Bob Curtin is the Vice President of AeroVironment, Inc. and Director of its Aircraft Design and Development Center, which he joined in 1980 at age 15. He worked part time through high school and college and began full time work in 1988.

In 1996, he received the Aviation Week Laurel Award, and was inducted into the Aviation Week Hall of Fame in 1997. His solar aircraft teams also won the NASA Group Superior Achievement Award in 1999, and his Micro-UAV teams won awards from the Defense Advanced Research Projects Agency (DARPA) and the Association for Unmanned Vehicle Systems International, also in 1999. He holds multiple patents for aircraft in his area of expertise, as well as a B.S. and M.S. in Physics from California State University Northridge.

Bob and his wife, Bonnie, live in California with a Yorkshire Terrier named "Hamlet" and two cats. In his free time, Bob enjoys working on automobiles, mountain biking, building & flying model airplanes, and fiddling with his personal computer.

5.15.01 Bill Pawley asked:
Watching your solar powered wing, it appeared that take-offs and landings can create some of the greatest windows of stress and difficulty. Did you consider launching in mid-air at high altitude (as an example: disconnecting from a series of attached weather ballons)to reduce launch stress and/or difficulties? Did you consider using a lighter-than-air-gas to fill in void spaces. I know it took countless hours of sweat, tears and dollars to get where you are; but you made it look like fun.

Curtin's response:
Hello Bill,

You are correct that if we compare stresses in the structure when the aircraft is flying (supported by aerodynamic lift) to when it is resting stationary on the ground (supported by its landing gear), they are very different. Of course the landing gear structure is designed for landing loads. Even though the loads in the wing are significant while the aircraft sits on the ground, it turns out that loads induced when the aircraft flies through turbulence drive the design of most of the wing structure.

Take-off and landing are always the most difficult portions of an aircraft's flight. Of course we hope to limit our exposure to these events by designing an aircraft that stays aloft for up to six months. By landing infrequently, we will be able to carefully select our take-off/landing time and location to avoid bad weather. We have looked at launching small airplanes from weather balloons. However, it would be difficult to gently lift something as large as a 250-foot span solar powered airplane with weather balloons. Also, the transition from balloon to aerodynamic lift would be tricky to manage.

Air at sea level weighs about 0.1 pounds per cubic foot. At the cruising altitude of Helios, about 60,000 feet, air weighs about 0.01 pounds per cubic foot. The volume of the Helios wing is about 1000 cubic feet. Evacuating all the air from the wing, would provide about 100 pounds of lift at sea level and 10 pounds of lift at 60K feet. Of course it would be very difficult to evacuate the wing. If, as you suggest, we replaced the internal air with helium, we would get 90 pounds of lift at sea level and 9 pounds of lift at 60K feet. A sample of air is about 10 times heavier than Helium if both samples are the same volume and at the same temperature & pressure. Unfortunately the weight of the seals and systems required to contain and manage the Helium would weigh many times the 9 pounds of lift achievable at 60K feet.

Bob.

5.15.01 Chad Fritz asked:
During the 'Eternal Wing' portion of 'Flying Free', there was a brief mention of utilizing fuel cells as a secondary power source. When do you think they'll have a fuel cell system suitable for your application? What component of the fuel cell poses the largest hurdle? I thoroughly enjoyed the program and would like to salute you on your many accomplishments.

Chad Fritz (real-life Okie from Muskogee)

Curtin's response:
Hi Chad,

We are developing a energy storage system (ESS) that will be charged with excess solar power available during the day and discharged during the night to provide power to keep the aircraft aloft. Under our NASA program, we are currently scheduled to perform multi-day flights in the summer of 2003. The ESS is often described as a fuel cell system or even as a "fuel cell". However, this name is misleading because the fuel cell is only one of many subcomponents that make the ESS possible. It will not be possible to attribute the ultimate success of the ESS to any one subcomponent; there are several challenging subcomponents and good engineering of the overall system is extremely important. The good news is that no new basic physics or chemistry needs to be discovered or developed. Fuel cells have been in use for decades. The largest hurdle is properly balancing development efforts between the subcomponents such that the resulting ESS is optimized for the solar aircraft.

Bob.

5.15.01 Dave Johnson asked:
I am an engineer and private pilot. My question is about the Helios aircraft: What certificate does the operator/remote pilot have and how do you stay in contact with ATC? Does it have a 'fail-safe' mode should it lose ground control? Other high flying aircraft such as the U-2 reach a point where the stall speed approaches max speed. Does Helios approach this condition?

