Got a little problem

[Mike Griffin]

Just primed my model and noticed that I had gotten a little carried away with sanding on some of the cap strips.  I know better but did not notice it till I primed it.  I used Klass Kote fast primer which is really good stuff but now I am wondering how can I correct the problem since the primer is on.  Any suggestions would be appreciated.

Mike

[Brett Buck]

Just primed my model and noticed that I had gotten a little carried away with sanding on some of the cap strips.  I know better but did not notice it till I primed it.  I used Klass Kote fast primer which is really good stuff but now I am wondering how can I correct the problem since the primer is on.  Any suggestions would be appreciated.

  What exactly is the problem? You went through the tissue?

    Brett

[bob whitney]

is it poly span or silk span

[Mike Griffin]

  What exactly is the problem? You went through the tissue?

    Brett

I think so Brett, I never had this happen before.  I am attaching a photograph of a problem area on one of the flaps but I have the same thing on a few of the cap strips.   The flaps are covered in what everybody commonly calls Dr. paper and the wing itself is covered in Polyspan.  I wanted to try the Dr. Paper on part of the plane and that is why I covered the flaps in it.  I have sanded the fuzzies out of Polyspan before by wet sanding it with 1000 grit but that was before I applied a primer.  Hope the picture will help.

Mike

[Mike Griffin]

is it poly span or silk span

Hi Bob, see my reply to Brett. 

Mike

[Avaiojet]

Mike, did you apply coats of dope to your capstrips and ribs?

CB

[Brett Buck]

I think so Brett, I never had this happen before.  I am attaching a photograph of a problem area on one of the flaps but I have the same thing on a few of the cap strips.   The flaps are covered in what everybody commonly calls Dr. paper and the wing itself is covered in Polyspan.  I wanted to try the Dr. Paper on part of the plane and that is why I covered the flaps in it.  I have sanded the fuzzies out of Polyspan before by wet sanding it with 1000 grit but that was before I applied a primer.  Hope the picture will help.

Mike

   I would just attempt to sand it very lightly, and apply more primer, sanding each time. The problem will be sanding into the paper, just sand the fuzz.

   Brett

[Mike Griffin]

Brett what grit would be best to use and dry or wet.  Thank you for the help.  I appreciate it.

Mike

[Brett Buck]

Brett what grit would be best to use and dry or wet.  Thank you for the help.  I appreciate it.

   I don't know, maybe 320, dry, and a very light touch. You only want to hit the parts that stick up, don't cut into the paper any more than necessary.

     Brett

[Mike Griffin]

   I don't know, maybe 320, dry, and a very light touch. You only want to hit the parts that stick up, don't cut into the paper any more than necessary.

     Brett

OK, thank you.  I will give it a try.

Mike

[Don Jenkins]

I know it's too late, but for the next project, sand all wind/flap surfaces with a 3 foot aluminum sanding bar with 320 or 220 grit paper.  This will eliminate any high spots and reduce the chances of sanding through.  At least this works for me.  Good luck.

Don

[Mike Griffin]

Thank you Don.

Mike

[Mike Griffin]

I know it's too late, but for the next project, sand all wind/flap surfaces with a 3 foot aluminum sanding bar with 320 or 220 grit paper.  This will eliminate any high spots and reduce the chances of sanding through.  At least this works for me.  Good luck.

Don

Thank you Don.

Mike

[Avaiojet]

I know it's too late, but for the next project, sand all wind/flap surfaces with a 3 foot aluminum sanding bar with 320 or 220 grit paper.  This will eliminate any high spots and reduce the chances of sanding through.  At least this works for me.  Good luck.

Don

Yes, knocking down those high areas is mandatory. You cannot do this afterwards once the covering material is in place. It's also important to really fill the wood grain before applying covering material, with one final scuffing of all wood areas.

Also, IMHO I feel it's necessary to apply dope to the rib edges and the cap strips. You can easily stay off the rib edges the first few coats of dope that's applied to the covering if you elect to.

Sanding the dope on open bays. I sand lightly with little pressure, just to scratch the dope up and you can stay off and away from rib edges with no difficulty.

And the "three' coats of dope?" You may need 4 or even 5 depending on your mix or if your covering material slackens and doesn't stay drum tight.

IMHO there should also be more conversations about the use of silk. I will never use anything except silk. I've been down the other road.

I find silk takes less dope to fill and with my CA method of applying silk dry you can cover a full wing in minutes ready for doping. Yes, there's stuff to know about this CA application, but once mastered I'll bet, "You'll love it, or list it." 

