06/07/02 DOPE & POLYTONE vs. URETHANE

I have been thinking about top coats for my Pitts lately and want to solicit some outside opinions. I like Dope/Polytone for the cost ease of application and repairability advantages but am wondering about a few things.

1. Can Dope/Polytonbe be applied to aluminum/fiberglass?
2. If so will it look different than the parts that are applied over fabric?
3. What about a multi system (Dope/Polytone and Urethane) paint job?

I like urethane for the glossy look and the durability but don't like the way it must be applied. I painted a Citabria with Poly Fiber Aerothane and was happy with the results, however it took a lot of time and effort. I have no experience with a dope top coat.

I have seen some dope paint jobs that look pretty darn good, I have also seen some dope paint jobs that look pretty dull. Since nothing in life is free, I would assume that a lot of time and effort went into these good looking dope jobs. Thanks, Dave
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Dave, first decide if dull to semi dull is ok for you. If it is, then you can use polytone as semi dull or satin finish is about the best you'll get with it if rubbed etc. If you want a bit more shine, you can finish in butydope and rub it out. That will give that classic, handrubbed dope finish I think you refer to like we did on the Gee Bee Z. A full gloss hand rubbed finish with buty dope is more labor intensive than urethane finishes.

What system would you like to use? Ceconite, Polyfiber, Airtech, etc? This choice is the first to make and limits the topcoat that you can use. Polyfiber>>Urethane of polytone, Ceconite>>urethane or buty dope colors, etc.

Polytone has been applied to metal before and there are some tricks to doing it. It is not really designed for that application though. Most use polytone on fabric, enamel or urethane on metal and in some cases, get the metal paint flattened to match th epolytone sheen.

We prefer polyfiber process with urethane topcoats. We have been using this system for 20+years and out of the 80+ airplanes we have built/restored here, 2 were not done in this way. these 2 were buty dope finish over ceconite or cotton covering.

If you feel the time and effort in applying the urethane colors was too much, be prepared for more work in a buty or polytone finish that you want to be shiny assuming you don't clear coat it.

I think you have seen our yellow and purple Pitts Model 12. It is polyfiber covering, double covered with no tapes, polyfiber coatings sanded one time with 220 grit wet, and then 3 coats yellow urethane. Simple enough. Great finish. We use this process on most of the aiplanes we build/restore. Lots less work that the 750hrs of rubbing we did to get the buty dope on the gee bee to shine nearly as good as urethane.

Durability of urethane finish is much better than the others. Gas spills, sweaty hand prints etc can stain of damage the finish of polytone and buty colors. Tender stuff. KK

01/10/02 NO FABRIC ON AILERON COVES, INSTALLING COVES

Kevin, I've noticed some completed airplanes have been fabric covered over the aluminum aileron coves while others, notibly the airplanes you and your dad have built have the aileron coves painted and installed AFTER the fabric work is done. Why?? - Darin
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Darin, the ailerons that are on the Model 12 and Super Stinker rely upon precise gaps between the aileron nose and coves for optimum roll performance. These gaps are different for the ailerons at neutral and at full deflection. We cover and finish the wing and ailerons, then we install the cove, setting the clearances at that time.

While they may look a little nicer, the airplanes you've noticed with fabric on the coves had their gaps set at an estimated amount to make sure the ailerons didn't physically hit the coves after fabric and paint. In all probability they are running too much gap, and thus have less than optimum control effectiveness and roll performance.

The general shape of the ailerons in the Model 12 and Super Stinker have roots in NACA data. What is unique is the cove design and how the varying cove to aileron nose gap affects the performance of the system.

Here's how to install the coves:

  • When building the wings, set the gap between the aileron leading edge and the cove block glued to the rear spar to 1/4" (.250").  The cove block is 3/4" square and therefore the aileron is 1" aft of the rear face of the rear wing spar. 
  • Rough fit the coves before you cover the wings and ailerons.  Drill or punch all screw holes, clearance holes for some of the drag wire ends and nuts, and notch the lower coves for the slave struts.  Refer to plans drawing 12-400 sheet 4 of 4 detail G-G.
  • NOTE: Since you'll have to flip the wings over to work on both sides, install ALL coves and ailerons BEFORE final mounting wings to fuselage.
  • Cover the wings and ailerons completely up through final color paint.  Paint the coves. 
  • Install the coves with the screws into the cove block only.
  • Install the ailerons with proper hinge bolts and nuts.  Check for full free movement of the ailerons on the hinges.  Note that the ailerons my bump into the coves at full deflection at this time.
  • Cut six 3/4" square shims from .063" (1/16"plywood is .070") thick aluminum. 
  • Deflect the ailerons until it's leading edge peak is pointed exactly at the peak of the cove.  While swinging the aileron into this position, insert the shims between the aileron and the cove at 3 to 6 places along the gap.  You can tape the shims in place if needed.
  • The shims hold the cove forward enough to produce the proper aileron to cove full deflection gap.  With the aileron, cove and shims in position, install the screws at the forward edge of the cove on the given side of the wing.
  • Move aileron to neutral and remove shims.
  • Inspect gap at full deflection once more.  If gap is proper, flip wing over and repeat procedure for second side.
KK

01/05/02 ABOUT FLYING WIRES

The Bruntons stainless steel wires sure are expensive, why can't we make our own from 4130?
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Let me start out by saying, buy the wires! These are precision made parts that are flight critical. The wires are a huge part of the primary structure of our type airplanes. Like the tubing, wood etc. We aren't (at least shouldn't be) using pine lumber from HomeDepot for spars or electrical tubing for the fuse frame.

Here are a few #s for you to consider....... 4130 Cond N is typically 95,000 PSI material. That is to say a 5/16" dia 4130 N rod can be loaded to about 4500lb (calc must be made at the thread root diameter not 5/16" rod Dia.) A 5/16" streamline tie rod (the real name for these things) is rated at 6900lb. So, you would have to use 3/8" round 4130 rods to get equiv load capacity as the streamline tie rod.

3/8" 4130 rod will weigh more than the 5/16" tie rods. The round rods will create a HUGE amount of added drag as compared to the streamline rods. On the order of 500%-700% more drag. Now, you are probably thinking that the wires are small and can't add that much drag to the airplane and therefore, round ones would be 7 times a small number and still be small. Well consider this.........A Bonanza with 4 of the round wire and round white fiberglass antennas on it gains 5-7mph when these ants are removed and replaced with the wide streamline fibergalss units!!! Seen it happen. These antennas are only 10" to 16" long for a total of 4 or 5 feet for round rod in the slipstream and changing them to streamlined antennas does this much good!! Replacing the round tail brace wires on some small airplanes with streamline rods results in a measureable gain in cruise speed. On most biplanes, there is approx. 125 feet of tie rods on the airplane. If 5 ft of rod makes such a speed difference what do you think 125ft will do?

Now, if you want too use the 4130rod and fair it in so that it is has a streamline shape, you might not see much of a drag increase. But, this is yet another thing you have to do rather than buy a ready made, proven part and install it. Do you want to mold your own tires too???

When you consider the price, keep in mind that you will still have to buy AN661 terminal ends, clevis pins, jam nuts and cotter pins even if you use 4130 round rod. These ends, nuts and pins are about half of the cost of a set or streamline tie rods.. This is, the rods are about $1400 where the ends, nuts, pins etc are about $1700 for a set of model 12 wires that sell for $3100. So, for a skybolt I recall Manuel posting that his wires cost something around $2400. So, expect the ends to be about $1500 of that. Round 4130 rod from Charlie V. is about $1 per foot and you will need about 150ft because of waste etc. So, the have rod rods would cost you approx. $1650 where streamline would be $2400. That is only a saving of $750. Out of that $750, BTW, 4130 does not thread that nice and you may scrap a few rods trying it. You will need to get them threaded at a machine shop for about $4 per end which would bring your savings! down to about $600. Or you could spend another several thousand dollars and buy a precision lathe and geometric die head and thread them yourself.