Thanks,
Dave

Curtin's response:
Hello Dave,
There are currently no laws that define a specific certificate a remote pilot must have. However, it does seem that eventually remote pilots may be required to have a certificate similar to the certificate a pilot needs to fly on instruments alone. Usually the remote pilot of Helios talks to air traffic control through a normal phone line. However, if the remote pilot is within radio range of air traffic control, then he uses the standard air traffic frequency used by other commercial or military traffic. Helios flies so slow that it doesn't approach a point where stall speed is the same as maximum speed. I think the U2 has this problem because stall speed starts to approach the Mach limit of the airframe. Even as high as 100K' the stall speed of Helios will be about 200mph, which is well below the speed-of-sound.

Bob.

5.15.01 Keith Tacia asked:
I was particularly interested in the flying wing part of Scientific American. If these planes are supposed to fly for six months, what happens if one or two of the engines go out? Does the plane start to lose altitude, do you have time to send up a replacement wing to bring the damaged one down? Also, wouldn't adding communication equipment for phones and television add too much weight to the craft?

Curtin's response:
Hi Keith,
The electric motors that spin the propellers are mechanically very simple. From a mechanical perspective, they are similar to a conventional ceiling fan. Simplicity helps us make very reliable motors. There are enough motors on Helios that normal flight can be continued even if one or several motors fail. The remaining operating motors will simply work a little harder to make-up for failed motors. After a motor or two motors fails, another aircraft will be sent to replace the one needing service.

Helios is designed to carry a 100Kg communications payload. The payload will require careful design to package a large communications capability within the 100Kg weight budget. The payload will be similar to others currently launched on satellites. However, Helios flies one-thousand times closer to earth than a geo-stationary satellite. This means that it will take one-million times less power to send radio signals to and from Helios (the power received by a radio-frequency receiver is inversely proportional to the square of the distance to the transmitter). The reduced power requirement will enable Helios to carry small, light-weight radio transmitters.

Bob.

5.15.01 Robert Sterchak asked:
I really enjoyed the "Flying Free" episode of Scientific American Frontiers. One thing that I was wondering about was the material that you use, not only to create the large flying wings, but also for the Small "flapping" and "gliding" planes. I appreciate any information you could provide. Thank you.
Robert Sterchak

Curtin's response:
Hi Robert,

The type of materials used depends very much on the airplane design. Small flapping aircraft that flap fast are usually covered with a Mylar type film that is about one-thousandth (0.001") of an inch thick. Very lightweight gliding aircraft can be covered with much thinner materials that are a fraction of one-thousandth of an inch thick. Main structural members are often made from balsa wood, Styrofoam, graphite, and/or fiberglass. I recommend that you visit your local hobby shop to get information and materials required to build small aircraft. Picking the ideal material for each piece of an aircraft's structure is important because the power required to fly goes up proportionally to weight to the three-halves power.

The key items that influence the design of an airplane are its mission, the payload weight it needs to carry, and the type of propulsion system selected. Typically these influencing factors are expressed as a list of requirements in the preliminary design stage of the design of a new aircraft. Preliminary design is probably the most important phase of the design process.

Bob.

5.15.01 Teresa Lynch asked:
Thoroughly enjoyed Scientific American tonight and its feature on your escapades. My husband is a sculptor and has been building ash-wood armatures that are oftentimes suspended. One of his sculptures is an imaginary plane and is hanging at the Portland, Maine Jetport. His latest series requires covering the ash armatures (sculptural shapes) with a transluscent/transparent gossamer-like material that can be made to be snug and conform to a variety of shapes. The material on your gossamer condor looks exactly like what he might want. Can you tell us what type of material it is and what manufacturer/outlet might have it available Thank you very much.
And keep flying,
Teresa Lynch

Curtin's response:
Hi Teresa,
I actually can't tell you specifically the types of plastic film we use, because we consider the information proprietary. Also, we have used many different covering materials over the years. I don't recommend that you use the same covering that was used on the Gossamer Condor, because its strength degrades rapidly when exposed to sunlight. Degradation in ultra-violet light is probably a factor you want to consider for a sculpture that will be on permanent display. I recommend that you inquire at your local hobby shop to get samples of plastic films available from several manufacturers.

Bob.