pictures tonite and put them up. The wing is in pretty bad shape. I don't think the spar is damaged but I'll have to inspect it closer. So far it looks to me to be a project beyond my skills but maybe with guidance here I could tackle it.

Pictures to follow, Curt
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Old Yesterday, 06:31 AM
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Wing Damage Photos

It's not pretty. The spar appears to be intact though.

Amazingly the rest of the plane looks good!
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Old Yesterday, 07:07 AM
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Nice meeting you at HHAEFI!

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Originally Posted by electrich View Post
I think I'm in space # 40.
Too bad we were on opposite ends of the world from each other. Glad I staggered down to introduce myself though. Had a great time other than the big crash, sigh. Wasn't a great weekend for you in that regard either. Better days ahead.

Later, Curt aka: Crashmaster
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Old Yesterday, 06:38 PM
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Prelude Wing Repair

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Originally Posted by tom1968 View Post
Post a picture. I smashed up the wing on my Grafas (just a bigger Prelude) pretty badly in New Hampshire a month ago but she was back in the air three weeks later. As long as the spar is intact, everything else can be repaired/replaced.
Tom, I'm a novice at balsa built-up wing repair. Do you have any reference material that I can refer to as I put together a plan to repair the wing?

I'm thinking you probably strip off all the old damaged covering keeping track of all the ribs and their location, so you can get sizes and shapes from the old broken ribs. I can use the undamaged wing as a reference also.

It is seems like a skill that you learn my doing. But, I would appreciate any advice or guidance that you guys can give.

Curt aka: Crashmaster
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Old Yesterday, 09:50 PM
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Curt, I'll do my best to explain it in words. Maybe I should have taken pictures of the Grafas as I went, but I was in a hurry. So here's what I did.

I had damage to the center panel, which is straight - that is, constant chord, all the ribs are the same. Then I had damage to the outer panel where it's tapered toward the tip.

I started with the center panel because that's easiest. I traced around one good end rib onto a piece of card stock then cut it out, glued it to a piece of 1/16" plywood and cut that out to the outline on the card. That left it a little oversize compared to the real rib. I very carefully sanded that to as close as I could get to a perfect match to the good rib. Then I drilled a hole, undersize, for the tubular spar and, again slowly and carefully, enlarged it and centered it to fit over the spar. A Dremel tool is almost a necessity for this. That plywood rib then became a template. You can trace around it onto a sheet of balsa, cut out the balsa ribs and sand them to match your template rib. In this way you can make as many ribs and half-ribs as you need. To fit the tubular carbon fiber leading edge, I notched the template rib making the notch too small, then worked it up to size with a jeweler's diamond file. Then that notch can be copied to the ribs. Keep it a little undersize and you can fit each rib to the LE as you go.

Oh yeah, you'll need to buy a carbon leading edge. If some of yours is intact, you can splice the new piece to the old. We'll get to that in a minute.

To start assembling and fitting the new ribs, I worked from the outsides in. On my plane the damage went to one end of each panel so I cut away the damaged forward part of each rib. On some of the ribs the aft part was OK but the glue joint at the trailing edge could be broken loose cleanly. For those ones I took the whole rib out. If the glue could not be separated at the TE then I left the last couple of inches and cut the rest away. All the half ribs came out. Clean the old glue off the spar too. This way I could slide a new rib along the spar past what was left of the broken ones. I got the first and last ribs into place and temporarily taped them to the spar, then held the new leading edge in place tied with broken rubber bands to keep it in place with minimum force. I taped the joint where the new piece of leading edge met the old one. cut the LE parts to put this joint halfway between two ribs. A dremel with a cutoff wheel is ideal. Avoid breathing carbon dust though.

At this point you should be able to see whether everything more or less wants to join up straight. If the trailing edge is sound and the spar is sound, the rest should line up.

