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=HelicopterJimR.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 - 07:55:08 CET
