Tethered R/C - A Solution to the FAA's Draconian sUAS Rules?
Prototype tethered R/C Carl Goldberg ½A Skylane on 35'
monoline, Futaba 75 MHz radio (legal because it is tethered), e-Flite Park 450 brushless motor.
Tethered R/C pivot post assembly.
Carl Goldberg ½A Skylane on 35' monoline.
Even to a casual observer, the U.S. Federal Aviation Administration (FAA) seems
determined to deal a death blow to the radio controlled (R/C) model aircraft sport
and competition flying community and industry. Its
being implemented for onboard electronic identification broadcasting and severe
limits imposed on flying sites have already caused great inconvenience to the
way aeromodelers have safely and legally conducted themselves for a century, and
threatens to kill even more activity. The proposed (and inevitable) electronic
ID and pilot licensing requirements will further discourage pilots and equipment
manufacturers due to increased operational costs. The root of these unreasonable
laws can be traced back directly to the September 11, 2001, attacks on American
soil by extremist Muslim terrorists. Our freedoms have been continually eroded
since that time. Remember which group of people needs to be held accountable for your
having had that inherited pocket knife of your grandfather's or a simple pair of
nail clippers confiscated at the airport screening station, and for all the surveillance
cameras and listening in to your telephone conversations over the last two decades.
For a long time I have been kicking around the concept of tethered R/C (TRC), where
the airplane would be completely under remote control, with its inboard wing
being attached to a tether that is in turn anchored to a pivot point in the
center of the circle. My first effort was to convert an electric-powered control
line stunt model to have R/C control of the elevator and motor speed. After
doing the conversion, I decided that it would be safer to start out with a
slow-flying, inherently stable model, so since I was in the process of building
an electric-powered, three-channel Carl Goldberg ½A Skylane, it was used
as the Guiney pig. The steerable nose gear was pegged in the center, and the
rudder pushrod was secured with a screw in the servo mount rail so that it has
permanent right rudder. A tether attachment point was epoxied into the left
wingtip. It weights 25.3 ounces ready to fly.
One of the drawbacks and potential disaster points with having the airplane
staked to a fixed point is that if a gust of wind pushes the model toward the
center of the circle, there is no ability to just step back and tighten the
lines. On the other hand, there is no requirement to have the line continuously tight if
control of the elevator is not dependent on the line(s). In fact, the
Stanzel brothers used that very feature to help pitch their monoline control
line system. Elevator control was affected by twisting the single metal line,
not exerting differential tension on two separate lines.
Just to be safe for
starters, I used an exaggerated amount of right rudder. There winds were at
about 10 mph with gust to 15-18 mph during the maiden flight of the
tethered R/C Carl Goldberg ½A Skylane, and at no time did the line go completely slack,
even though the model was flying at a fairly low speed. A faster model should
have no problem under those or even more unfriendly conditions.
A simple pivot post was made using ball bearing wheel assembly (bought at
Harbor Freight) with the wheel removed, and screwing it to a 4x4 with a plywood
base plate. A standard 8x8x16" concrete block provided enough ballast for this
setup. In order to estimate the tension on the line at flying speed, I used the
following centrifugal force equation:
F = W * v2 / (g * R) in pounds of force (lbf†), where
W = weight in pounds of force (lbf): 25.3 ozf = (25.3 ozf) * (1 lbf / 16 ozf)
= 1.58 lbf
v = speed in ft/s: 40 m/h = 40 mph * (5280 ft / mi) * (hr / 3600 s) =
g = acceleration of gravity = 32.175 ft/s2
Tension = [1.58 lbf * (58.7 fps)2 ] / (32.175 ft/s2 *
36.5 ft) = 4.64 lbf - which is not much!
A standard 8" x 8" x 16" concrete block weighs a little over 35 pounds, so it
was plenty of ballast for the pivot post.
Here is a video of the tethered R/C Carl Goldberg ½A Skylane's
† Be careful when using equations which use units of weight that you know
whether to use values for pound mass (lbm) or pound force (lbf).
I have intended for a long time to try my hand at tethered radio control
(TRC), especially as my aging body (now 62) does not tolerate turning in circles
as well as it used to. There is a not a lot available about it on the WWW, so
I'm on my own. I outfitted my e-powered Carl Goldberg 1/2A Skylane accordingly
by setting right rudder and using the throttle and elevator controls with a
Futaba radio system (see article on my AirplanesAndRockets.com website). The
single tether line if about 35' long and it attached at the wingtip. A pivot
post was made using a ball bearing caster wheel frame on a 4x4 timber, weighted
down with a concrete block. The test flights went well under light winds, but
got scary when gusts came along. Flying a faster model would reduce the effect.
Future plans include converting an e-powered C/L stunt model to TRC on a longer
line to see whether I can pull off aerobatics with it. Time constraints will
probably not see that happening for at least a year from now.
Even during the busiest times of my life I have endeavored to maintain some form
of model building activity. This site has been created to help me chronicle my journey
through a lifelong involvement in model aviation, which
all began in Mayo,