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Polyspan / Silkspan

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Jim Hoffman:
I’ve built three I-beamers over the years. Polyspan is my preferred covering. Stronger and more puncture resistant than silkspan. The resulting wing is pretty stiff in torsion.  I add extra coats of clear over the ribs to protect against sand through no matter what the covering used. 

Dave_Trible:
In my earlier years I preferred Ibeamers so did a number of them.   The sand through problem was irritating and had to do a lot of hole patching.   On a few I doped on a second narrow strip of silkspan over the ribs-sort of like the pinked cloth strips used on full scale over the ribs.   I might still go through the colored dope in spots but didn't damage the silkspan to the point of having to apply a patch.   Yes a lot of extra dope over the ribs will help too.   I have never tried Polyspan.   May be worth a try on my next Ibeamer-or just use silk.   I don't do as much (if any) wet sand and rubout stuff these days-mostly just well-retarded clear coats to save finish weight and a lot of elbow grease so for me it probably doesn't matter much.  I'd rather save a few ounces and hope the airplane flying better will gain back any loss in appearance points.  On my larger airplanes I'd have to put on another quart of clear to have enough depth to withstand a proper wet sand and polish.

Dave

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