Oratex Success Stories
Steve Harris' Bearhawk Four Place
Independent Weight Comparison
Bearhawk design engineer Bob Barrows made three test panels, one with Oratex 6000, one with 2.7 ounce Ceconite with very light coatings and one panel with normal coatings. The Oratex panel weighed 12 grams, the panel with light coatings weighed 20 grams and the panel with normal coatings weighed 30 grams. On an LSA weight savings are critical, so they were very pleased with the weight savings.
After just completing a Bearhawk 4 place that I covered with Oratex in Cub Yellow, I thought I would share a few thoughts on my decision and experience with the process. For those not familiar with the bearhawk, it is a 4 place aircraft with metal wings, tube fuselage, and all control surfaces (aileron, flaps, tail) all covered in fabric. Powerplant options recommended are Lycoming 180-260HP. My plane has a Lycoming O-540.
Choosing Oratex. First - a little background on my experience as a builder and with covering. I have previously completed an RV-4 so the metal and systems work was all familiar to me. My fabric covering experience however was limited to some minor repairs using the Polyfiber process on both a Citabria and a Tripacer I have previously owned. I looked at all of the fabric covering processes. The poly fiber is well proven as is the Stewart system. Of those two choices, I really liked the Stewart for the water based non-toxicity aspects and was leaning heavily that direction. Frankly, painting has always been something I don't care for. My RV-4 is polished rather than painted because I like the look, like the weight savings, and don't like to paint. A colleague at work that was working on another experimental, introduced me to the Oratex system. The Oratex material comes in a variety of colors and requires no painting. It is also all based on a non-toxic glue system that doesn't require any special care to avoid fumes or contact with the glue and there are no solvents other than water. I looked into the system and ordered some sample materials to try. I used the sample material to cover my seat frames. The Oratex system requires that you apply the water based glue to both the fabric and the structure and let it dry completely. After the glue is dry, you apply the fabric and activate the adhesive using heat. Lastly, after the fabric is completely attached, the fabric is shrunk to final tautness using a higher heat setting on the iron or heat gun. My test experience covering the seat frames was frankly mixed. I had not invested in the recommended heat gun nor iron and was using a standard household iron for both activating the glue and shrinking the fabric. Shrinking was not a problem, but because of the amount of fabric I had ordered (too little) and not doing a thorough job of heat activating the glue, the fabric didn't adhere to the frames as I expected. It was relatively easy to peel away. After consulting with Lars and visiting my colleague who was also using the Oratex system and had done some careful adhesion tests, I was convinced it was user error in the application. I also had some issues with the tapes and corners in not getting all the wrinkles out in the tight bend areas. Again, this was user error and frankly just not being aggressive enough with heat and stretching the fabric and tapes. In the testing I performed on the seat frames I discovered there is definitely a learning curve with the system but also I was very impressed with the strength of the fabric and happy with the look of the pre-colored fabric. Some comments here on the appearance are appropriate. The typical doped fabric has a shiny appearance and due to the layers of glues, fillers and paint applied form a very nice and smooth transition from the tapes to the fabric. As Oratex is pre colored, there are no fillers or paint that smooth the transition to the tape edges. In addition, the fabric is slightly translucent and when backlit the structure underneath is visible. Although this is a different look than the traditional fabric, I personally don't find it objectionable. If you are looking for the slick show-plane finish, Oratex probably isn't the right choice. My mission for my plane includes back country, rough surfaces & areas that are prone to create some damage from gravel or rocks. The Oratex fabric is very tough and extraordinarily easy to repair as compared to the other fabric systems. It is also substantially lighter. Those factors for me with the additional benefit of not having to paint made it a very good choice for my airplane.
Applying the fabric. I started my fabric work with the flaps and ailerons. These are a good choice in that there are no compound curves so it is relatively straightforward and enables you to gain some experience before moving on to the areas that require more skill with the system. The process went smoothly, the only issue I had was again initially in not getting the glue fully activated. It does require care and patience to make sure you get every bit of the joint surface to the activation temperature and apply enough pressure to get a good bond. Fortunately, it is easy to go back later and apply the heat and pressure and fully bond the joint. Once that hump was crossed, it was really quite straightforward. Once the flaps and ailerons were completed and put on the shelf, I moved onto the elevators and horizontal stabilizers. These surface are more complex in that they do have complex curves and also require rib stitching, another new skill to be learned! The learning doing these surfaces was really in how to get the curves and corners to lay down neatly without any puckers. I did end up with some areas that have some slight puckers at the corners. The lesson is to apply plenty of heat and stretch to really form the fabric or tape to the curve. A helper is really necessary here. Mine turned out pretty good, but if I were to do it again, I could achieve a much more perfect job. I saved the fuselage to the last for obvious reasons. It is by far the largest (read most expensive) pieces of fabric and has lots of areas that are curved or where there are transitions to be made. Additionally, there is no way to do it without some joints. A particular area of concern for me was right in front of the vertical stabilizer. There has to be a joint there and it also has a curve up for the vertical stab and the curved transition down around the sides of the fuselage. I chose to cover the fuselage in 3 major sections and one minor. There is a left and right side that start at the bottom of the fuselage and go up the side and over the top. At the forward end, the circumference of the fuselage is large enough that you can't quite reach an overlap with just the two side pieces. Overlap joints have to be made at a structure, not in free space. I covered both left and right side starting at the bottom and terminated at stringers on the top. I then had a long triangular piece on the top that from each stringer back to the vertical fin. After applying the glue to the structure and fabric, I started by firmly attaching the fabric at the bottom and insuring a good lap around the tube as required by Oratex and then stretching the fabric toward the top of the fuselage and tacking it in place temporarily as I stretched and worked out as many loose areas and wrinkles as possible. It is really critical to do this, although the fabric tightens up in the final shrinking, there is a limit as to how much it shrinks and it is best to get it as tight during the application as possible. It took time and lots of pulling and stretching but worked out very well. Actually the area in front of the vertical fin that I was so worried about worked out better and easier than I expected. Once the sides and top were completed, I applied the bottom section as my final step. I really like doing it in this order as it allows good access from the bottom for any final work that needs to be done inside the fuselage.
A few final notes. Access plates and inspection covers are pretty easy. I just cut out frames the size I wanted in aluminum, put in nutplates and then glued to the backside of the fabric. Once in place you can cut the fabric in the opening and trim, fold, and glue it back over the inspection plate. I also covered the doors and some fairings and other aluminum pieces with fabric. Application is similar and by doing this it creates a perfect color and texture match with the fabric that would not be achieved with paint.
Overall I am very happy with the process and results. I now have about 30 hours into my test flight period and have had no issues. The Oratex is a light, tough, and although there is a learning curve, straightforward to apply. I would use it again for a plane with a similar mission.