gobigdave

Matt, thank you for this great build thread. I have a quick question. How did you cut the holes in the ribs for the wing tube? Did you do it one at a time via a hole in the foam template, or did you stack the aligned ribs and drill?

MTK

Dave, that question has a considerable answer. It wasn't a straight forward thing on my particular set-up. I'll explain further down.

To your question: You need to know where your tube needs to go on the root, LE to TE. Plan your spars according to the tube socket. It's best to straddle the socket as much as practical. You also need to know how much dihedral angle you want. One convenient way to install the socket is to locate it such that the wing is flat when you have it upside down on your bench. For a flat top, the wing center line will have to be located about 11-14 mm below the thrust line for minimal to no roll couple with applied rudder.

That's true for classics and 2 meter types. Not for 40% types though. See, the classic span and thickness is only mildly different than the 2 meter wings. The dihedral angles when built similarly are very similar. For 40% tho, the span is much larger and the thickness is usually larger. The dihedral angle can be quite different, as much as 2 degrees different, which will require different placement on the fuse for zero roll couple.

You have to get the root ribs and the furthest most ribs that will house the socket, for both panels, identical. These are the major support ribs which require some plywood reinforcement. Cut one set perfect and match the other set. This took some time to get perfect, requiring a sanding tool made from an aluminum tube with coarse paper installed. The socket fit easily through each hole with practically no play, but wasn't snug.

The main consideration is getting the wing to fit perfectly onto the fuse and knowing, with your taper, where to cut the hole on the far rib such that the wing is fitted perfectly. The wing tube is straight of course so it's a good guide.

Once you have the root ribs and far ribs matched, left and right, the ribs that straddle the socket in between are cut accordingly. For a flat top wing, just measure the length between the top of the ready ribs and the top of the socket. In my case that length was 11mm. That length must be the same for all ribs such that the wing top is flat. The top location in each of the in-between ribs is marked accordingly. Then the fore-aft location is needed again to fit your taper. I cut these holes a little oversized (1 mm) to accommodate any slight misalignments.

You can cut the holes on the rib stack if aligned, but chances are good that the final fit will require slight adjustment to each rib hole individually. What you want is a socket that just slides in before attaching the top sheet.

In my wing tool, the existing socket screwed things up a bit. Turned out that the hole in the three outward ribs was too low, interfering with the spar. I had to reposition the holes such that the socket fit exactly in between the two spars. Not a big deal, I just filled in and added silkspan to the ribs around the socket holes for extra support.

Hope that helps. If you need more explanation please ask.

bandicootf16

Hi Matt

I have been following your build with interest. Lots of great information and ideas. I have a few questions if you don't mind.

How did you cut the foam wing and how did you allow for the rib thickness. I think you said you did it by hand but how did you achieve the accuracy needed to get square cuts.

What is the blue tape on the cut wing. What is it doing.

What glue did you use to attach the spar to the wing skin.

What glue did you use to tack glue the ribs

How did you attach the rib blanks to the cut core sections for sanding. Did you mark then cut the ribs with mininal sanding.

Thanks
David

gobigdave

Thanks, Matt. I think I got your process. I'm working out a plan to start a classic pattern bird using the lost foam method. My original thought was to cut the hole in the foam template following the method from Terry Brox (http://www.mackrc.net/patternwings2/pages/22.htm). Once I have that hole cut in the foam, I can put the ribs back in and mark each rib, one at a time. I will need several spacers to make this work. Also, if I can get the cores cut with dihedral already there, I can use the shucks to align everything up. To be as accurate as possible, I think I will do both methods. Measure twice, cut once. Right?

Thanks again for the great info. I've done plenty of straight foam wings. I'm challenging myself to a built-up, 2-piece wing this time. However, I'm struggling with how to get everything straight and flush when the fuselage side an airfoil shape. It should be interesting.

MTK

Dave, the solution to the airfoil shaped fuse and mating the wing to that shape is fairly straight forward. I left the sheeting 1/8" long at the root to do a final fit after the wing was completed. I planned for the skins to be extra long spanwise. Locating the first rib onto the skin (which overhangs the husk by 1/8") is the key alignment. Once the first rib is located the location of the remaining ribs is trivial.

