Oratex Fabric Covering Revisited

[jrevens]

I'm really glad we're having this discussion also. It's good to get some "real world" experience and data.
If you meant 0.27 oz. for the sq. foot of fabric, Lowell, that would give you 2.43 oz./sq. yd. - considerably less than the published Polyfiber data. I used a calibrated electronic scale, but I can't personally verify it's accuracy without test weights. I wonder about the accuracy of your scale too. However, like you said, any inaccuracy would probably occur with both samples. I look forward to your experiment with finishing the sample, as I would like to know the true weight of the paint also. That's the most important piece of data.

Of course I have thought of the fact that the volatile components of paint evaporate, and also that there is a lot of difference in "cured" vs "wet" paint weight depending on the amount & type of "solids", the curing method, etc. The wet vs dry weight difference is going to be greater with Poly-Tone than with a urethane or epoxy finish. This makes the difference between the weight of a gallon of liquid paint versus the cured or dried result of that gallon much greater with the Poly-Tone for instance. There will be more evaporation of components

On my T-18, I weighed everything I could, before & after painting, to come up with the 30# figure. I weighed & painted the rudder, vertical fin. stabilator, ailerons, flaps, wing panels, wing tips, wheel pants, gear leg fairings, etc., etc. all separately. I then estimated the fuselage based on that experience. Believe me, it was very accurate.

Finally, if you are painting your sample with Poly-Tone, I believe that the finished weight might be considerably heavier with Aero-Thane... just a guess.

[HighWing]

Thanks John for calling attention to the typo. It should have read sq. yard as the sq. ft. weight was .300 oz. Just too many numbers for this old guy.

(Edit) I do have some calibrated weights and find that my scale weighs 1% high. Multiplying all weights by .99 gives a corrected weight - not enough to worry about so I am going to continue to use scale weights.

I would also welcome hearing abouit any errors anyone might find on the spreadsheet.

I plan on painting with aerothane. I'll have to think about the possible differences between the weights of cured and evaporative drying. It takes about a week before you can wipe the aerothane with solvents before it is fully cured, so it would be lightened considerably with evaporation before final cure. Aerothane is thinned 3:1

[jrevens]

Another bit of interesting info from Poly-Fiber's website, "Frequently asked questions" -

"When Cubs rolled off the line, they had 75 pounds of Grade A cotton and dope on them.

A Ceconite and dope finish on that same Cub will probably weigh about 50 to 60 pounds.

A Cub done in Poly-Fiber has 40 to 45 pounds of finish weight.

A Cub done in urethane can get pretty heavy if you lay on the thick coats. Urethane is not known for its light weight.

Ultralights can be done in as little as 12 to 15 pounds."


I'm believe that there must be a LOT of possible variance in weight of paint jobs due to application techniques & "desired look", not to mention type of paint. Those things are taken out of the equation with Oratex. I also wonder if there is some possibility that the weight of Polyfiber fabric varies from batch to batch. It seems unlikely, but that might explain the difference between Lowell's & my 1 sq. ft. samples. I did obtain some test weights last night & verified the accuracy of my scale.

[HighWing]

Regarding weight comparisons, the elevator I have been working on, is finished to the two cross coats of white. I added these weights to the spreadsheet to give final results of the chemical weights up to the white Aerorothane only.

I would like to make several comments as to methodology.

I added a two inch strip of pinked medium weight finish tape to the square foot of fabric. An eyeball inspection of my model IV suggested about that much tape per square foot was on the finished airplane. Many of the tapes I used were one inch wide - false ribs and empennage ribs. The weight of the finish tape includes the weight of the Poly brush required for attachment. I took the liberty to add the same to the Oratex weight per square foot as that covering process also uses finish tapes. The weight was determined by calculating the weight of a 2" wide strip of the fabric based on John's measured weight.

My current Model IV has two colors. 100% of the surface is covered in Insignia White - as in the measured sample - as a base coat and an estimated 50% is painted in Lemon Yellow for the overall scheme. The numbers for the white is measured from the sample and the yellow is calculated as an estimated percentage of the white. This was to give me an estimate on the fabric weight for my personal airplane. If an Oratex covered airplane had a decorative design added either by painting or gluing on different fabric colors, it would add to the overall weight, but how much was impossible to estimate.

