RE: What is cubic wing loading????
Francis Reynolds, writing for the old Model Builder magazine, did originate one of the cubic loading formulas. And he had 2 versions of the formula.
The problem is that wing loading does not work when comparing airplanes of different sizes. Reynolds was making an attempt at creating a formula that would cut across size.
His original formula did include a variable for average wing thickness. This was later replaced by his less complex formula using the weight divided by the area and the square root of the area. This is area to the 1.5 power. The result was pounds per cubic foot. He claimed this formula worked just as well as the more complex one.
Another modeler, who was more sailplane oriented, used a formula that was weight divided by the area and the span. This one favored longer wings.
Reynolds also showed his Reynolds Performance Factor, which factored together cubic loading and power. The problem with this formula, in my opinion, was in 2 areas. First, the answers were in very small decimals. I feel that when the average modeler sees a number like .00013, his mind zones out. Second, the smaller value was better than the greater value. This may be fine for wing loading, but when you start adding in power, we tend to think of bigger is better.
Since I wanted to use the formula, I went into it, and disregarding units, revised it so the larger the number, the better and the answers came out in numbers like 75, 100, 150. Sizes we normally understand. I called this revised formula the Aircraft Performance Rating, or APR. Both Reynolds' formula and mine require you to enter a factor for the engine. This is a judgement area and it can influence the answer.
I will be glad to supply the formula to anyone and I have it done in Visual Basic on CD. I compiled it on a computer running Win 98SE, so I am not sure if it likes Win XP or not.
A couple of examples follow: EF = eng factor WL=wing loading. CL=cubic load, APR=acft perf rating
750 sq in 7.5 lbs .46 EF=1.2 WL 23.04 CL 10.10 APR 72.90
750 sq in 5.0 lbs .46 EF=1.2 WL 15.36 CL 6.73 APR 164.03
750 sq in 7.5 lbs .914s EF=.85 WL 23.04 CL 10.10 APR 51.64