SEN-517 December 14 2000
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News and Reports 2000 - second half
SCAT Electronic News 14 December 2000 issue 517
Table of Contents
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America's Cup and Jr W/C Selection - McKeever
Gard 6509 Airfoil - Bogie
Coupe DPR - O'Dwyer
Hooked up again - Hines
In response to Jim Bradley- Fantham
Chit chads - Malkin
Chad speak - Woodhouse
Chads and such - Hinson
Stretching Rubber - Malkin
America's Cup and Jr W/C Selection
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Author : This email address is being protected from spambots. You need JavaScript enabled to view it.
That is an interesting way to use America Cup scores for the Junior World
Champs Team. It would be interesting to see how that formula might work in
America's Cup standings. I realize, understand, and support a primary
function of current America's Cup rules is to encourage participation in as
many FAI events as possible.
I would not support America's Cup use for selecting the "Open" World Champs
Team. There are some interesting results looking at present Cup standings.
For example (and not to pick on a fellow "Mike") but Mike Fedor's excellent
2nd place in F1A is unusual in that he beat 31 flyers in his 4 counting
contests. Winner Steve Spense beat the same number in a single contest and
you have to go to 10th place to find a person defeating fewer flyers. I
don't want to pick on Mike again but in F1H Mike finished 4th by beating 6
flyers.
My point is not to blast Mike (and Mike I apologize for using the
examples-you're a solid flyer and deserve the recognition) but to suggest Cup
results aren't the best indicator of National Rankings for team selection
purposes. It could be with some tweaking, which seems possible in the latest
Jr Team Selection formulas. I'd be in favor of awarding the traditional
points for first through fifth as well as a factor for the number of other
flyers involved. There would be incentive to attend contests for placing
awards while at the same time recognizing a "difficulty factor."
I'm not sure we need to do that, the format is currently very popular, but
should it ever be a factor in team selection (as it is being used for the Jr
Team) some adjustments need to be made. As Dennis Miller says, "That's my
opinion, I could be wrong." Mike McKeever
Gard 6509 Airfoil
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Jim,
Here are the ordinates found in an old issue of SCATTER, February 1990.
Station Upper Lower
0 0 0
5 4.2 .6
10 6.1 1.2
20 8.25 2.3
30 8.95 3.25
40 8.9 4.0
50 8.45 4.35
60 7.6 4.35
70 6.25 3.9
80 4.7 3.0
90 2.75 1.75
100 .4 0
No idea on leading edge radius. I would make it rather sharp and round it
off during trimming, thinking of wood, of course.
I cannot guarantee orderly presentation of the above coordinates. Email has
its own ideas.
Bill Bogart
Coupe DPR
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The coupe DPR Mark Bennet referred to was a Klaus Salzer design that was
fairly simple. It worked fine for about a years worth of flying but
dirt, grass, etc. began to cause too many malfunctions. I think it was a
lot of help in wining the Americas Cup in '97 together with AR and VIT.
But poor workmanship eventually canceled all the advantages. I highly
recommend to you.
John O'D
Hooked up again
===============
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Hi Chuck,
Sorry for the delay---STUFF happened!
You wrote:
"I've been thinking about towhook placement and the "18mm in front of the CG"
guideline for F1A models. The more I think, the more I get confused. It
seems to me that the guideline is based on the glide trim of the model for
which the CG is an important consideration. The CG then affects the
angular difference (AD) between wing and stab. Could it be that AD is
more important than CG in determining the hook position?"
Let me start by saying, when I met Lepp in Argentina '89, I asked him
what he used as criteria for hook location, he looked surprised that anyone
needed to ask, but answered,
"For normal F1A, put CG @ 55% & hook(ie, ring pull point) @17-19degrees
forward and forget about it!"
Later I checked his AL33, which was a bit over 20deg. So what you said
regarding AD(angular difference) being important when locating hook rings
true, but I don't feel it is more important than CG location. Naturally AL33
is a flyoff/calm air design, not a "normal" glider(his definition of "normal"
glider-thermal-type design) and as such has more AD due to its own
aerodynamic needs.
