ORIGINAL: LearnedInUk
I have a SeaGull Edge with an OS 1.08 currently running a 15X6 prop. The problem is the speed is too fast for aerobatics. I currently need about 1/3 throttle for a comfortable speed but it wil not complete a big loop without stalling. What should i do to increase rpm to gain more Pulling power rather than speed? Larger proper or lower pitch or both?
You cannot expect to keep the throttle in one position and keep the plane at a constant speed as you are going thru a large loop. Do you mean that you are not increasing your throttle when you are climbing and not decreasing your throttle when descending?
How heavy is your Edge and what does your 1.08 turn your 15x6? It should pull very well if the plane is only around 8-9 pounds.
The 15x6 is a bad prop for the OS1.08. I say this because my OS.91 would turn a 15x6apc 10,200 and my OS108 would only pull the same prop another 300RPM. Start to load it in the 9's though, and it will out power the .91FX significantly. The best prop I have found for the OS108 is a good Skorepa 17x6(~9,100). Next a 17x6 apc or 16x6 apc. The 17x4W works OK also. My OS108 on pitts muffler has the same power on cheap 15% as my YS110 did on 30%(APC 16x6 ~9,500 for flying).
Well today was not a good fly day—too rainy and windy, but I did go out and get some thrust figures. The test was with a F90 with OS 108FSR , Jec pitts muffler, restrictor sleeve removed from the carb and VP30 pump. Fuel used was Cool Power 15%. Temp 51° Humidity 76% and dupoint was 44°. I used a Rapalla fishing scale that calibrates within 1oz at 10 and 15 pounds. Elevation is at about 300 feet.
I tried six different props and to my surprise max thrust was very close between them. The props are shown below in the picture and are ordered left to right lowest to highest thrust. My measurements were rmp at 10 pounds (about hovering rpm) of thrust and rmp at max rpm/thrust.
Prop RPM at 10 pounds Max RPM& Thrust
15 x6 apc 8,900rpm 10,600 – 13.7 pounds
16 x6 zing not measured 9400- 14.6 pounds
18x8n apc 6,400 8200- 14.9 pounds
16 x5 c zing 7,900 9800- 15.1 pounds
16 x6 apc 7,700 9520- 15.2 pounds
17 x6 apc 7,100 9,200- 15.5 pounds
I am extremely happy with the way the motor runs and transition is outstanding. I made a recording of it at the end when I had the 16 x 6 zinger on. Anyone curious to how fast this 2 stoke transitions please email me and I will send the wave file to you.