One may then cap the wing root or leave it open. It won't hurt anything to leave it open

Get as good a foam wing cut as possible from preferably heavier foam. The husks are your beds for building the wing. The foam stations you have cut are your spacers for the next rib. The next rib simply butts against the foam. One thing you should pay extra attention to is the rib tail; all rib tails must be cut precisely since they will be used to locate each rib on the skin TE.

Please note that I did not cut grooves for the spars in my stations. I did that on purpose. The lower spars are on the skin already of course. The foam station touches the spars when locating the ribs but doesn't go all the way down to the skin on purpose. Staying off the surface keeps it out of the glue. The foam stations are left in place until all ribs are installed and tack glued.

MTK

Answers in red David

bandicootf16

Hi Matt

Many thanks for the response to all my questions.

So when you are sanding the cut ribs you are simply holding them in position against the foam wing stations.

Your weight of 227 grams is impressive with a possible final weight of 300 grams.

Looking forward to the next installment.

Cheers
David

MTK

Exactly....it takes very little time and effort. I used a wood sanding block lined with firm foam under the sand paper. The grade that worked well was 180.

I started to bed the Esaki rice paper on the first panel. Here are some tips:

1- Esaki has a grain which unfortunately runs across the sheet. Since I wanted to run the grain spanwise, it took two pieces to cover the panel side. It also has a "smooth" side and a "less smooth side" which is intended to go down

2- Medium grade Esaki weighs about 7 grams per 24"x36" sheet so a whole panel uses about 1 1/2 sheets or roughly 10 grams of paper. Carbon tissue in comparison weighed about 4 grams for the panel. Kind of tells you that carbon tissue is full of holes which need serious filling and defeating the purpose in a way. But the carbon tissue gives so much torsional stiffness and strength in general, it adds tremendous value in this work

3- Even medium grade Esaki is fairly stiff and strong stock, standing up well to water spray. You've got to make sure there is nothing on the work otherwise it will telegraph right through.

4- After cutting the pieces necessary with a straight edge and xacto, I spritzed the paper with water (just a standard spray bottle) off the work and laid it onto the panel. A fine mist of water loosens the paper structure just enough. You don't want the paper dripping wet. It becomes a pain to work with. But at least it doesn't rip as easily as silkspan for example. You can lift it and place it again when wet.

5- Quickly doped the perimeter, smoothing out the paper. The doped edges grab the work immediately securing the paper. Esaki adheres exceedingly well to a doped surface, bonding to it almost as fast as the dope is applied. You've got to work deliberately and quickly.

6- I let the paper dry before doping it down. It dries drum tight as it shrinks. Then it was simple matter of doctor blading the paper with dope and a credit card. Comes out incredibly smooth. BTW- the dope is Non-Tautening nitrate thinned 1 part to 3 parts thinner. No reason butyrate or epoxy paint can't be used. I simply prefer nitrate for bedding. Must use this stuff with a mask intended for organic vapors and a well ventilated room or a large room such as my garage.

7- Esaki medium grade has a very fine grain structure with minimal holes. Still it needs one more coat of dope to fully bed and then two coats of sanding sealer, sanding in between the coats, then primer and paint.

8- The medium grade is only about 1 mil thick, or slightly thicker than the carbon tissue, so the panel has two layers of covering for a total thickness of about 1 1/2 mils. That's about 1/2 the thickness of plastic film and about 1/3 the thickness of 3/4 ounce glass (as applied). It should go without saying that ding resistance is minimal. You should be careful with handling.

9- The panel picked up another 13 grams of weight so it weighs now, fully covered, 240 grams. It needs finishing of course and hopefully I can apply it with a light hand.

Cost for the coverings is about 13 $ US per panel: that's 3$ for the Esaki and 10$ for the carbon (1 sq yd). It's more expensive than the plastic film for certain. By the time I'm done it would have cost 2X that of plastic film and probably 10X in terms of effort. But there's nothing as satisfying as a well finished supremely lightweight, painted surface, fully buffed to a mirror gloss.

MTK

Been busy building the opposite panel so nothing new to report. I've got it to the carbon tissue stage. It has gone well so far and within a few grams of the first panel. Hopefully I can prepare the aileron on this panel tomorrow.

