Everything you said about viewing wing loading as flying speed necessary to maintain flight makes sense. So I'm assuming an aircraft's speed must affect its lift. It must. Right?
yes, absolutely.
So if your airplane has greater wing loading than it will need more power for slower flight than a plane with less wing loading? Is that what you're saying?
No. Mixing apples and oranges here. More loading means more speed required for the wing to lift the load, period. You can't lower a wings stall speed just by putting more power on it. The min flying speed for a given weight is what it is. (OK you guys, don't argue that technicality w/ me here and confuse the poor guy even more, it won't be constructive for this aero 101 lesson) More power will get you faster flight, but not slower.
And also, with these fully symmetrical wings that are commonly used on 3D/Aerobatic models, the wings don't produce lift in level flight. Bernoulli's principle describes how a faster moving fluid over the wing relative to under the wing will cause a change in lift, BUT there is no change in speed of the fluids at level flight as the distance from the leading edge to trailing edge is the same.
We know what you mean, but to make things more clear for this and future discussions, let me help you say it better. Do not confuse LEVEL FLIGHT w/ ZERO ANGLE OF ATTACK. Any wing, even a symmetrical wing, IS making lift in level flight or it wouldn't be flying, right? Right. It's the angle of attack that you meant to refer to. But you were on the right track.
So my secondary question is: since we must adjust the wing attitude in slow flight to generate lift and prevent a stall, how come we don't have to do something similar in fast, level flight? I have noticed when I "punch" the throttle, the plane will maintain altitude. Why wouldn't the plane be falling as it's not producing any lift to counter its weight?
Hmmmmm. Well we DO need to do that ! Think of it this way: A symmetrical wing has 2 variables that determine how much lift it makes, AOA (angle of attack) and speed. They are in a CONSTANT trade off during flight. You wanna fly slow without descending? Gotta increase the AOA. Ya wanna fly fast without climbing? Gotta decrease the AOA. It's impossible, tho to see a change in AOA from, say, 3deg to 1deg as you speed up while maintaining level flight. It's there, just not noticable as your model rockets by. And believe me, there IS at least SOME small positive AOA or you're right, the model would definitely be falling. And re-think your understanding of "stall". Increasing the AOA is the ONLY repeat ONLY (seriously, ONLY !!!) thing that can create a stall. It aint (directly) a loss of speed. Research the term "critical AOA" and it's relationship to lift. I'd run it all down for you, but frankly, I'm tired.[&:] It's not a difficult concept, but it's a critical one.
When you talk about the trade-off of power vs. weight (i.e. 30% more power for 5% more weight), would you calculate that with difference in horsepower (a percentage, not actual horses) vs. difference weight (again a percentage), and then try compare them?
Sure. If I have a model that's not climbing well but is lightly loaded and glides just fine then I know I have some room to bargain. I won't mind adding some more weight in that case because the stall speed wont increase by much and the climb might easily double
(climb is a function of "leftover" pwr above "minimum" reqd for a given speed. If a 1 hp model is using up .9 hp just to stay level it only has .1 hp leftover to climb with. Bumping up to a 1.2 hp engine, igoring for simplicity the weight penalty, means that the model now has (1.2 - .9) .3 hp to climb with, a 300% improvement in climb from a 20% improvement in pwr. An extreme but valid example.)
Rodney:
I'm not quite sure what you mean with wing loading affecting airplanes differently from plane to plane, like a 1/4 IMAC plane to 1/2A. I thought wing loading was supposed to be a generalized statement about the loading on the wing. So, wouldn't a wing loading of a 15 oz/ft^2, for instance, affect the 1/4 IMAC plane the same as the 1/2A? If you could develop on this that would helpful
Not to speak for Rodney, but I think I'll speak for Rodney!
(Correct me if I'm wrong, Bro)
Think in terms of wing VOLUME, not just area. If a wing is doubled in area as the THICKNESS remains the same then it's apples to apples. Your manipulating twice as many air molecules. But the thickness of the wing usually increases along with span and chord, right? Sooooo, It's more of a cubed inches thing that a squared inches thing. Example: my Ultra Stick and my Giant Ugly Stick have roughly the same wing loading in terms of oz/sq in (giant slightly higher loading), but the Giant seems to have a slightly lower stall speed! For 90% of what we're doing tho, comparing sqares to squares works just fine.
Wow, long post. I need a nap! Hope this helped, Don.