SEN 729 - 18 Aug 2002
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SCAT Electronic News 18 August 2002 issue 729
Table of Contents
=================
military binoculars
Monofilament Lines - Cleman
Junior FF Color Commentary - Coussens
F1A optimum climb trajectory and bunt - Skykieng
Re: Nylon line - Gregorie
Lining up the Hammer - Matthews
Monofilament stretch - Hinson
Nylon lines, not - Abad
military binoculars
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We are supplier of military binoculars please visit our website:
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Regards,
Wentao
Monofilament Lines
==================
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A quick thought from a modeler that has also spent a lot of time
fishing. Nothing causes monofilament lines to loose both strength and
elasticity faster than sunlight and it doesn't have to be hot. So,avoid
leaving the model out of it's model box when not flying, or effecting
repairs or modifications in the sun lit shop.
Thermals,
Roger Coleman
Junior FF Color Commentary
==========================
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Junior FF WC Color Commentary
Tom Coussens
About an hour to go till the banquet, and a little time has passed to collect
some thoughts...
We would have taken overall team gold and F1C team gold if we had a third F1J
flyer. We MUST SEND A FULL TEAM NEXT TIME!!!!!
The Wakefield team was agonizingly close to a podium team and even individual
gold, but for mechanical Murphys rearing their ugly heads. The calm of the
boys under high pressure...Ryan with 4 minutes to go, the hub locks and will
not turn. Four kids descend on the model to fix it because there is not
enough time to wind the back-up. At 30 sec to go, they free it up and Ryan
shoots a great launch, and twenty Americans go into flapping action.
The model rides the bumps and is on its way to a max when in short DTs. But
then he flew on and maxed the rest of the day.
The total calm and business-like Eddie Avallone flying his way to a
fourth-place, maxes plus 51 seconds bonus. Total conservation of energy and
words.
The Israelis remarked with awe at the calm and poise of both Austin Gunder and
John Lorbiecki when they both had to deal with mechanical issues (and Austin
with timing issues), and then to see them lock the wires down in the 6 minute
fly off, the red sun desending behind them. They already had first and second
locked up, the Russian and Ukraine kids having dropped the five minute round,
yet they were competitors to the end.
It was decided in the early cool of this morning, two American flyers,
witnessed not only by their team and supporters, but by the entire German,
Israeli and Polish teams (there may have been more). John's number one model
went in inverted on a test flight moments before the fly-off, and he changed
gears and models to fly a superb flight of 4:20. Austin flew his back-up
model due to a DT malfuntion in the primary and stalled a lot but recovered,
achieving a 6:10 flight. The cheers rang out in the still countryside as the
models made good runs.
Volumes could be written about the chase teams, whose tireless and selfless
work contibuted directly to the success of the fliers. Among the efforts:
A six man relay for Austin's ship, especially noteworthy the 3/4 mile dead
sprint of Michael Avallone across a muddy plowed field. Charley "hound dog"
Jones working his magic in neck-high corn to find John's model quickly. Down
wind chase teams standing in water and mud for five hours straight, retrieving
Nordics in the rain as they drifted all over the map.
And of course the fathers, myself included, who stood by silently, well away
from the launch line, wracked with anxiety, knowing that it all came down to
this ; everything we taught the boys, everything they learned was put to the
ultimate test. An every father and mother there came away with such pride at
the boys' performance, attitude and bearing.
And finally, the whole support team. Many of the parents did not meet till
they arrived in Europe, and all took a liking to each other and got along,
more than got along, they just plain had fun together. There were no loners
in this happy, amiable group. It would be criminal not to mention the
invaluable help, encouragement and cheerfulness of Bob and Connie Pisechio.
And so, on to the Banquet, the trading, the last dance before we part tomorrow
and head our separate ways to our homes. A story of pride, cheer, suspense,
an d comraderie. How I hate to see it end!!
Tom Coussens
F1A optimum climb trajectory and bunt
=====================================
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I can't disagree with any of Bill Bogarts somewhat lean and cryptic
remarks.
>From my non-mathematical intuitive approach I can't see a 90 degree
release angle as being optimum for a Nordic. In any case bending over
backwards to shoot for that supposed ideal would be a real study in
diminishing returns since the geometric loss through triangulation from
say, ten degrees off wouldn't amount to a hill of old Wakefield motors.
In an early edition of Martin Simons' Model Aerodynamics he did an
analysis of the ideal climb angle for a powered ship. This came out to
be around 55 degrees. Considering the excess thrust to weight ratios now
extant that figure seemed a bit dated... although Martin when questioned
still stuck by his original figures. The concept to keep in mind is
that with the lower thrust values the higher climb is achieved with the
wing supporting a portion of the weight. Would the same principle hold
true for the Nordic as its speed and energy diminished? I would think
that is a strong possibility.
As Bogart seems to suggest, A steep initial phase with the angle
decreasing as the speed bleeds off. The bunt would amount to a gentle
fly-over.
