I use pushers, almost exclusively. I only use tractors if/when I cannot find an equivalent size pusher. APC has the best selection, including a handful of "F2B" selections. I have also built a couple twins and used opposite rotation props on each side.
APC has the best selection, including a handful of "F2B" selections. As Howard noted, APC has made few props directly to our requests, my role was typically to gather interest via SH to determine if a threshold could be met. I would then order (200 piece minimum) and distribute. Thankfully I was able to sell all the sizes except one so did not go broke on it. With my profits I was able to take my wife out for a Happy Meal! In most cases APC would keep the sizes available after that threshold order. The 10x5.8EP, 11x5.5EP, 12x6EP-F2B, 12x6.5WEP, 13x4.5EP, and 13x5.5EP all were produced as a direct result of this effort.
The APC's are good props, but they are a wee bit heavy! The light weight alternative appears to be wood. Xoar advertises them but supply is dubious. I have written Xoar directly about buying some, but did not get a response. Brodak got some through their Chinese supplier but tht supply has now dried up too. Inov8tive Designs (same place to get Cobra & Bad Ass motors) is supposed to be bringing out a series of pushers as part of their Bad Ass prop line. These are rumored to be Xoars, I guess we'll see.
I have encountered a single event of "weird hourglass" syndrome. In my case I determined it was pilot error - overcontrol. Why? There is higher (usually much higher) line tension in the top of the verticals & hourglass when using a pusher prop. ALL of the handle input shows up in the elevator, unlike a normal prop. Put another way if you fly an hourglass with the same control input (i.e., leading and pulling on the control) that you have learned flying normal props then you WILL overcontrol the top of the hourglass because you have more line tension and thus more control input into the airplane. That is not a good place to stall the airplane!
TRIMMING SUGGESTION - Up-thrust:
In the past year and a half or so I have started adding upthrust to my pusher equipped airplanes with good results. Pay-off is generally better groove, and in one case correction of an inside/outside problem. Why is that? I was put onto this trajectory after reading an article (see link below) by "Joe Supercool" (Stuart Sherlock) about stability of FAI speed models! Joe (Stuart) is a physicist and went through the math to predict the magnitude of the propellor gyro force and its effect on the stability of a speed model. In a nutshell, the gyroscopic effect of a normal rotation prop has the effect of holding the nose of a speed model UP. It follows that the gyroscopic action of a pusher prop would be to push the nose down, causing an unequal turn (turns easier outsides), or in less extreme cases, hunting. In the case of a stunt model, I think the effect is also caused by the fact that most of our airplanes still have the thrust line above the centerline of the wing, causing a pitch-down. That's (probably) OK for a "normal" prop because it has a nose-up input due to the prop-gyro counteracting the pitch-down. However, with a pusher the gyro effect is nose down, thus a double whammy! Of note, the only airplane I have that did not respond positively to up thrust has the thrust line only 1/4" above the wing. There are advocates for building in positive incidence (down elevator) into stunters to counteract the gyro, I speculate that building in down-thrust might be the alternative (& better?) solution.
Long and short of it, I am using a #4 washer at the motor mounting bolts to induce about 1 degree upthrust. The next round of airplanes will likely have that 1 degree built-in.
The article is here:
http://www.supercoolprops.com/home/articles/gyroscope.htmlEnjoy...