Now with $600 left in savings, you might spend half of that streamlining them. Another idea would be to use K&S model airplane miniature streamline tubing slipped over the 4130 rods to fair them in. This would cost a fortune as the K&S stuff aint' cheap!!

One last thing.....Stainless wires do not rust..........4130 will. Ask any owner of an antique airplane with steel wires if they love having to sand down and paint the rusty wires every year. Bet they will tell you that the wished they would have spent the few grand needed to buy the SS wires....Buy the wires...

More information/history on the wires. Bruntons wires are made with rolled threads. McWhyte wires were not. Hartshorn (biggest wire maker in the 30s) were not. Bruntons is the only ones to get rolled threads. About 10-15 yrs ago, an AD came out for Cub strut forks and the new ones had rolled threads. Since then, rolled threads became a buzz word. Hale used this to his advantange in promoting the Brunton line of wires. While rolled threads are stronger than cut threads, I have never seen a wire break at the threads. It has always been at a nick. Basically, every wire made and used in the USA up to about 5-7yrs ago was a cut thread wire. Stearmans, wacos, staggerwings, pitts eagles and skybolts and on and on. Why did Bruntons get into the US market? Hale went and got them. Why did they go with Hale? He asked and his name is Wallace which had historical significance in Scotland (see Braveheart the movie).

McWhyte went out of the wire biz as it was a side line industry for them. They had a long, drawn out stike by the work force that made the wires and a few other things. This killed that division. They sold the machines and materials to Bruntons after a few years of it laying dormant.

Are wires more expensive now than in the Mcwhyte days? No not really if you consider the price for an IO360 lycoming then and now or a the price of a gallon of gas.

There was a guy who had started to build up a new wire biz. He was in the process of building the equipment when he died in the TWA flight 800 crash. He supposedly had designed and started to build CNC wire forming equipment and was going to be able to really improve pricing on wires. Too Bad.

Someone asked about Russian wires. We have asked around and no one really knows were they come from or if they are still made to order or if the airplanes are just using war time left over stock. KK

12/23/01 MASKING TAPE, ALUMINUM PREP, POLYTONE, AIRTECH

I would like to paint my plane Yellow/Black/White and have some questions about my planned sequence:

1. Paint it white (coats?)
2. Mask and paint the yellow (coats?)
3. Mask and paint the black (coats?).

I could have sworn someone specified what type of masking tape to use, but I can't find that message. Will the paint bleed under the masking tape? Charlie
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Charlie, One cross-coat of white under bright colors (yellows, reds, etc) always improves appearance. You'll usually need fewer final color coats too, so no weight gain.

Yes, lay the yellow before the black. The tape is 3M FineLine. See your local auto paint distributor. It's blue and made of a vinyl-like material. Bends around curves, conforms to stitching bumps, etc. No bleed under the edge if you're applying to a smooth surface. If not, seal the applied edge with a very light coat of the base color. When you shoot the last coat of trim color, peel the tape as soon as you're sure it won't run. The wet edge will settle down a little and be smoother.

You'll still need lots of regular making tape. Outline the mask with FineLine, tape masking paper to the FineLine with regular tape. BTW, when you're at the paint distributor, get a roll of "real" masking paper. You'll like it. Tack cloths too. Tack everything just before you shoot. Dan
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I have painted more than 80 airplanes so far. If there is only one simple piece of advice I can give you it would be, BUY 3M!!! Tape, paper sandpaper, compounds, etc.

Your paint sequence is fine but may not be correct for the paints you are using. So, I have a few questions for you. You may not know that the yellow by Hale was done in butyl dope yellow and then clear coated. It has problems with the clear peeling off.

What covering system will be used?

What paint will be used, brand and type?

What quality of finish do you want, cropduster, nice, showstopper?

What spray equipment will you use?

Are you allergic to wetsanding?

Once you answer the above, I can offer more specific recommendations for paint application. For example, if you use the paint I use, there is no need for the white undercoat. With some brands of paint, you put 2 coats of white then 3 coats of yellow or 5 coats of yellow to get the same coverage. Weight and build up will be the same. Techniques vary depending on the level of finish you want to have. Rarely do builders want junk. Most want show quality with cropduster labor. The equipment you use to apply the dope and paint will have a great effect on the finish quality second only to the effects of the applicator's skill. If you want a nice-to-great finish, you need to wetsand no matter what brand of fabric system you use. The color paint has 3 basic jobs..............1. Make the object a pleasing color. 2. protect the object. and 3. To show off all the flaws in the object.

3M makes 2 versions of Fine line tape. The green fineline and Blue fineline. Both come in many widths and are used for layout work. Typically, use 1/4" wide for layout of trim. The green is great for long straight lines and curves down to about 6" radius. The blue should never be used for a straight line as it wiggles around too much but it is used for very tight turns of 6" radius down to near zero.

When using 1/4" fineline for layout work, rub it down 100% firmly and the follow it with a run of 3/4" masking tape to help hold it in place. That is, you put the 1/4" FL down, then cover half it's width with the edge of the 3/4" tape extending over the area to be papered over. This holds the FL down better. It is best to mask, spray and remove the tape within 48hrs. The FL will start coming loose if left for a long time.

Recently, 3M came out with a new masking tape to replace the tan or beige masking tape they made for years. This new tape is called 233+ and is bright green in color. It appears to be made of a reinforced paper like a Tyvek paint suit. It is tough and will last longer than the previous tape before becoming a permanent part of the surface. But here is the REAL NICE feature of 233+. It makes paint edges as sharp as Fineline tape does!!!!! Yes that's right. It does. For those who have seen the black and Purple model 12, much of the taping on it was done with 233+. So, if you have long straight lines, use 233+ as it is easy to keep straight, makes razor sharp lines and is the same tape use to seal up the paper. KK
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A related question: Can I use Polytone (Polyfiber color topcoat) to paint the aluminum parts? Is there any pre-coating recommended? Rudi
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Rudi, Polytone colors can be used on metal, fiberglass etc. But it seems that PF has gotten away from recommending this procedure. They now seem to push using their enamel or urethane on the metal.

The best prep for alum is:

Acid etch the metal, clean and dry it after per instructions. Alodine treatment if priming will not be within 8hrs of etching.

Prime with self etching primer usually called a wash primer. This "bites" into the alum for best bond and provides a better surface for epoxy primer to adhere to.

Epoxy prime. If using PF epoxy primer, be careful not to spray on too thick as it will fisheye and pinhole. If metal is new and slick, one coat should do. If you have bodywork to sand out, 2 or 3 coats as required for sanding.

Scuff sand epoxy primer with 400 grit paper wet. Do not cut thru primer or you will have to recoat.

Paint. The minimum # of coats is 3. Always use the same # of coats on every part and if possible, the same spray gun. Many times you can find airplanes that have different shades of color on the various parts. Some have 4 coats, some 2 some 6 because the repainted them. The gray/green color of epoxy primer is close enough to the color of the polyspray for most color matches except light colors. PF colors coatings have pretty low coverage ability and the lighter colors require undercoating the parts with white or similar color. KK
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I have found that I have a lot less bubbles on aluminum surfaces if I precoat the aluminum with PolyBrush before covering with fabric. Also, Carl and I are considering trying AirTech on one of our Stearmans. Every paint job I have seen with this process has a very high gloss. I've used it once on a Cub restoration, but I have no experience with reparability. Any thoughts? Jill
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Jill, The bubble situation does show up on alum leading edge more often than other places. Alum turtle decks too. The plywood areas seem to not have as much trouble. Seems that the impervious nature of the alum forces all the vapor out the top side only. When the part is in a hot location, in the sun, or in a breeze, the top layer dries fast and tends to trap the gas bubbles in the PB. Try thinning it more, or removing it from the outside influences mentioned above. Another way around it is to use the flannel precover on the leading edge. Works great for us many times over.