Took some time to install the security bolts and fit the incidence adjusters to the panels but that has nothing to do with the building tool we've been discussing or the results from the tool. Well, both panels aligned precisely with my incidence marks on the fuse so I know both panels are dead nuts to each other and much better than the foam wing I have been using on Delta. Delta is a good flier but with the new wings it should be better.....

MTK

Cut the aileron and faced it and then added the Japanese tissue over the carbon tissue. A few pics of the tissue bedding
This shows the carbon tissue only after two coats of 25% nitrate (75% thinner)

The Japanese tissue was cut to size, overlapping the LE and TE about 1/4"
The tissue was located exactly, then sprayed lightly with water
Water spray loosens the paper fibers, but starts drying immediately so working quickly is a must. You can see how the paper will fold as it dries, sometimes requiring more water spray. I don't get the paper saturated.

Then it is tacked down around its perimeter to hold it while it dries. If I screw something up, the tissue is very strong and allows lifting it off the surface and repositioning. If the nitrate is holding it in place, a quick brushing with thinner loosens it.
The paper becomes drum tight once dry making the final bedding simple. Esaki Japanese tissue has an exceptional surface appearance at this stage. It's extremely smooth to the touch similar to a sanded surface with 400 grit.

Carbon tissue when used alone required several more coats of filler to fill all the holes. The carbon tissue is exceedingly light and stiff but is so full of holes, it takes a lot of paint to fill it, defeating some of the reasons for using it as I stated before. Using medium and light Esaki as I'm doing here to cover the carbon is one light way around the problem.
Final bedding is done using thinner alone. The thinner penetrates the tissue easily and re-activates some of the earlier nitrate coats which adhere the paper. There is no real weight gain at this step. The paper will be sealed and filled tomorrow, making it ready for primer.


The right panel's weight to this stage is 243 grams or 2 grams more than the left panel. I hope to paint them as precisely....... we'll see!

jester_s1

I have a couple of questions about your technique.

1. How do you apply the dope? What I mean is, do you load the brush and flow it on like one would do with butyrate to make it flow out glossy, or are you stingy with it?
2. Do you brush on another coat of dope before putting on the tissue, or are you letting the coat you put on to adhere the carbon also stick the tissue?

And on a related note, is the Esaki tissue strong enough to use as a base for a sheeted foam wing, or do you need something stronger?

MTK

[QUOTE=jester_s1;12143224]I have a couple of questions about your technique (I wish I had invented the technique but I have not. It is age old, developed by many old timers from the beginning of model building. I taught myself to use the methods with mods to suit my taste)

1. How do you apply the dope? With a brush, 1" and 1/4" fine camel hair from Michaels-What I mean is, do you load the brush and flow it on like one would do with butyrate to make it flow out glossy, or are you stingy with it? Nitrate, Min Wax Urethane, Epoxy paint, whatever, is brushed on then doctor bladed with a hotel key card
2. Do you brush on another coat of dope before putting on the tissue, or are you letting the coat you put on to adhere the carbon also stick the tissue? Two coats directly on the wood first, drying between, of 50% thinned nitrate; then the nitrate is cut again to 75% thinned and the carbon is painted down and allowed to dry; then the tissue. It was explained earlier

And on a related note, is the Esaki tissue strong enough to use as a base for a sheeted foam wing, or do you need something stronger? Strongest paper for its thickness I've ever seen. It retains much of that strength when wet. It has a grain, being stronger in the cross direction. On a balsa sheeted foam core you don't need anything else. Medium grade is 1 mil thick and is all you need. The so called heavy grade is just under 2 mils thick and is at least as strong as 3/4 ounce fiberglass and definitely not required on a sheeted foam core. What are you trying to do??QUOTE]

jester_s1

I'm planning to build a plane for SPA next year. If I can cut some weight I will. I'm flying a Kaos ARF now and do pretty well with it, but I've come to see the value of a painted finish for planes that get flown a lot like these do.

dhal22

Matt, enjoying the work. Thanks for all of the details. Can't wait to see paint.

MTK

Dave,
I think this is done. It's all I wanted to show. Painting is not my forte and most do that better than me

maustin

My Feedback: (7)

Matt,
Please post some pics of your finished project. Would like to see the outcome.

Thanks,
maustin

MTK

Sure Mike, I'll do that.

