SCAT Electronic News 19 November 2001 issue 644
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SCAT Electronic News 19 November 2001 issue 644
Table of Contents
=================
Flamingo foils and a pot of pot pourie - skykieng
30gm. changes - Brooks
30gm. changes - Brooks
Photos from WC - Blackam
Eppler bird sections - O'Connor
Victor's Eyes see Santa
Thermal expansion of carbon and wire - Linkosalo
RE: Bird Sections - Gregorie
Hardys comments - Acme
SouthWest FAI Challenge F1G flyoff
Patterson #1 places
Re: F1C Power - Mennano et al
Saqqara Bird - Gregorie
Gummi Gossip - Andresen et al
CG position and a comment on turbulated taiilplane - Barker
Flamingo foils and a pot of pot pourie
======================================
Author : This email address is being protected from spambots. You need JavaScript enabled to view it.
Hi, fellow modelers and/or sportspersons
Concerning the bottom bumped airfoil as advocated by H.A.: I do have
some experience with such airfoils. As I remember they were once
refered to ages ago as "Flamingo sections." Somewhere in my readings
...perhaps in Raul Hoffman's little compendium of aeronautical facts
tittled "Aerodynamics Made Painless" it was pointed out that the so
called bottom bumpy bird airfoil was a characteristic seen of dead
bird's wings, and that in life they didn't have such a shape.
Whatever, and nevertheless, I used such a section on an early folder
wing that contained an arrowshaft for the main spar. To make room for
it I used a shape similar to the mysterious Serendensky turbine
airfoil that has a pregnant bottom, but sported a Nordic like entry
with a narrow, cusped nose. My airfoil was distinctive in that it was
much thinner, had knife-like leading edge, and was also equipped with
a "kicker" Gurney flap. The glide seemed excellent, but then there
wasn't much to compare it to as it formed a new breed of F1Cs. Of
course it was designed as a pure glide section and meant only to
operate at a generous positive angle of attack. I would hate to think
of the chaos in streamlines generated by flying the thing at a lower
angles of attack to reduce the CL -- such as needed during a climb.
Flutterville!
It seems that such a bump -- or even an exposed spar --could be
beneficial in that it would further slow the velocity flow on the
bottom and thus increase the circulation by increasing the upwash on
the wing. The forward cusp on the enty would enhance such a condition.
Since the bottom airstream is reduced in velocity any extra drag on
bottom would seem to be much reduced. The same could not be said
about putting such projections on the corresponding top surface where
the local velocity can be dramatically higher than the relative
ambient air speed.
My latest design retains the more extreme bottom nose entry, but the
flamingo bump has been removed. The "kicker" remains. One reason for
getting rid of the bump is not so much for aerodynamic reasons but to
allow enough space in the undercamber chamber to accomodate a generous
winglet in the climb configuration.
Weather is chancy from here on out, but I have a glider body that is
used to experiment with the folder wings. It would be interesting to
tack a projection on the bottom of a wing so as to get a rough idea
of any changes in performance. (It would be ironic if I ended up
glueing a half round bump on the bottom of my nifty new taco shells!)
My guess is that the best use of a partially exposed rounded spar
would be to leave the front as is but streamline the rear so as to
fair it into the undercamber.
It is confusing to me seeing different ideas about the ideal thickness
of our low Rn airfoils. Hermann advocates Bob Waterman's analysis that
shows the curved flat plate superior. Peter King, on the other hand,
has a computer analysis that indicates thinner is not always better. I
would like to hear Peter's views on this apparent anomally. As I
understand it the mean camber is not the only factor in generating
lift as thickness is also a contributor.
I was interested in Barker's contribution to the c.g. question. In
experimenting recently with my F1C glider I played around moving the
c.g. Since I use the HS3 symmetrical airfoil I know that zero lift is
at zero angle of attack. No confusion here as might arise with a
cambered foil. (Understand, that my configuration, although an F1C,
is more Nordic-like than that of a conventional Power ship). As I
moved the c.g. forward I went past a neutral point for the stab to
where stab tilt operated in an opposite manner from what is expected.
In other words, the stab had to have a download to maintain the proper
AOL on the wing. The c.g at the crossover point was rather far forward
and nowhere near the 50% point as reported. I would like to see the
analysis as reported by Barker repeated -- but using a symetrical stab
airfoil operating at zero lift. I'm curious if the predictions line up
with the values determined in calculating a particular lifting stab
operating at its AOL for minimum drag. Inquiring minds need to know.
