n00bs Gonna Build a Carden

[rc4flying]

Plus, one other thing I forgot. I only spend the extra sanding effort on the side that will be showing when done. The glue side of the sheeting, I just make sure there are no major glue drops or offset seams to interfere with the glueing to the cores. Heck, 150 is good enough for the glue side. Besides, you want to leave some wood so you can give the showing side a good sanding job. Also, vacum the wood often or otherwise you are sanding balsa dust over and over.
Again, Just my way of doing it.

[gareth.ky]

Gotcha.

One thing I noticed is in some places the seams are still a bit rough after sanding with the 150 grit. Mostly where the seam is lower than the surrounding wood. I figured it would be easier to get to the seams after the skin was curved over the foam. I was concerned about how much material I was going to sand through to get to those areas on a flat surface. Still I would just have to touch those areas up afterwards and not do the whole thing.

[gareth.ky]

I am down to 400 grit on all the panels now. It worked out really well, thanks for the tip rc4flying.

I would almost skip the 220 grit step. I switched to 180 grit on the first pass and then straight to 400. When I did the 400 grip pass I kept a small sanding bar (12") with 180 grip paper and switched to that whenever I saw a seam or something that needed material removed.

If I had this step to do over I would do all of the one sided panels first and get the technique down. The elevators and rudder panels are cut from one sheet so both sides have to be almost perfect. If I had done them after I learned how to make the joints really well I would have had less sanding to do. Some of the later panels like the hatch are almost perfect on both sides and required only minimal sanding.

The shop-vac is a must. Use a paper filter and put some water in the bottom to help catch the dust. I'm still finding dust on things.

Soon I should be ready to start skinning things!

[rc4flying]

	Quote: Originally Posted by gareth.ky
	I am down to 400 grit on all the panels now. It worked out really well, thanks for the tip rc4flying. I would almost skip the 220 grit step. I switched to 180 grit on the first pass and then straight to 400. When I did the 400 grip pass I kept a small sanding bar (12") with 180 grip paper and switched to that whenever I saw a seam or something that needed material removed. If I had this step to do over I would do all of the one sided panels first and get the technique down. The elevators and rudder panels are cut from one sheet so both sides have to be almost perfect. If I had done them after I learned how to make the joints really well I would have had less sanding to do. Some of the later panels like the hatch are almost perfect on both sides and required only minimal sanding. The shop-vac is a must. Use a paper filter and put some water in the bottom to help catch the dust. I'm still finding dust on things. Soon I should be ready to start skinning things!

Sounds like you are progressing nicely.

As for that dust thing, my wife hates everytime I sand my plane's skins, she finds dust for days, and she don't like it.

Keep up the great effort, guys are here to help whenever needed.

[gareth.ky]

I cut myself and bled on the hatch so the project is gonna be a success!

Seriously I skinned the hatch and the belly-pan is setting up now. Also the weight saving has started.

[gareth.ky]

I tried two different techniques for spreading out the poly glue. First is the credit card method. I actually used a "Bondo" scraper I got from Home Depot. It worked well and let me reduce the amount of glue on the skins pretty well. It didn't do a great job of laying on an even layer of glue though.

I went looking around and found this build thread by By Terry Brox. I tried the little foam roller on the rudder skins and the result is a really thin uniform layer of glue. I really like the result and I would prefer to use this tool but I'm not sure if it left enough glue though. I would guess that I am using 1/2 an oz on each skin so far.

I have read several threads where builders have said "less glue more weigh". Is there such a thing as too little glue?

I also noticed on the rudder that at some points along the edges the panels did not contact the foam. There wasn't enough glue to foam across the gap. I'm pretty sure this is isolated to the edges of the core and I'm not too concerned. Its probably due to excess melting in in these areas. The bulk of the core looks to be well adhered. I guess I wont really know until later this week when I cut into the rudder. I'm going to get that done before I do the wings to make sure its done right.

[gareth.ky]

I did a test swatch with the roller to see what kind of penetration I was getting into the foam. I tore up the test piece and the adhesion between the foam and the wood was very good. No peeling or separation, the wood cracks before the bond breaks. The glue went down into the foam structure about 5mm or about 1/5 of an inch.

Is that enough? Do you all generally see more penetration than that?

I would rationally think its enough. Its composite structure and as long as the wood is properly adhered to the foam its will be strong. The wood is there to resist tension and compression loads across the parts surface. The foam resists compression. On the test panel I can't break it in my hands in tension.

