SEN-446 July 27 2000
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News and Reports 2000 - second half
SCAT Electronic News 27 July 2000 issue 446
Table of Contents
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Ritz's Stab Section - Schlosberg
Texas Cloud Climbers Contest - O'Dwyer
decal info - Deachman
color and vision - Rozelle
Free Flight Flying at El Toro Airbase? - Kelly
In the Press - Glue - Bogie
Announcing SERENETTE - FAI Model Supply
Reynolds Number Effects/Aspect Ratio - Mattes
Re: Strain the paint? - Whiskey
Ritz's Stab Section
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Martin Dilly, in the discussion about the Benedek F-sections, noted that
using a B 6456F and the Ritz stab section 6-60-9b, he did not encounter
the stall "lock" observed Woodhouse and Schlosberg. The question is
what might be unique about this hybrid section, resembling a 9% clack-Y
to 40%, followed by a lower surface deep pocket, reaching a depth of
4.4% at 60% of the chord. (I understand that Ritz used a full length spar,
but don't know its location - at the entry to the lower cavity?)
While gliding, a stab generates a small amount of lift - a Cl around .2-.3
to balance the wing's lift which is ahead of the model's CG. Ideally, a
stab should function (have a positive dCl/dAlpha curve) within a range
of angles of attack, say +-5 degrees (measured relative to the zero lift
angle). The range is not unusual, corresponding to a sudden shock
upon entering a strong thermal flow.
A Clark-Yish section would suffer a lower surface stall when its angle
of attack (alpha) became negative. Once the lower surface detached,
the stab's downward force would weaken considerably, flattening the
Cl curve, or equivalently, making dCl/dAlpha zero. The lower flow
detachment is in effect a hysteresis loop, where a retachment would
only occur at a higher alpha. Typically, the model locks into a deep
stall, which might deplete most of its height before returning to a
normal glide pattern.
Delaying a stab's the lower stall can be archived a number of ways.
Clearly, a symmetrical section would perform well in this range, since
detachment (upper and lower stalling) would probably occur outside
the +-5 degree range. The popular Wobbinker section is probably
able top delay the lower stall since its blunt entry eliminates the upper
leading bubble at positive alphas, and lower leading bubble at
negative alphas. The blunt entry might make the section rather
insensitive and "draggy".
The lower pocket in the Ritz stab section might also be delaying the
lower detachment. The Dilly observation that his B6456F did not lock
into repeated stalling pattern might be attributed to a later lower
detachment of the Ritz stab section he was using. If the stab was still
effective at a negative alpha, it would be pitching up the wing -
preventing the wing's upper stream detachment point from locking
on the kink at the back of a B6456F section.
If the detachment of a Ritz stab section when alpha becomes negative
begins at the back of the lower section, the kink at the entry to the
pocket might anchor the lower flow for another 1.5-2 degrees. Although
the increase is moderate, it might signify the difference between an
average and an above average stab. (David Lacey thinks the effect
is below .5 degrees, making it insignificant.)
It is not clear whether the Ritz stab has such an effect, but I feel that
the section might warrant a second look.
As the co-ordinates of the Ritz might not be readily available (Malkin's
Airfoil Sections, '81) they are attached:
0 1.25 2.5 5 10 20 30 40 50 60 70 80 90 100
U 1.2 2.5 3.2 4.2 5.6 7.5 8.5 9.0 9.0 8.7 8.1 6.9 4.8 .6
L 1.2 0.6 0.2 0.0 0.0 0.0 0.0 0.8 3.1 4.4 4.8 3.2 2.6 0.0
Aram Schlosberg
Texas Cloud Climbers Contest
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The Texas Cloud Climbers Regional Free Flight Championships, were held
this year on a genuine cattle ranch. The venue was the beautiful
Beaumont Guest Ranch near Grandview Texas that was leased for the
two-day event. The cattle seemed to understand that they should move
into a large feeding corral as soon as the first model engine was
started. The Ranch owners were satisfied that we modelers were an
acceptable but different bunch of non- cowboys and have invited us back
for a contest next year.
The temperature was a normal Texas mid 90 with fair wind and big
thermals. The wind and unfamiliar surroundings were the reason two
minute maxes were flown in all classes. Since this was both an Americas
Cup and a National Cup contest, the turn out was pretty good. The
competition was close with fly- offs in many of the various classes.
