Sailplane with ATV

Here's some details on how the ATV installation went in the sailplane. Sorry, no pictures of the installed setup, because it was cannibalized before I got the digital camera.

The antenna was a "bent dipole" made from copper foil tape on the vertical stabilizer and the fuselage. Having a network analyzer at work made figuring out the dimensions pretty easy. I just stuck the tape onto a piece of paper, hung it up, and started adjusting the angle and length until I had a decent match. Then, I copied the design onto the airplane, and repeated for a final trim (negligible trimming was actually required). The feed was just a coax line running up the fuselage (balun? we don't need no stinkin' balun, who cares if the feedline screws up the pattern) terminated in a male SMA that connected to the TXA5-70's output (which had a female SMA).

The sailplane was an ARF (almost ready to fly) kit with a 2m wingspan. Adding the camera and transmitter to the nose made it a bit heavy, so the sink rate was pretty high and you had to fly it pretty fast (I had a friend fly it, since I am a lame R/C pilot). I did find out a few interesting things. The receiver was fed by a drooped groundplane type 1/4 wave vertical antenna on a mike stand. Multipath was EVIL. The picture would go from sparkling clear and full color (very impressive) to total snow and back in seconds. A most impressive demonstration of Rayleigh fading. The periodic station ID required was handled by the simple expedient of pointing the plane's camera at a piece of paper with W6RMK (my call) printed on it in big letters.

Here's the nose of the plane. The R/C receiver and its batteries installs under the push rods, instead of the nose where it normally would go on this kit). The R/C receiver antenna is fed through a lowpass feed through in the canopy. Copper foil tape provides the ground plane for the feedthrough, and also was used to create a shielded box for the receiver.

Eventually, the radio batteries were moved up front, under the nose.

fuselage thumbnail

(full size image 76 kByte)

Here's a view with the "canopy" removed. The video equipment (the PC board for the camera, and the PC board for the ATV transmitter) goes in the front compartment. You can see the copper foil added to make a sort of "shielded box". Nose of the plane is covered in PVC tape for two reasons: 1) To hold everything on; and 2) to hold the ballast weights in place.

open front fuselage thumbnail

(full size image 67 kByte)

The bent dipole antenna on the tail. RG-174 coax goes forward along the fuselage, and then comes up into the very nose of the plane, where the camera was mounted.

tail 70cm antenna thumbnail

(full size image 67 kByte)

Weight and Balance problems

The real problem with this setup is that it added enough mass to the plane to really increase the sink rate. In order to keep it flying, you had to be going pretty fast, or have a huge updraft wind to hold it up. Bob sith, my R/C flying friend, who was actualy trying to fly the plane, suggested a "power pod", and, if I ever fool with this again, that's probably what I'll do.

/radio/atvplane.htm - 31 Aug 2002 - Jim Lux
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