For me there is something fun and challenging about trying
to push something of lower performance to perform at close to an optimum level.
The people that build and race the full-scale solar cell powered cars would be
a good example of this. My challenge has been to build and fly an electric
powered free flight model using the STRIX motor timer, 7 mm coreless electric
motor, and one cell lipo battery of around 200 mah.
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| Sig Cub Electric |
Constraints of the timer dictate a motor run time of 10
seconds or less, and the size of motor and battery are limited also. I have personally limited myself
to not using a gear drive. The weight of the electrical components is around 12
grams, if I remember correctly. From my experiments with adding the electrical
system to various rubber models I believe optimum wingspan is about 22” to 24”.
The most recent plane that I constructed just for this electric system is the
Sig Cub. Several years ago I had built a Sig Cub for the intended rubber power
and lost it to a thermal with just hand winds.
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| Flying at 23 Degrees F Motor would cut out |
To cut the weight and the drag down further of electric
system I left off the landing gear and cut the height of the pylon down. For
the wing I used 3 mil mylar and then tissue just on the bottom for some color.
The tail surfaces are covered with Esaki tissue and sprayed with an art spray
which someone suggested might help the warping problem. It has not worked well
and at the right conditions the stab starts to look like a potato chip. I did
not pre-shrink tissue, but I think some type of plastic will be used to replace
the tissue on the tail.
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| Launched Too Steep |
Beyond the specifications of the airplane, I try to improve
the flight by constantly tweaking what I can easily adjust on the airplane.
That is position of the wing, rudder trim tab, and angle of launch. To get a
longer flight you want it to climb as steep as possible without stalling and
the plane transitioning from power to glide as close to level as possible. With
this rather weak power package a real steep climb results in bad stalling and a
very short flight. Other times I notice the plane climbing and diving in a very
gentle manner. No doubt it is stalling but by a smaller amount. The best
flights are in a constant climb angle with no hint of a stall with a fairly
large turn radius because too tight a spiral wastes energy also.
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| This Looks to be Good Altitude for this Power System |
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| Straight Pins Used on Rudder Trim Tab |
What I like about electric is it is possible to get a large
number of flights in because time is not needed to wind a rubber motor or fill
an engine with fuel. Batteries need to be swapped out fairly quickly however
because performance goes down with multiple runs. What I like about this weak
electric flight is the plane is relatively close in and easier to observe. A negative I have found is that the electric
system does not work well below 30 degrees F, but then that is not great flying
weather either.
Related Links
https://sigmfg.com/products/sigff1-sig-cub-kit Sig Cub on Sig Website
https://scienceguyorg.blogspot.com/2018/10/experiments-with-strix-free-flight.html
https://scienceguyorg.blogspot.com/2019/01/electric-free-flight-strix-timer-2.html
In the video the climb is not consistent all the way up and duration is not as good as it could be. Probably turning a little tight also.
