Re: Oratex Fabric Covering Revisited
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 Now, the glue is only available pre-mixed and the catalog is out of date.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.
Re: Oratex Fabric Covering Revisited
Good to know. Thanks Carl.
Eddie
Re: Oratex Fabric Covering Revisited
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.
Re: Oratex Fabric Covering Revisited
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
Re: Oratex Fabric Covering Revisited
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]
Re: Oratex Fabric Covering Revisited
Hi Carl,
The fabric I got was 75.6" wide. I purchased 25 meters (82'). I actually got a little more than that from them. The alternate covering scheme sounds reasonable. FWIW, I was able to cut the 4wing panels leaving a wide enough strip to get 4 elevator, 4 horizontal tail, & 2 rudder panels, with very little waste. I believe I cut the wing panels 46.8" wide, leaving almost 29" for the other pieces. Out of the rest of the fabric I cut all of the fuselage pieces as well as the vertical fin.
Re: Oratex Fabric Covering Revisited
Hmmm. I unrolled the fabric the entire length of the horizontal and cut it off. Folded the fabric around the horizontal like a taco shell. Wonder if the remaining length of fabric on the roll will be long enough to cover the wings length wise and the fuselage. Guess I will have to consider using the multi panel method possibly.
Eddie
Re: Oratex Fabric Covering Revisited
A few months back, John received fabric with a width of 75.6", but today's factory specs say "71". John was able to cover his tail pieces from the long fabric pieces leftover after cutting the wing panels. A reduction in width to 71" makes the cuts much more critical and might change the layout plans.
In a recent conversation with Paul Mills, Oratex Sales Manager, I asked about the actual width of the fabric being delivered today and mentioned the change. He explained the 71" figure was the "guaranteed flawless finish width of the fabric". The large fabric rolls make several passes through the coating machines and, despite extensive air filtering, impurities do sometimes make it onto the coating. During final inspection, when they find a blemish, they cutout that section of the fabric. Fabric width outside the specified 71" is still perfectly useful but there may be specs or other issues with the coatings that make is less than perfect. Paul said customers routinely layout covering panels so the blemished coating is overlapped by "perfect" fabric then, of course, tapes.
Oratex, being a German company, works in metric but a rough width of delivered fabric remains 74".
Re: Oratex Fabric Covering Revisited
As I explained in a private message to Carl as well as the post on 2/9/17, it should be relatively easy for anyone to cut out the wing panels and leave enough width of material to do all of the tail surfaces except the vertical fin with the remaining strip of fabric. Of course accurate cuts have to be made. Don't waste extra material on the wing panels... it isn't necessary. Take a little time and accurately determine the layout for how you'll cut out the various pieces. The stuff is too expensive to waste. I should have written a book.
Re: Oratex Fabric Covering Revisited
Get started on that book John! I would be happy to receive a rough draft in the next two or three weeks!