RACER7696

My Feedback: (3)

Hello gentlemen,Ihave a covering question and since up untill this point I have mostly delt with monokote i hope I came to thre right place.I have a greatplanes 1/12th scale f4u corsair.When I recieved this plane there were some defects in the sheeting so I had to uncover the wings and repair them.I also uncovered the fuse because there was a problem with the covering .Instead of the typical monokote Iwould like to cover this with koverall or equivelant.I know that this is alot more work and will add more weight to the model but I can not stand monokote anymore.The Main questions that I have are on a fully sheeted fuse do I have to glass it or can I directly paint the fuse to sane weight.Also what dou you do with the open parts of the wing will the koverall shrink on these areas ,also will this stuff shrink with nitrate or dope put on to the cloth when you apply the iron.So basicly what I am asking for is a step by step detailed instructions for this small aircraft,like I said I know this process will add more weight but I would really like to get proficiant at this process for my next 1/4 scale project.i feel that this is going to be a lost art soon and that will truley be a shame


Sincerly, Mark

Chip_Mull

My Feedback: (1)

Go to http://www.stits.com and compare the process. They are similar but the buck stops there. The Stits Lite fabric has a tighter weave and shrinks tighter, all the paints chemically bond to each other, and the process is lighter than dope.

In answer to your questions "on a fully sheeted fuse do I have to glass it or can I directly paint the fuse to sane weight": It's entirely possible to directly paint the fuse but I don't think you would like it in the long run. If you use the 3/4 oz cloth and epoxy, it will resist hangar rash and dints and dings better. We have a process where you only apply the 3/4 ounce cloth with the epoxy and then use FC-900 to fill the weave. Normally you would apply the second coat of resin which does nothing but fill the weave and add weight. The Feathercoat is solvent based and saves weight and is a "Bridge" between the fiberglass and our paints.

Also,"with the open parts of the wing will the koverall shrink on these areas": YES, any polyester shrinks with heat and will shrink over the open areas. Koverall and Stits Lite shrink with heat but.... dope continues to shrink during its entire life. This is why some planes experience dope cracking or coming off later. It doesn't chemically bond with the fabric. Apply nitrate dope first and then butyrate. Again, trying to obtain the chemical bond.

There are Q&As on the web site that address the Stits Lite method and free info is available. Hope this helps and feel free to call, e-mail or write for further info.

Stickbuilder

Well, first, Koverall is othing but a lightweight ceconite, or a woven Dacron polyester fabric. As such, it is heat shrinkable, and is very strong. If you have the fabric pulled tight when you begin to apply the heat, you can crush a weak structure. Having said that, I make sure that the surface that is to be covered is sanded extremely smooth, and cleaned to perfection. I use paper towells saturated with isopropyl alcahol. Some reccomend that you use a tack rag to remove the dust, but I have found that using these rags tends to leave a waxy residue behing, and that is not conducive to getting a decent bond when applying the covering.

First, I apply 2-3 coats of Nitrate dope to the entire structure. I sand the last coat with 400 grit wet or dry sandpaper. I then cut the material (make sure that the weave runs parrallel with the structure) I attach the material to the doped structure with lacquer thinner. Use a single edge razor blade to trim to your satisfaction (an xacto knife will not hold it's edge as well as a single edge razor blade) next dope the entire perimeter of the structure, rubbing the cloth down with the ball of your finger. Give the doped perimeter time to dry prior to application of heat. You can do the top and bottom of the wing panel as one piece if you wish, doing the bottom of the wing, and wrapping around the leading edge, and finishing at the trailing edge of the top surface. This method gives the best appearance, since you do not have a seam at the leading edge.

Once the dope is dry, you should use a monokote iron adjusted to medium high heat, and begin to shrink the fabric. Do not use a heat gun until you are experienced, since you can overheat the fabric, and cause the fibers to elongate. This will leave you with a very baggy surface that will never shrink again. Once you have the fabric shrunk taut, begin to apply nitrate dope thinned 50/50 with lacquer thinner. Brush on at least 3 coats, and check for pin holes. Hold the surface up to a lamp, and if you have pin holes, you will be able to see them easily.

