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Modified elevator cable routing for CH701
Problem: as left/right flaperon is applied, path length of the cable changes dramatically, because the top of the elevator control horn is located about 12” off the axis of rotation of the flaperon torque tube.
With cable tension set to 20lbs at neutral stick, I was seeing 10-15lbs at full left (very slack) and >35lbs at full right stick. This was tight enough to cause the elevator horn to bend!
Solution: I have added a pulley right behind the lower access hatch, on the bottom of the fuselage. It's pivoted so it can swing left and right, and about 3” right of center (because the horn is on the right of the torque tube). I have also lengthened the cable slightly by adding a linkage.
The change in path length is greatly reduced. The ideal location for the pulley would be lower still, but that’s not possible because of the upward slope of the tail-cone.
This results in almost no change in cable tension with full right or full left flaperon. I have tension set at 20lbs with stick neutral, and I am seeing less than +/- 3lbs through full left-right-up-down stick.
Elevator now does not feel stiff with full right flaperon applied, as it used to.
If anyone wants pictures, please contact me at seb.dewhurst@verizon.net
With cable tension set to 20lbs at neutral stick, I was seeing 10-15lbs at full left (very slack) and >35lbs at full right stick. This was tight enough to cause the elevator horn to bend!
Solution: I have added a pulley right behind the lower access hatch, on the bottom of the fuselage. It's pivoted so it can swing left and right, and about 3” right of center (because the horn is on the right of the torque tube). I have also lengthened the cable slightly by adding a linkage.
The change in path length is greatly reduced. The ideal location for the pulley would be lower still, but that’s not possible because of the upward slope of the tail-cone.
This results in almost no change in cable tension with full right or full left flaperon. I have tension set at 20lbs with stick neutral, and I am seeing less than +/- 3lbs through full left-right-up-down stick.
Elevator now does not feel stiff with full right flaperon applied, as it used to.
If anyone wants pictures, please contact me at seb.dewhurst@verizon.net
Comment
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Comment by Sebastian Dewhurst on July 12, 2011 at 9:37am
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For those wanting part numbers... I used a pulley and some tangs that my A&P happened to have, but another builder informs me that the following parts will do the job:
From Aircraft Spruce:
Pulley: 05-29725 (Homebuilders 1-1/2” Pulley)
From AIR-TECH (www.air-techin.com)
10 Tangs; part number CA2877
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Comment by Don Herbel on May 20, 2010 at 7:54am
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I received new drawings from ZAC. The elevator down travel is limited when it contacts the upper fuselage rudder hinge plate. A piece of aluminum angle extrusion is fastened to the elevator center hinge gusset (7H5-4) to act as a stop for upward travel. I found however, that the horn angle (7H5-3) contacts the gusset before it reaches the specified location of the new stop (7H5-5). I had to trim off about 4 mm of the rear edge of the gusset to allow the elevator to reach 35 degrees up travel.
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Comment by Jonathan Porter on May 11, 2010 at 5:40am
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Don, the elevator stops are set using the angle off of the top of the elevator - you file the physical stop points (and as discussed below can add materials to act as wear plates...) When you set up your elevator on the machine it will all become visible and easy to adjust - promise!
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Fair do's - we add a little bit of fairlead to the elevator stops to make it softer on the end stops - especially the down stop (in case you just let go of the stick at the end of a flight)!
Perhaps you should post some photos?
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Jonathan, I use the recommended stops - the two peices of angle riveted to the bulkhead to limit the flaperon travel, and the elevator is limited (I believe by design) by the horn itself contacting plates above and below. I have actually re-inforced said plates with a bit of "sacrificial" material, as they were wearing away, slowly increasing the total elevator travel.
I have had 6 or 8 emails agreeing with me that this is a generic issue, and the folks at the factory, who advised me on the details of the mod, seemd aware of the problem.
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Jonathan, how do you limit your elevator deflections? ZAC specifies degrees up and down but does not tell me how to mechanically limit that travel. Cessna single engine aircraft have adjustable stops for elevator travel.
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Deflections of Elevator and Flapperons.... I have looked inside both of our 701s and struggle to see your challenge with standard deflections....
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Deflection of the elevator?
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Sounds strange.... have you checked your deflections to make sure that you are not beyond the limits?
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