Thistle, Sport Electric Free Flight

The Thistle is a great little sport FF model, originally designed by Jim Duckworth for the Kenway KR-1D motor. As I intended to use the more powerful HiLine Mini-4, I scaled the plane up a bit, increasing the span to 18" from 14", and chord to 4" from 3". Other dimensions grew as well, to keep the look about right. Length overall is 16 3/4". Flying weight is 37.3 gms / 1.31 oz. Colored Japanese tissue was used for trim, the entire plane was sealed with a couple light coats of thinned nitrate dope.
Sharp eyes will notice 3 led's mounted on the plane. A red flasher above the motor, and red and green non flashers on the wing tips. It is a fun touch, and helps let me know when the batteries are running down.
The 2x50 ma battery is visible in the nose, and is charged by a handheld cluster of 4 1700 ma cells with a resistor to keep the current and voltage in check. Still air flights of about a minute are had from a 80 second charge. The batteries could take up to a 3 minute charge, but I would then be outclimbing the 75' hangar in which it is flown. Outdoor flights have been successful as well, though the first flight beyond trims ended up in a tree! So far, I have not charged it for more than 1 minute outside, due to restricted space.
Since I wrote the above, I have been charging the Thistle for up to the full 3 minutes, and enjoying several outdoor sessions with the model. Typical flights with a full charge are in the 2 - 2:30 range. Certainly not world beaters, but still enough fun to be worthwhile, with little fear of a fly away.
That all changed on Sunday, October 12, the last outdoor session of the Marin Aero Club 1997 season. After a bunch of trimming, due to recent repairs, I charged for about 40 seconds, expecting 20 seconds of power for a final test flight. Wait for the breeze to lull, launch, and hey, it is finally doing well. It climbs to about 20 feet, the power comes off, and as I walk along under it, it starts going up. Clears the very tall eucalyptus trees by the edge of the field, and keeps going. After a bit, I start my stopwatch, fellow flier Jerry Long gets my binocs, and I follow it for another 6 minutes before it seems to have descended below a ridge and trees about 3/4 mile to the south. As near as I could determine, the total flight was something like 10 minutes. Feeling I had a pretty good fix on where it went down, I decided to make an effort to find it. After buying some pumpkins for Halloween, I went south on the highway an exit, and parked near a bunch of tract housing. The plan was to climb the ridge between the houses and the flying field and look for half an hour or so. Well, we climbed the ridge and there were a few deer running about, so we got a little distracted. As the deer ran off, I looked slightly south, and there, about 40 feet away, lying in the middle of the path as if someone had just set it there for a photo, was the Thistle! Total searching time from closing the car door was less than 8 minutes. Less time than the flight itself. I must have been living well that day.
6/14/98 - More Thistle Updates. Well, the infamous El Nino rains are finally gone, and the sun has stepped in to fill the void. This morning's Marin Aero Club session was blessed with near perfect weather. While hot, there was little drift, and abundant thermals. The Thistle was up to it's old tricks again, regularly stretching past its average one minute indoor times. Several flights were over two minutes, which is really pushing the limits of the field, even on a low drift day. The penultimate flight ended with the model sifting 70 feet or more, down through some tall Eucalyptus trees. Yet a few more healthy squirts of super glue, and it was ready to go again. 75 sec of charge, and off it goes. Just like October, it catches a good thermal and starts heading up. Expecting it to kick out like it had so many times earlier in the day, I slowly started to walk along underneath it. Well, by the time I get to the edge of the field, the drift is increasing, and I start to jog to keep up. Boy am I out of shape after a winter of near solid rain! I keep chase up and over a small hill and through some trees, checking my watch from time to time. The hill seemed to disturb the thermal enough to kick out the plane, eventually setting down 4-500 yards from the launch point with a final time of 4:32. Shades of another fly away. I guess I should really put my name and number on this model!
For those interested, the design, with templates, was published in the February 1995 issue of Model Aviation. An R.C. version, slightly larger, was published in the March 1996 issue.
Martin Gregorie has reworked the original design a bit and allowed me to publish plans free for downloading here on my site.

Click to jump to the plans page

return to model index | Moffett Report | What Works List