Gliders Launched!

There was a mixture of feelings in the Advanced Engineering II class last week, as they put the finishing touches on their gliders. These thirteen students had conceived, planned, and brought forth finely-tuned creations over the past nine months. The thought of now—literally—throwing them to the wind was somewhat concerning, to say the least.

Aaron throws his team's glider from the roof to the field

Aaron, Caleb, and Megan had worked on a design with the shortest length from nose to tail, which resulted in the lowest weight of all four teams: 281 grams (a bit more than half a pound). They pulled cellophane over 3D printed ribs to create an aerodynamic lifting wing, and they opted for a balsa tail and body, connected by two carbon-fiber rods. Their team was also the only one to decide against undercarriage, relying instead on the rounded fuselage itself to land safely on the grassy field.

In total, this smooth sailplane made about four throws, with some repairs along the way! Sporting flashy silver and gold control surfaces, they reached a maximum distance of 68 ft. It also bears mentioning that the cumulative report with the conceptual and detailed design, plus appendices, came out to a whopping 23 pages. Well done!

Megan, Aaron, and Caleb standing proudly

Kylie, Luke, and Josh had the great honor of building the largest plane, dubbed by some The Spruce Goose. Click here for some serious aviation history behind that name! With a wingspan of 100 cm, a chord length of 22 cm, and a total nose to tail length of over 80 cm, it took to the air for an historic maiden voyage, with Luke at the helm.

Unfortunately, things did not fare so well for this 502 gram glider (a little more than 1 lb), which only made it 17 ft out into the field. Mr Meadth also tried his hand at throwing this one, but this was hampered by some sticky undercarriage. The good news is that the egg onboard was well protected!

Kylie proudly holds the Goose aloft

Luke, showing some signs of stress before the big throw

Left to right: Colby, Mikaela, Tys, Victor, Luke, Kylie, and Josh

Next in line was the Banana Grinder, so named in honor of some typographical errors early on in the design process. Tys, Mikaela, Victor, and Colby also chose to pull cellophane over printed ribs, but decided to rely heavily on the CAD skills of Tys and Colby to construct many other components of the aircraft, resulting in a high construction precision.

Colby and Tys did great work on matching the CAD model
to the real thing

The team worked powerfully together to build a sleek-looking machine. Others commented on the slender, low profile, the extensive use of carbon-fiber rods in wings, tail, and body, and Mikaela's cover page artwork! The Grinder's best launch took it an impressive 60 feet.

Colby waits for the wind to pass before making the throw

Our final team boasted several different features not seen on any other glider. Blue Wonder was the only glider to have a dihedral angle (where the wings slope upwards), it was the only one with a T-tail instead of conventional, and it had the longest wingspan of 120 cm, resulting in the highest aspect ratio. Aspect ratio is a comparison of the wingspan to the wing chord. The students had been taught in class that a high aspect ratio would lower the induced drag. Other teams had aspect ratios around the 4 to 8 mark; Blue Wonder was 12.6.

Eva, Gabe, and Claire also made extensive use of 3D printing and carbon fiber, much like Banana Grinder. Finally, they chose to skin the wing with tissue paper soaked in dope (a kind of glue that dries hard and pulls the paper tight). This resulted in a smoother, tougher lifting surface compared to the cellophane. Click here for the CAD model of their components.

The completed 120 cm wing and T-tail (not yet skinned), connected
by a carbon-fiber rod

It is an unfortunate fact of history that the maiden voyage of this aerial acrobat was a complete disaster. After several successful short-range tests, Gabe hurled the machine into the air... only to have it bank around to port and crash violently into a row of bleachers! With a total distance of only 4 ft and a broken tail, Claire brought out the masking tape to get it ready for another flight.

Gabe hefting the Blue Wonder down on the ground

A second throw left the crowd speechless, as the Wonder curved gracefully into the breeze. After gaining a dozen feet of altitude, it swooped down across the field, showing none of its port-side tendencies, and landed smoothly at 97 ft! Gabe and Mr. Meadth were both able to make a few more flights just as successfully before a few rough landings left it crippled and grounded like the others.

At the close of the experiments, Victor commented that he would never look at an aircraft the same way again; he now sees the c.g. and the balance and all of the work that went into it. And needless to say, Eva and Gabe and Claire were glowing with pride.

So—what was learned?

1. It is better to have high accuracy construction, which 3D printing perfectly lends itself to.
2. A dihedral wing angle really does promote roll stability.
3. The planes' distances were directly linked to their wing aspect ratios (how slender they were).
4.  Lighter planes flew further and better.
5. The doped tissue paper seemed to lower the drag compared to the cellophane.
6. Carbon fiber really is as awesome as it sounds.

With only a few weeks of school left, the students are now turning their attention to a special project, funded by a grant awarded by the EnergyPartners Fund. Broken out into five new teams, they are assembling electronic components for a quadcopter drone. They will design and 3D print the body of the drone, holding all the pieces together. More to come!