SCAT Electronic News 12 Nov 2001 issue 641
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SCAT Electronic News 12 Nov 2001 issue 641
Table of Contents
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Dick Korda - Rushing
F1C progress? - Boutillier
curved plate sections - Brooks
Stab turbulators
Re: C.G. Location, location, location - Kristensen
Turbulators on power models - Coleman
Lively CG Position - Morris
Dick Korda
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Clarification on the message concerning the 1939 Wakefield
Champion Richard Korda is that Richard died on the night of 10/12/01, of
numerous causes, he was 85 years old. I am sure that some of the people now
flying F1B by others will remember Richard Korda's original 1939 Wakefield
design, which won the 1939 Wakefield contest with a single flight of 43
minutes and 29 seconds (2609 seconds). Richard Korda was 24 years old in
1939, and at that time he was a member of the Cleveland Balsa Butchers, a
club that included Chester Lanzo, and George Reich the 1961 Wakefield World
Champion. The world of aeromodelers who have flown Free Flight Rubber owes a
great debt to leaders such as Richard Korda, his like will never be known
again.
Charles Dennis Rushing, author: "The Wakefield International Cup"
F1C progress?
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Hello Roger and Ian,
These are some thoughts about F1C for SEN &FFN:
When reading the results of the 2001 World Cup for F1A/B/C
one can see: 314 participants in F1A, 214 in F1B and 103 in F1C.
The F1C is slowly but surely regressing.
The category is ill from long time, it is now in the final phasis.
My opinion is that the coming of gear reductors will kill it for sure.
A reductor cannot be home produced, the price of what can be
found on the market is so high (a geared engine is sold from 700 to 800
US$!!)
that many flyers cannot afford to buy 4 to 5 geared engines, and will stop.
In Lost Hills, mainly during Canada Cup, we could see that geared ships
climb as high in 5 sec. that conventionnal ships used to climb in 7 sec.
The reduction in motor run becomes ineffective. So what ?
F1C ships were already too heavy; too fast i.e. too dangerous, now they
become too expensise.
We are in the rut, the face against the wall and nothing is done.
It is really time to think to start on something different.
Bernard Boutillier
curved plate 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. How would you build such a =
wing so that it was stiff enough to handle the burst, and light enough to =
be a good flier. The only idea that occurred to me was to mold a wing =
with CF bias cut and 1/32" balsa core. I'm not even sure that this would =
be stiff enough (the props I've made with this method aren't all that =
stiff) and I imagine that a 4" chord with 1% thickness could'nt be made =
stiff in anything less than titanium. =20
So, has anyone successfully translated this section into an F1B wing, and =
where can I find the coordinates for the curved plate section? =20
I've downloaded the Profili program and I can input these coordinates to =
generate any chord, taper I want.
Stab turbulators
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This email address is being protected from spambots. You need JavaScript enabled to view it. wrote :
> I don't recall ever having seen anyone using turbulators on an F1C model
or anything in print about their ineffectiveness. I can't believe they've
not been tried. Have they? What hapened? Are the higher Reynolds numbers a
reason that nobody uses them <<
As far as I know, turbulators help when the lift coeff is very high, as it
is on a wing in the glide phase. Our stabs work at low CL, say 0.2 to 0.3 at
glide, 0 or so at power. On the other hand the decisive efficiency of a stab
airfoil is not in his CL, but in his lift gradient, the lift change per unit
of angle of attack. If the section is thin enough, a turbulator doesn't
change this gradient. Perhaps it only makes the gradient more consistent or
straight, unlike at RN=17000 the Goettingen 795, which is a thick section
for us. - On a Slow Power ship I have used a turbulator on a sheeted stab :
the stalling behavior was markedly improved. - Regards.
Re: C.G. Location, location, location
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It is true that the nominal aerodynamic center of a wing is about 25% of the
chord. However, the center of lift moves backwards with increasing angle of
attack (lift coefficient). At the operating conditions of an F1A model, the
center of lift is probably close to 50-55% of the chord, the place where
most people place the C of G on an F1A. The stabilizer produces close to
zero lift on the avarage F1A.
In F1B I think the traditional aft position of the C of G dates from the
times before VIT - a low decalage was necessary to enable the model to fly
without looping tendencies thoughout the climb. You will note the trend
since 1980 (pioneered by Alex Andriukov and others) to move the C of G
forward on F1Bs as well.
Jens B Kristensen, Denmark
Turbulators on power models
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This has been tried by many of us power flyers. We find to a man that =
what you gain in the glide does not offset what you loose in the climb =
especially in early morning fly offs. Unlike the fly offs, The rounds =
are flown when thermals are at their strongest, and I've yet to see a =
thermal that checks out your wing for turbs. I'll give it a shot again =
in the near future. If it can be made to offer an advantage I'll let you =
know, what and how we did it. I think that the flappers and folders are =
the answer for power models. Inconsistency is still a problem with =
folders and flappers.
Roger Coleman
Lively CG Position
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We sacrifice a bit of glide efficiency (rate of sink) with the rearward CG.
However, in so doing we reduce decalage (longitudinal dihedral) which
provides a bit of instability that allows the model to follow air currents
toward thermals more readily. We believe the trade-off favors the "lively"
model in most, not all, contest conditions. We being me and all who share
this opinion.
Gil Morris
....................
Roger Morrell