BTW. I'm not the only one using this CA method.

Or, you can just use silk and apply it the "traditional way." I always iron the silk first.

Why do I pitch Silk? Try to tear silk. Good luck. Try to tear silkspan, polyspan, or covering "papers," a caveman could easily do it, even a child. Silkspan and similar papers will fight to be laid down at wing fillets or compound areas, silk will easily conform to compound shapes and fillets without having to make "split" cuts. I'm guessing here that this is done?

Silk, 5 yards only 15 bucks. Experiment a bit and I'll bet you'll fall in love with silk.

Last, primer. Best to not apply primer heavy in open bays. A heavy buildup of primer could crack or split in these areas. Wood areas you're good to go so knock yourself out. Most of the applied primer will be carefully sanded away. I sand the primer dry, vacuum, tack rag, clean carefully with a solvent then do my masking tape pull test. Ya gotta make sure all applied primer and paints stick as you progress. I do no wet sanding at all because I don't compete and I'm not pressed to finish, "front row quality."

Everything I've written above I've mention and I have many photos in my Build Threads showing this easy process.

Works for me every time.

CB







 

[M Spencer]

Sometime youve just gotta cut your losses . Say throw ( spray ) two generous coats of clear on . Then throw it in a corner for a week .
Reavaluate then if its going to get flown with minimum expenditure ( TIME & money ) from there , or if its decided to cooperate .

If the woods there the times better spent ' on the next one ' sometimes . One or two if jumped on a year earlier wouldve been far less debilitateing .Feng Shu of something . Or maybe fresh air .

========================================================================================================================

Id think a light coat 75 % thinner , sprayed ' in the cool ( air ) damp , followed by a couple imediately , to get a bit off build up . Then allowed to hardnen thouroughly  , might save it .
Another ditto the next day if still dotty . followed by the week in the dog box - ignored . Might do it .

Ive been a bit generous with the Banana Oil in the dope , on occasion . seems to glutenise rather than spraying till youre blind with still no surface . Bottles no here so the fancy name alludes me .
From the free flight crowd . about six or ten drop in the half full 500 gramme coffe jar . Not the instructed six drops a gallon , itll laST YOU ( THE BOTTLE ) FOREVER .

Isoamyl acetate, also known as isopentyl acetate, is an organic compound that is the ester formed from isoamyl alcohol and acetic acid.It is a colorless liquid that is only slightly soluble in water, but very soluble in most organic solvents.

APPARENTLY THE ONE FOR THE HEALTH FOOD FREEKS MIGHT NOT BE THE RIGHT ' BANANA OIL ' oops . Actually it might not have anything to do with bananas other than olfactoruily .

[Gerald Arana]

Mike,

Sanding polyspan is a NO, NO! It'll just keep fuzzing up, at least that is my experience. What I've done to alleviate the problem is to "cut" off the fuzz by holding a razor (single edge) vertically and scraping it. Dope, scrape, dope scrape should do it.
Good luck, Jerry

[Mike Griffin]

I want to thank everyone who contributed to this thread and I, as always, learned a lot with the information you all shared.  I will remember it in my future finishing.  I was able to knock most of it down with 320 and 400 grits sanding very easily.  I think I may use planked wings in the future. 

Mike

[Joe Ed Pederson]

Yes, knocking down those high areas is mandatory. You cannot do this afterwards once the covering material is in place. It's also important to really fill the wood grain before applying covering material, with one final scuffing of all wood areas.



IMHO there should also be more conversations about the use of silk. I will never use anything except silk.

CB

I was just wondering how many years a silk covered wing will last before it becomes brittle.  I was given a Cosmic Wind built in the 1960's a couple of years ago that had the original  silkspan and the silkspan was still strong and quite airworthy, but I've seen old silk covered models that were nothing but tatters.

Joe Ed Pederson

[Brett Buck]

I want to thank everyone who contributed to this thread and I, as always, learned a lot with the information you all shared.  I will remember it in my future finishing.  I was able to knock most of it down with 320 and 400 grits sanding very easily.  I think I may use planked wings in the future. 

     This would have been fine, just a little more attention to detail up front would be helpful. More-or-less, the appearance is determined by the underlying workmanship, it's disproportionately hard (or heavy) to fix problems the longer you let it go in the building process.

   Just like anything else, it's a learning process, and no one ever masters it, and everybody is someplace along the same learning curve.

