Covering Wingtips

[Garf]

Some styles of wingtips are harder than others to cover with Monokote. I am having major problems with the tips on the Trixter Barnstormer. Maybe I have lost my touch, but I don't remember having this much trouble on any of my other models. Any ideas?

[invisible]

Silk and dope!

[Garf]

I used to use silk on my combat wings prior to the days of Monokote. I got tired of patching the holes every time I hit a rock on landing. I quit using silkspan on my profiles for the same reason. I used to fly a lot. There might not be a lot of craftsmanship in Monokote, but there is a lot less frustration
(usually).

[RetNavySuppo]

Silk and dope RULES!!!!!!!!!!!

I used silk (or silkspan) and dope during the early part of my modeling career and then got lazy and went with the iron-ons for quite a while. After I retired in 2000, I resurrected my silk and dope skills and got serious about my supplies (buying the commercial stuff at Aircraft Spruce Specialities - about a 2 hour drive from me). The funny thing was that the better I got at silk and doping, the more my MonoKoting skills deteriorated. Go figure. Maybe I just have "X" amount of covering skills and as my silk and doping skills increase, it draws down from the MonoKoting skills.

Anyway, a verbal description of how to cover wingtips with MonoKote will never be as good as actually seeing it done. Tower Hobbies has a video and a DVD on MonoKoting techniques, including the dreaded wingtips. The VHS video is item number LXHX84 and the DVD is item Number LXKSB4. They are each an hour long and do a fairly good job showing you what to do.

Silk and doping is more work intensive than MonoKoting but the results can be so much better. We don't have the rock problem at our field, but as for durability, I think silk is more durable than a plastic covering, unless you are using a very lightweight Esaki silk. I have had items bounce off the silk while they shatter the MonoKote. The older a MonKote covering gets (with all the reshrinking), the more brittle it gets and of course, you have the inevitible wrinkles.

Most people shy away from silk and dope because of the work involved. Also, it is not something you can really learn well by just reading a written set of directions. Well, the actual work involved is less than most people think, once you know what you are doing. I am tutoring another retiree on covering and have shown him both Monokote and silk and dope. After sitting there and watching me do a couple models each way, he is chomping at the bit to do his first silk and dope job this winter (an old timer model - a Quaker Flash - transparent dyed red silk) in my shop.

I have been reading model airplane magazines for the last 30 plus years and have seen many written descriptions of the silk and dope procedure. Yet EVERY one of them has missed one or more important points that are essential to the success of the process. That is why it is better to watch the process of someone who is good at it rather than just reading about it.

For instance, there is a CRITICAL step that is required when you cover with a heavier silk (like the 5mm or 8mm Thai Silk) on larger models that is not necessary when you cover smaller models with lightweight Esaki silk. No write-up I have ever read has ever mentioned it. And from the complaints I have read back on the FliteLines forum about silk that won't tauten after doping, many potential silk and dopers have been turned off because they omit or never learned about this step. I learned this step by stumbling on it by accident - one of those EUREKA! moments.

But then, this is the era of ARF's and RTF's. We silk and dopers are a dying breed.

[tperry2054]

retnavysuppo said:

Silk and dope RULES!!!!!!!!!!!

And from the complaints I have read back on the FliteLines forum about silk that won't tauten after doping, many potential silk and dopers have been turned off because they omit or never learned about this step. I learned this step by stumbling on it by accident - one of those EUREKA! moments.

But then, this is the era of ARF's and RTF's. We silk and dopers are a dying breed.

I've covered with silk and plan on doing it again. My results were pretty good and I never had a problem with the silk taughtening. Your post make me wonder if I've been lucky or missed the Eureka moment. Rest assured I am not trying to come off as a wise a$$ here so if you have a secret will you share it?

Regards,

Tom Perry

[Garf]

Actually, I am, or at least I used to be very good with silk. I have also have done very well with silkspan. I feel that silkspan is harder to do a good job with than silk. The Barnstormer in question had silkspan on the wings, but the tips had some sort of brown paper on them. I don't quite know what to make of that.

[RetNavySuppo]

Tom,

The magic word is VENTILATION. And I don't mean just the ventilation of the room in which you are doping.

