SCAT Electronic News 31 October 2001 issue 635 - Halloween
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SCAT Electronic News 31 October 2001 issue 635 - Halloween
Table of Contents
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2001 World Champs - Helmick
Another Stab at the CG - King
C.G position - Magill
More tubes - Woodhouse
aft C.G. postion - Ellis
Answer to Jim Brooks on c/f spars - Brush
carbon fiber tubes (Jim Brooks) - Joyner
F1B Tubes - Bryant
Free Flight Champs? - George X
2001 World Champs
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To all: Have about returned to normal after the trip
to Lost Hills (about 1,100 mi./1,800km. each way) for
the express purpose of retreiving for a team from
another nation. I have done the same in '79 and '93,
and highly recommend this as a way to help overseas
visitors fly to their best standard...taking most of
the retreival work off their feet, if not worries from
their minds. It's a great way to be involved and get
to meet many modellers from abroad. Three WC's with
Livotto/Canada Cups prior, and all the team members I
worked for were wonderful to me (sometimes not easy!).
I would like to see other Yankee modellers to have
such a great experience. I'm not aware of any official
plan to match up volunteers (with motorcycles) to
teams, but there should be.
Having a chance to watch the organization of this
WC, it looked like everything was superbly planned and
very well staffed and equipped. I hope George will
write a "How to" book for future WC CD's. Great
weather, great food at the BBQ and Banquet, simply a
wonderful time for me and a stellar effort for the
miriad folks from SCAT and elsewhere that made it
possible. THANK YOU ALL! Thermals, Steve
Another Stab at the CG
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CG position (Peter King)
I agree totaly with Martin. The only good reson for rear CG and large stabs
is for stability and sometimes a compromise situation (Possibly open rubber
with long heavy motors or non gadget power models) As far as pure glide
performance is concerned, a lifting stab is very in-efficient. Youn are
trying to get meaningful lift from a low AR surface with an in-efficient
gliding airfoil, that is strugling in the turbulent wake from the wing !!
Of course a larger stab does help the DT situation, but in general, use as
much wing as you can get away with and use the stab for what it is designed
for: Stability !!
Peter King
C.G position
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Just to add my two cents worth to Martin Simon's question about C.G
position;
One thing that has changed over the years in Free Flight F.A.I classes, has
been that we are now making longer fuselages and smaller tailplanes, in an
effort to pack more area into the wings. Therefore you would expect to see
the old trends of rearward C.G positions change to a more foreward position
to give the model adequate stability, since the tailplane is now smaller. I
feel that C.G position is not the only thing to consider here, surely the
decalage setup would have alot to do with things too?
I've had similar experiences to Herman with flapped indoor Gliders. These
models seemed very intolerent to pushing the C.G back from around 30%, and
in this state of course, they were very easy to upset from the glide. Also,
i had lots of flights timed with a stopwatch, and observed that moving the
C.G rearward from normal did not increase the flight times at all. I once
had a high aspect ratio F.1.A(in the days of zooming)that had a small tail,
and long fuselage and try as i might, the model would only glide with the
C.G at 50%(not good for the zoom!); any further back than this, and the
model would glide well for a while, then start stalling as soon as it hit
any tubulence at all. I also did some stopwatch tests with this model, and
noted no difference between C.G at 50%, and at 56%(better zoom) in terms of
flight times. And so, in summary, i feel that a rearward C.G doesn't
improve the duration much(if at all) on the layouts we use these days, and
seems to only make the model unstable. The only times i use a "rearward"
C.G, is on my P.30, purely to control the first part of the climb, and that
only coz i havn't fitted the V.I.T system to it yet!
Thermals to all,
Jason Magill
New Zealand
More tubes
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Jim
Check my list!
Michael J Woodhouse, Norwich, UK
Free Flight Supplies now has secure internet credit card facilities.
All mail to: -
web site: -
aft C.G. postion
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The dominance of aft CG positions in free flight models is probably due
to the need to dampen the phugoid oscilation. Phugoid oscilation is far
better with the aft CG. [Phugoid motion is the "swooping" oscilation
that occurs when the model is trying to find its trim attitude. It is
most evident when the plane stalls and then does a series of subsequent
stalls before hopefully recovering. The motion is caused by a simple
trade-off between potential energy and kinetic energy - much like a
swing.] In a free flight model having this phugoid motion heavily damped
is an important feature. It has been a few years since a ran the dynamic
model for a typical free flight plane, but I remember that the dampening
was least when the CG was near the performance optimum. Dampening
increased if the CG was moved either forward or aft. Moving the CG aft
is less damaging is terms of perfomance. The phugiod period is so slow
that a pilot has no diffuculty controlling the motion, but a free flight
model desparately needs to have the motion heavily damped.
