SEN-518 December 16 2000
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News and Reports 2000 - second half
SCAT Electronic News 16 December 2000 issue 518
Table of Contents
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Gard Airfoil, Towhook & other Noise - Bradley
Points and Factorial possibilities - Hines
Looking for a Gizmo - Korsgaard
Non stretch rope for rubber testing - McGuckin
Thanks
Creeping stretch - Andresen
rubber stretching - Brooks
new url Gorban now has own domain - Myers
WC Date - Robbins
Gard Airfoil, Towhook & other Noise
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Author : This email address is being protected from spambots. You need JavaScript enabled to view it.
Roger,
I would like to thank all of you who responded to my request for information
on the Gard airfoils. For once everybody agreed. Dr. Hadas from Israel also
added that the nose radius is .5% on the 6509 and 7510. He also added that
the high point is 9% located at 33% on the 6509 section and 10% at 36% on the
7510 section.
I agree with Lee on towhook position. I have used a tow point located 18
degrees forward of the CG as a starting point for many years. I adjust from
there as required. My feeling as to why using a fixed dimension forward of
the CG also works is that most all F1A's are using similar pod front ends
that places the wing about the same height above the tow point. This being
the case, then a fixed distance works out very near 18 degrees.
Being old and slow I find myself moving the tow point back a little more to
increase line tension when launching from what I used in my younger F1A days.
Like Lee my rudders a straight to slightly opposite glide for straight tow
and I do not have any zoom rudder as I found it too hard to control flying
bunters.
On another note, there is no truth to the rumor that Florida will handle the
tabulation at the World Champs.
Jim Bradley
Points and Factorial possibilities
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Author : This email address is being protected from spambots. You need JavaScript enabled to view it.
Hi Mike,
I take your point re AM CUP format points.
We have considered factors as reward for beating more fliers,
as you may or may not know.
While there may be changes in that direction in future, it is hoped
that the low entry comps will gain some ground in the near term.
One never knows the entry til you arrive on site, naturally, but some
are historically lean and vice-versa.
My long time feeling is that, for example, if a flier is 5th of 5, he beat
no one and deserves zero points. On the other hand, a 10th pl with 30
fliers SB worth something. That flier may have even made the FO!
Look at the World Cup system: they award points half way down.
Getting and sorting the results in a timely manner might cause some
headaches, but future-tech might give relief. Stay tuned!
Ciao, LEE
Looking for a Gizmo
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Author : This email address is being protected from spambots. You need JavaScript enabled to view it.
Hi,
A friend of mine just sent me a magnificent P-30 propeller system
called GIZMO. Who sells it, and how much does it cost? Does anyone know`?
Merry Christmas
Jorgen Korsgaard
DEN
Non stretch rope for rubber testing
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Author : This email address is being protected from spambots. You need JavaScript enabled to view it.
Howdy Roger,
I just read John Malkin's part on the rope stretching during rubber
stretching. He went to a steel cable. Another option might be Spectra
utility cord that is used for rockclimbing. It is designed for non stretch
applications. REI carries it at $1.05 a foot which is pricey but it might be
less than a cable and it is very flexible. Any sports shop that carries
climbing gear would have it. It's breaking strength is over 1000 pounds. If
I remember correctly it uses some kevlar in the core.
Whatever one uses it might be smart to preload the cord or cable for a
while till the stretch is gone or at least greatly reduced.
Derek McGuckin
Ridgefield, WA
Thanks
======
Thanks to Mike Roberts and Jon Davis aka Mac the Bigot
for their donations in support of SEN.
rubber stretching
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Author : This email address is being protected from spambots. You need JavaScript enabled to view it.
As a bit of a yachtie in my spare time I've discovered that Kevlar line
has no appreciable stretch, and can be used successfully in a rubber
tester. I've used 1/4" dacron line as well and it seems to work ok. I
dead headed it with 100# on the scale and the length did'nt change to a
measurable degree.
On a related point. I've all but given up trying to stretch current
rubber. I used to go to 100# in stages for 8 to 10 minutes, and call that
broken in, but if I go over 70# now I ruin the motor. This amounts to
about nine and a half lenghts stretched before significant breakage
occurs, which is equivalent (sort of) to the length I used to get when I
went to 100#.
So, is it more important to measure the length stretched rather than the
#'s applied?? Or should I just go back to winding to a % of max winds?
Jim Brooks
Creeping stretch
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Author : This email address is being protected from spambots. You need JavaScript enabled to view it.
Roger,
That was an adroit observation by Mr Malkin re creep.
In the words of C J McKenzie, vibration test Engr "The whole world is made
of Jello" Is not too far off.
Creep is of special interest in transducer design as specs are so tight.
When used at less than the 1/4 ultimate stress, most metals experience 0.1
to 0.2% Elastic Creep which is reversible and exponential with time. So a
load that produces 0.1% creep between 5sec & 5min will produce another 0.1%
from 5min to 5hr. In 5hr of relaxing it will return to zero. This is not
the case as one gets to say 1/2 the ultimate stress, in which case the creep
gets much larger AND does not return to zero. Also not the case with most
organic matl like rubber plastics and wood. A steel frame should be better
than wood from a creep standpoint.
Would be interesting to measure stretched length of rubber during the test
with various cables, but then there are few enough FFers now.
I'd suggest that anyone purchasing cable for this application use 4x the
pull value for cable rating and don't stand too close.
Am surprised the rubber itself doesn't show more relaxation with time, but
then 1 valid test is worth 1000 opinions.
Better check the rule book re time for towline pull test.
Thanks John,
H
new url Gorban now has own domain
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Author : This email address is being protected from spambots. You need JavaScript enabled to view it.
Hello Roger;
Could you please change the url on the Gorban F1B/F1G page in suppliers?
The new url is Gorban's own domain.
http://www.gorbanfreeflight.com
Thanks much and many thermals,
Dick Myers
P.S. Some of use old guys have been thinking!!! 30g rule goes into =
effect 01/01/2002
not 2001, is this correct????
[2002 - Dick do we want it to go sooner so the good rubber
we have will lat longer - or not go at all because all
recent batches have been "sub-standard" or wait longer
in the hope that the rubber supplier will git it fixed
or another supplier will come along ?]
WC Date
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Author : This email address is being protected from spambots. You need JavaScript enabled to view it.
Do we have a World Champs date yet?
Herb Robbins
[Herb I assume that you mean the OUTDOOR WC ?!
I believe it is Oct 8-13 2001]
..............
Roger Morrell