Once you have the surface filled with the dope, you should sand it smooth using 600 grit paper. Then I use automotive primer to give a opaque base to do the final color. Add the color of your choice, and then color sand with 1500 or 2000 grit wet or dry paper (wet) until you get a uniform smooth finish. Use rubbing compound and polish to get the sheen that you desire. Done properly, the surface (over solid wood) will have the appearance of finished metal, and the finish over the open bays will have the appearance wo slick finished plastic with a hint of weave showing. Here is a photo of a WACO that I am in the process of completing. Pic taken last evening. Best of luck,

Bill, AMA 4720
WACO Brotherhood #1

Stickbuilder

Dang, It didn''t load. I'll try it again.
B.

Chip_Mull

My Feedback: (1)

Nice explaination with a couple of exceptions. When cutting the fabric, apply a strip of dope where the cut is to be made. Allow it to dry and the cut will be crisp with no "frizzies". You need to calibrate your iron to 250F and 350F to shrink the fabric. The Coverite iron with the thermometer on the dial is the best but any iron can be calibrated. Shrink it first to 250 then 350.

I would NOT use the automotive primer as it interupts the process. The reason you paint nitrate dope on the fabric is to chemically bond the paint to the fabric so the butyrate will attach to the nitrate. With the automotive primer in between, it's useless to use nitrate. You could have filled the weave with anything. Remember , all dope shrinks and it shrinks for its entire life. If you ever have dope crack or peel off, this is why. Also, automotive primer is intended to be used on metal with out flexing (hopefully). It could cause what we call "Ringworm" in the full scale world. When you handle the aircraft on the open structure it cracks the primer and looks like ringworm.

You didn't address finishing tapes or pinked tapes as the modelers call them. If you want to apply the pinked tapes, they go on after the nitrate dope is applied and just before the butyrate. If you put them on after the first coat as we normally do with the Stits process they will almost go away by the tenth coat of nitrate. So, we prefer to apply them just before the butyrate to make them stand out a little more. Atfer the tapes are applied, spray the entire airframe once more to fill the weave of the tapes. Now you're are ready for silver.

For a referance on covering a model take a look at: http://www.stits.com/RC_Model_instructions

Stickbuilder

Chip, I should have mentioned that I allow the Nitrate to outgas prior to application of the primer. I have been using the Automotive primer for years with great success. I suppose that there are as many successful techniques as there are builders. I spoke of what has worked well for me. I did not mention the various Pinking tapes or bias tapes, due to time constraints. My Bac. Please forgive.

Bill, AMa 4720
WACO Brotherhood #1

RACER7696

My Feedback: (3)

gentlemen,thanks for the explenations since I am a true rookie with this process I still have some questions.You guys keep talking about dope can I use epoxy instead or is dope what I should use.what about sig stick it should I use this first and what is this product doing.If I must cut the fabric where do I want the to pieces of fabric to meet,also how do I blen dthe seem in.Is the nitrate dope what sticks the fabric to the wing and if so than why do I need to use the sig stick it product.Sorry to ask the question again but you would cloth the fuse but use less nitrate is that correct.also is nitrate the stuff that keepshrinking over time and has the tendacy to crack,If it is is there anything else I could use.Again thank you so much for your time putting up with a rookie finisher

sincerly,mark

Chip_Mull

My Feedback: (1)

Stickbuilder, I am very impressed with your AMA number. You must know Charlie Nelson, "Mr. Waco". You are correct in as much as there are as many techniques as there are builders. I don't have the benefit of your experience, I can only go by the manuals and what I have learned over years dealing with the full scale mistakes and problems. By using the same techniques and procedures we can avoid re-inventing the wheel. What we have learned is stay with what has been proven and tested in the labs and don't mix procedures. If you start with dope, stay with dope. Also, if you start with Poly Fiber then stay with Poly Fiber. Dope is manufactured with about 85 per cent MEK and disolved cellulose. MEK is the solvent we use to clean off Poly Tone so it stands to reason NOT to mix the two. The MEK in dope will attack the Poly Tone.

