National Free Flight Society

SEN 2191

Table of Contents – SEN 2191

  1. Response to Ken Bauer
  2. Ken’s Riddle
  3. Parallel Universe
  4. some of Ladi’s F1Bs for sale
  5. grumpy old men bickering about some rule obscurity
  6. Dino wants to save it not bury it
  8. Dino Ignored

Response to Ken Bauer.
I have never bunt launched a glider in my life but I have read your Dad’s
articles many times and have a great faith in his judgement and I believe
his description of turning flight is correct.  What I do not understand is
your statement that: ‘it is well known that higher angle of attack on the
right wing will cause the model to turn right so the drag is dominating’.
The drag curve is actually flat at low angles of attack (at high speed)  and
much steeper at high angles of attack (low speed) so at the high speed of a
bunt launch one would expect the drag to be reducing in respect to the lift
as both are affected by the square of the speed.
I suppose the path of the glider on launch is some sort of geodetic line
which might give a different speed to port and starboard wings but I would
not expect that to be a large effect.  What does seem to be the odd man out
to me is the fin and rudder which will also be experiencing forces depending
on velocity squared with no obvious balancing forces.
John Barker – England

Ken’s Riddle
Ken Bauer’s riddle is a very interesting one, and not easy to answer in general terms, as the geometry of the model undoubtedly will modify the response. I tried to simplify the problem by considering a V-dihedral model of constant wing chord. There is a wash-in  on the right tip, linearly distributed so at the root there is no wash-in. Right rudder is applied that banks the model to the right and induces a right turn if the rolling moment due to side-slip is greater than the rolling moment due to the wash-in.

Doing the analysis I find that the rolling moment due to side-slip will predominate as long as :

sin(beta) >delta/(3*tan (gamma))

beta= side-slip angle
delta= additional angle of attack due to tip wash-in
gamma=dihedral angle

So, assume a  dihedral angle of 12 degrees, and a tip wash-in of say 5 mm on a chord of 150 mm to get an idea of the side-slip angle needed:
delta= arc tan ( 5/150)=0.033 Radians
tan(gamma)=tan(12 deg)=0.213

thus sin(beta)=0.033/(3*0.213)=0.0518
and beta= 3 degrees, nearly.

This side slip angle needed to turn right appears quite small, so it may explain why it is so easy to turn the glider even with very small fins. Other dihedral layouts and chord distributions will of course produce different results, but I believe that  they will not change the order of magnitude of the result above. I’d be happy to discuss this further off-line, there is no point in introducing maths in the SEN newsletter.

Sergio Montes (

Parallel Universe
From: Bernard Scott

Stuart Darmon has braved the wrath of the establishment with his analysis
of the state of FAI flying today, and in doing so has encouraged me to risk
commenting again. I have followed this group for many years, but withdrew
from participating when opinions from non-FAI flyers seemed to be unwelcome
by a section of the group (though I note that some of the ideas I suggested
were later put forward by recognised FAI flyers and given a better reception).

Which is the nub of what I have to say.  To find out what would encourage
participation, more is needed than closed-door debate between a tiny group
of established flyers as there is a natural instinct to protect the status quo.
This is understandable. Having a huge investment in a specific type of
model makes it hard to view new ideas objectively (no matter how beneficial
they may be) if they make this investment obsolete.

When a business wishes to expand sales, it doesn’t survey those who are
already customers, it surveys that much larger and profitable crowd – those
who are not yet customers.  Market research can be applied to any field.

Whether the results of such research into FAI flying were put to productive
use would depend on the willingness of established flyers to make individual
concessions to the greater good.

Bernard    (NO, not that one … another one).

some of Ladi’s F1Bs for sale
From: tony mathews

Hello Roger,

Ladi Horak has 4 F1B’s with Black Magic timers for sale. 3 models with
fixed pitch front ends and 1 with variable pitch (6 panel with BE airfoil
wings by Stefanchuk). Please email me ( for details.
Good models for starting F1B and the 6 panel is an excellent flyoff model.
They can be brought to Lost Hills in October if anyone is interested.

Tony Mathews

grumpy old men bickering about some rule obscurity
From: Paul Fynn

Re:  Altimeters.

The whole argument is academic as at the present rate of decline in our numbers there won`t be enough competitors to make a worthwhile event in any class.  As a group
we hide ourselves away in inaccessable locations as far away from the general public as possible. The internet allows some public exposure in the form of grumpy old men
bickering about some rule obscurity.  Who on earth would want to join us ?

Timekeepers can be our salvation from this dire situation in that we should recruit them and train them.  Only the interested ones will stay the distance and will eventually become good contest flyers.

At the Grantham Club ( U K )  we have developed a number of such flyers who have just turned up to initially watch and become hooked to a class that suits them. I am sure that if we were to actually advertise training for timekeepers we would get a usefull response and develop some to a high standard initially for timing and later contest flying.

In the meantime we can all dream about a self healing F1B flown by a robot.

Dino wants to save it not bury it
From: Michael Achterberg

Thank you Bernard.. Happy to see someone out there in cyber land who gets it!! Most of us dinosaurs can’t seem to remember their youth accurately, and how far our old free flight models went. I guess they went so far because we had high tech balsa , Jap tissue, and Tatone timers.. Damn high tech stuff..
Anyway, nice article and I totally agree. Altimeter timing helps save free flight , not bury it..
Thermals, Michael

OLIVER CAI 180 180 180 180 180 180 111 1371
IGOR FRADKIN 180 180 145 180 180 865

TOM VACCARO 180 180 180 180 180 180 180 210 630 1920
SARA RADZIUNAS 180 180 180 180 180 180 180 210 627 1917
ARAM SCHLOSBERG 180 180 98 142 180 180 960
CAROL ALLEN 180 180 155 180 180 63 938
ALEX ANDRUIKOV 180 180 180 42 180 762


Dino Ignored

Why didn’t you post what I write about renting altimeters for timing. I had 3?4 people think  its a good way to go..

Editors comment – Mike I did not ignore what you wrote about renting … because I do not appear to have it.

In general, and not just for Mike sometime an article gets delayed because of the effort required to put it in SEN and sometimes just overlook by accident. It is always OK to write and ask.

I can comment tht the Fly Dream altimeter as sold by Hobby King costs about $30 and even though as Tapio had pointed out they do not do the temperature correction properly it is more than adequate for Allard’s experiment.
Roger Morrell