Solar Challenger Photo Album These photos depict the building of the Solar Challenger Propulsion system, some early flight tests, and the team activities in England and France.

The electric motor armature for the Solar Challenger

Bob Boucher holds the sixteen slot motor armature. The lamination was 2.062 in diameter and 3.92 inches long. The armature was wound with high temperature 200C magnet wire, and the windings were wedged and epoxied in place and then the wound stack was turned on a lathe then balanced. The gray material seen at both ends of the stack is balancing material similar to Bondo. The special armature was supplied by Ken Stone of Specialty Motors in San Fernando CA.

The motor magnetic field-ring with samarium cobalt magnets

Bob used a two pole design because of the higher 75 volts of the solar panel would have been too high for a four pole design. The Samarium-Cobalt magnets had a zero air gap flux of 9000 gauss. The motor design resulted in a 4,500 gauss air gap flux and a flux density of 17,000 gauss in the armature laminations. The combination of high flux levels and the straight non-skewed armature stack with an even number of slots resulted in strong cogging. The motor required 9 amps to start, but no load running current dropped to 3 amps as soon as the motor started turning. In the weak morning solar flux the onlookers were always amused when I had to prop the motor to get it running after Ray yelled Contact from the cockpit. The Magnets were supplied by Spectro-Flux of Watsonville CA.

A Nicad Battery was used for the early flight tests

To simulate the 75 Volt solar array Bob built four of these battery packs made up of thirty 4500 Mahr NiCad D cells. The packs were wired in series parallel to deliver 75 Volts at 9,000 Mahr. After the Solar panels were installed these NiCad batteries were no longer needed and were removed from the Solar Challenger.

Initial Motor Installation

The motor with belt and chain drive to propeller shaft is seen above. Later for better cooling the motor was mounted out into the slipstream. A Don Monroe Photo

Final Version of Solar Challenger Cobalt Motor

The final version of the Challenger Cobalt Motor is shown undergoing bench testing at Astro Flight. External bolts allow the magnetic field ring to be rotated to maximize the motor performance at the specified voltage and running current of 45 amps at 56 volts or 2500 watts. The special carbon brushes, supplied by Kirkwood Carbon of Cleveland Ohio, worked flawlessly and showed very little wear even after 25 hours of flight testing.

Bob Boucher shown holding the Challenger Cobalt Motor with the Timing Belt Speed Reducer attached.

A 1/5 pitch timing belt and specially fabricated timing pulleys provided a 4 ½ :1 speed reduction that was followed by bicycle chain and sprocket reduction to provide a total of 22:1 reduction so that the propeller would spin at 318 rpm while the motor spun at 7,000 rpm. A Randa Bishop Photo

Twin Motors were used on Cross Channel Flight

Two motors in tandem were used on the Cross Channel Flights as extra insurance. Only one motor was used in all domestic flights. The spacer between the motor has two rows of cooling slots to allow the twin centrifugal fans to exhaust the heated cooling air. Each motor was rated at 2500 watts, but at altitudes above 10,000 feet we could expect over 4000 watts from the solar panels so we installed a second motor as insurance. The Challenger required only 1500 watts of power to maintain level flight at sea level, so with over 4000 watts available, altitudes of over 30,000 feet altitude would have been possible had the pilot been provided oxygen.

Bob Boucher and Ray Morgan attach solar panels to wing while Jim Watkinson in the background works on the horizontal stabilizer.

The team at Astro were loaned over 18,000 HS-318 solar cells from NASA. These were rejects from a Hughes satellite program and had average efficiency of 12% instead of the spec value of 15%. They first sorted all these cells by power output, then wired those of like power into strings, 144 long and three wide or three gross to the string. The strings were then taken to Simi and attached to the wing and tail with adhesive transfer tape. Sorting all the solar cells and building the strings took Bob Boucher, Margret Jewett and her two gals three months. A Don Monroe photo.

The Solar Challenger Crew at Shafter California

Dr. Paul MacCready, Pilot Janice Brown, Ray Morgan and Bob Boucher smiling after a successful test flight at Shafter California. Notice that we first had the motor installed within the fuselage but that provided insufficient cooling, so the motor was subsequently moved outside the fuselage and into the slip stream. A Randa Bishop Photo

Dr. Peter Lissaman runs alongside the Challenger

Pilot Janice Brown lands the Solar Challenger after a battery powered test flight at Shafter. Aerodynamicist Dr. Peter, the Lissaman designer of the flat topped airfoil used on the Challenger is shown running in foreground. A Don Monroe Photo

Janice makes a forced landing near Picacho Peak, Arizona

Janice Brown attempted a cross country flight from Tucson to Phoenix but the farthest she got was Picacho Peak. A Don Monroe Photo

She landed in desert

She landed in dale

She frightened coyote

She flattened out snail

Bob tries to fly the Challenger at Tucson

I was way too heavy at 165 plus pounds, the Challenger stayed glued to the ground even after using 3000 feet of runway at Marana Airpark near Tucson Arizona in the winter of 1980. The sun was too low and the motor too slow. A Randa Bishop Photo

Cadets get glider training at Manston RAF Base, Kent England

A Slingsby glider takes off on winch launch at Manston RAF base. The flight pattern is a winch launch to about 800 feet altitude, then a right turn over the channel shore and then another right turn and back to landing pattern. Typical flight duration is only a few minutes.

Steve and Bob ready for a glider flight

The Lads at Manston entertained the pilots of our Solar Challenger crew with a short glider flights in their Slingsby two place gliders. Challenger pilot Steve Ptacek is on the left and Bob Boucher on the right. We waited two months in vain at the Manston RAF Base, in Kent England for just one day of sunshine. Finally the weather changed and the wind shifted from out of the southeast so off the France we went.

Take off from Pointoise France July 7, 1981

The caps of two gendarmes seen at bottom of photo observe Steve take off that early morning on his historic flight from Pointoise Aerodrome France across the English Channel flight to Manston RAF Base, Kent England. A Randa Bishop Photo

Pilot Steve Ptacek in the cockpit of Challenger

Soaring above La Belle France

Solar Challenger over “La Manche Diabolique”

Steve Ptacek pilots the Solar Challenger over the Channel on July 7, 1981 on his historic world’s first international solar powered flight. Steve and the Challenger took off from Pontoise Airport northwest of Paris and are just leaving France and flying over the English Channel.

At last Jolly old England comes into view

Only a few minutes longer and Steve and Solar Challenger will land at Manston RAF Base, Kent where fame and fortune await.