A fly in the ointment is the lift-drag characteristics of Nordic-type
airfoils. Characterized by high camber and a drooped nose that style
airfoil is at its best at high lift angles. When on line and pulling
Gees like mad it is in its element ; but when cut loose at high speed
things change fast .. and to the bad. At zero lift (going straight up
after release) the drag is very high. And when nosed over in a premature
sever bunt it becomes a supreme drag brake.
If there was some practical way of changing the airfoil shape through
all the phases .... but that ain't goin' to happen .... Folding the
wing is illegal...so... Hey! Be younger, stronger, faster and build/buy
wings that don't break! Make friends with an old feeble guy who can
smell thermals that will lift cow pies off the ground. Accept your many
trophies with grace and humble dignity.
skyhigh
Re: Nylon line
==============
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Chuck Markos wrote:
> Many years ago, I had an F1A DT where the monofilament line
> apparently shrunk in length.
>
I'd expect this. Nylon monofilament, like some other polymers, has a
negative coefficient of expansion, so will tend to get longer when
hot. This, when coupled with the way it softens as it warms up, is a
recipe for disaster.
> I now use braided dacron (Cortland Greenspot Dacron
> Trolling line) 20-lb test.
>
This is good, but I think Spectra (Dyneema in the UK) is better. It
stretches less and is considerably more flexible and thinner. 80 lb
Spectra is about the same diameter as 20 lb Dacron. It does not take
a set and is extremely slippery; wicking cyano into knots is a good
idea. Its only disadvantages are:
- its very difficult to thread into a model because it will take no
push load at all. Flicking a boom like a fly rod will do the trick or
it can be zapped onto a piece of less flexible thread and pulled
through.
- if its allowed to rub on a rough surface the woven outer layer may
abrade and fluff up, but bending it round a metal tube, like the
Lynch bunt unit does is fine. It does not take a set.
For some years I've avoided all this palaver by using nylon coated
steel fishing trace for both autorudder and d/t lines. The trace
seems to have a similar coefficient of expansion to glass, kevlar or
carbon F1A booms. I sidestep the 'bend in the d/t line' problem by
using a glide stop hammer like an auto-stab power model, which works
well with my rear fin design. As a side benefit there is no line drag
while the d/t deploys. The hammer just flicks back and I use an
external Dacron strop to limit d/t angle.
HTH
Martin Gregorie
Lining up the Hammer
====================
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> The curious thing is that when I set the DT angle with the nylon-only line in
> my shop, which is quite a bit cooler than Bong in August, the DT angle was
> appropriate. I have never seen any data on the effects of heat and humidity
> changes on the characteristics of nylon monofilament line. That is, is there
> an direct relationship or inverse relationship as I apparently obsevered?
>
I had the same problem with an F1B. It cost me a max at a Max-Men when the line
to the D.T. arm stretched and the model D.T.'d during power!
To solve this problem, I went to a non-nylon line for the d.t. hammer. I
believe it is a Kevlar (or similar?) based line called "spiderline". It is
very thin (similar to the monofiliment) and coated with some sort of slippery
stuff to reduce friction (so no problem going around d.t. guides). The line
seems to be very stable with respect to heat and moisture, and stretches
very little.
What I found with monofilament was that it expanded with moisture, and shrank
with a lack of it. It expands with heat, and shrinks with cold.
I found that the best way to use monofilament was to make sure that the
pre-load on the line in use, is always higher than required to operate the
mechanism. This way, even when the line stretches from either heat or
moisture, the tension left on the line is still above that required to hold
down the mechanism.
I also found that there are lines available from your local fishing supply
house that are more moisture stable than others. I use Berkley Tri-line.
Some cheaper lines expand or shrink an incredible amount with changes in
heat and humidity. Look on the package and choose one that is "stable". Don't
get cheap. The best lines cost more but are worth it imo.
Tony Mathews
Monofilament stretch
====================
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BlankI have seen too many models DT early when using monofliament for
the figure 7 DT hammer on F1B. I adopted the same cure as Chuck Markos
many years ago. I use 12-15 pound test Dacron for the figure 7 hammer.
Rigging it is easy and does not require any type of spring in the line.
Run the line from the Fig 7 hammer up to the DT arm on the timer. place
a small piece of Aluminium tubing on the line, form a loop back thru the
tubing. Hook the loop over the timer arm. Pull the slack until the Fig 7
arm is in the flight position. While holding it in place, crimp the
tubing. There will be no problem hooking up the line for flight.
Rex Hinson
Nylon lines, not
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When I started flying modern bunt-F1A's , my models lines were thin
monofilament.
I strongly advice you not to use nylon. It stretches with heat and get a "set"
around bends in cold weather. Worse was while flying in damp/wet conditions or
early morning dew. When monofilament gets wet, will stick or drag much more in
holes or turning points. You can imagine what a lower dt angle will do with a
long wing model.
Now I use dacron 30 lb for dt and for bunt (with a spring online), for bunt
post a steel braided wire also with a shorter spring.
Hope it will help, but don't forget to change dacron sometime as it will wear
out with use.
Javier
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.............
Roger Morrell
