*heh*

Boy oh boy is THIS thread gonna release a pile of worms.

There's a couple of pretty basic principles going on here.

#1 : Angle of Attack. It is ALL about AOA.

At any given AOA and airspeed, a wing (and we can presume, from your original question, that both aircraft have identical wings....we'll drop subtle variations due to the build, etc) will produce X amount of lift.

We've got a couple of options to 'solve' this:

If we want to fly both airplanes at the same throttle setting, then the heavier airplane will need a higher AOA...and will thus encounter more drag, and find itself flying slower.

If we want to keep both airplanes at the same AOA, the heavier one will need more airspeed, thus requiring more throttle (and inducing more drag).

In either case, what we wind up with is a "slower" airplane. For any given amount of thrust, the heavier airplane will be slower than the lighter airplane.

AOA's also going to dictate some of the things jetmech mentioned above. Faster sink rate and quicker stalls for example. Again, it's simple a function of drag and lift. "engine off" is still a power setting...so given both airplanes deadsticked, the heavier one will either need to be more nose-down for higher airspeed, OR will need to have a higher AOA, slowing it down more quickly, and bringing it closer to the critical AOA.

Climbing, too, is about AOA. An airplane climbs because of excess power. It has more thrust than is required for level flight. Well...remember...increased AOA (necessary to produce the extra lift, remember) implies more drag too...requiring more power. Thus, if X power is sufficient for level flight in the light airplane, it'll take X+1, for example, for level flight in the heavier aircraft. Thus, at X+1 power, the lighter airplane is climbing, the heavier one is cruising level.

#2 : Wind

Hoooooooo boy.

Regardless of the argument's that'll be made otherwise, given a steady wind...say, wind is blowing N at 10 kts, airplane is flying S...neither airplane will know or care about the wind. Both airplanes will react exactly the same way. The heavier one will behave no differently than the lighter one with regards to the wind.

Now, admittedly, sudden and temporary gusts may be an exception here. There IS the issue of inertia in a lateral sense, and the lighter one's inertia will be overcome a touch quicker...that is to say if, in the scenerio above, a sudden 10 kt gust from the E shows up, the lighter one will change its ground track to the east a BIT quicker than the heavier one.

Where it'll make a definite and notable difference is updrafts, thermals, and what we like to call "chuckholes"...plain ole turbulence. Pretty clear that an updraft of, say, 5 kts will lift lighter things more effectively than heavier things.

So...find yourself out at the field with a pretty steady wind down the runway...they aren't gonna beavhe any differently (due to wind...they'll still have all the differences due to weight). Find yourself at the field on a day with variable and rapidly changing winds...you'll argue more with the lighter airplane.

==================================

Having said all of that....you asked if the lighter airplane will "fly better".

THAT is a pretty subjective thing.

My own personal "short answer" would be "Heck yes..lighter ALWAYS flies better". But then, I happened to have a STRONG preference...both in scale airplanes and RC....for the characteristics dictated by the lower AOA in the light airplane.

Inside a DA-20, for example, my light airplane's gonna fly slower before a stall, it's gonna start and stop maneuvers more crisply, it's not gonna sink as fast, it's gonna cruise at a lower RPM (using less fuel) or fly faster at full throttle (if I'm renting wet (heh*), etc. But there IS a tradeoff. On a hot day, lots of turbulence, I'm gonna get bounced around a bit more, and notice the impact of changing ground color (going from "over the grass" to "over the runway" for example) more.

I happen to think the advantages outweigh the disadvantages...but that's me. It's the same in RC. You want an airplane with more margin for error, capable of slower flight, easier to put where you want it, and more forgiving of mistakes? Fly light. But know that you'll argue with it more in unusual or dynamic conditions.