We recently used AirTech (AT) on a cub fuselage. As it turns out, the products and coatings in the AT system recently changed. My guess is that since PPG discontinued the Durethane line, both airtech and SuperFlight System II have changed. Both use PPG products for auto refinish. Anyway, We followed the instructions as they are now and it is a real pain in the rear. Spray on a coat, let dry for x days, then scuff and recoat, let dry for x days again, etc. The old AT way was much faster so I hear. This new way means you have to have 20 or 30 parts ready to prime or paint as you can only do a coat at a time on each and then wait for days. Not a production type system. We found that the AT was actually harder to sand than the PF system. Also, the AT system does not block all light.

One of my employees used to work for a guy in TN that uses Airtech and said, when he joined us, that he had always been told that the airtech system was far easier than PF. He was told horror stories about PF. After one airplane with us and PF, he now throws rocks at AT and much prefers PF. Application of the fabric, tapes, coatings, sanding are all easier with PF for a given finish quality. Now that this employee reads the new AT instructions, he thinks the PF is FAR better way to go. I agree.KK

11/09/01 KIMBALL DOUBLE COVER, STANDARD DOUBLE COVER

Gentlemen, I have read about using double layers of fabric in the covering process. I have the distinct impression that this was being done mearly for cosmetic purposes. I am confused about this. If double covering serves a useful function I would be enthused to hear about it!

However, if double layering of fabric mearly to get a better paint job is the objective I can't understand it! Why add all the additional weight to a acrobatic airplane where weight is paramount? I thought "keep it light" was a primary rule.

I'm covering my Acroduster II with the heavy weight fabric for strength and durability in acrobatics and plan to use the minimum paint coats necessary to get an acceptable finish. If that means the fabric appears a little rough, or the reinforcing tapes are not hidden ... so be it. I want a lean bird not a fat one. Glenn
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Glenn, we have been discussing 2 types of double covering here. Standard Double cover and Kimball Double Cover. Both are for large displacement, high HP engines on acro airplanes. Both methods result in an equal finish weight of the covering process. Standard Double Cover is acceptable to Poly fiber and still uses surface tapes, while Kimball Double Cover is not approved by PF and does not use surface tapes. Here's a summary of the various methods:

Single Layer: If you have a 4cyl, light acro airplane like and acro sport or S1, use 3.4oz heavy duty fabric, one layer, 4" tapes in the prop was on the wings, 3" on the tail and remainder of the wings. This is the way if you have covered less than 5 airplanes.

Standard Double Cover: If you have a high HP acro airplane that will see moderate or high acro abuse, use 2 layers of 3.4oz fabric in the prop wash area on the wings, 1 layer outboard and on the rest of the airplane. Tape sizes are as above. This is a good way if you have not covered more than 5 airplanes.

Kimball Double Cover: Now for the DELUXE Advanced method. If you have extensive covering experience, you can give this a try. BUT, it is NOT APPROVED by PolyFiber and cannot be used on certified airplanes. Also, if you use this method, you are on your own as PF will not be able to help you do it. Cover the airplane with one layer of 3.4oz heavy duty fabric. Stitch it. Cover it again, CAREFULLY, with a layer of 1.7of fabric which acts like one giant tape over the entire structure. It is pretty tricky to do and this is why I have been recommending style 1 and 3 above instead of this for beginners.

You wrote that you thought double covered might be heavier. Both double cover methods are heavier than the single layer. Don't use double if your airplane only requires single. But, if you have a big engine acro airplane, one of the double cover methods should be used to get reasonable life out of the airplane before you have to recover the wings when the tapes start coming off and stitches start to break. The weight of either double covers are the same for a given airplane. The Kimball Double Cover gives a superior, slick finish but it is harder to do. KK
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Kevin, this may be a stupid question, but when do you shrink the fabric when double covering? What is the highest number of flight hours you know of covered with your method? Thanks, Jill
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Jill, here's more detail on the two methods:

Standard Double Cover: Cover inboard propwash affected part of wings with 3.4oz fabric. Glue on and shrink, apply first coat(s) of polybrush. Cover entire wing with 3.4oz, glue as normal, shrink as normal, coat as normal first coat(s). Stitch. Tape. Continue with normal coating build up and sanding.

Kimball Double Cover: Cover entire airframe with 3.4oz, glue and shrink as normal. Apply first coat of polybrush. Stitch. Carefully install 1.7oz fabric. Bond on ribs and 1" each side of ribs with polybrush. Bond edges. Shrink with mid heat between ribs, careful to not over shrink and lift the 1.7 off of base fabric. Coat 1.7 to soak thru to 3.4 and bond. A few patches here and there. Spray and sand build up as normal. KK

11/09/01 LEADING EDGES, DOUBLE COVERED LEADING EDGES

What technique works best for covering the leading edges?
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We used the double cover process on the ailerons of our Skybolt to fix a clearance problem I anticipated in the aileron cove area. It may have worked OK to cover in the regular way but I thought I would try it. It worked great and as a bonus it really looks good too. We used two layers of 1.7 oz fabric. It completely eliminates the tapes on the leading edge. We also used a trick we learned from the Eagle builders manual to eliminate leading edge tapes on the wings as well. In this method you double cover the leading edge only. If you do the bottom first you carry the fabric all the way to the back of the front spar on the top of the wing. When you cover the top you again carry that fabric all the way around the leading edge and stop at the back of the front spar on the bottom. This looks almost as good as if you used felt under the leading edge tin as many classic show plane builders do and you only have three lateral tapes on the whole wing. The trailing edge and the front end of the rib tapes top and bottom. The one of those serving also to seal the fabric edge. Works for me. Keenflyer
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My question is about poly-tak'ing the fabric to the leading edge. For a bottom wing panel where you cover the bottom first, do I understand that you would:

1. Lay a 2" strip of poly-tak along the aft edge of the top of the leading edge to secure the bottom fabric layer, then once the bottom fabric is in place, you should

2. Lay another 2" stripe of poly-tak to the same area on the bottom of the wing panel, except this time directly to the fabric, in order to secure the top fabric cover the now wrapped-around lower fabric panel.

I would assume you would: 1. poly-brush the bare leading edge normally in preparation for this process, as in the manual, except in this case, after the first (bottom) fabric panel goes on, you would do the following: 2. polybrush well the first (bottom fabric panel) layer where it wraps around the leading edge to provide the same "sticky" (sort-of) base on the fabric (to promote adhesion) for the second (top fabric panel) when it wraps around the leading edge, or do you:

3. Leave the single layer fabric on the L.E. dry to allow the fabric to "slide" relative to each other when tightening, and then poly brush with, say, well-thinned stuff, to do the final "stick 'em together" adhesion of the (2) layers along the leading edge?

Please advise. Kevin, any comments? Thanks all! Scott
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Scott, We don't do the double leading edge thing on our wings. Pitts or antiques. It has been around for a lot longer than the Christen eagle II. Many people like it but it really does not do the same job as a flannel padded leading edge.

The main reason for the doubled over leading edge is to hide the glue seams at the spar where it is less expected to see them. People look for a smooth LE and if the glue seem is not there, it will be smooth. The other option is to do a good job of gluing up the seam at the leading edge and it won't be seen either.

The double leading edge method you are asking about should not have the first layer poly brushed prior to the second layer of fabric. To be a true proper and legal glue joint, the second glue area that is on top of the first fabric must penetrate thru the first fabric and adheare to the leading edge skin. This is why it is not legal to make a glue seam over a flannel covered leading edge. That must have a sewn seam.

BTW, if you read the manual, the methods for installing leading edge tapes (whether they are at the nose of the wing or if your leading edge seam is at the spar) state that the tape should extend from 1" past one fabric edge to 1" past the over edge. So if you have a 2" overlap leading edge, you should have a 4" tape. If you double lap the entire leadinge edge, effectively you have a 15" or 16" lap glue joint. So, that would seem to indicate the need for a 18" wide leading edge tape.......

