n00bs Gonna Build a Carden

[gareth.ky]

The first step in the Carden manual is to make sheeting for the various parts. I don’t want to stray too far from the manual but I was afraid that the sheeting might get damaged in the shop while I did the next few steps. I’ll do the sheeting at the last minute before its needed. I have a very generous offer to use some professional layup tables for skinning the flight surfaces on this project. So I’m going to work on getting them all skinned before I go any further.

The first big decision I had to make in the build was where to mount the servos in the wings. I really wanted to run 1 servo in each wing but I just couldn’t bring myself to do it. Saving 4oz and $300+ was really tempting. It probably would have worked just fine. I just don’t know enough to make that call so I went with the recommended 2 servos. My limited experience with model airplanes has been that servos are the worst place to be cheap.

I drew up the tapered ailerons to the dimension indicated on the plans and they looked fine to me. I just extended the aileron 1″ towards the wing root. I split the length into 4 and put the servos at the 1/4 marks, biased towards the root by 1″. Another big question was how far the servos should be from the hinge line. I looked at a bunch of build threads and came up with the magic number of 2 1/2 inches. I wouldn’t be surprised if they could be closer, there is enough thickness in the core for it.

I made up some servo boxes using the supplied servo rails (lengthened to 2 1/2 inches) and some 3/32″ ply. I made a little fixture to assemble the boxes so they where square. The main reason for the boxes it to make sure the servo rails go in square. The box internal dimensions are 21mm x 41mm. Standard servos are metric and about 20mmx40mm so the extra 1mm gives a little play. I used a paper template and the Dremel router to mark and cut pockets for the servo boxes. I just did the routing free hand and it worked out well. Just have the shop-vac handy to clean up the mess!

The tunnel for the servo wire is up next. I cut it with the Dremel to the same depth as the bottom of the servo cutouts. I did two passes guided by a straight edge to make it wider. The servo wire can wrap under the servo and into the tunnel and pass out of the servo box through the arch in the ply support. Study the plans and pick a spot on the side of the fuse clear of obstructions and run the channel out to that point. My exit was about 11cm behind the wing tube.
Finally I installed the servo boxes with Polyurethane glue. Once the first wing was finished the second one went much faster. I swear, the hardest part is just getting started!

On the the stabs. The plans call for a servo box up against the root of the surface. You don’t have much room to get creative here or the front of the servo box will come out of the bottom of the core. Also be careful not to put the servo over the tube socket, check the plans. I put the servo box 5mm in front of the stab, parallel with the tube (which is parallel to the hinge line) with one corner just touching the end of the foam.

I got my first scare after doing the first stab. I thought I had done it upside down! Then I checked everything over and it was alright. Unlike the wings, where there is an obvious left and right half and stabs are both identical cores. They both have the same side marked as “down” and that was what threw me off. If you follow that you will make two left stabs. You have to flip one over ad cut the ‘up’ side so you have both a right and a left. When you sheet them always put the side marked bottom on the table. One stab will be upside down in the shuck and the other upright. Confused yet? Good!

The whole ‘down’ side business is important. The bottom shuck has a perfectly flat surface but the top shuck is not flat. Sheet them upside down and you could warp the surface.

On to the wing tube sockets. I put the little dowel through the tube and added the 1/16″ balsa end cap, no problem there. Then I tried to fit the tube socket support plate and had my first real DOH! moment. At this point I had never picked the cores up out of the shucks for fear of causing damage to the foam. So I didn’t know that the hole the support plate goes in is cut clear through the wing core! I started jamming it into the slot and wondered why is was so far off center. I cut some material off one side. Luckily I realized my mistake before I cut too much for it to make contact with the wing skins on both sides of the wing.

Coat the tube and support plate up with lots of PU and do the push and twist ;-)

[gareth.ky]

Added pics of the H-stab servo locations and some to explain my confusion over the stab cores.

[HuckinChikn]

Lookin good, boss! your gonna have it finished by the time the St. Louis Huckfest
rolls around in 08, riiiiight???

[gareth.ky]

Hopefully long before that! First contest in South Central is at the end of March. I need to have it trimmed out by then.

[gareth.ky]

I put the second wing tube socket in last night. Not much time to work on the project this week. Too many late nights at work.

I guess humidity has dropped to 0 around here. When I took the weight and parchment paper off the joint this morning some of the glue was still sticky! When I do the wing skins I'm going to mist the cores with a spray bottle to make sure the glue activates.

[gareth.ky]

This weekend I took on step #1 from the manual, make the skins for all the foam parts. I gotta say this is one of the more mind numbing and labor intensive parts of the build. There is a technique you need to follow to get good results. The quality of this work will eventually play out in the covering so its best not to cut corners.

The sheeting in the kit comes “edge trued”. This means that the long edges of each sheet should be a mathematically perfect straight line. The lines don’t have to be parallel, just straight. As it was I found that just about every sheet in the kit had was slightly bulged in the middle. Sometimes its ok to just bend the sheet and hold it in place with masking tape. Most of the time you should sand the edge to make it straighter. I say should because you don’t have to, you could just fill the gap with glue. Of course I’m some sort of perfectionist so I had to go and true the edges myself.