Art Ellis
Answer to Jim Brooks on c/f spars
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Jim.....I stock the Russian hand rolled carbon fiber tube spars that have an
extremely high strength to weight ratio. They are lighter than sleeve drawn
tubes that absorb and use excess epoxy in the manufacturing process. They
provide superior torque, bend and sheer resistance for wings, stabs and
rudders. They will take the flutter out of high aspect ratio wings with
less weight than conventional balsa construction.
Available in 3.5 and 4 mm x 440 mm, 4.5, 5 and 5.5 mm x 550 mm. Typical
weights are: 1.1. gram for the 3.5 x 440 mm spar and 2.2 grams for the 4.5
x 550 mm spar.
These c/f spars are being used in the Win Star and Nova Star stabs, the
Candy/G, Honey/G, Pzaz30, and the Bob White Signature Line of P-20, P30 and
Beau Coupe MK II wings and stabilizers.
Please excuse my exuberant commercial.
Al Brush
Online catalog: www.inland.net/~abrush
Fly Free Flight For Fantastic Fun!
carbon fiber tubes (Jim Brooks)
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Jim:
I've been getting cf tubes from Al Brush (www.inland.net/~abrush/f1b2.htm)
he has a range of sizes (3.5, 4.0. 4.5 etc) that work for stabs. Price is, I
believe, $10 each plus postage.
I've built about a half dozen tubular spar stabs. Here are my thoughts:
* They are easy to build, especially if you vacuum bag balsa block with
unidirectional carbon, then slice off for ribs--much easier than capping
individually.
* weight is still a problem--mine end up around 4.2 g, but have a fairly
large leading edge of soft balsa to accomodate the Wobberking airfoil--doing
it over I would use a thinner piece set at an angle, but that would be
slightly more trouble to build. My stabs are also a bit beefy than others
(lots of ribs, gussets, center reinforcement, etc)
* sand the tube spar as much as you can/dare--spar weight should be around
1.1 g
* drilling holes in ribs is best done with a sharpened piece of brass tubing
in a drill press, all the regular drill bits I have tried tear balsa too
much. Another option is to make or enlarge hole with round needle file.
* Did you get a chance to see Russel Peers' stabs--he is selling a cf D-box
shell--D-box is 10 mm in chord--spar is 1mm balsa with cf on back side.
there is a very thin leading edge and balsa riblets--it seems much stiffer
than the tube type stabs.
* Several years ago I got some Gorban stab D-boxes from the late Ed
Turner--these were about 6 mm in chord and had a molded-in back (in other
words it was a D-shaped tube) These are no longer made. All the examples I
had showed a noticble curve to rear in plan (2-4 mm) but made a very strong
stab. As best I can tell these were made in a two-part female mold with a
foam core that was later removed!
* I made several of my own D-boxes similar in size to Gorban's but using a
conventional vacuum bagged taco shell and a balsa+ unidirectional carbon
spar. I used a 20 mm wide Rohacell "rib" at center and Rohacell plugs at
ends--no other ribs in D-box--Assembly was on a jig with the spar (which was
very curved) double-stick taped to the edge of a piece of 5mm
basswood.--these stabs actually were the best I've done so far, but I think
the Peers version with the 10 mm wide D-box instead of 6 mm will be better.
* Matt & Gail Gewain (www.cstsales.com) have some light (2.4 oz I believe)
carbon cloth that would be good for stabs. It is available bias-cut.
* Al Brush also sells a 3 mm cf tube, which I will be trying as wing wire
sockets, reinforced with heavier carbon sock from Mike Woodhouse. Good fit
with 3mm wing wires.
* Al also has tapered cf tubes for spar in all-moving rudder, also $10 ea.
Hope this is of some use.
Louis
F1B Tubes
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On Tue, 30 October 2001, SCAT user wrote:
> Re: TUBES FOR F1B STABS. If Fedorov is still producing, he sells excellent t
ubes. Kite tubes all seem rather heavy.
Graham Bryant.
Free Flight Champs?
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Author : This email address is being protected from spambots. You need JavaScript enabled to view it.
Hey Roger,
Is there going to be a FFC over the Veteran's Day week end? It seems to be
scheduled but I can't find any info about it, not even a CD name. Where can
I get a schedule of events?
George X.
[George
I know as much as you do ! .. hopefully someone else
has information ..]
...........................
Roger Morrell
