- Joined
- Jan 12, 2017
- Messages
- 658
For the HM293 Flea on Floats (Hydropou, s'il vous plait) I am building, I intend to add structure to the intersection of the seatback bulkhead and the lower longerons, in order to provide a mounting location for the rear float struts. For this I will probably just add corner blocks & gussets, as there is already considerable structure here. However, per plans, the rudder cables run through the seatback bulkhead verticals just above the lower longerons. For this reason, I need to re-route the rudder cables.
There is a second issue that concerns me. Per plans, the control stick assembly provides both pitch and yaw/roll control (the Flea being a 2-axis machine). As can be seen in the drawing below, the rudder control cable runs from the bottom of the stick through a copper tube fairlead brazed to a short section of tube which is mounted on the assembly's cross tube (and is free to swivel as the stick is pushed forward and back). This fairlead bends 90 degrees and is described as "a substitute for a pulley and must be frequently greased." Although the bend has a fairly generous radius of 50mm (nearly 2"), and although many Fleas have been built over the years with this arrangement, I have been advised that this is a bad idea. I agree. Although he never assembled the fuselage, the prior builder of my project fabricated a control stick assembly on which these fairleads are replaced by 1 3/4" diameter pulleys.
This also worries me because I have also been advised that 90 degree turns in 1/8" flexible SS control cable should never use less than 2 1/4" dia pulleys. Now that I have the basic frame of my fuselage built, I don't think even the 1 3/4" pulleys will fit the local constraints, anyway.
So...my thinking now is to add rudder pedals, and simplify the stick assembly for pitch only.
Running cables directly off the rudder pedals, no 90 deg turn is necessary, and I have more flexibility to route the cables around the seat, avoiding the to-be-fortified structure at the base of the seatback bulkhead. I think I can do this with only about 25 deg redirect of the cable inwards (and several deg down). Can a fairlead be used for this safely? If I use a pulley, is there a minimum diameter I should respect?
Thanks in advance.
There is a second issue that concerns me. Per plans, the control stick assembly provides both pitch and yaw/roll control (the Flea being a 2-axis machine). As can be seen in the drawing below, the rudder control cable runs from the bottom of the stick through a copper tube fairlead brazed to a short section of tube which is mounted on the assembly's cross tube (and is free to swivel as the stick is pushed forward and back). This fairlead bends 90 degrees and is described as "a substitute for a pulley and must be frequently greased." Although the bend has a fairly generous radius of 50mm (nearly 2"), and although many Fleas have been built over the years with this arrangement, I have been advised that this is a bad idea. I agree. Although he never assembled the fuselage, the prior builder of my project fabricated a control stick assembly on which these fairleads are replaced by 1 3/4" diameter pulleys.
This also worries me because I have also been advised that 90 degree turns in 1/8" flexible SS control cable should never use less than 2 1/4" dia pulleys. Now that I have the basic frame of my fuselage built, I don't think even the 1 3/4" pulleys will fit the local constraints, anyway.
So...my thinking now is to add rudder pedals, and simplify the stick assembly for pitch only.
Running cables directly off the rudder pedals, no 90 deg turn is necessary, and I have more flexibility to route the cables around the seat, avoiding the to-be-fortified structure at the base of the seatback bulkhead. I think I can do this with only about 25 deg redirect of the cable inwards (and several deg down). Can a fairlead be used for this safely? If I use a pulley, is there a minimum diameter I should respect?
Thanks in advance.
