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We all know that more weight means more speed but how much? My wing
reviews are obviously done with my 150 pound self so I'm unable to see
what happens at real high wing loadings since they don't make wings that
small. The Plasma 22 and Pluto 21 were the smallest production wings
I've tried lately and my Spice 22 is too big for me. To get a high wing
loading I have to fly a 17 and nobody makes those in enough quantity to
call them production.
So how much faster would a heavier pilot go on a Spice 22?
Thankfully, some brainiac aerodynamic types, Dana Hague and Carlos Curti
show how. The formula is
(SQRT (New Weight / Original Weight)) * Original Speed
(either airspeed or sink rate).
For example, lets say a 300 pilot+wing+motor wants to know what his
speed will be on a wing flown by a 250 pound pilot+wing+motor. Calculate
the square root of (New Weight - Original weight). So if the original
flight test was done at 250 pounds with a reported speed of 25 mph and
the new weight is 300 pounds you would SQRT (300 / 250) to get 1.095.
That is, 300/250 is 1.2 then SQRT(1.2) is 1.095. Multiply 1.095 by the old speed of 25 mph for a new speed of
27.4
mph. If the original sink rate was 400 fpm than the new sink rate will
be 1.095 * 400 or 438 fpm.
Risk of Small Wings
I love small wings and it's tempting to keep going smaller and
smaller but know the risks and tradeoffs you're getting into. I've flown
an 11 meter wing and will likely never do so again.
1. The main reason is what happens after a motor failure. If it quits
just after takeoff, you'll be faced with a surge and dive at very high
speed. The appropriate response depends on altitude; if you're a foot
off the ground, an immediate pull of brakes will do, if you're 10 feet
off then a brief pause to allow surging to a mostly level attitude is
followed by a pull of brakes to avoid having a big sink rate develop. If
you're above 100 feet than all is well as you would have enough time to
let the wing surge, establish a glide and do a normal flare.
2. You'll be running at break-leg speeds, especially at higher
elevations. Any foot dawdle or surface perturbation will have graver
consequences and will, generally speaking, suck in quite large
doses.
3. Another tradeoff is high fuel flow. Just like with reflex wings
trimmed fast, it takes a lot of power to overcome our draggy craft and
that means a lot of fuel burn.
4. Handling will be extremely sporty especially for those models that
are known for sporty handling to begin with. I can only imagine what a
16 meter Spice would be like (admittedly I'd love to find out).
5. Lastly, although speed is great, if you do suffer a collapse the
recovery will be, pardon the understatement, "dramatic."
So dive into small wings with understanding. Understanding that yes,
they're fast, they're easy to inflate and they're easy to carry but
they'll bite anyone not giving an appropriate amount of respect.
Glide Ratio And Weight
Glide ratio can be expressed either as the lift/drag ratio or, more
commonly, the distance you'll travel forward for the distance dropped,
and its the same at any weight. Every glider has a speed/configuration
that gives the best glide ratio and, in that configuration, (usually
neutral trim, no speedbar) you'll fly the farthest distance in calm
wind. Mind you, the speed at which best glide occurs will be
faster at heavier weights but the glide ratio remains the same.
A heavy pilot will fly just as far from 100 feet as a light pilot on
the same rig but the heavy pilot will get there faster. Both his sink
rate and forward speed will be greater.
Note that power required
is based on sink rate and weight so the heavier pilot, not surprisingly,
requires more power to stay aloft than the lighter pilot.
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