SCAT Electronic News 13 July 1999
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SCAT Electronic News 13 July 1999
Table of Contents
=================
Spinning A/2 - Horejsi
Babe Bee - Murphy
Spinning A/2 - Gregorie
Babe Bee - ready for the christening ? -Janhke
Spinning on DT - Dailey
Solution to odd-strand problem - Markos
Spinning F1A on DT, 28-30 Strands - Bogart
Measuring rubber for quality. - Bogart watching Andriukov
Junior built Model - photo attached - Davis
Hermann's spin on it - Andresen
Spin from a F1J point of view - Mousouris
[ Well after all of this Joe will have his Nordic fixed
of he will be completely confused !]
Spinning A2
==========
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Dear Roger, I found a subject which was always of my interest, I put
down a few lines. Will you fix my grammatical mistakes please.
Ivan Horejsi
[Ivan your English is just fine, certainly better than I can
correct with this PC with a Norwegian keyboard - I'm
in Oslo for a few days before going to Kiev]
Dear Joe,
I have some experience with the DT, not only with the F1A models but
also with the F 1E magnet steered gliders. I believe the comparison
might be interesting, I guess there is not many people who can
compare models of these two classes of gliders. It seems the ability
of spinning/ not spinning depends on the rate of model's momentum of
inertia vs. model's weight. The F1E models have much larger momentum
as the magnet weight is about 60 grams and it is located 250 mm + in
front of the wing LE. They usually fall flat. The opposite is truth
for F1A.
F1A models usually spin and it is the recommended pattern, as the
descent velocity is larger. The smaller the stab angle, the higher
velocity. It is possible to go down to about 30 deg but the descent
is too steep then. If you increase the angle, you can sometimes get
the flat pattern, but the falling velocity is lowered and, when in
strong thermal, your model will fly away longer distance and one day
will finally continue climbing. When the angle is increased enough,
the DT flight will loose stability, the model falls like a leaf and
will crash.
F1E models have no minimum weight rule, the lightweight ones, flown
in calm air, create often big problems in the DT flight phase: if
the angle is low, the model loops forever, if too big, it falls
erratically and will crash. Sometimes it is impossible to find any
correct angle in between. Here, the only solution is using a
parachute, which must be activated few seconds before the stab.
The model slows down and looses the kinetic energy what disables to
start loops. Or, to add some ballast into the CG.
I believe this text can help. It cost me many repairs and one lost
model.
Ivan Horejsi
Babe Bee Class
==============
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Jerry Murphy
FFBC Member Dist IX
The discussion of yet another beginner event makes me wonder why we
need another event in the days of slow open power, AMA gas, and
nostalgia. I believe the answer is none of these are simple enough
for a raw beginner. There is nothing like P-30 for the gas minded
flyer.
With this out of the way let me say that simply adding an event to the
rule book and then letting the rule change process make it work is a
bad idea. The world is a better place if a club adopts the event and
flys it for several years. This will give the event time to age and
the problems can be found. Issues such as the glow plugs that Doug has
identified can be worked out. Ideas such as target time have not
worked in the past and I suggest that it not be tried again. Adding a
timer to a Baby Bee is a simple task that can be accomplished by
anybody with a screwdriver and 1/8 inch drill bit. (Anybody who has
attempted to use an eye dropper tank can tell you that it is a bad
idea at best.) If the goal of this event is for it to be a training
ground for new flyers, lets give them the same procedures as the big
boys. Persons flying this event will then be facing the same
limitations as other event flyers with engine run restrictions that
can be changed to meet the filed and weather conditions.
A selection of kits would also help the development of this event.
Campbell's Super 30 and PP's One Night 28 have played a key part in
the development of the P-30 class. If the free flight community is
serious about making this event popular it might need to fund the
development of at least two kits by leading suppliers.
So, in closing I say go fly it for a few years, let the event grow and
then when it is ready, put it in the rule book. This is exactly how
P-30 and Pnut scale developed.
Jerry Murphy
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RE: spinning A/2
================
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As Roger says, all A/2s spin on d/t. Its not a problem unless they spin fast
enough to slow the d/t descent speed or make them first helicopter and then
tumble - usually just before they hit the ground. (Murphy's 43rd corollary)
Reduce the d/t angle if you have either of these problems.
Martin
Babe Bee - ready for the Christening ?
========================================
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Roger,
In response to Doug Galbreath's suggestions regarding a Baby Bee event:
1.) I was unaware of the glowhead cost problem and welcome the suggestion
to drop the rule. My next question is similar to Rex Hinson's on 7/12, are
the engines in Cox U-control models the same as the old ones (1970's) I
have? I know that the reed/needle/mount assembly varies and may not be easy
to attach to a firewall, but is the rest similar, or should I say useable?
It should be possible for someone to use these U-control engines if they
have them.
2.) What are the preferences for wing dimensions and overall weight? I
have an old Taibi Eaglet (36" span, 198 sq.in. wing, 190 g) that was the
basis for the numbers I proposed.