Now take off the LE and the end rib and start sliding all the ribs into position. You may find that some of the holes are too small (open them up) or too big (a little too big is OK). If any are really bad, now is the time to make replacements. Tape them approximately in place with masking tape or blue tape, and put the leading edge back on.

Next, wherever you have part of the aft end of a rib still glued to the TE, trim a little off the back end of its replacement rib so you can snug them up right next to each other. Hold them together, aligned as close to perfect as you can get them, with something like a clothespin. using a very sharp X-acto, trim the cut end of the broken rib at an angle, then trim the new rib at exactly the same angle. The aft end of the old rib and the remaining part of the new rib should join up fairly neatly to make one good rib. Just tape the 2 parts together for now.

Once you've done that for all the ribs, trim the notches for the LE on all the ribs so it just fits nicely. Again, just a little loose is OK - glue will fill small gaps. Now snug the rubber bands a little tighter and see if everything seems to fit and tends to stay in place.

At this point I made a sheet of posterboard with a line where each rib would go so I could make sure they were spaced evenly. The it was time to start the rebuilding.

I eopxied just the end of the new piece of LE and firmly butted and taped it to the old part. Then I slid 3-4 ribs out of position just a little and put 5-min epoxy on the spar and LE where they would go. I slid the ribs back into place and made sure everything was held straight while the glue dried. That meant setting the trailing edge and spar on pieces of straight wood and weighting the aft part of the wing down with books, leaving the front where I could sight along it. I also clamped my template rib to the end rib to keep things aligned.

Working along a few ribs every 15 minutes, the major gluing part of the repair is one of the fastest parts. When all that's done, remember all those ribs you cut and trimmed and taped together? Now you can go back and glue them with Titebond, Cut little pieces of scrap balsa, glue the joint, glue a little piece of balsa across the joint and put a clothespin on it. When dry it will be quite strong with little weight gain. Get the top and bottom surfaces aligned as well as you can, even if it means leaving a little gap in the joint - the scrap balsa brace will hold it.

Now we'll splice the leading edge. For this you will want some carbon tube that just slips over the leading edge. Cut a short section - equal to the space between ribs or a hair shorter. The slit this section lengthwise. What you want is a shallow C shaped piece. Epoxy this in behind the LE joint, nesting the LE in the hollow part of the C (does that make sense?)

That's basically it for the straight panel. Repairing the tapered panel is basically similar. The only harder part is that each rib is unique and you may not be able to make a template for each one. The solution is to make a template for the smallest and largest rib you have to replace. Then you cut each replacement rib as a best-guess-plus-a little. make them deliberately a little oversize. Position and tape them in similarly to the above. Carefully test fit and trim the leading edge until all the ribs are correctly positioned and notched for the LE. Glue them in, same as above. the problem now is, they are all too big, sticking out above and below the wing surfaces. These get bar sanded. Put masking tape over the undamaged parts of the wing and the template ribs. Glue sandpaper to a straight metal bar (sanding bar or a carpenter's level). Sand across the assembly until the sandpaper just starts to eat into the masking tape on both ends at the same time, and your ribs will all be neatly tapered between the templates.

If you have any broken plywood ribs, these can usually be pieced back together more easily then balsa. However they also need to be reinforced, since they are plywood for a reason & need to be strong. I made some local plywood doublers to double the thickness of the plywood across the joined areas.

Finally, sand any bits that are sticking up where they shouldn't, and you're ready to cover. Good luck!
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Old Yesterday, 10:13 PM
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Great explanation above. You can do it Curt. It's just time consuming. Pour a cocktail, put on some music and enjoy the ride. (I do my best work late night after the wife and kids are in bed) - no distractions. It won't happen overnight but it can be done. And once it is airborne again you will really appreciate the time spent fixing it.
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Old Yesterday, 10:35 PM
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Fantastic explanation! Thanks a million. When the weather turns I now have my big project. You guys are great, I'll keep you up on the project when I get started.

Your explanation should be made a sticky to help others with their repairs.

Once again, Thanks a million! Curt
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