This story was provided by AMA member Dennis Brackett.
To build and fly a large radio control glider and fly it off the rugged mountains surrounding the Owens Valley was a dream I’d had for years. Having spent my professional career as a physics, earth science and aerospace teacher at Bishop Union High School in Eastern California made it natural to want to do this with some of my students.
I have always been amazed and impressed with the accomplishments of teams of NASA scientists, exploring Mars with robots or flying a solar-powered aircraft. How neat it would be if some of the students at our school could experience in some way what it is like to be part of a scientific team trying to meet a difficult technological challenge.
Toyota Corporation awards fifty science grants a year to schools through the Toyota Tapestry Program. My idea for the Remotely Piloted Glider Technology Challenge (RPG Project) seemed to fit the application criteria, so I applied. I was gratified and amazed when I learned that my proposal was funded. Work began in the summer of 2000. I was fortunate to enlist the support of NASA advisors John Del Frate, director of solar-powered aircraft research, and Tony Frackowiak, an expert modeler who runs the Dryden Flight Research Model Lab. The RPG program began with a field trip to Dryden Flight Research Center at Edwards Air Force Base. We toured hangars filled with exotic aircraft and had an extended meeting with our NASA advisors.
Back home, we began to gather materials and ideas for the project. I felt it was important to use composite materials for the construction of the glider because these materials and construction techniques are at the forefront of aircraft design. Strong and light, composite materials are already used in many model- and full-scale aircraft. Although I had originally planned to have students design the aircraft, it soon became apparent that it would take too much time and the project would fall behind schedule. I began to design the plane with the advice of many people. After many hours at the computer, a design emerged that was a synthesis of many (already proven) model designs and structural techniques. There would be a one-half scale version, built to practice and perfect the building techniques and to verify the design. We hoped to build two full-scale versions. I knew almost nothing about working with composite materials. George Spar of Aerospace Composite Products and Matt and Gail Gewain of Composite Structures Technology came to the rescue with videos, phone advice and a vacuum bagging workshop. We were soon cutting foam wing cores with a hot wire system and learning to apply composite skins to the wing panels.
After school classroom and weekend work sessions were a mixed bag. On some days, we would get quite a lot accomplished but there was plenty of goofing off, too. Getting students to show up on time and stay for cleanup was sometimes discouraging. After teaching school all day, my organizational skills and level of patience were at low ebb on occasion. Proceeding cautiously, I soon realized that most students needed practice and experience working with hand tools before being turned loose on a composite glider wing. We were all low on the learning curve, and I found myself explaining construction techniques I had never practiced. Through all this time, we managed to keep the quality control high and the airframes took shape. A nucleus of students emerged that were committed to seeing the project fly.
The local radio control model club (Eastern Sierra Flyers) took an interest in this project from the start. Through the efforts of club president Jim Sack, the Eastern Sierra Flyers started holding Saturday morning training sessions so that students could learn to fly radio control aircraft. Over the summer, several students had helped to build a durable training glider to further instruction in the skill of radio control flying. We had two students who already knew how to fly radio control models; Jimmy Nelligan and Jonathan Kunze became primary pilots. They quickly assumed duties as student instructors during training sessions. Building composite model airframes is not an easy task, especially when you live many miles from anyone who already has the skill. The phone was often in my ear during my prep period as I tried to find out what to use and where to get it for a multitude of design and fabrication problems. We began by selecting an airfoil. We decided on the Eppler 374 section based on the description of its performance in large models. This same airfoil section is often used on large, cross-country model sailplanes. The model needed to be big because the mountains are gigantic. Visual tracking of a model flying out of towering mountains is problematic. One’s sense of scale goes out the window when among the peaks. OK, so we’re going to build a model twice as big as anything we had ever built before, using unfamiliar materials and processes we had never practiced. And still, we didn’t even know if we’d be able to see it. (No problem!)
