Scott Larwood

Co-designer of the Da Vinci III. PhD candidate at UC Davis (2007)

"You may lose money by building a craft that wins the formidable Sikorsky prize; however, you may end up being responsible for creating one of the most elegant and graceful machines known to humankind.  Thankfully, some people have already paved the way by getting off the ground." - Scott Larwood, 9 March 2007.

Interview by Gilles Lehoux, March 2007, for www.humanpoweredhelicopters.org.

Q: Thank you for taking the time for this interview. First of all, going back to before the HPH project at Cal Poly, what were your experiences with aviation and how did you end up at Cal Poly?

A: I had no close experiences to aviation prior to attending Cal Poly. I grew up next to the San Francisco Airport, but was not really hot for aircraft. I was more interested in bird watching as a child. I was also very interested and excited by the space program, so I wanted to be an astronaut. I thought being an astronaut would be the coolest job imaginable. I applied to the military academies because I thought that would be the best route. However, I did not get accepted due to my eyesight. In parallel I applied to aerospace programs in California. I was accepted to Cal Poly and Davis. I went to Cal Poly to take a different route from my brother who went to Davis. I also found San Luis Obispo to be very beautiful and appealing. By the way, I am currently getting my PhD at Davis!

Q: How did you join the Da Vinci project? Did you join at the beginning of the project or later on in its development? What did you expect it would be like?

A: In 1985 I heard a presentation from Prof. Patterson about the project. There was no one working on the project at the time, the first group of students had all graduated. I am not sure how I came to join the project, but I remember later meeting a group of students at the storage container where the parts were stored. Prof. Patterson wanted us to continue with the old machine, but with placing the pilot below the rotor instead of above. Also we had to investigate using new drive thread for the propellor shafts.

The prior summer I had read a book about the Gossamer aircraft, (Gossamer Odyssey: The Triumph of Human-Powered Flight by Martin Grosser) so my expectations were based on that book. I expected that we would have to learn how to manufacture everything necessary for the machine, which was exciting for a young engineering student. Luckily most of the main structural items had remained from the previous group of students. I expected we would be successful because we had access to advanced materials.

Q: So, you came in after the Da Vinci I and as work was starting on the Da Vinci II. There was work to be done both in designing and building. In which areas of design and which component construction did you particpate? Was the team big with plenty of people to help each other? Who did you get to collaborate with outside of the university (ex. industry, NASA)?

A: No, I came after the first group of Da Vinci I people graduated. We started testing Da Vinci I again with the pilot below the rotor and with the new Spectra 1000 drive thread. We soon realized that we were not going to get off the ground with this machine so Rob Faye and Todd Palm (class one year ahead of me- I was a sophomore) made the big push to build Da Vinci II. Rob worked with Fort Felker at NASA Ames to design Da Vinci II using CAMRAD. We got most of the composite material donations from US Polymeric, I can't remember the name of the gentleman there who helped us out. McDonnell Douglas had recently bought Hughes Helicopter and there was a Cal Poly alumni VP (Dean Borgman?) who got us time in Mesa AZ to build most of the primary components in their composites lab. McDonnell Douglas also donated the use of their C-17 hanger (prior to C-17 production) to conduct flight tests because the Da Vinci II rotor was too big for our gym. I was involved in all areas of construction, from filament winding of the spars to cutting out airfoil ribs. In design however, I deferred to my elders Rob and Todd. I did not have the engineering experience at the time. I would say the core group was pretty small, but would grow when flight tests were imminent. The core group was big enough to get the job done. As engineering students, some of us with even more commitments, I really don't know how we found the time!

Q: Were you there for any of the flight tests in the C17 hangar? Was there plenty of room? Was the aircraft slow and graceful? What was it like?

A: Yes I was there for the flight tests in the C17 hangar. There was plenty of room because C17 production had not started, there was only a DC-10 in for repair at the other end of the hangar. The tip speed had increased from Da Vinci I, but it was not noticeably faster. We realized immediately that the rotor was coning too much and would require some reinforcement. The pilot seat was skidding around but we had no good measurement method to determine how close we were to liftoff. The pedaling motion was very jerky and probably very inefficient. We came back later with a strut system which failed in further tests. So we went back to the drawing board again, to address all the problems with Da Vinci II.