I too had excellent results when I was using silkspan or Esaki (very lightweight) silk. The covering tautened properly and the silk dried nice and hard.

However, when I started silk and doping again, it was on larger models than I had previously silk and doped. I checked out the price of Esaki silk and got sticker shock. Then I learned about Thai Silks and their very low prices for their 5mm (momme) 8mm Habotai silk. Their silk came in whatever length you wanted, so i could cover the entire top or bottom of a wing, no matter how wide, with just one piece of silk.

So I ordered some 5mm silk and set about to covering a 60" wing. I followed my standard procedures and soon was having some misgivings. It took about 8 coats of thinned dope to get the silk to tauten. Even then, it still wasn't very tight and the dope, while dry to the touch, was still somewhat soft. So I let it sit for a week. No improvement. I let it sit out in the sun. No luck. I hit it with a heat gun. No improvement.

Since I wasn't getting anywhere, I decided to strip off the covering. I took a razor blade and slit into the covering over one rib bay. Now for the EUREKA! moment. As soon as the razor blade penetrated the rib bay, I immediately smelled a strong dose of concentrated dope fumes escaping from the rib bay.

This what happened. The thicker silk absorbed more of the dope and when the dope on the outside of the wing hardened (very quickly, as usual), it formed an airtight seal over the rib bay. This prevented the dope under the hardened surface from drying and the concentrated dope fumes had no way of escaping and remained in the rib bay. This kept the lower thickness of the silk from properly tautening and kept most of the dope in the silk semi-hard. This was the case in every rib bay as it would be in any completely sealed space. With silkspan and Esaki silk, the covering is thin enough for the lesser amount of dope to dry properly throughout the thickness of the covering.

So I stripped and cleaned the wing. Then I drilled two 1/8th inch holes in each rib. One hole was in front of the spar and the second hole was in the rib behind the spar. I did not drill any holes in the spar shear webbing. The last rib bay had no shear webbing. Then I made four 1/2 inch holes in the bottom center sheeting. This was 2 holes on each side, one of the two ahead of the spar and the other to the rear of the spar. Since this was a high wing plane, putting these holes in the bottom sheeting near the wing centerline effectively hides these holes when you mount the wing. For a low wing plane, you would put the holes in the top of the center sheeting.

Then I covered the wing in the normal silk and dope manner. Guess what? The silk tautened up nice and tight after the second coat of thinned dope. The dope also dried nice and hard. I was able to finish the wing to a nice finish using only half the dope of the previous covering job.

There are several ways you can allow the dope fumes to escape from the interior of the wing. If your holes are big enough, just normal diffusion will do it. You could also put the wing out in the sun or gently heat it with a heat gun. The heat will expand the air inside the wing, pushing some of it out and then when the wing cools, clean air without dope fumes will be drawn into the wing as the air cools and contracts. Now, if you really wanted to be spiffy, you could make the forward holes in the center sheeting the diameter of say, fuel tubing, and connect a low pressure air source to the tubing and insert it into the forward holes in the center sheeting and gently ventilate the interior of the wing a couple times a day for a few days. By omitting the last shear web in each wing half or by drilling a hole in just the last shear web, the air will flow into the forward hole in the center sheeting, through all the rib bays forward of the spar, come around through the hole in the last shear web, through all the rib bays aft of the spar and then out the rear hole in the center sheeting on that side of the wing.

You know, I should have had this EUREKA! moment much earlier because I always ventilate the wings I MonoKote. Think about it. The MonoKote, when ironed down, creates an airtight compartment over each rib bay. When you apply heat to shrink out wrinkles, think of the competing physics. The iron or heat gun is trying to shrink the Monokote covering the rib bay. However, the heat is also heating up and expanding the air trapped in the rib bay, causing the Monokote to swell up and stretch. You have two contradictory forces working against each other. No, this isn't the same principle involved in the silk and doping process, but it should have shown me that there is a problem with sealed air spaces in the model.

Tom, you now have the critical secret to using thicker silk on larger wings. Now I will have to kill you.

