SCAT Electronic News 14 November 2001 issue 642
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SCAT Electronic News 14 November 2001 issue 642
Table of contents
=================
Stab Turbulators and Chords - Schlosberg
USFFC as I saw it - Hines
F1C Power - Manano
Re: C.G. Location, location, location - Kristensen
Has Brokenspar lost it? - Skykieng
Southwest FAI Challenge F1H Results - Cowley
Re: Cambered Plate Airfoil Construction - Andresen
Re: Bird sections - Blackam
Stab Turbulators and Chords
===========================
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It seems that Jean Wartzeniether experience with a turbulator on a flat?
sheeted stab on slow power was helpful. In fact, most built up stabs
have them naturally in the form of a kink behind their balsa leading
edge. I think that the popularity of the Wobbeking section, with its blunt
nose, is due to the avoidance of a separation bubble above or below
the stab. (Note the CH 407 section.)
However, turbulators on stabs might not always be benign. Recently
I experimented with a large turbulator, from a 1/16 square balsa strip,
UNDER a slightly cambered stab at 10%. The combination proved
to be a disaster!
When the model dove and sped up, the large turbulator delayed the
separation of the airflow BENEATH the stab. Attaching the airflow
under the stab created some lift at the negative angle of attack,
countering the downward lift off the upper surface. This in turn,
diminished the negative Cl values at these angles of attack. But more
importantly, the dCl/dAlpha slope was flattened, which meant that the
stab did not generate enough negative lift to help the model recover
out of the dive. Removing the turbulator immediately resolved the
problem of getting locked into a dive.
Gill Morris experimented with a flap just above the trailing edge of a
fixed surface power model, to create a natural bunt (See the latest
Sympo). The problem was that the model occasionally locked into
a bunt and crashed.
A higher speeds, attachment of the air flow over or under the stab
can play an important role. The moral is not tinker too much with the
stab's section by adding turbulators, flaps or kinks.
On the other hand, a stab's Cl curve at positive angles of attack is
sensitive to low Reynolds numbers, particularly below 25,000.
Staying away from short chords is also a good idea.
Aram Schlosberg
USFFC as I saw it
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The USFFC, held at Lost Hills last Veterans Day 3-day
weekend was completed successfully just before the first storm of the
season hit at 1330hrs!
The awards were given out under the big tent under
very adverse conditions as many folks drove by on their way out before
the road flooded to the usual muddy slimepit.
As for the results(partial, & to my best recall),
on Sat, F1A & F1C went to 2 & 5 person Flyoffs,respectively, on Sun am.
Ernesto Busnelli won Nordic,beating Kate (Joyce)Koslyuk, who suffered a
mech problem it seemed.
Terry Kerger won the F1C event.
F1B was Sunday & Bill Booth did 360sec to win a seemingly liftless &
calm FO from Brian van Nest & John Sessums.
Tim Batiuk with 4 maxes plus, beat Lee Hines in OHLG.
Stan Buddenbohm won P-30, setting a huge new AMA record of 14 maxes(I
believe).
Monday had some breeze from south early, & since the forecast was for
storm coming in PM, all Mini-FAI events were flown with 45 min round
time.
This was very wise and fortuitious, as all 3 were
completed about noon & the bad weather was still a
ways off.
In F1H, Brian van Nest beat Ernesto Busnelli in a
fine FO. Bob Tymchek won F1G clean with no FO.
F1J was flown with a 10 min max by mutual agreement
of the fliers, with The Alien, Bob Gutai doing a
huge flight of 9+ min to beat Bill Lynch.
While all this was going on Catapult Glider was
hotly contested in the unusual & varied conditions
prior to the storm. The clouds were ominous, winds
would come, then calm again then swing all around.
Some spotty rain drops would fall, while off to the
west squalls were visible much of the day.
Lee Hines got a huge thermal to beat Tim Batiuk this time. Tom Jones
from Cleveland & Stan B were close
as well.
Attendance seemed down, probably since it was not a true holiday for
many.
Lee Hines
F1C Power
=========
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In response to Bernard Boutiller, F1C progress?
I was at the world Champs and Yes I saw that there was quit a few more
flyers in F1A and F1B then there were in F1C, but isn't that good that
we have so many flyers in F1A and F1B. F1C has less competitors because
it's harder, does that mean we should punish the great minds that bless
our sport with eliminating their inventions that work well, did You see
the great Russian folder fly with it's F1A looking wing when it
unfolded. innovation comes in many forms lets not hinder it by
restricting new ideas. as for the price of new technologies (geared
motors) the free market will work on them as time goes on. let me leave
You with this thought: I was seated in the front row at the F1C World
Camps fly off. The anticipation of competition between these great
flyers was at the height I only see in our major league football or
baseball. There was no were else I would have been at that moment, the
time and effort, the skill and dedication to Free Flight F1C that was
standing at their pole positions was second to none and has inspired me
to reach farther and focus on my F1C program.
