FlyX, actually, if you drop a penny and a quarter from a high enough tower, they won't hit the ground at the same time at all.

They WOULD if you did the experiment in a vacume. whats-his-name with the spheres way back when got kinda lucky in that he picked objects and an envrioment where the air resistance was not a measureable factor using his available tech. Because we aren't flying our models in a vacume. In fact, entirely the opposite, we are interacting with the air in all kinds of ways.

So, take a glider, trim for best glide, and throw it from a tower. If you measure the distance flown vs. the height dropped, you get a ratio that just so happens to match the Lift/Drag ratio of the glider. Now, add weight, and repeat the experiment. You get the same glide path, the same L/D ratio. (as long as you don't over-do it with the weight). So the glider will wind up at the same spot, however, it will do it faster, spending less time in the air.

The reason is that the airfoil is most efficient at a particular AOA. That's your best glide and best L/D ratio. That AOA is half of creating lift. The other half is airspeed. So, if you keep the AOA constant (most efficient spot), then you have to increase airspeed to increase lift to match the increase in weight. A glider will do this for you if you have it all trimmed out right.

In powered flight, if you add weight, you have the same thing going on. Either you increase airspeed to increase lift, or you increase AOA to increase lift. If you increase airspeed, then you fly faster, and come down faster. If you increase AOA, then you fly at the same airspeed, but you're closer to stall, and since you're at a higher AOA, you have more drag being created and the airfoil isn't as efficient.

Now, that doesn't mean that a higher wingloading makes you go faster. It means you are forced to fly faster (if you can) to produce enough lift to stay in the air. If you want to go fast, you want the lightest thing you can shove the biggest engine into. And you want the wing to be as efficient as possible, which means you want the AOA in level flight to be at the airfoil's most efficient point. That means that the wing has to be big enough but not too big.

Too small a wing, and the wingloading is too high, your AOA is high, and the drag is high, and you go slow at full power.
Too large a wing, and while the wingloading and AOA are low, you're moving more airplane through the air than you have to, and creating more drag than you need to.

"Whats his name" was Galileo, and he performed his experiment from the Leaning Tower of Pisa. In fact, Galileos experiment was inconclusive to his observers. He dropped two canon balls of differing sizes, and there was a discernable difference in the time when they hit the ground. Galileo had not worked out the friction, but theorized that was to blame. His experment was repeated by Alan Shepard on the Moon with a feather and a tool, and in fact both objects fell at precisely the same speed.

Wing loading is not perfect, but it can generally tell you how a plane will fly.

Typical numbers for the 40-90 size planes are:
Sailplanes: 5-7 oz/sq. ft.
Trainers: 17-20 oz/sq. ft.
Sport aerobats: 20-24 oz/sq. ft.
Warbirds: 26-30 oz/sq. ft.

Cubic wing loading is a good way to determine across the scale how well a plane will fly. I'm not an expert on the theory, but it seems to work. Do a google search and you'll find lots of discussion.

My preference in the sport category is wing loading in the 23-24 oz/sq ft range. It suits my flying style well.

Brad

I'm doing the new kmp corsair and putting a brison 2.4 in it. not finished but weighing all of the components i come up to around 17 lbs, the wing area is approximately 1007 sq. inches. and find myself around 38 oz. per square foot. is this a doable wing loading or should i try to get it lighter? anyone who can help please, will be much appreciated.
Louis

Here's a simple way to think about it. Throw one 180lb man out of a plane with a 20lb lead weight and another out of the same plane with a 20lb parachute, see which one hits the ground first.

Louis, lighter is generally always better, I don’t know that plane so can’t say for sure, but it is probably flyable due to it's size. To explain why the 38oz/ft loading may be OK I need to bring up a related subject that often gets lost or ignored in wing loading threads. Reynolds numbers. In simple terms, Reynolds describes the scaling factor and how it affects efficiency, etc. In general, as wings become larger, they become more efficient. It is not uncommon for 35%40% scale 3D ships to have loading well into the 30’s, yet they feel very light in the air. The reason is the larger scale makes the wing much more efficient than smaller versions. Put the same wing loading on a .40 sized 3D ship, it will fly like a garbage truck.

JohnW,
Thanks for that info. I know that the wing loading isnt going to be the only determining factor, this corsair has about a 74 inch span which isnt as big as i would like although it has a very long chord length, so i'll hope that its footprint in the air brings some efficiency to the equation to whatever weight it will come up to. Further looking into the manufacturers suggestion on motors they called for a G26 as an option, but for my intention i figured it wouldn't be as good as a larger motor. Surprisingly, the Zenoah G26 with stock muffler compared to this Brison 2.4 on a Bisson muffler has the Brison about 5 OZ. lighter which sounds promising insofar that if they say that weight of g26 will cut it then maybe im not too far of the mark after all. But of course anything i can do to make this bird lighter definately i'll do it.
Louis

A far better method than wing loading to determine how well an airplane will fly is "Wing Volume Loading" which is defined as
(weight of the model in ounces) divided by (wing area in square feet raised to the 1.5 power). This works for even the smallest park flier to the largest scale models. If you find the value greater than 11, chances are you have a lead sled and if it under 6, you will have a real floater on your hands. If the value falls between 7 and 10, chances are you have a nice flyer. I think you will find most good trainers running around 7 to 9 for WVL. This doesn't mean you can not fly a model with a WVL greater than 11, it just means you really have to keep the landing speed up and watch out for tip stalls.