I shot primer yesterday and sanded today. I use Klass Kote epoxy primer and really like this paint. I add about one volume of baby powder and double up on the thinner. I also strain the paint into the cup and use a screen filter into the gun. This isn't anything more than a small piece of 100 mesh aluminum screen material from McMaster Carr, rolled into a cone and inserted into the gun.

Sanding leaves a rather splotchy surface and depending on the opaqueness of the top color, silvering may or may not be necessary. Yellow is my color choice which covers poorly so I sprayed with silver to cover all of the splotches. I used Home Depot's brand of silver enamel from a rattle can (cheap and simple). It dries incredibly fast and covers everything with a minimum of weight gain (3 grams per panel).

The panels weigh 263 grams a piece before the finish coats. Only 37 grams to 300; it will be a stretch.

MTK

I have followed Pat Harris' thread on painting/finishing over the past 7-8 weeks. Its in the regular Pattern forum. Very good information in that thread; one hell of a lot of work too to take the photos and provide all of the links.

The way Pat finishes his models is not the lightest but the model finishes are art. He goes for all out coverage and appearance then sprays what sounds like a fairly heavy coat of clear that covers edge ridges. Nevertheless, some of the ideas he presented are extremely useful for any one wanting a finish that is a few notches above run of the mill. Some of you might find the information quite informative. Besides, since many of you still build and finish models, you are a better audience than regular Pattern crowd that's in love with Arfies

MTK

Using silver from Home Depot was a big mistake. Top coats did not adhere well and they lifted as I pulled off the masks.

i removed the paint down to the layer of carbon and repapered wings and ailerons. Just reshot primer earlier today. Had to pay a small weight penalty of about 10 grams.

i had a chance to use the House of Kolor paints Pat recommended. I painted trim on the stab and got the panels ready for clear. These paints are excellent, spraying very fine droplets and covering well at a minimum pressure of around 10psi. The paint goes on very thin so 3 light coats are better. I shot orange neon as part of the trim. Very vivid, bright color but this one took four light coats to cover fully.

Darker colors like red, blue and shimmering violet required one less coat and a lot less fuss. I'll shoot clear on the stabs to see how the colors pop.

dhal22

We're still here and following.

MTK

Kool Dave.

I sanded off practically all of the primer. Just a couple grams remain in the low spots. The surface appearance is splotchy so I started the finish coats with a couple of very light white base coats, I think they call it BC-26. It's a one part white that dries to the touch about as quickly as it is sprayed. This HOK paint is excellent for that capability. Also the fact that it is single component, uncatalysed, makes things move along fast and easy. Very easy clean up too, with regular lacquer thinner from Home Depot.

White is the base for the yellow theme base color. Yellow typically covers poorly so a little assistance is a good idea.

Each panel weighs 280 grams after the white. Another 30 grams of base, trim and clear is realistic. RTF each will come in 100 grams lighter than the foam sheeted panel it replaces.

Every build is an opportunity to learn. There are several areas that I'd want to modify, simplify and make lighter and stronger. Example, on the next set of balsa sheets I will laminate the carbon veil to the inside using vacuum and epoxy, set onto plate glass. It should make a more uniform panel without sheeting edges telegraphing. That's one good thing about a foam base, the supporting area is 100% uniform. Don't have that luxury with built up sticks.

BTW- as I was laying down the Esaki tissue, I got a little carried away with the water spritzing. Rather than waiting half an hour for the paper to dry and shrink, I used a monokote heat gun. It seemed that the Esaki actually shrunk even better, tighter, with the heat gun. I think it's a better technique.

MTK

So far I have used the light and medium Esaki tissue. Medium has been easier to work with and the tissue sealed with a minimum of dope coats, maybe 3 coats before the primer was sprayed.

A note about the primer....I use and highly recommend Klass Kote epoxy primer. I have come up with following formula that sprays easily, cures normally and sands and feathers super easy. I use 1 volume of primer and catalyst, mix it and then add 1 volume of Johnsons Baby Powder or slightly less. I let that incubate for 10-15 minutes.