Racer 7696, you asked if you can use epoxy. Of course you can, after you fill the weave of the fabric. And keep in mind epoxy is not designed to be flexible. You see Polyurethanes on full scale aircraft. You see dope on full scale aircraft and you see lots of Poly Tone on full scale aircraft. Never epoxy though. Why? Cause eventually it will crack. There are plenty of people out there that will confess to using epoxy for years and have never had problems with cracks. There are them that have and them that are gonna.

As for the seams, try to place them where they will be the least noticible. Also, if it's a scale project, the seams are covered with the pinked finishing tapes. Finishing tapes are usually all the way around the control surfaces, along the leading and trailing edge of a fabric covered wing, and along the ribs.

Attaching the fabric: http://www.stits.com/RC_Model_instructions.html#tak . Each fabric manufacturer has his own cement to attach the fabric. The idea being to establish a polyester bond. Whether it's Sig Stiks It, Randolphs Super Seam, or Poly Fibers Poly Tak, they are all intended to bond the polyester. The best situation is to have a polyester to polyester bond where the fabric is attached to fabric with one of the fabric cements. Chemically, they are all about the same.

Shrinking... All dopes shrink over time. This worked to our advantage when we were using cotton or silk. Not so good with polyester. The concept is to encapsulate the fabric with nitrate dope and then use butyrate. The nitrate sticks to the fabric and the butyrate sticks to the nitrate.

Covering the fuse with fabric... covering a compound curve can be tricky. But, it can be done. I still contend that on a Corsair it would be better to use fiber glass cloth instead of fabric. Then, I re-read your original post and realized we are talking about a 1/12 scale project. If you're using this as a test bed for different fabric techniques then press on. But, if it's a model to be flown and enjoyed, just paint the fuse without fabric or fiberglass.

Stickbuilder

Chip,
I do not personally know Charlie Nelson, although I have admired his work for years. I totally agree with what you have had to say concerning Epoxy. I think that we have spoken before (on the phone) when I was considering using the Stitts system on a plane sometime back. Best of luck to you.

Bill, AMA 4720
WACO Brotherhood #1

eagledancer

if using automotive paints i highly suggest adding a flex agent, that lessens the cracking with time
i have a 1/4 scale monocoupe that was covered with koverall 16 years ago, used clear automotive laquer to fill the weeve, then polyurethane color and clearcoat. i did not use flex agent in the laquer clear all those years ago and you can see the cracking if looking very close.
she is about to get a face lift this winter, a bit of sanding and repainting, (a few small repairs) but this time i will use the flex agent

but then again how long will the glue joints last on a model?......so far 16 years and still flying, and yes i do give her lots of snap rolls!!!

049flyer

My Feedback: (18)

I have been using Koverall for years with great success. I use nitrate dope to stick the fabric to the structure and to seal the weave. Butyrate dope for the color works well as do epoxy paints.

A few other points:

1. Instead of trimming the koverall with a blade, try a sanding block and sand away from the surface. This trims the fabric and helps to feather the edge so it is not as visable.

2. It has always been my understanding that Nitrate dope does NOT continue to shrink over time but butyrate dope does. In any event you can buy non-tautening butyrate dope or you can add "flex-all" from Dave Brown Products.

3. Mix talc with nitrate dope for a cheap light weight filler. 2 coats with a little elbow grease and a sanding block will yield a near glass smooth surface. Micro balloons may work even better but I haven't tried it.

4. On sheet balsa surfaces try silkspan applied with nitrate dope instead of glass and epoxy. Much lighter, fills with only a coat or two of dope and sands easy.

Properly applied, Koverall coverall adds no more weight than monokote but is much stronger and will last for years without bubbles or sags. It is initially more work to apply but much less work to maintain.