Nov 8, 2007 | Section IV
Theory & Understanding
There's more than meets the eye on how our unusual craft flies and it's not
Flight is a fine dance of forces that must remain in step to keep you
aloft and under control. We follow the same basic aerodynamic rules as
our fixed-wing brethren with a few important differences.
Bible goes into great detail about these but some additional material is
included here including what may be added to the aerodynamics chapter
(was added at page 226).
More Power to
Does it take more power to fly downwind?
Of course not! Your wing
doesn't care which way the air is moving. Or does it?
It turns out
that there is one little
exception where the downwind demon is real, albeit in a minor, rare way.
Check out the PDF file. It covers an
obscure situation where it can require more power to fly downwind
The gist is that, with a wind gradient very close to the ground, the
wing may be flying in different airflow than the motor 15 feet below.
The PDF explains how that requires less power when flying upwind than
downwind in such situations.
The discovery of this was kind of funny. At a fly-in Nick Scholtes
quietly pulled me aside and said "Jeff, now we both know that there is
no difference in flying upwind or downwind but I just got back and swear
that it took me more power to fly downwind than upwind." He went on to
explain how he did several runs to verify it and only noticed it down
low, at maybe five feet high. So I went out to see if I could duplicate
his observation and, sure enough, I did—needing several hundred more RPM
to go downwind as upwind. That's what got me trying to figure out what
was going on and a few days later put it all together. Read the PDF to
see what was happening.
Choosing a wing.
One important area of understanding is wing
loading. How much weight is carried per square meter of wing. It is the
all-up flying weight (pilot, motor, fuel, wing) divided by the wing's
Sales literature may not always say flat or projected
so double check that you're using the projected value. Add up your
weights, including fuel and wing then divide that number into the wing
For example, a Spice 22 has a projected area near 19 m². My 145 pound
self with a 70 pound paramotor and 10 pounds of gas under a 12 pound
wing gives an all up flying weight of 237 lbs. Wing loading is then 237
/ 19 or 12.5 lbs per m².
This important value should be
considered buying a different wing. Go
here to see