SCAT Electronic News June 11 1999
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SCAT Electronic News June 11 1999
Table of Contents
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Why the noise on mufflers ?
Noise and Duration models - Buskell
F1B span/aspect ratio observations
Marketplace
Why the noise on mufflers ?
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From "bbell"
Since free flight is always out in a fairly large area - where does the
idea of installing mufflers come from?
I can understand some people's inclination to tweak all rules but this
seems real way out.
Can you enlighten me on the subject?
Regards, B. Bell
[ Bill
There are a number of reasons, John Buskell mentions one the following
article... that of conforming to a general aeromodelling standard.
One of requirements of FAI Free Flight is that we have to
get in line with what people do in other countries and sometimes
other disciplines.
There are some sites in the US where FF sites are close to populated
areas, Sacramento, Mile Square Park in Fountain Valley, etc
Another is that if people want to fly quiet models then maybe
they should be permitted to do this,
Also participation in F1C is down so this is a general forum
to figure a way of 'fixing' it. Martyn Cowley's [aka Biggles] proposal
was more that just the muffler issue - it was a idea for
a way of running two different sets of rules concurrently
to see if that would attract more participation .. as well as
keeping the noise polution people happy. ]
Noise and Duration models
=========================
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I believe I am right in saying that the FAI has committed itself (and, thus
it's sub-ordinate organizations) to a strategy of reducing the overall
environmental impact of aviation sport, or at least those aspects over which
it holds jurisdiction. I believe the reason that the f/f sub-committee of
CIAM is being needled into coming up with some sort of noise code is that
f/f is now just about the only body within the FAI that has done nothing in
this regard. Rather the reverse in fact, the f/f rule book contains a clause
in the 'no-exhaust extensions' rule that actively mitigates against noise
control.
Still, this has become a healthy discussion, and, more importantly people
are fielding positive suggestions for a workable alternative to open
exhausts.
Noise is relatively easy and cheap to measure to a fair degree of accuracy,
the most important aspect of its' measurement is consistency. Sports outside
model aircraft that use internal combustion engines have been doing it for
years, auto-sport in particular.
Now, I can see that fitting a muffler; that is a removable exhaust extension
of approximately150mm overall length, 30mm max. diameter, and with an
exhaust opening(s) 1/2 the size of the exhaust opening(s) from the engine onto
which said extension is fitted, would be hard on existing models. All my
models have rear exhaust engines, and I would have thought that adding an
attachment to a side exhaust configuration would be easier. Anyway, if it is
prohibitively difficult, surely, fitting one twice as long is even harder
i.e. a tuned pipe. I can see the point about making the processing task
easier, but allowing pipes would cause more problems than it would solve.
Tuned pipe engines are fairly readily available, however F2A engines; they
run to $1000 (US) a piece, and produce what? 2.2 bhp at 38k rpm? Please, let
's have another suggestion'..As Martin Gregory said, we will be staring at a
3 second run, and models that still get high enough to do 8 minutes. Maybe
we are heading towards the amalgamation of F1B and F1C - no engine run and
no rubber; Hey, hand launch, now I can really fly that!. No, tuned pipes can
't be the way to go, surely.
This is an International issue, and the playing field must stay level. That
is everyone commits to, and follows the same rules. So far as I am concerned
that means that a figure for dB has to go into the rule book, and no flying
tuned pipe models against muffler equipped models (we all know the
difference even if we can't define it) - it won't work.
Let's put aside noise, engines, and propellers for the moment. Here is a
wider question; how do you hold a duration contest for models that don't
come down? All the F1 models are now supreme sailplanes capable of riding
out the very faintest trace of lift. Answer (my answer) - you have to either
load them up and make them come down, or constrain that which is most
responsible for their marvelous performance; I believe that to be aspect
ratio. Span limits for all models? Perhaps, afterall, we have it in F1D.
What about requiring them to fit (assembled, of course) in a rectangular
frame, or box on the ground? It might allow a little more design freedom
than a hard and fast span limit.
For power models, how about fixed propellers? (with apologies to Doug. Joyce
and Eugene Verbitski) - an instant 10% drag raiser.
John Buskell
[I think that it is not practical to distingush between mufflers
and tuned pipes. The only simple test would be a noise test
and there is not doubt that some exhaust 'devices' will decrease
noise and increase power.]
F1B span/aspect ratio observations
==================================
With the discusssion on wing span I have made a couple of observations.
Composition construction means that there are not structural problems
in making a high aspect ration model. It does appear that we have reach
a practical limit based on stability or Renyolds number. Andriukov has
a 2 [1.92 accordingto the catalog] meter span model that he does not
fly very often. His regular
1.52 model appears to perform very well. He used it to beat the higher aspect
ratio model of Bror Eimar in near perfect condtions at Sazena
in the '97 WC. Conditions where you would have expected the higher
aspect ratio to have come out on top. In trying to get better
performance some modellers, Eimar, Kulakovsy, Vivchar, Gorban, etc have
models with a span of 1.75 to 1.85 meters. These fly well but
do not handle strong winds well under power. I have a both
size Vivchar models and my long model certain flys better but
I made a big mistake flying it in the windy flyoff at
Big Al's shoot out on Memorial Day. It seems
that this is the practical limit for 'good' weather conditions,
while 1.5 to 1.6 meters appears to be good for all conditions.
The lower aspect ratio is easier to launch properly, reducing
the likelyhood of screwing up,.. or are we that good that
we do no screw up any more ?
It will be interesting to see what happens in Israel. The
conditions will be closer to Lost Hills thermal turbulence
rather than continental calm . Seeing the fly off will he held
the next morning it will start at 10 minutes, will this be
calm ? to suit a longer model ? or even at that time will
it have to ride some turbulence?
Marketplace
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Vivchar vp hubs
---------------
I saw a box of brand new Vivchar VP front ends at Mike Mulligan's.
They look very good. They are similar previous models but
have a number of detail improvments and appear to be made by
a different machinist. They still weigh about 34 grams.
Mike's number is 714 637 5244 tel him that you saw
it on the internet. maybe it will persuade him to get on line.
.....
Roger Morrell
