September 30, 2011
This morning I got in seven flights for the MIMLOCT Postal Contest. This is the last day for the memorial event. I will try to get some better flights in for the World Wide Postal Contest.
Last year I used a plastic freewheeler prop and a fixed balsa prop. This year I had made an 8″ balsa prop with a brass tube freewheeler. Flight tests confirmed my suspicion from last year that it needs more than two strands of 1/8″ rubber. This prop has a P/D of 1.8 and needs two strands of 0.17″ width motor. I could have made it four strands of 0.085″, but I decided to rush ahead with three strands of 1/8″. The motor is 33″ long, twice the hook distance, with an O-ring at each end.
I consult the weather reports and forecasts before going flying. Yesterday morning would have been a perfect time. There was no wind at the big field. But I was still processing the results of my propeller test flights and didn’t make the new motors and have everything ready to go until the wind had picked up mid morning. This morning was supposed to be slightly windy, with the least wind at the local small field. That would prevent me from making any long flights. Too much wind at the big field and only short flights possible at the small field. However, in the small park, the intended motor would fly far too high and too long. Instead I flew with an 18″ loop of 1/8″, two strands, the same motor I used for the prop test flights in an even smaller park.
The wind was forecast as 8-9 mph at the big field, but only 3-5 at the small field. Not as much to pack and not as long a drive, so I went to the local field, leaving about 9 AM. Flags were hanging down. No sensible wind on the field, drift from the south occasionally turned the prop slowly. I went to the south end of the field to wind the motor and launch. Everything went smoothly. Starting with 1,300 turns and a 20.19 second flight, 1,400 turns and a 39.84 second flight, then an ambitious 1,600 turns for a 2:05.47 flight that drifted through and among the trees on the downwind side of the field, through the poles and wires along the street, over the first row of houses and down into the back yard of a house on the next street. I followed at a quick walk and was able to see it go down. It hit a garden chime on the back porch, making a loud clanging noise. Nobody answered the doorbell, two times. So I went around to the gate. No way to open the gate, but I reached over and found a latch. It would not open, perhaps locked? I felt around and found a bolt had been put through. It slid right out. So I was able to open the gate and get the plane, replacing the bolt by feel when I left. Next flight with 1,500 turns made only 44.10 seconds. There was a rattling noise. I found that the prop shaft and bearing had bent, so the prop was hitting the base of the bearing. Bent them back. 1,530 turns, only 31.18 seconds, not climbing. I relubed the motor. 1,550 turns, 49.23 seconds, nearly hit a nearby tree. I was launching right under the tree branches to get as much downwind room as possible. 1,580 turns, 48.39 seconds, and the plane drifted among and through the supposedly upwind trees. The wind drift had shifted to the opposite direction. At this point, several people had arrived with dogs running off leash, in violation of Muni Code. I moved away from the trees and got almost to 1,500 turns when the motor broke. The wind had increased to where it would spin the prop. I was replacing the motor when a dog ran up to the plane. I picked it up just in time to avoid damage. Next attempt to set up, another dog ran by with its owner following, both narrowly missing the wingtip. I decided to move all the way to the other side of the field, since the wind was now steadily from that direction, although still light and variable. As I walked across the lawn, the sprinklers came on, so I went to the car and drove home instead. On the way home the flags were flying out from their masts. I got home about 10 AM.
The component weights of this Cloud Tramp are: fuselage 12.4 grams, wings 8.6 grams, propeller 1.9 grams, motor 3.2 grams for a total of 26.1 grams. The 8″ balsa propeller has P/D = 1.8 and a brass freewheeler. The motor is an 18″ loop of 1/8″ Super Sport.
The five consecutive flight times required for the contest are 125.47*, 44.10, 31.18*, 49.23 and 48.39, for a score of 141.72 seconds. The * times are the highest and lowest. They are excluded and the remaining three are totalled for the flight score.
At home, I checked the weather report again. Wind was coming from the south, averaging 18 mph and gusting to 31 mph. There is a storm coming. The wind at the larger, more distant field was less, but too much for flying. I was lucky to have an hour of still air.
San Jose, CA