[why_fly_high]

You need enough glue so that the penetration from both sides of the wing reach each other.

I am just messing with you. I would be pleased with the bond you got.

Dan

[gareth.ky]

It varies from 1/8 to 1/5 in places, depends on how porous the foam is. I sent a PM to Walt to ask him about it and he thinks its enough glue. I think we are good to go, I'm sold on the roller.

[gareth.ky]

On with the Sheeting. I did the Belly Pan, Hatch, both H-Stabs, Rudder and Turtle Deck in that order. Then I got help from Dan to do the wings (Thanks Dan!).

I used the method I like best for spreading the glue is a small foam roller that you can get at Walmart. This really gets a nice thin layer of glue evenly all over the sheet. Just keep rolling until the sheet turns a uniform color and you don't see any big globs of glue left on it. For the wings I think I used 6oz of glue and at least 1oz of that is waste that ends up in the roller. So at most there is 1.25oz of glue on each skin. Each wings had at least 400lbs on it.

I put parchment paper between the shucks and the skins. The upside of this is glue can't get through the skins (and it will!) and stick the part to the shuck. The downside is the parts tend to move around very freely until the weight is applied. Take some care and time to align the part with the shucks so its sits square. I used about 300 pounds of weight on all of the other parts in the form of various concrete blocks I got for a few cents each at Home Depot. Even with all that I didn't get good adhesion around the edges of some parts. I guess the gap between the shuck and the part was just wider there. Vacuum bagging would really help with the edges and I would probably go that rout if I was doing it again.

You want to take some care with the rudder sheeting alignment. I just joined the Fin and Rudder sheeting parts with masking tape over the plans so that they covered up the whole rudder. Put the foam over the plan and make some reference marks so you know approximately where you want the sheeting to lay down. Try and get the seam to run through the area that will be cut out for the hinge line. Don't do anything stupid when cutting off the excess sheeting. Use a sharp blade and then a sanding block to make it smooth. I chipped some parts with a dull blade and I'm regretting it now. A hobby saw works well for the curves.

So I'm sure you can see the holes in some of the parts. The hatch, belly pan and turtle deck are all cosmetic parts. They don't contribute much in the way of strength to the model. So they make great targets for lightning. I'm going to guess that I saved about 5oz off the airframe and much of that is from behind of the CG. This technique leaves the part fully sheeted so its easy to cover but it avoids large chunks of foam and the glue that goes with it. Here is the HowTo:

1.) Mark a reference line down the center of the part and the center of the sheeting.

2.) Make a template of the boundaries of 1/2 of the part.

3.) Draw your cutouts on the template and cut them out. Be smart, do triangles or cut in the same direction as the surface curvature.

4.) Place the template on the reference line and mark the cutouts. Flip and repeat for the other side.

5.) Cut out the foam with a Dremel router or hot wire tool. IMPORTANT: Keep the tool perpendicular to the surface. Put cutouts back into place with a loop of tape.

6.) Place overlapping strips of masking tape on parchment paper and cut out shapes.

7.) Use the template to position the cut out tape over the part.

8.) Then just spread glue as normal, peel off the tape and carefully align the foam part with the reference mark on the skin. Set up the part in the shuck as normal. When the glue dries you will have to pull out the routed foam pieces, none of mine stuck to the wood.

I tried a few different procedures on the hatch and belly pan. The above steps are more involved but the result is the best. The turtle deck isn't trimmed yet and it weighs 2.5oz (72g). 20g of foam was removed. I don't know how much I saved on glue because I had to work fast and didn't get the parts on the scale.

[capflyr]

Gareth great job I love the pics keep em coming your making it look so easy.

[gareth.ky]

	Quote: Originally Posted by capflyr
	Gareth great job I love the pics keep em coming your making it look so easy.

Don't be fooled, its a lot of work. Not too hard, just a lot of it. Everything about this project is big. I guess I'm about 1/3 the way through construction in 4 weekends and I'm single so I have the spare time. I don't want to discourage anyone, I'm really enjoying doing this build, just know what your in for.

This project is eating lots of 'stuff' too: 3 rolls of 3/4" masking tape, 3x 8oz bottles of Gorilla Glue ($12 each!), 3 dust masks, 4 rolls of parchment paper, 6 foam rollers, 3 sheets of poster board. I'm learning to buy consumables in bulk. I'm considering buying stock in 3M. I may be on a first name basis with all the cute checkout girls at Home Depot before this is over

I'll keep the pics coming.