Oratex Fabric Covering Revisited

[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.