About turbulators on power wings. I have used them on the folders.
When making a whirling arm test I found that a particular symmetrical
generated a large amount of turbulence at zero angle of attack. At
higher anlges say, 4 degrees, the flow smoothed out. Adding
turbulators in the form of 18 lb dacron line (top and bottom, of
course) anywhere on the front 40% -- got rid of the vibration and
noise. Under flight conditions I had noticed that the climb seemed to
struggle until it reached a certain critical velocity where it then
seemed to break loose from the grip of sticky molasses. (sorry, my
computer is doing strange things with the word spacing) Anyway, my
thought was that flying at zero angle of attack was reducing the local
air velocity over the front part of the aifoil and thus reducing the
effective Rn.
As an aside I would like to say I'm heartened by the fact that Hardy
Broders(E)n is alive and kicking -- even if somewhat incoherently
feisty. Incidently, he got my knickname wrong in return, IT is Whining
Willie, not Whiny Willie. (Jeez, Hardy, how can you forget so soon?)
I admit I know just enough to be dangerous. If I'm screwed up here --
anyplace-- please let me know. I get tired of perpetuating ignorance
even if I mean well.
Ps. My friends have been ragging on me that Leonid Fuzeyev has left me
far behind eating his dust. Yeh, well, all I can do is put on goggles,
keep on chugging, and keep my mouth shut ... or at least keep a goodly
supply of mouthwash handy. Leonid did real good with his articulated
Flaming Flamingo. In fact his feat verged on being splendid! Anyone
in contact with him please pass on my hearty congratulations and
encourage him to "keep them wings a floppin!"
Bill Gieskieng, aka Skykieng
30gm. changes
=============
Author : This email address is being protected from spambots. You need JavaScript enabled to view it.
I noticed a request for ideas re the changes to F1B design that are =
contemplated--to be sent to the author direct and not to SEN. I hope that =
you WILL sent them to SEN. Lively debate? Sharing of ideas?
I might even learn something???
30g. changes
============
Author : This email address is being protected from spambots. You need JavaScript enabled to view it.
So ok, I'll start it off.
I haven't even made up a 30 gm. motor yet, so I'm starting at less than =
zero, but I thought at least I'd try to clean up the prop. I've made up 2 =
very thin and very stiff props in balsa/CF composite to my current design, =
one with a bit of undercamber and one with quite a bit more. It's my =
impression that the highly undercambered one gets higher on 35g. but maybe =
I'm losing something because it isn't very stiff, so I'll clean that up =
and see what happens with a shorter motor run. I plan to stick with 28 =
strands and hope for 120 torque, same VP settings, shorter VIT/wiggler =
settings.
So tell me where I'm going wrong.
Photos from WC
==============
Author : This email address is being protected from spambots. You need JavaScript enabled to view it.
We had some problems with our photos from the World Champs. Would anybody
have any shots of the Australian fliers on F1B day, the last F1B flyoff,
or the presentations of the F1B prizes at the banquet.
thanks
Richard Blackam
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Eppler bird sections
=====================
Author : This email address is being protected from spambots. You need JavaScript enabled to view it.
Roger
In issue 642 Richard Blackam mentioned an Eppler work on thin airfoils.
He passed the photo copy on to me some years back.
The article is titled : Airfoils for Ultralight Airplanes
It was in a collection called :
Science and Technology of Low Speed and Motorless Flight Part 1
edited by : Perry W Hanson
The sections are : 376 , 377 , 378 , 379 , 748
They are meant to produce high lift and have a 'soft stall'.
Looks like 378 might be OK at model Re with saw tooth turb.
I have 8 pages (1 page of figs. missing).
If anyone desperately wants a copy I could scan it.
It would be 30 - 50K per page.
Sean O'C in Melb.Au
PS Some one asked about turbs on F1Cs
>From photos it looks like Fuzeyev had two on the folder.
Victor's Eyes see Santa
=======================
Just before he left to back to the Ukraine Victor Stamov showed
me a pair of Bushnell 7 X 50 binoculars with compass. Victor
is very happy with their perfromance and used them during the
endless October season. He had found a great deal
at www.outdoorelectronics.com as these were $159.
Looks like a great xmas gift idea.
Thermal expansion of carbon and wire
====================================
Author : This email address is being protected from spambots. You need JavaScript enabled to view it.