Walt(ref) has a fancy rig(ref) to true his sheeting. I didn’t have one so I improvised. The edge of the door that tops my workbench is very straight. I just moved the sheet to the edge and held it down with my large ruler. Then I took a 12″ T-Bar sander and sanded it square against the door. You wont have to take off much, the sheets are already 90% there.

I used a gram scale to weight all the pieces and split them up into piles of lite, medium and heavy. On the flight surfaces I put the heavy wood over the wing tube area and the light wood towards the front and back of the panel. On the other panels the wood has already been sorted and cut so you don’t really have any decisions to make about how to use the wood.

Once you trial fit the sheets and don’t see any big gaps its time to tape the seams together with 3/4″ masking tape. Here is the first bit of technique: rub the tape in hard so glue can’t get under it. On the first wing skin I didn’t press hard enough and got a lot of extra glue under the tape. the rest of them I really got it stuck down and the glue cant go anywhere. Once the skin is taped together its time to glue the seams. What worked best for me was to work 3 seams at a time. Apply the glue, remove the excess and then tape across all three seams. This makes for faster work and fewer pesky bits of tape to remove when its all done.



To apply the glue you are going to need some sort of syringe type device with a fine tip. I went to the local Walgreens and asked the pharmacist if they had any syringes and got a freebie! It came without a tip thought so I had to make something up. I cut the end off a dropper that I had for applying CA, I get them at my LHS. If you cant find these then the CA tips available at Hobby-Lobby on online may also work. Either way plan on having this tool before you get started. Even blunt tipped syringes cant be had at a drug store in the USA.



Once each panel is complete I found that it wanted to curl up due to the tension in the tape. Just flip it back over so the side with the seams taped is on top. I used books to hold the panel flat as it dried. I knew I would need that calculus book for something! I left each panel under the weight for about an hour. They come out very flat and uniform, much more so that some pics I have seen of other builds online, so I think I’m on the right track. I did some of the smaller skins first to get the hang of it and they went pretty well. I was using an old credit card to scrape off the glue and I didn’t realize that it had some bumps on it. This put some long scratches in the skins. I switched to a different tool, a soft silicone spatula, for removing the excess glue and this worked much better.



I had a couple of screw ups this week. The instructions show the rudder and fin (v-stab) coming out of some 48″ planks with some scrap on the end. the instructions even list these planks on the materials list. Last week I used some of the “scrap” off the end of a 48″ plank as end caps for the wing tube sockets. Turns out that the only 48″ planks packed in this kit are for the wings. The other bits come pre cut in bundles and that “scrap” isn’t in the kit. Luckily i didn't cut very much off the end so I was able to use the piece for the leading edge of two of the wing panels, cut diagonally.

I also managed to screw up the first wing panel by forgetting to include on of the planks. Not a difficult mistake to correct though. I just split on of the planks and inserted the missing piece. You would have to know it was done wrong to spot the mistake.


I still have a few more skins to do this week. I’m going to get them all done now because this part of the build is boring.

[gareth.ky]

I'm about 1/2 way through sanding all the skins out. What i have is medium (150) grit paper. This pass is just to knock down the seams and blend everything together. After the skins are applied ill do a pass with 220 grit and fill any holes/dimples with filler. Then a final pass with 400 grit. Still even with the 150 grit its looking great already.

I hate balsa dust. I have had to put on a dust mask for this bit. Its just too much. Its a good thing I put the paper filter on the vacuum too because its totally clogged now.

[rc4flying]

	Quote: Originally Posted by gareth.ky
	I'm about 1/2 way through sanding all the skins out. What i have is medium (150) grit paper. This pass is just to knock down the seams and blend everything together. After the skins are applied ill do a pass with 220 grit and fill any holes/dimples with filler. Then a final pass with 400 grit. Still even with the 150 grit its looking great already. I hate balsa dust. I have had to put on a dust mask for this bit. Its just too much. Its a good thing I put the paper filter on the vacuum too because its totally clogged now.

You say that you will do the 220 and finer sanding after the skins are applied. Just my 2 cents worth, but in all my Carden builds, I have found it easier to do all of the sanding right up through 400 while I can have the balsa skins laying flat on the table. I get better results this way. This way, when putting on the LE and TE pieces, there is only a final touch up if done correctly.

[gareth.ky]

	Quote: Originally Posted by rc4flying
	You say that you will do the 220 and finer sanding after the skins are applied. Just my 2 cents worth, but in all my Carden builds, I have found it easier to do all of the sanding right up through 400 while I can have the balsa skins laying flat on the table. I get better results this way. This way, when putting on the LE and TE pieces, there is only a final touch up if done correctly.

Thanks for the tip and for dropping in on the thread!

I'll give it a try this week.

[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.