We began the fabrication process by creating airfoil templates using Compufoil software from SoarSoft Software. The templates were made from formica cut on a bandsaw after applying the airfoil template with 3M spray adhesive. The completed templates were used with a “Feather Cut” hot wire foam cutting system to produce wing cores from two-pound density DOW “square edge” blue foam insulation. We had plenty of foam due to the generosity of DOW corporation, who donated foam that was scheduled to be recycled. We recycled it into a beautiful radio control glider to soar off the peaks above the Owens Valley. Once the foam cores are cut, they are fragile and prone to hangar rash from over handling. “Over handling” occurs quite frequently in a public school classroom. Curious students often leave their mark. The more we worked on the wing cores, the more dents and nicks they accumulated. We soon became Spackle Wizards. Student Patrick Koske McBride became the numero uno Spackle Wizard. He had no shortage of dents to fill. We soon needed to put the wing spars and skins on our fragile creations.
The heart of a glider wing is the spar. For a composite model, flight loads usually carried by a spar are often distributed through the composite “skin” of the model. This is known as “stressed skin” construction. The glider we were building had both a spar and a stressed skin. Master modeler Tony Elliot helped the effort by suggesting a spar design and wing joiner system that was up to the task. We followed his advice. The main panels of the wings are supported by a one-half-inch, full-depth plywood spar sheathed in unidirectional carbon fiber and fiberglass. The wing tip spars are one-quarter-inch plywood and balsa with carbon and glass side laminations. The wing is divided into four panels. The two center sections of the wing are held together by a three-quarter-inch diameter chrome molly tubing wing joiner, while the tips are joined using a five-eighths-inch diameter bent carbon wing joiner rod. The combination of a composite wing spar and stressed composite skin produced a very strong wing. The leading edge of the wing is sheathed in Kevlar. (Yeah, the stuff that stops bullets. Well, Kevlar might protect against bullets, but it was no match for the 400-million-year-old rocks of the White Mountains. Stay tuned.)
The foam flying surfaces are skinned with 4.7 ounce unidirectional carbon fiber cloth and 1.5 ounce fiberglass. The carbon fiber cloth gives the wing strength and stiffness, while the fiberglass cloth contributes a smooth surface finish. The composite cloths are applied using West System Epoxy and a vacuum bagging system from Aerospace Composite Products. The wing skin is applied using fiberglass resin to “wet out” layers of cloth on heavy Mylar carrier sheets that have been waxed to discourage epoxy adhesion. The Mylar and the wet layers of composite cloth form a “taco” that is folded over the foam wing core. This “wing sandwich” is then placed in an airtight plastic sleeve and connected to a vacuum pump. The air is pumped out of the bag and the vacuum created squeezes the layers together until the epoxy cures. The beautiful result of this process is a nearly complete and glass-smooth wing panel that you peel out of the Mylar carriers after twenty-four hours. It's like opening a Christmas present. Final trimming and sanding of flashing around the edges produce a strong and slick wing panel. We elected to build the tail surfaces of the glider using the same techniques used on the wing but without the internal spar. Tail surface cores have balsa outlines to protect the foam edges and to provide a surface to be sanded to an aerodynamic shape. The fuselage of the glider is constructed from plywood and balsa. The front of the glider is primarily three-sixteenth-inch plywood with plywood fuselage bulkheads. The fuselage aft of the wing is three-sixteenth-inch sheet balsa. The horizontal stabilizer sits on a plywood platform. The vertical stabilizer sits in a slot in the top of the fuselage. All flying surfaces are anchored by metal bolts. The fuselage is covered with 1.5 ounce fiberglass and Ultra Coat Plus covering film. The fuselage is basically a box style with internal bulkheads and corner reinforcements.
The project got a big boost from John Elliot at Airtronics. John was enthusiastic about the project and arranged a special deal for us to purchase four RD 6000 computer radios and trainer chords. Airtronics also supplied high-torque servos and extra extension wires for the spoilers. With the latest electronics installed in our birds, we felt encouraged and optimistic. Things were starting to fall into place.