My question is simple: what should one use as hookup wire to tail
feathers of a model to avoid different thermal expansion coefficients to
spoil the model trims between summer and winter? In other words, does
steel wire (as commonly used in F1A rudders) give trouble of changing
trims? Would kevlar thread or even carbon pull-rod be better, in a carbon
tailboom?
-Tapio-
RE: Bird Sections
=================
Author : This email address is being protected from spambots. You need JavaScript enabled to view it.
> Author : This email address is being protected from spambots. You need JavaScript enabled to view it.
>
> I seem to remember a European F1A flyer in the 60's or early
> 70's who used a bird derived section with some considerable success. The
> wing appeared to have a large diameter tubular spar which really protruded
> from the underside of the section.
You're thinking of Thomann's 'Flamingo' section.
I'm not sure where you'd find the section co-ordinates these days, but John
Malkin's aerofoils book would be a good place to start.
Martin Gregorie
London, UK
Hardys comments
===============
Author : This email address is being protected from spambots. You need JavaScript enabled to view it.
HARDY 1 OTHER GUY 0 ........
SouthWest FAI Challenge F1G flyoff
=================================
Author : scat
Jon
We held the flyoff for F1G at the Patterson
last weekend.
1. Roger Morrell 228
2. Bill Booth 204
Patterson #1 places
====================
F1A - Lee Hines
F1B - Bob Piserchio
F1C - Roger Simpson
F1H - Dallas Parker
F1G - Dick Wood
F1J - John Warren
Full results to follow
Re: F1C Power
=============
Author : This email address is being protected from spambots. You need JavaScript enabled to view it.
Frankie. Thought just for fun I would experiment by rewriting your
letter to SCAT. I have deviated from some of your ideas, but my intent
was to get the basic message across with less difficulty for the reader.
It is not perfect, but should give you the idea. I would suggest that
until you graduate english 101 you first send your important writings
to Chuckers for his editorial ministrations. He can clear up any
mispellings or grammatical glitches along with making sure that your
thoughts are going to get across to the readers. It has been said of
Power flyers they they can barely read -- even when moving their lips
--much less write a legible sentance. Chuck Etherigton is an exception
to that rule! Come to think of it I would be better off if I sent him my
stuff also. I do come up with more than my share of "howlers."
Frank Menanno wrote: (fiddled with by billlious Gieskieng)
In response to Bernard Boutiller's contribution: F1C progress?
I will offer this opposing view. I was on hand at the world Champs,
and Yes I saw that there were quiet a few more flyers in F1A and F1B
then there were in F1C. My thought about this disparity is that,
indeed, F1C it is a more difficult event . But simply because it has
become difficult, and thus even more challanging through added
complexities -- such as the geared engines -- that is no reason we
should react in a negative manner by squelching new innovations, and by
doing so squelching visionary thinking. I was thrilled when saw Leonid
Fuzeyev flying his amazing folder; its compact wing, suddenly
transforming into a virtual F1A wing at the top of its rocket climb was
stunning. Witnessing that superb aerodynamic and well-oiled mechanical
feat was a real treat for all! Specators rewarded him with rounds of
well deserved applause every flight. Please! Lets not squelch other
exciting advancements in this great event by slamming restrictions on
new ideas. As for the price of new technologies (geared motors) it is
an unfortunate burden, but how can we turn our backs on such brilliant
inventions and thus betray the efforts of our technological leaders?
There is no turning back. Who, flying at the present level, would be
interested?
let me finish with this thought: I was fortunate to have a seat in
the front row at the F1C World Camps fly off. The anticipation of the
pending competition between these great flyers was at a fever pitch that
I've seen only at our major league football or baseball playoffs. At
that moment there was no other place to be! It was with awe and
admiration that I considerd the vast time and effort these competitors
had dedicated to Free Flight F1C. The skill displayed by those flyers --
who had earned their right to be standing at their pole positions -- was
truly awesome. The end result of this experience has been an
inspiration to me to reach deeper into myself to find the qualities
needed to give real focus to my F1C ambitions!
Frank Menanno This email address is being protected from spambots. You need JavaScript enabled to view it.
Saqqara Bird
============
Author : This email address is being protected from spambots. You need JavaScript enabled to view it.
I ran across a reference to this object, an ancient Egyptian carved wooden
bird, the other day. I remembered seeing something about it in the NFFS
Digest, but failed to find the reference when I searched my collection.
