tech data on single vs double covering at very low Re?

[lincoln]

I have a 5 or 6 gram Porterfield Zephyr dime scale per the old Guillow's plan. Currently single surface covered. Trying to figure out if it would help to cover the bottom. Covering right now is top surface only, wrinkled because structure would warp if I tightened it. Re is probably around 12k or so, plus or minus a bit. Ribs look to be about 10 percent thick.

Anyone see any tech data on this? Profili (and therefore, I think, Xfoil) barfs when I try to simulate single surface.

[slipstick]

Sorry, experimental "data" only. Tried it once or twice over the years. Adding the weight of extra covering while reducing the airfoil camber has never out worked well for me.

BTW if that's tissue covering then it shouldn't be particularly wrinkled. Did you pre-shrink it before sticking it to the airframe ?

Steve

[lincoln]

I wrinkled it on purpose, so that it wouldn't pull hard on the framework. This is common on indoor stuff.

The camber of the single surface covering is FAR more than optimal. Since the ribs are 10% thick, the single surface covering probably has an effective camber close to 9 percent. (10 percent minus half the average of the l.e. and t.e. thickness)