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Building Tips and technical articles. => Building techniques => Topic started by: Leester on August 29, 2009, 01:20:11 PM
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I've only done one other foam wing and I used epoxy to attach those wing skins. I was watching Windy's foam wing tapes, refreshing my memory on the proceedures and since I had a can of the Super 77 adhesive I thought I'd give it a try. Well it's as easy as Windy makes it look, no problems at all on the R panel. It's alot easier and less messy than using epoxy. Are there any precautions I need to take if I decide to silk span and dope instead of using film ?? I got the skins from Lone Star they shipped the day before they had there fire.
I just bought a Kodak EasyShare digital camera so the pics are ?? Hope they turn out.
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Forgot to mention that the cores are from Crist Rigotti.
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The secound panel went as smooth as the first. The wing is for A. Brickhaus's Bucaneer 746 P, which will be powered by an T&L ST 51. Think I have the camera figured out....Maybe LL~ LL~
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It all looks really good Lee
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I use 77 at work on a regular basis. I've found it to lose its contact ability when things gets pretty hot like in a hot building. We generally double coat what were gluing and usually don't depend on it being the final adhesive especially when using it on Formica or likeness material. I can say that I'm not using it on wood and I've never used it on balsa. I was just curious how it holds up. Are you misting on a light coat on the balsa first ? Due to its contact like ability, do you position a piece of wax paper or monokote like backing over the core then place the skin over it? I've heard of this method before and would like to know. I have a Sig kit with foam wing that I'd be interest in trying. I would imagine this would save substantial weight over using epoxy. I would just be concerned how it holds up over time. Ken
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I've only done one other foam wing and I used epoxy to attach those wing skins. I was watching Windy's foam wing tapes, refreshing my memory on the proceedures and since I had a can of the Super 77 adhesive I thought I'd give it a try. Well it's as easy as Windy makes it look, no problems at all on the R panel. It's alot easier and less messy than using epoxy. Are there any precautions I need to take if I decide to silk span and dope instead of using film ?? I got the skins from Lone Star they shipped the day before they had there fire.
I just bought a Kodak EasyShare digital camera so the pics are ?? Hope they turn out.
Hi Lee,
The wing skins look good, but I'd be careful about using dope on the skins attached with 3M 77. Just don't flood the skin with dope and you will likely be OK. I have seen wings where 3M 77 was used and they looked good for a long time; I have also seen wings with 3M 77 that had signs of the 77 delaminating such as blisters. I'd recommend that you not paint them a dark color as the heat would be quite a bit higher when out in the sun. Kirk Mullinix out here in So. Cal. is the expert when it comes to cutting/building/finishing foam wings.
The only bad thing I see in your photos is the Chicago Bears clock on your bench...you know the Pats are going to win this season! Even with Cutler at QB for the Bears.
Bill
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Kenneth, I sprayed a fairly even coat all over the skins and like Windy showed in the tape better to much than not enough. I just held the foam over the skin and carefully positioned before I placed it down and rocked it back and forth untill attached. Not at all hard as long as you don't have the shakes. Thanks for the heat tip.
Billy, Sorry but I'm totally biased BEARS. VD~ VD~ LL~ LL~ Thanks for the tips on lighter colors, not sure if I'll dope or fabric the wing yet just keeping options open.
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In days of old 3M77 was what everybody used. Because it is a spray it ws sometimes inconsistant in how evenly it covered, and how much weight was added. Epoxy is easier to control that way.
No problem with a normal dope finish.
I have no hope for football season - I am a Lions fan... :'( :X HB~>
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Hi Lee,
The wing skins look good, but I'd be careful about using dope on the skins attached with 3M 77. Just don't flood the skin with dope and you will likely be OK. I have seen wings where 3M 77 was used and they looked good for a long time; I have also seen wings with 3M 77 that had signs of the 77 delaminating such as blisters. I'd recommend that you not paint them a dark color as the heat would be quite a bit higher when out in the sun. Kirk Mullinix out here in So. Cal. is the expert when it comes to cutting/building/finishing foam wings.
I echo this - 3m-77 is well-known for delaminating over time if you get it too hot or get solvent fumes in it. Usually it stays sound structurally but can look ugly. As ling as you are careful with the paint and don't leave it in a hot car you might be OK.
Back in the good old days that's what everybody used and it will probably work as well as it ever did now. I think epoxy is clearly more stable and much lighter, generally.
Brett
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I've only done one other foam wing and I used epoxy to attach those wing skins. I was watching Windy's foam wing tapes, refreshing my memory on the proceedures and since I had a can of the Super 77 adhesive I thought I'd give it a try. Well it's as easy as Windy makes it look, no problems at all on the R panel. It's alot easier and less messy than using epoxy. Are there any precautions I need to take if I decide to silk span and dope instead of using film ?? I got the skins from Lone Star they shipped the day before they had there fire.
I just bought a Kodak EasyShare digital camera so the pics are ?? Hope they turn out.
After seeing about 6 planes have the skins pop, and having that happen to me 2 times I quit using the spray back in the 70s, I have tested this and like sprays and most every other way to glue the skins and in my opinion a thin slow epoxy is best, lightest and forever.
I have sheeted hundreds and hundreds of wings, the only other glue I ever use is latex contact cement. All sheeting i use is sealed first on the inside of the skin with nitrate HS dope, one coat, sanded flat with 400 grit paper. This reduces by half the glue used and gives a much better bond. Plus it helps protect the foam from.