I thin it by adding 2 volumes or a bit more of their epoxy thinner depending on the viscosity. It's sprayed using my standard HVLP touch up gun with the 1.2 mm nozzle. I use a fine mesh screen in the gun. The openings are plenty large to permit the baby powder to flow. I use low pressure maybe 20 psi and hold the gun maybe 4-5" away, minimizing overspray.

this recipe adds volume to the surface and fills the small imperfections that I can't see to sand. It sands so easily and quickly, easily permitting full removal. We all have read by previous authors to sand nearly all the primer. Well, this recipe permits that without loading the paper as epoxy paint can do sometimes.

Anyway, back to covering with Esaki. I covered a pair of stab halves with the heavy grade to see what the differences are. First, the heavy grade is slightly more than twice as thick as medium, 2 mils versus less than 1 for the medium. But it is 5 times stronger and pretty stiff. It reminded me of carbon tissue in terms of stiffness, but it is much stronger than carbon tissue; it's also heavier. Example, a 130 sq inch stab panel picked up about 5 grams versus about 2 grams of medium.

It it took a bit more dope to seal, about double the coats. It also took twice the filler coats, 2 versus 1, to make it ready for the primer. After priming and sanding, the panels picked up a total of 11 grams, from 56 grams at the bare wood stage to 67. That's about twice as much as with medium Esaki. It's not a lot of weight I agree but it's all in the tail so every gram saved there means 3 grams may be saved at the nose. Weight wise, It compares favorably to using 3/4 ounce glass and epoxy paint but it is much stronger than the glass.

Well, my curiosity was satisfied with this worthwhile experiment. Medium Esaki is the best covering to use if you want to paint and you want to make it as light as possible. It lays down well, has very good wet strength meaning it's hard to tear, and it is primer ready in less time and work.

MTK

The earlier posts were mostly about built up balsa structures to build in lightness. Good enough....

Earlier this week I took weight from a set of foam stabs I have in the rafters. These were cut from half pound density foam, slated for future designs. The cores are very light.

I challenged myself to build these at an even lighter weight than the built up versions. These are identical to the built up as far as design. They required somewhat nonconventional ideas to build in lightness. Examples.... the tube sockets were made from glassed 1/32" balsa as I've done before. Sheeting is 1/32" with carbon doped inside. Esaki medium on the outside. Most importantly, I reamed the foam shaving about 25%. The skins were glued with gorilla. Rather than using commercial adjusters, I built the set from 1/32" a/c ply and aluminum nuts. At 1 gram each they were worth the effort.

After covering with the Esaki, I weighed them and was pleased with the result. At 44 and 45.5 grams, they are about 15 grams lighter each than the built up counterparts at the same level of completion. A considerable 25% lighter. So you can build foam as light as built up. It is actually easier. Strength wise, these should be adequate for the job.

doxilia

My Feedback: (3)

Matt,

please do post some pictures of your efforts. I'd be interested in seeing your adjuster design as well as hearing about your procedure for making tube sockets from 1/32" balsa and glassing.

David

MTK

The Griffin died a somewhat unconventional death.

First off, the weight of the crate was great (lol)) at 9# 13 ounces, rtf. It flew fantastic at that weight, very light on its wing, floating forever and doing everything at 1/3 throttle and 1/2 on verticals. I did one vertical check at full throttle with a bunch of snaps thrown in just to see, and I just gave up after 2000 ft. At 155 ounces, the gt33 gave it incredible performance. I had plans to reduce the weight another couple ounces by using my own wood carbon hybrid prop which weighs only 82.5 grams.

On the fateful day it was windy but I thought what TA heck I'm retired so go for it. Well there was a reason the model was lighter than usual. The fuse buckled in one of the snaps. I had a handful and tried as best I could to land it softly in the soy beans which were around 2-3' tall. With marginal control, it stalled in the heavy cross wind and that crash from maybe 5-6' finished the fuse, breaking it half just behind the wing.

Looking inside i saw what appeared to be 3/4 ounce cloth only on the herex. Sure it saved weight but the strength was marginal on this plane. Mike at F3A Unlimited thought it might be the only buckled fuse of the Griffin reported. They were buckling their wings early on but that was fixed. Anyway, what a shame. This was an outstanding flier. At least I got about 15 flights bringing the model close on its trim. Strengthwise it could have used some more glass, or better yet, some 3/32" balsa sheeting aft of the wing.

There was was little emotional attachment tho so I've moved on