While building was going on, there were other duties to attend to. The glider was designed to carry instrumentation. Like a NASA probe, our glider needed to collect data to advance the body of scientific knowledge. We decided to install a forward-looking video camera and a point-and-shoot camera shooting downward. In case the glider was lost in some remote canyon of the White Mountains, we also installed a borrowed animal tracking transmitter from the California Department of Fish and Game. If necessary, we would track down the wreckage with a directional receiver normally used to follow mountain lions or deer. (There were lots of jokes at this phase of the project.)
As the gliders began to take shape, we continued flight training and began working on a launching system. Many modelers advised that we use a twelve-volt electric winch to launch the glider. I did not think that was practical because of the rough terrain at the launch site. We ended up using a large diameter bungee purchased from Hollyday Designs. This rubber is an intimidating energy storage device, delivering over six thousand foot pounds of energy at three hundred percent stretch. This launcher pulled my full-size Toyota pickup over one hundred feet from a standstill in neutral. Community volunteer and long-time friend Gene Rasmuson came up with a launching ramp made from two twenty-foot lengths of aluminum irrigation pipe. The tubes are supported by a steel framework that is anchored at the front. The wings and stabilizer of the glider sit on the tubes. The glider slides along these tubes and hopefully climbs skyward as the bungee is released.
I began to have nagging fears that the plane would end up overweight and that the launcher might not have enough energy to get the large glider up to flying speed. Jim Sack offered to modify a large one-quarter scale Xtra 300 stunt plane and try launching it with the bungee. The engine was removed and replaced with a bulbous foam nose and lead weight. The model weighed in at twenty-five pounds. We now had a test plane to try with the launching system. The launch tests confirmed that the bungee had enough energy, pulling the big test model to over one hundred feet in altitude.
In early spring of 2001, weekend flying entered a new phase. It was time to practice transferring control of a model from one radio transmitter to another. This was also a chance to practice hand held-radio technique and do ultimate range checks with the radio control systems that we planned to install in the large glider. We were fortunate to have Don and Susan Kunze loan us reliable, hand-held radios for the duration of the project. Practicing this phase requires at least two teams of flyers, communicators and observers. The launch team was stationed on a hill overlooking the Owens Valley and the landing team was in the valley below. Following launch, the model was flown out toward the landing team until the limit of visual range was reached. At that time, the landing team acquired the plane visually and control was transferred. We had some successful attempts and others that didn’t go as well. During this time, the RPG team gained valuable experience and insight into flying and visually tracking models at a great distance, and using hand-held radios and binoculars. These flights helped build the team cohesiveness and gave some insight into the challenge ahead. What were we ever thinking?
To begin with, the White Mountains are huge. On every scouting trip to select a site for the flight, I was always amazed at how small our “big glider” seemed against this backdrop of lofty peaks and yawning canyons. And the wind, well, there are times when the wind isn’t blowing across the top of the ridges, but those times are fleeting. Wind could definitely influence the launch and flight of the glider. Or put another way, as the wind speed increases, the chances of a successful flight diminish.
On the other hand, the vistas from the crest of the White Mountains are truly magnificent. Home to the ancient bristle cone pine tree, the mountains are a near wilderness, with access by only a few dirt roads. To the west, the mountains plunge steeply toward the Owens Valley over a vertical mile below. Farther west, the valley floor ends abruptly at the foot of the Sierra Nevada front range, a wall of tilted and fractured mountains. The White Mountains and the Sierras are siblings, formed from gargantuan tectonic forces that stretch the Earth’s crust in this region. The stretching causes the crust to fracture into parallel faults that generally trend North-South. This pattern forms the famous Basin and Range geological province in Eastern California, Nevada and Utah. The Owens Valley floor is a huge down-dropped block of granite, slowly subsiding as the bordering mountain ranges rise. Eons of faulting, earthquakes, volcanic eruptions, and erosion have sculpted a rugged landscape that has no rival in the Western states. We planned to cast our glider off a saddle in the mountains toward the beckoning valley below.
