Saturday, May 7, 2016

Towel RC Airplane (2013)

After building our first short-lived but fancy F22 RC planes, my friend Pierre-Luc and I decided to go back to basics and build something that would be simpler to build, easier to fly, and more resistant to "adversity".  The build here was much faster than for the F22s, since the part contours were much simpler.  We did use the opportunity to improve our motor mounts using a piece of aluminum angle bracket I found in the trash in my neighbourhood.  Since aluminum is relatively soft, we were able cut it using a hacksaw and drill out some mounting holes.

Positioning the deck on the airframe.  You can see the motor's mounting bracket in the center.
Stress-testing the control surfaces.
Starting to come together.
For fun, we added a home-made ninja "decal" to Pierre-Luc's plane.  (The picture came from here.)  We did this by printing the ninja on a piece of paper.  Then, we added a large layer of packing tape atop the ninja, followed by another slightly smaller layer.  We ran the same piece of paper through the laser printer again, printing the same design, such that the toner would be deposited on the tape.  Then, we carefully added an extra two layers of tape atop that.  By peeling the corner of the second layer of tape we had deposited, the one that's just under the toner, we were able to detach the ninja, cut it to size, and affix it to the plane.

The decal in place.
An experiment with big z-bends in the control surfaces.  This make the plane floppy and very hard to control; the control surfaces had no authority.  We tried this out because we did not have proper control rods and/or linkage stoppers.
This time, since it was still very much winter, we even bothered to make our planes water-resistant.  We followed some directions from Flite Test.  Though this discolored the plane a bit, the time we spent on the treatment definitely paid off.

Out comes the Minwax...
...and onto the plane it goes.
About to step out and fly!
Out again into the icy, windy winter night we stepped.  But this time we met with success of a sort!  My plane flew a bit but control was impossible due to the give and play in my control rods, and Pierre-Luc had slightly better luck.  However we had difficulty getting our planes to gain altitude properly.

Back home, we ran a few experiments to figure out which propeller gave the most thrust for our battery and motor combination.  We did this by suspending the plane upside down on a luggage scale:

Measuring thrust.
By measuring the increase in weight seen by the scale when the plane was at full thrust using various propellers, we were able to ascertain that in our case, the 10-inch props were the best to use.  They provided about 650g of thrust for a 530g plane, which is a little over a 1:1 thrust-to-weight ratio.

To further test the thrust and make sure we would be able to climb, we built an extremely dubious launch ramp in my living room out of political signage.

Testing thrust-to-weight ratio indoors.
The next time we went out with our planes, it was a little warmer (but still below freezing) and there was no wind; with all the tests we had run, we were feeling pretty good about our chances.

The planes did climb!  In fact on the first launch, Pierre-Luc's plane's surfaces had so much authority he did a very tight loop close to the ground and immediately crashed.  A few tweaks and adjustments later, we were flying!  It's hard to see anything in videos but here is one.  We fly a bit in the second half:

Testing the waterproof coating.
Here are some videos of my other friend Greg flying my Towel on a nice day while I film:


I took the Towel out on many other occasions, even travelling with it a bit.  I've changed the control rods for wooden dowels, and that did wonders for control surface authority.  It has given me an incredible amount of fun over the years.  As of May 2016 I still have it in my workshop, though it hasn't flown in a while and is due for an airframe replacement.

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