Our VTOL quad plane concept show here without double T-Tail:
We think most UAV's will be VTOL in the near future!
Solar Dragon
A concept for a Solar powered milti-role UAV platform, at 4600mm wingspan, Dragon has fairly simple construction (by bearospace standards) including a triangular rear fuselage with solar cells on the top, a crucifix style tail, with the part above the fuselage being swept back to prevent shadow from being cast on the fuselage and horizontal stabilizer cells. The wing is a constant chord for most of the span, and without dihedral except for the turned -up wingtips. the airframe shape resembles solar impulse 2, but has a few changes that we feel would make it more practical for a smaller model. It was started several years ago as a concept, and has continued to evolve in design, even some during the build process, into what it is today. It uses 70 Maxeon c-60 cells which have an effeciency of about 22.5%, higher than the average home commercial cells, which are only about 14%. The Maxeon cells also are good at absorbing sunlight with almost no reflectivity at low angles, and have a solid copper back, which makes them more flexible, and resilient to shock and bending/flexing/vibration, but also heavier than many other cells. Their price point, physical properties, and efficiency make them the right choice of this project at this stage. The Solar cells are divided into 3 arrays, 2 of 23 cells in series, and one of 24 cells in series. Since the Ideal ratio per solar cell in series is 1 per .55Volts, The 23 cell series arrays have an ideal Maximum Power Point (MPP) of 12.65V, very close to a fully charged 3S Lithium Ion battery. So that is why Dragon uses a 3S battery. The first battery that we made for it is a 3S 7P battery made from NCR18650GA Sanyo Japanese cells. Each array is connected to the battery using an electronic 30Amp solid state switch.
Dragon has a Pixhawk 2 Cube black installed running Arduplane with some custom settings, but current stable firmware. We are using Mission Planner for the interface, for setup, calibration, settings, and also for flight planning, and monitoring of the telemetry in-flight.
Solar Dragon has great potential to grow for the future, and be a priceless test-bed for universities and startup companies looking at operating their own hybrid solar-electric aircraft, or atmospheric satellites. The cells are able to produce at least 50% more than the power required to keep aloft, even with losses. The airspeed we are currently using of 12 MPS is relatively slow, but could be slower, and a custom "low reynolds number" airfoil with deep drag bucket is used. Much technology has been borrowed from human powered flight programs, such as the spar design.
A lifting stabilizer is used, which contributes to the overall lift. It may not help the overall Lift to Drag ratio, and may actually hurt it, according to some sources, but should improve the sink rate. It's rare these days to see a lifting Stab. They were mostly used on free-flight aircraft. Flight endurance optimization and distance optimization are very different.. Needless to say, finding the correct CG for an aircraft with a lifting stab can be a bit intimidating, especially with a model the size of Dragon.
So far, Dragon has demonstrated a 1 hr flight which started and ended with a fully charged battery. The solar cells were disengaged using the Solid State Switches and Dragon was producing about 50% more energy than it was using on the second flight.
Why a solar/perpetual plane? What application could it have?
Perpetual aircraft could replace satellites for certain applications. They have advantages, and disadvantages. Of course, propulsion has to be maintained constantly, unlike satelites which need only an occasional boost to maintain orbit. There will be some minor vibration associated with that propulsion, probably more than with reaction wheels on spacecraft. And there is no line of Sight unobstructed by atmosphere for laser based communication with other satelites. Advantages are many. Positon can be maintained over a given area, such as with a geo stationary satellite, except that it can adjusted or changed at will, as well as being much closer than even a VLEO satellite. It is self launching, and self retrieving at any time, and not dependent of an orbital insertion from a vehicle which is geographically constrained in it's launch location. It can also vary it's altitude for purposes of conducting atmospheric research, and measurements. It is very difficult to track by anyone except the operator because it's location is unknown to others. even if It's communication transmissions were to be picked up on a RF scan, it would be possible to periodically change it's location, thereby necessitating a new search every time it was detected, similar to how the X-47B changes it's orbit once it is in space, to help in avoiding detection. Cost is a significant advantage over satelites, as sometimes, a communication relay or observation platform is only needed in an area for a very specific time. This provides the flexibility to do so. This solution is also sustainable, as Launch and retrieval is fully solar/electric, and does not require a rocket launch. The onboard systems will not be in a micro-gravity environment, so are not subject to the lack of gravity, which is critical for some sensors. This allows use of unmodified sensor packages, software, and circuit boards. It is also not necessary to position keep, but rather use this type of aircraft for waypoint missions, for data collection, and reconnaissance. they could even transport sensitive materials or the data that they collected to a distant geographical location which is different from the origin, or collection point, because they are not limited by range restrictions. They could also deliver payloads within restricted areas without detection. For such uses, It would be possible for the flight management system to disable the control system, telemetry, and any other RF communication equipment that is onboard, so that it cannot under any circumstances be used to track the aircraft. It would then turn it back on at a pre-defined place and time, in a safe location, for retrieval of data, or vehicle recovery at the end of a mission. At the high altitudes which it could operate at, it would be very difficult for local GPS jamming or spoofing to occur, especially if the aircraft existence and location were not known.
Possibility of use for a aerial recharging platform: Dragon could store excess solar energy and deliver it to another vehicle such as a "Future Star Hybrid rocket/electric space access research vehicle" (plane), allowing it to reach a higher altitude before firing it's rocket motors. In that case, the Future Star would be air launched from a Gemini V-2, climb to intercept the Dragon, recharge from the dragon, and continue it's ascent as stated previously. If this mid air recharge event happened closer to solar morning than solar evening for Dragon, but within that window, it would not have to affect Dragon's daily power usage beyond Solar evening, probably much less, So Dragon could remain at it's target altitude while performing it's tasks, without any other interruption.