The Owens Valley has long been known for its spectacular flying conditions. The dry climate in the valley results in generally clear visibility and good weather for flying. Big mountains and deep valleys spawn big winds. More than one pilot has been battered and terrified by the turbulent winds that patrol among the peaks. Many sailplane and hang gliding records have been set using the thermal lift generated by the mountains and valley. At greater heights, the mountains form what is known as a lee wave, a series of atmospheric ripples that form down wind off the crest of the Sierras. This Sierra Wave was explored using sailplanes in the 1950s. As winds from the west sweep over the crest of the range, the Sierra Wave forms and only the most experienced aviators venture into the sky.
By May of 2001, it became apparent that we were about a month behind schedule. The original plan for the challenge flight in mid-May was scrapped and we re-focused on the weekend of June 16 and 17 for our ultimate flight. As May wound down, we hurried to get the glider completed so that we could test fly it. The idea of building two giant gliders simultaneously was ludicrous, we barely had time to complete one! Having only one plane raised the anxiety factor a few more clicks. Community volunteers Jim Sack and Bob Woodson helped out on weekends, putting the finishing touches on RPG-14, and finally, on Memorial Day weekend, we were ready for the initial test flight.
Appreciate that firing a twenty-four-pound untested design with a giant bungee off a ramp made from sprinkler pipe still has a few inherent unknowns built in. During much of the school year, I would lie awake at night and ponder the various possible outcomes of every phase of this project. Show time was fast approaching. At least we completed the glider.
Sunday morning at the eastern cow pasture, we gathered for the maiden flight. Setting up the launcher and rigging the bungee for the appropriate stretch took some time. We worked methodically and somewhat nervously. I insisted on making this first flight since I was the most experienced glider pilot. A crowd of parents and spectators gathered. We photographed the plane with the students just in case this was the “only” flight. After a couple of hours of preparation and much chin rubbing, it was time to do it. The wind was not quite right - it never is - but oh well, “cut it loose.” The scissors cut a retaining line, releasing the bungee to do its work. The glider swished off the launching tubes, dipped its tail slightly, and started climbing straight away on tow! At about 150 feet altitude, the bungee was spent and fell away. Without enough altitude to maneuver, I executed a couple of cautious turns and lined up for landing. By this time, the plane was clear at the other end of the pasture. A rough landing bent a couple of wing bolts. “Strong wing,” we thought as we put the glider away. If we only knew then how severely the wing would be tested. We called it a day. Test one down.
The following weekend, we reconvened at the cow pasture for test flight two. The first flight was so brief I didn’t really learn much. We hoped to fly the plane several times today and give the student pilots a chance to fly. Launch set up went faster and we soon catapulted the glider off the ramp on its second test flight. Horrors! The tow bridle would not release and the glider remained attached to the towing bungee. I circled the glider for a hasty landing that cracked off the horizontal stabilizer platform. We were grounded for the rest of the day. “No practice flights for the students, hmmm,” I thought. We still had one more weekend.
The weekend of the final test flight off a two-thousand-foot hill east of the cow pasture was soon upon us. This was the final “dress rehearsal” for the RPG team. We had most of the people we needed and all four flight control teams were represented. The students were finally getting a chance to fly their creation after all those months of building. While the launch team prepared the ramp and bungee, the other flight control teams took up their stations down range. The landing team waited in the pasture below.
We flew the trainer glider off first for a warm-up flight. The downrange teams took control but were unable to glide out toward the pasture to effect a safe landing. The glider landed on the alluvial fan some distance from the cow pasture. “We have to do better than that everybody,” I admonished. The full-scale glider landing on the rough terrain of the alluvial fan would sustain damage. There comes a time when you just go with your original plan. Full speed ahead.