Anyway, this bird was apparently carved from sycamore wood and has a fin but
no stab and no traces of where one might have been fitted unless you count a
chip out of the top front of its fin where a T tail might have been
installed. There is no stab in any of the only four photos of the Bird that
have been published. As it has no sign of noseweight it would have balanced
behind the wing even without a stab. On the face of it there was no chance
of it flying.
I agree with Larry Orcutt (he runs the Catchpenny site, see below), who
thinks it was a wind vane off the mast of a small sailboat, but his site
quotes stories of it, or balsa replicas, having been flown successfully.
If you're interested, here are the web sites containing what I know about
it:
Pictures of the Bird:
http://www.geocities.com/TimesSquare/Alley/4482/Bird.html
Flight claims: http://www.catchpenny.org/model.html
3-view showing stab:
http://nasaui.ited.uidaho.edu/nasaspark/safety/basic/concepts.html
If any SEN reader has information about actual flights made by the Bird or
balsa replicas I'd be most interested to hear from you - especially if you
know of plans and/or photos of balsa replicas.
TIA
Martin
Gummi Gossip
=============
Author : This email address is being protected from spambots. You need JavaScript enabled to view it.
Subject : Fwd: [pmac] Tan II rubber
>From: This email address is being protected from spambots. You need JavaScript enabled to view it.
>Subject: [pmac] Tan II rubber
>Date: Fri, 16 Nov 2001 15:34:34 EST
>
>I just got a note from John Clapp with the new rubber prices:
>10 pound box $215pp USA
> 1 pound box $29.50pp USA
> 1/2 pound $17.00pp USA
> 1/4 pound box $11.50 USA
>
>!/8 inch will be available around Nov. 26, 2001 and all other sizes will be
>available
>the first of Jan 2002 ( this all depends on the rubber meeting spec.)
>
> This ain't a dime store hobby no more, Thermals, Dick Strang
CG position and a comment on turbulated taiilplane
==================================================
Author : This email address is being protected from spambots. You need JavaScript enabled to view it.
Roger
Thank you for publishing my paper on CG position as an attachment to
issue 643. Although that gave the reasons for the position of the CG on
an F1A it did not directly answer Martin Simon's criticism so I would
like to add something in that respect. I am limiting this to modern
gliders with total area constraints because that is the area of Martin's
criticism. I realize that the CG position on other types of aeroplane,
particularly the powered ones, are a much more interesting subject but
that is being dealt with very well by your other respondents.
I agree with Martin that the minimum sinking speed will be when the
tailplane is doing little work. This will be when the lift moments
about the CG and the pitching moments about the CG are such as to give
little tail load. Martin takes his arguments from full size gliding and
to some extent demolishes them immediately when he says: "The range of
CG allowed in full sized aircraft is determined
chiefly by safety requirements". Our priority is low sinking speed.
However there should be a difference between our CG positions and those
of the full size gliders because of the difference in pitching moments.
Full sized gliders use low cambered wing sections designed for the best
L/D ratio and sometimes (as Martin admits) fly them with negative flap
for even higher speeds. Pitching moments are consequently low and so
the CG should be well forward if the glider is to balance without high
tail loads. An F1A is completely different in that it uses a highly
cambered wing section designed for best Sinking Speed. Pitching moments
are high and need a more rearward CG to balance. My calculations
(given in the paper mentioned above) for a typical F1A give a CG of 53%
and I think any of the present generation of F1As will be about there
when trimmed for best performance.
At the instigation of Martyn Cowley, who sent me an email a couple of
days ago, I have used the same calculations on the same aeroplane but
with a symmetrical section tailplane rigged at zero lift. The balance
would be with a CG at 40%. I also ran the calcs assuming a much lower
cambered wing section with a moment coefficient of 0.075 and the balance
point should then be at 32%. Do not read too much into these figures.
Aerodynamic data are always difficult to obtain and perhaps moment
coefficients more than most. Also the low cambered figures will not
necessarily be accurate for full size gliders as I have no full size
data to hand However I think the figures do indicate the importance of
considering the moment coefficients when looking at trim balance.
That is the theory - Martin says where are the test results. What about
every World Championship for the past fifty years?
Comment to Aram Schlosberg - issue 642 The suggestion that the
enormous 1/16 square turbulator attached the flow to the bottom of the
stab and caused other strange things to happen which prevented the
aeroplane from pulling out of a dive seems a bit convoluted. Is it not
easier to conjecture that the large turbulator completely detached the
flow on the bottom surface of the stab thus preventing it from
generating any downward lift to pull out of the dive?
My best regards
John Barker
.....................
Roger Morrell
