Re: Optimizing a ministick
Cheetah in the tank... Tiger in the tank.. (An old Gasoline advert.)
Simply means you have a smooth running prop shaft, and other things
are holding back performance.
At existing weight and rubber section you can probably double the
flight time, or more.
Backing off turns is the standard for getting the optimum power curve
(stored energy) from the rubber. Rubber power follows a geometric
curve, similar to the edge line of a quartered ellipse. The vertical
axis for the curve is energy; the horizontal is turns. It's very
steep in the last 50 to 150 turns (generally un-useable energy), then
leveling out to what I call cruise torque, where the model is losing
elevation but so slowly you barely notice. It's a gradual power slope
down to a point where the prop turns but has no lifting power, the
model is generating lift by gliding only at the end.
Let's say optimum turns:torque (turns:energy) for your present motor
is a figurative 2100:10. It is far too much stored energy for safe
launch and flight. It has a power curve. Right now you wind in 600 to
1000 turns at a figurative torque of 4 for launch (1000:4) to make
flight managable. There is a different power curve for the energy you
put into the rubber.
To graphically demonstrate, draw two ellipses (well, quarter
ellipses). Make one 10 units long and 4 units high. Make the other 21
units long and 10 units high. Now, overlay the longer curve with the
baselines aligned. Slide the long curve over the short curve until
its curve intersects the short one at 4 units high. The space, area,
between the two lines is the extra energy and turns your motor has at
the same launch torque. Backing off turns is the equivalent of
sliding the higher energy curve to match the energy of your present
no-touch winding practice. Keep in mind, the space in the overlying
curve beyond the intersection is wasted energy.
By winding to maximum turns-torque and backing off energy, you are
optimizing the energy of the current rubber motor for the model.
Because your rubber section has more energy potential than the model
can handle at maximum turns:torque, the potential energy is lost -
you are carrying excess baggage in rubber. Therefor, you reduce cross-
section (and weight) to maximise the the rubber-weight-energy
capacity of the model. Excess weight hurts duration.
I mentioned A6 and that your current .039" (1 mm) was a good size for
it. A6 is has a 30 square inch wing, 120 grams and a flat 6" diameter
prop. With a 14" – 15" length of your rubber A6 will excede 5 minutes
in the same site, no-touch. The rubber section is optimized for the
bigger model and demonstrates how much excess power you are using.
I always say too much. Let's spare my arthritis, and save the rest of
the questions for later. Play with the rubber, weight, and torque
curve for a while. You will enjoy the results.
--- In Indoor_Construction_at_yahoogroups.com, matthew taudevin
<mattnsim_at_...> wrote:
>
> there's a cheetah in the tank?? what does that mean? I never even
considered winding to 90% capacity and then backing off to the torque
required for a no touch ceiling run.
>
> should i glue the front wing post to the fuse and leave the rear
post for trim adjustments?
>
> When you say WASH what does that mean? How do I get rid of it?
>
> and .027 rubber that is .68mm YIKES!! I have some .8mm that I might
try first to see what happens.
>
> How do i get a torque meter? Can I make one?
Received on Sat Dec 20 2008 - 09:17:56 CET
This archive was generated by Yannick on Sat Dec 14 2019 - 19:13:45 CET