Q: The Da Vinci model I and then model II failed to takeoff. Were there moments when you or the team started to loose hope? Was there a competition to see who's ideas would be incorporated next? Any big disagreements? Did any accidents or mistakes lead to stress?

A: I don't recall ever losing hope. Even when things weren't working, we still had fun. And it was exciting to have media coverage. The public relations department at Cal Poly was very good at promoting our project. As students, we seemed to have unlimited hope and energy, that is why these projects are so perfect for universities. There was no competition for the next phase. It was obvious that the 140 ft DaVinci II was not going to work, and we wanted to design something that would fit in our gym again. Because Rob Faye was graduating, it was my turn for the task. That summer (1988) I had an internship at NASA Ames, and Fort Felker said it was my job to design the new Da Vinci. The result was documented in the paper by myself and Neal Saiki.

Of course it is easy to look back and not recall any stress because there must have been some. I was finishing my undergraduate program, working on a completely separate senior project, and bicycle racing. Luckily I was financially supported by my parents. Other students had similar demands and more. It's a miracle how we all came together to work on this project.

Q: So, in the summer of '88 you designed the Da Vinci III. I assume building started when everyone went back to school in the fall. What was the hardest part of the build? Then the day came when it was all put together for the first time to try out. Did it fly on the first try or were there a series of trials and modifications?

A: At the time I called it the Da Vinci IIB. I kept it "II" because we were going to use the primary structural components over again. I was to graduate at the end of the Fall quarter in December, so I was not heavily involved in the construction of the machine. I did however, do some background work for the new construction. I consulted with Burt Rutan, a Cal Poly alumni, in regards to reducing the weight of our airfoil ribs, leading edges, and trailing edges. Also, I got a hold of the MIT Daedalus folks to find out what they used for wing covering. We always had trouble with what we were using. They (Peggy Scott?) got me the contact from ICI and I quickly got a roll of the same material. After years with the old stuff (Tedlar), the new material (can't remember the name) was absolutely perfect and much lighter weight. It was a breakthrough like the drive string was years earlier.

I then graduated in December 1988. Lee Peron took over project management and building of Da Vinci IIB. I went down to witness some flight tests of this machine that were taking place at Vandenburg AFB. I believe the Cal Poly gym was tied up at this point. After this, Neal Saiki took over the project. At the time I was working at NASA Ames (space shuttle life sciences payloads) and the crew came up to test the drive propellors in the Ames 7x10 foot wind tunnel. I then went down to witness the successful flight of Da Vinci III in December 1989. Neal and his crew definitely made the machine of the highest quality, making creative use of existing materials. For instance, they hung (not rigidly attached) the pilot under a primary spar section, eliminating much of the coning problems. The guy strut system was also very elegant. The team also made an extremely lightweight flywheel to eliminate the jerkiness in the pedaling motion, something we never solved earlier. Let us not forget Kyle Naydo's hand-made propellors, designed specifically for this machine. Previously we had been using Da Vinci I propellors, not taking care to optimize for the higher tip speeds. I'm very glad they used the rotor planform I designed, so I can have some credit in the first flight.

Q: So, you were there on the day of the first flight. Can you describe the events of that day and how people reacted? Were there a lot of people and reporters?

A: I can't remember much of the day. I do not remember how I got down to San Luis Obispo, or where I spent the night! All I remember was the time in the gym. There was a typical assemblage, perhaps a little more than usual because there was an FAI representative present. The first pilot was Chad Frost, a teammate and behind me in aero engineering. He was several pounds heavier and taller than Greg McNeil. I'm pretty sure that Chad lifted the machine off- so he might have been really the first. They quickly put Greg and did the next flight, which lasted until one of the guy struts touched down because of the rotor instability. After the flight there was much rejoicing and champagne. Neal Saiki was already decked out in tuxedo. I remember saying to Warren Baker, the president of the university, "Here's to learn by doing," the motto of Cal Poly. Probably the most jubilant was Prof. Patterson. I felt relieved that the goal had been achieved, even if by inches.