3.) I think NFFS should be involved in such an event, possibly including it
at the 2000 Nats as an unofficial event. I thought I might sponsor it at a
local contest next year as well.
4.) So now that I have the choir interested in a Baby Bee event, how do we
get in touch with the people who don't even know our church exists?
Ross Jahnke
Spinning on DT
==============
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Know I saw an article but cannot remember where regarding this same
problem. I think the author solved the problem by changing the angle on
the DTed stab and/or the rapidity of DT. That is, the DT mechanism was
not operating quickly enough. When rubber bands were replaced and stab
kicked up with authority, the spin went away. Hope someone else can
find the reference for you to verify my very foggy memory.
Ron Dailey
Solution to odd-strand problem
===============================
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The problem of using an odd number of strands has a simple solution if
you have access to a rubber stripper or know an indoor modeler who has
one. Just split the 1/8" into 1/16" width and make a loop of the
appropriate length. Remove a length equal to one strand from your
35-gram motor restrand it to 26 (for example) and add the loop of
1/16" to produce a 27-strand motor. No need to tie a bowline at each
end.
Chuck
Spinning F1A on DT, 28-30 Strands
==================================
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My solution to a spinning F1A would be to increase the stab area to something
beyond 20 percent. Years ago, I had an F1B that flew very well but was
extremely critical on the stab setting for DT. Beyond the small useful range,
the model would either spin down or loop down, either one generally causing
possible damage. The stab was 15 percent of the wing area.
28/30 strands---If the knots don't work for you, how about drilling another
rear peg hole?
Bill Bogart
Measuring rubber for quality.
=============================
Author : This email address is being protected from spambots. You need JavaScript enabled to view it.
Ulm/SCAT party. I asked Alex Andriukov how he determined the quality of
rubber. He said, "I will show you." He went to his car and brought back his
tools - a foot long tube for measuring tension good for 16 kg, a millimeter
scale for measuring the length of the test motor piece, a dandy vice (jaws
measuring 1by2 cm, rubber faced), which we attached to a board provided by
Ulm. Alex made a test piece from Bob Piserchio's stash about 10 inches in
length.
Then he put the two ends together, stretched the ends between the jaws as I
screwed in the jaws on the rubber. He hooked the tension device and pulled
it out till it broke the piece, where it broke at about 16 kg. Next sample
was put in place and stretched to 10 kg and the length measured on the mm
scale. Then he reduced the length in steps until the tension was gone,
recording the lengths. The difference in length between steps was multiplied
by the average tension, thus a measure of energy. All the energy increments
were summed. With a knife supplied by Fudo Takagi, he snipped off the rubber
from the vice and the test piece was placed on an accurate scale Alex
brought. The scale was 3by3 inches in size. We had to close the windows and
doors and shut off the fans because the wind gusts upset the scale.
Thus the total energy divided by the weight gave a measure of quality. Alex,
in making up motors, snips off a test piece for every motor and records it on
paper to be placed in the baggie.
Bill Bogart
Junior built Model - photo attached
===================================
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Hi Roger,
Not sure if you are interested in Photos but enclosed is one of my son Evan
Davis with his recently completed "Vivchar Simple Model". Evan was gong to trim
it at the recent MMM 14 rounder in Denver but the windy conditions were less
than ideal for trimming. He will be flying it at the NATs next month. By the
way, he built the entire model himself and did all the tissue work as well.
Other than an occasional suggestion or hint from me it's a full Junior built
model!
Jon Davis
Hermann's spin on it
====================
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Ah, Spinning Nordic Syndrome.
Having made some weird towliners, I know a bunch of things that encourage
spinning D/T's, which include:
Low D/T angle
Small stab
Small rudder
High AR
Asymetrical wing
Offset CG (spanwise)
Low dihedral
Stab tilt
Heavy wing tips
Heavy boom & tail
Major warps
Almost anything
Some of these were curable as D/T angle. Sanded stab LE to remove tilt in
D/T mode to cure some.
Had no major problems thru 96" span, but 120" Big Ten violated most criteria
above so a D/T wasn't incorporated, & was no problem as it had T-tail and
went into deep stall with turbulance.
Have never seen a Bilgri design that had a D/T problem & if it doesn't
behave with a bit more angle a check of any non-symmetry would be in order.
If all else fails, adding carbon to the wing can reduce damage.
Good Luck,
H
Spin from a F1J point of view
=============================
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Response to Joe's Nordic spinning in on D/T. Joe, I have had the same
problem on several F1J models. I ultimately found that on models with
relatively small stab area it is critical to SNAP the stab into the D/T
position very quickly. I tended to like to see the stab gently move to the
D/T position just out of compassion for the stab structure but this can cause
a problem. When the model D/Ts, if the stab motion is somewhat slow, the
model is forced into a stall. Then the nose drops and the flat spin begins
and it usually will continue all the way to the ground. Try snapping the
stab up harder and I think you will see the flat spin disappear. good luck,
Ron Mousouris
............................
Roger Morrell