An explanation of the results: The fabric combined weight refers to the sq. ft. of fabric plus an estimated 1 foot of 2" finish tape per sq.ft. The chemicals combined refers to the net weight of each additional layer of chemical - Polybrush, Polyspray and Aerothane - Not including the yellow. This was to compare equally finished airplanes. However the net increase of the yellow is indicated.

The final weight comparison between the Polyfiber process and the Oratex process is given at the bottom in both white and with the estimated yellow weight. The combined Oratex weight includes the estimated finish tape weight.

Finally, I can think of at least one variable that would influence the final weight vs. my measured square foot extrapolation. Possibly reducing total chemical weight by approximately two pounds. It is that not all of the fabric actually applied in the Polyfiber pricess has the finish chemicals applied to the surface because all fabric underlying seams would have none of the brush or sprayed coats of chemical. For example the 3 inch (or more) overlap on the leading edge of the wing would reduce the overall fabric surface by about 3.5 sq. ft. That would reduce the total applied chemical weights by a small fraction over one pound. To a lesser extent there is a half inch to one inch overlap on every foot of seam - leading edge, trailing edge and longeron length. The best way to get close total weight differences is by, as John Pitkin suggests, a manufacturer that uses the two systems in airplanes built to an exacting design and graphing the weights over time - SLSA.

Finally, I was surprised that the weight of the white Aerothane was as high is it was given that the pigment is titanium dioxide.

[Cherrybark]

It seemed useful to post this general information here rather than bury it in my build thread.

Today I had a conversation with Lars, Oratex Tech Support, Alaska. One question was the shelf life of the two component glue listed in their catalog. The instructions for this two component system said to mix the complete contents of the bottles. The factory learned builders were mixing small batches and the lawyers went nuts worrying about inaccurate measurements and liability issues. Now, the glue is only available pre-mixed and the catalog is out of date.

This news led to the obvious question of the shelf life of the pre-mixed glue. If you keep the bottles at a stable temperature and out of the sun, the glue is good for one year. Widely varying temperatures or exposure to sunlight can reduce this to three months.

[efwd]

Good to know. Thanks Carl.
Eddie

[Cherrybark]

Lars used the term, "First Class" fabric, while giving a rough estimate to cover a SS7. I asked, and he said Oratex offers "blemished" fabric. He gave the example of a bug landing on one of the rollers that applies top coat. As the fabric moves through processing, the color coat of the fabric has a blemish spot every "diameter" of the roller until the problem is caught. He says this cheaper fabric is very popular in Alaska because Black Fly season paints the wings anyway.

[bumsteer]

Thanks Carl. Guess I'll do some testing with the glue I have. It shows an expiration date of 12/1/2016 but has been kept in a relatively stable environment.

Rick

[Cherrybark]

Now, what I expect will be the most controversial point from the conversation. I rolled my eyes as he described this idea but, after giving it some thought, and going over the wing with a tape measure, I'm intrigued.

John was able to buy a wider 75.6" fabric and had useful pieces after covering his wings. The fabric goes through processing at a wider width but the edges, damaged by the material handling of the machines, is cut off and the finished width is now delivered as 72" useful. I hadn't read this thread and don't know for certain if the wider width is possibly still available. Let's assume the 72" width, quoted by Lars, is all that is available today.

Back of the envelope calculations here and I'm not completely up to speed on the required fabric overlaps but here goes. If you roll the fabric along the length of the wing, you'll have a roughly 168" x 72" panel and you'll be cutting around 20" of that 168" length as scrap. After covering the top and bottom of both wings, you will have around 56' (yes, feet) of this 20" wide strip of fabric. That width might be useful in covering the elevator but I believe it's too skinny for anything else, short of pre-gluing or other ugly approaches few of us would be willing to take.

Lars' passed along an alternate idea for covering the wings using much less fabric and saving money on this expensive material. Rather than going lengthwise, cover the wing "chordwise". Glue the 72" width of fabric to the trailing edge, wrap around the leading edge, then overlap and glue back at the trailing edge. Three 72" panels is more than enough to cover the wing. You can either trim the fabric so there is a 1" overlap at a rib or do a full bay of overlap and still have material left over. Lars would insist on rib stitching, but you're probably going to do that anyway. And 2" finish tapes completely hide the seams.

Again, rough calculations but this approach appears to save 11' of full width fabric - a very useful piece for covering tail feathers.

Comments are solicited please! And please don't be shy about correcting any miscalculations.

[Corrected typo on width of John's fabric]