Another option is to cover the bottom of the lower wings from the 2" glue area aft on the bottom. Cover the top of the lowers from the 2" lap on the bottom side up and around to the top trailing edge. This will give you 1 2" lap glue joint that is on the "non-showy" side of the lower wing. One 4" tape there at the spar covers it up and it meets the book specs. Likewise, reverse the sides for the top wing putting the joint on the top of the upper wing where you don't see it with the 4" tape.

Now, if you have round wing tips and a swept wing, you have some work to do at the tips for any of the above methods. You have to end the wrap over fabric at the tip rib and put the tip bow seam on the bow as you would do if you had a seam down the leading edge. So, you have a tip tape anyway.

Personally, I don't do any of the above here in our shop. On cover jobs with glue seams, we put the seams on the leading edge as the book shows but cut the fabric very, very straight. We have some secret shop treatments we do to the seam prior to applying the tape and after 1 sanding, the seam is gone. One way of looking at it as the fewer glue seams we have, the fewer chances for mistakes. Putting the seam on the leading edge allows the LE and tip tape, and in somecase the trailing edge tape, to all be one continuous piece. This looks very nice. Like a stearman top wing, the tape starts at the LE butt end and is one piece all the way around the tip to the trailing edge butt end. Very clean.

So, Scott, after all that wind, what are my comments? Do it like the book shows and be very neat with every step. The one thing I tell everyone who asks me for fabric advice is.......... Treat every step from gluing the wood, to filling, varnish priming, fabric install, stitching, tapes, spraying sanding and painting as though each is the last step you will do on that part. Treat each step as though you will have to show it to your friends and critical family. If you do this, by the time you put paint on it, you will have nothing to hide or cover up. Fabric and paint do not hide mistakes, they magnify them!!! A good cover job starts when you unroll the plans.........On the other hand so does a bad one!! KK

08/08/01 FABRIC WEIGHT, PARTIAL DOUBLE COVERING

I need to make a decision on what Stitts fabric to order for my 370HP two holer Pitts:

Given the high power, I am sold on going with heavy duty 3.4 oz fabric, but the coarse grain of this stuff (burlap) would take a lot of paint and sanding to generate any kind of a finish. I could double cover with a second 1.7 oz layer, but I would gain 20 lbs (assuming minimum finish applied in both cases; negligible weight gain for a "show" finish). 20 lbs is based on the 1.7 0z fabric being 0.004" thick, around 0.1 lbs per cubic inch when saturated, 350 ft^2 total surface area.

I want to stay light, and I want a thin and flexible finish to survive flying in cold (Minnesota) weather.

I am considering double covering with a layer of 2.7 oz and a layer of 1.7 oz Stitts, rib stitching through both layers at once. Total fabric weight is 4.4 oz, all fully stitched to the ribs, few tapes required elsewhere. Minimal coats of Stitts should give a decent finish and my weight penalty drops to about 12 lbs if I do the whole airplane this way.

Further weight savings if I cover ailerons, fuselage, and tail feathers with two layers on 1.7 oz, stitched through both. Total weight penalty would drop from 12 pounds to about 8.

What experience have you guys had with 3.4 oz total fabric on fuselage and tail feathers in a high powered biplane?

Having talked to Kevin Kimball and two others on their (three different) techniques used for double covering, I am convinced the two layers will stay well bonded, but I need to stitch through BOTH layers when using lighter fabrics in a high power airplane to keep from pulling the stitches through.

Like anything else, I am sure this will all be clear and simple after the job is done, but I am a neophyte with fabric! Tom
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Tom, did you see the yellow and blue model 12 at oshkosh built by Jeremy Mason? I hope you did. That was Jeremy's first ever attempt at building an airplane and the first time he has covered one too. He plans to work the airplane in airshows and lives in canada where temps get low.

Here is how it is covered: inboard part of each wing covered with 3.4 oz. Then entire wing covered again stitching thru both layers inboard and only the one layer outboard. 4" tapes in the prop wash on wings, 3" outboard and on tail. Ailerons 3" tapes fuse 3 and 2" tapes as needed. 4 cross coats of polybrush. 4 coats poly spray, sand 220 wet, 2 coats polyspray, scuff with 400 wet then paint. Results......I very nice finish with minimal build up even with the 3.4 oz fabric. This is the recommended proceedure we are issuing to model 12 builders.

The black and purple one was covered like our yellow one double covered.

The finer fabrics have a greater elongation than the heavier ones. 2.7 oz fabric is far stretchier than 3.4. On acro airplanes, stretchy fabric is bad. This is why stits recommends and we use 3.4 oz. double layer 2.7 is floppier than a single 3.4. Double 1.7 is as floppy as a single 2.7. We have tried alot of these combos already and have discussed this issue at length with the polyfiber guys.

My recommendation would be to use the process we recommend for our model 12 builders above. It will hold up better than any of the schemes you listed with the exception of the double cover method without tapes we use which is NOT a method for a novice. BTW, good to meet you at the show!! KK

08/07/01 DRAIN GROMMETS, DRAIN HOLES

I know that drain holes must be made in the covering at the trailing edges of wings and control surfaces to drain water and allow for pressure relief. Are the grommets really necessary? Second, are drain holes required on the rudder? One side or both?
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Simply burning holes in the fabric is fine for your airplane. Locate them in the area that has 2 or 3 layers of fabric like where the rib and trailing edge tapes are stacked on top of the base fabric. Use a pencil type soldering iron to burn the drain holes. One hole per rib bay is enough. Place it on the outboard side of each rib. Some people put a drain hole on both sides on all ribs but this is not needed. The way I do it is to burn the hole then imediately press the molten dope down with my finger making a smooth hole. If you don't press it, there will be a ring of dope that is unsightly. We burn the drain holes after all dope/polyfiber coatings are applied thru silver and just prior to applying the color coats. This keeps the water out during sanding but gets the holes painted. Your airplane is a typical one that gets mounted from the leftside. So, put drain holes on the RIGHT (out of sight) side of the rudder one or 2 as needed in the lowest portion of the rudder when it is in 3 point attitude on the ground.

Our policy on drain grommets is to simply burn holes on experimental or modern stuff like Model 12s or real fast stuff like the GEE BEE we did. We use alum grommets(because they are thinner than plastic ones) with a dollar patch over them to hold them on on all the antique airplanes we restore. KK

05/27/01 POLY-BRUSH APPLICATION

I Just started covering my project using the Stits process, an Acroduster II using the "heavyweight" poly fabric.  I started on the rudder, as this seems a simple piece to start on. The video seems to imply that 1 heavy coat of Poly-brush will completely fil the weave of the fabric and not allow for future pinholes. I didn't find this the case. I spread a good layer of Poly-brush but didn't get the "translucent" appearance shown in th video, probably because of the weight of the fabric. Question is: Can I apply another coat? Do I really have to fill the weave of the fabric?  I am not looking for a showplane, just a good finish.  Glenn
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Nope, one coat won't do it.  First you brush a heavy coat of Poly-Brush, enough to see it running on the inside surface of the fabric.  Later, after you lace, tape, etc, you'll spray several wet cross coats of Poly-Brush, as many coats as it takes to completely fill the weave. That's when it will get glossy. Next spray a few coats of silver Poly-Spray, let it dry, and carefully wet sand to get rid of any surface imperfections.  Wash with a mild detergent solution and rinse well. From here on, get religious with the tack rag before you spray.  Shoot another coat of Poly-Spray (enough to pass a light check) and move on to color coats.    Dan
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Did you thin the poly-brush prior to applying it to the fabric?  It should be thinned 3 to 1 or 33% for brushing.  If it did not soak thru making the translucient appearance of the video, you did not have it thin enough.  This product MUST soak all the way thru for proper bonding to the fabric.  This one thinned brush coat will come close to plugging up all the pinholes but you will still have a few to fill. After all your tapes and patches, you will apply several more coats of polybrush by spraying it on.  These coats will fill the remaining pinholes.  How much do you need to apply?  Whatever it takes to fill the pinholes.  KK

05/06/01 COVERING TAIL FEATHERS, FABRIC OVERLAP ON TRAILING EDGE

Whats your opinion on the various ways to attach fabric to metal ribs or structure? My Acroduster II has steel ribs in the rudder and horizontal stabilizer. I can use pop rivits( the special fabric ones) or I can use sheet metal screws. The fabric clips shown in Aircraft spruce seem interesting but looks like they would require precisely located holes, and might be more trouble then there worth.  Any comments?  Glenn
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Gluing with polytak on the trailing edge of your tail feathers is exactly correct.  The first layer to glue on will wrap the entire tube (visualize the letter P).  The circumference of 5/16 tube is 1".  Now the second layer will glue to half the tube so that means you need a 1/2" wide flat glued to the surface of the first side fabric adding up to 1" total.

