SEN issue 1097 - 25 May 2007

Table of Contents - SEN 1097

  1. Radio D/T reply to EoB
  2. Looking for Argentine World Cup
  3. Black and White on F1B
  4. Interesting safety Info
  5. SEN Admin

Radio DT in reply to EoB
Ken Bauer

In reply to Chris Edge's inquiry about frequency, my new Airtek RDT system operates in the 902 to 928 MHz area which is one of the "ISM" bands in the US, or Industrial, Scientific, and Medical and is license free and home to stuff like cordless phones, toys, gadgets, etc... Another ISM band is at 2.4GHz and these bands are somewhat universal in most other countries, but I can't say for sure. But I can say that the most universal rule for radio devices is that if you don't bother anybody and nobody can detect your transmission, nobody will care. The great thing about an RDT system like mine is that the transmission lasts for only a fraction of a second and is extremely unlikely to be noticed by anyone, and I've always stayed away from RC frequecies since it is best to not bother those guys.

I plan on publishing details and prices of my new system within the next month or so, so please be patient. Right now it is being tested in many different models to work out the bugs. I will also say that following the initial version which is designed to work with existing elec timers, I will offer a stand alone version which will directly control a micro servo and will therefore be possible to use in almost any type of model.

Ken Bauer
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Looking for Argentine World Cup


Does anyone out there know the results of the Argentine World Cup?
Curious that it has been 4 weeks now and no reports.


Now Black and White on F1B

At the risk of being non ... -PC I can say that the Yahoo FFML
produced a reply that is no longer red but more black and white .....

Jean Wantzenriether wrote on F1B Stability and CG ...

Firstly there was this ...
> I've been trying to fing a good location of CG on a new
> wakefield model. Found out that my models with Bob White
> airfoil seem to work ok with a relatively forward CG, but
> that just made me wonder how the CG location affects thermal
> behaviour.

G'day Tapio. For optimum cg location I use Rene Jossien's
formula. It includes a variable for your required stability.

I have a program that was converted to windoze by one of the
list members. I shall locate it in a day or so and put it into
the files section.

Cu later * Danny M *

To which Jean replied ...

Danny, find it at :

But be sure the formula doesn't apply to the modern F1Bs... Rene'
himself speaking.


Here only a partial answer, because I think nobody has found the
explanation of all the reactions concerned. Dean, I agree with the
majority of your remarks, but some of them must be specified.

Let's distinguish two kinds of places for the CG. 1/ on a given model,
one can place the CG more forward or more back by a few millimetres,
say by 5 or 8 mm; the wing-stab decalage will change for the glide, an
advanced CG gives a greater decalage. Let us call that the "fine" CG. --
2/ out of 2 different F1B models, with the same moment arm, one has a
stab of 4 dm2, the other a stab of 3 dm2: the first one will have a CG
at 80% or so, the second will have to glide with a CG at 65%. Call that
the "global" CG.

Now from some real flight experiences... or statistics of known champion

Both the "fine" and the "global" CG location have a same result :
backward CGs must glide with a smaller wing-tail decalage. Concerning
the global CG please read the statistics on : (select Static Stab)

A rearward CG means that the "static stability margin" SSM is smaller.
This in turn means that the model reacts more quickly and more
vigorously after a disturbance. The contrary proof is given by the HLG:
with his very small decalage such a model tolerates extreme changes of
the flight regime. Hitting a thermal is a great disturbance for our
gliding models. Turbulences inside the thermal are other disturbances,
which accumulate and do not cease. A model with back CG crosses these
swirls without raising the nose up, or by pitching up very slowly. In
the contrary, a forward CG means that the SSM is greater.
This in turn forces the model to pitch up very quickly.
too back a CG can remove all the reaction capacity of the glider… and
then the model starts to dive, sometimes to the ground.

These reactions are well known. What is less known, it is that the
“global” CG follows the same tendency, with lesser danger however (many
excellent wakefields flew with CG at 100% and more). In the 1950's lots
of Nordic gliders (today F1A and F1H) had very great stab areas, and
their CG behind the 65%. This arrangement was abandoned in a natural
evolution of the species (!) for three reasons: towing was not easy to
controll, the catch of a thermal not too consistent, and of course we
were seeking for smaller stabs and greater wing areas. Now the question:
why is a greater SSM more reactive to thermals ?

A stable model has a natural coupling between the longitudinal reactions
and the side reactions. Thus, a model which pitches up is involved at
once in a tighter turning. This phenomenon is marked and sure with a
forward CG, while with a rear CG the model does not turn tighter. Inside
the thermal, with the multiple hits of the turbulences, the rear CG
model can be forced to go straight away and to quit the ascending
column. Sure enough, we all have noticed that models forced to a dive by
the bubble can return to a normal glide when leaving the turbulent
thermal... Recently it was reported about a discus LG having a VIT
added: the ship made very great in thermals. Because its hability to
nose up faster, I think... having for the glide a greater decalage than
the fixed DLGs use.

Note that a too forward a CG -- a too great a decalage -- is rather
perverse. Too much nose-up in the turbulence, what means a greater drag,
less "penetration", less capacity to go through the turbulences
surrounding the bubble.

About tighter turning in a thermal... I never had differential wing
warps on F1Bs nor Coupes or P30s. The wing lateral equilibrium in the
glide requires that the circle inner wing is attacked "more positively".
This can be done by wing warping, or by a slight sideslip of the whole
model. In both cases the inner wing tip has a greater angle of attack,
and is led to produce more drag at the first turbulence coming from
down. In the case the inner wing is warped negative (todays F1Bs love
that...): for the regular glide the model is simply forced in a greater
sideslip... the inner negative tip becomes efficient only when the model
has acquired a greater velocity in the thermal. -- My only recipe for
thermalling is : pitch up quickly and "fall down" decidedly in your
turning (French expression...). Hungry to hear more about that...

Interesting safety Info

 RPM Limits for APC Props
Posted by: Al Lidberg on Yahoo FFML
Thu May 24, 2007 11:11 am (PST)

Go to _http://www.apcprop. com/html/ rpm_limits. html_
(http://www.apcprop. com//html/ rpm_limits. html) and click on the page for this information.

SEN Admin

One of the reasons we changed to way we distribute SEN was to empower you to make changes in your SEN subscriptions your self. You can change the e-mail address it is sent to by clicking on the link at the botton. You van also chnage to HTLM forma tand to un subscribe.

From time to time people sen e-mails asking for me to do that for them.  I'm very busy and may not get to that right away. Bceaue we have the way of you doing it yourself, this gets pushed down the priority list. 

Roger Morrell