At yesterday's O.F.F.C. meeting we did more testing for the RTP speed event. I brought another test hack, an ROG type stick model with the wing and tail surfaces of my Speed Merchant design. Jim Leuken brought his improved design from last week and we had the three foot pole called for in the rules. Bill Watson brought the electronic timing pylon that he built for the contest.
My test hack had the wing held on by a rather strong rubber band so I could easily adjust the incidence. As I had thought the airfoil I am using needs a degree and a half of incidence to get the model off the ground within the first lap. Although with the three foot pole everything seems to get off the ground in the first lap.
- Three foot pole.JPG (90.5 KiB) Viewed 14436 times
I was using a five inch, Guillow's red prop and easily getting up in the twenty mile per hour range with four strands of 1/8" flat, tan, sport rubber. One thing I did find is that winding a thousand turns, or more, into a motor with four to six strands of rubber will rip the free wheel dog right off the front of the prop. Since we don't need a freewheel for this kind of flying just bend the shaft over the front of the prop. A may actually use the test hack as one of my entries in the contest with a more aggressive prop, maybe a four bladed prop. Another thing I found was that if you forget to aim one of these short winged monsters out of the circle at launch the line will go slack and the torque will wind the model into the line. With these motor stick types the line gets wound into the motor. We will need to have spare lines at the contest.
- test hack2.JPG (86.26 KiB) Viewed 14436 times
Jim tried to find the maximum sized motor for his design. He is used to handling strong motors since he flies in international Wakefield competition. However, he found that he can make too strong a motor for this type of model since with a very large number of strands you can get tremendous acceleration on the first lap but if the motor has too many strands you can't put enough winds in it to finish the third lap. Since the timing is on the second and third laps it defeats the purpose.
Bill's timing pylon was a heavy, impressive structure made of particle board with the timing platform and line pivot arm on top. It had two methods of timing, a micro switch tripped digital stop watch and a Hall effect sensor with a remote readout. The aluminum arm had a disk center with a spiral groove track on the bottom. There were two holes drilled into the track for the start of the second lap and end of the third lap. The track ended in a circle after the third lap hole. A whisker, attached to the micro switch rides in the track. The micro switch was tapped into the start/stop switch in the stop watch which was attached to the platform on the top of the pylon. You start the model with the whisker at the outside of the track. As the model flies around the pylon the arm rotates starting and stopping the watch when the whisker hits the holes. You have to go to the pylon to read the time, reset the watch and the whisker for the next flight. After a few test flights we realized that this Rube Goldberg electronic timer was just too touchy to work reliably.
The Hall Effect sensor, on the arm, was connected to a remote box with the electronics programmed to do the timing on the second and third lap and calculate the miles per hour at the push of a button. It also has a reset button and an on/off switch. This rig worked flawlessly except that the miles per hour calculation needs to be reprogrammed since it did not take into account the length of the arm. There was some concern about the drag of the massive (relatively) looking arm but it was not justified since the arm was on a bearing from a CD player and did not lag behind the line by the end of the first lap. In any event, since the mechanically tripped timer will be deleted there will be a much less massive arm on the pylon next week. The electronic timer pylon will definitely be used in the contest because with the regular pole and stop watches we discovered that with multiple people timing the spread between the times of a run were plus or minus 2 tenths of a second. We will still get another test session next Wednesday before the contest on the 16th.
https://youtu.be/3X_Qm-9_uV4The 4.9 second time is 17.49 mph on rather tired rubber.
At the Black Sheep meeting, last night, Tony Naccarato brought some cut down Skystreaks that he converted into RTP racers. These are the new, improved Skystreaks (Still have the grain in the tail in the wrong direction.) with cut down wings. added landing gear, and the motor hook moved to the extreme rear of the fuselage. (Not to mention the paint job that he gave them.) These should easily get up into the twenty plus mile per hour range and don't take much time to build. At Duarte, last month, Dana Wall got a virtually unmodified Jetstream, with a four strand motor, up to 17 miles per hour where as a completely stock one would only get to 12.