My first introduction to flying models came in second grade. I lived in North Yorkshire, England, at the time (the same area where Sir George Cayley did his groundbreaking aeronautical research, although I was not aware of this). One day, our teacher put us in groups and distributed balsa sticks, tissue paper, and glue. We were to build a small biplane under his instructions.
The day ended with wetting the tissue paper, with the anticipation that the next day we would have tightly covered airplanes. The next day, when I came in, I saw the disheartening site of my team’s biplane in a broken mess on the desk.
Another student told me that the teacher felt our group’s plane was the best and decided to try to fly it. In retrospect, this was probably overambitious as there was no understanding of center of gravity, and the model was likely a simple static model anyway. I never even got to see it crash … My next introduction was with a rubber band launched delta wing plastic model. The local store sold toys that, on occasion, would become quite popular in our school playground. This delta wing plane briefly caught on with my friends. Its flight was basically continual loops until landing. The delta wing seemed quite futuristic.
For my seventh birthday, I asked my dad for a model airplane, and he did not disappoint. The fuselage was plastic with a black rubber nose, and the wing and tail was a plastic-covered wire frame. We had a field near our home where we could fly it. The plane was launched by running a string out from its nose about 20 yards, and then through a ring fixed into the ground. You launched the plane by running towards it while holding the end of the string – a human powered high-start. It flew quite well, and the rudder could be adjusted to have the plane circle around.
When I was nine, I moved to the U.S. and was introduced to the rubber-powered Sleek Streak balsa ROG plane. This was awesome, since it had landing gear and could take off from the ground. Of course, we had to try to increase the power by increasing the recommended number of turns in the rubber band motor.
This led to associated repairs but also modifications to the wing and control surfaces. The local toy store sold balsa wood and glue (at the time, we could even buy the glue without parental permission). The store also sold Estes rocket motors, which led to further modifications. With enough power, anything can fly (albeit chaotically).
Around this time, a couple of friends had Control Line airplanes (Cox PT-19) with 0.049 engines. This seemed to be a technology that was outside the reach of my family’s wealth. These engines were also somewhat like untamed beasts. They were difficult to start, could remove a finger, and sometimes, just as the fuel ran out, they would speed up uncontrollably. I tried Control Line flying but it just made me dizzy, and it was all I could do not to crash (or hurl).
A few years later, when I was in middle school, my grandmother visited us from England. It was during my birthday, and I begged her to get me a 2 meter balsa kit of a Schweizer 2-33 glider. It took a long time to finish building that model – which was dangerous, as my mom had a nasty habit of tossing out partially completed models if they hung around my room for more than a couple of weeks (“I thought they were garbage”). After finally completing it, I went looking for a good hill to toss it off. Looking for open fields with hills became something of a habit wherever I lived. I was becoming aware of the most basic aerodynamics and knew to set the CG and launch into the wind.
The 2-33 was a Free Flight model, and true to its nature, I watched it fly away, never to be seen again. I learned to put my name and address inside the fuselage of my models, to set the rudder for turns, and to pick less-wild areas to fly.
In high school, I had a job and realized I could afford an RC system! I bought an entry level Futaba radio and receiver and standard servos and planned to build a glider. I had a Gentle Lady 2-meter Free Flight glider and decided to refit with an RC system. The tail section had to be redesigned, and for some reason, I was fascinated by V-tail designs. For a V-tail mixer, I used the ball and socket scavenged from a roll-on deodorant. This system worked amazingly well and did not alter the CG when it was actuated (moving servos for a mixer seemed like a less-desirable solution). I spent many enjoyable hours slope soaring on the hills above the beach in the San Francisco Bay area.
After college, I had an even better paying job and realized I could afford to add power to my modeling. Electric power was becoming more common as NiCad batteries were affordable. I bought an Astro Flight system with dual 050 motors. Also, at this time, I was becoming more technically adept at building models. I realized that if I printed ribs using a laser printer, I could transfer the print from the paper to balsa wood using a hot iron. Then, I could precisely cut out the rib (and other parts). For some reason, at that time, I was also enamored with seaplanes, so I decided to design a dual motor electric seaplane. In a habit that, unfortunately, has been tough to break, I designed the model to be quite “robust.” On the plus side, there was a good chance of surviving the inevitable crash; on the negative side, the weight of the NiCad powerpack necessitated an exceptionally light airframe.
When the plane was finished, I went looking for an appropriate lake. Several interested people gathered around me when I put the plane in the water. I applied full power, but it quickly became apparent that it was not a seaplane, rather, it was a boat that didn’t turn very well. The crowd was disappointed (but at least it floated…).
My girlfriend at the time thought models were childish. As a couple, we did not last beyond the second year (I got kicked out). I was driving around feeling pretty down when I saw Sky Sailing airport in Freemont, California.
