Hello,
4" bellcranks seem to be the most popular for larger models, perhaps because you can simply buy them from Brodak.
Brodak sells one 4" bellcrank in which the arm length is ~0.8" (Item#BB-374) and there is only one pushrod hole and one 4" bellcrank (from SIG, Item#SH-754) in which there are two pushrod holes in the arm (~0.8" and 1.0").
If the pushrod from the bellcrank arm connects to the highest hole in the heavy duty flap horn from Brodak (1.3"), the elevator's pushrod usually connects 0.75" hole in the flaps horn to the 1.0" hole in the elevator's horn.
The pushrod from the b-crank arm and the elevator's pushrod may connect to the same flaps horn hole.
In this case, there are more choices to select the flaps to elevator's ratio but they are pre-defined by the holes position and only some ratios are practically in use while flying the pattern.
4.33" bellcrank (from Yatsenko) is also in use. There are also Yatsenko's adjustable nylon horns that allow for a very fine adjustment of the flaps to elevator's ratio. There is Igor's logarithmic flaps horn - interesting idea but it must be machined and is somewhat complex to build and setup properly.
Certain people build the customized bellcranks and horns having the geometry that suit them.
Lastly, there are choices of the handle lines spacing.
1:1 ratio between handle and b-crank is commonly used but there are some people that use slightly different ratio, custom build handles etc.
I trying to decide what to use in my large planes (one with Ro-Jett 76, one electric) in order to have the wide range of adjustments.
Yatsenko's b-crank and horns seem to provide the widest range of adjustments but some say that 4.33" b-crank must have 4.33" handle lines spacing.
This means the custom build handle as Brodak's handles I have do not provide such spacing.
Perhaps it is time for me to start building the customized handles?
Your comments and suggestions are appreciated as always.
Regards,
Matt