Frank Menanno This email address is being protected from spambots. You need JavaScript enabled to view it.
Re: C.G. Location, location, location
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Bill Giesking has pointed out to me tha I made a mistake in my recent
message on this issue: As we all know, the center of lift moved forward with
increasing lift coefficient. Stupid mistake on my part - I must have been
writing too fast! However, I still think the point I tried to make is
correct: On a highly cambered wing like an F1A, the center of lift is
probably around 50%, and the stab produces little lift.
Regards, Jens
Has Brokenspar lost it?
========================
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Dear, Roger
I'm concerned about dear old Hardy Broderson. Has anyone talked to
him recently? Was he coherent?
I tried Hardy's recomendation to put the c.g. just a bit ahead of
where the ship balances.To me it, at first reading, seemed a brilliant
shortcut through all that excess aerodynamic mathematical gobbly gook
Well, I soon ran into trouble. No sooner did I place the c.g than the
damn balance point crept up to it. I readjusted it time after time--
but couldn't seem to stay ahead of it. I finally gave up when the
long titaniam rod I had extended out of the nose broke off. at the
termination of a test glide. Perhaps I was premature in flying it
since I will admit I hadn't completly solved the problem yet, but
truthfully, I'm beginning to suspect that Hardy has "lost it."
Baffled in Denver
Southwest FAI Challenge F1H Results
===================================
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John,
* Here are the results of the Southwest FAI Challenge F1H Fly-Off,
decided at this weekend's USFFC held at Lost Hills, with a 10 minute
round flown at 7:00 am Sunday morning (in light rain) :
1 Martyn Cowley 326 sec (timer Daryl Perkins)
2 Dallas Parker (Jnr) 226 sec (timer Lee Hines)
3 Brian van Nest 88 sec (timer Janna van Nest)
4 Norm Smith 5 sec (timer Tom Jones)
5 Pierre Chaussebourg (FRA) (did not fly)
Thanks again for hosting a great event in Las Vegas
Re: Cambered Plate Airfoil Construction
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Thanks to Mr Brooks for reading the Sympo.
Wow, that's 3 people who admitted reading one of my Sympo articles. The
other 2 reported in an April issue of FF which featured Mr Verbitsky
sporting 2 right hands on the cover, obviously a spoof.
The key structural ingredient in a hawk or other soaring bird tip feather is
the tapered tubular spar hanging in the breeze at 20-25% back from LE on the
bottom. Hans Gremmer has some good drawings in Sympo88.
Glide tests on LPP, CatGlider, F1B and F1H showed an exposed spar, even
deeper than the airfoil height, improved the glide L/D and time over what
the same airfoil did without the exposed spar!
BTW Jim Richmond reports that what he considers his best indoor prop has the
monospar running all the way out to the tip as opposed to props where he
terminated the spar part way out.
For profile, the easiest starting point is the top coordinates of whatever
section you are happy with now. The added mean camber should improve the
performance, especially with higher aspect ratios.
Construction would vary with the class. For P-30 I'd start with a 1/4sq
balsa spar and smaller balsa outline. For stronger/stiffer carbon could be
added.
It should be noted that the material in a D-box, rolled into the same depth
round tube (with thicker wall) will have at least as good torsional
properties.
As to ribs, would probably start out with full depth but thin ones every
couple inches. Have yet to run meaningful performance tests, but I suspect
that even the exposed ribs add more end plate effect than drag in the glide
mode. Interestingly the bird feathers have hundreds of ribs that angle out
from the spar similar to Hank Cole's "featherettes" but on the bottom.
I encourage serious modellers (and who else reads SEN?) to observe feathers
under a good microscope and see how Mother Nature handles the aerodynamic
and structural problems at a similar RN.
Enjoy,
H
Re: Bird sections
==================
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>I read Herman Andersen's article on alternatives to turbulators wherein he
>discussed the possibility that a "hawk wing section" would be a better
>glider than the sections currently popular.
Jim, you might be interested in a series of sections designed by Eppler
for ultralight aircraft. I found them many years ago in an industry
publication whose name I can't recall (journal of flight??) along with a
very interesting paper on the topic of designing sections for low speed
flight. As I recall the sections were E385, 386, 387 (maybe some others
too). They were designed for CL's up to 2.0! but still somewhat higher RE
numbers than your average F1B! The sections were very similar to bird
sections.
The challenge is not so much to get that bird section gliding like an
eagle but to manage the variable camber. variable turbulation, variable
warps and self adjusting trim so that it climbs like a rocket as well!!
Richard
...................
Roger Morrell