Randy
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Thanks everyone for all the input, looks like I'll have to keep it out of the extreme heat and hope for the best.
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Thanks everyone for all the input, looks like I'll have to keep it out of the extreme heat and hope for the best.
Lee, don't you hate when everybody tells you not to use a product after you already used it? Happens to me all the time.
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I have used the 3M super 77 on several r/c pylon racers and had many flights over several seasons. These planes pull tremendous G's in the turns and I have never seen a skin delaminate. If you cover with plastic film use low heat to iron on the covering. As you mentioned it is much easier and cleaner than epoxy but the eoxy is very strong also.
Don
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Bob, if you followed Windy's procedure it should work okay. Now for the Bears, at least their not like the Chiefs. Had to cancel practices on the field when a white powdery substance was found on the field. They brought in the city, county and state health and science people to check it. Was on the verge of calling the government officials when it was pointed out the substance is used to mark the end zone. Practice resumed after several weeks. DOC Holliday
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But Doc did the end zone show Chiefs or Chefs LL~ LL~ LL~
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Hi lee,
While I personally think epoxy is better, I used 3M 77 on my SV11 back in 1993. It has finally popped up in a couple small areas. I covered the skins and cores with the spray before putting on the skins.
Mongo
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Hi Lee
I can promise you that the spray adhesive 77 does POP loose, I have seen it with my own eyes many times, had it happen to my planes also. And I have talked with people all over the country that has had the 77 POP loose.
This has been going on for decades now.
IF you just want to use a contact cement, try to get a bottle of Dave Browns Sorghum. it is far far better than 77 is.
Paint on 1 coat of full strenght dope on the glue surface of the wing skins, let dry, buff down the raised grain with 400 grit paper, and apply the contact cement...this works very well for most any type glueing and help tremendously in weight savings and getting a better glue area
Regards
Randy
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Beings he has them done already and reqady for paint. Don't use dope for the first coat. Get a can of water base poly-urethane or poly acrylic to seal the wood. Then goe with the finish you want. I have ljust pitched a slow rat wing I used to cut and do that was done with contact cement, another with epoxy, they were both loose, skins popping off the foam. Guess moisture in the basement got to them. DOC Holliday
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Applying a skin to a foam wing is a chore. I have used 77, epoxy, and a couple other items. My favorite one that I settled on some 25 +/- years ago is to use one of the off-white carpenter's glue thinned 50-50/60-40 or about, with water. Now this takes a lot of time so if in a hurry, forget it. It has worked well with balsa skins and 1/64 plywood.
Once you are ready, with thinned glue, brush on a coat on both the foam and the mating wood side. Press together, do both wing sides and place back into the foam blocks from which the core came. When all is aligned as you want, apply a LOT of weight. Old magazines are very good as the weight can be fairly evenly spread.
Now tend to business for a week. Remove the weights and the foam outer blocks. BE STRONG as you will think the wood is rotten. After a day or so out, the wood will dry out and look much better. Then back into the foam blocks and go about your business for another week. Again remove and let dry for a couple days then finish as you so desire. If this is a serious project, finish painting can be expedited by an application of thinned finishing resin, epoxy easier and less smelly, but polyester works well and sands easier. You have a nice base to finish, and the wood will not separate from the foam or at least it never has for me.
Just the other day, I was looking at an old model in the barn that is some 20+ years old. A good hard finish (polyurethane) is still there and no pop-ups (this one is 1/64 ply). The barn has no airconditioning and everything there is subject to the heat, humidity and cold of the South East TX climate.
It is a good procedure, however the long drying is IMO what makes said procedure work so very well.
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Any experience with CA foam compatable stuff for this job. The LHS had some , said it was foam compatable. Just wonder how it would fair in the long run.
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I've only done one other foam wing and I used epoxy to attach those wing skins. I was watching Windy's foam wing tapes, refreshing my memory on the proceedures and since I had a can of the Super 77 adhesive I thought I'd give it a try. Well it's as easy as Windy makes it look, no problems at all on the R panel. It's alot easier and less messy than using epoxy. Are there any precautions I need to take if I decide to silk span and dope instead of using film ?? I got the skins from Lone Star they shipped the day before they had there fire.
I just bought a Kodak EasyShare digital camera so the pics are ?? Hope they turn out.
I've got two 20 year old models that I attached the skins with 3M 77 and they have not delaminated. They are painted white with a small percentage of the total wing area painted red and blue. They've been in hot cars and vans all over the country so as long as you have good cleanliness on the foam and balsa when spraying the glue on, it'll probably last a long time.
Chris...
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That's good to hear Chris, I did follow Windy's instructions as far as the sanding and vacuming went so I should have gotten them clean enough. I have them epoxyed together and made up the adjustable lead outs, the first time I did this type. Just have to finish the weight box and outboard tip. Time will tell but the spray sure is easy enough.
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On BIG thing to watch. there are now two versions of 77. One will EAT foam.
It is due to various states air pollution laws.
I have switched to 3M 9020 (IIRC) that I get from the styrofoam section of the local Michael's craft store.
Another glue to try is polyurethane (Gorilla Glue). It can be applied very thin and relying on the foaming action to fill the pores of the foam.