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Building Tips and technical articles. => Building techniques => Topic started by: BillLee on February 03, 2013, 04:19:12 AM
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Getting ready to put 3/4 oz glass on a balsa structure (sheeted foam wing).
What is the technique that will result in the glass adhering to the wing without adding a lot of weight?
Many years ago I simply used clear K&B epoxy paint. Worked well. Soaked clear through the balsa and was heavy as the dickens. Has to be a better way.
Light sprayed coat of nitrate on bare balsa? Then use thinned epoxy? Or what? How?
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My favorite way, one of which I've used for close to 30 years on or off is to apply a medium coat of Aquanet hairspray to the balsa surfaces, when dry, lightly sand with 360 or 400 no-load paper. Now carefully vacuum or blow off all the sanded areas, lay on the cloth removing all the wrinkles as necessary. If you're using a quality epoxy finishing resin, mix as needed, a note here is to adjust the hardener to resin ratio by adding about 1 to 2% more hardener in the mix. This will assure that the resin will cure in the cooler weather this time of year. Something I found that helps the final sanding and finish quality is to add no more than 5% baby talc to the fully stirred epoxy mix. Apply the resin in a standard manner starting from the center of a panel with a small puddle and carefully squeegee outward toward the edges of each panel.
When all is fully dry, block sand the surface with 220 gray no-load paper. If you have an air supply keep the paper clean by blowing it often. At this point you should have a pretty flat uniform surface to apply primers or whatever.
Regards.
Dave
ama 41041
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I have used Z-Poxy finishing resin for many years. Apply the cloth with it, squeegee with a card to remove a major portion, then wipe it off with a paper towel to remove most of the excess. I use dope and talc to fill it.
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My favorite way, one of which I've used for close to 30 years on or off is to apply a medium coat of Aquanet hairspray to the balsa surfaces, when dry, lightly sand with 360 or 400 no-load paper. Now carefully vacuum or blow off all the sanded areas, lay on the cloth removing all the wrinkles as necessary. If you're using a quality epoxy finishing resin, mix as needed, a note here is to adjust the hardener to resin ratio by adding about 1 to 2% more hardener in the mix. This will assure that the resin will cure in the cooler weather this time of year. Something I found that helps the final sanding and finish quality is to add no more than 5% baby talc to the fully stirred epoxy mix. Apply the resin in a standard manner starting from the center of a panel with a small puddle and carefully squeegee outward toward the edges of each panel.
When all is fully dry, block sand the surface with 220 gray no-load paper. If you have an air supply keep the paper clean by blowing it often. At this point you should have a pretty flat uniform surface to apply primers or
whatever.
Regards.
Dave
ama 41041
Dave is correct regarding the use of Aquanet hair spray. I've used this method for years to keep the edges of glass cloth and Koverall from unravelling when cutting. I lay out the cloth on wax paper and spray a line of hair spray along the line I plan to cut. Let it dry and use your favorite cutting tool (scissors, electric scissors, x-acto, etc.). I cut the wax paper along with the cloth to prevent having to lift the cloth off the paper. This also keeps the scissors from walking around while cutting. Handle carefully when removing the paper and only touch the cloth along the sprayed area. Don't touch the unsprayed area. Prepping the balsa surface with the hair spray prevents snags as you lay the cloth on the dry surface. Since the balsa is not wet, you can smooth the glass into a perfect fit before wetting. So much easier!
Paul
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Bill,
I used glass cloth and resin for years, I mean years, and on plenty of models!
In all honesty, I'm starting to re-think all of this. Not sure any more if that "old," if you will, method is still popular?
Look at the models of the accomplished builders and finishers, they are using CF vail and dope! Unless I'm wrong?
Here's a clear example. I believe Derek used CF Vail on his fine Cutlass also.
Correct me if I'm wrong here.
I'm a bit away from covering with my current build, but when the time comes, I plan on digging in and finding out a bit more about this CF vail method, it appears as though it's catching on. There HAS to be something to it. There's always a reason.
Charles
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Bill,
I used glass cloth and resin for years, I mean years, and on plenty of models!
In all honesty, I'm starting to re-think all of this. Not sure any more if that "old," if you will, method is still popular?
Look at the models of the accomplished builders and finishers, they are using CF vail and dope! Unless I'm wrong?
Here's a clear example. I believe Derek used CF Vail on his fine Cutlass also.
Correct me if I'm wrong here.
I'm a bit away from covering with my current build, but when the time comes, I plan on digging in and finding out a bit more about this CF vail method, it appears as though it's catching on. There HAS to be something to it. There's always a reason.
Charles
Since I know Bill, I seriously doubt that he is building a stunter. More likely a racer of some sort. He probably needs considerably more compression strength that the Carbon Veil would afford. Hence the glass cloth and epoxy...much stronger. probably too heavy to consider for a stunter and unnecessary.
Although I know someone who will probably disagree with that statement (F4F Guy) and he is truly a master builder. Most of us cannot accomplish his methodologies.
Randy C.
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Most use .2 oz CF vail (mat) and apply it with clear dope, so they should not be expecting any strength from it. If you wanted strength, you'd surely use .5 oz CF vail and apply it with epoxy.
I have yet to use either, but I have used .6 oz FG/epoxy on F1A glider C-tube wings. SOP among the FAI FF guys is to put it on at a 45 deg. bias, for maximum strength and particularly torsional strength. Two thin coats of clear nitrate precede the glass/epoxy. Lay the glass on the lightly sanded surface and apply epoxy. Z-Poxy finishing resin would be perfect. Brush it on, get the stuff down smooth, and roll off the excess with a roll of TP. As the TP absorbs the excess, tear it off and dispose of it. You are looking for a uniform, matte finish with no glossy areas. It works very well on FG, dunno about CF vail, but I'd sure try it.
Some F1C guys would aggressively sand this until it was smooth, which cuts the strands in the weave, and reduces the strength radically. It does provide a very hard surface and pretty stiff, if not strong. I gave it a few coats of clear nitrate, sanded it lightly, and covered with tissue and more clear nitrate. Weight and visibility were a lot more important than smooth or shine, since we hoped to be viewing our planes from at least 200' and sometimes 3,000'.
The glider shown was one of three identical, built as a batch, in 6 weeks while working full time, from blank paper. That included designing and fabricating the three towhooks with a new timer start system. The wing is built much like a stunter, is roughly 5/16" thick, with 1/32" sheeting and cap strips over 1/16" ribs. Spruce spars. I found out these wings were plenty strong, but too brittle.
H^^ Steve