This instruction is one of those that you have to read both what is written and what is not written.  In other words, it says you have to have a minimum glue joint overlap of 1"(LE of wings 2") everywhere on structure.  It doesn't say the overlap has to be entirely in contact with the structure.  In most cases on tail feathers, it can't.

On attaching the fabric to the ribs of the tail, I suggest rib stitch.  We have done Model 12 tail feathers with rivets and stitches.  Stitches is much faster than marking, drilling, deburring, etc. and the stitches make smaller bumps in the finish.  KK
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You can rib stitch these just like you do the rest of the wing and such.  Just use the cloth tape made for that purpose to cover the sharp edges.  Do not use masking tape as it deteriorates in just a few years.  Poly-fibre has this tape on their supply list.   It also helps to make a small angle bend on the edge of the ribs to avoid the fabric touching the sharp edge.   You can also use the screws or rivets but you still need the cloth tape to protect the fabric.   Keenflyer

04/23/01 PAINT, FLEX ADDITIVE, CLEAR COAT

Kevin, I have a question about your standard finish, which abandons polyfiber after the poly-spray. Do you put  flex additive in the color and/or clear coats? What specific PPG products do you use? Darin
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Darin, The brand of PPG paint we use is now called Omni CV.  It is super flexable and we have been using it for years under 3 different names.  Normally, we don't clear coat the planes we do.  I actually prefer not to do so as it makes for less steps, less paint thickness, and fewer chances to screw it up. Our yellow 12 is not clearcoated.  The one we are doing now is clearcoated. Omni CV does not require flex additive.

04/03/01 SUPERFLIGHT vs. POLY-FIBER

I too, am approaching the point where I could begin doing some covering.I haven't heard anyone mention the stuff I was going to use, the Superflight system.My buddy covered his Eagle with it 6 or so years ago with no problems, other than a couple of not-unexpected cracks in prone areas.

Does anyone have any experiences they would like to share about the Superflight material?Sure seems like a lot less painting and sanding than using silver coats.All my metal surfaces are powder coated, wings finished out in L-26 a la Hale Wallace.Scott
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The Superflight system II system is a nice system.  I have used it and have friends that have used it who also have experience with Polyfiber or dope methods.  You can cover an airplane with less sanding than with some of the other systems but from our collective experience, the sanding you do with SFSII is a harder tougher sanding job.

To counter the argument that SFSII has less sanding that polyfiber, I offer the following.  Out Model 12 as well as 70 out of 80 of the airplanes we have restored or built, was sanded 1(ONE) TIME. Look at the finish we get with that ONE Sanding.  When we do a Staggerwing beech that needs a SUper deluxe finish, we spary and sand 2 (TWO) times.  That's it!!!  SO, don't take the 'sand it less time arguement' to heart.  If you sand one less time than we do with polyfiber, you won't sand at all and it will surely look like it.

Superflight System II seems to hold up well.  But it is a process that is only a few years old.  Stits, polyfiber system is over 30 yrs proven.  SFSII is auto primers an paint with flex chemicals added into it.  No one yet knows how that will hold up over extended periods of time as it is proven by tests that only fabric with 100% llight and UV blockage will last bwyonf 8-10 yrs.  SFSII does not have full UV an dlight block unless you choose black as your color.
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Scott,There are several "Superflight" systems as I recall. Back about eleven years ago I did a Clipped Wing Cub in "Superflight II". At that time this system involved three coats of primer that was rolled on with a 3" roller, like doing a house.  This was a muddy gray stuff that was to be sanded only after the second coat. It went on surprisingly smooth and sanded out very easily. It did not seem to be toxic or flamable. Next came two coats of a very high solids polyurethane paint. This was not so easy. Two problems came to light very soon. First this stuff is very toxic.It is recommended that this be handled only in a professional type spray booth using a complete paint suit with outside air source.  The stuff will kill you if inhaled or allowed on a lot of your skin.Needless to say I didn't follow these safety precaustions.I used a regular filtered mask and the stuff nearly killed me. For several months I would wake up at night not able to breath. It was scarry! I did recover without any serious problems but it made a believer out of me.The other problem I found was a quite long setup time for the color coats.In thirty minutes I was still picking the dust and bugs out of the paint. Being use to dope this was disconserting and a pain. Obviously I did not have a good paint booth. OK, so much for the down side, now the good part.Even with the bug picking the finish came out super. A deep shine that you could see to shave in almost every where. The long setup time I think helps this as it is nearly impossible to get orange peel or other things that can happen with dope. The other good thing is that the cover ability of this paint is fabulous. I found that one cross coat was enough with yellow even and you probably know how yellow usually covers.  (ten coats anyone!!)  I went ahead with two cross coats anyway but it was amazing to me.I did just use one coat with the black sunburst and trim. I just sold the airplane last fall and the finish looked just like it did when new. The airplane was always hangared and I washed it once a year whether it needed it or not.It was never polished or rubbed out in anyway, just that once a year washing with plain soap and water. The guy who bought it could not believe the finish was ten plus years old. The last thing I woould mention is the problems with patching an enamel or polyurethane airplane.  It's a bitch.  Well that is what I can tell you about "Superflight II". It has some good and some bad for the homebuilder.  In a professional environment like Kevins it would be great, but those downsides can be critical. Don't ignore them. Over the years I have used Randolph dope, the Superflight II and the Poly Fibre process. My opinion and what I will use on another airplane if I ever build another, is go with Poly Fibre with it's Polytone colors.  It is the best overall for the home shop builder. Of course you can go the Poly fibre system and still use Polyurethane for the final color, but with this you still have the patching problems. Good luck with whatever you decide.  Keenflyer
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I agree that Poly Fiber is the best overall choice of systems.  But, I must add that Urethane colors can be applied by the homebuilder/restorer without personal danger with a minimum investment in proper equipment.  Urethane finish is by far the most durable and needs repairs less often.  I have been very successful repairing fabric that is painted with poly paint.

The grey primer in the SuperFlight System II process in a poly urethane coating that uses the same toxic chemicals as the color paint in the system.   The grey stuff is a urethane high build primer made by PPG.  The paint is PPG.  The process is PPG.  The STC is Superflight.

Poly Fiber is the best stuff out there and I believe it is used by more pro shops than any other process.  KK

03/31/01 STITS, POLY-FIBER COVERING

I am building an Acroduster II biplane and am now ready to cover using the Stits process. I bought the video and manual on the covering process. It states that a glued fablic seam can only be made at structural members and that the seam must overlap by a minimum of 1" at the structural member. It also implies ( or at least this is the way I am interpreting it) that the structural member must have 1" of "glueable" surface.  On the acroduster the tail feathers (elevator and rudder) have a 3/8" trailing edge( 3/8 X 032" 4130 tube). Can I simply overlap the seam 1" and glue or do I have to hand sew the trailing edge seams?
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The polyfiber system is what we use.  I have covered 80+ airplanes with it and have sprayed about 7000 gallons of theri coatings!  I love the stuff and the system.  Here are a few pointers for ya.