I don't believe I ever saw the guideline "18mm in front of CG" written or
referred to, it just seems that many F1A gliders respond well at that setting.
Looking back to the 70s, drawings for the best Iron Curtain "normal" F1As
showed 13-15mm hook location and used B6356b section or very similar.
The AD was lower @ 2.5-3deg than Al33 and I venture most modern bunters
using M&K/Stamov/Ritz/Gard 7510 family of sections. The latter usually
use nega-stab(negative incidence) during tow, circle tow and 1st stage of
launch(pitchup phase). This seems to require a more forward hook vector
to compensate for the extra force induced by having 4.5(or more)degrees
present during tow/launch phases.
Also, you mentioned speed changes during tow causing veering to the outside
of turn, due to too much washin on inboard wing. This is usually corrected
by moving towrudder back toward turn direction, until tow is straight at the
fastest speed. I don't mind if tow hangs to right somewhat on slow towup from
ground level. This merely is the tow washin acting as drag at the high angle of
attack, and will change to lift as the plane levels and speed approaches
terminal velocity of launch. Sometimes a decrease of tow washin is necessary
if the divergence is volatile. Generally my tow rudder ends nearly straight or
.06 left for my bunters. I personally don't like to use much, if any, zoom
rudder deflection. It is a variable I am not comfortable using at this time.
I have, at times, done as you noted, dropped the stab TE during tow phase
to lessen the force and pitchup tendencies in windy conditions. But, in
general I find tow combinations which work in wind, are usually still close
to right in the calm, if you just open up the tow circle to match your
needs.
This is written before I fly my new bird with 3-pos wing-wiggler, so some
revision of my ideas may be necessary later on.
Hope that addressed your queries sufficiently.
Ciao, Lee
An SEN aside to Mac the Bigot!
Hey, the air must be VERY THIN out in CHAD CITY, New Mexico!
Chadism Indeed! Loved the CHAD-ideas you espoused(or spewed).
As I write this the Supreme FAT CHAD hasn't sung yet,
so I will say MERRY CHRISTMAS TO ALL!
>From Sweepettelee, the Ole Chad-challenged glider-guider
PS: for Jim Bradley's info re Gard section coordinates:
The 6509 and 7510 are in John Malkin's AIRFOIL SECTIONS book,
pages 72 & 73. We(Don, Vasi and I)use the 7510 on ou rLI'L AL
models, by the way.
Ciao and Double Ciao!
Sweepettelee
In response to Jim Bradley
==========================
Sender : This email address is being protected from spambots. You need JavaScript enabled to view it.
The following data, including the turbulator notes is from the Malkin book.
John shows the sections with a nose radius but doesn't specify a value. I
suggest you use 0.5% and change the first coordinate row to 0, 0.5, 0.5.
At least that makes the plot look like his illustration. The lack of data
between 0% and 10% may cause strange plots, but that's all there is in
Malkin - sorry. I've just done a comparison in the Kaynes software and the
7510 is the closest to the M&K/(AL33?) airfoil. ( I use the Motsch coords
from Free Flight News 11/96 for M&K)
Gard 6509
% upr lwr
0 0.0 0.0
5 4.2 0.6
10 6.1 1.2
20 8.25 2.3
30 8.95 3.25
40 8.9 4.0
50 8.45 4.35
60 7.6 4.35
70 6.25 3.9
80 4.7 3.0
90 2.75 1.75
100 0.4 0.0
Turbulate at 7% and 23%
Gard 7510
% upr lwr
0 0 0
10 7.0 1.4
20 9.1 3.0
30 9.8 4.2
40 9.9 5.0
50 9.5 5.2
60 8.6 5.1
70 7.15 4.6
80 5.3 3.5
90 3.1 1.9
100 0.4 0.0
Turbulate at 7% and 23%
Malkin also has Gard 7509 and 8910.