      I have used foam wings exclusively on my "serious" airplanes, for various reasons, but I wouldn't let this experience put you off built-up wings.   Note that this (and as referred to by Bob Hunt above) is the sort of problem I had been concerned about in the other Klass-Kote threads - the difficulty of sanding it over open bays without cutting into the material. It actually appears to be working better than I had expected.

   Polyspan is a much better choice than silk, if nothing else, it takes a small fraction of the volume of clear dope to fill it adequately.


     Brett

[Mike Griffin]

     This would have been fine, just a little more attention to detail up front would be helpful. More-or-less, the appearance is determined by the underlying workmanship, it's disproportionately hard (or heavy) to fix problems the longer you let it go in the building process.

   Just like anything else, it's a learning process, and no one ever masters it, and everybody is someplace along the same learning curve.

      I have used foam wings exclusively on my "serious" airplanes, for various reasons, but I wouldn't let this experience put you off built-up wings.   Note that this (and as referred to by Bob Hunt above) is the sort of problem I had been concerned about in the other Klass-Kote threads - the difficulty of sanding it over open bays without cutting into the material. It actually appears to be working better than I had expected.

   Polyspan is a much better choice than silk, if nothing else, it takes a small fraction of the volume of clear dope to fill it adequately.


     Brett

Brett everything you stated in your thread in the finishing section about the "fast" Klass Kote primer is absolutely true.  It gives you a very high build but you need to work fairly fast after mixing.  I had a few runs but that was because of me spraying it too heavy the first coat.   This particular model I am using it on is a Ringmaster Deluxe which has a profile fuselage.   It does sand fairly easily but I do not know that I will use it again on a built up wing because of the concerns you mentioned in your post or if I do, I now know how to handle it.  The only problem I had was on the open bays and between what Bob and you have posted, I think I can do a better job in the future. 

Thank you again for the time you and all took to help me. 

Mike

[Avaiojet]

I was just wondering how many years a silk covered wing will last before it becomes brittle.  I was given a Cosmic Wind built in the 1960's a couple of years ago that had the original silkspan and the silkspan was still strong and quite airworthy, but I've seen old silk covered models that were nothing but tatters.

Joe Ed Pederson

I would say the tattered model was built by someone else? You could be comparing apples and oranges, who knows what was applied to each covering?

I pulled silk off of a Super Ringmaster I picked up for 20 bucks. It was old, really old and I flew it for a day before starting my P-40 project on it. The silk was still fine.

All things being the the same, why would a fabric deteriorate quicker than paper?

You still have to fill the weave and keep fuel off of any covering. That's why I promote a two part auto clear finish. Even over dope filled paper.

I'll still bet on the silk for longevity.

[Mike Griffin]

Hi Mike:

I know this doesn't help you in your current situation, but here is a tip to get around that problem in the future.

First off, the best covering and finishing job will not hide surface flaws in the balsa beneath. Good wood fits and careful final block sanding of the airframe will pay big dividends in the end result. Another tip is to bevel the edges of the cap strips and the adjacent sheeting of the open bay areas to prevent the paper from being "cut" against a sharp  edge when sanding the filler coat.

Many of today's catalyzed primers can be a bear to sand over open bay areas, and if you push too hard when sanding you run the risk of "going through" at the edges of the cap strips. Silkspan can be filled adequately using either just a number of clear dope coats with minimal sanding between each coat, or by adding some of Aero Products' Aero 1 filler (powered zinc stearate) to the clear. The Aero 1 powders-off very easily and with very little pressure on the sandpaper. Then, when the paper is filler sufficiently, you can mask off the open bay areas and spray a coat of the catalyzed filler on the adjacent wood areas of the wing (leading edge sheeting, trailing edge pieces and the center section sheeting).

I did this on my last built-up wing model, the Second Wind twin, and it worked to perfection for me. Attached are a couple of photos of the Second Wind with the primer coat on the wood surfaces and the open bays filled with Aero-1. Two notes on the photos: The primer on the wood surfaces has not yet been sanded in these photos. Also, the dark color on the cap strips is not filler. I cover the entire wing with .2 ounce carbon mat before covering it with silkspan. I remove the carbon from the open bay areas before covering also. That's a trick I learned from the late, great Bob Gieseke!

Hope this helps a bit.

Later - Bob Hunt

Thank you Bob.  I made notes on all of this and will use it in the future.  I appreciate this very much.

Mike

[Joe Ed Pederson]

I would say the tattered model was built by someone else? You could be comparing apples and oranges, who knows what was applied to each covering?