Yes, you can make a glue seam on the 3/8" tube.  The available glue area for the first layer is approx 300 degrees around the circumference of the tube or about .98".  That's pretty close to the required 1" of structural contact needed.  The second layer is to be glued to the first and should be glued to the outer 180 degrees of the tube(first layer already glued there too) which gives .59" of glue area.  If you trim the edge of the second layer to be about 1/2" aqdded overlap from the tangent point on the tube, you will have just over 1" total glue lap on the second layer.  This is the intent of the instruction.  Many make a mistake and make a 1" flap on the second layer.  This is far too long and makes hiding it with a tape difficult.

The single most important tip I can give a newbie to fabric work is to treat every step as if it were the last one and you want to show all your buddies your work.  When applying glue, trimming fabric edges, applying tapes, spraying coats, make them all count.  Errors or sloppyness is very hard to hide and the fabric magnifies errors rather than hiding them.  Don't cut the farbic so it looks like you used an axe.  Be very neat with your first brush coats.  Don't believe the video and books when it says it will not show.  Be very neat with the glue.  I use masking tape on the fabric next to a glue joint to keep from getting sloppy with the glue.

When using anti chafe tape under fabric, put it on a few places as possible. Many people over do this and cover the entire structure with tape.  Never use masking tape.  I prefer 3/4" wide scotch tape. Even scotch tape will show thru the finish of you use gloss paint.  Be neat with it too.  The only places you really need to use antichafe tape is over nails in leading or trailing edges or any sharp edge that will make you BLEED when you drag your hand across it.  Nothing else.  Never put anti chafe tape where you need to glue the fabric to the structure.  The joint will only be as strong as the stickum on the tape.  

Cover the to parts such that the glue lap joint of the second side is on the 'non-showy' side.  That means cover the bottom of stab, elve, lower ail, lower wings, before the top and lap the top to the lower side.  Cover the top on the upper wing/ails lapping the bottom over to the top.  Cover belly of fuse first, then right side then left side.  Right side of rudder then left.

The trick here is knowing how nearly all people approach and look at an airplane.  I have studied this over the 20+ years I have been doing this. Take a typical flyin attendee.  He(she) walks up to the prop and reads the card to see who, what, when, where.  Then takes a few steps back and looks the ship over as he(she) strolls around the left wing tip.  Takes a brief look at the left wing tip and if they are familiar with taildraggers, feels under the tip to check for evidence of a ground loop repair.  Next, a peek into the cockpits from the left side aft of the wing.  Then takes a step back and surveys the left fuse side.  Then on to the tail observing the left stab and elevator as they move to a position to view the airplane from the rear.  After that, they move on to the next airplane.  So, the moral of this story is to make the nose, left wing, left fuse side, and left tail look the best you can.  The right half is rarely given a second glance!!!!

A note about rib stitching or rib lacing as polyfiber likes to call it now. We use the standard 43.13 knots above the fabric tying method with round cord.  Place the knots on the bottom of lower stuff and tail, top of upper parts and right side of vertical parts (unless it is a cub, champ, Bird biplane then use left of vertical).  I have done many tests on cord and knots.  The above the surface knot is always tighter than the hidden one because the connector string is an important part is the lacing system and it is usually loose in the hidden knot method.  The hidden one is not needed as the string is small unlike the huge string used in WWII on staggerwings where the hidden knot was developed.  Most people can't find the knots on the jobs we do here. We don't use flat cord for 2 reasons.  First, it is a pain in the neck to keep from having twists in it and second is that it is only 2/3rds as strong as round!  Yep flatter is weaker!  KK

01/22/01 SLAVE STRUTS, VIBRATION

Yes, the stall string is placed at the max thickness point on the strut on one side of each strut.  This stalls one side letting the side load it to dampen the shake.  This is Standard op on eagles and S2Bs etc.  The model 12 doesn't need it for some reason.  

I don't know what amount of weight added in what location on the strut would affect the strut in what manner.  I don't know of any one who has done this.  I have heard of bad things happening when the mass balance weight for the ailerons was put in the slave rod rather than in the ailerons.  I can't recall specific examples right now.  

I am sure that a $25,000 vibration survey of a skybolt would show the cause for the slave rods to shake.  But, that is alot of $ for little gain or as Dad says, " Alot of sugar for a nickel".  The round rod is on the S2A which according to the skybolt historians, is the airplane Lamar was trying to copy to some degree.  BTW, the S2B uses the 1.349x.571x.049 SL tube for its slave rods.  We used the 1.18x.5x035 on ours and Ben's.  Later, we switched ours to the same as the S2B and S2C and this is the size we sell in our kits.  Why?  Looks better, not so skinny and and it is easier to fit the top and bottom fittings onto.  We adjusted the balance weight in th eailoerons we sell to correct for the weight change in th eslave struts.  Both sizes work fine with no shake on our Model 12.

The Mac newsletters may have more ideas on what and how to get streamline struts to work great.  I don't know.  I have never seen any of his info.  I haven't built a skybolt or had more than a quick glance at the drawings.  

I made reference to the Super stinker that was the orignal prototype model 11 N11PU.  It was built by Curtis pitts and friends and had an IO540 250hp engine in it.  At that time when it was white with red and blue trim colors, it had no slave rod shake problem (it had a bad 'g' pull buffet problem though).  The airplane was sold to super stinker inc, then Ben Morphew, then Aviat aircraft.  They rebuilt it and the engine pumping it up in hp to 300 plus, a new 3 blade prop etc.  After that, the slave rod would shake very badly and even damaged one of them and a hinge if I recall correctly.  They then added huge alum fairings over the slave rods to help control them.  Eventually, they did a vibration survey on the airplane to see what had changed.  They found out that it was not airflow causing the shake but rather the increased hp of the engine combined with a different style and part number lord mount rubber caused the harmonic vib in the strut.  I suppose that is why they call these kinds of airplanes 'experimental'.  We have a customer building a Model 12 with a PW R985 450hp engine on it.  Who knows what he will see shake besides his teeth.  A lycoming on a Model 12 might make the slave struts shake, I don't know.  Funny things these Flyin' Machines!!!   KK

10/13/00 PAINT GUNS

Charlie,  the "turbine" or vacuum cleaner gun systems do not give the same high quality of finish as a conventional Binks or DeVilbiss spray gun.  You can read thru the Stits Polyfiber literature and you will not find a recommendation to use a turbine system.  Go to your local paint and body supply store and ask them for a recommended gun to shoot poly urethane paint.  That will get you a gun that'll do great on dope, polyfiber, poly paint, primer, whatever. 

We tried one, the best made that cost about $2000 for the machine and 1 gun.  Did one airplane with it and were very disappointed with the finish.  Sold it for $1000.

Do you have an air compressor?  If yes, buy a good quallity DeVilbiss or Sharpe spray gun.  If you plan to do more than one plane, car, boat , trailer paint job, by a good gun.  If you do not have a compressor and don't plan on buying one and only plan to do this one airplane, use a turbine system.  I know that many people out there have gotten a finish quality that is OK for them with one of these systems.  But, after covering and painting over 80 fabric airplanes, I find that nothing yet beats the good old high pressure gun for a smooth, gloosy finish.

To answer your last question, yes if you get a turbine system, you can use it to paint the house.  After all, that was what it was originally designed to do along with painting dump trucks.  KK
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We bought a Graco Series 700 in 1996 from C J Spray in St Paul, MN for $525 (Retail $750).   We liked it verry much once we learned how to use it.   They fail to tell you in the instructions that you only use enough air pressure to move the paint.   They only tell you this in the problem solving area of the manual.  To answer your questions:
1) Yes there are different parts for different paint consistancies.   The sets are fairly high priced, but they will give you the right set for what you are using. (dope, poly-fibre, etc.)   You will probably need a different set for latex house paint.
2) There are many paint guns that are called HVLP by there manufacturers that are really just ordinary guns operating at lower pressures.   The best systems are the full turbo types and Graco is considered the best by most for a home system.
3) The turbines generate a lot of heat and water was never a problem for us. I think that it evaporates before it gets to the gun.  Incidentally for most of our aircraft paints you want to buy a hose extension to reduce the heat at the gun.   We were told to add a 15 foot hose to the 20 foot hose that comes with the system.   This works well as it also allows you to place the turbine completely out of the painting area which is good for the filters.   We never collected any crud in our filters.
4)  I think the 700 is a single stage but I am not sure.  (it is presently on loan to another builder)
5)  Yes, with a different set of nozzles.  Call C J and they can tell you all about this. C J Spray's telephone number is 1-800-328-4827 Ext 1240.