A few minutes later, the full-scale RPG-14 was on the launch, tubes poised for flight, a brisk wind blowing over the nose, and conditions excellent. We made a quick radio check with the other teams to announce the imminent launch. “OK, I’m ready,” said student pilot Jimmy Nelligan. “Snip” and the glider launched. The wind sang on the line as the model climbed out straight and true. At the apex of launch arc, the strong lift coming up the mountain built up so much tension in the bungee that it would not release from the plane. The plane slowed for an instant as it passed over the anchor point and then nosed over in a sickening dive. We could hear the wind scream on the taught line as the glider disappeared over the crest of the hill in an accelerated terminal dive, still attached to the heavy bungee. I never dreamed of this crash scenario in all my sleepless nights. An instant after the crash, I remember having this brief wave of relief, “Well, I guess we won’t have to worry about making the big flight next weekend.” I went to look down the hill at the crash scene. Silent helpers scrambled down the steep, rocky slope to retrieve what remained of the glider. The glider had hit the steep slope of the hillside with the bungee still under tension. The initial impact shed the wing with its mounting plate and shattered the front third of the fuselage. The nose ballast and radio electronics were hurled further down the slope.
The crash wasn’t quite over yet. Free of its wing and internal workings, the shattered fuselage was unceremoniously jerked up the hill by the bungee, shearing off the tail and its mounting. I quipped cynically that we would auction off the parts when we got up to the trucks. The down range teams checked in by radio to inform us that they not only saw the crash, but heard it. The thump of the impact carried over one half mile. Discouraging.
As often happens with model builders, once the initial shock of a bad crash was over, we came back to assess the wreckage. It was sort of model triage. What happened and how bad was the damage? The problem was traced back to the towing bridle and the double tow hook. Under strong tension, the box-like fuselage shape would not let the bridle release from the tow hooks. The glider had told us this on the second test flight, but we did not appreciate the message. Close inspection revealed that, while battered, the glider was quite repairable, but it would take a few days. Two hours after the crash, we were hard at work putting the glider/patient back together. After three long days of repair, the glider was again ready for adventure. This was a critical step in our quest to attempt the final challenge flight.
The unanticipated crash and repair left little time to organize for the upcoming challenge flight. High winds in the Owens Valley early in the week had me watching the weather closely. The outlook was for high pressure and calm conditions over the weekend. The challenge flight team was a combination of students, staff, parents, and community volunteers. On Saturday morning, June 16, we loaded into four wheel drive vehicles and headed for the Moulas Mine Road. This road is steep and precipitous. It took most of the morning to scout out the control stations and set up a camp at the eight thousand foot level in a pinon grove.
We reached the launch site after a twenty-minute drive further up the road. A brisk wind was blowing straight up from the valley. The students were soon flying an expanded polypropylene slope-soaring glider in the big slope lift. The rest of the team got busy measuring out several possible launch sites, so we could choose quickly depending on the wind direction next morning. After a couple of hours, we returned in the afternoon to our high mountain camp site.
Back in camp, we had a final team meeting to discuss the upcoming flight. The student pilots each inspected their radios and performed a control check on the glider. We reviewed radio communication protocols and practiced transferring control from one radio to another. We were as ready as we were going to be. It was time to relax and enjoy the camp scene. That evening, we enjoyed hamburgers and watched the mountains light up as the sun set on another day.
Rising at around 6:00 AM, we quickly got ready to travel to our assigned stations. We decided to take one last photo of the student team holding the glider. Following that, each team set out for the control station locations. The launch team headed for the launch site just as the sun crested the ridges above. At the launch site, a light cross wind was blowing. The launch direction was chosen and the ramp was aligned and anchored. The bungee was made ready to stretch. All down range stations were in position and radio communication was perfect due to a repeater station boosting our radio signals. We conducted one final control check with each station below range checking their radio. I was gratified to find that even the landing team had control potential at a range of over four miles.
