Thanks Joshua for responding!
I'm getting times around 1:45 with about 1.4g of .125" rubber or 1.86g
of .155" rubber. In the first case I am left with a good amount of
winds; in the second I am left with almost none. How many winds left is
ideal?
Do you have any advice for breaking in or prestretching rotors? (#2 on
my last message)
-Chris
--- In Indoor_Construction_at_yahoogroups.com, jwfinn@... wrote:
>
> Chris,
>
> How convenient that I just finished gluing the seam on my new
helicopter motorstick... So in no particular order...
>
> I'm not a big fan of the style of heli's being used by Freedom Flight
and others. Some have have a lot of success with them, but they are
woefully inefficient. Unlike airplanes, heli's do best with blade
featuring no helical twist, meaning they should be built flat with a
traditional central spar and an airfoil typical of a wing section. In
theory, more camber near the hub would be better, but I have not tested
this concept and don't know of anyone who has.
>
> Something that you haven't mentioned is stability. I am a huge fan of
Jim Richmond's swiveling vane stabilizers, which are simple, light, and
incredibly effective. If you start pushing the performance limits of a
heli, stability goes out the window, and the vane is the only solution
I've found for the low-speed operation of these models. Here is a link
to Richmond's plan:
(
http://www.smallflyingartsforum.com/YaBB.pl?action=downloadfile;file=He\
licopterJimR.jpg)
> Make sure your rotor blades are stiff enough. If they aren't they will
tuck at high torque and the model will truly go nuts.
>
> With no minimum weight, you'll want to go off the finished weight of
your model. Most of my heli's perform best with a motor weighing around
50% of the airframe weight, but I build for AMA competition, where there
is no minimum weight. I suspect that you'll find a motor of 2-3 grams to
be best.
>
> Good flying,
> Joshua
>
> --- In Indoor_Construction_at_yahoogroups.com, "spinecho" spinecho@
wrote:
> >
> >
> > Hi. I am a high school student participating in the Helicopter event
in
> > Science Olympiad. I have several questions that I would like to pose
to
> > the group. I would really appreciate if anyone could respond to some
of
> > my questions or thoughts. Even though most of my questions are
general
> > and apply to pretty much all free flight models here is some
background
> > on the helicopter: I am using a standard design: top free rotor,
bottom
> > fixed, 3.5 grams min weight without rubber. Rubber is around 1.5g
and
> > 1/8". The basic design can be seen on this page
> > (http://freedomflightmodels.net/ <http://freedomflightmodels.net/>
).
> > Both rotors are fixed pitch. Longest flight time wins.
> >
> > Rubber Motors--
> > 1. Consider the following statement: When you use a rubber motor for
a
> > flight, you need to let the motor rest before you use it again. If
you
> > don't, you need to put in more winds to get an equal flight time.
> > However, after a couple of hours of rest the "power" or "energy" of
the
> > motor will be close to the origional. How true is this? If this is
true
> > what is the best way to trim? A lot of trimming is trying to change
only
> > one variable and see the effects, mainly on flight time. If I am
trying
> > to see how the position of the rotor on the motor stick affects the
> > flight I would like any parameters related to the rubber motor to be
> > constant. If a motor gets "weaker" each time I perform a flight, how
do
> > I know if a change in flight time depends on the motor or the
different
> > rotor position. Perhaps the motor gets "weaker" only if it is wound
> > close to the breaking point? Then the solution would be to trim with
> > fewer winds than what you would use during a competition? (I
remember
> > reading that FAI model supply suggests that you use a new rubber
motor
> > each flight, but that this was only applicable if you were winding
close
> > to the breaking point.)
> >
> > 2. What is the best way to prepare or break-in rubber motors? I lube
> > with armorall, but I have read advice on this group such as, "wrap
the
> > rubber motor around the hotel door the day before the competition"
> > perhaps to prestretch the motor. Why is this done and what other
> > techniques in regards to rubber would be beneficial (and increase
> > times)?
> >
> > 3. For the first time in Science Olympiad, there is no restriction
on
> > the rubber motor mass. However, in regular free flight, this seems
> > commonplace. Does anyone have any advice in regards to this new
> > "freedom"?
> >
> > Rotors--My motors are fixed pitched so some of these questions are
not
> > completely relevant but I am still interested.
> >
> > 4. How do you measure pitch? What is the pitch/diameter ratio? In
one of
> > the previous posts regarding the helical prop blocks I saw one of
them
> > 28". How is pitch measured by a unit of length?
> >
> > 5. In my current design, the spars for the rotors are straight
pieces of
> > balsa wood (see link). How great are the benefits of using a true
> > helical rotor design in which the spars are curved like most props
in
> > advanced FF classes?
> >
> > Thanks for reading,
> > Chris
> >
>
Received on Sat Mar 24 2012 - 16:16:59 CET