Regards
Mike Fantham
Chit chads
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Roger,
Jon has forgotten his early modelling days when he had to repair
all the chads in the wings etc after flying over those areas with stylus'
type growth, but then I suppose he now only has to iron them out.
Of course the main item that he forgot was when he did irreparable
damage to his model, which I assume would be chadostrophic!
Keep up the good work Mac,
John.
Chad speak
==========
Author : This email address is being protected from spambots. You need JavaScript enabled to view it.
on 12/12/00 2:16 pm, SCAT user at This email address is being protected from spambots. You need JavaScript enabled to view it. wrote:
> Depending on who our next President is I may or may not attempt to implement
> this program but any efforts from the readership on other possible chadizims
> and chad combinations are welcomed. As they are saying in Florida the
> election is not over until the Fat Chad sings.
>
> Mac the Bigot
All I can say, just replace the Anglo Saxon - "Chad off!"
Michael J. Woodhouse
Chads and such
==============
Author : This email address is being protected from spambots. You need JavaScript enabled to view it.
Hi Roger,
I enjoyed Jon Davis jokes about chads. Since I live here in Florida
where all of the action has been on the election, here are a couple of
comments for all.
The United States is about the only country left in the world where the
citizens are allowed to own guns legally. The U.S. is one of the few
place that you do not see armed soldiers, citizens, or tanks on TV news
on election days. Even thought we have not settled the presidential
vote, we are not having riots. The people understand that the problems
will be solved, and we will still have a government elected by the
people.
Sure we have our problems with our voting system, most places do. On
January 20th we will have a new president. No matter who it is, the
country will go on and continue to be the becon of freedom for all.
Rex Hinson
Stretching Rubber
=================
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Roger,
You may remember during one of our trips to Lost Hills (when I
wasnt asleep) I was talking to you about the stretching of rubber motors
on our test rigs and the doubts I had about using nylon ropes to haul the
rubber out to length due to its ability to stretch.
I proved this conclusively with two methods, one by just hooking one end
of the rope onto the scales and cranking the winch out up to 80 lbs. This
method resulted in the rope stretching, after 10 minutes so that the spring
tension relaxed back to 65 pounds.
The second method I used was to place a "steel link" representing a
stretched rubber motor and once again pulling the unit up to 80 lbs and
this time the rope tension relaxed the spring back to 76lbs.
This was done using a twisted nylon rope of about 3/8 inch in diameter
but I also tried it out using a braided nylon sash cord of a similar diameter
with the resultant that the tension only relaxed back to 78lbs.
As I use my unit to both test the motor for energy and to "run it in "for
flying I decided to change the rope/cord to a steel cable and purchased a
plastic sheathed stainless steel clothes line and tested that out but found
that there was still some relaxing of the cable due I think to the plastic
deforming slightly where it went around both the turnaround and also
around the winch spool, so went down to the nearest Ship Chandler and
purchased some stainless steel cable as used by the yachties. The
diameter is 1.5mm and it has a breaking strain of approximately 210lbs so
there is a sufficient safety margin available, and using this there is no
stretch whatsoever.
I tested out some motors with the new cable and found that the rubber
relaxed very quickly for the first minute to the order of 7lbs but for each
subsequent minute up to 10 minutes the stretch became less and less
until at about 8 1/2 minutes I could not measure it on my scales.
It would appear as though the ideal time span for stretching the motors is
about 8 1/2 minutes but I intend to carry on using the 10 minute period as
to date I have not had problems, but at least now I will know that
whatever tension I read on the scales ( calibrated reasonably accurately)
from now on will give me a better understanding of each motor.
I would be interested to hear if any others have done any such tests.
John.
[As a futher explanation, both John and I have rubber testing
rigs that we use for testing full F1B motors. These consist of
a long beam, boat winch and large spring balance. The winch
is used to stetch the motor against the spring balance. One
question is - that are the results affected by some
elasticity in the rope that is used to stretch the rubber ?
and how much of the hysterisis due the the rope and
how much the rubber ?]
.........
Roger Morrell