They offered soaring lessons, so I thought, “what the heck,” and signed up for one. The flight involved a tow to 3,000 feet and then about 15-20 minutes of flight before landing. Once we landed, I realized I had completely forgotten about my troubles during the flight (I think I was more focused on the fact that I was in a plane with no engine). Right then, I decided to get my glider pilot license. In a twist of irony, I was flying a Schweizer 2-33, the same as the Free Flight model my grandmother bought me years ago. One of the most important skills taught in glider school is coordinated turns, and the idea of adverse yaw.
I subsequently decided to go to graduate school, and during this time I got married, had kids, and did no modeling at all (and also had no glider airport nearby, so that was the end of soaring). After graduate school, I did a postdoc and managed to build a traditional trainer of my own design. It flew well, but I let a friend of mine try to learn to fly with it, and it crashed.
After my postdoc, I got a position as an Assistant Professor, with a notable increase in salary. I also got very interested in tailless aircraft, and read some work by Dunne, Horten, and Lippisch. The adverse yaw issue was very interesting. The basic problem seemed to be a need to have a control surface deflection at the wing tip that simultaneously increased drag and reduced lift. Spoilers would accomplish this; however, that did not seem like an elegant solution. While thinking about this, it occurred to me that control surface deflection on an inverted airfoil would accomplish the desired effect: an upward deflection of inverted airfoil would increase its (negative) camber, increasing drag; at the same time, this would increase the (negative) lift – i.e., causing a downward moment. These two effects should produce proverse yaw. Re-reading Dunne and Lippisch showed they had explored this design element in their early work. I decided to try to design a flying wing with an inverse airfoil at the wing tip (combined with substantial washout). I used a wire foam cutting approach for this model. I went with my family to my kids’ school to see how the design might fly. I managed to take off, climb to about 30 feet, and make one turn before hitting some trees. The kids asked why I hit the tree. They said they could see it was going to hit the tree but said nothing (thinking I would turn). It was then I realized my depth perception might not be the greatest. In the one turn that I managed to make, it did seem like there was proverse yaw, but I could not be certain.
I decided to focus upon very simple unpowered (i.e., hand chuck) gliders to explore different tailless designs. I was evaluating a variety of parameters systematically, including sweep angle, airfoil (symmetric, cambered, and reflexed), washout function, and dihedral/polyhedral. Achieving a non-linear washout function with a foam cutter was problematic unless the airfoil panels were cut individually. I purchased a laser cutter and this was a game changer for building with balsa, as precise parts could be printed from PDF files output by model aircraft design software. I constructed approximately 50 different designs, varying the above parameters. Some of these flew extremely well, with L/D of ~25 and apparent dynamic stability. I was now ready to attempt powered flight.
Around this time, I also purchased a 3-D printer, and this was another game changer for building model aircraft. I used it to print out horns, hinges, folding propellers, spinners, hubs, winglets, wheels, and landing gear. I investigated getting a new radio transmitter and servos and was stunned with modern prices and performance. I purchased a 6-channel transmitter, which has a variety of advanced functions including mixing and elevon, a 6-channel receiver, and two 5g metal gear servos for less than $100! The RC hobby seems to be one that is unaffected by inflation. The power options are also vastly improved, with light and powerful brushless motors and LiPo batteries (also highly affordable).
My goal in tailless design is to have an efficient two channel glider, exhibiting proverse yaw, and with dynamic yaw stability. I have not been able to achieve this latter requirement in the absence of winglets (albeit quite small winglets). When comparing Dunne, Lippisch, and Horten tailless aircraft, it is only the Horten aircraft that lack vertical surfaces. However, Walter Horten claimed the HoIX was unsuitable as a gun platform due to a lack of dynamic yaw stability (despite proverse yaw behavior). Furthermore, their powered designs typically utilize dual engines (which can negate engine torque) and motor housing or wheel spats with significant vertical surface area. It has been asked “why don’t birds have vertical tail surfaces?”.
Birds don’t have motor torque; they also have biomorphic wings (with dozens of muscles and nerves). Most importantly, they have a neural computer that evolved over millions of years to adjust dynamic flight stability in real time. There is a YouTube video (https://youtu.be/OT8WWw6ViBE?si=ILjtlHrb6KTlV50Q) of a hawk looking intently at something on the ground, its head not moving at all, while gusts buffet its body. Its control over flight is remarkable. I believe proverse yaw and dynamic yaw stability are two different things. I continue to explore them using model aircraft.
I have also experienced structurally weak designs. To save weight, I have minimized spars and introduced lightening holes. However, such designs are unable to resist warping when applying heat shrink coverings or they exhibit multiple cracks after landings. Thus, I now appreciate the balance between weight and strength – especially in torsional rigidity. I have learned so much from modeling that I am surprised that I sometimes feel somewhat alone.
While my local modeling club is most welcoming, I am the only member that appears to design and build their own aircraft. There are also few gliders and few flying wings. Additionally, my interest in flying is not aerobatics, it is in seeing how long a flight I can get using the least amount of power and few are interested in this type of flying.