We found this system far superior to a high pressure gun for the non-professional painter. (We definitely fit that discription)   Much less overspray, once you figure out the air pressure setting, and the paint flow is real good.   I have always had problems spray painting anything, got runs, sags, orange peal and about everything else that can go wrong.   With the Graco even I can do a smooth even paint job.   I have used it on several model airplanes as well.  ( My son did most of the Skybolt as I always hated to paint anything)   Now I don't hesitate to paint anything. This probably sounds like a commercial but really I have no stock in Graco or C J.  Just a very satisfied customer, but I wish the instructions had explained the pressure regulation.  We left it full on at first an oversprayed everything in the shop.  After we learned how we took down our makeshift spray tent as it was not needed.  Keenflyer
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A little added info on the paint gun question for you.  Most of the people who will recommend a turbine system have not used poly urethane paint with it.  The few guys I know who like it finished their airplane with polytone or buty dope.  If you plan on using poly paint on your airplane, the turbine system will have to be adjusted to a point where you give off just as much over spray as a conventional gun plus you will have to over thin th epaint so much that it's characteristics change and it behaves funny.  Likewise for polyfiber or dope build up coatings.  The material savings with a turbine system is very minimal in terms of total dollars spent.  Why?  You buy and use alot more thinner with a turbine system.  We restored 2 great lakes biplanes back to back in our shop a few years ago.  I did all the covering, spraying, and painting on both using conventional spray equipment on the first and the turbine system on the second.  Again, we bought the best unit out there from the company that invented the system and later licensed it to graco.  Looking back at my notes, it took 1.5 gal less polybrush and 1.75 gal less polyspray using the turbine.  It took 11 gal more RR8500 reducer and we also added some 8600 retarder not normally used with the onventional gun.  Taking a look at the prices of the above chemicals in ACS catalog, we saved $162.40 in brush/spray while spending $186.00 in extra thinner and retarder showing that it costs $23.60 MORE to use the paint saving gun.  This doesn't even include the color coats.

Poly paint like we use gets more orange peel texture with the turbine system as does the undercoating of dope or stits stuff.  The hot air heats the paint and doesn't let it flow out as smooth.  Also, the paint is not atomized as well with the turbine adding texture to the finish. 

Finally, the time it takes to paint a given part with a turbine system is about a third longer than with conventional equipment.  You have to move the gun much slower to get the proper coverage and build assuming you have the gun set up for this type of paint.  We found a total of 37hrs longer spraying time was required in the 2nd great lakes than the first.  Sanding time was longer too by about 15% to smooth out the texture to get our normal quality of finish.

Again , as I suggested in my previous post, if you have a compressor, don't waste your money on one of these systems.  Take a look at the Polyfiber manual and note the photos there and count how many times you see an conventional gun vs. a turbine gun.  See the picture of a great lakes on the title page, that is the one done with conventional gun in our shop as well as 2 other airplanes shown in the book( we had a hand in the rewrite of the manual).  Call Jon Goldenbaum at PF and ask him which type he uses and he will tell you conventional.  They  use a turbine at their weekend fabric classes because it is a self contained system and most assume from that experience that it is the best thing to buy.  KK

07/13/00 KIMBALL FINISH, KIMBALL DOUBLE COVER, FABRIC WEIGHTS

Here is the run down on how we use the Stits process.  First, we don't use stits color paint of either type, poly tone or Aerothane.  They both suck.  We use the Stits process up thru the silver as required by their STC and use a 2 part acrylic Urethane top coat color we have used for 20 years.

We use the HD 3.4 oz fabric on acro or big engine airplanes.  2.7oz medium on all else.  We have used HS90x and others in the past with great success too but you have to choose the proper farbic for the type of flying to be done.

Our standard finish is:

1 coat poly brush then stitch and tape.  The 4 more coats P brush sprayed on with 33% thinner.  follow that with 4 coat p spray with 15% thinner and let dry.  Sand wet 220 grit with jitterbug removing as much silver as possible without going thru pink.  Spray 2 coat p-spray with 20% thinner.  Scuff and spray 3 coats color paint.

On a staggerwing or similar high dollar plane, we add and extra round of 4 coats of p-spray and 220 sanding before the final 2 coats of p-spray to get a super deluxe finish.

How was our Model 12 done?  Here goes...The Kimball Double Cover...

Cover with 3.4oz polyfiber fabric.  Coat with 1 rolled on coat of poly tak glue thinned 50-50 with MEK. Stitch as normal. Brush another coat of 50-50 ploy tak mixture stitches and 1" each side of all ribs on base fabric. Drape 1.7oz fabric over entire surface very loose. Start in midle of part at middle rib and carefully soak 50-50 tak mixture thru the 1.7oz fabric to the base fabric, rib, and stitches 1" left and right of that rib. When done move to next rib and so on. When all rib areas glued down, glue down perimeter. See how the 1.7oz is one giant patch or tape over the whole part? When dry, shrink 1.7oz to the medium temp with iron careful not to pull loose from rib areas.  Then apply another coat of 50-50 mix polytak thru the 1.7oz to bond it to the 3.4oz. Apply any other patches near holes etc as needed. Result is very stiff, no tapes to peel off, and very slick look. Next I spray on 4 coats p-brush pink followed by 4 coats p-spray silver. 220 wet jiterbug sand. 2 more coats p-spray, scuff and 3 coats color. This resulted in a per square foot weight that was the same as the standard techniques due to the reduced fill required by the thin fabric and lack of tapes etc.

We did a stearman one time that flew in for rebuild.  It had cotton/dope on it.  We weighed it, used the same engine after o/h, same radios, metal etc.  End result after covered with stits our way was 186lb lighter!!!!!! that is a man's weight or 31gal of gas!!!  Quite a difference.  On a cub, using dope color, poly tone color, or poly urethane color over stits process or dope process won't make much difference in weight, maybe 5lb max.  The 20-30lb you refer to is minimum dope job say for banner tow cub, vs. PPG, Airtek, SF SII, system on a cub.  The all urethane systems use heavy primers in place of pink and silver.

Polyfiber is still the only system of coatings specifically designed for dacron fabric on aircraft.   KK
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Looks good huh?  Everyone thinks we did alot of spraying and sanding.  This is the same process Jim Younkin did on the Super G Staggerwings he did.  Not officially endorsed by polyfiber though.  So, we advise our customers to use 3.4oz fabric, 4" wide tapes with a second layer of fabric in the prop wash area.  This is how many acro planes are covered.  Of  course if you use plywood on your wings, no second cover.

Stits got a bad reputation when the very light fabric came out.  Everyone wanted it.  It would not take acro abuse.  Again, right fabric right job whatever the system you use.

