September 2000 QST

elative power levels of the control signaland ATV transmitter are calibrated to allowthe ATV link to fail before the radio controllink goes down. The rule of thumb is, if thepicture starts getting fuzzy, it’s time to headback!With a smaller and fully symmetricshoulder wing, the Ugly Stick is fullyaerobatic. The video from doing loops, rollsand spins is truly spectacular! It’s likeactually being in the plane, except you getto keep your lunch. The extra weight anddrag from the ATV package, however, leadsto longer takeoff rolls and screaming-hotlandings. The camera package represents alarger fractional increase in weight forthis airplane and maintaining sufficientairspeed is critical with the high wingloading. But even though it glidessomewhat like a streamlined brick, ithandles pretty well once you get used tothe “heaviness” of the stick.The TH-60 has enough wing area (875square inches) and power to easily carry theATV package without strain. This airframealso provides superior wind penetration andcrosswind landing characteristics ascompared to the motor glider. Increasingthe wing incidence one degree over stockand outfitting the airplane with fullyfunctional flaps dramatically improvedflight characteristics at minimumcontrollable airspeed and helped to slow thelandings to more normal speeds. I’verecently installed a second-generation ATVtransmitter inside the TH-60 fuselage.Although the weight is still about the same,getting rid of the extra drag of the exteriorATV package yielded significant handlingimprovements. The forward-lookingcamera is mounted in a small box attachedto the windshield and the down-lookingcamera looks through a hole in the bottomof the fuselage. As before, the look anglecan be selected in flight. Microscope slidesserve as windscreens to keep bugs and fuelspray off the camera optics. A future projectwill explore the use of a two-axis gyro tohelp stabilize flight in gusty winds.Rocket PlatformsWhile the students at K-SAT build theirthree-foot-tall rockets, the adult kids buildtheirs. The big kids’ “heavy lifters” stand11 feet tall and carry an ATV transmitterwith video overlays that display GPSposition, speed, heading and altitude.Constructed under the expert guidance ofBill Wagner, these rockets require FAAcoordination and need lots of empty landaround them to fly. After months of raindelays, we finally got a chance to fly one ofthe big rockets in May 1999 at a 22,000-acre cattle ranch in southern Texasbelonging to Rik Hoffman, K5SBU. Therocket carried a side-looking color camera42 September 2000Figure 2—Big Yeller takes to the skieswith GPS and ATV payloads.The Hondo airport as seen from the TH-60.Figure 3—Looking down the rocketfuselage at Hondo airport.and a 1.5-W ATV transmitter. After the prefiledclearance was obtained from Houstoncenter via cell phone, we started a quickcountdown and hit the switch. The rocketleaped into the air atop a mountain of fireand roared away with Doppler-shiftedthunder, ever decreasing in pitch as therocket accelerated to 401 MPH. During itsseven-second burn, the rocket consumed$360 of solid fuel at a rate of slightly morethan $50 per second. The rocket thencoasted straight up for another 23 seconds,reaching an altitude of 7000 feet.The ATV system worked flawlessly,providing spectacular video for the entireflight. The view was particularly impressiveas the rocket approached, penetrated andascended above a thin cloud deck at 3500feet. As the rocket passed apogee and beganto descend, the computerized altimeterssensed the increase in barometric pressureand deployed the parachutes. Five minuteslater the rocket landed in a mesquite treejust over a mile from the launch pad. Aftertouchdown, the ATV signal was still comingthrough, showing an excellent view of thethick underbrush and reporting its landingcoordinates on the GPS data overlay. Wepunched the coordinates into a hand-heldGPS unit and went right to the landing site.A photograph of the launch is shown inFigure 2.A second rocket with its own ATVpayoad was constructed, this time with adown-looking black-and-white camera.Both rockets were launched on December4, 1999. You can see a view from one ofthe rockets in Figure 3.Cameras and OpticsSmall CCD cameras are still evolving.Our first ATV transmitter used a single boardblack-and-white camera with a pinhole lensand required 9-V dc at 100 mA. Our firstcolor camera ran on 10.5 V, had three PCboards and required 300 mA. Our presentcamera is a much smaller single-board colormodel that requires 10 V at 100 mA. A seriesstring of 1N4001 rectifier diodes is used todrop the 12-V ATV transmitter batteryvoltage to about 10 V dc. The cameras wereobtained from Supercircuits (see theEquipment Suppliers sidebar) in Austin,Texas.Cameras are available with pinhole ormultielement lenses. Both give a 70 to 90°field of view, with the wider view preferredfor airborne operations. The multielementlenses have less barrel distortion than thepinhole versions, but are physically larger.The apparent curvature of the earth evidentin some of the aerial views isn’t real—it’scaused by the barrel distortion of thecamera lens.The picture quality obtainable fromoutdoor operations can be improved byadding filters in front of the camera lens.Most CCD cameras are set up for low-lightperformance and suffer from overexposurein bright sunshine. The symptoms caninclude blank-out or streaking if the suncomes into the field of view, sluggish AGCresponse and excessive contrast, causingloss of ground detail below a bright sky.This can be fixed by adding a neutraldensityfilter to the front of the lens. Values