SCAT Electronic News August 16 1998
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- Category: Archive 1998
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SCAT Electronic News August 16 1998
Table of Contents
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How much porous is bad ?
More Administriva
Bunt System - van Wallene
How much porous is bad ?
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I have an F1B, the one I flew in Sazena, that never did
quiet as well I I wanted it to. Most times this is not a problem
because a good thermal makes up for a lot of other problems.
I felt that the covering [Polyspan] was too porous.
I did put more dope on it and it seemed to make
an improvement. However I completely recovered the wing in Mica film
that tis air tight and it flys better. [i.e. stays up longer
in dead air]
I compared a number of my airplanes, simply and non scienticaly
by putting the tailing edge of the wing in my mouth and sucking.
While not measurable I certain could tell the difference.
The Micafilm and mylar wings were air tight and the polyspan
covered ones varied. There are differend kinds of 'polyspan'
and dope.
More Administriva
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We did lose a little e-mail last Thursday and Friday.
If you sent us something that has not been published.
Send it again [except for Allard Van Wallene who sent some
stuff on electronic bunt mechanisms - we are converting
the image from a bmp to a gif .. and have gotten behind.
It will appear real soon now
Bunt System
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Author : This email address is being protected from spambots. You need JavaScript enabled to view it.
Dear Roger,
I've designed a new tail system for servo operated bunters that might be of
interest to the readers of the SCAT page. Some flyers already asked me to
make a copy. Distribution by SCAT makes life easier.
I read the article on bunt systems in the latest Sympo 98 (nice article
Aram!). Each system appeared to have one ore more drawbacks as there are:
-Off trim due to servo and temperature drift (not Nyhegn)
-Complex wiring (not Bauer and Gewain)
-Necessity of extra DT line to limit DT angle (not Nyhegn)
-No glide trim by screw (not Stamov, Makarov, Gewain and Nyhegn)
-Possibility of 'bounce back' of tail at rough launches (not Makarov and
Gewain)
-And last but not least: damage when model lands with tail in glide
position like broken ribs or bent/broken bunt lever (not Gewain and Nyhegn)
At least these disadvantages are overcome by the system as attached. Please
note that the bunt lever consists of a disk and a hammer, joined together
by a thin piece of steel blade (razor blade). It can flex sideways to avoid
the above mentioned tail- or system damage. Four M1.2 screws are used to
fix this 'hinge' (see rear view)
The glide position of the lever is vertical, so minimal trim change at
servo/temp. drift and easy to trim push rod length (optical check).
A combined push rod with a thin braided flexible part in series running
around the pulley. Please note that the connecting bush situated between
the stiff push rod and the flexible cable fits in a small recess in the
pulley (not shown) to avoid sliding away from the pulley when the pulley is
pushed by the push rod (DT and VIT).
A T-shaped screw on the glide screw to limit DT angle (adjustable)
A glide trim screw with a Teflon head, running on a polished steel blade in
the tail.
Carbon tail mount at 20% cord with torsion springs.
The first long vertical screw mounted on the pulley serves as 'bounce back'
protector.
The second short screw serves to fix the flexible part of the push rod.
The push rod can be mounted absolutely straight from servo system to tail
system. This in combination with a pulling action for the bunt results in
minimal friction between the push rod and the tube.
The push rod can be easily removed from the tube for servicing, by
disconnecting it from the servo and pulley, and pulling it from the tail
end.
The system is drawn full size for a tail boom with 9 mm dia at the thin
end.
The pulley is equiped with a radial ball bearing (might not be necessary).
The system will be mounted in a new model with Basic Stamp based timer,
programmable by a PSION 3C palmtop and a servo for the rudder.
Have fun with the bitmap!
Allard
...........................
Roger Morrell