Randolph over then past 6 or 8 yrs has totally changed its formulas due to both regulatory and other issues.  They have added so much plasicizer to try and keep the stuff limber, that it never dries.  It always stays gummy.  After 1 year, you can put a piece of masking tape on it and leave a mark.  The stuff balloned loose on one of the gee bee wings after 10 hrs and we recovered it with classic aero which isn't much better.  The one cotton and dope job we did came to us with some 1970's randolph dope, the good stuff.  It sprays different, smells different, dries different etc, from the later stuff.  The old stuff met Mil spec.  New does not match mil spec formulas.  The pitts factory was having lots of trouble with the dope jobs over ceconite then switched to cotton and found out the the reformulated dope reacted with the reformulated fabric process and the cotton would fail punch test after 3 years.  They had to eat 15 or 20 cover jobs.  Then they switched back to ceconite and again had adhesion problems like those that Kurt said Stits had.  Tapes have left stits jobs but not huge amounts of coatings leaving the bare fabric like dope has.  So, then aviat went to the PPG system that has been in existance for nearly 15yrs.  No one used it much until Superflight got an STC to use it calling it Superflight system II.  So, basically, aviat uses SFsII but buys the stuff direct from a PPG dealer.  Kevin

06/24/00 PROP WASH DAMAGE

From what you are saying, it sounds as though the bottom of your wings do not have ply covering in the prop wash area.  Is this how there are?  One thing you might like to know is with big engine acro planes, the tape on the lower surface of the wings takes as much of a beating as those on top.  On the M-14P powered birds like yours and ours, the most abused wing surface is the bottom of the lower right and the top of the upper left.  This is where tapes fell off of the black 12 and the areas culp had trouble with in the first 15hrs.  Our buddy with the M-14P powered upf-7 had trouble with the underside of the lower right wing.  We double covered our 12 and have had no trouble for 150hrs half of which is acro time.   KK

06/16/00 AILERON STOPS, RIGGING

Group, the Model 12, as well as all of the airplanes that have come thru our shop with one exception, have no stops at the aileron.  The exception is the Cub which has stops at the aileron to control travel.  I don't know if a Pitts design that uses both stops at the stick/torque tube and the ailerons.  At the stick only is good.

Aileron movent measurement is easy.  Set aileron to neutral, place smart level on upper surface.  Take base angle reading.  Deflect aileron up, add final reading to initial, gives up travel.  Move aileron to down limit and take reading again, subtract initial base reading from down reading, gives down travel.  Note that the upper ailerons will not travel the exact same amount as the lowers, that's ok.  Use the lowers to set travel.  Check both left and right.

Aileron droop is mainly used to correct for aileron cable stretch.  Most old airplanes with cable driven ailerons droop them on the ground so they are in trail in flight.  The lift "sucks" the ailerons up a bit.  On a Skybolt or Pitts that use pushrods, just line them up with the trailing edge with no droop.  A balanced aileron is the best plan for killing flutter.  I have never heard of droop being used as antiflutter.  I suppose it loads the system a bit to delay the onset of flutter.

The Model 12 has mass balanced ailerons, totally unbalanced tail feathers as are typical on Pitts designs.  NO flutter problems.  I don't know if a skybolt has been tested without the lead in the elevators or if it was added without testing from the begining and continued.  Andy? Bob?  Our Model 12 has been to 250mph, Vne is 239.  No flutter.  Sean Tucker's Pitts has unbalanced tail feathers and goes near 300mph every flight.  That lead in the tail may be correcting some other problem or just be balast.   KK

06/13/00 SQUARING WINGS, LOWER WING FITTINGS

Charlie,  a 1/8" tolerence is a perfect airplane.  A tolerence that tight makes a few assumptions.  You must assume the fuse is straight and that the wings are both trammed perfectly.  I'm not saying that it is impossible to have such fine parts, but it ain't the norm. 

SO, when he says 1/8" difference, that means using a tape measure measure from some convenient point on the wing, says the rear I strut bolt hole, to a point on the tail post, say at the lower longerons.  Repeat for the other side of the plane.  If these numbers are within 1/8" of reading the same left to right, that is a PERFECTLY SQUARE lower wing set.

What is good enough?  In our shop, I have seen as much as 1.5" difference in this measurement.  Our personal limit is 1/2" difference.  Keep in mind that we deal with alot of very old, previously wrecked airframes.  In the Model 12 world, we don't give a number for the builders to look for when measuring the squareness of the wings.  We tell them to measure the lower wings and write down  the measurements.  What ever the difference, set the upperwing to the same difference which will set the upper wing directly square with the lowers which is more important than how they square with the tail.

What are some tricks to use for a Skybolt or S2 Pitts type top wing with a center pylon??  First, do this measuring BEFORE you install you leading edges.  IF you can, do this before you weld on the lower wing attach fittings, measure the squareness and clamp perfect then weld on the fittings. Or if your fittings are welded on and leading edges are off, retram the lower wings to get the measurement good enough to suit you.  Then  install the leading edges.

Top wings on a center pylon airplane are tough.  You have to get the pylon on perfect and the fitting perfect of wait and drill the fittings when you install the wing for the first time and measure the squareness to the tail.  Again here, if the LE is not on, you can do the best you can with the fittings, then retram the wings to get them to have a satisfactory measurement.  Here use the EXACT SAME POINT to measure the upper wings as you did the lowers.  You can have some slight lean in the tail post if it is not rigged perfect with the tail wires.  So, eliminate the chance of error when aligning the upper and lower wing by using the same EXACT reference point, say the tail post at the lower longerons.  Keep in mind that the diag measurement for the upper wing will differ from that of the lower wing.

Hope this helps answer your question..................KK

04/05/00 KIMBALL DOUBLE COVER

We have done a/c with the 3.4 and 2.7 using the same # of coats. 97% of the people out there wouldn't know the difference.  Yes, the 1.7oz fabric replaced the tapes.  The only tapes on our 12 are on the leading and trailing edges, basically.  The process is tricky so I won't go into the details. I have avoided telling people how we did it.  Not to keep the secret but to avoid 4 ka-zillion questions from beginers.  Most of our builders are using 2 layers of 3.4 in board, one layer outboard and tapes.  This follows the  manual better...........Our double cover system used polyfiber coatings, but NOT in the way they are normally used.  We have not done this to a customer plane yet.  Only the yellow 12.  It's not legal on a certified a/c. Every fabric surface on our 12 is double covered.  Wings, ailerons, tail, fuse, I struts, everything!!    KK

03/12/00 COVERING, TAPE LOSS, PROP BLAST, KIMBALL DOUBLE COVER

The "tape loss in the prop blast" issue has been around forever.  We have seen this on a few airplanes including Yaks, Pitts etc. as you wrote. The issue is how much unsupported fabric you have in the suspect area.  By this I mean the square footage of open bay fabric between the ribs and from LE to Trailing edge.  If you have a cub for example, the ribs are far apart and the wing has a large chord.  This makes for a large span of fabric between the ribs and allows for greater amounts of fabric movement from prop pulses. In the case of the Model 12, the ribs are very close together leaving a smaller fabric panel.  A second consideration here is the fabric you choose to use. A few years ago, the trend was to use the lightest fabric avail to save weight.  Honestly, the weight difference is very small, like 5 lb so it isn't worth it.  The finer the weave of the fabric, the greater the amount of elongation and movement.  Think of it like this, the fine fabric has a thread count of 94TPI, and needs a thread of X length to zigzag up and down to span that inch.  A fabric with a count of 62TPI needs only a thread about 2/3X long to span that same inch because it zigs up and down 30+ less time than the fine weave fabric.  The fine weave fabric will grow larger as the threads becoiime straight.  Think of it like a phone cord.

A second major factor is the prop.  Square tips, especially BIG ones like the V-530, give off nasty tip vortices that destroy the fabric in its wake. The length of the Yak52 is such that the spiral hits the tail and beats the crap out of it.  Put a 3 blade prop on and you have no more fabric problems. If you need or want to keep the 2 blade prop, you can double cover the surface to get good fabric stiffness and stand up to the loads.  We have double covered in the prop blast zone and use 4" tapes on the ribs there several planes with good success.  We tried completely double covering our Model 12. Those of you who have seen the yellow and purple Pitts Model 12 have seen this double covering in action.  Most people cannot believe it is Stits/polyfiber because it is sooo stiff.  Many think it has tons of coating on it and lots of sanding.  NOPE!! Actually, the plane is double covered, one laver 3.4oz, one layer 1.7oz fabric.  There are no tapes on it except the edges because the second layer acts as the tape over the stitches.  It actually was sanded ONE time in the polyspray 4 coat ploybrush, 6 coats polyspray, 3 coats color, and scuff sanded once in the color stages. That's it!!  Not much coating thickness there.  Another key to controling the cracking problems.  To date, N360KJ has 140hrs or so on it, mostly acro and airshow and no cracks.    KK