Advantages of Pneumatic Servos (from KitePlanes to
Megascale AWES Units)
Review, with updated explanations-
Conventional UAS methods have severe disadvantages for AWES deployment.
For instance, typical electrical systems are radar reflective, creating
excessive radar clutter, especially if deployed aerobatically in large
numbers. Electrical flight servos are a particular UAS problem area- they
are expensive, heavy, fragile, and just don't last long enough (100-hour
inspections, with 1000 hr typical continuous-duty lifecycle, at moderate
The "standard" servo duty-cycle predicted for complex AWES UAS is a full
orbit occurring every few seconds, for months at a time. The Achilles-Heel
of ordinary servos is shock-loads, which hammer individual gear teeth.
Once a few teeth break, the servo fails. Heavier gears add unwelcome mass.
The only electrical-servo solution that currently makes engineering and
economic sense is actuation by cheap massive long-lived industrial servos
kept on the ground.
We can invent new UAS AWES technology to resolve existing limitations.
Pneumatic servos are an interesting option. They are typically rated for
tens of millions of work cycles (10,000 km of travel). Compared to
gear-based servos, they are inherently tough and shock absorbing. They
come in all-plastic nonconducting versions to alleviate radar and
lightning concerns. They are the lightest actuator solution (highest
power-to-weight). They typically cost about 1/4 the cost of a comparable
electrical actuator (by power).
One can find claims that electrical servos are somehow better that
pneumatic servos, but these are not true inherent advantages, only
successful legacy cases improperly presented as conclusive
systems-engineering evidence. Similarly, hydraulics have many successful
cases, but specific inherent defects (like dependence on maintaining a
hydraulic fluid supply, compared to freely available "weightless" air).
All in all, ordinary air is good stuff, and pneumatics use only grows in
modern control engineering.
We even have recourse to create wonderful new methods of large
low-pressure actuators based on air-bladders and blowers, for megascale
AWES actuation aloft. Existing UAS electrical servos are fine for toys and
many conventional flight platforms, but they simply do fit AWES super-duty
needs, nor scale well for giant AWES use.
Comment and development of this topic will be occurring here.
All, send notes, links, drawings, papers, videos, plans, safety-critical
findings, and photographs!
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