[RetNavySuppo]

Here is a question for you controlline types. Both in this forum and in the controlline sections of Model Aviation Magazine I see much more interest in silkspan and silk and dope finishes than I see in R/C forums or R/C magazines. Why is that? I know what dope fumes do for my "happiness level", but why the difference in interest level?

Any ideas?

[tperry2054]

Now I see why I never hat that eureka moment. I can't think of a plane I have built that didn't have the wing already vented. Dont forget we have control lead outs from the belcrank and the center section has a hole for he flap/elevator push rod. We also have the lead out holes in the end of the wing. Some people do not cut holes through the ribs on the out side wing but I always do as I stack a whole set of ribs at once for cutting and do them all the same.

The BOM or builder of the model rule is still being used for stunt competition. Some of us believe that a dope and silk coating is much stronger. The model is more easily repaired with dope and silk/silkspan.

As you may or may not know ARFS and ARCS are getting more popular in C/L.

I don't have the statistics to prove it but as a whole I believe the average age of control liners is a lot closer to room temperature than RCers.

[invisible]

That is very interesting. I have not had problems for two reasons. Esaki silk ( I have some packs I bought for $2.95 ;D and up). Secondly, I have always ventilated my wings and other structures because I thought if I did not there would be a problem with them sitting out in the sun and getting hot. With the Esaki silk, starting out with very thin dope, it takes 5 or 6 coats before all the pinholes are filled.

I've done a few monocoat wings in the past, and simply like tissue, silkspan, or silk better. Silk is very easy to use around compound curves etc. I also like Sig Plyspan or Litespan, which is very much like silkspan, comes in colors and is pretty tough. It is a little stiffer than silkspan and thus a little harder to get stuck down around corners, etc. There is some silkspan on the market, from different suppliers, which is not silkspan by any stretch of the imagination, but rather like thin gift wrapping paper.

[RetNavySuppo]

Esaki silk at $2.95 a package? Say Jim, was your previous military service in the Union Army or the Confederate Army? ;D

I know what you mean about "supposed" silkspan. I solved the silkspan problem by simply buying a box each of the three grades of K&S Engineering silkspan (through Tower Hobbies). This way I have known weight, known quality, etc.

For silk, now that I know how to use the heavier silks properly, I use Thai Silks 5mm ($2.30/yard!!!) and 8mm Habotai, K&S Engineering Heavy Duty Silk (through Tower Hobbies) and I have scooped up a lot of Silron (remember that?) and some Esaki Silk off E-bay.

I go mostly for the white/natural silks since I am then free to dye it any color for which I can find dye. I dyed 12 linear feet of Habotai 5mm with Rit Scarlet dye in preparation for covering the Quaker Flash. I had to dye the silk twice in order to get a consistent color, but it came out really nice - a warm, rich color. It's going to make that Quaker Flash look sharp. All I lack is an idea for a suitable trim scheme to go on what will be an essentially transparent scarlet covering.

I have no experience with Litespan or Plyspan. Are they iron-ons? If they are, can they go around compound curves using heat?

Another covering type I really like are the fabric iron-on "-tex's". These are sold under the names of Solartex, Worldtex and Colortex - they are all the same thing. They are much, much easier to use than the plastic iron-ons, have a nice fabric texture, and laugh at compound curves. The disadvantages are that they are heavier than the plastics and need a couple coats of clear butyrate dope of polyurethane or else they attract scuffs and dirt like a magnet. I tried another fabric iron-on, Super Coverite, and was totally unimpressed with it.

[invisible]

To be specific, it is Sig Super-Flite Plyspan, 24" x 35-1/2" made in Japan, comes in tubes of 12 sheets and retails at $2.25 a sheet. I just got a dozen sheets of yellow, my favorite, from one of our two LHS's going out of business. It is not an iron-on, but is like medium weight silkspan. It has a shiny and rough side and has a grain. It goes on wet just like silkspan.

Also there is Spectra Art Tissue, 5914-6 Black. 42 sq ft for $1.60 some time ago. This is what I cut numbers, letters out of. It absolutely does not fade. It is a Bemiss-Jason product available at your local craft store. It does not run in water or dope. I am going to make a small airplane some day with black wings and orange fuselage and trim. It seems plenty strong for covering a 1/2A wing.