Side note - Stress testing Oratex UL 600

About a year ago I discovered the existence if a new kind of fabric for covering light aircraft. It is an iron-on polyester fabric very much like what is used for model aircrafts. I contacted the company (http://www.oracover.de) and they proposed to send me a free sample of Oratex 600 UL in the colour of my choice. At that time I was thinking that when re-covering my Avid Flyer it would be yellow so I asked for Cub Yellow.

Oratex is glued to the construction with a thermo activated glue (hot melt). It looks like white glue and smells about the same, i.e. almost nothing compared to traditional glue for covering fabric. The glue should dry before applying the fabric and it is then activated through the fabric with an iron. The tension is obtained with a heat gun. Finished, no paint, no nothing!
Compared to the pain of traditional covering (glue, fabric, dope, UV protection, primer and topcoat in multiple layers) and a total weight of 110-130 g/m² this sound too good to be true... 

Just like with the Simonini engine the question is "will it age well?".

To make an extreme aging test I made and covered 3 small profiled frames (20cm * 17cm). On each of the covered frames I glued a rectangle of fabric like for a reinforcement or repair. The first frame stayed in my office without receiving any direct sunlight.

The 2 frames mounted outside

The second frame was mounted outside but under a protecting roof. Facing south and exposed to sun and wind all day but fairly well protected from rain and snow. The third frame was mounted outside but without any protection. Facing south and exposed to sun, wind, rain and snow…

The frames were left for 9 months from the beginning of December 2010 to the beginning of September 2011 (somewhere between Lyon and Grenoble, France, with an average of 2000 hours of sun per year). We had a lot of snow during the winter, rain in the spring and a lot of sun and strong heat during the summer.

9 months, 1500 hours of sun, equals 100 hours per year for 15 years. I’m happy the years I get 100 hours in the air...

So, after 9 months I took in the frames and cleaned them (regular dishwashing liquid, warm water and a soft brush). This is what they looked like:

Reference frame                 Protected under roof                Fully exposed   

My reference frame, the one that had been sitting on my desk, didn't show any sign of aging at all. Anything else would have been very surprising and put a rapid end to the test... 

The second frame came out smelling like a rose...

After sitting in the sun, but under a protecting roof, during 9 months it was in so good condition that it was almost only the holes from mounting it on the wall that visually differentiated it from the reference frame. I can hardly see any difference in colour between this one and the reference frame. The fabric sticks just as well to both other fabric and to the frame as on the reference frame.

The third frame had suffered badly (but what else to expect?). 

Water, from rain and snow, had made its way inside the frame. The frame itself and the fabric shows sign of mould. Where there was mould the fabric would no longer stick when glued onto fabric and stick noticeably less, or not at all, where glued directly to the wooden frame. It is also very difficult to get the fabric clean. 

It should be noted that the square patch has suffered much less as being less exposed to the permanent moisture accumulated in the wood.

The Oratex fabric is surprisingly resistant to penetration (much stronger than my current traditional covering).
I have without success tried to penetrate the fabric by pushing my thumb (nail first) as hard as I could at the centre of the frames. My thumb hurt but the fabric resisted on all 3 frames...

Penetration with a sharper object (a BIC crystal medium point) is possible and there is a difference in resistance between the frames. 

The fabric on the reference frame is penetrated by the pencil at a pressure of 2 kg. The fabric on the second frame offers slightly less resistance: ~1,6 kg, while the fabric on the third, fully exposed, frame breaks at just under 1 kg.
 
It is difficult to compare this with traditional covering as I don't have a sample frame, but when I (by mistake) put a screwdriver through the side of my plane I didn't have the impression of using much force. To put the same screwdriver through even the third frame takes significant pressure. I feel confident saying that even the fabric on the third frame offers better resistance to penetration than what I have today.

The second frame, exposed to sun and wind for 9 months, could probably be said to be the most representative or realistic of the 3. I don’t normally leave my plane outside in bad weather except when travelling and not having a choice (and it would not be snow and ice, only occasional rain).

I'm impressed by the result of this stress test and will definitely consider this as a most interesting alternative when I decide to re-cover my plane (not this winter, but maybe next...). 
But I think I will do it white...