SEN- January 9 2000
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News and Reports 2000 - First half
SCAT Electronic News 9 Jan 2000
"SCAT - 40 Years of FAI Free Flight Competition"
Table of Contents
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Eastern Free Flight Championships - Kerr
King on Coupe
GA(W)-2 - O'Reilly
Seen at Taft
Eastern Free Flight Championships
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Roger - We would like to have the Eastern Free Flight Champs listed for the
America's Cup events. The date of the meet is April 8 and 9, 2000. Will
you please contact the appropriate persons? If you have any questions,
please email them to me. Thanks, Tom Kerr
[Tom, [and other America's Cup CD's] the America's Cup 'Commisioners'
are Jim Parker [This email address is being protected from spambots. You need JavaScript enabled to view it.] and Tom Coussens [This email address is being protected from spambots. You need JavaScript enabled to view it.]
I did forward your e-mail on to them.]
King on Coupe
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Reply to Dick Wood.
Dick asks the following questions.... I have offered some answers for what
they are wirth !!
D.W. Please help to educate me on airfoil selection for Coupe so that I
might at
least know why I am copying a given airfoil.
P.K. Let me say none of the answers are the final word on the subject but,
for what it is worth, here are my own beliefs and opinions about your
questions.
D.W. How would the best airfoil for a large quiet air Coupe differ from the
airfoil of a good Wakefield airfoil? The Coupe Renolds number is lower 25000
vrs 38000. Should the camber be lower?
P.K. (Yes, I believe the average camber, (if you taper it towards the
tips), should be ca 4.5 to 5.5% max.
D.W. Is the thinnest possible best?
P.K. In general, Yes but with these things to bare in mind..
Try to avoid seperation on the underside which is even more likely at RE
< 25,000 ie avoid going too thin if the max camb is on the high side. I
use Max Camb ca 5.0% Max Thickness ca 5.0% at the root going to,
respectively, ca 4.5% and 4.5% at the tip. I believe too thin and too
sharp a leading edge radius can be counter productive and can lead to a
situation where a sharp LE can cause stability problems and prevent you from
reaching the optimum CL for the glide. I would suggest good turbulators
and a reasonably rounded LE is more easy to trim up to the max performance.
D.W. Should the high point of the camber be at 40% or 60%?
P.K. I believe, for Coupe in particular it should be 40% at the most
rearward. Any further back and the low RE will cause too much seperation
over the rear upper surface.
D.W. Are these things known? Are they secrets?
P.K. Secrets? NO , but they are only known in so far that they seem to
be born out both from some tunnel tests and, most importantly, in practice
as far as we can tell.
D.W. What other factors should be considerd?
P.K.
1. Aspect Ratio, between say AR = 6 and AR = 10, there is a big gain in
performance but higher than that, RE inefficiencies take over . My own
calcs have shown an optimum for F1G of ca 10 and for F1B, ca 18.
2. Planform, to some extent, but bare in mind, it would appear that the
lower the AR, the less the losses from a poor planform shape. Also the
higher the AR the more important are the exact variations in wing angle of
attack distribution for opt efficiency.
D.W. Turbulators?
P.K. (Vital, for F1G especially with the low RE Nos.involved)
D.W. If so, how high and where?
P.K. Very dificult to say except by trial and error. My own feeling
is... just one turbulator of ca 0,4 to 0.6mm, ca 10% back from the LE.
Too many and too high just causes too much drag.
D.W. It is necessary to make compromises
in glide for the climb? What are the tradeoffs?
P.K. There is always a compromise but I think it is more about the size
and position for the glide, as mentioned above. Regarding Compromising
between Climb and Glide, the simulations I have done would suggest that the
drag penalty in the climb from using a high lift airfoil is grossly
exagerated when considering the rubber classes. (Unlike in Power). The
reason is, for ca 75% of the climb of a rubber model, the wing is operating
at close to it's glide CL anyway. Even in the vertical part of the climb
you gain very little over the usual 3 to 4sec Burst, by using a low drag
section. This surprised me but it vwas the reason I ruled out the idea of
using a 'Flapped' F1B !!
D.W. Who are the best authorities on the subject?
P.K. I think we know who are the most knowlegeable. You mentioned several
already, but if you meant me when you said Peter, I would not consider
myself a good example, for the simple reason I do far too little flying.
;-))))) I try to collate my simulations with the vast experience of the
World's best people with what ever experience I have gained myself. I
still believe strongly that I am near the mark because opinions are, in fact,
quite consistent about these matters these days. I would also strongly
recomend Jean Wantzenriether as a good man to listen to as he bases all his
theoretical work on actual flight tests done by himself and several other
French experts over many years and being French, he has had the finest
background in the art of Coupe d'Hiver, going back to when the class was
first formulated. The French have always insisted, for instance on the
value of thin, low cambered sections and large models with longish motor
runs for the class.
All the very best
Peter King
GA(W)-2
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Printed on System : aeromodel dot com for scat
on Date : Sat Jan 8 06:33:24 2000
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Francisco,
I believe that the correct designation of the airfoil is GA(W)-2 and it is
probably one of a series developed by Wichita State U. in the late '70s or
early '80s. I have a Society of Automotive Engineers Technical paper on the
GA(W)-1 but nothing on the -2. The -1 is a big, fat (hopefully) laminar flow
'foil intended for general aviation use. In fact(I think) the designation
stands for General Aviation (Wentz)-1 after Dr. W. H. Wentz of WSU. Dr.
Wentz is now retired from WSU but, as far as I know, is still in the Wichita
area.
Jim O'Reilly
Seen at Taft
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SCAT founding memeber Bill Hartill was at Taft for the Desert Challenge -
with an F1A, actually I think it was an A/2. They performed admirably
in the perfect conditions. I comment on this because while Bill had flown
gliders in the past, I do not remember seeing him with one since I have
been flying regularily with SCAT and that's over 10 years.
Obviously you can't keep a good man down.
Bill has been busy orgaizing the SCAT 40th banquet. It's going
to be held in the Van Nuys area, only a stone's throw
from the site of the first scat meeting. The date is Saturday
January 29 2000 - if you an ex-SCAT memeber who would like
to attend please e-mail us.
There is also an informal contest between Hector Diez and Ed Wougoulis
who is going to get their new house on the California Central coast first.
The CIAM is nothing compared with the local planning authorities
for general red tape.
Andriukov secret revealed ? Around the campfire the dicussion got to
alternative substances for rubber lubes. Alex said that years ago when
he was teaching some juniors they used castor oil for lube, they also
kept epoxy in the same bottles. One of his students lubed his motor
with the epoxy - and one the contest ! What's the secret, did he use
the epoxy or the hardener ?
Finally the last word has to go to Kit Foxes who are still there as
large as life.
........................
Roger Morrell
