AUTONOMOUS HIGH ALTITUDE RECORD AA241X students – Stanford Aero & Astro Advisors: Profs. Juan J. Alonso and Ilan M. Kroo

AA241X – Design, Construction, and Testing of Autonomous Aircraft  Stanford Aero & Astro course taught by Profs. Alonso and Kroo since 2002  In one quarter (about 10 weeks): design, build, flight test and autonomous airplane to fulfill a specified mission, provided:  On-board computer with 4 Hz GPS, microprocessor, pressure altitude (1 oz of weight)  Motor, battery, propeller combination  Note that, while the board is capable of having gyros and accelerometers, these are not allowed so that the students have to design a stable airplane

AA241X – Spring 2009 Edition  Design an electric airplane (< 5 Kg of mass) that autonomously, from launch to landing, is able to set a world altitude record  Target: approximately 15,000 ft AGL  Initial flight tests at Lake Lagunita (Stanford Campus) by climbing to 500ft, descending, and repeating until out of battery (FAA restricts to < 500 ft)  All 4 teams demonstrated between 12,000-15,000 ft of cumulative climb AGL  Flight tests at DFRC, September with no ceiling limit. Achieved 8,200 ft because of limitations on the area allowed for flights.

The entire AA241X class at Lake Lagunita – June 09

Changes for DFRC: New Sensors and Radios  Pressure sensors for altitude measurement  Voltage reading to automatically determine end of climb. Planned to use for trim scheduling of elevator and rudder  Xbee’s 2.4Ghz have high baud rate but small range. Migrated to the XSC 900Mhz.  Tested range using a balloon test with the help of Jennifer Schmerling (only tested receive capability)

Issues before DFRC: Autopilot Reliability  Board Resets started happening.  Decided to save critical data to EEPROM: Became robust to board resets  Board Freezes incidents: Lost 4 planes, system became almost unusable (guaranteed crash after ~20 minutes or so)  Major review of the code. Found a memory leak that was fixed. More error checking for GPS packages. No more problems

High Altitude and Long Range  Tested that control law was able to fly back to HOME point from a large distance. Flight tests from Roble Pool then from Sand Hill.  Made sure climb performance and stability were acceptable at high altitude by flight testing at Lake Tahoe.

Configuration modifications during summer (getting ready for DFRC)  Suave’s wing + Cero’s fuselage = CeroSuave  Tested 2600mAh batteries: BluePanther did worse, CeroSuave soared to a total of 4200 m (14,000ft)  Best performance when close to stalling

State Machine  For fly off: Initialize → Climb → Land  Except special cases complicate things:  Loss of GPS Lock  Loss of Communication (required by NASA)  Flight Termination outside of allowable airspace (required by NASA)

Weaknesses  Never tested Yagi antenna properly  Never tested the beacon (important for loss comm) in long range  Drift with the wind when climbing  Inverted servo arm on CeroSuave

Record attempts at NASA DFRC  First day  Beautiful windless day  Limited to 3000 ft by DFRC (range being used by others)  Tested both planes  Noticed communication issues with Yagi  Servo arm on CeroSuave kept breaking

Record attempts at NASA DFRC  2 nd day  Early morning start  Attempted to trim CeroSuave with different controller… Lost the plane 20 seconds after launch  3 Attempts with BluePanther 2161m, limited by Communication range 2175m, limited by Winds aloft 2498m, Violated airspace limits (provided by DFRC) and engaged flight termination mode automatically  Only used ~40% of battery capacity

Record flight at NASA DFRC

Flight Termination Westerly Winds 2.8 m/s climb rate, 30 m/s dive speed

18km/h Westerly Wind

Media Coverage  Story by David Orenstein on Stanford news  blog posts on Wired, AviationWeek, Popular Science  German article on presse.at  Podcast by Geoff Bower (TA) on DIYdrones: their next contest is going to try to beat our record using cumulative climb!

Shuttle Landing Picture taken by students on the same day they set their record

Setting up at DFRC: 5:45 am 9/11

Getting ready: students with Mike Marston, DFRC

During flight 1: checking the info on ground computers

Students getting ready for flight 2: Mike Marston and Starla Carroll, our DFRC hosts, in background

Zouhair Mahboubi launches flight 2

Team picture: Stanford students, profs, DFRC hosts, and the observer (for certifying the altitude record)

With our thanks to NASA and DFRC