I pulled silk off of a Super Ringmaster I picked up for 20 bucks. It was old, really old and I flew it for a day before starting my P-40 project on it. The silk was still fine.

All things being the the same, why would a fabric deteriorate quicker than paper?

You still have to fill the weave and keep fuel off of any covering. That's why I promote a two part auto clear finish. Even over dope filled paper.

I'll still bet on the silk for longevity.

Thanks for answering.  Yes, the tattered model was a model someone brought to the flying field to sell.   I didn't know the history of the silk covered model, and I didn't know if silk had a limited lifespan or if this model was just one example and not the rule.  It is good to know that silk can last for many years. 

As a teenager (50 years ago) I covered a Ringmaster (what else?) with silk.  That model didn't make it to old age.  I do remember that I used a brush exclusively to apply clear dope (no color) and in the initial coats I got runs on the inside of the silk.  I'm pretty sure that in those days, I didn't even know to thin the clear dope.  I'm pretty sure I applied the clear straight out of the bottle or can. I think the silk was a dark blue and it seemed very pretty to me with just clear dope. 

 My friends and I hardly knew what we were doing, but we did have fun and were happy to run the tank of fuel out without crashing.    We did wingovers and inside loops, and learned to fly upside down (up high).

Joe Ed

[john e. holliday]

Yes Joe,  I think most if not all went through the learning curve unless we belonged to a club or had a mentor.  I used silk on short lived planes as it didn't cost that much back then.  Nylon was the covering of choice because of its life using dope.  Now I don't use dope and the price of epoxy is out rageous to me.  Just finished an all Monokote plane for 15 carrier and fun flying.   

[Shorts,David]

While we're on the topic. BRETT, I read your explanation of Klass Kote on the other thread. Why use Nitrate dope when coating the frame and tacking down the polyspan? Is it preference? When I did my blacktiger (on my other thread) I needed the butyrate super cote to get it drum tight. Is this my lack of skill, and that's why you can get away with nitrate, or is there a chemical compatibility issue. My Junar is getting awfully close to covering and I consider everything I've done the practice to try to get a covering job correct.

Also open to anyone else's input for polyspan or Klass kote. I think I've got the dope process figured out if I go that way.

Oh, does DR's paper shrink if I use that on the wing?

Also, I loved working with straight silk. It was very easy to stretch around wingtips and curves, but had a very large grain pattern which I finally decided looked good enough and abandoned the idea of filling in. I think 1 pound of clear would not fill it in. (No, I didn't use a CA method.)

Thanks everyone for your advice on this thread.
David

[Brett Buck]

While we're on the topic. BRETT, I read your explanation of Klass Kote on the other thread. Why use Nitrate dope when coating the frame and tacking down the polyspan? Is it preference?

   I am primarily concerned about adhesion of the primer to the dope. Butyrate is known to have much less adhesion to the primer. It might be OK with epoxy primer, but, I didn't want to find out the way some of my cohorts have, that is, the hard way. And, it outgasses for eternity whereas nitrate is done in a few weeks.


And:

When I did my blacktiger (on my other thread) I needed the butyrate super cote to get it drum tight.

Drum Tight!? That's why most people are concerned about butyrate (particularly Super Coat clear). The extreme shrink that just keeps going. It distorts the structure, and also, makes filling a nightmare, because unless you wait months before you fill it, all the grain will just pop out again. Almost everyone using butyrate at least uses Lite Coat or "non-tautening" dope to avoid this issue, at most, one coat of "tautening" dope on the open bays only, to shrink the covering just enough. "Drum tight" is alarming and he first hot day, it will get drum tighter, and warp something, cause a "starved horse" effect, or something like that. And that goes on for decades.

 

Is this my lack of skill, and that's why you can get away with nitrate, or is there a chemical compatibility issue. My Junar is getting awfully close to covering and I consider everything I've done the practice to try to get a covering job correct.

   As above. I would use polyspan for the covering, heat-shrink it as well at it can, and probably use Lite-coat as the dope. It is not like an I-beam, you are not entirely dependent on the covering keeping it straight, with the quasi-Warren Truss "tilted rib" construction. I probably would not consider using either real silkspan or the exam table paper at this point, it's too fragile, or silk which is too hard/heavy to fill. Bobby's example is the way to go. I would never use supercoat clear or "tautening" butyrate or nitrate, too much shrink.

     Brett

[Shorts,David]

Goldmine! Thanks for the clarification.

David