I thought I would mention more about Greg. He was a member of the National Team and he came to talk to the Cal Poly cycling team in 1988. Noticing his stature and that he was located in Ojai I approached him after about piloting the Da Vinci and he said that he was applying for engineering school at Poly. I found out later that he had one of the highest horsepower to body weight ratios in the country. I knew then the project had a perfect pilot.

Q: You had already graduated by the time the first flight occurred. So you went back to work at NASA. I guess there was some mention in the news media. Did this project ever come back to touch your life after that? Were you interviewed? Did people ask you about it? Did you participate in conferences? Was it brought up much in job interviews?

A: Neal and myself completed the paper on the aerodynamic design after the flight. I believe Neal presented this at the conference, I was not present- I might have been on travel for work. There was media coverage of the flight, most importantly in Aviation Week. However, there was not as much flurry of media as in the early years. I guess we kind of burned out media attention early on.

NASA paid for my trip back to Washington to receive the NAA Award with the rest of the group (Neal Saiki, Rob Faye, and Bill Patterson). Other than that I have had no involvement with the project. It never comes up in interviews and no one asks me about it. Kind of funny in a way. It seems that people in the "real world" are most interested in what you are going to do to solve the current pressing problems. One thing I saw was kind of nice, Cal Poly had its centennial and in the brochure was a picture of the Da Vinci. So it is an important part of the school's history.

Q: What are you currently working on and where could one go to find out more?

A: My dissertation is an expansion of the work on wind turbine blades with curvature. I presented a paper about this. There was some interest in this for helicopters, but has not been incorporated into production designs. I will be modifying an existing wind turbine analysis code to account for blade curvature, and hopefully validating with field experiments. Then I will do some design studies to see how the concept scales. The idea is to increase the rotor diameter to increase power capture, and use curvature to aeroelastically tailor the blade to maintain loads at the levels of the smaller-diameter, straight-bladed rotor. I am struggling right now to model the natural modes of vibration for the curved blade. These modes are then incorporated into the overall analysis code.

I am also conducting a study of the wind turbine rotor fragment hazard. I wrote a survey report about this issue for the California Energy Commission. It is a hot topic in the industry because it affects how many turbines can be sited at a particular wind farm. I am currently developing a ballistics model of a rotor fragment coming off a turbine, and a statistical model to determine what the risk of impact is around the turbine. That way we can have some guidance on what turbine setbacks should be to minimize this risk. This is part of work I do for the California Wind Energy Collaborative at UC Davis. It pays my tuition and graduate student stipend. We do a lot of technical work on policy issues impacting wind energy in California, along with conducting short courses on wind energy.

For fun, I am knitting an Aran cardigan sweater for my wife and wool cycling vest for my brother!

Q: What part of the Da Vinci project did you enjoy the most? Do you have any advice for engineering students or professors who are considering starting an HPH project?

A: The best part about the project was working with some great people. When I look back I think of the moments our team had together more than the actual event of the successful flight. It is very satisfying when a group of people come together to accomplish something that has not been done before. Everyone has their quirks, but these traits all seem to work together.

Let's see- advice. A faculty advisor, such as Professor Patterson, maintains the project continuity. So I think an advisor is absolutely necessary for school projects. They don't have to invest too much time, or give too much advice, they just have to know what the challenges are, what has worked in the past, etc.

For people considering working on a project- take a good look at what has been done in the past. The Da Vinci started as an evolution of the Gossamer Albatross - applied to rotors. I would seriously look at improving on the Japanese craft, perhaps also looking at a single three- or four-bladed rotor. The tip drive concept works, but I'm not sure about stabilizing a two-bladed machine. The goal now should be to win the Sikorsky prize. Perhaps the AHS can be lobbied to increase the prize money.

Find the best pilot you can and test them. Don't just pick someone who seems fit. Almost invariably the pilot should be a "svelte" racing cyclist with strong sprinting abilities.

Get the best materials you can. It should not be too much trouble to get donations of overstock and expired goods from companies. It also helps to have a little bit of media exposure so these companies can see some marketing potential. Your school's media department should be eager to help out.

Focus on quality, lightweight construction. I believe this was the key to Neal Saiki's team's success. I was pretty sloppy with epoxy in my youth, but I think I have learned.