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There are many reasons to want to build a light, strong structure.
They can be summarized in a single sentence: lighter planes fly
better! Here's why:
- More load capacity: All other things being equal, the
lighter plane can carry more ``cargo''. This means the
plane can carry more fuel, larger servos or nicads, airborne cameras,
piggy-back sailplanes, floats, etc. High-performance electric planes
in fact depend upon a lighter structure to offset the increased
weight of power nicads.
- Better climb performance: Again, everything else being
equal, the lighter plane will climb quicker. For us, that means better
vertical performance for aerobatics, among other advantages.
- Better acceleration, quicker control response: Good old
Newton said F = ma! Given a certain amount of force (thrust) from
the engine or flight controls, the lighter plane will
accelerate quicker. This makes for a responsive plane in flight. The
heavier plane will be ``softer'' and more ``mushy'' to fly.
- Lower stall speed: The lighter plane can fly slower
without stalling. This translates to short, quick takeoffs and
slow-as-a-walk landings. This is especially relevant to float planes.
- Higher top speed: Well, sorta. Because the heavier plane
must create more lift to fly, and that increased lift induces some
additional drag, a lighter plane is usually slightly faster.
- Wind/turbulence: Ah, you say, here comes the BAD part! Well,
yes - and no. The lighter, more responsive plane will react more
quickly to wind gusts and shifts to be sure. But corrections you make
will also take effect faster. Problems with wind, turbulence and gusts
are more related to wing loading (flying speed) than just to weight
itself. If we took some weight out of a plane, then lowered the wing
area proportionally, then the plane's behavior in the wind would
remain ``about'' the same.
One more comment on lower aircraft weight. If you can save weight
somewhere, you may be able to save even more somewhere else! The
lighter your plane, the less structural "beef" is required. An
obvious example would be landing gear - a lighter plane can use
lighter landing gear. This principle applies to the entire
plane structure.
Another point of contention here could be crash survivability. The
critical point is that lighter structures can be just as strong -
good results depend on excellent structure design! It's easy to make a
heavy, stout plane - a lightweight strong plane is harder to come by. The
fact is, crash damage is a result of how well or how badly a plane can
absorb the energy that must be dissipated in a sudden stop. That
energy is, again, related to the plane's weight - less weight, less
energy to absorb in the crash! If you also consider that the
lighter plane has a good chance of crashing at a lower airspeed, then
the light plane actually may suffer LESS damage in the same
circumstances! The trick is to ``build strong where needed'' and build
lightly everywhere (else).
Next month we'll dissect a few popular kits to illuminate
exactly how you can safely lighten the structure while maximizing
strength. Use these tips for building that new plane (or converting
your favorite glow kit to electric power...grin). I close Part I
with a couple tips from Clay's article on structure lightening.
Next: Until Next Month...
Up: Building Light for Better
Previous: Building Light for Better
Craig Kulesa
Fri Dec 4 18:49:42 MST 1998