The challenge flight differed from the other test flights in a couple of ways. First, it was much longer and higher than we had ever flown before. We had replaced the two-hook launch system with a proven single-hook system on the belly of the plane. There had not been any chance to test this new hook system. On this flight, the RPG-14 would carry a small Sony digital video camera. Shooting out over the nose, this camera held promise of spectacular video as the glider flew out of the mountains. My friend and colleague Joe Profita and I had discussed the camera installation and were worried that we might inadvertently change settings while we were securing the camera in the plane. We did not have time to develop a solution, other than to be careful, while we were installing and turning on the camera.
As it happened, the camera settings did get changed as I placed padding around the camera and secured the hatch. Unknown to us at the time, the camera was now focused on the nose of the glider, while the magnificent mountain vistas were fuzzy and out of focus. I came to call it my Hubble Telescope mistake.
Once the camera was running, we were anxious to get the glider in the air. The bungee was already cocked and waiting to launch the glider onto the early morning wind. Student pilot Jimmy Nelligan and I decided that I would launch the glider, quickly check the trim, and then pass the transmitter to Jimmy to fly the glider out to station two. I cycled the controls one last time and told Jimmy to give a ten-second countdown. The pre-flight challenge was over. The flight challenge began. “10-9-8-7-6…….”
The big model launched easily and without incident. I felt a wave of relief and actually enjoyed flying the model for a few quick turns. A few clicks of forward trim and the plane was flying smoothly. After one minute of flight around the launch area, the glider was still above us. It was time to fly the glider out to the next control station. Pilot Jimmy Nelligan took over.
With many pairs of eyes watching, Jimmy expertly guided the model through a series of gentle S-turns and drifted out toward station two. The plane got small very quickly, but Jimmy was able to track it visually by turning the plane occasionally so that it flashed the white topside of the aircraft. Stations downrange were reporting that they also had the model in sight.
It was soon time to transfer control to station two. Each transfer was worrisome, because it is always possible that the transfer will leave the model out of control, with only a limited amount of time to figure out the problem. The transfer went smoothly and student pilot Eliot Gann guided the plane further out of the mountains toward station three, two thousand feet below and a mile and a half downrange.
Station three was critical. This team, from a position overlooking the broad alluvial fan at the mouth of Paiute canyon, several thousand feet above the landing field, had to maneuver the plane over a mile across unforgiving terrain into position for the landing team to take over. Although we worried that the plane might end up low and in close proximity to the rocks of the mountains, this in fact never happened. The glider seemed quite efficient and stable, passing high above each tracking station. Student pilots Katie Mulder and Patrick Koske McBride skillfully guided the plane out of the mountains and over the valley to team four whose job it was to bring the plane down and effect a landing in the cow pasture.
Once in control, ace student instructor pilot Jonathan Kunze concentrated on flying smoothly while straining to see the tiny speck that was the glider. More relaxed and in control, Jonathan let go with an exuberant (and unauthorized) loop. Deploying the spoilers, Jonathon continued to smoothly guide the model in its descent for approach and landing. It looked as though we might really pull this off.
Up at the launch site, we strained through binoculars to follow the flight as it moved out over the valley. “Do you see it? No, oh, there is, north of the three trees! OK, I got it!” Over the radio, we heard, “Station four has the glider overhead at two hundred feet, setting up for landing.” I watched breathlessly through binoculars as the glider turned over the pasture for landing. Suddenly, the plane’s shadow appeared on the pasture. The plane and shadow met as the plane slid smoothly to a landing. The Challenge Flight was in the bag.
After many handshakes, hugs and backslapping, we headed back down the mountain to break camp and head for the valley. We were soon bouncing down the mine road, savoring our accomplishment. We arrived at station four to an appreciative crowd of project supporters and team members. The glider looked beautiful, intact on the green grass of the pasture. I felt a sense of pride and satisfaction at completing the final challenge flight.
It seemed we all experienced in some small way, what it is like to be on a NASA science team - a successful NASA science team.
