Who's your momme?

Warning: Long, potentially boring.
I like silk.  It’s beautiful and works well, but is it feasible for Half-A?  Too heavy?  Too expensive? Too much trouble?  Let’s find out.  The nice feature of our hobby is the opportunity to take varied approaches to reach the same end – having fun.

Habotai silk is what modelers use for covering and is classified by weight, i.e., how much a bolt 45” x 100 yards will weigh – the measurement is in momme’s.  5 momme (mm) silk will weigh 5 pounds/bolt; 8 momme silk weighs 8 pounds/bolt.  A bolt is equivalent to 125 yd².

So, what are comparative weights of popular covering materials?
Monokote (opaque) --- 59 gr/yd²  (average)
Silkspan (GM) ---  14.8 gr/yd²
5mm silk --- 18.14 gr/yd²
8mm silk --- 29.03 gr/yd²
28.35 gr = 1 oz

I am not Ken Cook (Ken says, “You got that right, Bubba!”).  Ken flies competitively and each gram is important.  I’m a duffer and if I come home with my planes in big pieces or fly out a tank without getting dizzy and falling down, it’s been a good day.  

Let’s put these weights in perspective. I’ve estimated a Baby Ringmaster wing area to be about 110 in².  To cover requires 220 in².

For covering the Baby Ringmaster wing, here are the weights:
Monokote: 10.02 grams
Silkspan:  2.51 grams
5mm Silk:  3.08 grams
8mm Silk:  4.93 grams
Silk and silkspan will require dope (clear and maybe, color) which reduces the weight differential with Monokote.

However, silkspan and 5mm silk come in white only, so if you want color, you’ll have to paint, which adds weight.  8mm silk is already dyed (30+ colors available from Dharma Trading).  5mm is almost gauze like and will require more dope to fill the weave.  5mm and silkspan:  2 coats clear, 2 coats color, 1 coat clear.  8mm: 2 coats clear, maybe 3 for a better finish.

With clear dope only, the difference (5mm vs 8mm) in weight for the wing is around 1.8 grams.  Unless you’re a drug dealer, most of us don’t have a good feel for weight in grams.  Take a piece of typing or copy paper and cut a 4.25” strip off the bottom – that strip weighs between 1.8 and 1.9 grams. The weight difference lessens when you paint the 5mm silk.

Why not just dye the lighter silk?  For me, dyeing silk is like making my own biscuits --  the results aren’t that good and it’s not worth cleaning up the mess.  Besides, the dyeing process removes some of the shrinkage from the silk.  However, there are excellent silk dyes available and in a myriad of colors.

Silk is too expensive!!  

Cost to cover 220 in² + 15% (oversize and screwup) ~ .20 yd²:
Exam table paper (silkspan substitute) --- $0.02 (needs dope and color)
5mm silk --- $0.93 (needs dope and color)
Silkspan --- $0.96 (Brodak, needs dope and color)
8mm silk --- $1.74 (clear dope only)
Monokote --- $2.07

With Monokote, you’re one and done.  With the other coverings, you’ll need clear and/or colored dope.   Compared to Monokote, the 8mm colored silk is lighter and cost effective dollar wise.  

But, there’s always a “BUT”.   Many folks don’t like the odor of dope (or divorce).  Butyrate dope has become extremely expensive, particularly in hobby amounts.  I buy Randolph clear (tautening and non-tautening) from Aircraft Spruce and have simple color schemes. Consequently, to use silk, you’ll have to go all in. Brushing, spraying and clean-up – another topic; another day.

Is it feasible for Half-A – the big question?  From my perspective, yes.  It’s more work and will require a greater initial investment, but the cost/weight factors are well within Half-A limits.  Secondly, the majority of my flying involves larger RC planes, many scratch built, so I’m not stuck with enough material for an additional 185 Half-A controlliners.