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3.. Should one keep the circle tow stab incidence during the pre
launch acceleration phase for extra line tension or should one lower the
stab for extra speed? I plan on circle towing with extra wash-in on the
inside wing and extra stab incidence to compensate for the effect of the
towline drag and give a tight circle with a realistic sink rate for
assessing the air the model is in. Should I keep the extra stab
incidence during acceleration to help get good line tension and rely on
this to pitch the model up at release or should I take it out to get
extra speed and have a quick blip of up to pitch the model upwards on
release? (I presume personal timing sequences are top secret but if
anyone is prepared to give me some suggestions they would be very
gratefully received.)Niel Murray posted by Jim Parker
3. Stab incidence on tow question – there are lots of opinions on this
one! For circle tow kick up the stab above the glide setting until it
just starts to become stally while on the line. Being right on the edge
of the stall is good for making the model turn quick on the line, for
calm conditions a little less incidence might be good. I ususally use
the same position for straight tow, although in wind lowering the stab
during straight tow closer to the glide position can be good to lower
the pull and help the steerability. For maximum launch speed when the
model is unlatched and accelerating, there are some people that lowering
the stab is good to lower the drag and increase speed. However I
believe that it is the pull on the line that generates the speed and so
I put the stab where the model will pull the hardest which is usually
more up than glide position, or about the circle tow position. You can
try adding more and more incidence to generate more pull, but there is a
point of diminishing return where the model won’t fly right anymore.
One trick tried by some super tech nordic guys like Allard V or Rene
Limberger, is to have the stab gradually increase in incidence during
the acceleration, the theory being that more incidence is needed just
before launch to counter act the loss of pull that happens when the
model gets overhead. Those guys can comment on that. I definitely
believe that it is good to have extra incidence in the stab before
launch to pitch the model up immediately and quickly, rather than trying
to blip the stab after launch... Should one keep the circle tow stab incidence during the pre
launch acceleration phase for extra line tension or should one lower the
stab for extra speed?
Depends on the wind. M&K models have the option of changing the tail
incidence when the hook is fully extended (OLA). If it is calm this can be
used to increase incidence to maintain tension. If it is windy you can
reduce tension in order to get more speed without excessive tension.
You do need considerably more than glide incidence for circle and straight
tow.
One of the big advantages of the electronic bunter is the ability to reduce
incidence for the “cruise”. To get the best height the model should pitch up
quickly to vertical (pitch up incidence is about a degree or so more than
tow incidence and tow incidence is about 2 deg more than glide). As soon as
the model is vertical incidence is reduced to a degree less than glide to
prevent the model looping over onto its back. With a mechanical model the
climb has to be done at the tow/pitch up setting and hence the model will go
past vertical.
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