F1A sec
Mike Fedor 1037
Steve Spence 770
Jeff Fedor 759
F1B
Fred Pearce 1115
Ed Wiley 1054
Richard Wood 622
F1C
Faust Parker 840
Bob Johannes 838
Reid Simpson 812
F1G
John O’Dwyer 582
Richard Wood 566
Ed Wiley 555
F1H
Mike Fedor 422
F1J
Bob Johannes 659
Jason Greer 638
Dan Berry 638
½A Gas
Faust Parker 661
Dan Berry 641
Russ Snyder 545
A Gas
George Avila 597
Russ Snyder 595
Jason Greer 572
B Gas
Jason Greer 600
Bob Junk 476
John Irwin 349
C/D Gas
George Avila 480
Bob Junk 359
Mulvihill
George Hilliard 540
Dan Berry 532
Ed Wiley 240
P-30
Leo Langevin 507
Larry Kruse 500
John O’Dwyer 438
Cat Glider
George Avila 249
Gerald Brown 164
Faust Parker 154
HLG
Dan Berry 118
Gerald Brown 105
Jerry Genow 100
HLG (JR)
Robbie Musk 28
Small Field Combo
Jean Andrews 354
Jack Sheffer 266
Submitted by John O'Dwyer
decal info
==========
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I am very new at a lot of this. A friend got me into building a Hawker
Hurricane. Here in Canada it seems to be very difficult to find decals
for this plane. We have finished most of it and want to finish. Is
there any addresses that could supply the decals we need. I started
this to help settle nerves but finding parts is not helping. If you can
help me it would be appreciated.
Thanks Bert.
color and vision
================
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Color and Vision
Last evening, in thumbing trough the just-arrived September issue of Model
Aviation, I almost skipped over an article titled, "Radio Eyes," as it is
brimming with photos of dazzlingly colored RC pattern aircraft.
Fortunately, I noticed the subhead: "Beneficial facts about your eyes and the
effects of color."
This article appears to be the most authoritative I have encountered on how
the human eye works and reacts to a model's color against various sky
backgrounds, and how these conditions change as the eye matures (read: as we
get old!). It contains some surprising information. Example: Certain vivid
color combinations can begin to "gray" at distances of 160-175 meters. It
also says that the most vivid colors for one person may not be those of
another. But it does NOT tell us how to change a model's color to best suit
the visual perception of our timer of the moment!
But the article does contain some concise suggestions on how we can best
color our models for maximum visibility under typical conditions. It
suggests how we can ensure optimum use and care of the only eyes we'll ever
have=F3including some specific guidelines on how what we tell the
ophthalmologist can affect how well we see when we are flying
I heartily recommend this reading to anyone in the free-flight community.
Walt Rozelle
Free Flight Flying at El Toro Airbase?
======================================
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Dear Roger; I recently got on the SCAT electronic newsletter list and am
enjoying reading the discussions. I am not sure that I understand how to
properly use these computer resources but I am going to try starting
with this note.
Recently I noticed a newspaper picture of a man flying a RC model at the
El Toro (former) Marine airbase in Irvine. It dawned upon me that if he
could get permission to fly there, then maybe we free flight modelers
could too! Now that the plans for the use of the base seems to be in
limbo, at least for the near future, maybe we could use it for testing
competition models and/or sport flying. Maybe we could even use it for
small field contests! Does anyone here in Orange County have any
knowledge about this situation? Paul Kelly
In the Press - Glue
=====================
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Louis Joyner always has something worth reading in each issue of Model
Aviation. His page starts on 126 of the September issue. Just ahead
of him on page 122 is Fernando Ramos who writes on Sport and Scale.
His subject this time is the most complete review of adhesives for model
aircraft. Fernando classifies these glues into Lacquer-Base, Epoxies,
White glue, Aliphatic, Cyano Acrilate, Willhold R/C-56, Contact Cement,
and Loctite. He mentions various names of the glues in each category.
This is the most complete exposition of adhesives I have ever seen in one
writing.
Bill Bogart
[also in the same issue did you see Biggles aka Martyn Cowley in
the sunglasses ad ?]
Announcing SERENETTE
====================
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Dear Roger,
We now have a new coupe called Serenette to go with the Serena . These
two planes are loaded with outstanding features. Most notable are the 3
different prop diameters available, which are all made with very fine
craftsmanship! Each size prop has adjustable pitch hangers. These same
type hangers are available to fit : Bukin , Teeny Torque, and Burdov
front ends.
Reynolds Number Effects/Aspect Ratio
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Roger,
I would appreciate any information, (data, discussion, guesses)
which might help
determine the how far one can stretch the aspect ratio of a F1C wing without
regard to structural limitations. There should be a point where the reduced
Reynolds Number and resulting lower airfoil efficiency offsets the performance
improvement from the increasing aspect ratio.
Also is there any information available to optimize wing planform other
than using a series of trapezoids to approximate an ellipse?
Bob Mattes
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Re: Strain the paint?
=====================
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Ken, I don't know the best way is to strain the Floquil, but I use my... I
mean my wife's discarded panty hose. It works. 8-)
Gene Smith
..................
Roger Morrell
