SEN issue 1138 - 1 October 2007
- Category: Archive 2007
- Hits: 607
- RDT and Instant Release
- Arizon F1E Champs report
- Mathewson for AMA President
- RDT for sale
- Taft Field Closed ?
RDT and Instant Release
In glider world, RDT is universally considered as a means to
remotely dethermilize a model. It can be used to safely land a
model while trimming, DT the model before the max if it's in a
strong thermal, to keep it on the field, or as a back up DT
system. A necessary requirement is an e-timer that can listen
to a RDT signal and that it operate a servo controlled stab.
One can consider an e-timer as reading a set of instructions in
the form of rows from a data file. (These lines are those across
your Palm PDA). Each row is executed for a specified amount
of time, and the entries across the row specify the different
servos heads positions. Normally, the e-timer starts reading
the data file from the top, one row at a time, and when it
executes an instruction called DT it might put itself to sleep -
to save the batteries power. More importantly, it does not read
the following lines.
An RDT signal will force the e-timer to starts reading the data
file from a pre specified line. This line is typically after, or below,
the line that ends a model's standard flight plan with a DT. By
definition, the RDT line includes a DT instruction.
The line to which the RDT skips to, however, can include other
instructions. These could be plan B for the flight - which is the
point where the ancient twanger comes to mind.
The twanger, to those who used in the sixties and early
seventies, was a means to instantly release a glider in the
zoom era. The hook had an inbuilt spring which would release
the line if the line tension suddenly drop. Obviously, any trip
or hiccup would also release the line, which is why twangers
were disregarded within a few years.
A twanger hook is particularly useful in two circumstances.
First, in the mother-of-all-thermals, a bunting model is
particularly difficult to launch. The model has to be circled
around, gain enough speed to get a reasonable launch.
I've messed up this maneuver many times and ended up
in a large sink hole behind the thermal or with a poor launch -
producing a cliff hanger.
The second situation is when one is kiting the model in a
strong wind. When a thermal passes, the model, if it's worth
it's salt, will pull forward (an old observation by the Israelis).
Again, turning the model around for a launch is difficult, and
not always successful.
So, under these circumstances, one might consider "plan B"
or the functionality of a twanger hook. Although a good bunt
might gain 20 meters, it's irrelevant in a humongous thermal.
A good bunt might gain even more altitude in a strong wind,
but with a chance of missing the thermal altogether. A twanger
or an instant release is just a way to circumvent the risky
maneuver of turning the model around for a bunt launch.
An instant release requires a hook controlled by a servo.
Currently, the hook-controlled-servos are designed to relatch
if the model is not release within a prescribed amount of time.
So the can decide not to launch the model after all (typically
with a poor launch trajectory or path).
For an instant release hook to work, the hook's servo has
to perform two function:. to open the latch and to dismount
the line's ring. Dismounting is important since the model is
being released at a tow-line glide speed, typically slower than
it's gliding speed - due to the higher decalage and the line's
weight. (And yes, I know that some athletic fliers tow their
models at a glide decalage).
A tentative "drop the line" functionality, for a hook servo that
drives a pin through the back of the hook, is to include an
elastic wire enclosing the ring, connected to the servo's pin
on one end and the back of the hook on the other end. When
the pin is pulled further away, the wire is stretched - pushing off
the ring. For hook servos with a swinging latch, an additional
arm could be added, whose function is to push off the hook
at a higher rotation angle.
Instead of a sensor activating the hook servo via the e-timer,
it would be operated directly from the e-timer, following a
instant release signal from the flier below.
Imagine this. You are in a great thermal with the model pulling
like hell. You press the instant release button and the model
just floats off the line. Second take. You are kiting and the
model suddenly pulls forward in a strong thermal. You press
the instant release button and the model just floats off the line.
Happy ending (if your decisions were correct).
Remotely communicating with the model via radio signals is
perfectly legal if done prior to the model's release.
Arizona F1E Champs Report
Saturday at North Sheba Crater near Flagstaff, AZ was very windy with rain most of the day and through the night. Because of the weather forecast there were only 3 contestants. Tom Ioerger who flew in from Baltimore, then Dick Wood and Peter Brocks. The day of the contest, Sunday, Oct. 23 was sunny, warm but with a non-typical stormy wind. The bottom at Sheba is at about 5,600 ft. The flight line was set up at about 5,800 ft. Dick Wood flew his small magnet controlled model at 9 AM when the wind was only 12 mph. The model went up like in an elevator, was slowly blown back and in about 2 min. disappeared over the top of Sheba (6,400 ft). Tom and Peter waited for the wind to get calmer but it got continually windier. They flew from well below the flight line at the end of the 1 hour round when the wind was between 15 and 20 mph . Even though they had ballast added to their windy weather models, the lift was so strong that both also went quickly very high into the much stronger gale force wind and also over the top of Sheba. Climbing up Sheba was quite a task because at the top the wind was blowing close to 50 mph (measured).
We then delayed the contest until the wind would get less - which it never did. Finally in the afternoon we decided to fly the rest of the rounds combined from 1:30 PM until 5:00 PM with the max capped at 2 minutes. Tom and Peter then flew from points close to the bottom of Sheba and each just put in 2 max flights. Dick Wood worked on his windy electronic model and after some attempts put up a decent flight in the wind. Tom damaged the pilot of his model and stopped flying. The other two put in token flights to end the contest.
1st Peter Brocks 81.25 (104s), 100 (120s), 100 (120s), 25.88 (22s), 40 (6s) = 347.13%
2nd Dick Wood 100 (128s), 4.17 (5s), 5.00 (6s), 100 (85s), 100 (15s) = 309.17%
3rd Tom Ioerger 67.97 (87s), 100 (120s), 100 (120s), DNF, DNF = 267.97%
The area at North Sheba Crater and Merriam Crater is a very pretty place and well suited for F1E flying. It was just bad that the weather did not cooperate this time.
Mathewson for AMA President
As a primarily free-flight club, the Brooklyn Skyscrapers are endorsing Dave Mathewson
for the AMA presidency and we urge all free-flighters to mark their ballots for him.
We urge all free-flighters to read his campaign statement in Model Aviation and check
out his website>www.mathewson4pres.com<. Although he makes no mention of free-
flight, he has worked diligently and hard to preserve the use of the Galeville site for
free-flight. He is not unaware of us and the needs of free-flight in his proposed programs.
Dave Acton, president, the Skyscrapers
RDT for Sale
Taft Field Closed?
From: Yahoo Free Flight Mailing List
We went to Taft today, Sunday, to do some test flying before the SAM
Champs. There was what looked like an oil-drilling rig on the field,
and another big flatbed with sacks of concrete. The Rent A Cop who
turned us away said they were drilling core samples or some such. He
said he had orders to keep everybody off the field. He also said
that that it would be this way for a couple of months. The drilling
company's address on the truck was in Norwalk.
Maybe with the increased price of oil the new owners think they can
make some money. A smaller company would have fewer fixed costs and
might be able to make a profit where a big outfit like Standard Oil
would have too much overhead to make it attractive to extract
marginal oil from the area. I dunno.
Just wanted all to know and not spend half the day driving to Taft
and find it's off limits. We were too disgusted to go further up the
road to Lost Hills.
I don't know who owns the field now, or how to contact them.
Obviously, if there will be permanent structures on the field it
will no longer be a case of "I don't know who owns it, there is
nobody I can sue if I get hurt." I'll let those more savvy in
politics and litigation figure it out. In the meantime we will be
testing at Perris this week.
John, Mikey and Ed, disgusted in the PRC